AMCP 706-210, Fuzes

AMCP 706-210 REFERENCES a-t Lettered re ferences are listed at the end of 3. H. B. Smith, A Summary o f Mechanical and Electrical S a fe ty and Arming Devices (V), U.S. this handbook. Army Harry Diamond Laboratories, Washington, 1. Notes on Development Type Materiel: T1012 D.C., Report TR-311, 1 November 1956 (C o n fi* Electric Impact and Time Fuze for Hand Gre­ nade (U), U.S. Army Harry Diamond Labora­ dentia I). tories, Report TR 649, W ashington, D.C., 17 4. J. W. Utecht, et a l . , D e v e lo p m e n t o f T905E1 and T905E4 Electric Bomb Fuzes (IT), U.S. O c t o b e r 1958 (Confidential). 2. R. E. Rouse, T h erm a l Tim e D e la y , National Army Harry Diamond Laboratories, Report T R - 159, W ash ing to n, D. C., 15 April 1955 ( C o n fi ­ Bureau of Standards, NBS Report 17-189 Wash­ dential). ington, D.C., September 1953. 7-9

AMCP 706-210 CHAPTER 8 OTHER ARMING DEVICES 8-1 GENERAL tions; and (2) F lu e ric s - the area within the field of fluidics, in which fluid components and sys­ While mechanical and electrical approaches are tems perform sensing, logic amplification, or con­ the most used arming techniques at the present trol functions without the use of any moving time, there are other devices that can be used in parts. The terminology, symbols, and schematics arming systems. These include fluid, chemical, used with flu e ric systems are contained in a pro­ and motion-induced arming devices. These addi­ posed M IL-S T D 3. tional devices are useful primarily in providing the arming delay that is necessary to permit safe The application of flu e ric techniques to fuze mechanical separation. arming systems is in its infancy. However, a start has been made to apply these devices to fuze de­ 8-2 FLUID DEVICES sign4 \"9. Much of the original research and devel­ opment was concerned with the invention and 8-2.1 FLUID FLOW improvement of flueric components. Present pro­ grams are more and more concerned with the de­ Matter is fluid if the force necessary to deform velopment of complete flu e ric systems with in­ it approaches zero as the velocity of deformation creasing numbers of the individual components approaches zero. Both liquids and gases are being available off-the-shelf. However, the fuze classed as fluids. Their distinguishing character­ designer will still find it necessary to have some istic concerns the difference in cohesive forces: of his components specially developed. Present gases expand to fill any volume; liquids coalesce technology predicts that many of the control and into the lower regions of the volume with a free sensing functions, now primarily in the domain surface as their upper boundary. In addition to of electronics or other nonfluid power tech­ true fluids, there are certain materials such as niques, can be accomplished by flu e ric systems. tiny glass beads or greases and pastes which, In fact, flu e ric analogues exist for most elec­ while technically not fluids, behave very much tronic devices. like fluids. These pseudofluids are frequently use­ ful under particular circumstances. 8-2.2.2 Flueric Components Used for Arming In general, fluid-operated devices can be used In a typical electronic fuze timer, the funda­ to transfer motion with an amplified force or mental components are an oscillator and a binary displacement, provide arming or functioning de­ counter. A flu e ric timing system can be built up lays, and program events for complex devices. in the same manner. In a present flu e ric timer, The field of fluid mechanics is large and complex the oscillator consists of a proportional fluid but well covered in standard texts’ ’2. amplifier with modified sonic feedback loops coupled to a digital fluid amplifier. Fig. 8-1® is a 8-2.2 FLUERICS diagram of the amplifiers. The digital amplifier, as do many flu e ric devices, depends upon en­ 8-2.2.1 Fluidic and F lu e ric Systems trainment in which a stream of fluid flowing close to a surface tends to deflect towards that While the use of fluid devices with few or even surface and, under proper conditions, touches no moving parts can be traced back to ancient and attaches to the surface. The attachment of history, it is only in recent years that a spe­ the stream to the surface is known as the Coanda cialized technology has grown making extensive effect. The proportional amplifier uses the prin­ use of such devices. This technology is now desig­ ciple of jet momentum interaction where one nated by two names: (1) F lu id ic s- the general stream is deflected by another. field of fluid devices and systems with their associated peripheral equipment used to perform The digital amplifier (Fig. 8-1 (A)) consists of sensing, logic, amplification, and control func­ a fluid power supply 5, two control ports C and CB , two attachment walls INA and , and two 8-1

AMCP 706-210 o u tp u t p o rts 0, a n d 0,. T h e o u tp u t p o rts serv e Figure 8 - 1 . Schematic of FlugfiC Amplifiers as conduits for directing fluid pulses to the suc­ ceeding elem en t’ in th e fluid circuit. In th is d e­ s h o w n in F ig . 8- 28. T h e lo w e r p o r tio n o f th e vice, a gas supply S of constant pressure is pro­ vided to form a jet stream through nozzle IV. The circuit consists of a proportional amplifier having je t stre a m w ill e n tra in fluid from th e space b e ­ so n ic fe e d b a c k p a t h s Pa a n d PB c o n n e c te d fro m tween the stream and the wall, lowering the pres­ t h e p r o p o r t i o n a l a m p l i f i e r ’s o u t p u t s 0 , a n d 0 , sure. The higher atm ospheric pressure will force to its control p o rts CA a n d Cg . T he p u rp o se of the stream against the wall. The geometric con­ the sonic feedback paths is to m ake the m ain jet fig u ratio n of th e fluid am p lifier can be con­ strea m oscillate from one o u tp u t p o rt to th e structed in such a m anner th a t the jet stream will always attach itself to one preferred wall. This is accom plished by placing the p referred w all at a sm a lle r an g le w ith th e c e n te rlin e of th e flow of the jet stream th an the nonpreferred wall. The figure shows a jet stream attached to wall an d a n o u tp u t je t stream from o u tp u t con­ d u i t 0 B . If it is desired to provide an output jet s tre a m from co n d u it 0 , , a co n tro l je t stre a m to control conduit CB will cause th e m ain jet stream to becom e d etach ed from w all . E n tra in m e n t on th e opposite side w ill cau se th e je t to sw itch over to becom e a tta c h e d to w all . T he p h y si­ cal relationship which occurs in accomplishing the sw itching functions is th a t of m om entum in te r­ action b etw een th e control je t stream a t C an d th e m ain jet stream a t right angles to each other’s direction of flow. The fluid am plifier is properly called an amplifier because the switching of the main jet stream which has high momentum can be accom plished by a control je t stream w ith relatively low.momentum. The ratio of momenta or g ain of a n am plifier can be as h ig h as 2 0 or above, depending on design req u irem en ts. The h ig h er th e gain, th e less stab le th e a tta c h m e n t of the jet stream to the attachm ent wall. T h e p r o p o rtio n a l f lu id a m p lifie r (Fig. 8-l(B )) h a s no a tta c h m e n t w alls. T he m ain je t stream flows in a symmetrical pattern through the noz­ zle to th e v e n t so th a t no o u tp u t is p ro v id ed a t e ith e r co n d u it 0 , or 0 , w h en th e re is no con­ t r o l j e t s t r e a m i n e i t h e r c o n d u i t CA o r Cg .When a control jet stream is applied at C R , the m ain jet stre a m w ill be deflected to w ard o u tp u t co n d u it 0 , in p ro p o rtio n to th e m o m en tu m of th e con­ tro l je t stream . C orrespondingly, th e o u tp u t je t strea m th ro u g h co n d u it 0 , w ill be p ro p o rtio n al to the deflection of the m ain jet stream. In a sim­ ilar manner, an output jet stream in conduit 0 B will be caused by a control jet stream in conduit C A' A fluid oscillator can now be m ade up of a fluid circu it u sin g th e se tw o com ponents as 8-2

AMCP 708210 other. T he ra te of oscillation dep en d s on th e tal amplifier will decrease its switching frequency sp eed (sonic velocity) a t w h ich th e p o rtio n of th e o u tp u t je t stream trav els th ro u g h th e feed­ with increasing pressure. In addition, a small de­ b ack p a th b ack to in te ra c t w ith th e m a in je t stream, causing it to deflect to the opposite out­ gree of com pensation for tem p eratu re variation, p u t p o rt. F o r ex am p le, w h en th e je t stre a m is deflected to 0 , of th is p ro p o rtio n al am plifier, is o b tain ed w ith th e com binations. A s a result, th e portion of th e je t stream in th e feedback path P which is causing the deflection then be­ variations in the frequency of oscillation are +10 comes zero. However, the m ain jet stream being deflected over to 0 ; now p ro v id es a n o u tp u t to p e rc e n t for v a ria tio n s in p re ssu re from 6 to 18 p a th 0, a n d fee d b ack p a th P A . P a r t o f th is o u t­ p u t is now d iv erted b ack along P to in te ra c t p sig a n d te m p e ra tu re v a ria tio n s from -65” to w ith th e m ain je t stream , causing th e m ain je t stre a m to oscillate to th e opposite side. T he fre ­ 165°F. quency of the oscillation is directly proportional to th e velocity (speed of sound) of th e o u tp u ts Although the accuracy of this oscillator is suf­ in th e feedback paths. ficient for some safing and arm ing applications, T he o u tp u ts of th e p ro p o rtio n al am plifier in other applications often require a greater degree Fig. 8-2 drive a digital amplifier so th a t the out­ of accuracy, particularly over the above military p u ts from th e prop o rtio n al am plifier are con­ n ected d irectly to th e control p o rts of th e digi­ tem perature range. An oscillator, which is insen­ tal amplifier. In this m anner, the m ain jet stream of th e d ig ita l am p lifier is sw itch ed to follow th e sitiv e to b o th p re ssu re a n d te m p e ra tu re v a ria ­ oscillations of th e p ro p o rtio n al am plifier. T he purpose of connecting the two types of amplifier tions is described in par. 8-2.2.3. This oscillator, in ta n d em is to provide a n oscillator (the com ­ bination) which has an oscillating frequency th at w h ic h u t i l i z e s a n R -C -R (resistance-capacitance- is relatively insensitive to variations in the com­ m o n su p p ly p re ssu re (Sp - SD) T he p ro p o rtio n a l resistance) feedback network, exhibits frequency am p lifier w ill in h e re n tly in crease its oscillating variations of less than + 1 % over the above pres­ frequency w ith increasing pressure, an d the digi- sure and tem perature ranges. Even greater accu­ Figure 8-2. Schematic of Flueric P r e s s u r e - compensated O scillator racies may be achievable with simple moving part types of oscillators. T he b in a ry co u n ter or frequency d iv id er for the tim er can be built up from a num ber of flip- flop sta g es. A co m p lete c o u n te r sta g e is sh o w n i n F ig . 8-3®. T h e p o r t s PA ^ ) a n d PB r W) a r e u s e d to preset the counter. If this were the first stage a f t e r t h e o s c illa to r , t h e n t h e o u t p u t s fro m the oscillato r w ould be connected to th e tw o control ports I a (B) and I B(b ) o f t h e b u f f e r a m p lif ie r . T h is w ould cau se th e m a in je t stre a m of th e b u ffer am p lifier to sw itch b ack a n d fo rth b e ­ tween its two attachm ent walls at the same fre­ quency as th e oscillator. O ne o u tp u t of th e buffer amplifier is v ented so th a t pulses are sup­ p lie d to in p u t I v o f th e W a rre n loop a t h a lf th e f r e q u e n c y o f t h e o s c illa to r . T h e o u t p u t s 0, (W) a n d 0 B(W) o f t h e j e t s t r e a m o f t h e c o u n t e r a r e connected to th e tw o co n tro l p o rts of th e buffer amplifier of the second stage in the same m anner a s th e o u tp u ts o f th e o sc illa to r a re co n n ected to the first stage. Similarly, the second stage is con­ n ected to th e th ird stage, an d so on u n til th e last stage. T he o p e ra tio n of th e c o u n ter is a s follow s;’ A jet stream of gas, supplied by pressurized gas from power supply 5 ^ , is caused to flow through th e orifice a n d w ill a tta c h its e lf to one of th e walls. Fig. 8-3 shows the stream attached to wall VI a (H) after being switched by th e buffer am pli­ fier signal apphed at in p u t I, . W hen th e buffer amplifier signal is removed from input I w a par­ t i a l v a c u u m w i l l n o w b e f o r m e d a t t h e attach­ m e n t w a ll ItA f (Bernoulli's principle), causing 8-3

amcp 706-210 a n e n tra in m e n t flow of g as fro m th e co n tro l E ach counter stage receives pulses at a specific freq u en cy , d iv id es th a t fre q u e n c y b y tw o, a n d p o r t o f t h e w a l l Wa (w) a r o u n d t h e W a r r e n provides pulses at this reduced frequency to the next counter stage which, in tu rn , rep eats th e op­ loop in a clockwise direction. W hen a signal from eration. For example, the first counter stage re­ ceives a n in p u t of 640 p u lse s p e r second from th e b u ffe r a m p lifie r is re a p p lie d a t I, i t follow s th e o sc illa to r. I t d iv id es th is fre q u e n c y b y tw o, producing an o u tp u t of 320 p u lses p er second th e preferred direction setup in th e W arren loop which are provided as input to the second stage of th e co u n ter. T he second stage sim ilarly pro­ (clockwise) an d causes the m ain stream to switch vides pulses to the third stage at a frequency of 160 pulses p er second, a n d so on. to 0, . W hen th e b uffer am p lifier sig n al is While other devices are required and are being rem oved, th e e n tra in m e n t flow in th e W a rre n i loop w ill re v e rse to a co u n terclo ck w ise direc­ tion. The buffer amplifier signal, when reapplied, w ill be d ire c te d a ro u n d th e W a rre n loop in a counterclockw ise direction and sw itch the m ain s t r e a m b a c k to 0 A ^ , a s s h o w n i n F ig . 8-3. I INPUT CONTROL I B(B) Figure 8-3. Schematic of Flueric Counter Stage 8-4

AMCP 706-210 SETTING GAS SUPPLY OUTPUT PORT GAS RINARY COUNTER (12 STAGES] VENT PORTS AMPL. POWER JET AMPLIFIER PORTS VOLUME: 5 CUBIC INCHES FLIP FLOP SETTIN G : 2 11200 SECONDS POWER JET POWER GAS SUPPLY 0.1 5EC INCREMENTS OSCILLATOR FREQUENCY OIVIOER ( 5 STAGES) Figure 8-4. Flueric Timer developed for a com plete a rm in g system , those the preset signal from the rem aining ports. Any d iscu ssed above are th e b asic b u ild in g blocks. time from 2 to 2 0 0 seconds can be preset, in this F ig . 8-4® s h o w s a t i m e r c o n s t r u c t e d f r o m u n i t s o f t h i s t y p e w h ile F ig . 8-5® s h o w s s a m p le ele­ m anner, in 0.1 -second increm ents. T h e v o lu m e o f t h e flueric s y s t e m is 5 in.3 o f m ents used. The oscillator of this tim er has a fre­ quency of 640 p u lses p er second. T he oscillator w h ic h t h e t i m e r (1/2 x 3/4 x 1-1/4 in.) accounts is follow ed by 18 c o u n ter stag es. H ow ever, th e OSCILLATOR OUT PUT 10 OSCILLATOR f i r s t 5 s t a g e s a r e n o t settable a n d a c t a s a f r e ­ PLATE PLATE DIGITAL OSCILLATOR quency divider. The last stage is always set one ’ ROPORTIONAL AMPLIFIER w ay because, w h en it sw itches, it deliv ers its output to whatever function the tim er is to trig­ AMPLIFIER PLATE FEED COUNTER PLATE ger. In b etw e en th e se tw o en d p a c k ag e s are 12 & INPUT BACK LOOP MEMORY settable b in a r y c o u n te r s ta g e s . T h e c o u n te r c a n PLATE OSCILLATOR o s c il l a to r OSCILLATOR SEPARATION be built up so th a t if n counters are connected in FEED BACK LOOP series, the output frequency of the final stage is PLATE red u ced by a factor of 2 ” over th e frequency p rovided to th e first stag e by th e oscillator. Figure 8-5. Sample Flueric Timer Elements T herefore, if th e frequency of th e p u lses pro­ 8-5 v id ed by th e o scillato r to th e firs t stag e is 640 pu lses p er second, th e frequency of pu lses sup­ p lied by th e se v en te en th stag e to eig h te e n th stage, causing the eighteenth stage to provide an o u tp u t, is 640 divided by 217, or 0.0048828125 pulse per second, or approxim ately 2 0 0 seconds p e r p u ls e . T h e 12 settable s t a g e s c a n b e s e t b y m eans of a card which allows a preset signal to be ap p lied to th e d esired co n tro l p o rts a n d blocks

AMCP 706-210 fo r a b o u t 1/2 in! w h ile a ir s u p p ly s y s te m o c c u ­ cillato r output which causes a back pressure. The back pressure induces the oscillator power jet to pies the rest of the space. spread and forces a portion to feed back into the 8-2.2.3 Relaxation Oscillator R-C-R network initiating oscillations. A r e la x a tio n o s c illa to r (F ig. 8- 6)9 is b a s ic a lly The binary amplifier and the oscillator have a com m on su p p ly so th a t a ch an g e of in p u t p r e s ­ a n R -C -R feedback type; som e of th e flu id from su re in one is accom panied by a change in th e th e pow er je t is re tu rn e d to th e control p o rt other. This action is needed because some of the th rough the feedback netw ork causing th e u n it in c re a se in flow th ro u g h th e o scillato r nozzle is to oscillate. The am ount of fluid entering the ca­ conveyed to th e low er p re ssu re reg io n in th e p acitan ce is d eterm in ed by th e resistan ce , binary amplifier control ports. p laced in th e u p p er p o rtio n of th e capacitance, an d th e fluid leav in g it by th e resistan ce R2 » In ad d itio n , th e b in a ry am plifier is provided located at the bottom of the capacitance. Hence, w ith a set of bleeds, located in th e sep aratio n R i , R 2 , and the capacitor volume determine the reg io n . T h e fu n ctio n of th e b leed s is to e x h a u st filling tim e of th e capacitance, which will in tu rn any increase in back pressure th at arises when the determine the frequency of the oscillator. amplifier is loaded. The binary amplifier is used as a buffer because an appreciable gain is needed T he oscillatory m ode is excited only for p re s ­ to amplify the oscillator output. su re ra tio s for w hich th e je t sp read s to occupy the full width of the output channel. This is nec­ The compensation in the network takes place essary to achieve a feedback process th a t will in­ a s follow s: A s th e te m p e ra tu re rises, th e re s is t­ duce oscillation. T he sp read in g of th e pow er je t ance of the network increases, causing the bias is a function of the input pressure and the pres­ flow to d im in ish . I f th is in c re a se in re sis ta n c e sure of the field into which it is operating. If the w ere th e only ch an g e in th e n etw o rk , th e fre ­ pressure at the output of the oscillator is atm os­ q u en cy of oscillatio n w ould dro p . H ow ever, th e pheric, a high pressure at the input is required to tank capacitance decreases with higher tem pera­ achieve the pressure ratios necessary for oscilla­ ture w ith a consequent rise in frequency. Hence tion. Such behavior is normal and is characteris­ by adjusting the size of the resistances and vol­ tic o f je t flow . um e of th e capacitance so th a t one com pensates th e other, te m p e ra tu re in sen sitiv ity can be achieved. Pressure independence is achieved in a similar manner. W ith proper design, tem perature and pressure insensitivity can be achieved simul­ tan eo u sly . A s a resu lt, v aria tio n s in th e fre ­ q u e n c y o f o s c i l l a t i o n a r e +1 p e r c e n t f o r v a r i a ­ tio n s in th e frequency of 30 p sig an d te m p e ra ­ tu re v a ria tio n s from -65” to 200°F. 8-2.2.4 A rm ing C onsiderations Figure 8-6. Flueric Relaxation Oscillator The size lim itatio n s th a t fuze arm ing devices place upon the designer create a special problem In this particular case, the oscillator exhausts w ith re sp e c t to flueric sy stem s, nam ely , th e into a binary device (Fig. 8 -7 )9 which has a pres­ p ro b lem o f th e p o w er source. To d riv e a flueric sure below am bient in its interaction region. The system, one m ust have a reservoir of fluid of suf­ am plifier control area sets a fixed load on the os­ ficient size to deliver th e proper am ount of fluid 8-6 for th e desired period of tim e. M ost of th e p re s­ e n t th in k i n g h a s r e s u lte d in th e u s e o f self- contained p ressu rized gas bottles. If tim es are sh o rt a n d space is n o t too critical, th e n g as b o t­ tles are a valid solution. If tim es are longer and space p ro b lem s are critical, sm all volum es m u st be used w ith the fluid at high pressure. Since op­ e ra tin g p re s s u re s for ty p ic al m in ia tu re flueric

AMCP 706-210 BLEEDS RELAXATION OSCILLATOR CAPACITOR TANKS ASSEMBLY Figure 8-7. F lueric Relaxation Oscillator and Digital Am plifier devices are 1/2 to 20 psi, rather sophisticated assembly w hich provides for an arm ing delay pressure regulating equipm ent w ould then be after firing. The delay, 1-1/2 to 6 sec, is achieved required. by an external bleed dashpot1 1• The fuze is show n in Fig. 8-812 . A fter the setback p in (not One of the more prom ising possibilities for shown in this view) has moved rearward and the military applications is to make use of ram air bore-riding pin (G) has been ejected, the slider (F) after the projectile starts moving. This source of is driven into the armed position by a music-wire energy will be widely used within the atmosphere spring. However, slider motion is retarded by the on projectiles w ith velocities in excess of 400 ft. cap assembly. This assembly consists of alum i­ per sec. n u m cap (R), alum inum plug (S), a n d a sintered m onel alloy restricter (T). A ru b b er O -ring (U) Table 8-11 0 com pares the fluidic approach is fitted on the slider to provide a seal so that air w ith the other logic and control techniques. can pass only through the restricter. A plastic Problem s still rem ain in fluid systems, but the disk covered with pressure-sensitive tape (V) pro­ prom ises of flueric system s a p p e ar to outw eigh tects the restricter during shipping. their problem s and to offer an effective tim ing and control mechanism for fuze application. The present design was empirically developed for interim use due to the need of m ortar fuzes 8-2.3 PNEUMATIC DELAY with a delay function to provide for the safety of mortar crews. Additional developmental work is Arming delays can be achieved using the prin­ required to improve its storage and temperature ciple of a fluid dashpot. Industrial dashpots often characteristics. use oil in a piston-cylinder arrangem ent w here the oil is bled through a small orifice or through 8-2.3.2 Annular Orifice Dashpot a p orous m em ber. Oil dashpot u n its cannot be applied to fuzes because of leakage problem s A n annular orifice dashpot is show n in Fig. and variations in time w ith tem perature. W hen 8-91 3. The \"orifice\" is the m inute clearance be­ air is the fluid, leakage is elim inated, and vis­ tween piston and cylinder. By selecting materials cosity changes can be m inim ized by various de­ for piston and cylinder having different thermal sign features. coefficients of expansion, the orifice w ill change with temperature, thus affording a means of ap­ 8-2.3.1 External Bleed Dashpot proaching a constant flow in spite of air viscosity changes with temperature' 4 . A glass cylinder can Fuze, XM717 is one of a fam ily of single­ be accurately produced and the piston can be action, superquick mortar fuzes that has a slider 8-7

00 00 TABLE B-l. COMPARISON OF FLUID Characteristics Fluidics Electrical Solid sta te Relays Electronics Size small, miniaturiza­ about the same as smaller than current fluidics • potential tion capability current technology about same in fluidics none Moving none requires moving damaged by high Parts Parts temperatures Tempera­ not affected by damaged by high ture Effect temperature temperatures Radiation do not affect cause damage cause damage Effects performance (degradation) of insulation IflfltG’ could resist high A cceler., do not affect rials accelerations if Shock performance properly supported Vibration high accelerations about the same easy to fabricate affect performance order of com­ Produci- and produce plexity as fluidics bility fabrication more complex than fluidics cost ultimately, low on a production probably about the cost ■ though basis, higher same as fluidics not yet achieved requires electrical requires electrical Interface single phase to mechanical or to mechanical or Require­ (fluid) systems fluid interfacing fluid interfacing ments generally not safe generally would be Response safe for use in for hazardous en­ safe for hazardous To Hazard hazardous GH* vironments •with­ environments ous Envi- rironm ents out special pre­ cautions

DICS WITH OTHER LOGIC TECHNIQUES AMCP 706-210 Integrated Conventional Conventional M e c h a n ic a l C ircuits ( e lec tro n ic ) Hydraulics Pneuma ( ic Logic System will always be always larger than larger •ultimately always larger smaller than fluidics much larger than fluidics fluidics none always moving always moving always moving damaged by high parts Parts Parts temperatures could be damaged could be damaged may or may not cause damage or rendered inop­ or rendered inop­ erative by high erative by high be affected by temperatures high temperatures temperatures depending on design probably cause probably cause probably not damage damage affect performance would resist high high accelerations would be affected would be affected accelerations affect performance by high accelera­ seriously by high acceleration rates tion rates about the same relatively complex relatively complex relatively complex or slightly less fabrication process fabrication process fabrication process complex to pro­ duce less costly will likely always probably more probably more be more costly costly than costly than than flu id ic s fluidics fluidics requires multiphase single phase (liquid ) single phase (gas) single phase (mech­ interfacing system capability system capability anical) capability safe for hazardous may or may not may or may not not likely hazard­ environments ous be hazardous, be hazardous, depending on con­ depending on con­ trol means trol means

AMCP 706-210 ground from ceramic or metallic materials. re c ta n g u la r d u c t o f th e sa m e d im e n sio n s, i.e., The piston is pushed by a spring. The holder, w id th e q u a l to clea ra n ce a n d le n g th e q u a l to circumference. The clearance of silicone ru b b e r or p o lyethylene, ho ld s an d seals th e p a rts. M odels h av e b een m ad e from ' 677 r l 2 P 1 1 1/3 ( 8-1) h = --------------------- 1/8 in . d ia m e te r a n d 1/3 in . lo n g to 1-1/2 in . ■JJ (P? ~ P 22) d ia m e te r a n d 6 in. long. T im e d elay v a rie s b e ­ w here h is the clearance from piston to cylinder, t w e e n 0 .1 s e c o n d a n d o n e h o u r . T h e dashpot h a s b e e n u s e d i n e x p e r i m e n t a l fuzes a n d is in .; i s t h e v is c o s ity o f t h e a ir , slug/ft-sec; r is p l a n n e d fo r in c o r p o r a t io n i n Fuze, X M 4 3 1 fo r t h e 2.75-inch r o c k e t’ 5 . th e radius, in.; I is th e length of air travel, in.; is the pressure in the cylinder, psi; P2 is the am ­ A - STRIKER bient pressure, psi; and t is the desired tim e de­ B - SPRING lay, sec. C - F IR IN G PIN 8-2.4 DELAY BY FLUIDS OF HIGH VISCOSITY D • HEAD 8-2.4.1 Silicone Grease E - PIN F - SLIDER T he v iscosity of silicone g rea ses an d g u m s 8 - S A F E T Y PIN offers resistan c e to m otion. T he te m p e ra tu re v iscosity curve of silicone g rease is fla tte r th a n H - G U ID E PIN th a t of other oils and greases. In th e past, use of th is su b sta n c e h a s th e re fo re b e e n a tte m p te d to i . DETONATOR provide tim e delay. However, the leakage prob­ K - B O O S T E R LEAID lem was severe: the grease gummed up the arming L - TFTRYL BOOSTER m echanism so as to render it useless. This prob­ PELLET lem was overcome in Grenade Fuze, XM218 and M - BODY XM224 by sealing a silicone gum in a plastic sac R - CAP m ade up of h eat sealable M ylar tape. This fuze S - PLUG p ro v id es safing, arm in g , a n d fu n ctio n in g for a num ber of grenades and bomblets. The fuze arm s T - RESTRICTER when a specified spin rate is achieved by the de­ II . “0 ” RIN G scending g ren ad e. A t th a t point, cen trifu g al forces d isen g ag e from four lock w eig h ts to p e r­ Figure 8-8. Fuze, XM7I7 m it a d eto n ato r ro to r to tu r n 90” to th e arm ed position thus releasing the delay assembly. Figure 8-9. Pneumatic Dashpot for Arming Delay T h eo ry of o p eratio n is b ased on th e com ­ F ig . 8-101 6 sh o w s th e sa c a n d ro to r d e la y p re ssib le flow of a ir th ro u g h th e orifice. T he a n n u la r orifice, in th is case, a c ts th e sam e a s a m echanism of G renade Fuze, XM 218. T he sac assembly consists of a metal backing disk and a p l a s t i c c a p s u le , a b o u t 3/4 in . i n d i a m e t e r a n d 1/8 in . th ic k , c o n t a i n i n g s ilic o n e g r e a s e . T h e periphery and a segment of the plastic disk are h e a t sealed to th e m e ta l d isk to form a pocket for th e d elay fluid. T he sac assem b ly is placed ag ain st th e delay rotor assem bly (the space b e­ tween the two assemblies in the illustration was in tro d u ced solely to show th e sac assem b ly clearly). In operation, the delay is obtained when the four blades of the delay rotor, by virtue of a torsion spring, slide over the surface of the fluid sac, th u s displacing and m etering th e fluid from one side of each b lad e to th e o th er. A fter ro ta ­ tion of the delay rotor, a firing pin is released to 8-9

AMCP 706-210 initiate the explosive train. The design described from crown-barium type glass have been used in was obtained by empirical means. The analysis is these devices. It is critical that beads are near complex because the flow in the fluid sack pas­ perfect spheres or they tend to interlock. Pre­ sages varies as a function of rotor radius. Analyti­ conditioning of parts and assembly areas with cal techniques relating to the interactions of controlled atmosphere are required to exclude timer geometry, silicone fluid properties, and moisture which causes sticking. Properly applied friction levels have not yet been completed. dry surface lubricants, such as molybdenum di- suplhide, improve performance. At low g values, sac- difficulty has been experienced with static elec­ ROTOR a SAC. tricity. Generated by the rubbing beads, static ASSEMBLY electricity tends to make the beads stick and impede flow. Silver plating the glass beads mate­ \\-ROTOR BLADE rially improves the dissipation of static charges. -ROTOR DELAY 8-3 CHEMICAL ARMING DEVICES Figure 8-10. delay Assembly of F uze, XM278 Chemical reactions are used to provide heat, 8-2.4.2 Pseudofluids to dissolve obstructors, or to activate electrical batteries. The first example, heat processes, in­ It has been found that small glass beads flow volves explosive reactions described in par. 4-2, somewhat like a fluid. Hence, their use has been and the last example, electrical batteries, is de­ investigated for arming delays and safety detents scribed in par. 3-4.3.3. in fuzes and S&A’s’ 7-2 0 . Glass beads are em­ ployed as follows: Motion of a piston caused by Time bombs may contain a chemical long- acceleration is regulated by the flow of beads delay fuze. One form contains a liquid that dis­ through an orifice. Either a central hole or the solves a link in order to release a firing pin. This annular space surrounding the piston can serve as is usually termed a functioning delay. The liquid that orifice. is kept in a glass vial that is broken to activate the system. Fig. 8-11 illustrates a system in Glass beads have the advantage that their op­ which a plastic collar is dissolved in acetone so eration is much less temperature dependent than that the firing pin will slip through and strike that of true fluids, Glass bead delay mechanisms the detonator. have been successfully tested in mortar fuzes with launch accelerations from 500 to 10,000 g. This delay is relatively simple to build but the Other glass bead safety switches have been used time interval is not consistent because the rate in missiles and rockets under accelerations of of reaction is so strongly dependent upon ambi­ 10-50 g. ent tem perature. Further, if the solution is stirred or agitated, the reaction rate increases; Factors that affect the performance of glass bead accelerometers include: (1) Orifice, piston, andcontainer configura­ tions (2) Bead size and material (3) Bead shape (4) Moisture content (5) Surface lubrication (6) Electrostatic charge No design parameters have been established for the size relation of orifice, piston, and con­ tainer; past, designs have been empirical. Beads o f approxim ately 0.005-in. diam eter form ed 8-10

AMCP 706-210 and if the original concentration varies, the re­ very strong interactions. They have been used action rate varies accordingly. For simple reac­ mainly for the initiation of fu zes but they could tions, the Arrhenius equation is a good approxi­ be applied to arming process. Also commands mation for the rate of reaction* 1 . could be relayed to munitions to control their fuzes. K = Ko e -H/RT (8-2) ELECTROMAGNETIC INDUCTION signifies w here Ko in reactions/sec and H in cal/mole that an electromotive force is induced in an elec­ are constants, R is the universal gas constant, tric circuit when the magnetic field about that and T is the absolute temperature. For first circuit is changed. The basic equation is order reactions Kg is approximately 101 3 re­ actions per second and for second order re­ where Eg is the induced voltage, in volts; N is the actions it is about 109. (A first order reaction is number of coils of wire through which the mag­ one in which the rate of reaction is directly pro­ netic flux 0 , in webers, changes. portional to the concentration of the reacting This is useful in sea mines as shown in Fig. substance. A second order reaction is one in S-12. The earth’s magnetic field is shifted by the which the rate of reaction depends upon the iron ship so that the magnetic flux threading the concentration of two reacting substances.) coil is changed as the ship passes over the mine. The electric voltage induced in the coil actuates For first order reactions, the concentration T a sensitive relay which closes the detonator firing after a time t is circuit. (See also par. 3-4.3.2.) 1- = OT e ~ K t (S-3) COMMA ND F U Z E S operate by receiving sig­ nals from an operator. For example, harbor de­ where r o in moles/cc/sec is the initial concen­ fenses have been operated thusly; an observer tration and K is given by Eq. 8-2. Although these notes when enemy ships pass through mine fields equations are valid, they should be used only as so that he may explode the mines by remote con­ an approxim ation. Then, em pirical methods trol (see par. 13-3). should be employed to set the dimensions. These tests involve measurements of concentrations Munitions are sometimes operated by radio which can be done in any of the following ways: signals. Usually, this method is reserved for (1) measure the solution concentration by quan­ guided missiles in which other signals are re­ titative chemical analysis (the most reliable but ceived via radio as well as arming and initiating expensive), (2) measure the volume of gas pro­ signals. duced (simple but greatly affected by tempera­ ture), (3) correlate the concentration with light absorption (continuous measurements), (4) meas­ ure the density of the solution (comparatively simple and widely used), (5) measure the re­ fractive index (continuous and not too depend­ ent upon temperature), (6) measure the viscosity of the solution (slow, inaccurate, and incon­ venient), and (7) use radioactive isotopes as tracers (expensive and not as well known). Once the rate of reaction is determined, the approxi­ mate delay time may be found by calculations. 8-4 MOTION-INDUCED ARMING DEVICES Figure 8-72. Electromagnetic Induction Sea Mine 8-11 Moving arming devices are possible in certain cases. They require high relative velocities or

AMCP 706-210 REFERENCES 1. R. L. Daugherty and A. C. Ingersoll, Fluid 11. Nathan Seiden and Donald Ruggerie, P ro d u ct Mechanics, McG raw -H ill Book Co., Inc., New Improvement of th e M 5 2 A 2 F u ze , P ic a tin n y Arsenal, Technical Report 3568, Dover, N.J., York, N.Y., 1954. February 1967. 2. H. W. King and E. F. Brater, H a n d b o o k o f 12. TM 9-1 30 0-20 3, A r tille r y A m m u n itio n , Dept. of Army, April 1967. H y d r a u l i c s , 5th Edition, McGraw-Hill Book 13. D.S. Breed, The Theory and Design o f a Pneu­ Co., Inc., New York, N.Y., 1963. m atic Time D elay M echanism , Massachusetts 3. MIL-STD-1304 (proposed), Fluerics, T e rm in o l­ Institute of Technology, Cambridge, Mass., ogy, Symbols, and Schem atics, Military Stand­ Master of Science Thesis, September 1961. ard, Dept. of Defense, April 1967. 14. PAOD, A P n eu m a tic A n n u la r O rifice Dashpot Suitable for Use in Ordnance Safety a n d Arm ­ 4. R. A. Shaffer, The A p p lic a tio n of P u re F lu id s ing Delay Mechanisms, Breed Corp., Fairfield, Technology to A rtillery Fuzes (U), Frankford N.J., January 1967. Arsenal, Report M 6 6 -2 0 , P h ila d e lp h ia , Pa., May 1965, AD619 054, (Confidential). 16. U.S. Patent 3 ,1 7 1 ,2 4 5 , Dashpot Timer, 2 March 5. The A p p lic a tio n o f F lu eric D e v ic e s to O rd ­ 1965, assigned to Breed Corp., Caldwell, N.J. nance Timers, Journal Article 51.0 of the 16. I.P. P a r is i, Product Improvement of the XM218 JANAF Fuze Committee, 3 May 1967, AD-834 F uze a n d D e v e lo p m e n t of the S h o rt D ela y 083. XM224 F uze (V), Picat inny Arsenal Technical 6. R. A. Shaffer, \"Fluid-Mechanical Problems Report 3425, Dover, N.J., August 1966 (Confi­ A sso c ia te d with a Flueric T im er D esig n ed fo r A rtillery Fuze A pplications, ” P roceedings o f dent id I). the Timers for Ordnance Symposium, Vol. 1, 17. G la ss-R e a d S tu d y (U), Eastman Kodak Co., Sponsored by U.S. Army Harry Diamond Labora­ Final Summary Report, February 1959, Con­ tories, Washington, D.C., 1 5 -16 November 1966, pp. 59-78, AD-813 504. tract DA-30-1 1 5 -5 0 l- O R D - 8 7 3 (Conf identia I). 7. Carl J. Campagnuolo, F lu id ic S a fin g -A rm in g 18. In te g ra tin g A rm in g D ev ic e f o r F u ze s U sed in System (U), U.S. Army Harry Diamond Labs., Report TR-1333, Washington, D.C., Dec. 1966, Non-Rotating Ammunition (U), Magnavox Co., (Conf identia I). Summary Report, 1 December 1960, Contract DA-1 1 -0 2 2 -5 0 1 -O R D -3 1 2 1 , (Confidential). 8. I. Berg and L.A. P a ris e , Flueric T im er E v a lu ­ 19. Parameters A ffe c tin g P erfo rm a n ce o f P e lle t ation fo r Ordnance A p p l i c a t io n , Picatinny Ar­ Flow A ccelerom eters, General Electric Co., Missile and Space Vehicle Dept., Final Re­ senal, Technical Report 3613, Dover, N.J., February 1968. port, June 1962, C o n trac t D A - 3 6 - 0 3 4 - O R D - 3230 RD. 9. C. J. Campagnuolo and S. E. Gehman, Flueric 20. D e v e lo p m e n t S u m m a ry R e p o r t on F uze S u p ­ Pressure- and Tem perature-Insensitive O scil­ porting R esearch Investig a tio n T ow ard a la to r for T im er A p p lic a tio n , U.S. Army Harry M o rta r Fuze Integrated A rm ing D evice (U), Diamond Laboratories, Report TR 1381, Wash­ ington, D.C., February 1968. Magnavox Co., 1 July 1963, Contract D A -1 1- 0 2 2 -O R D -4 0 9 7 (Confident ia I). 10. Russ Henke, “ Flu idics Control: Yesterday, Today a n d Tom orrow ”, Electromechanical D e­ 21. E.B. Millard, Physical Chemistry for Colleges, sign 12, 5 (1968). McGraw-Hill Book C o . , l n c . , N . Y . , 1953, p. 450. 8-12

AMCP 706-210 PART THREE-FUZE DESIGN INTRODUCTION will contain a safety mechanism so as to prevent premature functioning as described in Part Two. There are few, if any, mechanical devices for In Part Three, considerations for fuze design are commercial or military use that must satisfy as discussed and then applied to simple but repre­ many stringent requirements as the fuze for am­ sentative fuzes. Subsequent chapters are devoted munition. It must not only withstand the rigors to sample designs of specific fuze features and to of transportation, field storage in any part of the fuze testing. world, and launching under a multitude of condi­ tions, but also it must function as designed upon It should be stressed that the examples given the first application of the proper stimulus. From are not meant to restrict the principles to the few the assembly line at the loading plant until use described. That is, examples of sliders and rotors on the battlefield, the fuze must be safe to are given for fuzes of spin-stabilized munitions, handle. but such fuzes are also armed and functioned with sequential arming leaf systems, setback ac­ Thus, the fuze designer’s problem is twofold. tuated devices, and clockworks. To avoid repe­ He must design a fuze that first will amplify a tition, different items have been discussed with small stimulus so as to detonate a high explosive various munitions to cover as many types as charge as described in Part One, and second that possible. CHAPTER 9 CONSIDERATIONS IN FUZE DESIGN 9-l GENERAL may be designed for a specific round that is used with one particular weapon or it may be designed A designer’s ability to develop a fuze is con­ for assembly to any one of a given type of pro­ tingent on his knowledge of exactly what a fuze jectile, say all HE projectiles used for guns and must do and of all environments to which it will howitzers ranging from 75 mm to 175 mm and be exposed. The purpose of this Chapter is to dis­ 8 inch. The first fuze satisfies a set of specific re cuss the more basic safety and e n v iro n m e n ta l re ­ quirements, whereas the second must be operable quirements; to present a general plan for the over a range of launching conditions, muzzle ve­ major phases of development from first pencil locity of 420 fps (105 mm howitzer) to 3000 fps sketch to final fuze acceptance for production; (175 mm gun). In addition, the fuze is designed and to illustrate the sequence of design and the for different tactical situations-for ground de­ application of the principles developed in Parts molition (on the surface or after target penetra­ One and Two. tion) or for air burst. 9-2 REQUIREMENTS FOR A FUZE These illustrate the scope of target and firing conditions that may dictate design considera­ Fuzes are designed for tactical situations. They tions for only one series of ammunition items; are used with various series of ammunition items; artillery projectiles, aircraft bombs, sea mines, similar lists could be made for the fuzes of other small arms, rockets, and guided missiles. Each series. Therefore, before undertaking the develop­ series has its own set of tactical requirements and ment of a fuze, a designer must be thoroughly launching conditions which govern the final de­ familiar with the tactical requirements of the sign of its fuzes. Within a series of ammunition fuze and the conditions prevalent in the weapon items (artillery projectiles, for example) a fuze concerned. All fuzes, regardless of tactical use, m ust satisfy definite basic requirements of environ­ ment and safety. 9-1

AMCP 706-210 9-2.1 ENVIRONMENTAL FEATURES w hen subjected to th e proper ta rg e t conditions. The tactical situation often requires the use of a T actical req u irem en ts vary for specific fuzes, very sensitive explosive train -o n e th a t responds b u t every fuze will undergo a num ber of environ­ to sm all im p act forces, to h ea t, or to electrical m e n ta l co n d itio n s from assem b ly to use. W hile energy. A nother of th e designer’s im portant con­ all fuzes do not undergo the sam e environm ental siderations is safety in m anufacture, in loading, conditions, th e m ore com m on are as have been in transportation, in storage, and in assembly to sta n d ard iz ed and grouped to g eth er for conven­ th e m unition. In som e cases, th e forces ag a in st ience’ . A c c o rd in g ly , t h e s p e c if ic a tio n s fo r n e w which the fuze m ust be protected may be greater fuzes can be w ritten simply by reference. The en­ th a n th e ta rg e t stim u lu s. S afety th e n is a re a l vironm ental conditions influence choice of m ate­ challenge for th e designer. N o p h ase can be ig ­ rials, method of sealing and protecting th e fuze, nored because an u nsafe fuze m ay becom e a lay o u t an d design of com ponent p a rts an d subtle weapon for the enemy. m eth o d of p ack ag in g . M an y of th e w idely u sed fe a tu re s are in clu d ed in th e follow ing lis t (for A fuze d esigner know s th e safety re q u ire ­ more details, see pars. 15-3 and 15-4): m ents; th ese govern th e ap proach he tak es. A t each step in d esign a n d d ev elo p m en t of a fuze, (1) OPERATING TEM PERATURE. The fuze h e m u st be conscious of safety. S afety ap p lies m ust w ithstand tem peratures ranging from an air n o t only to th e com plete fuze b u t also to each te m p eratu re of 1 2 5 °F (ground tem p eratu re of step during processing and assembly of the vari­ 145°F) in hot-dry climates to an air tem perature o us co m p o n en ts of th e explosive tra in . If th e o f -5 0 °F (g ro u n d te m p e r a t u r e o f —6 5 JF ) in req u isite deto n ato r can n o t be m an u factu red cold climates’ . Tem peratures can drop to —8 0 ° F safely, then the design of the fuze may have to in bom b b ay s of h ig h flying aircraft, a n d aero ­ be changed. dynam ic h e a tin g can raise th e te m p e ra tu re of m issiles launched from high speed p lan es above S afety en te rs every facet of fuze an d com po­ 145” F. n e n t developm ent. In ad d itio n to th e b ro ad a s ­ pects, there are safety features in fuzes th a t are (2) S T O R A G E T E M P E R A T U R E . T h e fuze m an d ato ry , desirable, or both. F req u en tly , th e m ust be capable of withstanding storage tem per­ desirable featu res can be included a t th e d e­ a tu re s from -70” to 160°F a n d be o p erab le s i g n e r ’s d i s c r e t i o n w i t h o u t i n t e r f e r i n g w i t h t h e a f t e r r e m o v a l f r o m s t o r a g e ’. b asic design. It should be n o ted th a t th ese ‘f e x t r a ” f e a t u r e s r e p r e s e n t t h e d e s i g n e r ’s c o m ­ (3) H U M ID IT Y . T h e fu ze m u s t w ith s ta n d petence and ingenuity. relative humidities up to 100%2. A card in al req u irem en t for all fuzes is th a t t h e y b e de torn.tor safe, i.e ., f u n c t i o n i n g o f t h e (4) R A IN . T h e fu ze m u s t fu n c tio n a s in ­ d eto n ato r ca n n o t in itia te su b se q u en t explosive tended even when fired in a rain storm. tra in com ponents p rio r to arm in g . A n in te r­ rupted explosive tra in (mechanical separation) is (5) W A T E R . T h e fu ze m ay , in c e r ta in in ­ the basic method for attaining the detonator safe stan ces, be re q u ire d to be w aterproof, show ing feature. Examples are out-of-line elements such no leakage, and be safe and operable after im m er­ as a slider or a rotor. T he in te rru p te r should sion in w a te r a t 70” + 10°F u n d e r a gage p re s ­ h av e a positiv e lock w hile in th e safe position. su re of 15 + 5 p si for one hour. The detonator m ust be assembled in the safe po­ sition so th a t the fuze is safe during all final as­ (6 ) R O U G H T R E A T M E N T . T h e fu ze m u s t sem bly steps and during su b seq u en t handling. w ithstand the rigors of transportation (including A rtillery projectiles, m o rta r projectiles, an d perhaps parachute delivery), and rough handling. r o c k e t s m u s t b e bore safe. T h e f u z e m u s t b e so d esig n ed th a t th e d eto n ato r w ill n o t in itia te a (7) FUNGUS. The fuze m ust be able to w ith­ b u rstin g ch arg e w hile th e projectile or ro ck et is stand fungus growth. in th e lau n ch in g tube. H ence, it m ay be n eces­ sa ry to ad d a device to d elay th e arm in g of th e (8 ) SU R V EILLA N C E. The fuze m u st re m a in fuze u n til after th e m u n itio n h a s left th e safe and operable during and after storage in a launcher. sealed can for 1 0 years (2 0 years are desired). 32.2 GENERAL SAFETY FEATURES T he b asic m issio n of a fuze is to fu n ctio n re ­ liably, a n d to receive a n d am p lify a stim u lu s 9-2

A M C P-706-210 The fuze must never remain in the partially 93.1 PRELIMINARY DESIGN AND LAYOUT armed position. As soon as the force that caused partial arming is removed, the fuze must return Many times, tactical situations in the field es­ to the unarmed position. For example, if a fuze tablish the need for a new fuze or a revision of an existing fuze to extend the use or lethality of that became partially armed during transporta­ a weapon. In either case, the first step in the de­ tion were loaded into a gun, that fuze might be velopment of a fuze is a thorough analysis of neither bore safenot d eto n a to r sa fe. what firing’ conditions the fuze will encounter and precisely what the fuze must do. Further­ Fuzes must have two independent safing f e a- more, the fuze designer should maintain close tures whenever possible, either of which is ca­ liaison with the designers of the complete pable of preventing an unintended detonation weapon system just in case specifications are before the munition is projected or emplaced. changed. It is discouraging but true that impor­ The philosophy is based on the low probability tant changes have gone unnoticed until it was all that two features will fail simultaneously. If pos­ but too late. sible, both safing features should be “fail safe” and each should be actuated by a separate force. A good fuze design includes the following features: (1) reliability of action, (2) safety in The safety requirements for Army fuzes are handling and use, (3) resistance to damage in contained in a MUCOM Regulation3 while those handling and use, (4) resistance to deterioration for Navy fuzes are contained in a MIL-STD4. in storage, (5) simplicity of construction, (6) ade­ quate strength in use, (7) compactness, (8) safety An arming indicator is an example of a de­ and ease of m anufacture and loading, and sirable safety feature for fuzes if it can be seen in (9) economy in manufacture. the assembled round. The indicator clearly shows whether the fuze is safe or armed. Some bomb With the knowledge of what the fuze must ac­ fuzes and safing and arming devices already have complish, preliminary sketches are prepared to this feature, and it is becoming more popular for depict the components of the explosive train and other fuzes. An anti-insertion feature is also con­ arming device. venient in the field. Some fuzes cannot be in­ serted in their fuze cavity unless properly Present manufacturing policies dictate layout adjusted. and design of all components. A design, even in the preliminary stages, is subject to severe criti­ Some fuzes and fuze components are assem­ cism if it is not kept in mind that parts must be bled in production by mechanical spin assembly mass produced economically. For assembly line equipment. To insure that spin-actuated fuzes of techniques, the components of a fuze must be 37 mm and above are not armed by this opera­ relatively sim ple, difficult to om it or malas- tion, the fuze must at no time be spun in excess semble, and, of course, safe to handle. of 300 rpm nor can the fuze be accelerated to 300 rpm in less than one second’. Thus the de­ 93.2 DIMENSIONAL DESIGN AND CALCULATIONS signer must insure that production methods can­ not compromise the safety features of the-fuze. 9-3 STEPS IN DEVELOPING A FUZE After the preliminary design has been ap­ proved, the required explosive train has been es­ Development of a fuze is considered successful tablished, and the basic arming actions have been and complete only when pilot lots have passed selected, the detail drawings are prepared from all tests and the fuze has been accepted as a which prototype models can be made. Materials standard item ready for mass production. Many are considered. As was done in the preliminary steps are involved between the first preliminary stage, all tactical, environmental, safety, and de­ sketch and the production of standard fuzes. sign requirements for fuzes are reviewed criti­ Throughout development, the designer must con­ cally. Other similar fuzes already in production sider a myriad of details at each of four basic should be examined for typical parts that might phases: (1) preliminarv design and layout, (2) di­ be used interchangeably (screws, shafts, and col­ mensional design and calculations, (3) model lars); this step frequently reduces manufacturing testing and revision, and (4) final acceptance, costs. safety, and proving ground tests. At this point, the designer evaluates forces 9-3

AMCP 706-210 acting on the fuze, selects materials, and de­ nents to the required setback and centrifugal termines component sizes. External forces to forces. Model tests of partial assemblies and sub­ which a fuze may be subjected are shocks and vi­ assemblies in the early stages of development will brations that occur when a fuze is transported or often reveal flaws that are not evident on the when accidentally dropped. Accelerating forces drawing board. on different fuze parts occur during launching (setback), during flight (centrifugal and creep), Model tests at each stage and detailed layouts and at the target (impact). All these forces the of the design are important for the successful de­ fuze must be able to withstand without changing velopment of a fuze. They permit early evalua­ its operating characteristics. Forces must be com­ tion and revision of component parts before the puted in detail. Finally, the choice of materials design has progressed to the advanced stages. It and dimensions for the parts depend on elastic is possible that a change in one component might modulus, strength, corrosion resistance, machin- precipitate a series of changes in other compo­ ability, availability in times of emergency, and nents that are already being fabricated in the cost. During this phase, performance is calcu­ model shop. lated and reliability is estimated. 9-3.4 FINAL ACCEPTANCE, SAFETY, AND PROV­ Secondary effects that might necessitate a change in shape or balancing of parts are reso­ ING GROUND TESTS nant vibration frequencies, Coriolis effects, and overweight. Those who are familiar with hand­ A fuze that has passed all of the preliminary ling, storage, and tactical requirements may sug­ model tests satisfactorily is ready for rigorous gest other changes. safety and surveillance tests and for proving ground acceptance tests. These are generally per­ The final drawing-board layout should include formed on samples selected from a pilot lot, and different views, so that interferences may be de­ thus are nearly representative of production tected and the correct motion of every part may quality. The safety and surveillance tests are be assured. The failure to make such checks is described in pars. 15-3 and 15-4. often responsible for costly delays in the model shop and in scheduling proof tests. See also The only completely reliable test for the effec­ Chapter 14 for additional guidance on design tiveness of a fuze is the firing or proof test that details. is made under actual conditions of use. The fuze, if it functions, is destroyed; hence, design fea­ 9-3.3 MODEL TESTS AND REVISIONS tures must be judged good or bad by the applica­ tion of statistical analysis. The evaluation of a The complexity of forces acting and the strin­ proof test is extremely important. Sometimes gent requirements imposed on a fuze emphasize the results are surprising and perhaps discourag­ the need for extensive tests after the prototype ing. Accumulated tolerances and compromises or model has been fabricated. The actual schedule by designers of other components of the weapon used and the number of items tested for evalu­ system (projectile, gun chamber, and propellant) ating a fuze design depend on the type of fuze, cause the operating conditions to differ from severity of requirements, available time and those on which the fuze designer based his calcu­ funds, and related factors. On one hand, the lations and thus can cause malfunctions. This evaluation must be reliable. On the other hand, should encourage the fuze designer to learn more it must be realistic, must permit design revisions about the complete weapon system and to main­ at various stages of testing, and must allow short tain close liaison with the designers of the other major components to arrive at a well integrated cuts when indicated by the particular applica­ system. tion. The tests are described in more detail in Chapter 15 on Fuze Testing. The proof test may indicate the need for basic modifications to the fuze or an area for compro­ While most tests are performed on the com­ mises so that the fuze can be used throughout an plete assembly of the prototype fuze, model tests ammunition series. Likewise, the pilot plant pro­ during the preliminary layout stage can be most duction run may suggest other refinements to en­ helpful and may save many headaches. For in­ hance the ease of manufacture. These changes stance, a novel idea for an arming action could be must be made and evaluated by additional model evaluated by subjecting the pertinent com po­ 9-4

AMCP 706-210 and firing tests. In the end, the success of the de a current fuze are sum m arized in par. 9-4.4. sign depends on w hether the fuze is practical and its cost reasonable. 9-4.1 REQUIREMENTS FOR THE FUZE 9-4 APPLICATION OF FUZE DESIGN PRIN­ A n ew w eap o n sy stem can evolve in one of CIPLES tw o w ays. E ith e r a co m b at e lem e n t d eterm in e s a n eed to m e et c e rta in ta ctica l situ a tio n s or it A review of the foregoing p arts of this H and­ cap italizes on a b rillia n t id ea (designs in som e book show s th a t concepts an d form ulas have cases) for a new weapon. In either case, the tacti­ been presented for functioning and arming of a cal req u irem en ts provide th e in p u t d a ta for ex­ fuze. T h e p u rp o se now is to develop a n d illu s­ tensive ballistic stu d ies from w hich th e g en eral trate the rudim ents of a design procedure. Such size a n d sh ap e of th e com plete p ro jectile or a p ro ced u re could be illu stra te d in tw o w ays: missile are derived. Assume now th a t a fuze for a (1) the voluminous notes, sketches, calculations, projectile is required. W ith scale factors in hand, and drawings of a fuze could be edited and tran ­ th e th e o rist allow s space for th e fuze b ased on sc rib e d a s a n e x a m p le 6 o r (2 ) a c o m m e n ta ry on existing standard projectiles. (He has already es­ the highlights of a step-by-step development of a tablished the outside surface of the fuze by fix­ fuze could be p resen ted . T he la tte r h a s b een ing length and radius of th e ogive.) All these are chosen. The discussion will treat the problem as shown on w hat is term ed a caliber drawing of the though it applied to a new fuze for a new weapon projectile, Fig. 9-l. At the same time, th e theorist system . has calculated the am ount of high explosive to be carried by th e projectile. A d d itional d a ta avail­ The fuze selected for development was chosen able are ballistic curves for the, weapon in which for its simplicity. It illustrates the design princi­ th e p ro jec tile w ill be fire d (Fig. 9-2). F ro m ples discussed above and lends itself readily to a these, the fuze designer can determ ine the forces step-by-step p resen tatio n . H ow ever, it does n o t available during projectile travel in the gun tube necessarily meet all of the current fuze require­ an d a t th e m uzzle. T he ta ctica l use estab lish es m e n ts no r u se th e la te s t av ailable com ponents. the minimum arming distance and how the fuze H en ce, th e follow ing p re se n ta tio n serv es as a should function. sam ple d esign p ro ced u re ra th e r th a n as an ex­ ample of current fuze design. Design features of A ll D im e n sio n s In C a lib e rs Figure 9-1. Caliber Drawing of 40 mm Projectile 9-5

AMCP 708210 The requirements which govern the fuze de­ TABLE 9-1. REQUIREMENTS AND DESIGN DATA sign for the illustrative example are summarized FOR SAMPLE FUZE in Table 9-l. From the Ballistic Curves In addition to the specific tabulated require­ ments, the designer must keep in mind the gen­ Maximum Gas Pressure 40,000 psi eral requirements (par. 9-2) and the acceptance Gas Pressure At Muzzle 9000 psi tests (pars. 15-2 to 15-5). Muzzle Velocity 2870 fps Rifling Twist The fuze designer has his assignment; the re­ Bore Diameter 1 turn in 30 cal quirements have been outlined. In essence, he Projectile Weight 1.575 in. (0.1312 ft) has been handed a chunk of metal with the limi­ 1.985 lb tations shown in Fig. 9-3. Into this space he must fit explosive train and arming mechanism. Other i t 9-4.2 DESIGN CONSIDERATIONS Arming Distance Bore safe i Booster Pellet Material Tetryl The first step is to make a series of sketches, Impact of which Fig. 9-4 might be one, to illustrate the Type of Initiation PD SQ components of the explosive train. It is first nec­ Functioning Action essary to apportion the available space among the components. At least a booster charge, a det­ the space allotted. This space can be machined onator which can be moved away from the open­ out of single block for the fuze or it can be gen­ ing to the booster charge, an arming device, and erated by assembling separate pieces. For this the firing pin are required. Thus, the design of small fuze, a die cast block may be cheaper to the fuze will include three basic su b assem b lies- manufacture than any other type. Then for con­ booster assembly, detonator assembly, and ini- tiatingassembly-all of which must be fitted into venience in the loading plant, booster, detonator, and initiating assemblies should be encased in 9-6

AMCP 706-210 FIRING PIN WRENCH DETONATOR FLAT 7*30 BOURRELET NOTE ALL DIMENSIONS IN INCHES Figure 9-3. O u tlin e o f Fuze C o n to u r BOOSTER PELLET their own housings. A description o f these as­ semblies follows. Figure 9-4. Prelim inary Space Sketch 9-4.2.1 Booster Assembly ating the bursting charge. Enough space must be provided for metal side walls on the booster to The booster assembly includes the booster properly confine the explosion. pellet, the booster cup, the lead, and a closing disk. From start to finish, the designer must al­ Since the booster should be held in a housing ways consider, in addition to fuze functioning as described above, Fig. 9-5 shows the fuze with and operating requirements, the manufacturing the booster pellet encased in a cup that is and loading techniques that are in common use. screwed into the fuze body. Since the cup is One may decide that 5.4 grams o f tetryl at a den­ open end out, a closing disk has been placed over sity o f 0.057 lb/in! are required to initiate the the output end o f the booster to retain the tetryl bursting charge” . For best output, the length to explosive filler. diameter ratio should be greater than 0.3 and less than 3 (see par. 4-4.4). Two standard tetryl The bottom of the booster cup at the input pellets (each 2.7 grams, 0.56 in. in diameter, and end of the booster, however, must have a thick 0.42 in. long) could be used. This will still leave wall, so that if the detonator should explode enough space for a stab detonator between firing prior to arming, the booster will be adequately pin and booster. protected. For initiation at the target stimulus when the detonator is aligned, a small central The above figures are based on the assumption hole is pierced in the cup. Another complica­ that the pellet is allowed to extend into the pro­ tion now arises: the detonator cannot reliably jectile cavity to increase the reliability o f initi­ initiate the booster if the gap (hole through the booster cup) is too long. To assure reliability of 9-7

AMCP 706-210 the explosive train, the same type of explosive as shown to be sufficient to initiate a tetryl booster the booster pellet, tetryl, is inserted in the hole and the input sensitivity is great enough for this to carry the detonation wave to the booster. This fuze (shown later). is termed a lead. This component is initiated by the detonator and leads the detonation into the In order to provide detonator safety, the deto­ booster. nator must be moved out of line with the lead. A simple device for doing this is a disk rotor that 94.2.2 Detonator Assembly carries the detonator. In the unarmed position, the explosive train is completely interrupted be­ In this simple fuze, the detonator converts the cause the firing pin is blocked from the detonator kinetic energy of the firing pin into a detonation and the detonator output end is not close to the wave. Thus a stab detonator is required that will lead. In the armed position, the disk will be ro­ be sensitive to the results of the expected target tated so that both of these safety precautions impact and yet will have an output that will re­ will be removed. Fig. 9-5 shows these features. liably initiate the tetryl booster. The rotor diameter must be just larger than In accordance with the desire that standard the length of the detonator (0.41 in.), and the components be used wherever possible, a stab rotor thickness (the detonator has a diameter of detonator is sought that will fulfill the require­ 0.11 in.) must surround the detonator with ments. For example, the MARK 18 MOD 0 stab enough material to provide adequate confine­ detonator has an input sensitivity of 24 in.-oz. ment (see par. 4-3). These considerations fix the The explosive components part of the Army- dimensions of the rotor. Detents are added to Navy-Air Force Fuze Catalog” and the volume hold the disk in the unarmed position; the detent on Explosive C om ponent^ list additional data. springs are held in place by the detonator assem­ Output is given as an indentation of at least bly housing shown in Fig. 9-5. 0.090 in. in a lead disk. This output has been Fig. 6-14 shows a representative disk rotor. The approximate dimensions of the rotor will be DETENT -BOOSTER CLOSING DISK (A) Front V ie w (B ) Side View Figure 9-5. Booster and Detonator Assemblies 9-8

amcp 706-210 s e le c te d a s 7/16 in . in d ia m e te r a n d 5/32 in . Table 9-2 lists the various moments of inertia for th e ro to r an d its p a rts as calcu lated by th e th ick in o rd er to p ro p erly h ouse th e d eto n ato r. usual formulas. By using Eq. 6-46 with 6 0 = 55° Rotor m aterial is selected on the basis of den­ a n d 6 ' = 0 , th e tim e to arm a t th e sp in for th e muzzle velocity (Table 9-1) is found to be about sity, confinement, and safety. An alum inum alloy 3 m sec. Since th e frictio n p re se n t alw ay s d e­ th a t can be die cast would be convenient. cre ase s th e velocity as e v id en t in Eq. 6-47, th e tim e to arm w ill be g re a te r th a n 3 m sec. W hile N ext, th e designer d eterm in es th e arm in g lim its. W hile in th eo ry a fuze a rm s a t a ce rtain the lead weights decrease the arming time, they instant, in practice, allowances m ust be made for also in crease th e stab ility of th e ro to r in th e dimensional tolerances and variations in friction. armed position which increases the reliability of H ence, bo th m inim um an d m axim um arm in g the fuze to initiate the bursting charge. lim its m u st be selected. T he specified arm in g levels are co n v erted in to u n its applicable to th e To restrain the disk in the unarm ed position, particular design, such as setback or spin levels. d eten ts are in serted th a t are held by springs. The minimum arming level (must-not-arm value) If friction between detent and rotor hole is con­ m ust be sufficiently high to assure safety during sidered negligible, these springs are set w ith an h an d lin g an d testin g . T he m axim um arm in g in itial com pression equivalent to th e centrifugal level (m u st-arm v alu e) m u s t be w ell w ith in th e force p ro d u ced by th e d e te n ts a t th e m in im u m cap ab ility of th e w eap o n an d m u st fulfill th e sp in to arm . A t th e la tte r sp in ra te th e d e te n ts sta te d req u irem en t. T he sp read betw een th ese w ill be in eq u ilib riu m w hile a t an y h ig h e r spin two values m ust be reasonable from a viewpoint ra te th e y w ill m ove rad ia lly o u tw ard to release of manufacturing tolerances. Experience dictates th e rotor. Eq. 6-17 defines th e m otion for th e which of the many values th a t meet these broad detents. Two item s are im portant: (1) the spring limits are optimum. force in creases as th e sp rin g is com pressed, b u t the centrifugal force increases at the same rate; For the sample projectile, the spin at the muz­ th erefo re, once th e p a r t m oves it w ill co n tin u e zle is fo u n d from F ig. 5-5 a s 730 rp s o r 44,000 rpm . R easonable arm in g lim its, b ased on th e to move rad ially o u tw ard ; and (2 ) th e frictional above co n sid eratio n s, w ould be 1 2 ,0 0 0 a n d forces arise from the torque induced in the rotor. 2 0 ,0 0 0 rpm . The resisting torque on the rotor is represented by th e second te rm on th e left-h a n d side of Eq. W ith th e e q u a tio n s in p a r. 6-5.1, th e tim e to 6-45. F ro m th e v alu e of th e d isk assem b ly in arm (th e tim e for th e ro to r to tu rn in to th e aligned position) is calculated. For a first approx­ T a b le 9-2, th e to r q u e is f o u n d to b e 3 .7 2 x 10'3 imation Eq. 6-46 m ay be solved for t by neglect­ ing friction. T h is v alu e should be th e m in im u m lb -ft a n d th e fric tio n a l force on each d e te n t is arming time. 0.15 lb. T h e c e n trifu g a l force o n th e d e te n t, w eig h t 4 g rain s, is ca lc u lated from E q. 5-11 as N ote from E q. 6-46 th a t th e tim e to a rm d e­ 0.37 lb. The initial spring load, according to Eq. p en d s only up o n th e ratio of th e m o m en ts of 6 - 1 7 m ust be a t least 0 .2 2 lb to prevent arm ing below the spin of 12,000 rpm. The spring design inertia of th e disk. However, density is not an ig- is explained in par. 1 0 -2 .1 . n o ra b le factor. The individual moments of inertia depend upon density of rotor and its components. TABLE 9-2. COMPUTATIONS OF MOMENTS OF INERTIA, Slug-Ft2 Solid disk 1 .1 7 4 X 10'8 1.042 x 10'8 1.042 x n r8 0 X 10'8 Hole for lead 0 .0 7 8 0 .0 8 2 0 .0 0 9 2 0 .0 7 3 0.014 0.151 -0 .1 3 7 H ole for d e to n a to r 0.151 0.0032 0.0019 0.858 0.0013 Hole for detent 0.0046 0.836 0.0954 -0 .0 2 2 0.0106 0.038 D isk 0 .8 3 0 0.340 1.029 -0 .0 8 4 8 1.527 0.302 D etonator 0.0954 0.498 Lead weights 0.322 Disk assembly 1.569 9-9

AMCP 706-210 9-4.2.3 Initiating Assembly sp rin g is co n v e n ie n t to ho ld th e firin g p in d e t­ This assembly, shown in Fig. 9-6, contains the ents inward. See par. 10-3.2 for the calculations firing pin, the firing pin extension, two detents, a firing pin housing, and the spiral spring. One appropriate for such a spring. n o tes th a t th e firin g p in w ill be su b ject to re a r­ From th e specifications provided for th e ogive w ard motion on setback. Since this is highly un­ d esirab le (the p o in t w ill be dam aged), som e shown on Fig. 9-3, an enlargem ent of Fig. 9-1, it m eans are usually provided to prevent such rear­ is noted th a t th e nose of th is particular projectile w a rd m o tio n . F ig . 9-6 in d ic a te s tw o h o u rg lass is ra th e r long. Hence, the designer should use a shaped detents between firing pin shoulders and lig h t firin g p in in o rd er to d ecrease th e in e rtia l co n tain e r to p re v e n t re a rw a rd m otion. T h ese effects. A p lastic firin g p in ex ten sio n on th e detents are subject to the same considerations as m e ta l firin g p in w ill suffice if th e tw o p a r ts are ro to r d e te n ts rela tiv e to le n g th an d clearan ce (see par. 6-4.1). The hourglass shape provides a rigidly connected to provide for oblique impacts. m o re p o sitiv e lock th a n a cy lin d er b ecau se s e t­ T he firin g p in itself can be red u ced to a w eig h t b ack te n d s to cock th e d eten ts to re s tra in th e ir motion. Therefore, these detents will be released of 1- 1/4 grains an d the firing pin extension to 2 at a higher spin than the rotor detents. This ar­ ran g em en t assu res th a t th e firing p in cannot grains. m ove u n til th e d eto n ato r h a s ro tated into line. Will this firing pin assembly provide the neces­ O nce th e setb ack acceleratio n is rem oved, th e detents are free to move radially outward just as sa ry 24 in.-oz to in itia te th e d eto n ato r? O ne the rotor detents are. could calcu late th e k in etic en erg y for a rea so n ­ able firing pin velocity, say 130 fps, m aking the F o r th is geom etry, a sp iral (w rap-around) n ecessary assu m p tio n s for friction in th e firing p in m otion for b o th sq u are an d oblique im ­ p acts. H ow ever, su ch co m p u tatio n is n o t of m u ch valu e. It is m ore reaso n ab le to assu m e th a t th e firin g p in sto p s (in effect) on im p act, an d th a t th e energy of th e projectile is available to fire th e d eto n ato r. H ence, th e d eto n ato r h a s a satisfactory input sensitivity for this fuze. 9-4.3 TESTS AND REVISIONS F in ally , th e d esig n show n in F ig. 9-7 is derived. P arts are m an u factu red and assem bled into th e fuze. T he design m u st now m eet proof te st standards. W hen the fuze passes the appli­ cable te s ts of p a rs. 15-2 to 15-4, th e d e sig n e r h as achieved h is goal. 9-4.4 DESIGN FEATURES OF CURRENT FUZES 9-4.4.1 Example of Current Fuze Design Figure 9-6. Initiating A ssem b ly F u z e , XM539E4, is a p o in t- in itia te d , b a s e detonated fuze for the XM409 HEAT C artridge. I t h a s few m oving p a rts (no clockw ork), a s a m a tte r of fact, h a s few to ta l p a rts. I t m eets strin g en t safety req u irem en ts through m echani­ cal and electrical safety. It is spin arm ed and has delayed arm ing. The p o in t-in itiatin g elem ent in th e nose is th e piezoelectric P ow er Supply, XM22E4 (s e e p a r . 3 - 4 .3 .1 ). The fuze is shown in Fig. 9-87. During storage an d h an d lin g , th e explosive tra in -th a t con sists 9-10

F ig u r e 9-7. C o m p le te Fuze A s s e m b ly AMCP 706-210 of the XM65 Electric D etonator, a lead, and the booster pellet-is interrupted by the out-of-line position of the rotor. The rotor is locked in the out-of-line, or unarm ed, position by two op­ posing and spring-loaded detents that engage into holes at each end of the rotor. Two set screws serve as thrust bearings on the ends of the rotor shaft. A return arm assembly, consisting of a weight brazed to the return frame is pivotable about a return pin and is held against the rotor stop pins by the rotor return spring. All are contained in an alum inum die-cast hous­ ing that in turn is contained in the body, and held by the booster cap assembly. A plastic plate carrying the rotor stop, terminal post, and contact leaf is held betw een body and rotor housing. Centrifugal force, generated by the high spin velocity of the projectile, acts on the detents forcing them to move radially outward, unlock­ ing the rotor. Setback and centrifugal forces, also acting on the return w eight, cause the re­ turn arm to pivot aw ay from the rotor. The rotor is then free to arm. Spin forces acting on the dynamic unbalance of the rotor induces the BOOSTER r cup \\ _ S P I N DETENT WA3HER(2) F ig u re 9 -8 . Fuze, PIBD, XM539E4 9-11

AMCP 706-210 rotor to rotate until the detonator contact is i against the stop, and the detonator is aligned with the lead cup. In this position, the detonator Figure 9-9. Head Assembly far Fuze, M557A1E 1 makes electrical connection with the contact (Rain Inserts Hive) leaf. Electrical energy transm itted from the nose element upon impact or graze initiates the drops 4 mm and larger in diameter and reduce detonator that propogates through the explosive their momentum to a level sufficiently below the train. threshold energy for initiation. Four drain holes, spaced equally around the base of the cavity, The return arm will return the rotor in the expel by centrifuge action any accumulation of event that the fuze does not function if the spin water. drops below 2000 rpm. This insures against firing of a prearmed fuze and provides for safe disposal This type of head is also effective in desensitiz­ and handling of spent projectiles that were not ing fuzes for more effective penetration of jungle destroyed by target impact. canopy. In this type of environment, the bars and the recess serve to cup up all foilage, 9-4.4.2 Example of Rain Insensitive Design branches, etc., encountered, filling the cavity while providing a delay beneath the canopy. An effective empirical rain desensitizing fea­ When the cavity is completely filled, the fuze ture for point-detonating fuzes consists of a re­ functions in the regular impact mode. cessed cavity in front of the superquick element (which consists of firing pin, firing pin support cup and a detonator) as shown in Fig. 9-9. The head assembly is the one used to make Fuze, M 5 5 7 A 1 E 1 rain insensitive. The cavity dimen­ sions can be varied so as not to seriously affect functioning against normal targets. Dimensions of the cavity illustrated are 1/2 in. diameter and 3 / 4 in. deep. The recess is baffled by three cross bars of different depths and orientations in the holder. These bars effectively break-up rain REFERENCES a-t Lettered References are listed at the end of S a fe ty C rite ria For, Dept. of Defense, 16 this handbook.1 June 1967. 1. AR 70-38, Research, D evelopm en t, T est and Evaluation o f Materiel f o r Extreme Climatic 5. M IL -A -2 5 5 0 A , Ammunition and Special Weapons, Conditions, July 1969. General Instructions For, Dept. of Defense, 15 2. A. W. Baldwin, Humidity as a Factor in Fuze December 1961, Paragraph 4.8. Design and Evaluation, Journal Article 26.0 6. R. L. Graumann, History o f Design and De­ of the JANAF Fuze Committee, 1 February velopment o f Mk 2 7 PD F u z e , Naval Ordnance 1963, AD-296 582. Laboratories, White Oak, Md., Memorandum 3. USAMUCOM Regulation 705-11, Research and 7868, 5 September 1945. Development o f Materiel, Fuze Design, 11 7. F. S p in d le , Fuze PIBD, XM539 Series a n d S u p ­ June 1964. p ly , Control Power, XM22 Series (U), H e s s e * 4. MIL-STD-1316 (Navy), Fuzes, N avy, Design Eastern Div., E v e re tt, M ass., Final S u m m ary 9-1 2 Report, 14 February 1966, Contract D A - 1 9 -0 2 0 - ORD-5442 (Confidential).

AMCP 706-210 CHAPTER 10 FUZES LAUNCHED WITH HIGH ACCELERATION 10-l GENERAL 10-2.1.1 Restraining Motion As stated in par. 5-3, munitions are launched Assume the following problem : Design a with a high or a low acceleration. Munitions are striker spring for a fuze head assembly as shown normally called projectiles if fired from guns, in Fig. 10-l. The spring is required to prevent the howitzers, and recoilless rifles. The projectiles forces experienced in flight (exterior ballistics parts must withstand great setback forces and forces) from driving the firing pin into the deto­ yet retain their operability. This requires strong nator until the target is struck. Approximate di­ parts. While the projectile is in the gun tube, set­ mensions are scaled from the outside dimensions back forces all parts rearward along the munition of the head. axis. Motion in the tangential direction for both arming and functioning can begin when the set­ FIRING PIN /-STRIKER SPRING back acceleration is sufficiently reduced after the projectile leaves the muzzle. Mechanical STRIKER arming and percussion initiation are the simplest Fig ure 70-l. Fuze H ead A ssem bly for the fuzes. This Chapter contains design examples of parts found in projectile fuzes. Springs, rotors, sliders, lock pins, and sequential leaves are typical parts. 10-2 f u z e c o m p o n e n t s f o r f in -s t a b i­ l iz e d PROJECTILES Fin-stabilized projectiles either do not spin at The drag force on the striker is calculated by all or spin at a rate below that required to stabi­ Eq. 5-3 in which KD - 0 .3 5 , d = 0 . 8 2 in ., P = lize projectiles. The centrifugal forces acting on 0.0806 l b / f t 3 , and the velocity = 700 fps. Hence, the fuze parts cannot be used for arming because the drag force is 2.0 lb. Note that, because of the they are not sufficiently different from those of streamlining of the projectile, the overall drag normal handling. Tail fins on these projectiles coefficient is 0.066 for the 60 mm Mortar Pro­ prevent tumbling during flight. Arming is accom­ jectile, M 4 9 A 2 1 . To prevent firing pin motion, a plished by means of springs and initiation by the firing pin spring must be designed to have an ini­ effect of target impact. The springs may move tial compression load of at least 2.0 lb. sliders, hold lock pins, or turn rotors. Each must be designed according to its purpose. If a helical wire spring is used, the wire diam­ eter may be estimated from the empirical formula 10-2.1 COIL SPRING DESIGN One common problem for a fuze designer is where F is the load at solid height, say, 4 lb; d is that of designing a spring to support a certain the mean diameter of the spring, in.; and r is the safe shear stress in the wire, psi. From Fig. 10-l load. Usually the designer calculates the load and the allowable mean diameter is 0.45 in. Let this then fits a spring into the available space that will be d and the allowable stress be 90,000 psi. Eq. support that load. He determines wire size and 10-l indicates the wire diameter to be 0.040 in. material, number of coils, and free height neces­ sary to fulfill the requirements. An approximate Although the spring formulas take into ac­ design is made that may be modified later, if nec­ count only torsional stress, the stress caused by essary. The following example illustrates the procedure. 10-l

AMCP 708210 transverse shear may be accounted for by in­ tor of safety of 2 is preferred. However, if a high cluding the Wahl factor Kv . This correction fac­ safety factor is required, the sensitivity of the fuze will be decreased. tor depends upon the ratio of the mean diameter of the spring to the wire diameter. 10-2.1.2 Controlling Motion For this spring C = d/dw = 11.3 (10-2*) Helical springs may also be used to control the motion of a mass. As an example, the lock­ The Wahl factor Kw is estimated from ing action of a setback pin on another pin will 1 . 2 0.56 0.5 (10-3) be discussed. A suggested interlock is shown in Fig. 10-2. K C C2 C3 During launching, setback forces drive the set­ back pin rearward which releases the safety pin so that Kv = 1.12. The designer calculates the so that the safety pin spring can pull the pin out­ actual shear stress under the given load by the ward. Since the setback pin is free to return fol­ equation lowing launching, the designer must be certain that the safety pin moves far enough during or r _8_F_dKw 8 0 , 0 0 0 p s i (10-4) just after launching to prevent the setback pin ” dl from re-entering the locking hole after setback forces cease. which is within the allowable limit. The following parameters are needed to com­ The motion of the safety pin is controlled by the frictional force P ^pa ' ■where p is the coeffi­ plete the solution: cient of friction, is the weight of the part, lb; (1) Pitch Ph of the unloaded helix (0.14 in.) and a’ is the acceleration, g. During setback, a’ is large so that p^pa' > F which predicts that the Ph QFd n h (10-5) safety pin does not move during launching. G'd4 + d ■+ c Therefore, it must move fast enough after launch­ ing so that the setback pin does not re-enter the where hc is the clearance between coils (usually locking hole. (This is the marginal condition.) 10% of the wire diameter or of the first term of Eq. 10-5) and G’ is the shear modulus of the Let the design set the condition that the safety wire; pin will move a distance greater than 1/4 the diameter of the setback pin before it returns to (2) Number of active coils jV for a closed lock the safety pin. The mass of the pin is 0.455 end coil . x 10\"3 slug,, its spring constant is 1.31 lb/in., and the coefficient of friction is assumed to be 0.20. /V= — - 2, coils (10-6) This safety pin is acted upon by the spring, the dV friction force resulting from creep P-^pa' , and the frictional force / caused by the slider shutter where hs is the solid height, 0.60 in. (the height at load minus the dead coils divided by the wire diameter plus the clearance). For this case, N is 13 active coils; (3) Free height h of the coil (1.94 in.) hf = Np„ + 2dw, in. (10-7) The formula for the spring constant is given in S E T B A C K PIN SAFETY PIN SPRING Table 6-1 from which the constant is found to be -SA F E T Y PIN 3.1 lb/in. Therefore, if the designer specifies an (BOTTOM POSITION initial compression of one inch, there will be a safety factor of 1.6 because the load to be re­ .079 in. F R O M sisted was calculated to be 2 lb. Usually a fac- S A F E T Y PIN) *From Mechanical Springs by A.M. Wahl, Copyright 1963. Figure J O - 2 . Interlocking Pin Used by permission of McGraw-Hill Book Company. 10-2

AMCP 706-210 pressing on the pin. The equation of motion for acceleration m ust be greater th an th at resulting th e p in is s im ila r to E q. 6-12 w h e re f is 0.25 lb from a drop b u t less th a n th a t p roduced by a and a \" is 10 g. To solve for th e tim e to move the properly fired projectile (see par. 6-5.4). distan ce x o - S , th e in itial com pression of th e The th ree-leaf m echanism used as the safety spring x ; m ust be known. This is typical of de­ device in th e 81 m m M o rta r F uze, M 532, is shown in Fig. 10-3. O peration is as follows: Upon sign problem s: assum ptions are m ade, com puta­ setback, th e first le a f tu rn s ag a in st its spring. tions are performed, and then the original dimen­ W hen it rotates far enough, it perm its the second sions are corrected if necessary. leaf to rotate, and th a t in succession releases the la s t leaf. T he la s t le a f m oves o u t of th e w ay to H e n c e , if x q is 1.5 in . a n d if th e p in m u s t release the arming rotor. move 0.029 in. (1/4 of 0.116 in.), th e tim e in ter­ The mechanism utilizes a large portion of the v a l w ill b e 1 .1 x 10'3sec f r o m E q . 6 -1 2 . H o w f a r area under the acceleration curve because succes­ sive leaves are assigned to successive portions of will the setback pin move in this time? Fig. 10-2 show s th e p e rtin e n t dim ensions for th e setback th e curve (see Fig. 6-19). Each leaf is designed to p in . L e t th e s p rin g c o n s ta n t be 1.31 lb /in . a n d the pin weight 0.0022 lb. To obtain the greatest operate at a slightly different minimum accelera­ d istan ce th a t th e p in w ill m ove, th e effects of tion level by using identical springs w ith geomet­ frictio n a re neglected; in th a t case Eq. 6-5 w ill rically sim ilar leaves of d ifferen t thicknesses. serve in which x is approximately 0.45 in. Thus Each leaf operates when it experiences approxi­ * = 0.39 in. whidfi m eans th a t the pin will move mately half of the average acceleration occurring 0.06 in. T h erefo re, th e se tb ac k p in m u s t be in the interval to which it is assigned. For exam­ bottom edat least 0.060 in. aw ay from the safety ple, th e firs t le a f is d esig n ed to o p e ra te w h en it pin. 1 experiences a n acceleratio n of app ro x im ately 450 g for 2.5 m sec. T he to ta l d esig n velocity The setback pin will strike the safety pin some tim e later th a n 1.1 msec, and the p in will not be change is approximately 110 ft/sec. able to re-enter the hole; hence the fuze will con­ tinue to arm. T he m e ch an ism h a s b een sh o w n to be safe 10-2.2 SEQUENTIAL LEAF ARMING w h e n s u b je c te d to 40-ft d ro p s. T h is s a fe ty r e ­ F o r p ro jectiles th a t do n o t ro ta te , a rm in g is su lts from th e fact th a t th e im p act velocity in a usually accomplished by setback forces. The mo­ tion of sliders and rotors th a t is impeded by set­ 40-ft d ro p ( a b o u t 5 0 ft/sec) is le s s t h a n h a lf th e back can be used to achieve bore safety. Acceler­ ations resulting from a drop are higher (Fig. 15-5) design velocity change for the mechanism. How­ but are not sustained as long as those resulting ever, the parachute drop imposes the most strin­ fro m firin g (F ig. 5-2). H e n c e , m a n y dev ices a re built to discriminate between firing setback and gent requirem ents on this mechanism3 . It sped- im pact forces due to drops. fies th a t the fuze m ust w ithstand the ground im ­ P e rh a p s th e e a sie st w ay to d iscrim in ate b e ­ p ac t forces th a t re su lt w h en it is delivered by tw een th e tw o is to b u ild a device th a t is a c tu ­ p arach u te. The m echanism w ill p rev en t arm ing ated only by the accelerations present under fir­ w hen the am m unition is delivered by a properly in g conditions. A n ap p ro x im atio n to th is accel­ functioning parachute because the impact veloc­ eratio n can be o b tained w ith a seq u en tial leaf ity is less th a n th a t for a 40-ft free-fall drop. However, if the p arach u te m alfunctions during mechanism2. T h e m a i n f e a t u r e i n i t s d e s ig n is delivery, the velocity change at impact is greater th a n th e design velocity change. I t is, therefore, th e req u irem en t of an ex ten d ed acceleration, possible th a t a fouled p a ra c h u te d eliv ery could much longer th a n th a t present in a drop impact produce th e m in im u m design acceleration for a into an y m edium u su ally encountered. W ith a length of tim e sufficient to arm the mechanism. p ro v isio n for re tu rn to th e u n a rm e d po sitio n , th is device can w ith sta n d m a n y drop im p acts 10-3 FUZE COMPONENTS FOR SPIN-STABI­ w ith o u t becom ing com m itted to arm . LIZED PROJECTILES Sequential leaf mechanisms are designed to re­ The arming operations of munitions stabilized spond to a th resh o ld acceleratio n su sta in e d for by sp in m a y m ak e u se of th e forces du e to som e period of tim e. T he p ro d u ct of tim e an d the spin on the fuze parts. Sliders can be moved by th e c e n trifu g a l force field, ro to rs m a y be 10-3

AMCP 706-210 repositioned by turning, and detents can be with­ ogive. An angle of, 75” will serve as a first ap­ drawn against spring pressure. proximation. The final angle depends on the ratio of setback to centrifugal forces. 10-3.1 SLIDERS A retainer spring can satisfy requirement (2) Sliders form a convenient way to hold the as well as the rough handling requirements. It re­ detonator out-of-line. Here the designer is in­ mains to adjust the’spring constant and the posi­ terested in the time interval, after firing the tion of slider mass center with respect to the projectile, during which the fuze is safe or the slider has not moved. He calculates this from spin axis. Fortunately, requirement (3) is ob­ estimated dimensions of the slider. The time tained with the same calculations. interval requirement may be stated in this fash­ ion: (1) the time interval for sliders must not Since the slider will generally continue to begin until after the projectile leaves the gun be­ move once it starts (the spring force is balanced cause the fuze must be bore safe (the separate by the increasing centrifugal force and the ki­ time delay, required while the fuze is in the bore, netic friction coefficient is less than the static is usually achieved by setback), (2) the fuze must one), the designer needs to know the conditions not arm below a certain spin velocity (the cen­ under which the slider will move. Set x = %o in trifugal field is too weak to cause arming), and Eq. 6-29 and reduce it to (3) the fuze must definitely arm above a certain spin velocity. These concepts are discussed more m = ~kx - WaVsind) + acosd>) ( 10-8) fully in par. 9-2.2. 0 If the slider is placed at an angle less than 90” + no2rg (cos<f> - y sin<j>) to the spin axis, setback forces will have a com­ ponent that opposes radial outward motion of Fbr requirement (1) x < 0 for all possible the slider. This provision can satisfy requirement values of co, for requirement (2) x < 0 for a ’ = 0 (1). For a nose fuze, a convenient angle is that and where o is the lower spin specification, and which makes the slider perpendicular to the for requirement (3) x > 0 where o ’ is the creep deceleration and <u is the upper spin specifica­ tion. As an example, suppose it is desired to find the angular spin velocity necessary to arm a fuze LEAF NO 58 SHIFT ASSEMBLY F igure J O - 3 . L e a f A rm in g M e c h a n i s m o f F u z e , M53 2 1 o-4

AMCP 706210 having th e slider shown in Fig. 6-7. The d ata are ball? S uppose th e d e te n t sp rin g is a b ery lliu m <f> = 15” , *0= 0.300 in., ro= 0 .0 6 2 in ., fi = 0 .2 , co p p er strip 2.505 in. long, 0.115 in. w ide a n d and the spring constant k = 1.0 lb/in. Table 10-1 0.005 in. thick. This is wound into a coil 0.65 in. shows a summary of the conditions and calcula­ in diameter when unloaded. Therefore, the rotor tio n s . F o r x < 0, k x Q+ Ha' (sin + + fi cos 0 ) > unit will appear approximately as shown in Fig. 10-4. A sp rin g stop is n ee d e d to p re v e n t th e moj2r o (cos</> - pi.sin<£) w h i c h i m p l i e s t h a t spring from walking around the ball. kxo + Wa' (si n<j> + ficos<f>) (10-9) By taking advantage of th e axis of sym m etry v 2 < — --t-n-r----(}-c--o--s- 0\"7---•-«----f-i--s-\\-n: <Tp7) through the spring stop, deflections need be cal­ cu late d for only tw o d eten ts. T he deflection of T he specifications sta te th a t th is fuze m u st n o t the spring at detent B will be calculated because arm a t 2400 rpm b u t m u st arm a t 3600 rpm . if B can m ove fa r en o u g h to release th e rotor, C alcu latio n s show th a t th e specifications are th e n A, b e in g c lo se r to th e o p e n e n d o f th e satisfied. spring, will also release the rotor. The spring de 10-3.2 ROTOR DETENTS flection a t B w ill b e c a u s e d b y t h r e e e ffe c ts o f Another device used in fuzes to obtain detona­ centrifugal forces: (1) th e cantilever action pro­ to r safety is a sp h erical b all ro to r as show n in d u c e d a t B b y th e m o tio n o f d e te n t A, (2) th e Fig. 6-22. The ball in a spinning m unition tries to motion of d etent B, and (3) th e expansion of the align its p olar m om ent of in e rtia axis w ith the spring itself. spin axis (see par. 6-5.7). This alignm ent m ust be p rev en ted bo th before firing an d u n til th e p ro ­ Spring analysis shows th a t the rad ial deflec­ jectile clears th e gun. U su ally d e te n ts hold th e tio n of th e sp rin g yB a t th e d e te n t B by a force ro to r in th e u n a rm e d position. In tu rn th e detents are held by a spring. Fa a t t h e d e t e n t A o n F ig . 10-4 is A 57 mm recoilless rifle projectile will serve as Figure 10-4. Spiral Spring for Ball Rotor an example. Ballistic constants are th e following: m u z z le v elo city = 1200 fps, w e ig h t = 2 .7 5 lb, rifling tw ist of 20 cal/turn, and a propellant pres­ su re a t th e m u zzle of 2000 psi. E q. 5-4 s ta te s t h a t t h e s p i n a n g u l a r v e lo c ity i s 2 0 1 4 rad/sec while Eq. 5-2 shows th a t the projectile accelera­ tion at the muzzle is 2876 g. To keep the rotor dynam ically balanced, four cavities are drilled radially into it for the detents. B e c a u s e o f t h e r o t o r ’s s m a l l s iz e , o n e t u r n o f a flat spiral spring serves to hold the detents in the ball. How long should the designer m ake the det­ ents and how far should they penetrate into the T A B LE 10-I. S U M M AR Y OF CONDITIONS A N D C A LC U LATIO N S General Condit ions A ctu a l Values Spring a’, kx o ' CO to arm, in Use Requirement x a’ a Arm g lb re v/mm No (1) <0 very large setback reasonable value No No 13,600 0 59,000 muzzle value setback muzzle spin No Yes 25,000 <0 muzzle spin ‘N o Yes 2,500 0 0 muzzle spin Yes 2,980 ( 2) <0 < 0 (creep) 0 0.300 2,520 (3) >0 -10 0.300 10-5

AMCP 706-210 cos (a. 2 10 10dj) + % sin a COS “ i ( - ) I T e r m s 'are d e f in e d i n t h e f ig u r e . T h is e q u a t i o n c a n b e u s e d for effec ts (1) a n d (2) b u t a } = a 2 for e ffe c t (2). T h e th ir d effect, th e e x p a n s io n of t h e s p r i n g y BC , i s c a l c u l a t e d w i t h t h e e q u a t i o n ( 10 -1 1 ) where N O TE:- A LL D IM E N S IO N S IN INCHES E = Y o u n g ’s m o d u lu s , p s i F ig u re JO-5. E ffe c t o f D etent Length I, = second m o m en t of th e cross-sectional 10-11, an d 10-12, th e length of th e detent can be area, in? determ ined as a function of th e spin velocity o) p = d en sity of th e spring, lb /ft3 yBA + yBB + yBC = yfa) (10-15) t - spring thickness, in. The follow ing d ata apply r = ra d iu s o f th e sp rin g loop, ft a 2 = 120” 2 “i = 60” N o te t h a t F = mrcgcu for th e d eten t w here r = 0.0360 f t rcg is the radial distance to the center of gravity t, = 0.005 i n . o f t h e d e t e n t . F ig . 10-5 s h o w s tw o e x t r e m e s fo r P = 531 slug/ft3 th e le n g th of th e d e te n t. T h e b all d ia m e te r is 0.563 in. a n d th e sp rin g d ia m e te r is (0.136 + E = 18 x 106psi 2.505)/77 = 0 .8 4 1 in . T h e re fo re , th e le n g th o f detent extending outside of the ball is 0.139 in. I A = 1 .2 0 x 10'9 in : The distance to the center of m ass for the detent is r eg in. (10-12) and (10-13) Ap = 8.62 x 10'5 f t 2 y = (l ~ 0 . 1 3 9 1 , i n . The expression for l as a function of a becomes w h e re 1is th e le n g th o f th e d e te n t, in ., a n d y is the radial deflection of the detent, in. l - 0.0116 = (0.7361 - 1 0 .3 8 12 + 0 .0 0 1 5 5 ) J x 10‘ 5 Since th e d e te n t m a ss is m = p lA p, th e force F is (10-16) The rotor m ust not arm at 2525 rpm. Hence, 1 lb (10-14) ca n be 0.246 in. T he sp rin g h a s b ee n d eflected 0.432 — 0 .6 5 0 /2 = 0.107 in. during assembly so w h ere p is th e d en sity of th e b ra ss detent, th a t th e d e te n t w ill n o t m ove u n til th e spin lb /in .3, a n d Ap is the cross-sectional area of the reaches at least 2525 rpm. W hat spin is required d e t e n t , in? T h u s b y c o m b i n i n g E q s . 1 0 -1 0 , w ith an initial spring deflection of 0.107 in. if l is 0.246 in. long? A ccording to E q. 10-16, th e 10-6

AMCP 706210 d e te n t w ill release th e ro to r a t a sp in of 2560 rpm which is in the specified range. There is one feature th a t has been neglected: the torque of the ball rotor squeezes the detents la te ra lly . T h is w ill p u t a frictio n . force on th e d e te n ts , w h ich w ill h in d e r th e ir te n d en c y to m ove outw ard. T herefore, th e spin m u st be greater than the value calculated to cause arm ­ ing, or th e le n g th of th e d e te n ts c a n be less. In th e a c tu a l fuze, th e d e te n t is only 0 .208 in. lo n g w h ic h a c c o r d in g to E q . 10-16 w o u ld r e ­ lease the rotor at 2370 rpm. 10-3.3 ROTARY SHUTTERS S ince th e b u rstin g ch a rg es of h ig h explosive A -B O D Y J-ROTOR LOCK PIN LOCK projectiles are relativ ely in sen sitiv e to shock, a co m paratively pow erful deto n atio n is n ecessary D - COVER K -C E N TR IFU O A L PIN to in itia te th em . T h is is p ro v id ed by a booster. E -O N IO N SK IN PA PER L -R O T O R P IV O T PIN F --R O T O R S T O P PIN H -L E A D F o r e x a m p le , B o o s te r M21A4 is u s e d in c e r ta in G --DETONATOR N - BOOSTER CUP H -R O TO R 0 - BOOSTER CHARGE fixed, sem i-fixed, a n d se p a ra te lo ad in g p rojec­ I-R O T O R L O C K PIN P -C E N T R IF U G A L PIN L O C K PIN til e s . F ig . 10-6 s h o w s t h i s b o o s t e r w i t h tw o m a ­ Figure 70-6. Booster, M21A4 jo r p a rts : (1) th e b o o ste r cup w h ic h c o n ta in s a B ooster, M 21A 4. B asically, th e s h u tte r is a disk tetryl charge, and (2) a brass body containing a with two large segments removed. It fits a circu­ te try l lead and a detonator-rotor assem bly. The lar cavity. The segments are cut out to create an latter provides an out-of-line feature w ithin the unbalance so as to shift the m ass center to a point booster in order to make it safe, if handled alone. diametrically opposite to the detonator. This will in su re th a t th e d eto n ato r can m ove to w ard th e T he ro ta ry sh u tte r is u sed to p iv o t th e deto­ spin axis. Since these rotors can be sliced from an n a to r in to a lig n m e n t w ith th e o th e r explosive extruded bar or made by a sintered metal tech­ elem en ts in fuze an d booster. T he ce n te r of nique, it is n o t difficult to p roduce th is shape. g rav ity of th e ro to r is n o t on th e cen ter line of W ith the limited space allotted to the rotor, r s th e ro to r p ivot an d n o t on th e sp in axis. T he cen trifu g al force th a t is developed w ill th e re a n d ffw ill be sm a ll (on th e o rd e r o f 0.1 in.). E q. fore ro ta te th e ro to r. D e te n ts are u se d to lock 6-56 in d icates th e torque req u ired to accelerate the rotor in both unarm ed and arm ed position. th e rotor. S uppose th e frictio n al to rq u e effec­ tively acts at the center of gravity; it will be T h e s h u tte r a c tio n is d e sc rib e d in p a r. 6-5.5 and illustrated in Fig. 6-20. The torque caused by the projectile spin is calculated with Eq. 6-56 in which the driving torque term is G= r r sinc/> (10-17) Sp r w here m is th e m ass of th e shutter, slug; a is the angular velocity, rad/sec; 0 is an angle, rad; and rs and rp are radii, in., all defined in Fig. 6-20. In order for the shutter to turn, G m ust be greater t h a n t h e f r i c t i o n a l t o r q u e Gf ( a f t e r t h e lo c k in g detents are removed). W h en th e angle becom es zero, th e d riv in g Gf = lb -ft (10-18) to rq u e ceases; therefore, th e d eto n ato r m u st move into alignment before becomes zero. Fig. 6-20 show s th e a c tu a l ro ta ry sh u tte r of in which a’ is setback or creep acceleration, and 1 o-7

AMCP 706210 Wp is the weight of the rotor, lb. Table 10-2 lists rounds require longer running times and might the various conditions for /x = 0.2. undergo angular acceleration during flight (while the timing mechanism is in operation). Also, the If the rotor moves, G must be greater than Gf levels of setback and spin in rocket-assisted pro­ or jectiles will normally be lower, for the same ranges, than levels for regular service projectiles. (02 rs sinewy a 'p g (10-19) In addition to designing the fuze so that it will For the above cases, r = 0.22 in. and </> = 145”. have to sense two different environments before arming, special considerations are necessary to TABLE 10-2. SUM M AR Y OF CALCULATIONS provide safety in the event of rocket motor mal­ function. Rocket motors m alfunction if the Setback a’, g >V lb n V /< Gr lb- f l motor fires when it is not desired, producing a projectile with a longer range than planned. Al­ Creep 20,000 0.050 0.2 0.00833 1.66 ternatively, the motor may not fire when de­ 10 0 . 0 5 0 0 . 2 0 . 0 0 8 3 3 8 . 3 3 x 10'4 sired, producing a short-range projectile. In the former case, a sensor would be desirable to func­ At what spin will this condition be true? By solv­ tion the projectile in the air before it passes be­ ing Eq. 10-19, ox is found to be 550 rev/sec for yond the intended target. In the latter case, it setback and 12 rev/sec for creep conditions. Thus would be desirable for the fuze to dud any pro­ the booster will not arm during setback but will jectile that falls short of the target. arm once the projectile is out of muzzle. Arming probably occurs largely in that interval when set­ 10-4 MECHANICAL TIME FUZES back changes to creep and g forces are momen­ tarily zero. Mechanical time fuzes are used to provide a preset functioning time. They are applicable to In order to obtain a rough estimate of the antiaircraft projectiles, bombs set to burst above time to arm, the designer may use the expression ground, or artillery projectiles set for air burst. They are initiated when they are launched rather (<t>0 = Vi 4> t 2 (10-20) than when they sense the target. A large number of timing mechanisms has been employed in where (<P0 - <f>) is the angular displacement rad, fuzes in the past4 . Note that rocket-assisted pro­ and the angular acceleration, </>', is assumed con­ jectiles will require longer running times and stant for the time t . From Eq. 6-56—with the might undergo angular acceleration during flight conditions m = 0.0016 lb slug, a = 12,000 rpm, (while the timing mechanism is in operation). a n d l = 1.4 x 10'6 slug-ft2 -the initial accelera­ For details of clockwork design, see par. 6-6. tion </> is 0.154 x 106 rad/sec2. If (<f>o <f>) = 1.71 rad, then t will be 4.5 msec. 10-4.1 C LO C K W O R K DRIVE Once the arming time is found to be within In current fuzes, the clockwork is driven by a the proper order of magnitude, the designer may prewound clock-type power spring (see par. solve the problem by numerical integration or he 6-2.3.1). Older fuzes in spinning projectiles were may build a model and test it. Usually a certain sometimes driven by the action of two centrifu­ amount of computational work will be worth­ gal weights in the centrifugal field produced by while; however, this depends upon how valid the the spinning projectile. Although this drive is no assumptions are and how closely the mathematics longer used, it is described here to illustrate a de­ will describe the actual conditions. sign approach. 10-3.4 S P E C IA L CO NSID ER ATIO N S FOR ROCKET- Fuze, MTSQ, M 5 0 2 A 1 , is an example of a fuze having a centrifugal drive. Its timing movement is ASSISTED PROJECTILES shown in Fig. 10-7S . The centrifugal weights at­ tempt to move radially thereby applying a torque When designing fuzes for use with rocket- to the main pinion which is geared to the es­ assisted projectiles, certain factors need to be capement wheel and lever. The safety lever plate considered. Mechanical time fuzes for these locks the escapement lever in position until the 1 O-8

AMCP 709410 ^ SAFETY LEVER \" PLATE FIRING PIN SAFETY PLATE ESCAPEMENT LEVER Figure JO-7. Timing Movement of Fuze, MTSQ, M502A1 fuze is spun at a rate approaching that produced the setting pin and the setback pin drops away during launching. The firing pin is spring-loaded from the firing arm shaft. As the projectile spins, but is held in position by the firing pin safety plate until the firing arm rotates into the firing the safety lever plate moves so that the escape­ notch on the timing disk. A setback pin prevents ment lever is free to swing. Release of the es­ premature rotation of the firing arm shaft until capement lever allows the centrifugal weights to move the main pinion (the gear train is free to it shifts on setback. The timing disk is rotated move) and hence to rotate the timing disk. with respect to safety disk and main pinion when the time delay is set. Upon launching the pro­ When the upright of the firing arm indexes jectile, the hammers depress the setting lug from with the firing notch in the timing disk, the firing arm shaft rotates and releases the firing 10-9

AMCP 706-210 pin safety plate. The firing pin spring then drives cause there are friction and bearing losses within the firing pin into the primer. the gear train, only 28% of the theoretical torque will appear at the escapement shaft or 0.0040 10-4.2 DESIGN OF ONE COMPONENT in.-lb. Since two centrifugal gears are always used in a drive system of this type, all torque values The fuze can be used only in spin-stabilized should be doubled. This value is of the same projectiles because centrifugal force is required order of magnitude as quoted in par. 6-6.3 where to drive the timing mechanism. The centrifugal the clockwork escapement is discussed. Particular weights, acting as the power source for the es­ attention is given to escapements in that para­ capement, move radially outward thereby creat­ graph because they represent the heart of the ing a torque on the centrifugal gear about its clockwork. center shaft. This gear forces the main pinion to turn. The torque on the centrifugal gear is ex­ The timing disk rotates with the main pinion pressed in Eq. 6-56 as so that the centrifugal gear rotates the timing disk at a rate controlled by the escapement lever. G = mo2 r r sin<£ (10-21) Thus the clockwork measures the functioning Sp delay because the explosive train is not initiated until the firing pin is released. The firing arm is where G is the torque on the pivot shaft, m is the spring-loaded and counterbalanced to assure that mass of the gear segment with its center of mass it will release the firing pin when the firing at A, the radii rp and r are shown in Fig. 10-8, notch presents itself. and 4> represents the angle through which the gear could be turned by this torque. 10-5 SMALL ARM FUZES For this gear, the mass is 0.014 slug; r s and r P Cal .3 0 and cal .5 0 ammunition do not require are 0.48 and 0.16 in., respectively; and is 135 °. separate fuzing with out-of-line detonator safety. Let us assume this projectile and fuze are fired The quantity of explosives and incendiary mixes from a 105 mm howitzer with a velocity of 2200 used in them is so small and the damage possible fps at a spin of 225 rps (see Fig. 5-5). This pro­ due to propagation is minimal. The chemical duces an applied torque of 39.5 in.-lb. The gear compositions in these bullets react on impact. ratio is 275 so that the torque on the escapement For example, incendiary and spotting charges shaft is decreased to 0.0144 in.-lb. However, be- will ignite themselves upon impact. Tracer and some incendiary cartridges are ignited by the Figure 10-8. Centrifugal Drive propellant through a pyrotechnic delay”. On the other hand, 20 mm and 30 mm rounds require fuzes having all safety features just like larger projectiles. There must be two independent arming actions’. Small arm rounds differ from larger calibers in three main respects: (1) Obviously, they are smaller. The initia­ tion and arming mechanisms must be compact because little space is available for them. Arming devices most commonly used are disk rotors (see par. 6-5.1), ball rotors (see par. 6-5.7), and spiral unwinders (see par. 6-4.2). While the booster is small-because the main explosive filler is small-it nevertheless occupies a signifi­ cant portion of the space allotted to the fuze. (2) Spin rates of small arm fuzes are higher than those of larger sizes. Rates of 35,000 to 100,000 rpm are common. (3) Small arm fuzes are subjected to addi­ tional forces while being fed into the weapon. During feeding from magazine or belt into the 10-10

AMCP 706-210 chamber of the weapon, the cartridges, and ceases and a spin of 70,000 rpm is reached. therefore the fuzes, are subjected to acceleration and impact in both longitudinal and transverse C-RING ROTOR DETENT directions. High rates of fire require considerable velocities in the feeding operation that leads to F ig u r e 10-9. 20 m m F u ze , M505A3 severe impact loading on sudden checking in the chamber. Fig. 10-9 shows a typical small arm fuze, the 20 mm point-detonating Fuze, M 5 0 5 A 3 . The fuze is used in the M210 and M 5 6 E 2 Cartridges. Its construction is simple-consisting of a fuze body with windshield, a firing pin that shears on impact, an unbalanced rotor that holds the det­ onator out-of-line, and a sealed booster assembly. The rotor is restrained’ from turning by a C-ring detent that will release the rotor after setback REFERENCES 1. H a n d b o o k o f B a llistic a n d E n g in e erin g D ata Paper No. 12, Washington, D.C., 13 March 1966 f o r A m m unition (U) , Ballistic Research Labora­ (Confidential). to ries, Aberdeen Proving G round, Md., Vol. 1, 4. S u r v e y o f M echanical Im p a ct D evices fo r Use July 1050, p. 60-l-49 (Confidential). on M ec h a n ica l Time F uzes, Hamilton Watch Co., Contract DA-36-038-ORD-18508, June 1957. 2. William E. Ryan, A n a ly sis and D esign; R otary- 5. Fuze, M TSQ, M 502A1, Frankford Arsenal, Notes Type S etb a ck L e a f S& A M echanism s, U.S. Army on Materiel, Report MTF-8, Philadelphia, Pa., Harry Diamond Laboratories, Report TR-1190, January 1954. Washington, D.C., 11 February 1964. 6. AMCP 706-185, E n gin eerin g Design Ha ndbook, M ilitary Pyrotechnics, P art One, Theory and 3. R. 0. N itz s c h e , E ffects o f Parachute D elivery A p p lic a tio n . Requirem ents and R ecent D rop Studies on D e­ sign o f Fuze M echanism s (U), Second Fuze Sym­ 7. AMCP 706-2 39 (S )/ Engineerin g Design H a n d ­ posium, Diamond Ordnance Fuze Laboratories, book, S m a ll A rm s A m m unition ( U). (now U.S. Army Harry Diamond Laboratories), 10-l 1

AMCP 706-210 CHAPTER 11 FUZES LAUNCHED WITH LOW ACCELERATION 11-l GENERAL through the atm osphere. C hapter 10 discusses examples of fuzes u n d er­ 11-2 ROCKET FUZES going high accelerations during launching. Accel­ erations on the order of 10,000 to 50,000 g and R ocket fuzes u su ally cannot depend upon ro ta tio n a l ra te s of 10,000 to 100,000 rp m are spin for stab ilizatio n or arm ing. In general, the com m on in those item s. fuzes in m o d ern high-g ro ck ets are of th e sam e general type as those used in artillery projectiles. M u n itio n s h av in g accelerations of less th a n A rm ing m eth o d s su itab le for rocket fuzes are 10,000. g m ay be classified together for purposes d isc u sse d in C h a p te rs 6-8. Tw o ty p e s of ro ck e t of d escrib in g th e force fields u se fu l for arm in g . fuzes are mentioned because they are of histori­ Examples are rockets, guided missiles, grenades, cal interest. an d som e m o rta r projectiles. R ockets have ac­ 11-2.1 HISTOR IC AL FUZES c e l e r a t i o n s i n t h r e e r a n g e s : u p to 4 0 g, from 4 0 Early rocket fuzes had wind-driven generators to 400 g, and 400 to 3000 g. The last are usually or w ere gas arm ed. W ind-driven g en erato rs de o b tain ed by v irtu e of an a ssist (gun-boosted pend upon air flowing p ast th e round while it is rockets). Guided missiles generally have acceler­ in flight to tu rn a generator which supplies the ations of less th a n 100 g. H and grenades have b ut a few g’s, and rifle grenades may experience ac­ v o l t a g e n e c e s s a r y f o r f u z e o p e r a t i o n s . Wind- celerations up to 1000 g. O n th e other hand, the acceleration of m o rta r projectiles d epends upon driven generators were popular for electronic cir­ the am ount of charge used. Hence, their fuze de­ sign is more complicated. c u i t s c o n t a i n e d i n lo w a c c e le r a tio n , nonspin T herefore, th e forces av ailab le to m ove fuze munitions because they were small, rugged, and com ponents for arm in g in m u n itio n s lau n ch ed had a long shelf life. However, while these gen ­ w ith low acceleration are sm aller th a n those for e ra to rs w ere th eo retically very su itab le for h ig h -acceleratio n projectiles. F o rtu n ately , th e rocket fuzes, they introduced problems of sealing tim e d u ratio n of th is acceleratio n is co m p ara­ and position-dependence in the round which have tiv e ly long, fro m tw o to fo u r seco n d s in som e caused them to be practically dropped from con­ rockets. In th ese rockets, acceleratio n s of 20 g sid eratio n . T he fuze of to d ay is e n tire ly sealed, may be developed at launching. The bulk of the has no external pull pins or vanes, and in many cases can be located an y w h ere in th e round. m unitions launched w ith low acceleration are fin- G as-arm ed fuzes used the pressure developed stabilized. W ith a few exceptions, therefore, cen­ by th e ro ck et m o to r to o p erate som e device. F or trifugal forces are not available for arming. proper design of such a system, one m ust deter­ mine the available pressure as a function of time A differentiation will be made between rockets in order to know how long it would take to com­ p lete a given action. G as-arm ed fuzes can an d and g u id e d m is s ile s . I n m i l i t a r y u s e , t h e t e r m have been used effectively, b u t th eir use makes the fuze dependent on the detailed motor design ro ck et describes a free flig h t m issile, m erely an d closure p ressu re. T he ten d en cy is to elim i­ p o in ted in th e in te n d ed d irectio n of flight, an d nate fuze mechanisms th a t can be used only with d ep en d in g upon a ro ck et m otor for propulsion. G uided m issiles, on th e o th er h and, can be d i­ o n e m o t o r a n d w a r h e a d . While it is tru e th a t a rected to th e ir ta rg e t w hile in flig h t or m otion, e ith e r by a p re se t or self-reactin g device w ith in fuze, as such, is designed for a particular round th e m issile, by radio com m and o utside th e m is­ a n d ogive, m o d e rn fu ze s a re b eco m in g m u c h sile, or through wire linkage to th e missile. Note more versatile. Hence, gas-arm ed fuzes are now also th a t a b allistic m issile, w hile com m only practically obsolete. grouped w ith guided m issiles, is guided in th e upw ard p art of its trajectory b ut becomes a free falling body in th e la tte r stag es of its flight 11-l

AMCP 706-210 11-2.2 SELF-DESTRUCTION le n g th s o f d e to n a tin g c o rd fitte d with P E T N r e ­ S elf-d estru ctio n devices are ad d ed to guided lay caps connect th e o u tp u t of th ese m ech an ­ m issiles (and projectiles) designed for d efeat of aircraft. Such devices are to prevent arm ed am ­ ism s to th re e w arh ea d s. O nly one of th e p a th s munition from falling to the ground and causing dam age in friendly territory. The following m ech­ need be com pleted for successful m issile o p era­ anisms, m any of which are also used for arming and have been described elsewhere in this hand­ tion. book, are used to provide self-destruction: Even though several of the fuzes described in (1) A n o rd in a ry m e c h a n ic a l tim e fu ze co n ­ the foregoing text might operate in guided mis­ taining a clockwork th a t will detonate the bu rst­ ing charge at the end of a preset time interval; if siles, th e co n d itio n s on th e se m ech a n ism s w a r­ the target range is too short, the missile will over­ r a n t d esig n s p ec u lia r to th e m alone. A t th e shoot, in which case the clockwork acts as a self­ destruction device (see par. 10-4). present time, missiles are limited to an accelera­ tion of about 60 g; therefore, th e arm ing m ech­ (2) A pyrotechnic delay elem ent th a t is usu­ ally d esig n ed to be in itia te d on setb ack w ith a anism m ust be designed to operate with this ac­ sep arate firing p in ; th e o u tp u t of th e delay ele­ m e n t tie s in w ith th e explosive tra in (see p a r. celeration. A lthough a w ound sp rin g m ig h t be 4-4.1). used as a source of power, as a general rule any (3) I n c a s e o f a s p i n n i n g r o c k e t, s p in d e c a y devices may be used; the devices may consist of arming system th a t uses stored energy is thought seq u en tial lever m ech an ism s (o perated by cen ­ trifu g a l force), of d eten ts, or of c e n trifu g a l to be undesirable. Perhaps the best power source w eig h ts th a t release a spring-loaded firing p in for these low accelerations involves a tim e accel­ (see p a r . 6 -5 ). eration integrator. (4) A b a ro m e tric d evice w h ic h w ill in itia te the weapon when it has fallen below a predeter­ S uppose a n arm in g device is req u ire d for a mined height. hypothetical missile th a t has the following char­ 11-3 GUIDED MISSILE FUZES acteristics: (1) it shall arm w hen under an accel­ Guided missile fuzes contain an arming mech­ anism and an explosive train ju st as other fuzes’ . e ra tio n o f 11 g if th is ac c e le ra tio n la s ts for five H ow ever, th e v ario u s fuze com ponents m ay be separated from the w arhead as well as from each seconds, and (2) it shall not arm w hen under an other. The te rm for th e separate arm ing device is the safing and arm ing (S&A) mechanism. The ini­ acceleratio n less th a n 7 g for a p eriod of one tiation sources may be physically separated from th is m echanism . The S&A m echanism m ay also second. C onsider th e arm in g device show n in be separated from the w arhead, the only connec­ tion being a len g th of d eto n atin g cord or an Fig. 11-l. Setback forces encountered during ac­ electric cable. S& A m e ch an ism s are th e subject celeration of th e missile apply an inertial force to o f a compendium2. th e slider. T h u s a fte r a specified tim e, th e d e t­ T he guided m issile is a large, expensive item w ith h ig h fu n c tio n in g p ro b a b ility re q u ire d so o n ato r w ill be alig n ed w ith th e b o o ster a n d th e th a t m u ltip le fuzing is com m only em ployed. The advantage of the multiple paths is th at the prob­ la tc h w ill drop dow n to lock th e slid er in th e ab ility of failu re decreases exponentially. F or exam ple, one w arh ea d d eto n atin g system of a arm ed position. If a t an y tim e d u rin g th is p ro c­ m issile co n sists of tw o p ara lleled S& A m e ch a n ­ ism s, e a ch c o n ta in in g a d e to n a to r. T h e n five e s s th e a c c e le ra tio n d ro p s b e lo w 7 g, th e s lid e r 11-2 m u st be re tu rn e d to its in itia l p o sitio n by a re ­ tu rn spring. B ecause of its w eight, th e slider w ould m ove too fa s t u n d e r th e se ac ce le ra tio n s; hence, a restraining force is necessary. It is possi­ ble th a t a clockwork escapement may be used to regulate the motion. The following d ata and as­ su m p tio n s w ill h elp to d eterm in e th e size of sp rin g s a n d w eig h ts: (1) n e g le c t fric tio n in th e system, (2) a tan g en tial force is needed to over­ com e th e in itia l re s tra in t of th e clockw ork, (3) th e w e ig h t to b e fo u n d in c lu d e s th e in e rtia l effects of th e whole system, and (4) th e spring is not stretched beyond its elastic limit. In order to prevent motion of the slider under setback accelerations less th a n 7 g, an initial te n ­ sion F = kxo is given to th e assem b led spring. The differential equation of motion can be used to determ ine th e restraining force F r W ( 11- 1) - x = a'W -kx - F g

AMCP 706-210 FLIGHT DIRECTION At any other acceleration a'2 the time to arm will be different. By substituting Fr in Eq. 11-1 OPENING i and using a new acceleration a ' , the time to move the distance S may be found by solving the TO BOOSTER transcendental equation 5 ------- - ( a ' - a' ) cos t+ _ - a\\) gk L 1 \\ gk (11-4) + v 0t + 1) FROM Since solutions of these equations are obtained CLOCKWORK by interpolation formulas, it is best to estimate slider weight and spring constants (note that (!' Figure I I-I. Sating and Arming Mechanism and k always occur as a ratio), then to calculate arming time and adjust as necessary. where x is the acceleration of the weight with re­ spect to the mechanism, a 'is the acceleration of In some fuze applications, the slider is made the mechanism in g, and k is the spring constant. light and a separate weight is coupled to it with By assuming that the velocity of the weight a spring so as to cushion the clockwork against reaches a steady value quickly and then remains shock loads. This additional spring changes the constant until the arming process is completed, a equation of motion for the mechanism. long arming time can be realized. The expression for the velocity x may take the form An example of this type of mechanism is the Safing and Arming Device, GM, M30A1 shown i = v0 (1 - e ~ t/Tc) (H-2) in Fig. 11-2. This device is, of course, much more refined than the example cited. Some of the data for the above example were taken from this device. in which the velocity is zero at t = 0 and ap­ 11-4 GRENADE FUZES proaches vo , the initialvelocity, as t becomes infinite. The time constant o f the equation T c 11-4.1 HAND G RENADES fixes the time for x to reach 37% of vo . By inte­ grating Eq. 11-2 to obtain x , differentiating it to A hand grenade is a munition hurled against obtain x , and substituting these three ( x, x , and the enemy. Its function is explosive (blast or frag­ 5c) into Eq. 11-1, Fr is determined as mentation) or chemical (irritant, incendiary, or smoke). Unlike projectiles that strike on their F = (at W - kx + kv T ) - kv t nose, the trajectories of hand grenades are un­ stable so that the direction of target impact can­ + kv t \\ e ~ t/Tc (11-3) not be set. They experience no unique forces that can be used for arming, none that are not g Tc ° CJ also present during normal shipping and hand­ ling. For this reason, the requirements for out- This equation contains three terms: a constant of-line detonator safety and an independent arm­ term as expected, a time-dependent term that de­ ing force have been waived for all past grenade creases to compensate for the increase in the fuzes. While there are no present grenade fuzes spring force, and a transient term that is neces­ having the detonator safety features, it is highly sary to allow the weight to accelerate to the desirable that a practical detonator safety device velocity v 0 . The time-dependent force is typical be developed and incorporated into future de­ of the forces produced in an unwinding clock. signs. Grenades are treated more fully in a sepa­ Hence, a clockwork escapement is applicable. rate publication3. Eq. 11-3 determines the design of the clockwork. With this force function it will produce the re­ Fuze action is either time (4-5 sec) or impact. quired arming delay. Impact action fuzes also contain a 1-2 sec arming 11-3

AMCP 706-210 F ig u r e 7 7-2. S a f i n g a n d A r m in g D e v i c e , G M , M 3 0 A 1 delay and a self-destruction feature th a t will ex­ th e grenade leaves th e operator’s hand. The trig ­ plode the grenade in 4-5 sec. Since tim ing accu­ ger mechanism of hand grenades is similar to that racy is n o t critical, a pyrotechnic elem en t is th e of th e firin g device sh o w n in Fig. 135. T he simplest and most widely used method to achieve delay. The explosive train consists of a percussion M204A2 E la n d G r e n a d e F u z e is s h o w n in F ig . primer, an obturated delay element, and a flash 11-44 . An example is given in par. 13-4 in which detonator or b lastin g cap th a t w ill detonate the g ren ad e. T he d eto n ato r base charge m ay be the design features of the striker spring are dis­ o m itted in chem ical g ren ad es w here th e m ain cussed. charge is merely ignited. L et u s design a ty p ical h a n d g ren ad e fuze S in c e t h e g r e n a d e ’s o r i e n t a t i o n to t h e t a r g e t using the firing device and other standard com­ a t th e tim e of fu n ctio n in g can n o t be predicted, p o n e n ts w ith a fu n ctio n in g d elay of 4 to 5 sec. im p a ct actio n is difficult to achieve by m e c h a n ­ The energy used to initiate the percussion primer ical means. With an electric detonator, an omni­ is derived from the potential energy Hs stored in d irec tio n a l sw itch w ill solve th is p ro b lem . Tw o the spring and released when the striker swings tre m b le r sw itc h e s (Fig. 7-l) a t r ig h t a n g le s to each o th e r p erfo rm th e d esired action, b u t th is Hs = GO = [ n k d r d d (11-5) a rra n g e m e n t is p ro b ab ly too b ulky. T he M 217 Jo G r e n a d e F u z e (F ig . 11-3), fo r e x a m p le , h a s a n where G is the torque that is proportional to the all-w ay s b all sw itch. E n erg y is p ro v id ed by a d e f le c ti o n (= k 6 ) , a n d r is t h e r a d i u s a r m o f t h e th erm al battery having an activation tim e of 0.5 s t r i k e r t h a t s w in g s t h r o u g h n r a d i a n s ( 1 8 0 ”). sec. This interval plus th a t of a therm al arm ing S ince r is 0.5 in. a n d k is 28/ n lb/ ra d s w itc h , c l o s in g i n 1 .5 sec, p r o v i d e s t h e a r m i n g Hs = 7 77 lb-in. s 352 in.-oz (H\"6) delay. A self-destruction switch closes in 4.5 sec. M anual arm ing of grenade fuzes occurs in two I f t h e d e v ic e i s 5 0 % e f f i c i e n t b e c a u s e o f fric­ steps: the operator pulls a safety pin (pull ring) tion, the energy available as the striker hits the and a safety latch (hand lever) is released when 11-4

AMCP 706210 Figure 11-3. Hand Grenade Fuze, M217 percussion delay element ‘is 1 7 6 in.-oz. The Unlike those for hand ‘grenades, the fuzes o f velocity of impact is important, too, but the explosive rifle grenades must contain all o f the specifications are not so easily set (see par. 3-3). required arming features. Fired at a velocity of about 150 fps, the grenades are subjected to set­ A suitable obturated, pyrotechnic delay is se­ back accelerations of 500 to 1000 g, about m id­ lected in regard to time, size, input sensitivity, way between hand grenades and small mortar and output. The output would be a flash that can projectiles. This, setback force in combination ignite a standard flash detonator. A standard with an escapement timer can serve for arming blasting cap will then be sufficient to initiate the bursting charge. safety. Grenades are treated more fully in a sepa­ rate p u b licatio n 3 . 11-4.2 RIFLE GRENADES Rifle grenades are commonly used today for It is recognized that the current standard serv­ HEAT or chemical rounds. Chemical rounds (sig • ice rifle is not designed to accommodate a rifle nal or smoke) are set off by a simple igniter. grenade. The inclusion o f fuzing for a rifle gre­ HEAT rounds require a base-detonating fuze nade is for the record and to make the handbook complete. Rifle grenades are used by the infantry (point-initiated) to make room for the shaped- to hurl larger charges of explosives longer dis­ charge cone in the nose. Mechanical fuzes (spit- tances than can be thrown by hand. They are back or firing pin backed by a high-inertia mass) fired from a rifle by use o f a grenade adapter. are no longer used in rifle grenades because of their low reliability and slow action. The best design is a piezoelectric nose element that ini­ tiates an electric base fuze (see par. 3-4.3.1). 11-5

AMCP 706-210 SPRING 11-4.3 LAUNCHED GRENADES PULL RING A grenade launcher has a function similar to STRIKER that of a rifle grenade, namely to propel a gre­ nade farther than it can be thrown by hand. ASSEMBLY Grenade launchers have a range of about 400 meters. The launcher differs from the rifle in momF i g u r e JJ-4. H a n d G r e n a d e F u z e , that it also imparts spin to the grenade. Hence, both setback and spin can be used for arming in a grenade launcher. Fuze, PD, M551 (Fig. 11-5) is used for gre­ nades launched from the 40 mm XM79 Grenade Launcher. It functions by impact or graze and requires the following four actions to arm: (1) The setback pin retracts from the rotor against its spring retainer due to setback, and the pin locks into the retainer at the 4 leaves, in the rear position. (2) The hammerweights of the wagon-wheel centerplate assembly pivot outward against the hammer-weight spring under centrifugal force allowing the firing pin and spring assembly to push forward on the push pin, thus disengaging the firing pin from the rotor. SPRING RETAINER SET BACK PIN ROTOR GEAR M557F i g u r e 7J-5. G r e n a d e F u z e , P D , 11-6

AMCP 706-210 (3) A t 3000 to 6000 rpm the centrifugal wheel on each oscillation. This action provides force is sufficient to cause the centrifugal lock to an arming time o f 66 to 132 msec, correspond­ compress its spring and unlock the starwheel, ing to 60 to 120 ft in range of the temperature thus allowing the escapement to operate. extremes. (4) The rotor spring rotates the rotor gear Upon impact, the hammerweights pivot inward assembly (containing the detonator) into the due to their inertia and strike the push pin which armed position, but its m ovem ent is slowed in turn strikes the firing pin. The firing pin initi­ down by the verge through the starwheel and ates the M55 Detonator causing detonation in pinion assembly. The verge oscillates with a turn of the booster. On graze impact, one regular beat governed by its weight and rotor hammerweight provides sufficient energy to ini­ spring torque, releasing one tooth of the star- tiate the detonator. REFERENCES 1. K. A. Van Oesdel, Primary Factors That Af­ Article 27.0 of the JANAF Fuze Committee, fect the Design o f Guided M issile Fuzing Sys­ March 1962, AD-346 125 (Confidential). 3. AMCP 706-240 (C), E n g in e e r in g Design Hand­ te m s, Naval Ordnance Laboratory, NAVWEPS book, Grenades (U). Report 5953, Corona, C a l i f . , 8 July 1960. 4. TM 9-1330-200, Grenades, Fland and Rifle, Dept. 2 . A C o m p e n d i u m of Mechanics Used in M issile of Army, June 1966. Safety and Arming Devices (U), Part I, Journal 11-7

AMCP 706-210 CHAPTER 12 BOMB FUZES 12-1 GENERAL rack. The other end is threaded through the arm­ ing vane so that it prevents the vane from ro ­ A bomb fuze, like other munition fuzes, must tating. When the bomb is released, the wire being arm at an appropriate time after release and func­ attached to the bomb rack is withdrawn from the tion at or near the target. However, certain pecu­ fuze, the vane is free to rotate in the air stream, liarities arise from the following considerations: and the arming process can begin. This feature gives the vane-actuated mechanism a definite (1) The bomb is dropped, rather than pro advantage over a clockwork because the clock­ jected, usually from fast flying aircraft. work is only held inoperative by the arming wire. If it becomes necessary to jettison the (2) Bomb fuzes do not experience setback bombs, the arming wire is not withdrawn from forces. the fuze but is allowed to fall with the bomb. (3) After release, the bomb follows the air­ While the arming process appears straight­ craft closely for a short time. forward and is usually successful, certain diffi­ culties may arise and steps must be taken to min­ (4) A large risk to personnel and materiel is imize their danger: the wire may break before involved in the delivery of a bomb to a target. the bomb is released so that the part remaining in the fuze will prevent its arming; the wire may (5) Two and sometimes three fuzes are war­ not be securely attached to the bomb rack so ranted to increase the probability of function­ that it falls with the bomb, and when the bomb ing. is jettisoned, the wire may catch on the aircraft and be withdrawn unintentionally. On the other (6) If an electric power supply is used, it hand, air integrating zero-g devices could be used must be of a type that will operate at the low that would operate when the bomb is in free fall. temperatures encountered at high altitudes. Such a device must be capable of differentiating between free fall of the bomb and free fall of the (7) Bombs released in clusters may experi­ aircraft with bomb. ence cross detonation, if prematurely set off. Fig, 12-1 shows the trajectories of a bomb These considerations account for some differ­ after release from an aircraft in horizontal flight ences in fuze actions compared to artillery fuzes. at various speeds. Parameters commonly used In turn, the action affects impact, time, and spe are indicated on this figure and are defined as cial bomb fuzes. Additional information on bomb follows: fuzes is contained in bomb manuals’ and a cata­ log on air-launched weapons fu z in g 2 . (1) SVD: Safe vertical drop, SVD, is the vertical 12-2 FUZE ACTION distance below release altitude in which the Fig. l-4 illustrates a typical general purpose fuze must be safe. The distance along the bomb bomb. Nose and tail fuzes are shown and the im­ trajectory to this point is called minimum safe portant parts are identified. A transverse or body air travel, or Min SAT. Hence, SVD is the vertical fuze is not shown on the drawing because it is not component of Min SAT. The arming zone is that used in this type of bomb. Attention is directed part of the bomb trajectory in which the arming particularly to arming wire and arming vanes. process is completed. Even for fuzes of the same type, the arming process is not complete at the Bombs are commonly armed by a vane. Ex­ same point in the trajectory. This spread is cre­ cept for clusters, functioning action is the same ated by the existence of manufacturing toler­ as that for other fuzes. ances and the variatiSfij! of speed and altitude of the plane at the moment of release. 12-2.1 THE AR M IN G PROCESS When a bomb is carried in an aircraft, the fuze arming process is held in abeyance by one or more arming wires. One end of the wire is at­ tached by a swivel loop to a pawl on the bomb 12-1

AMCP 706-210 SVD * SA FE V E R T IC A L DROP p la n e sp e e d a n d tra je c to ry . F ig . 12-23 d is p la y s MDA • M A X IM U M DROP TO ARM a n exam ple of th is com plex situ a tio n w h ere tim e of flig h t is a fu n ctio n of release angle, & •* PBSSTT<WDIN0 6 F FftUVMTE AST B®(9W b ' WPWST trajectory, and altitudes. Q ■■FRtegintBJ^ ©F P LA N ! AT 500 12-2.2 THE FUNCTIONING PROCESS 400 j : A bomb fuze functions like any other fuze. If it is d esired to d eto n ate th e bom b in air, th e o300 mph p ara m ete r used m ay be tim e, b aro m etric p res­ sure, or ta rg e t stim u lu s. (Proxim ity fuzes are 400 mph SV^D r - \\ \"\\ Lr1. ' \" T I 100?! i t h e s u b j e c t o f o t h e r h a n d b o o k s p' \\ ) I f a b o m b i s “ V~ ____ —4Q>_ o n n < to be d eto n ated a t th e m o m en t it first co n tacts the target, this is accomplished either by means •-^ Z fM D A - ^ - - \\ -----------® ~ 2 0 0 of a strik e r or by th e in e rtia of som e m ovable com ponent. If p e n e tra tio n is desired, a delay 6 0 0 m ph feature is built into the fuze. 3000 As in projectiles, the nose fuze in a bomb may RANGE, f t be d esig n ed to fu n ctio n before, at, or a fte r im ­ pact. A co m b in atio n of nose a n d ta il fu zes is Figure 12-l. Bomb Trajectories often u sed to in su re d eto n atio n of th e b u rstin g charge. For example, a typical combination con­ (2) M DA: sists of an im pact nose fuze having m echanical The m axim um drop to arm, MDA, is the time action and a n o n d e la y tail fuze having im ­ p act in e rtia action. W ith th is com bination, th e vertical distance below release altitude at which nose fuze is expected to function in the air after th e fuze m u st be arm ed. The m inim um release th e ex p iratio n of a ce rtain tim e in terv al. B u t if altitu d e, M RA, is a m in im u m altitu d e a t w hich im p act occurs before th e in te rv al expires, th e th e bom b m ay be released an d still have an firin g p in w ill in itia te th e nose fuze. F u rth e r, if arm ed fuze upon a rriv a l a t th e ta rg e t, it is th e the nose fuze fails, the tail fuze will be initiated same distance as MDA. on im pact. N ose an d ta il fuzes u sed to su p p le­ m ent each other in this way are known as com­ An inherent disadvantage of basing arm ing de­ p an io n fuzes. In th e case of ce rtain v ery large la y d irec tly on a ir tra v e l is sh o w n on F ig. 12-1. bom bs, th ree fuzes of th e sam e type are som e Bomb trajectory depends upon aircraft speed, the tim es em ployed to in su re in itiatio n . g rea ter th e speed th e fla tte r th e trajectory. Hence, arm ing m easured by air trav el does not Figure 12-2. Typical Bomb Release Curves provide consistent safety distances between bomb and plane. However, the vertical drop is a direct fu n ctio n of tim e, p ractically in d e p en d e n t of plane speed. For th is reason an arm ing delay sys- te rn b ased on tim e in stea d of air trav e l is de sirable. Such a system is readily obtained by at­ ta c h in g a c o n sta n t sp eed g overnor to th e fuze mechanism. Another method involves construct­ in g th e v a n e s w ith flexible b la d e s so th a t th e y tend to rotate at a constant speed. The trajectories shown in Fig. 12-1 present the sim ple case w h ere bom bs are drop p ed from an aircraft in horizontal flight. It is common, how­ ever, to forcibly eject bombs when the plane is in a dive. For this condition, the initial bomb veloc­ ity due to ejection-on th e o rd er of 5-10 fpsis a n o th e r fac to r to be co n sid ered . A lso, v e rtic a l drop tim e is now no longer in d e p en d e n t of 12-2

AMCP 706-210 12-2.3 CLUSTERING of the arming stop rotate the striker body assem­ bly (5) that in turn drives the striker pin and Clustering accomplishes two purposes. First, it guide assembly (6). Arming delay is determined enables an aircraft to carry its full bomb load re­ by the arc through which the striker body assem­ gardless of individual bomb size. For example, a bly must rotate before it indexes with the index certain plane is designed to carry two 1 0 0 0 -lb stop (7). At this time, the striker body spring (8) bombs. In order to carry the same weight of forces the striker body assembly forward to make 100-lb bombs, these sm aller bombs can be contact with the bottom plate on the arming grouped into two clusters of 10 bombs each. Secondly, clustering also provides a convenient stop. Immediately thereafter, a striker ball (9) is means of releasing bombs for area bombing in forced by spring action into th e void above the contrast to point bombing. striker pin. Cluster bombs are held together and suspended At the same time, a longitudinal slot in the from the plane by means of a cluster adapter. The striker pin guide indexes with the rotor release adapter may be designed to open immediately plunger (10) allowing it to move forward by upon release from the plane or after a delay. Us­ spring action. This frees the rotor assembly (11) ually, a mechanical time fuze with its associated to rotate by spring action bringing the detonator arming wire opens the adapter. Each bomb in into line with the rest of the explosive train. A the cluster is equipped with its own fuze, the detent (12) locks the rotor in the armed position. arming of which may be started by withdrawal of an arming wire, by opening of a fuze vane Subsequent impact on the nose of the fuze lock, or by other means. shears the lugs holding it in position allowing the entire nose assembly to move rearward. This mo­ 12-3 IMPACT FUZES tion forces the striker body assembly against the striker pin which in turn initiates the explosive Impact fuze is a term used for bomb fuzes just train. as for other fuzes. The tactical purposes of bomb fuzes are depicted in Table 12-1. The general Various arming delay times are selected by de­ categories of detonation when approaching, pressing the index lock pm (13) and rotating the when contacting, and after impacting the target nose assembly as a unit. This establishes the arc are also typical of other items of ammunition. through which the striker body assembly must ro­ tate before it indexes with the index stop. A min­ Bombs do not strike the ground at 90° but al­ imum arming setting of 2 seconds is provided by ways at a smaller angle depending upon release the index ring (14). altitude and aircraft velocity. Table 12-2 gives approximate striking velocities and angles for Superquick action and functioning delays of two altitudes and several bombs. This table indi­ 0.010, G.025, 0.050, 0.100, and 0.250 sec are cates that the fuzes must be initiated at an ob­ selectable by inserting the proper Delay Element, lique impact. M9, in the fuze cavity just aft of the striker pin. This is a pyrotechnic element, shown in Fig. 4-7, 12-3.1 SUPERQUICK O R SHORT DELAY FUZES which contains Primer, M42, a pyrotechnic delay column, and an Element Relay, M6. The output of the element flashes into an additional lead azide relay and thence into the detonator. 12-3.1.1 A T yp ica l Fuze 12-3.1.2 Gear Trains Short delay fuzes are exemplified by Fuze, Gear trains are needed in bomb fuzes because Bomb Nose, M904E2 (Fig. 12-3)1 ’4 . Operation the power source for the fuze is a high speed is described as follows: propeller. Normally, the propeller vanes turn at a high speed with a governor used for regulation. Rotation of the vane (1) drives the governor The rotation must be transferred to low speed drum and spindle assembly (2) directly. A gov­ arming shafts that actuate restraints on the arm­ ernor spring (3) holds centrifugal weights in con­ ing mechanisms. tact with this drum; design of spring and weights provides for a governing speed of approximately When designing a gear train for bomb fuzes, 1800 r p m . This motion translated through a gear reduction rotates the arming stop (4). Drive lugs 12-3

AMCP 706-210 TABLE 12-l. TACTICAL PURPOSES OF BOMB FUZES Bomb Position Relative Character-is t ic Position o f Poss ib le Type to Target at Detonation of Fuze Functioning De lay Fuze in Bomb M echanical Time A pproaching <0 (A irburst before N ose or \\A c o n ta c t) Tail Nose Proxim ity F irst M inim um x Nose I m p a c t—SQ C ontacting (in sta n ta n e o u s) (instantaneous) Penetrating, S h o rt T ail Im p act inertia- B ouncing, or Nose nondelay R esting in Tail Co. n ta c t Im pact— with short delay Im p act inertia- sh o rt delay M edium Tail Im pact in e rtia triggered— m edium delay Long T ail “I m p a c t ” c h e m ic a l or m echanical trig g e re d long delay Plus antiw ithdraw al TABLE 12-2. BOMB BALLISTICS AH r e le a s e d fro m a n a i r c r a f t a t 4 0 0 m ile s /h o u r Altitude 10, 000 Feet 2 5 ,0 0 0 Fee t Bomb No. Weight , S trik in g Angle o f S trik in g Angle of Velocity, Velocity, u> Impact, .Impac t , fps fps O 0 A N -M 30 100 750 61 850 72 A N -M 57 250 800 A N -M 64 500 850 59 975 72 A N -M 65 1000 850 A N -M 66 2000 875 55 1050 69 A N -M 56 4000 850 55 1050 64 55 1050 68 57 1050 69 th e following factors are im portant: gear ratio of The gear ratio is usually large, about 1000 to the tra in , torque output desired, space allotted, 1, so t h a t m u ltip le p a i r s o f s p u r g e a r s a r e indi- frictio n losses, m a n u fa c tu rin g costs, a n d m a te cated. S ince th e re c a n n o t be le ss th a n six te e th rials to be employed. on pinion gears for efficient operation, an upper 12-4

AMCP 706-210 BOOSTER CUP ROTOR COVER DISK M SS DETONATOR DETONATOR ROTOR ASSEMBLY © Figure 12-3. Fuze, Bomb Nose, M904E2 limit is placed upon the gear ratio. Space may be of 3,3,3,3,3,4 produces an overall ratio of 972:1. saved with internal gears, but they are more ex­ pensive and require more complex mountings Five identical pairs and a last internal gear can than spur gear trains. Hence, their use should be limited. A main shaft and a countershaft can be be fitted into the two-inch cavity. For a gear arranged with identical pairs of gears and pinions. ratio of 3: 1 the spur gear can be % inch and the The spur gears are designed with these criteria: (1) metal gears satisfy the 2 0 -y e a r shelf life re­ pinion Vi inch. A safe value for the face width of quirements better than plastic or fiber gears; (2) stampings are satisfactory for gears because the gears can be computed from the Lewis their life span is short; (3) involute tooth con­ tours are considered better than cycloidal tooth formula which assumes that the load F^ is spread contours by some designers, however, the relative virtues are still unresolved. Gears of standard evenly across the tooth face pitch eliminate production bottlenecks for the manufacturer. In general, many of the design nan bF, ( 12- 1) considerations are similar to those used for clock­ lb works discussed in par. 6-6. >fPd The M904E2 Fuze contains a gear box be­ where a n is the allowable normal stress, PShSy is tween governor and arming stop assembly (see Fig. 12-4)’ ,4 . The first gear speed is limited to a safety factor (say 3); b is the tooth face width, 1800 rpm. A 240” rotation of the last gear is de in.; pd is the diametral pitch, in.; and Ff is the sired for a maximum arming delay of nearly 18 form factor for the tooth (approximately 0.1). seconds. These data require a gear ratio on the For brass, crn is about 25,000 psi so that with order of 1000:1. The use of integral gear ratios Fg = 3 lb, the face width will then be 0.055 in. Usually the pinions have a wider face (150%) than the spur gears to prevent the teeth from be coming malaligned axially. 12-3.1.3 The E xp lo s iv e Train The explosive train o f a bomb fuze is designed to convert the target impact forces or the results 12-5

AMCP 706-210 PINION SHAFT -REDUCTION -INTERNAL (counter shaft) GEAR GEAR AND PINION Figure 12-4. Gear Assembly of Fuze, M904E2 of target influence into a detonation that will ini­ w ill be sufficient if used as a cylinder w ith a tiate the bursting charge of the bomb. This is the length to diam eter ratio of 3:2. This makes the same action that is required for any other fuze cylinder 2 in. long (density of tetryl is 0.056 explosive train. Specifications for bom b fuzes lb /in ? ). It is usually convenient to m ake u p the commonly require that a functioning delay be booster charge of two or three pellets. The cup incorporated into the explosive train. One bomb m ay be m ade of alum inum because it is easy to may be used against many different targets and form, is readily available, is light, will protect the its effectiveness against each target often depends tetryl against effects of rough handling, and is upon the functioning delay. It is convenient to compatible with tetryl (see Table 4-2). provide plug-in delay elements to make the fuzes more versatile. The initiating input requirement for tetryl is a detonation wave that is provided by a detonator. Delay is usually achieved by pyrotechnic A detonator is sensitive to shock and heat, so for means. A prim er is needed to initiate the delay safety, it m ust be placed out of line w ith the element because it requires input energy in the booster: Thus it w ill be held in a movable part form of flash or flame. Further, since deflagra­ and shielded from the booster charge until the tion of the delay elem ent does not produce a flash that w ill initiate a detonator, a relay is fuze is armed. A large thick plate is used to sepa­ needed to amplify the output of the delay ele­ rate them , as sh o w n on Fig. 1 2 - 5 1 >4 . W hen the m ent. Of course, the detonator is required to detonator swings, into alignment, there will be a produce a detonation wave. A booster is neces­ large gap (the thickness of the shield, 0.30 in.) sary to enlarge the detonation wave for reliable betw een it and the booster. W hile possible in initiation of the high explosive bursting charge. Further, a lead is useful to guide the detonation some designs, it cannot be assumed that the out­ wave into the booster. These components (firing put wave from the detonator will carry across pin, prim er, delay, relay, detonator, lead, and this gap and reliably initiate the booster charge. booster) form the explosive train. Hence, a tetryl lead (same explosive as booster A designer might start his work at the output charge) is added to elim inate part of the gap. end of the train. The size of the booster charge is It is necessary to center the lead over the determined from empirical data. For the M904E2 Fuze, 1100 grains of tetryl pressed at 10,000 psi booster face. A pproxim ately 1.5 grains of tetryl w ith a specific gravity of 1.45 to 1.60 encased in an alum inum cup is sufficient. A slight gap be­ tween detonator and lead is desirable in order to 12-6