5. Slipstreaming for two

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Alexandros Markoulakis Supervising teachers: 2nd General Lyceum Eugenia Potiriadou of Kamatero The e-Twinning Group: “Sport Science Stories” 1

Contents Volume 1, Issue 5 14/02/2018 Sport Science Stories Inside this issue: Front Cover 1 Contents 2 Worksheet 3 Our Video 5 The Experiment 6 Conclusions 7 Activity 1: Watch the drag! 8 Activity 2: Feel the drag! 11 What Physics tells us 12 Slipstreaming in Sport 26 Fly like a bird: The V formation 28 Planes benefit from the V formation 29 NASA Experiment 30 Sport Science Stories 31 Photos 33 Back Cover 34 2

Worksheet Volume 1, Issue 5 14/02/2018 Sport Science Stories Supervising teachers: Alexandros Markoulakis Eugenia Potiriadou Use a candle’s flame and a pie pan to see the air stream that racers like to ride. What You Do 1. Light the candle and hold it in your right hand. Hold the What You Need pan in your left hand. Keep the objects shoulder width apart. #1 A candle Move both of your hands to the left at the same speed. Observe the candle flame. Which way #2 Matches does it point? (and adult per- 2. Now, move the pie pan to mission to use about 3 centimeters (3 cm) the matches) from the candle and repeat. Which way does the candle flame point this time? #3 Aluminum pie pan 3. Put out the candle. 3

School: Sport Science Stories 2ο GENERAL LYCEUM OF This worksheet’s activities as well as KAMATERO the following activities/exercises should Phone: ........................ be uploaded (as videos, pictures, ppt, Fax: ..................... E-mail: ........................... word etc) on the Twinspace platform. Deadline: 17/02/2018  Write and explain some theory be- hind the physics slipstreaming/ drafting.  Find and write down stories about athletes and sports that you think they are worth mentioned. What’s Going On? This activity is a demon- when your hands are close can go faster because you stration of slipstream- together the flame stays are being slowed down ing (or drafting) which is upright or actually bends less by the air. a technique where two ve- towards the pan. As the hicles or other moving ob- pan moves, air going But something else hap- jects are caused to align in around the pan creates a pens, too. You’ll be pulled a close group reducing the swirling air current called along with the front racer overall effect of drag due to a vortex. by the air, giving you a exploiting the lead ob- free ride. That means that ject's slipstream. In motor This vortex spins quickly you don’t have to expend racing and cycling, slip- and, according to Ber- much energy (power from streaming (or drafting) can noulli’s Principle, fast burning gasoline in your significantly reduce air creates lower air car’s engine or from mus- the average energy ex- pressure. This leads to cle energy). penditure of the vehicle or object required to maintain less air resistance. So, if At car racing, the pull can a certain speed. you are directly behind make both cars travel at another racer—it doesn't The candle’s flame is matter if he’s a runner, a greater speed than their blown with the wind when driver or cyclist—you feel engines are able to create. your hands are apart, but less air resistance. You 4

Our video Volume 1, Issue 5 14/02/2018 Sport Science Stories https://youtu.be/114tT4pI1pE YOU TUBE 5

The experiment Volume 1, Issue 5 14/02/2018 Sport Science Stories The experiment: 1. We keep the objects (candle and baking pan) shoulder width apart. We 1. 2. move both of your Κίνηση των χεριών προς τα Σε κοντινή απόσταση. hands at the same δεξιά — Κίνηση της φλόγας Η φλόγα παραμένει κατα- προς τα αριστερά. κόρυφη. speed. The candle flame point back- wards. 2. Then, we move the pie pan to about 3 cm from the candle and repeat. The candle flame points upwards. 6

Conclusions Volume 1, Issue 5 14/02/2018 Sport Science Stories Conclusions: The candle’s flame is blown with the wind when your hands are apart, but when the hands are close together the flame stays up- 1. 2. right or bends to- Κίνηση των χεριών προς τα Σε κοντινή απόσταση. wards the pan. As δεξιά — Κίνηση της φλόγας Η φλόγα παραμένει κατα- the pan moves, air προς τα αριστερά. κόρυφη. going around the pan creates a swirl- ing air current, a vortex. This vortex spins quickly and, accord- ing to Bernoulli’s Principle, fast air creates lower air pressure. This leads to less air re- sistance. 7

Activity 1: Watch the drag! Volume 1, Issue 5 14/02/2018 Sport Science Stories Background What you need: ● Two light-weight 3-dimensional models of cyclists sitting up- right & in racing attitude. ● flax thread or thin and flexible string We have all experienced the increased ● a stand to suspend the model difficulty of riding or running into the cyclists wind. Physics tells us that, as we try to go faster, more of our energy is used in ● a hair dryer overcoming this wind or air resistance. ● a background panel, eg card- It has been calculated that increasing board, inscribed with lines for speed by 25% needs double the power measuring deviation. output. Cyclists go to much trouble, therefore, to reduce the forces of wind What you do: resistance or ‘drag’. They change their 1. Suspend the model cyclists on riding position, wear tight clothing, strong thread/string from a and use a streamlined helmet and stand. streamlined bicycle. 2. Use a hair dryer to simulate the effects of wind and air re- sistance on a cyclist. 3. Note the extent of deviation caused by the ‘wind’ on the two cycling positions. Which cyclist was more affected by the ‘wind’ from the hair dryer? 8

Activity 1: Watch the drag! Volume 1, Issue 5 14/02/2018 Preparing the activity: Some photos Sport Science Stories taken in Physics laboratory 9

Activity 1: Watch the drag! Volume 1, Issue 5 14/02/2018 Sport Science Stories Data and Conclusions The upright rider be- fore and after the “hair dryer” test . The crouched rider avoids more of the wind resistance tucked up. 10

Activity 2: Feel the drag! Volume 1, Issue 5 14/02/2018 Sport Science Stories Roll your window down and stick your hand out. That force on your hand trying to pull it back to- wards the back of the car, that’s drag. That’s how much physical drag you have on your hand. You’ve got lower pressure on the back side, higher pressure on the front side, so it just wants to push your hand back. Drag is essentially that back pres- sure on the car. Compare the force you feel when you hold your hand perpendicular to the ground, to the force you feel when you hold your hand parallel to the ground. When your hand is parallel, it has to push fewer air molecules out of the way, so there’s less drag. Less drag is a good thing. 11

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us SLIPSTREAMING OR DRAFTING Slipstreaming or drafting is a technique where two objects remain very close to one another. This reduces the effect of drag or aerodynamic resistance by using the lead object’s slipstream or low pressure wake. How does slipstreaming help a race car driver improve his speed? When two cars remain bumper to bumper they can both travel 3 to 5 mph faster than if they were alone. The low pressure behind the lead car reduces the aerodynamic resistance on the front of the trailing car while the trailing car pushes high-pressure forward so less fast-moving air hits the lead cars rear spoiler. Both cars have less drag and both cars go faster. 12

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us SLIPSTREAMING OR DRAFTING Slipstreaming or drafting is a technique where two objects remain very close to one another. This reduces the effect of drag or aerodynamic resistance by using the lead object’s slipstream or low pressure wake. How does slipstreaming help a race car driver improve his speed? When two cars remain bumper to bumper they can both travel 3 to 5 mph faster than if they were alone. The low pressure behind the lead car reduces the aerodynamic resistance on the front of the trailing car while the trailing car pushes high-pressure forward so less fast-moving air hits the lead cars rear spoiler. Both cars have less drag and both cars go faster. 13

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us Bernoulli's Principle Bernoulli Effect: states that the pressure of a fluid (liquid or gas), decreases as the fluid (liquid or gas), flows faster. The variables P1, υ1 and h1 refer to the pressure, speed, and height of the fluid at point 1, whereas the variables P2, υ2 B e r n o u l l i ' s e q u a t i o n : and h2 refer to the pressure, speed, and height of the fluid at Bernoulli's equation relates point 2 as seen in the diagram below. the pressure, speed, and height of any two points (1 and 2) in a steady streamline flowing fluid of density ρ. Bernoulli's equation is usually written as follows: 14

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us Bernoulli's Principle — Slipstreaming Physics & Galmer G-92 The Bernoulli Effect means that: if a fluid Andy Brown of Galmer Racing gave Race Car (gas or liquid) flows around an object at Engineering the following figures for the different speeds, the slower moving fluid will Galmer G-92. This is the car (driven by Al exert more pressure than the faster moving Unser Jr.), that won the 1992 Indianapolis fluid on the object. The object will then be 500 mile race. forced toward the faster moving fluid. Drag reduction is more critical on the speedway than on other circuits. Since the drag force is proportional to the square of the speed, minimizing drag is a primary concern in the speedway setup. Lap speeds can average over 228 mph and top speeds can exceed 240 mph on a speedway circuit. 15

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us Drag force, Statistics & Galmer G-92 In the days before roof fairings a Cd (drag coefficient) figure of 1.0 was typical for a high drag truck. Trucks are now down to a Cd of 0.6. This shows a 40% drag reduction using a fairing. This is important in fuel economy. The figures quoted for the 1991 Indy 500 winning Penske PC20 in speedway trim were 3010 lbs. of downforce at 220 mph. with 1075 lbs. of drag. (Load/ Downforce, L/D=2.80). Brown stated, \"I'm always a little cautious of comparing figures from different wind tunnels. Experience has shown them all to vary slightly. The L/D figure, however, is usually close.\" The L/D or downforce to drag ratio is important data because it reflects the necessary car modifications determined by the racing circuit (in this case the short oval compared to the speedway). Drag reduction is particularly important Πηγή: in the speedway setup of the car. Note the drag and https://www.nas.nasa.gov/About/Education/ downforce difference in comparing a short oval setup to the speedway setup. Racecar/statistics.html 16

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us The aerodynamic forces acting upon a car are usually considered in terms of  lift (or downforce),  drag force  and center of pressure. The influence of slipstreaming on the performance of a Grand Prix racing car The performance of any racing car around a circuit is strongly influenced by the changes in the above forces when following in the slipstream generated by another car. Most obvious to any driver or observer is the reduced drag force and the corresponding increase in forward speed that occurs when one car follows in the wake of another — a phenomenon that is used to good effect when drivers attempt overtaking manoeuvres. The effect of following in the slipstream of another car upon the lift and drag forces is shown in Fig. 1. The offsets presented here are given in terms of Z/W, where Z is the actual offset and W is the width of the car’s bodywork. Figure 1: The influence of the slipstream on lift and drag. The aerodynamic forces acting upon a Grand Prix http://journals.sagepub.com/doi/abs/10.1243/ car are greatly reduced when running in the wake from another car. At a vehicle separation that is generated in an undisturbed airstream. typical of that occurring at the start of an This results in higher straight line speeds but overtaking manoeuvre the drag reduced by 23 per lower cornering speeds. cent relative to the forces that would be 17

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us This diagram shows the pressure on and around a car going 190 mph, high pressure on the front of the car, low pressure behind it. Those pressures applied over the frontal area of the car determine the aerodynamic drag. (Red is high pressure, blue is low pressure). 18

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us The only way to go faster is to reduce aerodynamic drag, hence, the newly realized pas de deux of two cars running nose to tail, literally touching and both cars together ramming the combined block through the air. Notice that the high pressure area on the nose of the second car fills in the low pressure void behind the lead car. The result is to reduce the overall drag of the two cars together. 19

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us A surprisingly small gap between the cars is sufficient to mitigate the drag reduction compared to two cars in contact with each other. The pas de deux with a trailer just isn't as streamlined as two. 20

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us The power consumption (force x speed) due to aero drag increases with the cube of speed, that is: (speed x speed x speed), so it increases dramatically with speed, and it just keeps on going up. At 190 mph the force required to ram a NASCAR Cup car through the air is on the order of 700 lbs or more. 21

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us The net power (engine less aero drag) describes what is left for accelerating the car. A plot of the difference between the two curves illustrates the frustration of drivers with restrictor plate racing, when the two curves cross there is zero left to accelerate the car and when the net power gets to zero that's as fast as the car will go. 22

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us Note, as the car approaches its terminal speed, the available power for acceleration is also approaching zero, i.e., the car becomes more and more \"sluggish,\" it has no \"throttle response,\" you push the accelerator peddle farther down but the car doesn't go any faster. 23

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us The two cars have much less drag than the sum of two individual cars, about 27% less drag as shown in these studies. 24

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories What Physics tells us As a result of the lower aerodynamic drag the speed at which the net power for accelerating the car is zero has increased in the pas de deux, contact drafting. Thus, two cars together go motoring right by a single car or a long string of cars. http://fasttrackrc.blogspot.gr/2010/04/talladega-pas-de-deux-why-restrictor.html 25

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories Slipstreaming in Sport Slipstreaming or drafting is used to reduce wind resistance and is seen most commonly in Slipstreaming or drafting:  bicycle racing, Slipstreaming or draft-  motorcycle racing, car racing, and ing or is a technique  speed skating where two vehicles or other moving objects are  cross-country skiing, caused to align in a close  downhill skateboarding group reducing the overall effect of drag due to ex-  running ploiting the lead ob-  some forms of triathlon allow drafting. ject's slipstream. Especially  swimming as well: both in open-water races (occurring in when high speeds are in- natural bodies of water) and in traditional races volved, as in motor racing in competition pools. In a competition pool a swimmer may and cycling, drafting can hug the lane line that separates them from the swimmer significantly reduce they are abaft of thereby taking advantage of the liquid the paceline's average en- slipstream in the other swimmer's wake. Drafting also occurs in competitive longboarding. ergy expenditure required to maintain a certain It is believed, but not yet conclusively proven, speed and can also slightly that Thoroughbred racing horses draft each other, especially in longer races. reduce the energy ex- penditure of the lead ve- hicle or object. 26

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Sport Science Stories Slipstreaming in Sport Slipstreaming: A driving tactic when a driver is able to catch the car ahead and duck in Slipstreaming in Olympic behind its rear part of the car cross-country skiing. to benefit from a reduction in drag over its body. Pay Attention!! Paying attention to your sur- roundings is doubly important Slipstreaming in running. when slipstreaming. A mis- take on your part can cause a big pileup . By staying close behind a The bicyclist, as he moves lead swimmer, you can save through the air, produces a effort by \"surfing\" on the turbulent wake behind him- slipstream they've created self. It makes vortices. in the water. Speed skaters can benefit from drafting, which is to Slipstreaming Reduces Drag say in Horse Racing up to 66%. from slipstreaming behind another skater. 27

Fly like a bird: The V formation Volume 1, Issue 5 14/02/2018 Sport Science Stories Just as aerodynamic Watching the autumn we see migrating birds estimates would pre- fly in a V formation. This is a common phe- dict, the birds posi- nomenon but scientists have long debated tioned themselves to why this is so. A new study of ibises finds that fly just behind and these big-winged birds carefully position their to the side of the bird in front, timing wingtips and sync their flapping, presumably their wing beats to to catch the preceding bird’s updraft—and catch the uplifting save energy during flight. eddies. When a bird flew directly behind another, the timing of To definitively say that the birds are drafting the flapping reversed off each other, however, the exact location of so that it could mini- the eddies and the areas of downdraft would mize the effects of the need to be measured on ibises, which would downdraft coming off require flying them in a wind tunnel—a far the back of the bird’s more intrusive process than simply carrying a body. “We didn’t think this was possible,” Ush- data logger. erwood says, consider- ing that the feat re- quires careful flight Scientists do not know how the birds find that and incredible aware- aerodynamic sweet spot, but they suspect ness of one’s neighbors. “Perhaps these big V that the animals align themselves either by formation birds can be sight or by sensing air currents through their thought of quite like an feathers. Alternatively, they may move around airplane with wings until they find the location with the least re- that go up and down.” sistance. 28

Planes benefit from the V formation Volume 1, Issue 5 14/02/2018 Sport Science Stories Energy saving Boeing Co. and NASA have found an inexpen- The wing creates lift, sive way to cut airline fuel bills by borrowing a which is upward force trick from the world’s greatest long-distance on the wing. According to principle of action aviators: migratory birds. and reaction, there must be a downward force acting on the air. This force creates a downwash behind the wing. As the accelerated air interacts with the Think of a car drafting a truck, or one bike rid- still air further away it er drafting another. It essentially allows you, if turns to the sides and you are flying in the right spot, to reduce your back up, creating a fuel burn. But you’ve got to be there for a long slight upwash outside of time. the wingtips. Flying in this upwash adds a bit of lift on the next flying thing which in turn means it can fly Wake surfing, as the avian technique is known, at slightly lower angle involves harvesting energy from a lead plane — of attack and have less a potential way to cut fuel bills, which typically induced drag. This re- rank as the biggest or second-biggest expense covers some energy for airlines. A researcher at the National Aero- from the wake vortex nautics and Space Administration points to stud- that would otherwise be ies showing fuel savings of 10 percent to 15 per- dissipated as heat. cent, on a par with pricier options such as up- grading engines or installing winglets. 29

NASA Experiment Volume 1, Issue 5 14/02/2018 Sport Science Stories NASA Experiment A study that wrapped up this year may help debunk the view that airlines would need extensive cockpit upgrades to fly in tight formation. NASA measured considerable fuel savings that could be gained without making passengers or air crews uncomfortable, said Hanson, who is based at NASA’s Armstrong Flight Research Center in Edwards, California. “We were able to fly in a stable, commanded location within the wake for long periods of time,” said Hanson, who is based at NASA’s Armstrong Flight Research Center in Edwards, California. The agency is still analyzing data and won’t publish the findings for months. 30

Sport Science Stories Volume 1, Issue 5 14/02/2018 The eTwinning Group: “Sport Science Stories” 31

Sport Science Stories Volume 1, Issue 5 14/02/2018 The eTwinning Group: “Sport Science Stories” 32

Photos Volume 1, Issue 5 14/02/2018 Alexandros Markoulakis Supervising teachers: 2nd General Lyceum Eugenia Potiriadou of Kamatero 33

Slipstreaming for two Volume 1, Issue 5 14/02/2018 Alexandros Markoulakis Supervising teachers: 2nd General Lyceum Eugenia Potiriadou of Kamatero 34