The Importance of AERODYNAMICS

1
The Importance of AERODYNAMICS

• The following presentation will provide students
  with information about the RESEARCH of how the
  performance of vehicles is affected by air as
  they move through at higher speeds. This is a
  branch of science dealing with objects as they
  move through a fluid called Dynamics.

2
What is AERODYNAMICS?

• Aerodynamics is the science that does research to
  discover the effects on an object as it moves
  through air.
• Scientists have been studying how objects move
  through air for thousands of years. Sails on
  boats, arrows, bullets, and artillery shells,
  baseballs, golf balls and footballs have been
  tested and are still being researched to improve
  their accuracy, distance and flight all for the
  improvement of performance.

3
Automotive Aerodynamics

• For this module, we will focus on the principles
  of air that affect a vehicles abilities to reach
  its highest performance when accelerated to very
  high speeds. While a student can design a VW
  Beetle or Honda Accord or even a BMW 325i, the
  goal for this research project is to design for
  performance not looks or styling. Those goals
  are called AESTHETICS.
• Most cars are not expected to go faster than 85
  miles per hour. The next time you look at a car
  instrument panel look and see how fast the
  speedometer will measure.

4

• You will see the term, Dragster, many times while
  discussing vehicle aerodynamics. Be aware that
  most cars since the fuel shortages of the early
  1970s forced all passenger car makers to pay
  attention to how they could improve a models fuel
  mileage and range. Most specialty cars come from
  the modifications done on regular cars.
  Dragsters, hotrods, muscle cars, dune buggies,
  and now foreign or sport-compact tuner cars
  are all born from the cars made by Ford, GM,
  Dodge, Toyota, Honda, and Mitsubishi

5

• Only a few true sport cars purposely built for
  maximizing performance over everything else are
  actually produced and ALL are very expensive.
  Most of the following sports cars sacrifice many
  features you see on even the cheapest economy
  cars today. No stereo or speakers, no electric
  windows or no roll down windows at all, forget
  about cup holders and even air conditioners are
  optional.

6

• Where does everyone sit? Most have no more than 2
  non-reclining racing seats. No sound
  insulation-who needs to talk when you can listen
  to the engine rev and tires chew the road.
• Everything is sacrificed to reduce weight or
  save weight for the massive brakes, wheels and
  large exhausts. Compare these cars to the
  vehicles you rode in to school or to the store.
  Where would you put your book bag, sports
  equipment or grocery bags?

7
True Sports Cars

• Acura NSX
• Aston Martin
• V12

8

• Chevrolet Corvette
• Dodge VIPER

9

• Lamborghini
• Mazda RX-7 3rd body style

10
Exotics
Ferrari
Ford GT-40
11
True Sports Cars

• Toyota Supra
• Porsche 911

12

• McClaren 3 seats!

13

• Also and just as important was the difficulty in
  the ability to make the shape of the car out of
  steel. It was possible to make straight flat
  sides with corners or simple curves but it was
  way too expensive to make complex curves for
  most car buyers. Today, lightweight aluminum,
  high strength steel alloys, plastics, or plastic
  composites like fiberglass and carbon fiber give
  a vehicle the same strength at a greatly reduced
  weight. The same vehicle depending on the
  materials it was made out of would differ in
  weight in as much as 1000 lbs!

14
Big Cars Big Drag

• Additionally, the pollution from big older
  engines made governments force car makers to use
  smaller cleaner running engines to reduce smog
  and other forms of air pollution. In order to
  keep the performance up designers began looking
  for ways the keep cars fast but not use up all
  their fuel to keep passenger cars going down the
  highway.

15
Reduce the Weight of the Car

• The first method designers tried was to make the
  cars weigh less so the engine making less power
  would not have to use all of the power to keep
  the car moving or accelerating too slowly. The
  problem designers ran into was in order to make
  it lighter this usually made the car smaller
  because they were still using the same material,
  mild steel, to make most of the body. Mild steel
  is relatively cheap and engineers and designers
  know how to build with mild steel- used a lot.

16
The Limits of Weight Reduction

• Although new materials continue to be develop by
  scientists and engineers, the need to improve
  performance led carmakers to start rethinking and
  asking questions they never bothered to ask
  before about how the shapes of their designs
  could if at all changed to somehow improve the
  PERFORMANCE of their cars. It is not that
  aerodynamics was discovered in the 1970s but
  that the science of technology was finally
  considered as having benefit to cars HMMM!

17
The Early Years

• The first attempts were to copy examples of other
  products that went fast and could be controlled
  at speed. Aircraft and jets, which had been
  designed using aerodynamics since their
  beginnings, all had common shapes and features
  rounded edges, graceful and gentle curves, and
  low swept features and minimal parts stuck on the
  outside surfaces of the bodies.

18
Hi-Tech Wind Tunnel

• Designers began using these types of features and
  began to ask aerodynamicists how to test to see
  if the designed would work. Now car makers began
  to hire scientists instead of designers because,
  FORM FOLLOWS FUNCTION Depending on how much
  money a car maker/designer had they could measure
  or compare the efficiency of one design with
  another how much resistance, DRAG, was indicated
  by blowing air over a model in a machine called a
  wind tunnel. They would weigh how much force the
  car would push back or down on a scale and record
  the amount in pounds or kilograms.

19
Tuft Testing

• Some car makers used a low tech low cost method
  of testing by attaching five to seven inch long
  pieces of string in rows to the car to see where
  turbulence, Disturbed AIR, were created at
  different parts of the car while driving down a
  test track. Both of these methods are still
  being used today together to show the amount of
  turbulence or drag the shape feels as it moves
  through air at speeds as low as 35 miles per hour
  (MPH). Your car will be exceeding 150mph and
  cover 66 feet in as little as 1.5 seconds!

20
The Rookie Designer

• What are some things you can know about car
  design which will put you ahead of your
  classmates design?
• Recognize the purpose and goal of this module and
  remember it as you design you car Performance!
  Go as fast as you can within the specifications
  (rules)

21

• Read and pay attention to the following
  aerodynamic testing results others have done
  before you.
• Notice how the shapes with flat rears have higher
  drag numbers than curves or tapers.

22
Results of Shapes

• Drag Coefficient means how much pull or drag each
  shape feels as it was moving through the air.
• Remember these are blocks.
• Which shapes cause higher drag? Curves or corners?

23
Frontal Area
Frontal Area should be as small as possible. It
is the face or front surfaces of your car front
tires, bumper, grill, hood, windshield the air
would run into as your car moves through the air.
Reduce or avoid any flat vertical surfaces on the
front. Wheels and tires are the worst! Hide them
in the car!
24
Rake

• Side view showing Rake. The tilting or leaning
  back of a surface to deflect the impact of an
  object hitting a surface.
• Try to keep lines leaning back 30 degrees or less
  from horizontal. 7-10 degrees is best. Students
  should use a protractor to make sure the design
  has angles 30 degrees or less.

25
Rake
Notice how much the windshield and front nose
lean back
26
Taper

• A taper is the gentle reduction or shrinking of
  the size of a shape from the center to the end.
  This can be from the front to the center or
  center to rear. Scientists discovered that by
  tapering the shape of an objects sides it reduced
  the amount of drag by allowing the airstreams to
  gently come back together as they leave the
  objects rear.
• In vehicle design this is called boat-tailing

27
Tapered front and rear ends
28
Cropping the Tail

• Cropping is the process of removing material from
  the bottom rear of the object to allow an upward
  taper for airstreams to follow as they leave the
  vertical sides and under side of an object.
  Scientists and engineers discovered this design
  also acted like a upside down wing causing the
  rear of the object to hold to the ground MUCH
  better. The taper cannot be more than 20
  degrees.

29
Cropped Tail Examples
Examples of cropped tails
No crop causes red swirl arrows-drag
30
Choosing Wheels and Tires

• Big wide wheels may look cool but they are bad in
  two ways
• The bigger the wheel/tire the heavier it is and
  more power it will take to make it turn.
• The co2 cartridge pushes the car so you do not
  have to worry about traction.
• Friction Drag. The wider wheel touches more of
  the road grabbing and rolling against more road
  just like dragging you hand down a wall while
  running. The heat you feel is caused by the
  friction of the two surfaces. It is stealing
  your power! Naughty Friction!

31
More Evil Wheel Drag

• Wheels cause their own special drag that can be
  minimized.
• The wheel edges are corners all the way around
  the wheel on both sides of each wheel. If you
  measured the circumference of each wheel,
  multiplied each by 2 for both sides and then
  multiplied by 4 for all the wheels corners then
  draw a line to that length you would see how long
  a corner you would have on your car because of
  the sneaky wheels!

32
Wheel Problems

• Wheels and tires also spin through the air
  cutting and ripping through the air like an axe
  upwards, downwards, rearwards and forwards all
  at the time. If you were running a race would
  you like someone to hit down on your head and
  kick the bottom of your feet? Karate Chop!
• Research testing shows exposed wheels make up 45
  of the total drag on a car.
• Hide the wheels in a hole in the car called a
  WHEEL WELL. The well allows the wheel (cylinder)
  to sit inside protected from the air.

33
Wheel Well Design

• In order to make wheel wells and the wheel/tire
  work the need to close to each other but never
  touch. Your car does not have a moving suspension
  or axle so the wheel well radius should be 1/8th
  in. or 4mm larger than the wheel.
• The outside edge of the wheel should be even with
  the outside of the well or air will rush into the
  well and cause a mess of turbulent air. (See
  illustration)

34
Porsche 993
35
Mazda RX-7 3rd body style
36
Dark area behind wheel is disturbed area causing
serious DRAG
37
Shaded bulge around wheel as viewed from the top
shows turbulent air causing drag
38
More drag as air finds tries to find a path
around the spinning wheel
Notice the arrow inside the rectangular wheel is
pointing in the opposite direction of the air
going around the wheel. The spin of the tire is
forcing air to be thrown forward smashing into
the air going over the wheel!
39
Wheel spin throws air forward
40
Conclusion

• Reduce the size of the body reducing weight
• Shape of body should use curves or raked angles
• Frontal area should be a minimal as possible
• Taper the front and rear vertical corners
• Keep wheels out of flow of moving air