CO2 Dragster Notes

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CO2 Dragster Notes

• Its all about AERODYNAMICS!!

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4 Basic principles to Aerodynamics
A. Lift
B. Thrust
C. Weight
D. Drag
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In an airplane, when Drag Thrust Weight
Lift the plane will fly STRAIGHT LEVEL  
4

• In a race car (Indy or F1 style) the car is
  designed like an upside-down airplane wing which
  creates downforce rather than lift. This keeps
  the car on the ground and prevents lift-off.

• With cars, the principles of design are the
  same which is to have the 4 aspects equal each
  other thus maximizing its aerodynamic efficiency.

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• Cars create thrust using engines.
•  

• If drag increases and/or thrust decreases the
  car will slow down
•  

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The Bernouli Effect

• If a fluid (gas or liquid) flows around an object
  at different speeds, the slower moving fluid will
  exert more pressure than the faster moving fluid
  on the object.
•  

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• Again, the shape of the chasis is similar to an
  upside down airfoil (airplane wing). The air
  moving under the car moves faster than that above
  it, creating downforce or negative lift on the
  car. Airfoils or wings are also used in the front
  and rear of the car in an effort to generate more
  downforce. Downforce is necessary in maintaining
  high speeds through the corners and forces the
  car to the track. An Indy ground effect race car
  can reach speeds in excess of 230 mph using
  downforce. In addition the shape of the underbody
  (an inverted wing) creates an area of low
  pressure between the bottom of the car and the
  racing surface. This sucks the car to road which
  results in higher cornering speeds.

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Because of the amount of downforce a race car
creates, (in theory) if a race car is traveling
at high enough speeds (200kph) it could travel
along a wall or even upside down on a road
without falling!
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Drag

• Aerodynamic force that resists the motion of an
  object moving through a fluid (air and water are
  both fluids).

• Try this next time you are in a car put your
  hand out a window and rotate it. You will notice
  much more force (drag) when the palm of your hand
  is open and vertical then when it is open and
  horizontal

The amount of drag that your hand creates depends
on a few factors, such as the size of your hand,
the speed of the car and the density of the air.
If you were to slow down, you would notice that
the drag on your hand would decrease.
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        When you are driving along at a constant
speed, the power produced in the engine is
converted to force at the tires. If the drag and
force (engine) are equal then you maintain your
speed.
Drag gt force slowdown
Drag lt Force speed up!
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Thrust

• A force that moves an object (vehicle) through
  the air

•  
• Thrust is generated by the engines of the
  aircraft or vehicle
•  

 

• Thrust is used to overcome the drag of an
  airplane or car, and to overcome the weight of a
  rocket.

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Mass

• Mass - the measure of how much matter an object
  or body contains -- the total number of subatomic
  particles (electrons, protons and neutrons) in
  the object. If you multiply your mass by the pull
  of Earth's gravity, you get your weight.
•  

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• Acceleration - Newton's Second Law states that
  the acceleration (a) of an object is directly
  proportional to the force (F) applied, and
  inversely proportional to the object's mass (m).
  That is, the more force you apply to an object,
  the greater the rate of acceleration and the
  more mass the object has, the lower the rate of
  acceleration.
•  

  As mass increases (and engines stays the
same size) you will not accelerate as quickly  
  With your CO2 dragsters, everyone has the
same size engine (CO2 cartridge) but the smaller
the vehicle (lighter weight) the faster it will
travel (in theory)!  
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Rolling resistance

• Sometimes called rolling friction, is the
  resistance that occurs when an object (e.g a
  wheel or tire) rolls.

• Rubber will give a bigger rolling friction than
  steel

• Sand on the ground will give more rolling
  friction than concrete

• A vehicle rolling will gradually slow down due
  to rolling friction, but a train with steel
  wheels running on steel rails will roll much
  further than a car or truck with rubber tires
  running on pavement

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Factors that contribute to the rolling friction a
tire generates
Material - Tires with higher sulfur content
tend to have a lower rolling friction (this is
one strategy that most hybrid car vendors use to
improve fuel efficiency)
  Wheel/Tire Dimensions - rolling friction is
related to the flex of sidewalls and the contact
area of the tire. For example, at the same
pressure wider bicycle tires have less flex in
sidewalls and thus lower rolling resistance
(although higher air resistance)
 
  Extent of inflation - Lower pressure in tires
results in more flexing of sidewalls and higher
rolling friction.

• Smaller wheels, all else being equal, have
  higher rolling resistance than larger wheels