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CO2 Dragster Notes

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					CO2 Dragster Notes
    It’s all about…
AERODYNAMICS!!
4 Basic principles to Aerodynamics:

      A.    Lift
      B.    Thrust
      C.    Weight
      D.    Drag
        In an airplane, when:
    Drag = Thrust & Weight = Lift
the plane will fly STRAIGHT & LEVEL
• 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.
• Cars create thrust using engines.

• If drag increases and/or thrust decreases the car
will slow down
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.
• 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.
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!
                       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.
 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 > force = slowdown




Drag < Force = speed up!
                         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.
                         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.
• 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)!
            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
 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

				
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