Transcript CO2 Dragster Design

CO2 Dragster Design
http://www.science-of-speed.com/science.asp
Research and Development
Objectives
Research in CO2 auto design involves the study
of a few sciences related to the motion of your
dragster.
• Aerodynamics- the study of how solid objects displace fluid
air and other gases;
• Physics- the study of matter in motion;
• Tribology- the study of friction;
Research and Development
Objectives
Development of CO2 auto design requires• Understanding the problem or purpose- trying to achieve the
fastest speed and/or best appearance;
• Knowing your limitations- being aware of safety regulations,
materials allowed, specifications, tolerances and
functionality;
• Making intelligent decisions- taking what you learn and using
it to your best advantage;
• Testing your solution- comparing results with your
classmates to see what works better;
Terms to Know- Aerodynamics
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Fluid
Mass
Aerodynamics
Drag
Lift
Rear Suction
Down Force
Frontal Area
Aerodynamics in race cars Circle Track magazine
Aerodynamics in race cars Hot Rod Magazine
Research- Aerodynamics
 Air– Is a type of fluid such as water that can be
directed or displaced;
– Has mass and is measured in terms of pressure;
– Applies direct and frictional forces to objects in
motion;
Research- Aerodynamics
 You should be aware of four aerodynamic
principles–
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Drag
Lift/Down Force
Drag Coefficient
Frontal Area
http://www.hotrod.com/techarticles/body/hdrp_0609_aero_tricks_tips/
Research- Aerodynamics
 Drag is a combination of two forces that will
work against the acceleration of your CO2
car.
– Frontal Pressure occurs when tiny molecules of air hit the
front of your car and is forced away to make room for
other molecules to hit it.
– Rear Suction occurs when an empty pocket of air is
created in the back of your car resulting in a vacuum
cleaner effect that tries to pull your car backward.
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.
Suction
Notice that liquid is pushed up
a straw when the balanced air
pressure is removed. The
same effect happens to objects
in motion. The air traveling
around the object can create a
pocket of less air pressure
causing suction to occur
Air Flow
Rear Suction
Research- Aerodynamics
 Lift is similar to rear suction in that a thin
empty pocket occurs as air passes over a flat
surface causing the car to lift.
 Down Force is due to high pressure in curved
surfaces that causes the car to be pushed
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.
In an airplane, when:
Drag = Thrust & Weight = Lift
the plane will fly STRAIGHT & LEVEL
• Cars create thrust using engines.
Your dragster will use a CO2 Cartridge
• If drag increases and/or thrust decreases the
car will slow down
• 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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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!
Air Flow
Lift
Down Force
Air Friction and Lift
When a ball rotates in motion,
it causes the air around it to
flow with the rotation, often
changing the direction with
lift and down force.
The dimples in a golf ball are also used
for reducing air friction with the surface.
But…read this -->Golf Ball Dimples & Drag
Research- Aerodynamics
 Drag Coefficient is a way of expressing how
slippery a car is.
 Here is a tip to increase your speed and lower
your drag coefficient(the more ways you can eliminate drag, turbulence,
rear suction, lift and down force, the faster your
car will go)
Research- Aerodynamics
 Frontal Area is the total of all surfaces in the
front of your vehicle which cause drag.
Area = Length x Width
Review
With one hand, which can be
thrown further, a football . . .
or a soccer ball?
Review Tips- Aerodynamics
 Avoid flat upright surfaces in the front of
your car to reduce turbulence.
 Avoid flat upright surfaces in the back of
your car to reduce rear suction.
 Shield as much air at the bottom of your car
to maintain traction.
 Keep the surface area exposed to
oncoming air to a minimum.
Terms to Know- Physics
 Force
 Acceleration
Research- Physics
Force = Mass x Acceleration
Heavier objects require more effort to move at the
same speed;
It is easier to push a CO2 car out of the ditch than to
push an actual car out of the ditch.
Everyone’s force on the CO2 car will be the same.
The less mass, the greater the acceleration
Research Physics
Heavy Mountain Bike
•Durable
•For Rough Terrain
•Requires more Energy
Light Racing Bike
•Fast
•For Long Distance
•Requires less Energy
Research- Physics
How does the angle of your CO2 cartridge
affect the efficiency of your car?
Review Tips- Physics
 Avoid unnecessary extensions and ornaments that add
weight to your car.
 The lighter you design your car, the more power will be
used out of your CO2 cartridge.
 Make sure that your drill holes are straight and accurate to
reduce extra forces acting on your car.
Research- Tribology
Tribology is the study of friction between solid
surfaces.
 Friction is a force that resists movement.
 Friction is found between moving parts and
surfaces.
 Without friction, objects would never come to
rest.
Where will you find friction forces acting on
your car?
Research- Tribology
How many wheels should you have and why?
Research- Triboloby
Does the paint job affect your car: Why or
why not?
Research Physics
Heavy Mountain Bike
•Wider Ground Contact
•More Surface Friction
Light Racing Bike
•Narrower Ground Contact
•Less Surface Friction
Review Tips- Tribology
 Painting your car will reduce aerodynamic
friction.
 Axel design is important to reducing friction.
 Lubrication of the axels can reduce friction.
 Less ground contact wheels have with the
ground, the less friction will be present.
Review Tips- Aerodynamics
 Avoid flat upright surfaces in the front of
your car to reduce turbulence.
 Avoid flat upright surfaces in the back of
your car to reduce rear suction.
 Shield as much air at the bottom of your car
to maintain traction.
 Keep the surface area exposed to
oncoming air to a minimum.
Review Tips- Physics
 Avoid unnecessary extensions and ornaments that add
weight to your car.
 The lighter you design your car, the more power will be
used out of your CO2 cartridge.
 Make sure that your drill holes are straight and accurate to
reduce extra forces acting on your car.
Review Tips- Tribology
 Painting your car will reduce aerodynamic
friction.
 Axel design is important to reducing friction.
 Lubrication of the axels can reduce friction.
 Less ground contact wheels have with the
ground, the less friction will be present.