CO 2 Dragster Notes Its all about AERODYNAMICS

CO 2 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 F 1 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 (+200 kph) 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 CO 2 dragsters, everyone has the same size engine (CO 2 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