Design Tips for a CO2 Dragster Car

Written by richard rowe
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Design Tips for a CO2 Dragster Car
CO2 dragsters have more in common with jet aircraft than cars. (Aircraft engine image by Andrew Breeden from Fotolia.com)

One of the stranger aspects of any type of sport, be it motorsport or otherwise, is the ratio of time spent preparing to compete versus the time spent actually competing. Drag racing epitomises this aspect of motorsport; some racers will spend literally hundreds of hours designing, building, testing and modifying their machines to win a race that might be over in a few seconds. Indeed, 99 per cent of any drag race's outcome is decided before the car ever sets a wheel on the track.

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Reduce Frontal Area

While most CO2 racing classes place limits on car wheelbase, length and ground clearance, you should do your best within those constraints to increase stability and keep wind resistance to a minimum. The easiest way to do this is to reduce frontal area, or the size of the car when viewed from the front. Keep the top and bottom of the body as low as possible, and keep it as narrow as possible. However, never reduce frontal area by creating any blunt front or rear surfaces, as these will increase wind resistance and drag.

Boat-Tail the Rear

Aerodynamic effect on any car is all about reducing the car's effect on the surrounding airstream without causing the air to tumble or compress. The energy required to compress the air (ahead of the car) or tumble it into turbulence (behind the car) has to come from somewhere, and that "somewhere" is your car's propulsion unit. To return the airstream to its undisturbed condition without causing it to tumble, the rear of the car should (within class limitations) taper smoothly to a point just like the front. That point can be in the centre or the car (vertical taper), or along the track (horizontal taper).

The ideal car would have a flat bottom, a sharp point in the front tapering up to a smooth bulge in the middle, which tapers to a matching taper in the rear. This is much like the high-speed airfoil on fighter jets.

Use a Gas Diffuser

A CO2 car uses jet propulsion, meaning that it moves by using energetic gas to push against the atmosphere. If this jet thrust comes out in a very thin, fast-moving stream it will simply punch a hole in the air without exerting much force upon it. A thicker, slower moving gas stream will exert more of its energy on the surrounding air. Diffuser nozzles are the cone-like things on the bottom of NASA rockets. They fine-tune the rocket thrust so that it efficiently moves the vehicle.

You can't surround your CO2 cartridge with a cone-shaped diffuser because most tracks require that the rear of the CO2 cartridge be flush with the launch plate. However, you can put the CO2 cartridge inside a smooth copper tube so that, upon puncturing, the cartridge will shoot forward two inches or so into the car body. The impact effect of it slamming into the body should slingshot the car forward to overcome initial resistance, and the copper tube will capture the expanding CO2 gas and internally pressurise to emit a fatter, slower-moving jet stream. Make sure to keep friction in the copper tube (copper has a higher lubricity than steel) to a minimum with dry graphite lubricant.

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