Daily Archives: March 10, 2007

digression into aerodynamics

From the very start you have to have an aerodynamically clean design. Its a challenge to do that with the dimension rules in the Canary Derby, and also with the budget limit. At the speeds at which the competitive cars were running last year (34-37 kph at the corner, probably faster at the finish line), aerodynamic drag is the major force on the car. I’ll get into a wheel discussion later, but rolling resistance is a minor component of overall drag (except for the cars last year using soapbox and skateboard(!) wheels). The Carmanah Technologies car, had in my opinion, the best running gear in the field. They used racing wheel chair wheels and tires (700c?) and the test runs the week before the race were done with no body and were quite fast. But the body shape they chose was not very good, and I think that cost them the race. The Aspreva car had slower wheels (20″) but a faster shape (albeit not the best shape possible), and won.

design and construction tips 2.

The previous entry about laying out a plan view of the car is directly applicable when you are making a car with a flat base to the chassis, ie. cut from a sheet of plywood. If you are going all out and will be making a “curved in all 3 dimensions” body, its still good to have that plan view layout. It may not be the base of the car but will probably be a plane on which the axles will be mounted. Its important to have a reference plane if you want front and rear axles to be aligned. The soapbox derby construction┬ámanual on classic soapbox racer construction says more about this. Its a very good document to read.