Expert: Paul Soderman - 1/22/2009

Question
I am trying to find out if it would be beneficial to add lift to a derby car( to help reduce friction on the wheels) or if the drag would out weight the benefit.
The area of the car is 2”x7”
I think the top speed of a gravity powered derby car is around 6mph

My guess is at low speed it may take too much drag to lift the car. Like a water skier moving very slow in the water.


Answer
Greg
At 6 mph, which is somewhat faster than I can walk you will not have much aerodynamic force.  But theoretically, you could reduce the wheel friction by adding lift.  But I believe the wheel friction goes as weight whereas drag goes as lift (weight reduction) squared.  So, without doing an analysis of your specific geometry I think you would generate more drag than thrust from gravity. Plus, the lift vector has a component opposed to thrust.  You could find out for sure if your idea works by giving it a try but I suspect your wing would act like a little parachute.
Paul