"Yeah," said my son,"and I hadn't shaved in ten years..."
Pretty witty for a fourth-grader!
Here are this year's Pinewood derby entries:
The Flying Hamster is the boy's,
Racing is first weekend in Feb....can't wait. Hopefully better than last year:
The green car only placed 3rd in 3 of the heats and 2nd in one.
So what did we learn?
There are many variables. Some are more important than others, but viewing the results of the final championship races; two cars tied for 6th with the same times to the 10,000th of a second (yes four decimal places!) so the difference in even the least important categories may still decide a race.
Weight: some of the 5oz cars were as quick or quicker than many of the 8oz adult cars, so there may be an upper limit where weight adds so much extra rolling resistance down-track that it offsets the benefits of the added thrust. First order of business is to buy a digital scale that measures to 0.1oz and get exactly accurate weights from the get-go.
CofG: weight distribution makes the biggest difference. The further aft the weight, the higher the center of gravity of the car on the start ramp and the greater the potential energy that can be translated to forward speed at the round-out. BUT, the farther aft the c/g, the less directional stability and the more likely the car is to shimmy between the guide rails, inducing drag.
Wheels: polished spindles and plenty of graphite lubricant help but so should a bit of negative camber that means the wheels ride on the inner rim, and are pulled towards the tip of the spindle so are less likely to drag on the body. A small amount of toe-in may help with directional stability (but so should a big vertical fin - and there's no vertical limit...!
Shape and surface finish: with timing to four decimal places, aerodynamics do matter...but only if the rest is done right.