I put up some fishing line that I had in the tackle box (new stuff) and hooked it up. With 100 winds, the thing regularly starts off by twisting up and over the fishing line. This slows it down a great amount. When it does this, the thing only makes it 10 - 15 yards before running out of steam. When it somehow resists the urge to circle the string, it takes off and runs a good 20 yards, very quickly.
I'm wondering if the type of line could be the problem, or the fact that I am starting it by moving my finger away from the prop? Any ideas?
You are observing the reaction torque of the propeller accelerating to speed. This means your rocket is REALLY light. That's one trick to winning this race. I sanded the nose over a little at a time to an angle opposite the direction of spiralling around the line so that I counteracted the reaction torque. The propeller ends up pointing off line.
What I have done for ADULT space derby is carve a kit until I could see light in several places. I lightened, feathered and polished the propeller, and made the hanger a space frame. I even drilled through the middle of the rod that holds the rubber bands at the back. The whole thing weighs 9 grams, including the rubber bands.
Hope this helps.