My greatest modeling blunder has served as a lesson I've never forgotten. This goes back to the days of free flight, 1939. I was flying a Bunch Scorpion Major powered by a Baby Cyclone but it didn't want to climb as well as usual. First thing was to put on a flatter pitch prop. For good measure I also put a 3/16 square piece of balsa under the leaading edge of the wing. Cranked it up and the Scorpion climbed like a homesick angel. For those who don't know, the Cyclone had a gravity feed fuel system. When Ol' Scorp went straight up the engine sagged terribly which induced a stall. When the nose pointed down Cyclone started to roar and pulled Scorp up into another stall. Repeat performance. On the third repeat the straight down part ended on the ground and washed out a lot of the fuselage. Lesson to be learned. I never knew which adjustment, caused the wreck. Now I never make more than one change at a time. At least I know what causes the crunch and enough not to repeat it.