Actually, I had a couple of props come loose while starting the engine. One came off during flying when my engine seized after a crank pin failure but nothing much else.

Earlier I used to use a 4-way spanner to tighten the nuts on the 55ax. However, on the 75ax and fs91sII, the nuts were larger and I couldnt use the 4-way. Then I broke the spanner socket on both my 4-ways and began to use an adjustable spanner. Though this is more secure, I found that, inspite of adjusting tightly to match the nut size, it slipped several times and finally rounded the nut. I had custom nuts made for the 55ax (the crank doesnt have standard threads) which were a bit smaller so that I could use a locknut but the problem of slippage is still present. As yet I dont see a way around this issue

Ameyam