I screw on each prop until it stops, then I take the tightening tool and turn each prop at least 1 1/4 turns. It works for me - I have never had a prop fly off since I have been doing this.
I had a prop fly off a couple of times on landing, too. Make sure you really tighten the props - screw them on , then take the the tightening tool and tighten each prop 1 1/4 turns. It works for me.