Hi there. I am a flight instructor and I have played with an Aerobird Challenger for awhile. I had a student give me a .40 trainer that he had flown twice and crashed twice. I fixed it and I'm attempting to fly it. Here is the problem. The propellor keeps coming lose when i start it. It seems to happen when it is a little bit flooded. I'm using an electric starter and a plastic spinner that he gave me. I have tried a lock washer. And double nutting it seems to work but the second nut doesn't fit on all the way. Should this be loctited? Any help would be greatly appreciated