This is the third time this has happened: On my Hobbico Superstar with OS 40LA, I'm applying the electric starter and suddenly the prop nut comes loose inside the spinnner . This is the stock spinner that comes with the RTF with 2 screws that go into the backplate of the spinner, but the prop is a Master Airscrew G/F 3 series 10X6. From the backplate of the engine going forward: is the back of the spinner, then the prop, then the black flatwasher, then the nut. Seems like on this hard plastic prop there ought to be a lockwasher under the nut, but my other planes don't have one either. I thought I used plenty of torque on the nut since this has happened before. Luckily it's only happened when starting, but worried it could shake loose in the air too. Help!