Fantastic Fan "helicoptering"

We recently thought we were hearing distant helicopters flying off in the distance at night. I then noticed that shaft on our Fantastic Fan was wobbling, and we realized that it was the source of the noise.

I first took everything apart and cleaned the fan (first time in three years). It was less noisy, but the helicoptering still happened from time to time.

We've been on the road now for 98 straight nights and we as yet have never deployed the stabilizing jacks. Most of the time we are close enough to level (both fore and aft and side to side) that it is simply not worth the bother when we are only camping over night.

So when we first realized that the 'helicoptering' was coming from the fan we were on an uneven camping pad. Last night we were dead level and the shaft was spinning smoothly and there was no 'helicoptering' sound.

My conclusion is that the fan acts much like the bicycle wheel exhibits at many local science centers. You spin the wheel and then try turning the wheel to one side. You'll find it hard to hang on to, due to effects of centrifugal force plus the turning motion.

The fan will be quieter when the trailer is perfectly level, and at some point of being unlevel in one or more directions, the fan shaft will start to wobble, possibly to the point where is causes the 'helicoptering' noise.