[4kilo]

This morning I noticed some unusual slop in my ailerons. Investigating after landing, I found that the nut holding the forward heim bearing on the control column had loosened to the point that the heim bearing could swing from side to side, allowing a considerable amount of play in the aileron control circuit.

For those unfamiliar with the RV-8 control column, it is suspended fore and aft by two heim bearings which function as pivots to allow the column to rotate from side to side for aileron control. The forward bearing is affixed to a bracket on the forward side of the wing main spar, with a jam nut on the lower side of the bracket and a nyloc nut on the top side of the bracket. I suspect that it was actually the jam nut which loosened, allowing the play in the bearing.

I would really like to prevent a repeat of this occurance (it could get a little ugly during low altitude acro). Right now I am leaning towards using an all-metal lock nut on the top side with a dose of locktite on both the jam nut and the lock nut. Another possibility is drilling the upper part of the heim bearing for a castillated nut, again with locktite on the jam nut. Anyone have any other suggestions?

Pat

 

[DanH]

Pat, I suspect the locktite will do fine, but you could run the lock nut all the way down until it binds at the end of the threads, then install a machined aluminum spacer (or stack washers) above it to set the correct pivot distance from the bracket.

 

[Bill Wightman]

The jam nut on the underside of the pivot mount bracket really should be a locking type nut. Loctite should work fine on a simple AN316 jam nut also.

On the top side of the bracket, I used the NAS679-A6 nuts that were specified for use on the landing gear bolts (which I replaced with NAS1804-6). The 679's are a low profile all metal lock nut, and allow for more vertical adjustment of the heim bearing if used in lieu of the AN365's the plans call for.

I used the same hardware on the aft control column pivot.