flap motor clutch info (long)

[jjconstant]

Short version: I found out that the clutch in the flap motor will be inoperable at the actuator fully retracted position (flaps fully extended position for RV7A) if the rod end bearing is screwed it too far, or it is too long.

Full story: I was showing off my installation of the Flap Positioning System to a friend. I raised the flaps, then lowered them, one stop at a time until the 40 degree deployment position. It worked as it was supposed to: motor stopped at 10, 20 and 40 degrees with each activation of the momentary down portion of the flap switch. My friend and I started talking, but the master was ON. After about 2 minutes I noticed smoke from the flap motor

It turned out to be a combination of incorrect installation of the FPS which they (Brian at ShowPlanes) helped me troubleshoot, and when I called back to verify that it was working correctly, they were the ones that said that I must have some kind of binding going on somewhere in the flap system. It is supposed to be that after the 40 degree position, you should be able to push the momentary down position on the flap switch and hear the flap motor clutch. It didn't. It just drew current (DVM showed 8Volts) with NO noise.

I removed everything and started with the motor and noticed it would clutch at the actuator extended position but not retracted. I called Vans, who had me call the manufacturer who said send it back. When I asked if I should remove the rod end they mentioned that if the rod end is too long it would prevent the clutch from working! I tested it by unscrewing the rod end 1/2 a turn and the clutch worked!

My panel is completely installed, as is just about everything else electrical, and it is the first time the magic smoked found an escape route. I confess it gave me pause that something would smoke when I thought it was "OFF". 2 things were wrong (initial installation error on FPS and rod end) and it combined in an unknown-to-me failure mode that really got my attention.

I hope this might help someone else troubleshoot.

Jeremy

[lorne green]

I've heard it said that:
It is better to find magic smoke on the ground than on short final,
at 400 feet doing 85 miles an hour!
regards