29 April 06 - Electric Flap Stuff

Today, just for something completely different, we're messing around with the electric flaps. We're continuing to think about getting wires from the front of the plane to the back, and we've got to get this finished up before that happens.

Probably best to say something about this here: Every once in awhile, someone will ask about the design of the flap motor on one of the RV lists, and the implication always seems to be that the design is flawed in some way. Generally, two separate discussions follow: (a) a (generally) well-reasoned and insightful discussion about how the design can be improved, and (b) a somewhat more hostile discussion about how flawed it is, if at all.

My take on this is that (disclaimer: do your own research, make up your own mind, and contact the guys that make the kit, don't take my word for it) it's sort of a weird design. What you can't see in the pictures is that the flap motor moves up and down by spinning, and the spinning has to be stopped (hence the safety wire) for the motor to actually move the rod up and down. If the spinning doesn't stop, the motor can spin the rod off of the rod end bearing, at which point you have a fairly interesting problem because the flaps don't have anything holding them up or down. The effects of this have been debated, and there's no consensus: some folks think it'll pull the wings off, and other folks just think it'll scare the pilot. Bottom line is that no one can point to any instances of this happening to an RV, so we're not entirely sure.

On the other hand, unless I'm mistaken, Dan Checkoway didn't even put safety wire on his, and just used loctite. He's got (at this point) 875+ hours in his airplane, and no problems.

So, there's no real conclusion, here, but what I'm doing is (a) using the safety wire and the stop nut that the plans for, and in addition (b) putting a bunch of loctite in there, even though the plans don't tell you that this is necessary. Can't hurt, though. Between those three safety system, we should be okay. It's probably worth checking this safety wire on the annual inspections, though.

Enough about that! Let's put it together:

The plans call for a hole to be drilled in the end of the flap motor actuator, like this. (This was the smallest drill bit we had - 1/16 inch - and the largest safety wire.)	Here it is together - note that safety wire goes inside, around the bolt.
Other end: we've got the cotter pin in there.	It's a bit tricky to get the safety wire in there and the flap actuator attached when the top end (next to the motor) has already been put on there with the cotter pin. This is how we did it - helps if you run the motor all the way out. However, you still have to take off the canopy latch rod (upper left of picture).
Darn! The canopy latch rod has to bend to get around the part that holes the electric flap motor. That's not good. Not sure why this is, but we didn't put this together originally with flush rivets, so we'll try replacing those. (You can't see the non-flush rivets, but trust me, they're there - behind the canopy latch rod).	These rivets have been replaced with flush rivets, now, and although it's not quite so bad, the parts do still interfere, although you wouldn't know it from this picture (we had the rod out just so you can see the rivets).

Well, looks like we'll be making a few spacers or something for this thing, so it can move without rubbing. Not sure what caused this - maybe parts weren't bent correctly, I have no idea. Should be simple enough to fix, though.

Previous log entry

Back to the log

Next log entry