[Steve Brown]

Flap linkage jammed

Just got back from a trip to Co (KAPA). Twice on the trip I had the experience of thinking the flaps were all the way down, but they weren't.
On landing KAPA I didn't notice until I was on the ground. Landing KTPH for fuel on the way home, I noticed when on final the airplane was gliding forever and then finished lowering them.
In Colorado I was a little annoyed with myself for an apparent lapse of following pre-landing checks. at Tonapah I was very concerned that I had become a lame pilot.
At the end of the trip landing at RHV when I went to put the flaps down on final they didn't budge at all. After a few moments of denial I readjusted my strategy for no flap landing.
When I dug into the problem yesterday I found that the linkage at the flap actuator weldment was completely jammed. No play, wiggle, or movement. It looked as though the safety wire had caused the jam. I guess during the two partial flaps incidents I heard the moter run, including the sound of it hitting the stop (so I thought), glanced to see they were "down" and assumed they were all the way down. Obviously this procedure has holes in it which I need to plug.
Anyway, see DWG 33, DETAIL E
I think there were only two washers in the assembly. It is possible I lost one in the tunnel, but I searched carefully.

Here is some confusion with DWG 33:
Left side view, area detail E calls out 3 washers
The exploded isometric view shows only two washers
Detail E doesn't mention any washers

When I reassembled it, I noticed that the flap actuator fell naturally to one side of the flap actuator weldment, so I put two washers on one side (pilot side).
Also, I didn't wire it as shown in detail E, because I thought that was the source of the jam. I put the safety wire hole in the flap actuator rod facing
aft, and put the wire around the pilot side tab on the flap actuator weldment. Pictures below
Cycling the flaps down and up, everything seems to work fine. The safety wire seems to not be in position to cause another jam or fatigue when cycling the flaps.
I guess I could wire it as shown in the plans and replace one of the washers with the wire. I'm reluctant to do so because I think that was the source of the jam.
Any comments on this?

Picture quality a little poor, but I think good enough:

 

[JonJay]

Now I am confused

I dont have that drawing to look at but on my actuator I drilled a diagonal hole through the end of the actuator, as you have done, and then drilled a hole in the jam nut and safety wired those two together.
I did not wrap anything around the weldment.
I did this after several incidents of flap actuator unsrewing themselves but before there was any documenation on how to fix it. So, it may not be the best way, but 300 hours and no issues.

 

[Bavafa]

I would think the way you have done it, positioning the hole to the aft side, will create more bending movement on the safety wire as it goes up and down and eventually break. Think about the way that the actuator moves in relation to the weldment. The lease amount of movement (bending type movement) is when the safety wire is on the side and that is how the plan shows it.

 

[Steve Brown]

Thanks for the comments

I think there are two potentials for fatiguing the wire. One is the up & down motion and the other is the twisting motion when the screw is turning. I think the twisting is worse, but that's just a subjective opinion.

I didn't like what was in the plans and I wasn't particularly happy with my change. So I left it open.

I'm going to see if I can use this solution by Alf Olav Frog until I think of something better:
link to better safety wire solution

It has neither fatigue problem. However, I think safety wire is meant to keep a nut from loosening, not for handling the load on the nut. In the event the jam nut comes loose, the flaps will be operating via the safety wire.

There will be no indication that this has happened until the wire fails, which I think it will.

I think the design is flawed. Jam nuts work fine in other control rod situations because there is only pushing and pulling, no twisting. In this case there is twisting both directions so it seems like it is constantly going to try and loosen itself.

Right now I'm wondering why the rod end bearing cannot be welded in place.

 

[frazitl]

I'm thinking about just drilling a hole through the black tube and threaded portion of the Heim joint and installing a roll pin. Only downside I can see is if I ever needed to adjust the position of the Heim joint, I might need to buy a new one.

What do you guys think?

 

[nucleus]

Not a Good Spot for Safety Wire IMHO

Nylock nut and call it good...

 

[mikehoover]

The plans call for three washers: two on either side of the bearing and one under the nut. The plan makes it look like the safety wire should be around the bolt between the bearing and a washer. I have mine so the safety wire is not wedged in between anything; it loops around between a washer and the rod end bearing. The rod bearing is rounded and the safety wire rests on its surface and up against the washer, left or right movement blocked by either the washer or the bearing. Tied straight up to the flap actuator, I would think the movement of the safety wire should be minimal. Not sure this is totally correct and I haven't flown mine yet, but I did give it one heck of a work out after getting the flaps installed and the flap motor operating. I thought I would wear that motor out sitting in the workshop making airplane noises. Of course I used full flaps for all my pretend landings.

 

[Steve Brown]

Final fix

After reading the comments and seeing Alfs solution, I went back and modified mine:

I'm still not 100% satisfied, but I think it will do for now. When I do my next annual I may take it apart and put it back together with some tenacious thread lock, use jam nut, and just skip the safety wire.