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Has this flap-problem happend to you?

A

ao.frog

Well Known Member
Hi.

After engine start a couple of days ago, I noticed that the flap took much longer time to raise than normal. (I always shut down with flaps full down and raise it after engine start)
The flap-motor sounded like it was running normal.
I tried to lower the flaps with the same result: flap-motor seemed to run with the normal speed but the flaps moved slower than normal.

I shut down, opened the flapmotor housing and found that the end of the flapmotor-rod had unscrewed itself from the flap-motor.
The reason this had happened, was that the safetywire had broken off, so the flapmotor rod could rotate when the flap-motor was running, allowing the end to be unscrewed.
(sorry for the possibly wrong english words)

The safetywire was mounted per plans and per Vans SB.

To avoid the same safety-wire mounting, I drilled a small hole on the end-bolt and used that for securing the safetywire.

I have about 110 hrs on the plane now and this schouldn't have happened so early I think?

My question is: has this safetywire breakage happend to anyone else?
If so: how did YOU fix it? Maybe someone else has a better idea than mine?



 
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No, this hasn't happened to me

yet! But, I like your fix and will take a look at mine ASAP.
 
True, it is a better fix. The SB has you drill a hole in the actuator and tie the safety wire around the rod end shaft. The wire, if drilled next to a flat of the jam nut to prevent it from turning will work, but even a little bit of turn on the jam nut renders it useless. The rod end can unscrew itself. Drilling throught the rod end as well, as depicted by Alf should solve this possible problem. Good catch Alf.... I'll do this myself....

Scott
 
If the end of the shaft is tied per the SB and the rod end has a bolt through it how can the rod end bearing back off... unless the entire tube is turning. Now that could be an issue I guess. I used an internal lock washer and locktite and hope i never need to get it off. If the nut is locked down with locktite, the nut and rod end bearing are not going to move. Really! Alf has a good idea too.

kevinh said:
Really? If you are talking about http://vansaircraft.com/pdf/sb07-4-12.pdf it sounds like he had already done that. He's proposing what seems like a better fix of drilling next to the bearing.

Alf, you might want to send this to Van's and see what they think.
Click to expand...
 
Last edited:
To Van's: "I told you so"

I identified this design flaw back in Jan 2006, when I started working on my flap actuator assembly. I talked to Van's about it, and they insisted it was not a problem. I was not and am not convinced. The "safety wire" is not really a safety wire, since it is in tension in only one direction of actuation and not the other. It won't keep the tube and rod end from rotating from one side to the other on every change in direction of the motor. The rod end will still endure torsional loads, and could still potentially turn enough in the tube to loosen the jam nut. The "safety wire" will also likely fatigue crack eventually due to the repeated reversals of motion.

If you sense some frustration in my voice, it's because this problem was totally foreseeable, and Van's was uninterested when I pointed it out to them in detail four years ago. I think what happened to Alf will unfortunately keep happening to other RV's because Van's won't acknowledge that there's still a problem.

Anyway, I remedied it on mine by adding a mechanism that prevents rotation of the tube without putting any torsional loads on the rod end. Write up and photos here: http://www.kalinskyconsulting.com/rvproj/flapsactuator.htm I'm not making any claims as to the suitability of this solution for anyone else, but that's just what I did. Another option I considered was to add a scissor fork between the outer and inner tube, sort of like what you see on oleo strut landing gear. In any case, the key point is to prevent rotation of the inner tube relative to the outer fixed tube by means other than the rod end bearing.

I think Alf's idea is also an improvement over Van's, but the fundamental problem is still there. There are still torsional loads on the rod end, and potential for enough rotation to loosen the jam nut and/or break the "safety wire" over time. I'd also be a bit concerned about the hole weakening the rod end bearing, but that's secondary.
 
.

Hi again.

Thanks for the inputs folks.

Yes, the cause for the breakage of the safety-wire, was that it moved a little every time the flapmotor ran the other way. It's impossible to tighten it enough to prevent the rod end shaft from not moving at all when the flap is used.
And the small movement will break the safetywire over time.
I'm glad it happened on the ground....

In addition to drilling in the rod end shaft, I also went up one size in safetywire, from .32 to .41.

Anyway; I'll contact Vans and let you all know what they say.
 
Flap actuator

Roee,
I really like your elegant solution to the flap motor issue.
consider it stolen!!

Thanks a million,
Chris
 
Had the same thing happen during the fist 10 hours. After landing during a stop-n-go, the flaps came up 1/2, then went back down. I found the safety wire had broken and allowed the bearing to back out. I upgraded to .041 wire and haven't had a problem in the last 140 hours.
 
recommend that the tube be secured using a vise or plier with a rag to protect it and tighten the lock nut TIGHT before installing the safety wire. many early RVs have flown since assembly without the nut coming loose without safety wire if tightened. Just a thought. :) Larco
 
Sort of off the beaten path here but could use some advice on the saftey wire...

How do you go about drilling the hole in the actuator? I have broken a number of drill bits attempting this!!

Do you drill two holes perpendicular to each other until they meet or should I be trying to drill one hole at an angle? The latter is not working for me....


Thanks in advance.
 
I drilled it in an angle and yes it was a bit difficult and took time. Even in an angle it is a bit hard to tread the wire thru it if you are going to use .41 which I would recommend.

Also, how about using a bit of blue lock tied for the jam nut so it won't ever come off on its own. I have not put any lock tied and inspected mine today and it looked OK. I have about 125 hours on the plane.

Good luck
Mehrdad
RV7A IO360M1B
 
Yes it's true, I believe this thread is much like the builders that forgot to tighten down there fuel pick-up tubes. Thousands have flown with no issue at all. I would take, Van's might see this as the same issue builder error. If the nut is TIGHT... locked down for sure, this is probably never an issue tied or not. I would tie mine for the benefit of knowing.
 
ao.frog said:
Hi.

After engine start a couple of days ago, I noticed that the flap took much longer time to raise than normal. (I always shut down with flaps full down and raise it after engine start)
The flap-motor sounded like it was running normal.
I tried to lower the flaps with the same result: flap-motor seemed to run with the normal speed but the flaps moved slower than normal.

I shut down, opened the flapmotor housing and found that the end of the flapmotor-rod had unscrewed itself from the flap-motor.
The reason this had happened, was that the safetywire had broken off, so the flapmotor rod could rotate when the flap-motor was running, allowing the end to be unscrewed.
(sorry for the possibly wrong english words)

The safetywire was mounted per plans and per Vans SB.

To avoid the same safety-wire mounting, I drilled a small hole on the end-bolt and used that for securing the safetywire.

I have about 110 hrs on the plane now and this schouldn't have happened so early I think?

My question is: has this safetywire breakage happend to anyone else?
If so: how did YOU fix it? Maybe someone else has a better idea than mine?



Click to expand...

ao.frog, from your pictures, I can't really tell where the "tail" of the safety wire is (the part where the two ends are twisted together. Is it on the other side of the bearing; the side that is away from the camera?
 
So whats the worst case failure mode here, flaps go down and won't come back up?

Is there possibility of full disconnect whereby the flaps would be able to float/flutter with no connection at all?
 
What's the general thought of using loctite on this (and other places) along with safety wiring it?
 
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