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Vance Harral

Replacing aileron control horns

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At our annual earlier this year, our mechanic flagged the left side aileron control horn as having enough slop to warrant concern (part #35 in the attached picture from the parts manual).  The aircraft is a 1976 M20F, but I think all models have this same hardware.  The problem is that the lower holes - the ones which capture the aileron control rod end - are a bit hollowed out, and this allows the aileron to wiggle even when the yoke is held firm.  The obvious concern is flutter.

We were able to obtain a replacement part from Mooney shortly before the factory hiatus, but we're running into trouble installing it.  The bolts which fasten the horn to the aileron spar cannot be turned from the bolt head side, because the flanges of the horn actually capture the head and prevent it from turning.  The only way to remove the fastener is to completely remove the nut from the "back" side (i.e. from inside the aileron).  The aileron spar does have access holes, and it's possible to get a wrench on the nut.  But with a conventional wrench, you can only turn the nut about 1/8th of a revolution before having to remove and re-seat the wrench.  As you can imagine, this is a painfully slow process.  After fiddling with it for over an hour, the mechanic only manged to turn the nut about 1 full rotation, and he essentially gave up (said it wasn't cost effective to keep doing things that way).  He suggested it may be necessary to drill out some of the rivets on the aileron skin, and peel back enough of the skin to get reasonable access to the nut.

If that's the only viable fix, we can go that route, but it seems like a major deal to partially (or fully) de-skin the aileron.  Anyone ever made this repair and know of a trick?

 

1927043978_2019-12-0217_42_50-PartsManual_044.jpg-Photos.thumb.png.247442cc2c55a71184bbf6899c752b5e.png

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I’d see if you could washer/shim  the bolt and rod end the best you could, then torque it down tight. I don’t understand why people don’t let the rod ends work as they should. Citation does this too. They believe anything with a cotter key should spin freely. The bolts spin, wear out material, and then the rod ends lock up and freeze due to lack of movement. 
I’ve had good luck with tight connections don’t allow extra play.  
-Matt

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17 minutes ago, MB65E said:

I don’t understand why people don’t let the rod ends work as they should

That is likely the reason why this control horn is worn in the first place - the bolt holding the rod end was not tightenened, and the bolt was allowed to work in the hole rather than the rod end working as it should.  We'll be sure to tighten the rod end bolt properly on re-installation.  But we're not comfortable with just cranking the rod end bolt down on the existing horn with washers, and assuming it will stay tight enough not to wiggle.  It might be possible to ream the existing horn and insert a bushing, but the no-apologies fix is to replace the horn with the new part.

Edited by Vance Harral

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Wallowed out?

wearing the hole larger, due to movement of the fastener....
MS term of the day... if I got it right... :)

Vance, where are the pics?

Best regards,

-a-

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Mooney is famous for slipping shim washers between rod end bearings and fittings everywhere.  Maintainers are famous for not looking at the mechanics of the connection and leave cotter pinned hardware loose and leaving these shim washers out.

Drilling out the rivets that hold the skin to the inboard rib and leaving the rib to spar rivets May allow the rib to be opened enough to get a long extension and socket on the nuts.  Once the fitting is replaced, rivet the skin on with Cherry Max rivets.

Clarence

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7 hours ago, carusoam said:

Wallowed out?

wearing the hole larger, due to movement of the fastener....
MS term of the day... if I got it right... :)

Vance, where are the pics?

Best regards,

-a-

Think of a pig wallering in the mud.  Now you get it.

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17 hours ago, carusoam said:

Wallowed out?

wearing the hole larger, due to movement of the fastener....
MS term of the day... if I got it right... :)

 

Must be a regional dialect thing. I've heard it all my life. With that exact definition.

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Makes some good sense, Don...

I spent two years working in a machine shop behind RedBird airport in the 90s...

I erased my Boston accent while learning some Dallas machine shop vocabulary.

the streets in the area were named after metals... gold, copper, silver...

Started learning to fly and building a family at that time...

:)

-a-

 

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I knew you couldn't be all bad if you spent time in Texas:P

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Thanks to everyone for the replies.  We have an appointment with Beegles in Greeley this Friday to take a look and give us an estimate on the job.  I'm hoping they'll be able to get a bucking bar in the aileron and refasten the skin with conventional rivets, rather than Cherry Max.  Not because I personally think Cherry Max rivets are "bad" in any functional way, but just because they'll cosmetically look out of place.

I confess I'm concerned this is going to get pretty expensive - probably involves checking balance on the aileron after repair, etc.  But we want it repaired the right way.

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14 minutes ago, Vance Harral said:

Thanks to everyone for the replies.  We have an appointment with Beegles in Greeley this Friday to take a look and give us an estimate on the job.  I'm hoping they'll be able to get a bucking bar in the aileron and refasten the skin with conventional rivets, rather than Cherry Max.  Not because I personally think Cherry Max rivets are "bad" in any functional way, but just because they'll cosmetically look out of place.

I confess I'm concerned this is going to get pretty expensive - probably involves checking balance on the aileron after repair, etc.  But we want it repaired the right way.

I have used Beegles twice to fix my plane. They always did top notch work, especially airframe work. The last time I worked with them was in the 90s, but back then they were great. Just take them the aileron and let them do it.

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28 minutes ago, Vance Harral said:

Thanks to everyone for the replies.  We have an appointment with Beegles in Greeley this Friday to take a look and give us an estimate on the job.  I'm hoping they'll be able to get a bucking bar in the aileron and refasten the skin with conventional rivets, rather than Cherry Max.  Not because I personally think Cherry Max rivets are "bad" in any functional way, but just because they'll cosmetically look out of place.

I confess I'm concerned this is going to get pretty expensive - probably involves checking balance on the aileron after repair, etc.  But we want it repaired the right way.

FWIW, take a look at the rivets that are already there.   On my J many of the factory rivets on the control surfaces are locking pop rivets.  If you give it to somebody else, it may come back with pop rivets, just because there's no way to get a bar in there for final assembly, or because that's what's already there.

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59 minutes ago, N201MKTurbo said:

I have used Beegles twice to fix my plane. They always did top notch work, especially airframe work. The last time I worked with them was in the 90s, but back then they were great. Just take them the aileron and let them do it.

Yeah, Beegles is nationally known.  We're fortunate to be just 20 minutes away by Mooney, or about 45 minutes by car in a pinch.  The initial appointment this Friday is just for them to take a quick look and discuss options.  When it's time to do the actual work, we may take the whole airplane there, or just drive the aileron over.

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50 minutes ago, EricJ said:

FWIW, take a look at the rivets that are already there.   On my J many of the factory rivets on the control surfaces are locking pop rivets.  If you give it to somebody else, it may come back with pop rivets, just because there's no way to get a bar in there for final assembly, or because that's what's already there.

Excellent point, I'll take a closer look next time I'm at the hangar.

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