cover between empennage and stinger assembly - screws loose

[tmo]

Some of the screws that hold the covers (edit: found them in the IPC - section 53-50-00 item 7 - fairings, pn 470002-009 and -010) between the empennage and stinger assembly skin (pn 420001-013) that cover the trim jackscrew don't hold as well as I think they should. Edit: I guess I used the wrong words, they are empennage fairings, and have nothing to do with the stinger assembly as such.

What is the proper way to fix that? Would installing a rivet nut in the empennage skin be acceptable? Using a larger screw just means the problem will return later.

Edit: the IPC lists 14 AN530-4R5 screws and 14 A18914Z1 speed nuts. This is definitely not what I have - there is no trace of said speed nuts, and the screws are not all the same. Even if I wanted to use the speed nuts, I don't see how I can install them in the lower two screws (per side, 4 total); the upper five (per side, 10 total) are trivial.

Edited August 22, 2020 by tmo
Found relevant sections / part numbers in IPC.

[carusoam]

See if this helps...

I’m not quite sure of the location that you described...

Are you describing the sheet metal that covers the hinged area?

These screws use a small spacer under the sheet metal... the sheet metal piece has a bevel leading edge... the rubber spacers are about as tall as the bevel...

 

The tinnerman type speed nuts are made of a spring metal...

Expect the springiness to age and not work very well over time...

Aircraft spruce (Europe?) usually has both the nuts and screws for most sizes...

The screws are typical sheet metal screws with rounded safety points on them...

 

Most of these parts get lost after the first few annuals... they probably get replaced without the spacers...

There is a recent thread about these spacers and hardware... if we are discussing the same thing..? 

PP thoughts only, not a mechanic..

Best regards,

-a-

[MB65E]

Yes, new rivnuts are acceptable. I used the smallest you can find. I think I replaced all mine with #8 rivnuts. Makes for a nice clean install with all of the screws the same size. 
-Matt

[OR75]

I believe you are talking about this fairing 

there is an inspection hole that allows you to place the tinnerman nuts 

one side can be a one person job
other side you may need help unless you open both inspection panels 

 

Edited August 22, 2020 by OR75

[tmo]

Yes, the picture from @OR75 is exactly it - the rectangular-ish cover that starts below the stabilizer and goes down to the tie-down.

The top 5 screws are trivial, but I don't see how I can access the bottom 2 on each side - you can see the second-to-last one in the picture, the last one is either missing or not visible from this angle, it is right by the tail tie-down. They are under a bracket / shelf (perhaps item 40 from section 53-10-03 of the IPC - stiffener plate / charlie weight shelf). Maybe I need to take a look with a mirror or a borescope, but if rivet nuts are acceptable, I'm tempted to go for them - they seem like an easy and permanent solution. I can do the tinnerman speed nuts for the top 5 if the collective says it is better for whatever reason, or go with rivnuts all around and call it done.

Thanks for any and all suggestions!

[tmo]

1 hour ago, carusoam said:

Are you describing the sheet metal that covers the hinged area?

These screws use a small spacer under the sheet metal... the sheet metal piece has a bevel leading edge... the rubber spacers are about as tall as the bevel...

Yes, this sounds about right, also see the picture from @OR75 above and my reply.

Definitely no spacers / washers there; will look for the thread about them, haven't been able to keep up lately, too much interesting stuff in the hangar.

The tinnerman nuts are definitely not there, and I don't see how they could escape from the bottom two holes - it looks next to impossible to me, but maybe I'm looking at it wrong, or just don't have the plane smarts yet. But the Part66 fellow that is helping me make sense of all this locally doesn't see it either, and he is the one that suggested rivet nuts.

I really should figure out a way to post pictures from a phone...

[OR75]

For me rivnuts are a good option but always as a last resort in a case like this 

i would try to place a tinnerman (there should be a way to access ) , grease or aluminum tape may be your best friend to keep it in place 

[tmo]

I don't question the statement, but can you say why "last resort"? Inquiring minds and all that.

[OR75]

See post right before mine ... you will need to drill a bigger hole to install the rivenut. Most likely you will be fine. But not great to have to remove a rivnut. In this case, not that big a risk , I d say . But as a principle I prefer to delay going that path. 

[buddy]

After about 25 yrs On my 1980 M20J I used rivnuts on the holes that were stripped out and they worked great.

[PT20J]

Delving into the IPC shows that Mooney changed from PK screws to machine screws and rivnuts beginning with 24-1418. So installing the appropriate rivnuts just brings it up to date. Note that at the same time, Mooney also changed the fairing sheet metal. The old ones had a gap at the bottom between the two halves whereas the newer ones wrap around the bottom for a cleaner look. 

Skip

[M20F-1968]

If I were to use spacers as suggested above, what material should they be made of?  Seems like making aluminum or Nylon would work.  What may be best?

John Breda

[Vance Harral]

Another vote for rivnuts.  We worked with our A&P to install them as a minor mod, after one of our fairings departed the airplane in flight and had to be replaced.  That was about 10 years ago, no issues since.

[PT20J]

22 minutes ago, M20F-1968 said:

If I were to use spacers as suggested above, what material should they be made of?  Seems like making aluminum or Nylon would work.  What may be best?

John Breda

John,

The parts book doesn’t call for spacers and I don’t think they are a good idea. The leading edge has a slight inward bend so that when the fairing is screwed down tight it will keep air from getting under the fairing perhaps stressing it and adding drag. Spacers could interfere with this design feature. One thing that is a good idea is to put teflon or UHMW Polyethylene tape on the inside aft edge to keep it from scratching the paint on the empennage which moves with trim.

Skip

[carusoam]

The spacers that we’re remaining on my M20C, looked similar to pvc tubing that had been cut off...

Hard to say if they were glued in place, or just stuck there by heat and pressure...

Odd that air speed doesn’t get under the leading edge of it...?

There were certain locations on my C, where the speed nuts went missing and sheet metal screws were used properly sized to fill the existing hole... (not recommended)

PP thoughts only, not a mechanic...

Best regards,

-a-

[tmo]

1 hour ago, carusoam said:

he speed nuts went missing and sheet metal screws were used properly sized to fill the existing hole... (not recommended)

This seems to be the case here as well.  To add insult to injury, there are of random size and possibly pedigree.

Will make a good attempt at speednuts all around and, if that fails, will install the smallest rivnuts for the two lower screws.

Thanks Mooneyspace!

[PT20J]

These are panels that should come off every year for inspection. If it were mine, I’d take a few minutes and install rivnuts and be done with it. 

[tmo]

On 8/22/2020 at 8:34 PM, MB65E said:

I replaced all mine with #8 rivnuts

I know I'll sound stupid, but #8 means 8/32" - right? Edit: ok, it is "gauge" which ends up being 2*diameter in mm, so #8 is ~4mm which is the one I want.

So if the screws are ~4mm I can order #8 (edited) cadmium plated aluminium rivnuts and patiently wait for delivery.

Or is some other combination preferred?

Edited August 28, 2020 by tmo
Learned about gauge

[OR75]

2 hours ago, tmo said:

I know I'll sound stupid, but #8 means 8/32" - right? Edit: ok, it is "gauge" which ends up being 2*diameter in mm, so #8 is ~4mm which is the one I want.

So if the screws are ~4mm I can order #8 (edited) cadmium plated aluminium rivnuts and patiently wait for delivery.

Or is some other combination preferred?

If you are going that route, your mechanic will  need the #8 rivnuts, the #8 machine screws and the tool to install the rivnuts 

you really don’t need to worry about whether those are mm or 1/32 of in 

a good length for the machine screws would be 1/2 in 

[MB65E]

Thanks OR!!

-Matt

[Yetti]

This has been kind of handy for say radio trays and such.  https://www.harborfreight.com/3-in-1-riveter-kit-94100.html

Aircraft spruce has the replacement corrosion protected thingys

Edited August 29, 2020 by Yetti

[tmo]

So, just to make sure I got this right and did not forget anything (getting stuff shipped to me takes time and extra money, so I want to minimize avoidable errors).

The updated Mooney solution is A6K75 rivnuts, which are now called NAS1329A06K75 / MS27130-A7K. Those are #6, so might be too small to properly mount in the existing holes, so I'll also get the #8 ones, A8K75 / NAS1329A08K75 / MS27130-A13K. The appropriate drill size for those are #12 and #2, respectively.  Also ordering a bunch of matching screws: AN526 632R8 and 832R8. Also other common screws, just to have them on hand.

Any good reason for keyed rivnuts that Mooney used as opposed to plain ones?

The tool Yetti mentioned is already in the shopping cart - I understand it will do both 6-32 and 8-32 rivnuts; I'm also ordering a set of drill bits (are cobalt / titanium ones worth the extra $$ for casual use?). Anything else from the aviation section of Harbor Freight I might want? They don't seem to have TRIFLOW

[OR75]

Keyed to prevent spinning