Tie down ring stripped

[Ross Woodley]

The wing receptacle for the tie down ring was now completely stripped out and the ring basically just falls out when inserted.  Does anyone has come across this and knows how to repair it. 

[Hank]

You need a Heli-Coil. Its an insert, threaded on the outside to screw into (a new, larger hole in) your wing, and threaded on the inside for your tie down ring.

I don't remember the tie down thread size. Your best bet, if Clarence, sabremech or someone doesn't post it, is to walk into your local industrial supply shop, set it on the counter and ask which heli-coil you need. Just don't mention "airplane"! (It frightens some people--tell 'em its a movable tie down ring to fasten things to a trailer.)

They should know, or the package should say, what size hole to drill. They are simple to install. But because you'll be drilling into your plane, better involve your A&P!

[Yetti]

Or you can buy the laser jack/tie down points.  Open up the wing panel get a nut grind off part of it and screw it all together.  Replace access cover.

[Captnmack]

I have the same issue but have not got to the repair yet. I also bought the Lasar kit. TBD....

[Guest]

6 hours ago, Ross Woodley said:

The wing receptacle for the tie down ring was now completely stripped out and the ring basically just falls out when inserted.  Does anyone has come across this and knows how to repair it. 

It should be a 5/16-18 NC thread.  The wing fitting is about 1/4" thick so it will require a short Helicoil.  Your maintainer may have a Helicoil set as it's common to may engine studs.

Clarence 

[Raptor05121]

4 hours ago, Yetti said:

Or you can buy the laser jack/tie down points.  Open up the wing panel get a nut grind off part of it and screw it all together.  Replace access cover.

We did this, of course I never use my tie-downs. Of the rare occasion I overnight somewhere, I just tie to the main gear truss

[Ross Woodley]

Thanks for all the great advice...

[Jerry Pressley]

The tie down does not go thru the spar so using a tie down ring with longer threads with a nut on top applied thru the access panel takes a few minutes.

[podair]

I have been meaning to do that for a while, using the Lasar jacks with a bolt on top via an access panel. Silly question however. Any risk of dissimilar metal corrosion between the Home Depot bolt and the wing or am I just showing my complete lack of understanding of it?

[gsxrpilot]

I had the same problem with my C. The @Yetti solution was spot on. I even modded it a bit further by using a piece of all-thread with stacked nuts on the bottom as well. That gave me a built in GoPro camera mount.

[Vance Harral]

I'm resurrecting this thread to try to better understand the options for a fix, as we've discovered the threads on one of our tie-downs is shot.  I'm not having much luck with detail in the parts manual, and it will be a couple of days before I can get out to the hangar and actually look at the airplane.

First, can anyone explain what structure the original tie down rings thread into?  Is it the spar?  A bracket attached to the spar (which could be replaced)?  Something else?

Second, did the original structure from the factory contain a helicoil?  It's unclear to me if the comments from @Hank about installing a helicoil refer to replacing a helicoil that's part of the original design, or drilling/tapping/installing a new helicoil that isn't part of the original structure.

My preference would be to fix this problem by keeping the original design and structure, but obviously that's not practical if it involves replacing the spar.  If we can replace a bracket and/or helicoil that would be nice.  If not, I agree the @Yetti solution seems practical.  Note that we actually already have the LASAR combination jack points and tie down rings, maybe the fix is as simple as installing a nut on the back side.

 

[Yetti]

It's not the spar.  Is a piece of angle alum.  Nut is easiest.  You have to grind one side of the nut a little to fit up against the backside of the angle alum.  Take the inspection port off put the nut on and be done with it.

[tmo]

@Yetti - your posts are quite frequently ones that I have a hard time deciding if I want to "like" them or say "thanks" for posting something that is simple and to the point.  Many others here do as well, a good asylum from CAMO driven gold plating that is seen this side of the pond way too often...  Go N-reg!

[Guest]

This is what the fitting looks like. It is fastened to the aft side of the main spar.

Clarence

[N201MKTurbo]

If you want to use a nut, you may need to get a hoist ring with longer threads. McMaster Carr has them.

[Shiny moose]

If you put a nut on a tie-down ring, then you will have to remove the nut every time  you want to jack the aircraft, then your jack points are slip fit not screw in(Lot of aircraft are slip fit but not the design for mooney) helicoil is the cheap easy fix, keeps things simple for your mechanic, it might even be cheaper than buying new longer hoist rings, nuts, and washers.  The laser jackpoint/ tiedowns  will screw in perfectly

my .02

[Mooneymite]

I'm wondering how the tie-down ring threads get damaged.

Has the tie-down been damaged during a high wind event, or was an improper jack point used to lift the aircraft?  I doubt the tie-down threads were designed to repeatedly support the aircraft weight.

Or something else?

[Bryan]

23 minutes ago, Mooneymite said:

I'm wondering how the tie-down ring threads get damaged.

Has the tie-down been damaged during a high wind event, or was an improper jack point used to lift the aircraft?  I doubt the tie-down threads were designed to repeatedly support the aircraft weight.

Or something else?

I would think over-tightening the tie-down ring either during install or turning more aligning the rope when cinching down.

[Vance Harral]

Thanks to everyone for the additional detail, especially @Clarence for the photo and @Shiny moose for expounding on the helicoil solution.  As I mentioned, we already have the LASAR tie-down ring/jack point combo, which eliminates the issue with R&R'ing a nut every time we need to jack the aircraft.  I'm going to venture out to the airport this weekend, pull the appropriate inspection panel, and verify the tail of the bolt extends up far enough through the bracket for the nut solution.  It occurs to me this morning that the nut solution is easily undone if we change our minds about a fix.  To be clear, whatever fix we choose will be done at our upcoming annual, under appropriate A&P supervision.  Thanks again!

[Yetti]

1 hour ago, Shiny moose said:

If you put a nut on a tie-down ring, then you will have to remove the nut every time  you want to jack the aircraft, then your jack points are slip fit not screw in(Lot of aircraft are slip fit but not the design for mooney) helicoil is the cheap easy fix, keeps things simple for your mechanic, it might even be cheaper than buying new longer hoist rings, nuts, and washers.  The laser jackpoint/ tiedowns  will screw in perfectly

my .02

If you have the jack point along with the tie downs from LASAR bolt them on and be done.

They get stripped because it is soft threaded alum with steel threads under a wing where things don't get put in quite square.   viola stripped threads over 40 years.

I had some extra alum and don't like the idea of balancing the plane on a point so I made these up.

 

[Vance Harral]

5 hours ago, M20Doc said:

Out of curiosity, has anyone here ever tried to replace this bracket?  Looks like it's attached with pull rivets.  Can you get to both sides of the spar with drills and rivet pullers to safely R&R in situ, or is this something that's simply not practical without removing the wing skin (which is a non-starter)?

Edited February 6, 2020 by Vance Harral

[PT20J]

Those are Huck bolts. 

I pulled a tie down ring out 30 years ago when I got distracted during a preflight and missed removing a tiedown chain. It popped out surprisingly easily. If it had been attached with a nut, it could have done some real damage. It took 10 minutes to drill, tap and install a helicoil.

Skip
 

 

[Vance Harral]

That's an interesting point about the nut solution causing spar damage in the event of a mistake.  Tie-downs should be robust enough to hold the airplane in place in "moderately high" winds, but not so robust as to bend the spar.

Edited February 6, 2020 by Vance Harral

[Ragsf15e]

31 minutes ago, Vance Harral said:

That's an interesting point about the nut solution causing spar damage in the event of a mistake.  Tie-downs should be robust enough to hold the airplane in place in "moderately high" winds, but not so robust as to bend the spar.

I guess, but I think if the winds are strong enough to rip out the tie down, they’re going to do significant damage to the airplane tossing it around when it’s unsecured anyway.  
 

Ropes should be tight enough that a forgotten tie down makes taxi at/near 1000rpm is impossible.  When full power is required for taxi, shut down and remove chocks and/or tie downs.

[Vance Harral]

11 minutes ago, Ragsf15e said:

I guess, but I think if the winds are strong enough to rip out the tie down, they’re going to do significant damage to the airplane tossing it around when it’s unsecured anyway.

Sure, but the rip-out force should be somewhere around the lift force generated by winds at about stall speed.  Any less and the tie-downs aren't really helping the way they're supposed to.  Any more and there are some corner cases where you want them to break away because it results in minimal damage.  I agree those corner cases do not include gale force winds that flip the airplane upside down.  Your point that the corner cases shouldn't include a tie-down mistake either is fair.