Spar Fitting Holes Worn... Help

[VictorBravo]

Does anyone have experience with the wing attach fitting bolt holes getting worn, resulting in the wing moving slightly with relation to the fuselage?

Today, I lifted up on the strut/wing attach points to let the landing gear bungees pull the wheels into position. When I lifted the fuselage off the ground, I heard a clunk. Not the kind of clunk you like to hear, by the way!

We looked a little closer, and found that there was play in the fittings, probably worn bolt holes. There was about .020" play.

SO FAR, the best idea seems to be to drill and ream for the next size bolt. It apears that there is enough metal on the fitting to have 1/16" larger diameter bolt and still not have an "edge distance" problem.

Anyone with experience is welcome to offer an idea, but information on the official factory approved ,method is very welcome. I'd rather do this without a welding torch if it is possible. Forrest, do you know what the usual way to fix this problem is?

This is probably going to stop me from attending the Columbia CA fly-in this weekend...DAMN!

[Robert Lees]

Re: Spar Fitting Holes Worn... Help

Bill: try close tolerance bolts first. "Normal" bolts tend to be a few thou (mil) undersize; close tolerance are much closer to the actual size. You would need AN174-16 for the rear fitting; AN175-16 for the front (add the suffix "A" on both if you need undrilled bolts).

This should improve things a bit.

I personally would not wish to go to the next size up...I would rather make little steel bushes to fit into slightly larger drilled-out holes.

Rob

[Carl Ellis]

Re: Spar Fitting Holes Worn... Help

Today, I lifted up on the strut/wing attach points to let the landing gear bungees pull the wheels into position. When I lifted the fuselage off the ground, I heard a clunk. Not the kind of clunk you like to hear, by the way!

Bill -

How many hours are on the airframe?

Don't let no airplane stop you. Jump in your car and drive up.

- Carl -

[VictorBravo]

Re: Spar Fitting Holes Worn... Help

Thanks for the advice, and I'll be glad to hear any/all additional.

Rob, if my bolt holes have been worn to a shape that is not round, then a close tolerance bolt may not work. If I could ream out the hole just a bit, and the close tolerance bolt is tight, then it might work. But I'd be frightened that the hole might still be too big for the bolt in some other area.

I think mine uses a 1/4 inch bolt in the front, not a 5/16. It's a pre-war model. I didn't measure it or remove it yet, so it could have been a 5/16.

What is the advantage of using bushings in an oversize hole, versus larger bolts?

Carl, I might just drive up there...or if I can fix my stupid problem I might fly after all. Not sure of anything just yet.

Bill

[Carl Ellis]

Re: Spar Fitting Holes Worn... Help

Bill -

Yes, hope you can make it. Saturday night is the spaghetti feed.

How many hours on your airframe?

- Carl -

[NC36454]

Re: Spar Fitting Holes Worn... Help

Thanks for the advice, and I'll be glad to hear any/all additional.


I think mine uses a 1/4 inch bolt in the front, not a 5/16. It's a pre-war model. I didn't measure it or remove it yet, so it could have been a 5/16.


Bill

Bill,

My 1941 uses 5/16 front and 1/4 rear...maybe you have the wrong bolts?...wouldn't that be an easy fix!?

Ken

[VictorBravo]

Re: Spar Fitting Holes Worn... Help

The log says TT 2123 as of February 2005, but you can never be sure about times in logbooks.

I do know that it's not 10,000 hours or anything like that.

If the bolts are 1/4 inch in a 5/16 hole, that would indeed be an easy fix, but I'd be pretty damn angry about it. I'd have to check every other bolt in the whole airplane...

[NC36454]

Re: Spar Fitting Holes Worn... Help

The log says TT 2123 as of February 2005, but you can never be sure about times in logbooks.

I do know that it's not 10,000 hours or anything like that.

If the bolts are 1/4 inch in a 5/16 hole, that would indeed be an easy fix, but I'd be pretty damn angry about it. I'd have to check every other bolt in the whole airplane...

Bill,

It was a mostly tongue in cheek comment, but.....stranger things have happened. One could probably fly for years with the wrong bolts in place. (excluding being caught at annual) Only takes a few minutes to check. Seriously though, I hope this turns out to be something very easy to correct! I guess you will only know by removing the bolt and checking for either a round or oval shaped hole.

I'm beginning to wonder how they would wear anyway...(no motion...no wear??)

Ken
1941 BC12-65
W4SWK

[alwaysoar]

Re: Spar Fitting Holes Worn... Help

Are you sure it's the spar fitting and not the strut? If it's the strut, there's a fix for elongated holes that's shown on page 4-46 of AC 43-13. It could also work with spar fittings, but an IA would have to determine that. As far as clunks go, I had a phone conversation a couple of years ago with Forrest about clunks. He told me that originally hardware was a little larger, but that newer AN hardware was smaller and allowed some play that gradually elongated holes. He said that usually these holes were filled (welded) during recover. If you do weld them, you are supposed to re-heat treat anything that was heat treated to begin with. I'd attach this page if you want to email me at [email protected] if you don't have access to a 43-13.The holes in my aft strut adjustment screws elongate causing significant clunks--I replaced them. If you haven't done it check that and your struts.

[Robert Lees]

Re: Spar Fitting Holes Worn... Help

VB wrote:

What is the advantage of using bushings in an oversize hole, versus larger bolts?

From purely an engineering perspective (and perhaps not an FAA-compliant one), it leaves more cross-section of original material...of course, if there is adequate material after going the next */16 size up, than that would be OK, but might require a stress analysis?

The next convenient size up from a 1/4" bolt is 17/64...or even the next size of 9/32...or even a metric size such as 7.0 mm, depending on the amount of ovality/wear in the existing hole.

The next convenient size up from a 5/16" bolts is 21/64...or even a metric size such as 8.5mm, again depending on the amount of ovality/wear in the existing hole.

So for the 1/4 hole, I would make a "top-hat" bush, with 1/4 ID; 17/64 (or whatever) +0.002 OD, and the same depth as the fitting to be bushed. The reason for the extra two thou on the OD is so that it will be an interference fit (press-fit) into the opened-up hole. If pressing it in squeezes the internal diameter, the bush can be reamed in situ.

If the bolts are 1/4 inch in a 5/16 hole

If the front attach bolts are indeed so, then the wings will be able to sweep back quite noticably...look along the leading edge from one wing tip to the other.

Hope this helps.
Rob

[Forrest Barber]

Re: Spar Fitting Holes Worn... Help

.250 & .3125 are the bolt holes..... the bolts are probably .002 to .003 under when installed...
. When we recover I heat, weld fill or peen and then drill under and ream. Mic the new bolts & I bet they are undersize.
New hardware just does not conform to old specs.... Sooooo if they are elongated, remove and replace the butt fittings, ( or repair) I think we are discussing "clunks" in the butt fittings. If at the strut attach points then we have to check struts & fittings & bolts....
Sometimes a metric bolt will do , sometimes have a standard bolt plated heavy to bring it up to a fit. It is correct that if there is no movement , then there is no wear...... "clunks" need checked.
I would probably make that one more flight to a fly-in....... if the bolt is not "grooved".

[Guest]

Re: Spar Fitting Holes Worn... Help

.250 & .3125 are the bolt holes..... the bolts are probably .002 to .003 under when installed...
. When we recover I heat, weld fill or peen and then drill under and ream. Mic the new bolts & I bet they are undersize.
New hardware just does not conform to old specs.... Sooooo if they are elongated, remove and replace the butt fittings, ( or repair) I think we are discussing "clunks" in the butt fittings. If at the strut attach points then we have to check struts & fittings & bolts....
Sometimes a metric bolt will do , sometimes have a standard bolt plated heavy to bring it up to a fit. It is correct that if there is no movement , then there is no wear...... "clunks" need checked.
I would probably make that one more flight to a fly-in....... if the bolt is not "grooved".

Hey Forrest, regarding the weld fill how do you deal with AC43.13-1B 4-60(4) that preculdes weld fill? Is there a T-craft repair procedure that superscedes Ac43.13? If so how can I get a copy? Thanks, Dave.