How to handle a split rear spar at butt end

[John Sowles]

Recovering and discovered longitudinal split about 1/3 down from top and extends 7 inches from butt end inboard. Lowest bolt for wing attach fitting below split, center bolt perhaps thru split and upper bolt is above. See photo (wing upside down).

Is there a safe and legal alternative to entire spar replacement or scarf joint?

[Robert Lees]

Re: How to handle a split rear spar at butt end

Hello, John, and welcome to the Taylorcraft forum.

Yes there is a solution...I had the same problem here in the UK and got approval for a repair scheme (what you might call a 337). The UK approval might bear some weight with the FAA in terms of "approved data" for a repair in the USA.

Do you have a photo of your problem?

Rob

[John Sowles]

Re: How to handle a split rear spar at butt end

I am very new to this. Did the photo come through?

[astjp2]

Re: How to handle a split rear spar at butt end

You are looking at a spar splice to repair correctly, with that said, it would be easier to replace than repair. Tim

[PT13Pilot]

Re: How to handle a split rear spar at butt end

Umm, am I missing something, or in this case is his spar.......like the end of the spar being milled down and plywood reinforcements being glued and nailed on? Looks like one piece of spar wood from that picture. If that's the case, no wonder it cracked. And is it my imagination or is the left most strap bolt been so overtightened to the point the strap looks like it's almost flush with the wood?
By the way, welcome John.

[crispy critter]

Re: How to handle a split rear spar at butt end

Your correct about the left fitting bolt in the pic,it is overtightened and that is one of the reasons they put the plywood doubler on the butt end of the spar. The other reason is to help prevent the spar from cracking at the butt end..... Anyway,you can splice the spar but when you splice the new butt end on MAKE SURE you install the reinforcement doublers. Also,make sure you have the doublers at the wing strut attach fittings at the middle of the spar.

[Buell Powell]

Re: How to handle a split rear spar at butt end

If whoever rebuilt that wing did the other one you need to take them both apart.It's not that expensive for materials and with some extra time you can have virtually a new set of wings. Aircraft Spruce has the spar wood,plywood for doublers,@ hardware.

[N96337]

Re: How to handle a split rear spar at butt end

I agree with the others, but I'd never waste the time to splice it.... that's more work than just replacing (in my opinion). I'd also pull fittings on the other 3 and really give them a once over, as stated before. If any of them don't have the plywood reinforcing plates, they'd be a wall hanging pattern in my shop.
John

[1938BF50]

Re: How to handle a split rear spar at butt end

John,

Don't get the idea that splicing is "bad". Properly done it is an acceptable and APPROVED repair method. As already highlighted by others, you may have other issues beyond splicing.

[John Sowles]

Re: How to handle a split rear spar at butt end

Thank you to all. Your knowledge is incredibly valuable. Indeed, I am not fussing around and will order both the rear spar and front as neither have the doublers. It seems the split spar wing is prewar and other is postwar with doublers. But my A&P and I have a question. On the postwar wing, the last 6 inches of the butt end was planed from 5/8th inch to 4/8th (1/2 in) to accomodate the two 1/16th inch doublers (to equal the full 5/8th in thickness). Is this proper proceedure? Seems it would significantly weaken the beam strength.

Best,
John

[Buell Powell]

Re: How to handle a split rear spar at butt end

John,
If you talking about where the doublers are and it was planned to the same thickness as the rest or the spar then that is correct. Are you using pre-war or If you are using stamped ribs and the but rib is nailed to the spar butt you might consider making an end cap from the plywood used for the doublers. A common problem for the post war is that the nails wont hold to the end grain the nails work loose-the hole gets enlarged and moisture rots the end grain around the nails. Sure glad you are consensus enough to make sure the wings are done right--there is an earlier post about a bad spar because it had been neglected. It had been inspected for years WITHOUT having the inspection holes cut-full of bird and mouse stuff, and the guy was doing aerobatics in it! Those guys should have known better or someone should have told them--the guy that was flying that plane should have known better also.
Let us know if we can help with information-there are several here that have rebuilt wings and would be glad to help.
Best of luck,
Buell

[T.Taylor]

Re: How to handle a split rear spar at butt end

John, don't feel real bad about your spars, I just finished mine, you just need to keep after it, my spars were old and a few splits so they came out, but I have kept an inboard section of the rear spar cause when I was in High School in the mid '60's I remember this plane being worked on at an FBO where I worked after school, an old, old guy who probably learned A&E work on wooden aircraft opened the wing on the airplane, and spliced the rear spar, I don't remember exactly how long it took, but I don't think it was more than 3 days, anyway it is a work of art, I just wish he would have autographed it, wish you the best, and thanks for the memories, T.T.

[high time cub]

Re: How to handle a split rear spar at butt end

John,

This should help get you in the mood.....

http://www.joea.com/phpBB2/viewtopic.php?t=2333&postdays=0&postorder=asc&start=0

HT.

[Robert Lees]

Re: How to handle a split rear spar at butt end

significantly weaken the beam strength.

The main force at the butt end of the rear spar is compression. Relatively little lift load is taken at the butt end; it's mainly compression load down the length of the spar.

The main spar loads are actually taken at the strut attachment location.

The largest force affecting the rear spar length as a whole is the shear reversal (is that the right expression?) at the strut fitting, 2/3 out from the butt fitting.

I got permission for a glue repair of a split in the rear spar through a bolt-hole, as your photo suggests, at the butt end, but mine were the ply-reinforced type, and the spar was not overly-compressed by the bolts.

Rob

[Ray36048]

Re: How to handle a split rear spar at butt end

You gota love these old wings with wooden spars. I am rebuilding a set of wings using new spars. Based on the repairs to the old rear spar at the tip, the plane had been ground looped at least once. But, what is very interesting is the split in the main spar for about 18 inches centered around the front strut fitting. One can only wonder how long this wing was flying with this damage.