J3 wood spar repair ideas

[planenut]

I'm looking for any ideas how to do a legal and safe repair to the rear spar butt ends. We had a local cub hit a hanger during a hand propping gone wrong. Engine and motor mount already replaced. But both rear spars are cracked at the butt fittings. I can see in part 43 that i can do spar plates for small cracks like these, but it doesn't allow it to be done under a steel fitting.
I'd rather not replace the entire spar, these wing are in great condition otherwise.
another idea is to do a spar splice outboard from the butt area.
Have any of you A&P's done any repairs like this and got it past your local fsdo.
Thanks
Dan

[12 Geezer]

AC4313

http://rgl.faa.gov/REGULATORY_AND_GUIDANCE_LIBRARY/RGADVISORYCIRCULAR.NSF/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2001.pdf

[planenut]

Thanks for the help
Here's where i'm stuck on. page1-16 para1-44 allows plates for longitudal crack repair and references fig 1-10. But that figure says no fittings in the area of the plates.

[d.grimm]

Clipwing?

[planenut]

Probably not. It's used daily for primary training.

[Steve Pierce]

Scarf splice it outboard of the wing attach fitting so you have no doublers under the wing attach brackets.

[planenut]

That was my second choice. Have you had good luck cutting the scarf joint with the spar still in the wing?

[bob turner]

I bet getting a perfect scarf will take longer than replacing the spar - and it will still be ugly and require the second rib to be modified. I am sure there is a machine that will make the proper angle scarf, but I cannot imagine what it would look like or how much it would cost to rent.

[Steve Pierce]

Bob, Pretty easy to make. http://www.aircraftspruce.com/catalog/topages/planer.php

I have never scarfed one myself.

[planenut]

That is a cool tool for sure, but it only has a slope angle of 8 to1.
But it gives me ideas on how to do it.
Thanks

[Tom Jones]

I had a friend do a scarf splice in place on the rear spar of a lower Stearman wing. He put about a four foot piece in.

I would have replaced the entire spar and recovered the wing, and thought he was nuts to try it. He figured he had nothing to lose but the effort, and didn't want to have to repaint the other three wings to match.

He peeled back about 6 inches of fabric back along the trailing edge on the bottom of the wing, then made a fixture for the correct angle and cut and sanded the spar by hand. No expensive tools involved.

It took a couple of weeks, but in the end it was a beautiful repair and is quite invisible from the top, and damn hard to find from the bottom.

I sure wish I was that good.

[Longwinglover]

The L4 Structural Repair manual has complete instructions.

John Scott

[two-12sfernow]

I have spliced a bunch of them and it is just work. The old school method of getting enough ribs out of the way and clamping the new section to the existing, then cutting both with a NEW, quality handsaw will give you an near perfect angle match. Remember you need to offset the spar and splice section when you do it this way or you will end up with a beautiful repair that is short by the length of the scarf.
Mark it on all faces, do a bit of relaxation yoga, go to it and then marvel how wonderful the splice is and how you could have replaced the spar with new fresh wood for about the same effort.

[bob turner]

Yeah - and to go far enough in there to keep the plates out of the area where the attach fitting goes sounds like removing half the ribs.

[planenut]

Thanks for the ideas guys! I'll try splicing it in the first bay or two. I know it would be alot less work than dismantling a wing to replace the spar and then a recover job on the wing. Besides i'm not sure if the guy can afford that. I should get at it in the next few weeks.
Thanks Again
Dan

[skywagon8a]

You don't need to recover the whole wing to replace a spar. I replaced a rear spar in a Citabria and only slit the fabric span-wise and rolled it forward enough to get my hands in there to disconnect the ribs etc. Slid the spar out the end, slid the new one in and refastened everything. Joined the fabric back with a small strip, about 3" or 4", of unshrunk fabric which was used to tighten the whole cover. Worked fine. I suspect that it would have taken just as long to splice the spar. In the end, no splice.

[mike mcs repair]

You don't need to recover the whole wing to replace a spar. I replaced a rear spar in a Citabria and only slit the fabric span-wise and rolled it forward enough to get my hands in there to disconnect the ribs etc. Slid the spar out the end, slid the new one in and refastened everything. Joined the fabric back with a small strip, about 3" or 4", of unshrunk fabric which was used to tighten the whole cover. Worked fine. I suspect that it would have taken just as long to splice the spar. In the end, no splice.

ditto, have helped replaced many rear spars on covered -18 wings. quick you can have old one out and new one in in a day, and then it just takes time for the glue to dry, no marks on wing just undo seem hidden in middle of trailing edge and add a tape( if wing was covered in blanket method).... no dope repairs anywhere seen..... do it with wing upside down... you only undo some bottom fabric, leave top on... use cardboard shipping tubes to keep fabric from bending to tight and cracking where your roll it back... no need to add strip of fabric to shrink it.. just reglue tight as possible and carefully hit with heat...


have only done one splice and that was way more work, and only at a wing tip area... wow, didn't have the fancy spruce planer things, just hand saw..thats quite cool looking..

[Steve Pierce]

What about the rib stitching?

[d.grimm]

When I rebuilt a J-3 the IA had me replace all the wood spars because they were "improperly spliced." He said no splices were allowed between the butt of the spar and the strut attach fittings. This was 33 years ago and I was just working on my A&P at that point so I don't remember any other details.
Dave

[mike mcs repair]

What about the rib stitching?

you cut laces at bottom fabric by sliding a razor blade between rib and fabric as you open it up, after carefully undoing bottom fabric in trailing edge...

some just tie them only to top cap strip(you are only are cutting 3 or 4 back stiches).

or if you wish to spend some more time, you tie off forward existing ones you cut to lock row, then take a small thread and attach new lace to each & pull out each of the cut laces & slide new ones in same hole under tape carefully and tie each individually as you close bottom fabric... good thing laces were waxed :-)

hardest & longest part of job is getting the darn screws out of spar...

also back off each brace wire the same amount and write it down! so you can return it to same position easily and not loose tram...

the only area you have to paint is hidden in trailing edge if you do it right

it's actually a fun job, with the amount of time and $$ you avoid....

[mike mcs repair]

Ok it was the bottom!

http://lh5.ggpht.com/_BOkp4HhMtPc/Sw7AuwkHcVI/AAAAAAAAeLg/NiGYfJm8VfM/s400/01010096.JPG

http://lh4.ggpht.com/_BOkp4HhMtPc/Sw7AvHpdYWI/AAAAAAAAeLk/RcmOWiWu1Wo/s400/01010098.JPG

http://lh4.ggpht.com/_BOkp4HhMtPc/Sw7AvfRAK0I/AAAAAAAAeLo/956vXTFJnwg/s400/01010097.JPG

[d.grimm]

Does anyone have the Service Memo's handy? I found Piper Service Memo 3a that states no splices inboard of the strut attach fittings but it only references the metal spar.
Dave

[bob turner]

I dunno - looks easier to recover the whole thing. Doubt that skipping the four rib stitches on the bottom is legal, although I am sure it is safe.

[Longwinglover]

Does anyone have the Service Memo's handy? I found Piper Service Memo 3a that states no splices inboard of the strut attach fittings but it only references the metal spar.
Dave

Quote from AC43-13.1B in alking about wood structures:

1-40. SPLICING OF SPARS. Unless otherwise
specified by the manufacturer, a spar
may be spliced at any point except under the
wing attachment fittings, landing gear fittings,
engine mount fittings, or lift and interplane
strut fittings. These fittings may not overlap
any part of the splice.

John Scott

[mike mcs repair]

I dunno - looks easier to recover the whole thing.


definitely NOT..... this is super quick job... 20 times more work to recover plus $$

[planenut]

This is wood spar j3. I'm not so sure you'd be able to pull all the nails on the ribs and pull the spar out without without wrecking the 65yr old ribs in the process. I've rebuilt wood spar cub wings before, and with all the cover off it was next to impossible to remove the spars without breaking things. There is spar reinforcement plates at the strut attach point and you'd have to drag that through all the ribs inboard of that.

[mike mcs repair]

This is wood spar j3. I'm not so sure you'd be able to pull all the nails on the ribs and pull the spar out without without wrecking the 65yr old ribs in the process. I've rebuilt wood spar cub wings before, and with all the cover off it was next to impossible to remove the spars without breaking things. There is spar reinforcement plates at the strut attach point and you'd have to drag that through all the ribs inboard of that.

you can do it,

could you glue the plates on after installation?.... just chop old spar in pieces to remove(mark new spar first if needed), usually so you don't have to do more ribs than you can reach at once on way out...

[Steve Pierce]

I've seen and have original Piper Cub wood spars with splices all over from the factory signed in 1939 by the workers that are inboard of the strut.

[d.grimm]

I'm not saying it is true, I'm just saying I had to put in 4 spars and this guy
(now deceased) was pretty sharp on the old planes.
Dave

[bob turner]

Steve - did the factory splices have those huge plates on each side, protecting the edge of the scarf joint?

[skywagon8a]

The new spar which I installed in the Citabria was purchased from the factory. It was made with three scarf joints without gussets, four pieces of wood. I had the FAA inspector look at it and he said that it was OK since the factory did it. I was rather annoyed since I had bought a new spar and expected it to be one piece. Apparently that is what they were doing for a while. This was during the early 70s. I would be curious whether any of you have come across a Citabria with the spars spliced in this manner.