Thorp Air Command - T18.net

I would not consider this a bend, a slight distortion maybe. You put more of a bend in the 580-10 joggle than you have here, True you do not bend then straighten, but again this is not a bend. Replace the angle if you feel it's not to your standards.

I will probably also seek advice and opinion from a couple A&P and IA friends once I remove the wing skins and can get a really good look at it.

The distortion seems minor but I do understand and respect the idea that the yield strength has been exceeded and is worthy of thought and investigation for sure.

The root spar cap has a doubler with two angle extrusions. Clearly done to increase the strength to carry the higher loads. So just thinking "outloud" here: if this area has been weakened slightly, why would not a section of a similar double angle places across and for a distance exceeding on both sides not provide increases strength to make up for some or all of what may have been lost due to the distortion? If the strengthening worked at the root, why would it not work in this application?

On the other hand. If during the drilling out of the rivets for re-skinning (no matter how careful and deliberate I am) if I mess up a few of the rivets and elongate the hole in the spar cap, I would then be in a position I think to replace the whole spar cap anyhow. So this MAY all become moot.

Again I intend to get local IA's opinions and maybe even get FAA FSDO inspectors to take a look and weigh in with their experience and knowledge.

Does anyone here know of a structural or aeronautical engineer at the likes of scaled composite or other professionals that would be willing to take a look at my situation? (off the record of course!)

I think this is an important discussion, and it's good that you are doing your homework. Again, this is the main spar of a wing section. If it was a fuselage longeron it would be a different situation. As I commented originally, a splice or repair could possibly be fine in this situation, but don't just guess. It's a pretty minor bend, with some surface damage. I've expressed my opinion about what I would do, and I don't want to cause any unwarranted paranoia about it. I would be equally or more concerned with carefully checking the attach fittings at the root.

I've lost 3 friends due to wing failures in flight. One was a Sidewinder, & one was an S-18. The Sidewinder was shown to have had previous hidden damage to the spar. The S-18 had been involved in a ground loop incident prior to the unexplained (to my knowledge) loss of a wing, killing the man & his wife. These things make a prudent individual think pretty hard about damaged wing spars.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

The center section (inner wing) all seems perfect and no damage. But measurements and comparison to the plans will be made none the less.

Same is true for the attach plates etc for the outer wing panels as well. Visually they all look completely untouched and undamage. I may use dye penetrant on them too. Both the center and outer panel connectors.

I have been feverishly drilling out rivets on the two outer panels.

I only have the rivets in the spars on both wings to complete. I hope to have the skin removed prior to the start of Oshkosh.

The first wing I will remove the skin on will be the subject wing with this spar cap "ding". at which point I should be able to get better pictures with straight edge etc. And I will post.

Also if in fact there is a day for a "fly out" breakfast etc from Oshkosh. I would offer an invitation to a suggestion that is selfish on my part. There is an airport west of Madison that has a great little restaurant on it. The 3 letter ID is LNR (Lone Rock) then on the way back if anyone would dare want to stop into my house at the Airpark in Waunakee (6P3) to get actual eyeballs to look at the wing and offer recommendations it would be great!

Also on the east side (GA terminal) they also have a REALLY great restaurant at Madison (Dane County Regional MSN) for breakfast.

I would caution folks however to look at my home airport (6P3) before they land. It has a narrow east west 9/27 paved runway of 2,223' by only 30 feet wide. The grass along the south side is used for turf runway. The runway is NOT level but is sort of slightly dished in the middle. There are some trees although off to the south of the runway alignment off the east end of the runway to be aware of but not really a problem.

I have ample room for several airplanes in front of my hangar.

Maybe in the future my place could be a rally point for a "mass" fly in of Thorps flying into Oshkosh. As it is almost directly in line from 6P3 to the Fisk Arrival to OSH. I think I could even work out ability to get fuel for folks. So that you would land at OSH with only about 30 minutes used of fuel and no need to buy any at OSH.

At Oshkosh I sought out opinions as to what to do with my warped spar cap. I got a lot of advice from lots of knowledgeable people. The consensus with IA's and a aeronautical structural engineer came to straighten it. assuming (verify with dye penetrate) no cracks and then add a doubler. This should extend according to AC 43.13 four fasteners each side of the ding. So that is what I decided I will do.

Last night I was able to straighten it out. I would say 99% perfect. I was able to do it with a few steel bars and bridging the area and then Squeezed it with a small c-clamp. And then slow try and try again until it was as straight as I thought I could possibly get it.

It actually was not all that difficult.

Now to just have to figure out how to get an aluminum angle extrusion corner ground down to a round radius and shape of so that it "nests" tightly inside the existing spar cap angle. So what is the best way to shape this doubler? ("S"' on convertible wing)

I have used a 21 inch belt sander and 9 inch disc/belt sander to make the profile . Sand/grind...check . Sand/grind...check . A little smoothing with some 180 grit sandpaper and 3M Scotch Brite will make it fit tighter than Stink on a June Bug !

RB
Shazm !

It sure will be nice when I order new parts and start putting things together rather than disassembly and repair! I'm almost there!

The doubler extrusion I envision and intend to make will be a single piece and it will have three sections. The middle 1/3 will be the full width of the extrusion centered span-wise across the damaged area. The outer 1/3 on each side will be tapered down to get to the minimum edge distances for the last rivet location at both ends of the extrusion. This should help allow any stress to transition into and out of, the doubler. Rather than abrupt 90 degree perpendicular ends. Maybe this is added and unnecessary work. But it will at least look nice too! Not that anyone will ever see it.

I just want to do the best job I can and do things the right way to the best of my abilities.

I think that seems like a good plan, Tom.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

I like to use a router table for this type of work. A Freud 34-104 1/8'' radius round over bit from Home Depot seemed to make a nice fit. If you go this route, one caveat would be to verify the inside radius of your angle as it seems to vary a little with different vintages/manufacturers.

Tom