Another Wing Spar Question

[jeffcoaj]

I had previously asked about dihedral and appreciate the responses and direction.

I am at the beginning of a build and just mounted the wings on the fuse. I've got kitfox wings with the old spar where you don't have to insert the I-Beam. I understand that scuffing the spar with 220 grit is acceptable according to the manual and other posts. However, underneath the strut brace, the spar was prepped with something closer to 80 grit. Since the strut brace is riveted and hysoled to the spar, this is like a "doubler" or reinforcement (to me). Of course, I am not sure.:confused:

I believe I have to start over with the wings which sucks greatly, but was wanting some concurrence. Naturally, I think about it after everything is mounted.

Pictures show the scratches-(no other parts of the spar are scratched as such).

Thanks and look forward to your responses and expertise-

Joey

[jtpitkin06]

Why not sand and buff to remove the deep scratches? It's not going to change the wall thickness an appreciable amount. It doesn't have to be perfect as you normally prep the area with 220. I'd start with 220 and see how it goes.

[jeffcoaj]

Thanks for the reply!

I did debur the holes prior to riveting... but I won't be able to sand down- I didn't make clear that the wings are installed (glued and riveted). This is where I am - all measurements are perfect on both sides in washout in 12" increments all the way down the wing as well as squareness, length and dihedral.

In doing some reading about these spars, it seemed even the slightest scratch would lend the spar to be useless.

Now, I think I may not scrap it but keep going? In this light, sound reasonable?

Thanks again!

[Esser]

I think you’ll be fine. They don’t look deep and that area is being reenforced with the strut attach plate.

[jeffcoaj]

Thanks Again! I am moving forward. Started the day off with no wings. Now I am looking forward to mounting the engine, Rotax Rick 582.

[jiott]

I personally don't like the look of those scratches at all; many of them are circumferential, which is the worst possible direction for a scratch (stress riser). That spot, where the struts attach is the highest stressed part of the whole spar. That is why there is usually an I-beam insert at that position. I don't understand why you say the insert isn't required; I thought all models had some sort of an insert (I realize the insert design has changed over the years). If it were mine, I would get new spars with up-to-date inserts.

[avidflyer]

He has the Kitfox 2 spars that had a full length center web in the spar. Look at the end of the spar in the one picture that shows it. That's why he doesn't have an inserted spar stiffener. JImChuk

[Dave S]

Joey,

I am a little reluctant to express an opinion because It is next to impossible to empirically evaluate this from only a photo - a person needs to be in a hands on situation. It is true that crosswise scratches can lend themselves to stress risers. Also noted that the lift strut attachment point is the highest stress area of the spar.

A couple thoughts.

1) FAA Advisory Circular 43.13-1B, available on the FAA's site, should address this kind of damage/repair evaluation so you have something solid to go in. It is true that not everything is black and white but a person should know which side of the line something falls on.

2) A person could ask themselves.....if Boeing had a part like this - would they put it in an new airplane?

3) One of the best bits of advice I ever got from a much experienced person about both building and flying is this.."If you have to think about it this long....you already know the answer"

In the end you have to decide if this is safe or not.

Almost forgot:o....if you have an EAA chapter near by, there is often a tech counselor at that chapter or another chapter who can take a first hand look at a part which a person has a question about.

[efwd]

Ummm, is it concerning at all that there are a dozen holes drilled into the spar under the mount. Their right in the bottom side of the spar where all the stress is. Sure there are rivets to be placed through them but it seems to me rivets don't hold a piece together. Sure, they hold two parts together but they wont strengthen the spar just by filling a hole in it. What if I drilled a hole two inches away from the bracket, oops, then just put a rivet in to repair. No way right? Scratches, all retained under the bracket and filled with Hysol? Dang, its a tough one. If the bracket and Hysol maintain the integrity of the spar after all those holes then I am not sure it would not retain the scratches. Just me thinking.
Eddie

[southwind32]

I was in a similar situation. I bought a partially completed Kitfox SS7. with the wings covered. After getting it home I discovered a rats nest, upon further inspection I discovered corrosion on one spar (probably from urine).......it was very questionable of how bad it was, but didn't take me long to decide I didn't want a new airplane with a spar like that, besides worrying about it every time I flew..............so I'm in the process of replacing that spar. By the way, hard to tell by pictures, but I would say your scratches were similar to my corrosion as far as damage.
I have to ask, and don't take this wrong, I'm not pointing fingers.......but you have pictures of the scratches, so I take it you were aware of them, was there a reason you didn't address them at that time? How did the scratches get there?
Do all the spars have scratches? or just one? If it's a front spar, it takes some work to replace it, but can be done, I can give you a couple of tips, that I wish I had known if you decided to replace it.
You could try to just remove the spar attach fitting, but you have to be very careful not to get the spar to hot when trying to remove the hysol........personally, I think it would be next to impossible to do and not damage the spar.
Good luck on your project.
Brian

[jeffcoaj]

Thanks guys.

Back to square one, I've got enough doubts. Avidfoxflyers say stress riser is mentioned in the avid manual. I do not have an avid manual, and I did not see it mentioned in the 1989 KF manual (maybe its in there). 43.13 does have it so no excuse.

Under load, I can see a stress riser that may originate from it.

EAA around here mainly builds RV's, and they would have valuable input.

[jiott]

One other point that I feel needs to be addressed are the statements about sanding out the scratches starting with 220 grit. I believe the manual (which I don't have at hand right now) states in the build tips section, do not use sandpaper on aluminum if the grit has silica in it, which most sandpaper does. It can get into the surface (especially scratches) and cause corrosion. The manual recommends using only Scotchbrite (maroon) to scuff aluminum in prep for gluing or painting.

[southwind32]

Thanks guys.

Back to square one, I've got enough doubts. Avidfoxflyers say stress riser is mentioned in the avid manual. I do not have an avid manual, and I did not see it mentioned in the 1989 KF manual (maybe its in there). 43.13 does have it so no excuse.

Under load, I can see a stress riser that may originate from it.

EAA around here mainly builds RV's, and they would have valuable input.

My 2 cents.........I think you're making a good decision..........better to be safe then sorry.

[Av8r3400]

The only downside to replacing this spar is finding the same material to replace it with. I don't believe anyone makes this extrusion any more.

If you use the standard tube with reinforcing I-beam in the middle, it will have different flexing properties than the fully reinforced extrusion. This could lead to unintended handling problems.


Food for thought.

[jeffcoaj]

Thanks, I did not realize the I beams did not go full length of the spar. In replacing the spar, 12’ lengths are standard for 6061. Possible to use this length? Thanks again.

[jiott]

When you insert the I-beams in your replacement spars be very careful not to scratch/gall the inside of the new spars. Follow the manual precisely and use baby oil in addition. If they hang up, NEVER pound them in. I learned this the hard way.

[jeffcoaj]

Ummm, is it concerning at all that there are a dozen holes drilled into the spar under the mount. Their right in the bottom side of the spar where all the stress is. Sure there are rivets to be placed through them but it seems to me rivets don't hold a piece together. Sure, they hold two parts together but they wont strengthen the spar just by filling a hole in it. What if I drilled a hole two inches away from the bracket, oops, then just put a rivet in to repair. No way right? Scratches, all retained under the bracket and filled with Hysol? Dang, its a tough one. If the bracket and Hysol maintain the integrity of the spar after all those holes then I am not sure it would not retain the scratches. Just me thinking.
Eddie

Your point has been expressed by many I've talked to recently. An experienced guy said that the hysol is packed in tight underneath the sleeve, esp. with the rivets. West systems epoxy even recommends 40 grit on aluminum when making a structural bond for the epoxy to key (of course after al prep, and al oxide pads). Also, I don't see any evidence that the scratches could make the joint any weaker. Originally I thought stress risers could emerge, but they could emerge just as easily from the holes given constant tension and compression under the spar. Dang is right. Wish I had some pictures of other's spars to compare to mine. Back to still thinking.

[Esser]

What’s the wall thickness of the spar and what’s the depth of your scratch’s? I think you are going to be within tolerance.

[jiott]

FWIW, a smooth deburred hole is much less of a stress riser than a deep scratch with a sharp V bottom.