Please help: Wing Rigging problem

[lr172]

I purchased a partially completed RV-6A that I am finishing. The fuse and wings were quick builds. The previous builder had already installed the wings and I have been losing sleep for the last two months about him getting the rigging wrong. Well, today I finally installed the wings and

I've got 7/8" of forward sweep in the right wing and 1/2" in the left. When measuring from the center line in the tail, I get 1/4" longer on the right wing, seemingly consistent with the sweep differential.

The incidence on the right wing is pretty close and the left wing is the same at the root. The problem is that the incidence changes on the left wing as I move out to the tip. By the time I get to the tip, I need a 3/16" spacer on the 3.03" jig on the rear spar to get the same incidence. It looks like about .5 degrees of more/less incidence. The right wing is consistent from root to tip.

This raises two issues. First, the twist in the wing. Will the increasing/reducing incidence in one wing cause flight problems? If so, any ideas on how it got twisted and how I repair it? Could it have been the installation of the top skin?

Second, I am assuming that I will need to address the fwd sweep. Is there a method of addressing this without pulling the spar in the fuse or wing, or worse, both? I've thought about using a drill jig to bore the hole larger to swallow up the offset and use a larger bolt. This might kill the 5/8" edge distance, however.

Not a good night. I would appreciate any guidance from those that have dealt with this before.

Thanks so much for any assistance that you can provide.

Larry

 

[kiwipete]

Larry

I know vans are on holiday, but make sure you get the final ok for any changes from them.

I doubt the sweep will ever be noticeable in flight and not make any difference.
But the twist may, it can probably be countered with aileron and flap adjustment to fly straight but may induce a wing drop at the stall. Again consult vans, they'll know what's acceptable.
I have a feeling they'll say all is fine, plus at least it's washout not wash in. Considering they are quick build wings built in vans jig. It's most likely normal.

Peter

 

[Andy Hill]

Hi Larry

I've thought about using a drill jig to bore the hole larger to swallow up the offset and use a larger bolt. This might kill the 5/8" edge distance, however.

Bear in mind a larger bolt requires larger ED

Vans are very sensitive to rear spar attach / bolts / ED after the RV-3 problems. If you are really concerned about the sweep, and/or it is judged the twist might be compensated be altering the incidence, a replacement rear spar carry through might be an idea. On the RV-3 (maybe the 6?) this is 1 bar of AL riveted to a fuselage bulkhead. De-riveting this bar, and replacing it, might be a way ahead?

 

[lr172]

Thanks for the posts here. I really wish I did this yesterday. I had to put all my cars on the driveway to get the wings on. I hope the snow holds off for a bit.

I have done a bit more research and thought on this. Drilling out larger won't be enough change, so it looks like a spar replacement if this has to be dealt with. I am thinking that the sweep can be tolerated, but I am concerned about the difference in the incidence. I took a bunch more measurements and the left wing only matches the right for about a foot from the root and by 3 feet it is at the 1/8"-3/16" deviation and it follows all the way out to the tip. Hopefully I can get through to Van's on Monday.

Larry

 

[lr172]

I have a feeling they'll say all is fine, plus at least it's washout not wash in. Considering they are quick build wings built in vans jig. It's most likely normal.

Peter

I sense this is not uncommon. Had the incidence been set based upon the average or majority, I wouldn't be concerned. I think the prior builder just measured at the root and drilled away.

Larry

 

[Kevin Horton]

The wing sweep doesn?t concern me. It does affect the CG envelope though, as the forward sweep means the wing, as an average, is a bit further forward than the design location. The centre of the right wing is 1/4? forward, and the left is 7/16? forward, for an average of 11/32?. Move the aft CG limit forward by 0.35? to have the same pitch stability as a nominal RV-8.

The wing twist is certainly not ideal. I don?t think it is worth rebuilding a wing to correct for 0.5 deg washout. But, you really want to adjust the rear spar mounting point so the average incidence of the two wings is as close as possible. As Andy suggested, the simplest repair is probably a custom rear spar carry through made from wider bars, with the in-fuselage portion machined down to the normal size. The extra material outside the fuselage would allow you to adjust the rear spar mounting point while maintaining edge distance. Definitely get Van?s input on this one. They may very well tell you that this is far from the worse they are aware of, and that you stop fretting over it. Or maybe not.

I guess in the end it comes down to a personal decision on how perfect an aircraft you want, and how you want to balance build time/money/etc. The ultimate fix is to build a new left wing, but that is a lot of time and money.

 

[William]

Hi Larry another option you could do if you have enough edge clearance to do it on the rear spar of the wing. There are 2 doubler plates that are riveted to the rear spar and the rear spar bolt goes through. You could remove these 2 doubler plates and install new ones then re drill for your wing incidence. I had to do this on my rv6a and it really is not that big of a job. Maybe 4 hours total to drill out the old doublers and install new.

Bill

 

[lr172]

Thanks for your input Kevin. My goal here is to have a good flying and safe aircraft that I enjoyed building. I am not after perfection and would lose no sleep if my RV-6 was 3 knots slower than the average if it avoid an effort the size of the wing rebuild. Unpleasant stall characteristics are another matter and I care quite a bit about that.

After more measurements last night, there really is not much wash out/in. The first 1-2 feet out from the root is different, but the remaining wing, out to the tip is pretty consistent.

My current plan is to reset the rear spar attach on the right wing to match the average incidence and sweep of the left. Then reset the Horiz stab. incidence to coincide with the new wing incidence. the guidance from Van's seems to indicate that that actual incidence is not critical, but matching Port to Stern is. They suggest matching the horiz stab incidence to the wing incidence via the jigs and a common level point.

I studied the plans last night and it seems the easier fix is to replace the lower spar doubler and plate on the wing. I will cut this myself so that I can build in a bit of extra size at the attach point area to help keep the 5/8" ED after adjustment. The holes on the fuse spar are well within the 5/8". I'll line up the wing and run a drill through to set it. I am not sure that I can get a tight hole through all three pieces, so I'll find the next closest bolt (M9 is only .04" larger) and drill out for it while clamped. That should leave me a clean repair.

I will call Van's when they return to see what they have to say about the incidence mismatch.

Thanks for the assistance.

Larry

 

[lr172]

Hi Larry another option you could do if you have enough edge clearance to do it on the rear spar of the wing. There are 2 doubler plates that are riveted to the rear spar and the rear spar bolt goes through. You could remove these 2 doubler plates and install new ones then re drill for your wing incidence. I had to do this on my rv6a and it really is not that big of a job. Maybe 4 hours total to drill out the old doublers and install new.

Bill

Great minds think alike Our posts must have crossed on the way in. Thanks for posting your idea. This is likely the route that I will take.

Larry

 

[lr172]

Well, I took the wings off this evening to replace the rear spar doubler. Turns out that the previous builder took off too much of the spar attach point to clear the fuse. I'm replacing the right, so didn't care. The left only had 1/2" edge clearance, so I guess that I am doing both The upside is that I can even out the incidence trade off between the two wings and get rid of all of the sweep.

Thanks again for the assist.

Larry

 

[rvbuilder2002]

After more measurements last night, there really is not much wash out/in. The first 1-2 feet out from the root is different, but the remaining wing, out to the tip is pretty consistent.

If this is the case, then consider doing some more checking/measuring... You may not have any twist in that wing at all.

Sometimes while dimpling the flanges of the rear spar, the bend angle on the flange changes. Do some checks to confirm that the skin lays the same on the entire wing trailing edge. Another effect is that the wing walk doubler is between the top skin and the rear spar flange at the root end of the wing. This can also induce some measurement error at the inboard end.

 

[lr172]

Hi Larry another option you could do if you have enough edge clearance to do it on the rear spar of the wing. There are 2 doubler plates that are riveted to the rear spar and the rear spar bolt goes through. You could remove these 2 doubler plates and install new ones then re drill for your wing incidence. I had to do this on my rv6a and it really is not that big of a job. Maybe 4 hours total to drill out the old doublers and install new.

Bill

I spoke with Van's and they are concerned with the 1/2" edge distance, so I will be replacing both rear doublers. Removing them seems simple, but I am struggling to figure out how I will install the rivets on the new doublers. The lightening holes are too small for me to get in there. It seems that I will need to lift the skin to get in there, but not sure how to get new rivets on the skin. Should I just use cherry rivets where I can't get a bucking bar in (i.e. the rivets on the webs)?

Thanks,

Larry

 

[William]

Hi Larry I used the longest bucking bar I had. It is surely a tight fit and I did end up with some cuts on my arm from reaching and positioning the bucking bar through the lightning holes.

Bill

 

[lr172]

Hi Larry I used the longest bucking bar I had. It is surely a tight fit and I did end up with some cuts on my arm from reaching and positioning the bucking bar through the lightning holes.

Bill

Thanks William. I should be able to make a long bar to get in there. Good to know it can be done.

Larry