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Underbent Rear Spar Flange?

WingsOnWheels

WingsOnWheels

Well Known Member
I did a bunch of searches and couldn't find anything. I could swear I read about this same issue before though.

I didn't notice this problem until I was riveting the inboard portion of the rear spar and top skin. It would appear that the flange on the rear spar is a bit underbent. If I set a straightedge on the top wing surface (parallel to the ribs) with one end of the straightedge even with the aft edge of the skin I get around a 1/4" gap at the center over the rear spar rivet line.

I don't have any pictures to post at the moment (I'll add some this evening). The skin doesn't follow a smooth contour all the way to the trailing edge. This problem is pretty consistant across the entire length on the rear spar.

Has anyone seen this problem before. The angle difference is very slight, but could definately be a problem. I didn't notice this issue on my other wing, but will go back and check.
 
Talk to Van's about the magnitude and do what they say. The trailing edge will pull up somewhat as a consequence of riveting.

I helped a friend who received the very first pre-punched wing kit for his -6. It had a number of fabrication issues. The rear spar top flange was insufficiently bent, yet he had proceeded with both wings unawares of this particular problem. Van's has a purpose-made tool he borrowed to tweak the bend with the skin riveted in place. Both wings. Full span.

Hope yours isn't in that condition.

John Siebold
 
Last edited:
you are right

this is a known issue. I recall that Van's advised that the "ski jump" at the trailing edge of the wing that results from an underbent flange may be corrected, even if the wing skin is rivetted on, by carefully increasing the bend on the rear spar flange. This can be accomplished by using a 2X4 piece of wood with a slot cut into the end that is deep enough so that you can slide the slot over the skin trailing edge and rear spar flange. A bit of levering of the 2X4 on the rear spar flange will bring the bend to where it should be. This may have been mentioned in the RVAtor, I am at work, so don't have access to the "Years of RVAtor" to look.
Bill Brooks
Ottawa, Canada
RV-6A finishing kit
 
C-GRVT said:
this is a known issue. I recall that Van's advised that the "ski jump" at the trailing edge of the wing that results from an underbent flange may be corrected, even if the wing skin is rivetted on, by carefully increasing the bend on the rear spar flange. This can be accomplished by using a 2X4 piece of wood with a slot cut into the end that is deep enough so that you can slide the slot over the skin trailing edge and rear spar flange. A bit of levering of the 2X4 on the rear spar flange will bring the bend to where it should be. This may have been mentioned in the RVAtor, I am at work, so don't have access to the "Years of RVAtor" to look.
RV-6A finishing kit
Click to expand...

The 2*4 with slot..............is the trick. And that's the whole point of building these airplanes. If something doesn't look right, then adjust the bend, shim, or what ever is required. I'm a sheetmetal person by trade, and can cheat by having access to larger brakes. But I did use the 2*4 myself for a few adjustments.

Another good tool that is available at Home Depot/ Lowes for adjusting bends on smaller parts, is a folding tool. Comes in sizes from 8" to 24" long. Has a slot on each side for bending. I used this, along with 4 & 6" hand seamers for many slight adjustments.

http://www.malcoproducts.com/products/seamers/foldingtools.asp

L.Adamson ---- RV6A
 
L.Adamson said:
The 2*4 with slot..............is the trick. And that's the whole point of building these airplanes. If something doesn't look right, then adjust the bend, shim, or what ever is required. I'm a sheetmetal person by trade, and can cheat by having access to larger brakes. But I did use the 2*4 myself for a few adjustments.

Another good tool that is available at Home Depot/ Lowes for adjusting bends on smaller parts, is a folding tool. Comes in sizes from 8" to 24" long. Has a slot on each side for bending. I used this, along with 4 & 6" hand seamers for many slight adjustments.

http://www.malcoproducts.com/products/seamers/foldingtools.asp

L.Adamson ---- RV6A
Click to expand...

That 2X4 sounds like it would do the job. I think the biggest concern is making the bend even along the full length of the spar. I'll take some pictures and measurements today and give Vans a call in the morning.

Thanks,
 
I do not know whether it is a factor in this case, but sometimes the incorrectly bent angle on the rear spar flange is caused when the rivet holes are dimpled Particularly on an RV-4 or 6 wing when the holes may have drifted fwd a bit since it is not pre-punched. If the face of the dimple die interferes with the bend radius even a little bit, it can cause the bend angle to be progressively opened down the length of the spar. Something for builders to watch for.
 
I took some pictures of the problem this evening. As you can see, the "ski Jump" is definately there. It is slightly more pronounced on the .032 skin than the .025 skin. I was thinink about the 2X4 fix. The only downside is that my aileron gap fairing is already riveted to the skin (not to the spar yet). I am hopeful though, I was able to straighten the very inboard egde with just palm pressure.

Near outboard edge
cimg3948.jpg


Looking inboard
cimg3951t.jpg
 
How did you get on with straightening the flange ? Mine is ok on the aileron end ..but on the underside ..flap hinge .. I have a slight rise ..due to the flap brace .. I have not rivet on the hinge yet ... but holes are drilled ..
 
Jan,

I spoke with Vans and per their advice, I used a slotted 2X4 to make the slight bend in the flange required to get the skin flat. Worked ok. I would rather make a tool that doesn't flex as much as the wood...it did the job though
 
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