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Leading Edge Skin Woes

D

Derek

Active Member
All,

Firstly fwiw this is my first post.

Introduction: Ive recently taken over a partly built RV-4. Ive built aircraft before, just not in metal.

Problem: Im attempting to fit the port wing LE skin, regardless of how much tension I place on the tie down straps I cannot seem to get the wing skin to line up with the tank, Im talking about where they are both positioned on the spar flanges. At present on the upper surface flange I have the tank and LE skin in perfect alignment and the gap between the two is uniform right around the entire D nose, however on the underside edge the LE skin is short of the tankskin by 3/16".

As an exercise, I removed the Sta 55 nose rib and pulled eveything back down tight, without the rib and doubler in place I can reduce the gap to 1/16".

I guess my question is, is it OK to have a 3/16" gap between the 2 pieces or is there something I'm doing wrong ??

Ive (hopefully) linked some pictures of my issue.

Derek106



http://s1118.photobucket.com/albums/k610/Derek106/
 
Last edited:
Wing

Hi several things spring to mind, the first is how did you or the original builder come to build the tanks first? When I build mine I did the leading edge first and the tank was built to the leading edge.

Secondly, have you checked the dimensions of the tank skin........ Vans make some of these to size, they also supply an oversize skin.

Third, have you checked the dimensions of the LE skin....... perhaps they cut it too short.

The last thing that I once had a problem with was the leading edge ribs, they had supplied ribs which I think came off an 8 and were slightly larger, enough make this difference.

regards
steve
 
Steve's advice is good - measure the skins and figure out where the difference comes from - if it is a difference in the skin dimensions or location of the leading edge bend, and it sounds like that is probable if the underlying structure is properly located and lines up, then what to do?
Don't use too much force with the straps - they can exert a lot of force and bend the skin or the underlying ribs, or create "dings" at the leading edge where the skin wraps around the rib nose. Use the straps to get everything snug and in place. Then see where you are.
The tank and leading edge skins should align - the main skin butts up against them. I remember when I did mine (RV-6) I trimmed one of the trailing edges to align the skins. You would have to trim the tank skin. But be sure that you have enough to properly locate the rivet line and screw hole line along the spar with proper edge distances on the skins. (I don't know whether the 6 and the 4 are different in this area).
Bill Brooks
Ottawa Canada
RV-6A finishing
 
WAM120RV said:
Hi several things spring to mind, the first is how did you or the original builder come to build the tanks first? When I build mine I did the leading edge first and the tank was built to the leading edge.

Secondly, have you checked the dimensions of the tank skin........ Vans make some of these to size, they also supply an oversize skin.

Third, have you checked the dimensions of the LE skin....... perhaps they cut it too short.
Click to expand...

Hi Steve,
Thanks for your response.

The previous owner has built both the tanks built first. I have checked the dimensions of both the LE skin and the tank skin, suprise, suprise the LE skin is 2mm narrower than the tank skin. Nowing this I can't see how the 2 will ever line up.

Not really sure what my options are now.

Regards

Derek
 
C-GRVT said:
Steve's advice is good - measure the skins and figure out where the difference comes from - if it is a difference in the skin dimensions or location of the leading edge bend, and it sounds like that is probable if the underlying structure is properly located and lines up, then what to do?
Don't use too much force with the straps - they can exert a lot of force and bend the skin or the underlying ribs, or create "dings" at the leading edge where the skin wraps around the rib nose. Use the straps to get everything snug and in place. Then see where you are.
The tank and leading edge skins should align - the main skin butts up against them. I remember when I did mine (RV-6) I trimmed one of the trailing edges to align the skins. You would have to trim the tank skin. But be sure that you have enough to properly locate the rivet line and screw hole line along the spar with proper edge distances on the skins. (I don't know whether the 6 and the 4 are different in this area).
Bill Brooks
Ottawa Canada
RV-6A finishing
Click to expand...

Hi Bill,

Thanks for your response, looks like the leading edge skin has been cut short.

Like I said previously, my options now seem limited.

Regards

Derek
 
If the lower skins are not installed yet, you could slide them forward a bit to close some of the gap, and still meet all edge distances.

I presume these are not pre-punched...

A new outer forward skin would be the best solution though...
 
Derek said:
Hi Bill,

Thanks for your response, looks like the leading edge skin has been cut short.

Like I said previously, my options now seem limited.

Regards

Derek
Click to expand...

Actually, your options are pretty much wide open. If the rivet holes in the ribs and spar haven't been drilled, it'll be pretty easy to make and fit new skins.

Making the leading edge bend is a little bit difficult, but far from impossible. When I last needed to make a leading edge skin (not for an RV, but similar), I made a simple Pazmany-style guillotine brake using several 2x6 boards and a length of 1.3" OD water pipe.
 
az_gila said:
If the lower skins are not installed yet, you could slide them forward a bit to close some of the gap, and still meet all edge distances.

I presume these are not pre-punched...

A new outer forward skin would be the best solution though...
Click to expand...

Hi Gil,

Thanks for your response. The problem with the idea of sliding the lower skin forward to close the gap is that it will bring the flap hinge line forward as well ( the lower rear skins are cut to the exact width ) this would then make the flap TE not in alignment with the aileron TE.

Thanks anyway.

Regards

Derek
 
Bob Kuykendall said:
Actually, your options are pretty much wide open. If the rivet holes in the ribs and spar haven't been drilled, it'll be pretty easy to make and fit new skins.

Making the leading edge bend is a little bit difficult, but far from impossible. When I last needed to make a leading edge skin (not for an RV, but similar), I made a simple Pazmany-style guillotine brake using several 2x6 boards and a length of 1.3" OD water pipe.
Click to expand...

Hi Bob,

I might just take the easier option of making 2 new lower aft skins, (no bending required). All that will be required is to make the 2 skins 2mm wider, by doing this it will enable me to get the flap hinge line in its correct position.

Thanks for your response

Regards

Derek
 
skin fit

Are the tanks already drilled to your spars. if not can you trim a bit off the tank skins so they slide back some?
 
danweseman said:
Are the tanks already drilled to your spars. if not can you trim a bit off the tank skins so they slide back some?
Click to expand...

Hi,

The tanks are not yet drilled to the spars. However if I trimmed 2mm off the tank skin, the rear skins would slide forward 2mm, bringing with it the flap hinge line. This is because both the lower skins are supplied exactly to size.

Regards

Derek
 
move tank back

I was thinking move the tanks back. but if your outboard LE skins are already tight on the ribs ... I see that wont work ,sorry. If you wrap a tape around the tank to measure the total skin length and did the same for the out board skin, do the match? Also i have 2 -4 le skins i dont need on my HR-2 build .I will measure this afternoon and you could measure yours. I would sell you mine cheap? PS Dan I guess shipping down under would be HI... Sorry again
 
Last edited:
Where abouts in Sydney are you? There are numerous '4 and '6 builders around Sydney who could give some advice.

Does the '4 have the doubler piece installed between the LE and Tank skins? The 6 has slightly smaller rib (W408) under the doubler than the other LE ribs.

If the markings are lost on these ribs then you may have the wrong one installed and this would prevent the skin sitting down properly.

Doug
 
Doug said:
Where abouts in Sydney are you? There are numerous '4 and '6 builders around Sydney who could give some advice.

Does the '4 have the doubler piece installed between the LE and Tank skins? The 6 has slightly smaller rib (W408) under the doubler than the other LE ribs.

If the markings are lost on these ribs then you may have the wrong one installed and this would prevent the skin sitting down properly.

Doug
Click to expand...

Hi Doug,

Im located on the Central Coast. You're correct the doubler and the undersize rib are part of the problem. I had to adjust the front part of that nose rib slightly, this then allowed the LE skin to come down a bit further.

Here's what I know for sure:
The LE skin is not the same width as the tank skin, short by 2mm.

The 2 lower wing skins are supplied exactly to size and they have to be positioned / riveted on the spar flange in the precise location in order for the flap to be in alignment with the aileron (ultimately) I should of done this part first, then butted the LE skin up against them.

I have a better understanding of what the issue is now and have a fix planned.

Regards

Derek
 
Derek said:
Hi Gil,

Thanks for your response. The problem with the idea of sliding the lower skin forward to close the gap is that it will bring the flap hinge line forward as well ( the lower rear skins are cut to the exact width ) this would then make the flap TE not in alignment with the aileron TE.

Thanks anyway.

Regards

Derek
Click to expand...

If they are not pre-punched, just get another blank sheet of 2024-T3 cut slightly oversize locally.

A slight gap at the flap hing line would be much less noticeable than at the LE-main skin seam.
 
Skins

Hi Derek

Sorry I am away in China at the moment and its difficult getting on line here but..... have you actually determined whether the tank skin is too long or the LE skin too short..... I would dothis first as the plan to fix should be based on this.

Secondly, I suspect the tank has been built in a jig which could mean that the tipsof the ribs could be closerto the skin than they might be had the tank been built on the wing.This would mean that the skin would sit lower on the spar....... and if you built the lower skins to this they would be too low moving the flap brace down a bit.

So please determine this before proceeding with any fix........ all you might need to do is trim the tank skin.

Regards
Steve
 
Hi Steve,

Thanks for your response. The tank skin is indeed oversize, Vans manufactures it this way. My mistake was to attempt to fit the LE skin to the wing first, when infact for my kit it's mandatory that the lower skins be reveted in place first as they are supplied exactly to size, then mate the LE skin up to it. All is well, Im out of pocket for a new set of lower skins only. A lesson learned ;<)

Regards

Derek
 
Derek said:
All,

Firstly fwiw this is my first post.

Introduction: Ive recently taken over a partly built RV-4. Ive built aircraft before, just not in metal.

Problem: Im attempting to fit the port wing LE skin, regardless of how much tension I place on the tie down straps I cannot seem to get the wing skin to line up with the tank, Im talking about where they are both positioned on the spar flanges. At present on the upper surface flange I have the tank and LE skin in perfect alignment and the gap between the two is uniform right around the entire D nose, however on the underside edge the LE skin is short of the tankskin by 3/16".

As an exercise, I removed the Sta 55 nose rib and pulled eveything back down tight, without the rib and doubler in place I can reduce the gap to 1/16".

I guess my question is, is it OK to have a 3/16" gap between the 2 pieces or is there something I'm doing wrong ??

Ive (hopefully) linked some pictures of my issue.

Derek106



http://s1118.photobucket.com/albums/k610/Derek106/
Click to expand...

I know you are not building an RV10 but I had a similar problem with the bottom two skins lining up as you are describing. I did not have 3/16 but rather 1/8 or so. My issue was there was proseal in the way on the fuel tank rib. I removed the extra and it fit nearly perfect. That was my experience with my 10ER tanks. Just wanted to put that out there.
 
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