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14-02 skin mating question

propsync

Well Known Member
Hi Group,

I did a search here on vans and didn't really turn up anything. Took a look on Google and Youtube as well without luck. I'm looking for some tips/advice on completing skin mating, but I do have an RV14 specific question on the mating as well.

21ouij6.gif


Notice in the illustration, Vans is saying that the area is 1" by 1" (I think, although 25mm is about an inch). This doesn't seem correct. In order to do this step correctly, you have to measure the skin overlap right? Assuming that's the case, you would be looking at 1 5/8". The illustration does show the removal of material that covers 2 rows of rivet holes but clearly that is not 1".

I'm looking for some guidance on completing this step.

Also, what is the best way to remove material in such a way as to get a good fit? I was thinking maybe something like this--

Start with the same amount of strokes with a file across the entire area and then move away from a reference line in 1/8 inch increments at a time with the same number of strokes at each increment each time (hopefully that made sense). I may be overthinking this as the area is so small and so thin.

As always, thanks for the help!
 
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I made mine larger than Van's one inch to accomplish a good fit. I did not find an easy way to taper the corners. I used a small disc sander, but would not recommend it to others as it's an easy way to destroy a skin( I took the chance and succeeded). Your 1 5/8" sounds about right to me.
On the RV-10 , Van's has you taper the entire seam (about three feet) on both skins. Now that took time for me.(edit "see correction comments in post 5")
 
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I made mine larger than Van's one inch to accomplish a good fit. I did not find an easy way to taper the corners. I used a small disc sander, but would not recommend it to others as it's an easy way to destroy a skin( I took the chance and succeeded). Your 1 5/8" sounds about right to me.
On the RV-10 , Van's has you taper the entire seam (about three feet) on both skins. Now that took time for me.

The RV-10 build manuel doesn't instruct the builder to tapper the entire edge of the skin, and I would strongly recommend that builders do not do that. Only just the fwd corners as shown here in this thread at scarfed/tappered (the RV-10 and RV-14 wings build basically the same... just with some dimensional differences).
 
I was going by memory, but after reading RV builder2002, I looked up that section in the manual. Obviously he is correct. I did follow the instructions so obviously I only did the corners. On the 10 it took forever and it only took a short time on the 14. Practice on the 10 must have helped with completing the 14. Never had a good memory, so I don't expect it to improve.
Sorry for misleading.
Ron
 
Wing skin mating, to remove or not remove material?

As discussed agreed that VANs have the measurement too small and that the removal of material must come back to the edge of the overlap.
But we are considering not removing any material at all and just breaking both edges to avoid gaps. What are the issues you see with us skipping (not doing) RV-14 16-02 Step 6? Is this a cosmetic issue or will it cause drag and or risk?
As far as I can see not doing this will simply result in ~1 3/4" of edge being higher then the leading edge/fuel tank.
I will also email VANs support and ask them.
 
I may have a way around this.

Today I did the skin mating on the left wing top skins as suggested on page 16-02 and I'm not really happy with it. The result is okay but I hope the skins won't show fatigue crack in the future.

The thing is, it is nearly impossible to control the material removal without risking to overdo it. There is no way to consistently remove just enough material without ending up with too thin a material. Besides, from a geometric perspective, the final shapes resulting from material removal can not coincide. It is simply impossible. It like trying to fit a square bloc in a round shape. It looks nice on the drawing but totally impractical. For what it worth, the risk is extremely high to ruin the skin just to get it flush with the fuel tank skin. I just hope I didn't.

In my case, I intent to do this differently. In order to avoid the .025 gap between the W-00003 skin and the main spar, I will fill it with some Bondo plastic metal. Its made by 3M. I'm no aeronautical engineer but I'm sure this will provide a much stronger solution to this skin mating than "grinding out" some precious tiny aluminum sheet.

I trust that a "hump" of .025in over a distance of 1.75in won't ruin the aerodynamics of the airfoil.

I'll post few pictures later once I'm done.
 
You said "grind out", I can see that would be a problem. I used a file and sand paper. Took a couple hours but turned out well. I'm pleased.
 
The thing is, it is nearly impossible to control the material removal without risking to overdo it. There is no way to consistently remove just enough material without ending up with too thin a material. Besides, from a geometric perspective, the final shapes resulting from material removal can not coincide. It is simply impossible. It like trying to fit a square bloc in a round shape. It looks nice on the drawing but totally impractical. For what it worth, the risk is extremely high to ruin the skin just to get it flush with the fuel tank skin. I just hope I didn't.

In my case, I intent to do this differently. In order to avoid the .025 gap between the W-00003 skin and the main spar, I will fill it with some Bondo plastic metal. Its made by 3M. I'm no aeronautical engineer but I'm sure this will provide a much stronger solution to this skin mating than "grinding out" some precious tiny aluminum sheet.

The technique described has been recommended and been used since the very first RV-6's were built (possibly even the RV-4, but I can't remember), so I think that is enough proof that even with the variability of a bunch of different amateur builders doing it, it is not a problem.

Personally I am a lot more concerned when people use any type of fillers. Especially when it is not something with a proven track record in a specific application.
 
Ahhh... now it makes sense!

I just started section 16 (new numbering) and was having a lot of trouble understanding the purpose of the scarf. I understand what a scarf joint is, but why was just the leading edge corner being scarfed?

The illustration with it's improbable geometry made things more confusing and searching the web found lots of people tapering the whole edge (which rvbuilder2002 says is *NOT* the point). I thought it was for the aesthetics of the leading edge, but then tapering the whole joint would make more sense.

What I was missing was that this is really just seems to get the leading edge to lay flat along the spar with no gap. Clearly this is needed to get the rivets to lay properly.

(it was the comment about filling the gap between raised skin and spar that finally triggered the visual image I needed to understand it -- something that rvbuilder2002 clearly frowned upon!)

With this in mind, it will be much easier to shape it appropriately.

Pat
 
After f$&ting around with files and other objects of destruction on the first wing, I used a 3m Roloc and a maroon Roloc pad (different coarseness than maroon square pad). Takes minutes, good control, and fits like glove.
 
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