C

charliet

Member
Has anyone used the pre punched wing skins on a 4 kit in the last several years? I am wondering how the holes lined up on the non punched ribs. Or should one try to get non punched skins and do the old fashioned open close open close and then back drill? Also, since I built my 6A eleven years ago and CRS is taking hold, do the leading edge skins come flat or pre shaped? TIA.
 
Leading edges come pre-formed. I can't advise pre-punch vs non punched, but if you decide to go non punched, you can get preformed leading edges/tank skins from Harmon Rocket, LLC. Also, if you don't mind a tad extra weight, you can go with 0.032 one-piece main skins.

As far as drilling non-prepunched skins, on the tanks, I drilled the ribs to the baffle then carefully measured the spanwise position of each one as close as possible, then pre-drilled to 1/16" the rib lines in the skins off the skeleton. Then I drew the centerlines on the ribs, strapped on the skins, checked alignment, and final drilled the skins to ribs.

On the main skins, my plan is to clamp the skins to the aligned skeleton, mark the rib flange positions on the inside of the skin, predrill the skin off the skeletion, then final drill on the skeleton.
 
Yes. Not very well. The holes in the pre-drilled spar don't seem to be quite in the right place to line the ribs up with the prepunched skins, and this seems to be a common complaint, based on what I've read. Not sure why this discrepency persists. I was able to make it work, but just barely. That included using 1 inch stock on many of the reinforcement angles in order to get E.D. on the mounting holes. In other cases, the bolt heads are right up into the flanges, requiring you grind a good part of the bolt head off.

If I did it over, I'd drill my own spars, put the ribs where I want them. The prepunched skins are a good thing.


Cheers
Chris
 
Maybe yes, maybe no...

....having built my 6 with some prepunched skins and some not. If your skeleton is built perfectly with all the ribs exactly in place, it will work with minimal pushing and pulling of ribs for alignment. If a rib is out of place you start to run into edge issues.
Now, if you have the skins in advance of building your skeleton you can check them against your rib alignment and it makes things a bit quicker as you can draw a center line on the rib flange and sight it through the prepunched holes.
 
I did what JonJay did... mark the center of each rib with a felt marker so I could see where I was at when drilling through the skins. Also, I set the skins on the spar first and marked where each rib would go, in accordance with the holes in the skins and with where the plans showed. (I suppose I coulda measured it with a tape measure, but the holes in the skins don't measure wrong) It took a very long time to get everything in place but when I laid the skins down to drill through the ribs, there was nothing but black ink to be seen through each hole. ymmv
 
Charliet,

Bottom line is that while the prepunch skins are perfect, the predrilled spars may not be, and that is the crux of the problem. If you use the prepunch skins (which I recommend), order your spars undrilled so you can easily build your skeleton to match the skins.

Chris
 
Thanks for the info guys, always a great resource. Think I'll order the wing kit without skins and buy one piece top skins like I did for 191CT. Might as well buy bottom skins from the same source. I would like to use .025 all the way around. This 4 will be very light, no acro and low powered by the 0-235 sitting in the hangar, or will it fall out of the sky if I am trying to save about two pounds a side, and close up the tips ala a 12? Your thoughts?
 
My thoughts....

charliet said:
Thanks for the info guys, always a great resource. Think I'll order the wing kit without skins and buy one piece top skins like I did for 191CT. Might as well buy bottom skins from the same source. I would like to use .025 all the way around. This 4 will be very light, no acro and low powered by the 0-235 sitting in the hangar, or will it fall out of the sky if I am trying to save about two pounds a side, and close up the tips ala a 12? Your thoughts?
Click to expand...

...I have never heard of it being done, while the .032 one piece, as you know, has been done a lot. For the 4 lbs savings, not worth the potential risk.
 
Changing the skins to .025 will definitely make the wing weaker, but by how much? I can't imagine making such a change without an engineer's careful analysis. I would also suggest that resale value will be greatly reduced. I'd find another place to lose the weight.
 
Look at a later...

...pre-punched kit rib vs. the ribs that came with your kit.

You should see that Vans added an extra "slot" in the flange near the ends of the rib. This allows the rib to be slightly moved sideways during assembly. A neat way of allowing for production tolerances...:)

You might consider slotting your flanges to be like the pre-punched ribs to give yourself a bit more "wiggle room"... usual edge distance and deburring needs to be done on the slot, of course.

Millionrivets said:
Yes. Not very well. The holes in the pre-drilled spar don't seem to be quite in the right place to line the ribs up with the prepunched skins, and this seems to be a common complaint, based on what I've read. Not sure why this discrepency persists. I was able to make it work, but just barely. That included using 1 inch stock on many of the reinforcement angles in order to get E.D. on the mounting holes. In other cases, the bolt heads are right up into the flanges, requiring you grind a good part of the bolt head off.

If I did it over, I'd drill my own spars, put the ribs where I want them. The prepunched skins are a good thing.


Cheers
Chris
Click to expand...
 
My kit came with pre punched skins, most of the holes lined up fine except on the rib that carries the skin join. I think this may have been my fault, I replaced the rib on the left wing due to edge distance issues
 
Great tip, thanks. Many of the the holes in my spars were a good 1/8" off, incidentally. Seems a little wide for production tolerances, even on the TLAR RV-4 ("that looks about right"). Could have saved me a bunch of time and labor if they had just located them according to the plans. : )

Chris

az_gila said:
...pre-punched kit rib vs. the ribs that came with your kit.

You should see that Vans added an extra "slot" in the flange near the ends of the rib. This allows the rib to be slightly moved sideways during assembly. A neat way of allowing for production tolerances...:)

You might consider slotting your flanges to be like the pre-punched ribs to give yourself a bit more "wiggle room"... usual edge distance and deburring needs to be done on the slot, of course.
Click to expand...
 
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