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Wing Bottom Skins

asw20c

Well Known Member
After 6 months of scratching my head and agonizing over how to get the bottom skins riveted I finally threw in the towel and called Synergy Air and asked them to send out one of their experienced "buckers" to help. Well worth it in my opinion. We had all 4 bottom skins installed in about a day and a half. The point of this post though is that the way we did it, and what the plans suggested were very different. I suppose to each his own, but it was helpful to have someone who had done this a few times before to point out what had worked for them in the past. Frankly this was the most difficult part of the build for me so far; even worse than the fuel tanks.
I feel like I can breath again and get on with the project now. Just flaps, ailerons, pushrods and bellcranks, magnetometer, roll servo, VOR/ILS antenna, tips, etc. Sheeesh!!
 
Here are a few things that turned out to be helpful: First, don't try to rivet the skins while the wings are in their wing-stands. It is far easier to lay them on a table, or between tables with the gun operator on one side and the bucker on the other. The tables will need to be low enough that the bucker can lean over the wing, or give them a step stool. Next, start at the inboard rib, aft end and work up and out. The innermost 4 ribs in the wing-walk area are the toughest. We did a LOT of clecoing and unclecoing. Buy a curved mushroom head rivet set about 6" long for your rivet gun to work around the flap brackets. Next, try different positions where in some cases you could work directly between ribs with the skin peeled up, and others you had to work through lightening holes and access hatches. After a few "squares" the technique/pattern starts to become more obvious. And lastly, you can't get away from the necessity for the bucker to have long arms. Long arms and strong hands are absolutely necessary for those few that require a full reach with only fingertips on the bucking bar. A bucking bar that has a slot cut in it that makes it easier to hold with fingertips was also helpful. Stuff a t-shirt or pillow underneath where you are bucking so that you don't cause damage to the top skin if the bucking bar is dropped. Use only tungsten bucking bars and have a variety of shapes and sizes to get into all the nooks and crannys.
 
I agree with all of the above except I had good results doing the bottom skins with the wings vertical in the wing stands. The key was to brace the inboard and outboard aft spar ends with a 2x4 against the opposite wall from the side you are riveting. This provided the needed rigidity to get a consistent rivet. Without this the structure moves and vibrates and makes ugly looking rivets. I nailed a cross piece between studs on my garage wall about 7 feet off the ground to support the 2x4 and used a clamp to hold the rear spar flange on the inbd side and outboard aileron bracket on the outside to the other end of the 2x4. This made it rock solid and will save your back from bending over the wing if you do it horizontally.
 
Nothing fun about it, but the bottom wing skins are no big deal. My wife and I knocked them out in three riveting sessions per wing.

FWIW, my wings were built entirely on a 4x8 table, flipping them over as required.
 
I don't know what the chord-length difference is between a -14 wing and an -8, but for those rivets at or close to the rear spar I think you would be hard-pressed to rivet them by yourself with any consistency or quality. Kudos if you can, but for me it was just this side of impossible. You will be doing yourself a favor if you can find someone who can help with long arms and experience in blind-bucking.
 
I should have rented you my wife. The only thing is, she was born in Texas and raised in Oklahoma so she prefers to shoot!


(Click to enlarge)
 
Just drove the last rivet in my wing skins 10 min ago (my son actually had the gun and I had the bar. My only regret is that I put the pitot mast in the bay inboard of the aileron bellcrank. Now I have to do some creative plumbing to clear the aileron push tube. If I did it again I would go one bay outboard of the aileron crank mount. This would entail drilling a few more holes in some ribs for the bushings but otherwise no problem.
 
I don't know what the chord-length difference is between a -14 wing and an -8, but for those rivets at or close to the rear spar I think you would be hard-pressed to rivet them by yourself with any consistency or quality.

I resigned to the fact there will be a few smilies in my RV by one-man riveting job. I haven't got to the bottom skin stage yet but I hope my friend will get better at running the gun.
 
I resigned to the fact there will be a few smilies in my RV by one-man riveting job. I haven't got to the bottom skin stage yet but I hope my friend will get better at running the gun.

Using less experienced help, you may want to consider one of these

http://www.cleavelandtool.com/Swivel-Mushroom-Set/productinfo/RSMS75/#.XMNT2-hKiUk

As shown in the photo Bill posted
6%20days%20before%20the%20wedding.jpg


Note the position of hands... one on the set itself to assure it doesn't walk out of possition.

For them to work well they should be modified slightly.... the rubber cup thickness at the end should be reduced about 50% on a sanding belt to make it more flexible. Once that is done it will just about 100% eliminate the possibility of smiles.
 
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I did the exact same thing. I think the reasons I chose that bay is because that was the same location as Van's simple pitot, and also because I didn't realize at the time that this location would put it in conflict with the push tube. Had I known that I would have put it outboard just as you suggested. After scratching my head about this for more than a month, I chose to use 90 degree AN fittings to turn the corner just below the push tube. These are the ones where you simply push the plastic tubes (AOA and Pitot) into the fittings. I also chose a polarized Molex plug for the pitot heat because I knew that installing the pitot and plug would have to be done blind and by feel from the access hatches on either side of this bay. I wanted it so that the plug could only engage one way and that everything could easily be done by feel.
 
Using less experienced help, you may want to consider one of these


Note the position of hands... one on the set itself to assure it doesn't walk out of possition.

For them to work well they should be modified slightly.... the rubber cup thickness at the end should be reduced about 50% on a sanding belt to make it more flexible. Once that is done it will just about 100% eliminate the possibility of smiles.

Thanks for the tip
 
couple of additional suggestions

First, thanks for all the info from this post; very helpful!

Struggled with the first rivet forward of the J-stiffener on each rib when working on the right wing. So when completing the left wing bottom skin we riveted the first rivet forward of the J-stiffener long (with the exception of the rivets where the inboard and outboard lower skins overlap) PRIOR to sliding the J-stiffener long in place, then riveted the J-stiffener after that was done. Much easier.

Also, when working forward of the J-stiffener long, riveting order was key, first noting which direction the flanges of the ribs are facing. We started with the bay formed by the 3rd and 4th most outboard ribs completing that bay by peeling up the skin slightly. Then, working outboard/inboard from that bay worked great.
Juliette
 
I don't know what the chord-length difference is between a -14 wing and an -8, but for those rivets at or close to the rear spar I think you would be hard-pressed to rivet them by yourself with any consistency or quality. Kudos if you can, but for me it was just this side of impossible. You will be doing yourself a favor if you can find someone who can help with long arms and experience in blind-bucking.

It is doable. I did the bottom skins on my 10 QB wings by myself. I think there were a few rivets that required someone else working the gun, as the bar was just too hard to hold with accuracy while also holding the gun..

I do have relatively long arms and the small inboard skin was already installed due to the QB option. The only poor rivet heads were the one's where my son worked the gun. The key to close quarter work is to learn to use the tapered edges of the mushroom head (gun must be held at the correct angle). Takes a bit of practice, but can be done.

Larry
 
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