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Bottom Skins

asw20c

Well Known Member
This past weekend I started on the dreaded bottom skins; the inboard left wing bottom skin to be specific. It was as difficult and miserable as I feared, made worse by some of the additional conduit I ran through the ribs for possible future upgrades that made accessing and bucking the rivets on the rear spar and the aft flanges of the ribs very difficult. I ended up with bloody hands and sore muscles after just a few hours.
But the main reason I'm writing now is because I physically could not get my arm with the bucking bar in my hand up between the wing-walk ribs at the inboard edge to buck the rivets around the flap bracket, nor on the rear spar, nor the aft ends of the ribs. It physically isn't possible to get my arm in between the ribs. How in the world did you guys buck the rivets in this area? Find some skinny kid with 3-foot arms? I'm thinking I'm going to have to use blind rivets. This really troubles me that the required riveting seems to be virtually impossible. Or is there a technique I'm missing, because clearly others have overcome this obstacle? Any advice?
 
If you are doing this by yourself you will be finding it very challenging.
I used a skinny 6'6" kid, bred in anticipation. ��
 
Same here, arms don?t fit, could not have done without help. It?s a very frustrating area but you?ll get through!
 
I?m 5-9 and I did them all myself. But you have to carefully plan in advance the order in which you will rivet so you can gently roll back the skins to access those rivets next to the bracket. Very slow and patient. One night I think I did three rivets and felt a triumph. I could only produce daughters, none of whom were much interested in my riveting problems. Also, if your plane doesn?t have your blood in just about every potential space then you are cheating.
Greg Beckner
N557GB
 
Greetings.

I hope this helps, but you may already be committed by virtue of having any rivets set. Perhaps this will help with your approach for the other wing?

I was able to rivet the both inboard bottom skins by myself (as documented for the left side and right side). I did the left side first and it took me 9 hours. The right side took me 4 hours.

As suggested by others, strategic riveting order and cleco'ing allow you to preserve access as you progress through. I used these bucking bars during the process.







I didn't have this one at the time, but I imagine it would be nice to have too (I bought it to set some of the rivets around the step-attach inspection area when finishing the baggage area).


A key strategy is to match your direction-of-access with the direction of each rib's flange. I suspect Van's selected these orientations with bucking access in mind. For example, (ribs numbered inobard-to-outboard):
  • Rib #1 can be squeezed. Do it last.
  • Ribs #2 and #3 flanges point inboard, access them from inboard through the lightening holes.
  • Ribs #4 and #5 flanges point outboard and inboard, respectively, access them through the inspection panel.
  • Rib #6 flange points outboard. Access it through the lightening holes of rib #7.
  • Lay towels down on the wing spar so when you drop the bucking bar, nothing gets dented.

I reviewed my time lapse video to see what I did so I can share that with you in hopes of helping. The wings remained in the cradle. I was on my knees the vast majority of the time reaching upwards or inwards. I forewent the plans' suggest riveting order. I could not find a way to follow that order as a one man operation. I have noticed no "oil canning" on the inboard bottom skins.

  • Taking the J-stiffener rivet line as the demarcation between aft- and forward-halves of the skin, the aft half of the skin was cleco'd in place to include the J-stiffener rivet line. See image below.
  • The aft-spar rivets were all riveted.
  • All clecos were removed.
  • All ribs, from aft to forward, up to but not including the J-stiffener, were riveted. For the first few upper rivets on each rib, I used a cleco two holes below the rivet being bucked to help keep things aligned.
  • The J-stiffener was riveted.
At this point, all rivets between and including the J-stiffener to the aft spar were set.
  • The outboard-most rib (#7) was cleco'd to the inboard bottom skin. This rib does not get riveted until the outboard skin is in place.
  • Rib #6 was cleco'd then riveted (aft to forward).
  • The main spar rivets between ribs #6 and #5 were riveted.
  • Rib #5 was riveted (aft to forward).
  • AHRS tray was cleco'd riveted.
  • Rib #4 was then riveted (aft to forward).
  • The main spar rivets between ribs #5 and #4 were riveted.
  • Rib #3 was riveted (aft to forward).
  • Rib #2 was riveted (aft to forward).
  • The main spar rivets between ribs #4 and #1 were riveted.
  • Rib #1 was squeezed (aft to forward).

Here you can see the aft spar rivets in-progress. Note that the forward half of the skin is not cleco'd at this point. This permitted that half of the skin to bend as I reached for access.

 
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