PA-12 Wing Rebuild Question

I am currently in the process of rebuilding the wings and doing the PA-18 flap STC on my 1947 PA-12. Its coming along nicely and the new ribs from Dakota Cub look great. I think I understand how to trammel and square everything while I tighten the drag wires. Before the leading edges are installed, it is suggested that you build in some wing wash so the LEs wont oil can latter on.

My question is this. The wing is setting on the saw horses now. With both spars square and leveled with a bubble level, how much wing wash do you build in and how is the best way to do it? Is there something published on paper that gives instructions and specs.

Thanks in advance for any help!

Kevin

2.5 Degrees deference between the bottom of the butt rib and the bottom of the outboard aileron rib, don't use this dimension on the spars. You can use a smart level or a bubble protractor. When I get the spacer right, I take a bungee cord and wrap it around the horse and the spares to keep it in place. Note: the screws at the leading edge skin seams hold the wash.

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Trammel and the put in the washout. I was working on my wings at the house late one night and couldn't understand why I couldn't get them square at the tank bay. I finally figured out I had a washout block under the rear spar.

Now I am confused

Flapman said:

When Piper built Super Cubs at Vero Beach they specified that the wing washout would be set up on two leveled sawhorses. One under the # 1 rib and the other under the # 15 rib. A block of wood would then be placed under the # 15 rib flange just beneath the rear spar. This block of wood measured 1 and 3/8 inches.
As an aside, this washout was put in the wing BEFORE the drag wires are tensioned. If the wires are tensioned while the wing is flat, they will be out of tension spec and out of square when the washout is added.
Regards,
Flapman

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Steve Pierce said:

Trammel and the put in the washout. I was working on my wings at the house late one night and couldn't understand why I couldn't get them square at the tank bay. I finally figured out I had a washout block under the rear spar.

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When you put the tank bay rod in place it squares that bay for the most part. With the rod in place and the washout block installed I could not square the wing. There were lots of four letter words being used and luckily Lee was asleep. Someone please explain it to me also.

Start by making sure that the saw horses are level, very stable and rigid, and their location is fixed. To rig the washout put a 1-3/8" block under the rear spar adjacent to the outboard aileron rib. The wing spars should be firmly supported directly on the saw horses at the wing root and immediately adjacent to the outboard aileron rib. If for some reason you chose to support the wing on the root rib and the outboard aileron rib than use a 1-3/16" block under the rib directly under the rear spar. The 3/16" difference in the blocks is because the rib profile is different as it passes over the front and rear spars. The installation of the "hard leading edges" will make twisting of the leading edges very difficult and will induce stresses into the structure. If you are very careful to maintain the accurate washout during the assembly of your wings it will make their installation and rigging much easier.

Thanks for everyones imput. I have been mulling this over in mind mind for the better part of 2 hours now and what I come up with is this.

1. Assemble the entire wing with the ribs installed, compression struts installed, drag wires installed (loose) the full wrap leading edge attached to the lower spar only and trailing edges off.

2. Level both spars accurately with a bubble level under the #1 butt rib and at the #15 rib.

3. Tension the drag wires with a fish scale while keeping the entire wing square. Check, recheck and check again.

4. Put a 1 3/8" wood block under the #15 rib at the rear spar.

5. Attach the leading edge at the top spar tightly using cargo straps or the tightening tool as per the instructions on the dakota cub web site (link is at top of this discussion).

6. Attach rear false spars IAW dakota cub instructions.

Am I missing anything? This is a great discussion and I appreciate all the imputs. I really want to do this the correct way and not dive into anything in the "exparemental" area. Also, I think once the wrap around leading edges are installed, the wing will be very stiff and there will be less room for errors and adjustments once they are actually on the plane.

As a side note, when I disassembled everything, the drag wire attach fittings were coated with some nasty looking paint (maybe rustoleum). I cleaned them all up and they look great. Is there any reason to prime them or the drag wires? Arent they all stainless?

Kevin

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Stewart-

Can you post some pics of your plane as it was being built? Interior stuff would help me.

Tim