Wing Skin Install Process

[bob865]

I'm struggling with the directions regarding the wing skins. Below is the excerpt from the Vans provided directions. The part I'm struggling with is the part in bold

Cleco the forward row of holes in W-702 and W-703 skins to the matching holes in the main spar. Cleco the W702 and W-703 skins in place using a cleco in every fourth hole.

Don't forget to insert the doubler between the ribs and the W-702 skin. The main skins overlap at the eighth rib from the root. The outboard skin should fit on top of the inboard one.

Gently pull ribs into position if the matched holes do not align with the skin holes. Drill all the holes to final size.

Start drilling in the upper middle of the panel and work down and out toward the edges, work out any slack as you go.

Move the clecoes down one hole (into the drilled holes) and drill all the remaining holes.

Draw a couple of lines on the main skins that intersect at the center of the hole for the tiedown eye.

Remove the bottom main skins before fitting the leading edge and tank skins. Leave the top skins clecoed.

Where I'm lost is it tells me to remove the bottom skins, but it never tells me to install them. The installation is only the top skins. Further, it tells me to start drilling before checking the wing for any twist. This feels like it could cause me to build in a twist.

So questions:
1) Do I need to install the bottom skins also before drilling?
2) Do I need to worry about a twist in the wing before I start drilling?

 

[PhatRV]

You can be sure by cleco both top and bottom skins. They will help to stiffen up your wing on the wing stand. I found that with the wing skin cleco in place, the wing is very stiff that the floor support for the rear spar support wasn't even needed.

 

[wirejock]

Skins

I am fairly OCD. I used 50% clekos. All skins installed. Checked and clamped in the jig. Drill the open holes. Swap the clekos. Drill.
After each skin was riveted and the wings were measured for twist and sag before moving on.
Interesting observation. After the top skins, I was suprised I could actually twist the wing in the jig. Not much but measureable. That's why both were clamped in the jigs till every rivet was set. After that it was pretty solid.

 

[bob865]

What this a pre-punched kit? There aren't any jigs for the pre-punched kits.

How did you measure twist? I didn't see anything in the direction of a way to measure twist.

I am fairly OCD. I used 50% clekos. All skins installed. Checked and clamped in the jig. Drill the open holes. Swap the clekos. Drill.
After each skin was riveted and the wings were measured for twist and sag before moving on.
Interesting observation. After the top skins, I was suprised I could actually twist the wing in the jig. Not much but measureable. That's why both were clamped in the jigs till every rivet was set. After that it was pretty solid.

 

[PhatRV]

You will find the wing has no twist if you mount the spar flat and level, from the root to the tip. If the ribs are cleco correctly and the wing skins are cleco, you should see no twist. You can measure the twist yourself after you have done all these steps.

By the time you are building the wings, Vans instructions do not list all the little steps that you are used to see in the empenage section. If you need to check for twist, then check the twist.

 

[dwollen89]

What this a pre-punched kit? There aren't any jigs for the pre-punched kits.

How did you measure twist? I didn't see anything in the direction of a way to measure twist.

I just did this. What I did was mount the spar assembly on the wing rack. I used a laser level to make sure each mount was level side to side, then used a bubble level to make sure each platform was level front to back. Clamp the spar assembly down. Then using a plumb bob, hang it from the highest hole on the wing rib and the lowest hole on the wing rib. Do this on each end and make marks on the floor where the plumb bob hangs. Measure the difference between the two marks. The difference between the left and right side is your twist.

 

[wirejock]

Twist

I just did this. What I did was mount the spar assembly on the wing rack. I used a laser level to make sure each mount was level side to side, then used a bubble level to make sure each platform was level front to back. Clamp the spar assembly down. Then using a plumb bob, hang it from the highest hole on the wing rib and the lowest hole on the wing rib. Do this on each end and make marks on the floor where the plumb bob hangs. Measure the difference between the two marks. The difference between the left and right side is your twist.

What he ^ said.

 

[bob865]

I just did this. What I did was mount the spar assembly on the wing rack. I used a laser level to make sure each mount was level side to side, then used a bubble level to make sure each platform was level front to back. Clamp the spar assembly down. Then using a plumb bob, hang it from the highest hole on the wing rib and the lowest hole on the wing rib. Do this on each end and make marks on the floor where the plumb bob hangs. Measure the difference between the two marks. The difference between the left and right side is your twist.

Perfect! Thanks!! Now I know what I'm doing this weekend.

 

[wirejock]

Measurement

Perfect! Thanks!! Now I know what I'm doing this weekend.

Nothing wrong with that. In fact, I doubt it could twist very much even without a jig.
I measured from the plumb bob string to the rear spar. It took sime practice to do it without touching the string! Difference between the two is twist. Adjust the jig till the twist is gone. Check it between skins.