wing alignment

[ken nougaret]

when i unfold my wings open, the leading edge needs to be lifted at the root end about 3/16" up to be pinned. this is causing the fuel tanks to not sit level in the folded configuration. they sit level in flight configuration. i got the quick build wings pre-rigged. the only thing i can think of that would have caused (fixed) this issue is the placement (bonding) of the #1 rib. but i bonded the #1 ribs in flight configuration. this situation doesn't seem right. any thoughts please?
ken (building ss7)

[Lion8]

Hi Ken. I'll be interested in a response to, as I bought a Model IV that when I unfold the left wing, I have to really move the front spar a lot to get the pin in.
Just wondering if I should remove the spar tab and re-adjust it. -Tom

[ken nougaret]

just wanted to add that this wouldn't be big concern if i thought the rtv for the tanks would hold. but i'm affraid that when i install the tanks and then fold the wings back that the strain will be too much for the rtv.
thanks, ken

[t j]

Here's my story. Mine is a classic 4 I built and rigged myself. I chased the rigging for about two weeks trying to get everything perfect in the folded and wings spread configuration. I finally was satisfied except that one wing front spar would drop about 1/4 inch when folded.

I called the Skystar tech (old kitfox factory) and he said that isn't too uncommon and not to worry about it.

My opinion is don't worry about the RTV. If it was applied correctly it will never come loose.

Also just my opinion, I would't try to change the rigging until you fly it. If it flys hands off and you still want to change the rigging so that the spar doesn't drop when folded, change the dihedral a half turn at a time on both front and rear spars on that wing until it stays level when folded.

[jtpitkin06]

Let’s see if I understand your questions as I’m not sure whether your concern is for the fuel tank or for the spar. Then maybe we can help.

I assume you have mounted both wings in the extended position and adjusted the dihedral to be the same on both sides. You have also checked the wing sweep, and adjusted the wing washout. In other words, everything looks good in the flight position with all pins installed.

You say when the wings are slightly folded the leading edge of one or both wings is 3/16 of an inch low when unsupported. I would consider this to be normal. The weight of the wing will cause the unsupported forward spar to sag a bit. If you adjust the lift struts so the wing will simply unfold and slide onto the forward spar without interference, then your wing tip washout will be incorrect.



The sag is not a problem. Just use a little hand pressure when unfolding the wings to push the spar up or down as necessary.

Now for the fuel tank. The same thing goes here. When the wings are folded the forward spar is unsupported and it will droop. If you are installing your wing tanks you may want to support them on saw horses or a building jig with wing tip washout shims in place. As for the tanks sitting level use a level or straight edge across the tanks and ribs to ensure the tanks are not protruding or sitting lower than the ribs. You may need to use a few shims to ensure a smooth transition between the ribs and the tank. One of my fuel tanks fit fine. The other was not so good and it required a little work. The bum tank also had a 8-10 inch diameter sag in the upper surface that required ¼ inch of filler. I used a lot of filler on both fuel tanks to ensure a smooth appearance when the fabric was applied.

Once the tanks are installed with the silicone sealer/adhesive, they won’t go anywhere and they do add a lot of stiffness to the wing. Use the zig zag pattern shown in the build manual for the adhesive. When the tanks are permanently installed the leading edge sag when unsupported may improve a bit. Your fabric covering will also stiffen the wing.

Another issue that pops up once in a while is the relative position of the wings when folded. You may find that one wing tip is higher than the other when the wings are folded. Slight variances in measurement when setting the dihedral and tiny variances in the frame welding can affect the folded position. You can correct it by taking the same number of turns on each lift strut rod end. Extend the low wing rod end and retract the high wing. One half turn on each rod end will move the folded wing tip up or down about ½ inch. If you are within a half inch I wouldn’t do anything. Be sure to recheck the washout rigging on both sides after adjusting the folded position.

John Pitkin
Greenville, TX

[ken nougaret]

thanks to all who replied, i feel a lot better now. i'm glad to see i'm not the only one who has noticed this or had concerns about it. john p., my concern was for the spars and the tanks.
i wasn't sure how strong the rtv is, but you guys make it sound like it will hold without a problem.
my plan was to rtv the tanks in with the wings in flight position and everything looking good with all pins installed. i thought this would be better than with wings on sawhorses.
john p., did you use superfill for all your filling over the tanks? if so i'm assuming that stuff is resistant to cracking.
thanks again, ken

[HighWing]

Another issue that pops up once in a while is the relative position of the wings when folded. You may find that one wing tip is higher than the other when the wings are folded. Slight variances in measurement when setting the dihedral and tiny variances in the frame welding can affect the folded position. You can correct it by taking the same number of turns on each lift strut rod end. Extend the low wing rod end and retract the high wing. One half turn on each rod end will move the folded wing tip up or down about ½ inch. If you are within a half inch I wouldn’t do anything. Be sure to recheck the washout rigging on both sides after adjusting the folded position.

John Pitkin
Greenville, TX

This was addressed by the factory in the old days. The official word at the time I was building my first Model IV (1993-1998) was to rig the wings in flying configuration, then fold the wings. It was common to have the wing tips a couple of inches or more out of symmetry. This phenomenon was largely due to structural warpage after the welding process. The advice then - if the wing tips were not level - to adjust the rod ends on the lift struts to straighten things out. Then one guy posted the question to the then quarterly published Kitfox Times, Why, when the wings are adjusted correctly for flight would we want to change the geometry so the airplane would look pretty with wings folded on the ground. I seem to recall, that after that question, the factory changed the advice to adjust only if the horizontal stabilizer interfered with wing folding as sometimes they did. The tips on my first Model IV were uneven to about 4 inches when folded, but were as close to perfect extended as my digital level could place them and I left them that way.
Lowell