Adjusting Wing Fit

[ravenstar]

I attached my wings to my fuselage for the first time this weekend, an exciting time because the project really starts to look like an aircraft, even if the tail cone still isn't attached. It's been two years since I finished the wings, and I was happy to see that all the tabs lined up and fit the fuselage. But, not everything was perfect: The holes in the spars for the spar pins don't quite line up and it's not possible to push the spar pins through both spars simultaneously. They're close enough that I can fully insert the pin through either wing spar by itself. There's absolutely no play in the wing when it's installed this way, and no contact between the wing skin and the fuselage or rivets so I figure it's just a matter of carefully dressing the subspar tabs so that the wing can be inserted slighly farther into the fuselage. Given that those tabs were initially fit to the receptacles by hand filing before everything was assembled, I doubt this is an unusual situation, and because I expect to be removing the wings to store the aircraft, I want to take my time and get this fit as close to perfect as possible.

Does anyone have any tips for determining how much and where to file the subspar tabs? The misalignment of the holes is a fraction of a millimeter, just enough to be a problem since the tolerance on these holes is nearly 0.

Thanks!

 

[N8DAV8R]

Did you have a helper when you were trying to fit the spar pins? It can take a surprising amount of movement at the tips, mostly in the vertical direction to get things just right. On my plan you can observer exactly what you describe, but with a helper giving some lift and wiggle at the tip the pins will go into place easily.

If you are able to get the pins in individually, I would not expect the stub spars to be the issue.

 

[KEG]

I have a similar issue. The first time (and only time so far) I installed the wings I had to clamp the two wing spars together to eliminate what appears to be a slight twist of one or both of the spars. Like you, the pins go in smoothly without the wings inserted. I spoke to Van's and they said it was not unusual to struggle with installing the pins and that the issue would probably get better with use.

 

[ravenstar]

Did you have a helper when you were trying to fit the spar pins? It can take a surprising amount of movement at the tips, mostly in the vertical direction to get things just right. On my plan you can observer exactly what you describe, but with a helper giving some lift and wiggle at the tip the pins will go into place easily.

If you are able to get the pins in individually, I would not expect the stub spars to be the issue.

I did have a helper, but we couldn't figure out any way to move the wings that would get the pins to slide through. When I put the left wing on first the pins actually slid in relatively easily once we found just the right position for the wing tip. But with the left wing in place, no amount of moving the left wing would line the holes up perfectly. You've got me wondering now if I had a helper on each wing if that might help. No doubt the weight of the first wing will be trying to twist the pins.

 

[Bob Y]

Your description doesn’t sound like you’re leaving the pins in place after they insert through the left spar. Once you get the pins in the left spar, you need to back the pins out just enough to barely clear the back side of the left spar so the right spar can pass behind the pins. It takes some wiggling of the right wing to get the spar holes to line up with the pins, but they should line up.

 

[jsalley]

You can also try using a tailpipe expander - there was a previous thread discussing this, and several posters had good success with this repurposed tool.

 

[ravenstar]

Your description doesn’t sound like you’re leaving the pins in place after they insert through the left spar. Once you get the pins in the left spar, you need to back the pins out just enough to barely clear the back side of the left spar so the right spar can pass behind the pins. It takes some wiggling of the right wing to get the spar holes to line up with the pins, but they should line up.

Sorry if I wasn't clear, but yes, I am leaving the pins in place after installing the left wing. My photos are through the aft hole in the center bulkhead, through the right wing spar to the pin. I was reluctant to post them because they don't represent the problem very well, but here's one that might help. It's looking forward from behind the center bulkhead through the right spar to the pin inserted through the left spar. It looks as if the right spar needs to move a tiny bit further in, but I couldn't get it to match better no matter how much we pushed the wing around.

 

[ravenstar]

You can also try using a tailpipe expander - there was a previous thread discussing this, and several posters had good success with this repurposed tool.

I have seen those discussions, but I'm reluctant to resort to force until I'm sure I've done everything else correctly. Maybe I'm being too paranoid.

 

[Bob Y]

I do have to use a heavy rubber mallet to drive mine in. Just installed them last week after my condition inspection and they went in the quickest in the five years I’ve had it. Not sure if we’re getting better at installing them or if they’re seating themselves better now, but mine don’t just slide in.

 

[daveyator]

Look closely at the point where the spars contact the small plastic blocks in the centre section. A little judicious trimming of those blocks is often what is needed to fine tune the spar pin fit. If you’re worried about trimming them, first just try loosening the bolts to see if they are interfering Can’t think what they are called, (F-1204. Looked it up) but they position the top of the spar end. Once I trimmed mine, the pins became an easy tap in fit.
Cheers DaveH

 

[scottmillhouse]

On both older 12 kits I built I had to removed some metal on the inboard aluminum piece that ties the fuselage spar box side supports together. It was so tight against the top of the spar for the opposite wing that it would not allow the wing to lift the spar for hole alignment. I believe I filed about a 1/16 notch and it allowed enough movement for pin alignment.

 

[ravenstar]

Thank you all for your advice. I'm building in my garage, so I have to roll the fuselage outside to test fit the wings and the weather hasn't been particularly cooperative so it has taken me a while to test all these ideas. I'm happy to report after trying the various ideas that Dave H.'s advice turned out to be the solution to my problem. I loosened the retaining blocks and put the wings back on, and suddenly the pins slid in with almost no resistance at all. Once the pins were in place, the wings were rock solid. I'll have to go back to file down the blocks to get them just right, but now I know both that the wings will go on smoothly and what was preventing them from going on before. I'm much relieved, again, thank you all!

 

[bobg56]

I believe if the pins were made just a bit longer with a bit more taper these problems would go away. If a aluminum alignment tool could be manufactured that would also help with this issue. It would be nice if Vans sold one. Mine are a little difficult to install but do able, but I add a few 4 letter words while doing it!