Do I need to plumb the wings?

danielhv · #1 10-11-2008, 02:57 PM

Im ready to rivet the main ribs to the spars... I've got the fishing line across the holes pretty straight and even all the way down. Is that sufficient on a pre-punched kit? Or do I need to plumb the ends and stuff?? Just want to make sure I dont have any twist in the wing after I rivet the ribs... I've got everything cleco'd together and ready to go!

cnpeters · #2 10-11-2008, 03:34 PM

Plumbing the wing is important when drilling more than riveting. There is not much that you can do once drilled, though I would still try and ensure a straight wing before riveting. It sounds like you have it level, and I ran plumbs down each side and measured to this from the rear spar, then clamped the latter to brackets attached to the wing stand. This locked everything in place when I drilled. I have read some threads about whether this is really necessary in these factory CNC drilled assemblies, but I couldn't find anything beyond 3 people who drilled and riveted without checking for twist until when it was done. An N number of 3 doesn't cut it for reliable data in my book on such a critical issue as wing twist.

danielhv · #3 10-11-2008, 03:49 PM

Quote:

Originally Posted by cnpeters

Plumbing the wing is important when drilling more than riveting. There is not much that you can do once drilled, though I would still try and ensure a straight wing before riveting. It sounds like you have it level, and I ran plumbs down each side and measured to this from the rear spar, then clamped the latter to brackets attached to the wing stand. This locked everything in place when I drilled. I have read some threads about whether this is really necessary in these factory CNC drilled assemblies, but I couldn't find anything beyond 3 people who drilled and riveted without checking for twist until when it was done. An N number of 3 doesn't cut it for reliable data in my book on such a critical issue as wing twist.

Well I guess I can be added to that list... because I didn't plumb when I drilled!

I just did the fishing line and used a digital level to make sure everything looked good...

Hope all is well!!!

So should I just rivet this thing together using the fishing line & digital level?

Vlad · #4 10-11-2008, 03:49 PM

Daniel I think two bobs on each wing is very good preventive measure. Watch constantly for twist either drilling or riveting, especially if you are working alone. Check plumb lines often, it's not that time consuming. You will be rewarded with straight wings anyway.

danielhv · #5 10-11-2008, 04:01 PM

ok... so let me ask... Is the measurement on each end of the spar supposed to be the same? If so, im a little confused because I have one end of the spar 1/2" higher than the root end because of where I ran bolts through the end rib to attach to the wing stand... if that makes sense... Or am I ok, and just make sure the measurements dont change during riveting?

Im lost if ya cant tell!

Transporter · #6 10-11-2008, 05:57 PM

Level your main spar (using the spar web as the horizontal plane) from end-to-end and side-to-side.

Hang one plumb line at each end of your main spar; I tied the plumb lines onto clecos at opposite ends of the same rivet line with good results.

Once the plumb lines stop swinging, use a rule or dial caliper to measure from the plumb line horizontally to the bottom spar (again, using the end points on a common reference line, such as a rivet line on the bottom spar). The measurements at each end should be the same. If you get a different measurement you've got some twist in the wing and the wing stand/fixture should be adjusted to remove the twist.

Hope this helps,
Mike

alpinelakespilot2000 · #7 10-11-2008, 06:20 PM

Quote:

Originally Posted by danielhv

Im ready to rivet the main ribs to the spars... I've got the fishing line across the holes pretty straight and even all the way down. Is that sufficient on a pre-punched kit? Or do I need to plumb the ends and stuff?? Just want to make sure I dont have any twist in the wing after I rivet the ribs... I've got everything cleco'd together and ready to go!

It sounds like you're talking about the skeleton, not the skins. When you are drilling and riveting the skins, you should plumb everything as the plans instruct. However, when you're just putting the skeleton together there is absolutely no reason to worry about plumbing anything. I suspect most builders rivet the skeleton up on the bench. Van's instructions were very clear on the wings for the -9, so I'd imagine that if you follow them for the -7 you should be just fine.

DaX · #8 10-13-2008, 07:14 AM

Quote:

Originally Posted by alpinelakespilot2000

It sounds like you're talking about the skeleton, not the skins. When you are drilling and riveting the skins, you should plumb everything as the plans instruct. However, when you're just putting the skeleton together there is absolutely no reason to worry about plumbing anything. I suspect most builders rivet the skeleton up on the bench. Van's instructions were very clear on the wings for the -9, so I'd imagine that if you follow them for the -7 you should be just fine.

Ditto what Steve said. I riveted the skeleton on the bench, then hung the wing skeleton on the stands, leveled, dropped plumb bobs, and got the rear spar within 1/32" of no twist. Then I attached and drilled my skins.

I will re-check plumb bobs before riveting the wings after the skins come back off for deburring and dimpling.

TerryWighs · #9 10-13-2008, 02:05 PM

Use two plumb lines at each ends of the main spar, and an additional "fishing line string from the aft rib holes on the outboard to the inboard ribs. When you jack up the middle of the wing to take care of the sag.... the fishing line should pass by the center of each aft rib hole.