osxuser

osxuser

Well Known Member
I'm pretty slow, but I think I should have figured this out by now. I spent most of yesterday building the jig for the -4 wings that already about half done (two builders ago). I finally settled on -4 (not rocket) and full length wings, still thinking about expanding the tanks, but I think the wings already too far along for that. What I'm trying to figure out is how do I know where to hang the bottom spar? I got the hanger set up for the main spar, and still working on clamping that level, but I can't find the dimension for where the rear spar is supposed to be hung.

I know i'm supposed to level the spar, which is weird enough with the web sitting on the angle at the tip, and the buildup part sitting on the angle at the root (I put the angle at the same height, not anticipating that thickness differential.)

I know I need to square the closeout spar to the main spar through the jigging holes. But how do I know how far down to mount the closeout? I have two sets of plans, one from the early 90's, and one from '02... can't find it in either.
 
The procedure on the -6 was to attach the ribs to the front and rear spar to set the distance. Then, with the main spar leveled in the jig, you could roughly place the rear spar supports. Next, you used plumb bobs to position the rear spar in location relative to the main spar (laterally and up/down relative to the airfoil) and shimmed and clamped the rear spar onto the spar supports. The ribs set the distance between the spars. It's easiest to position the rear spar supports a little low and shim up to them. Don't worry about jig perfection; you're not flying the jig.
 
Don't forger you will have to put a support in the center of the wing between the floor and the rear spar to keep the wing from sagging in the center and keep it level. If you are using wood for the jig, you will have to keep checking it to make sure it doesn't warp and everything stays level and plum.
 
I see the center support, looks pretty simple, I don't even see anything supporting the closeout spar on their jig other than that single piece to prevent the center from sagging But their way of clamping seems pretty good.

Is there any reason to consider supporting the main spar in the center until the time comes to skin the top?

So first shim up and clamp the main spar, then set the closeout spar up with the ribs. And then on level attach another 4x4 to the floor, and support the center of the closeout spar with more shims.

I don't know why, but in the -4 build book, none of the stuff is mentioned that I can find. It just kinda says... build the jig.
 
Stephen,

Never heard of a "closeout" spar. It's a rear spar. Just look at the entire assembly as a ladder up on edge. The rungs (ribs) will keep the legs (front/rear spars) parallel. Push up on the bottom leg in the center, and the top leg will move up as well. So no, you don't need any support in the center for the main spar. A 2x4 will work just fine for leveling the rear spar. Tap a 1/4-20 hole in the top of the 2x4 and insert a hex head bolt. The head of the bolt will bear on the back of the rear spar. Run a fishline from end to end on the rear spar, then back the bolt out until all the bow is removed. Your plans should show the location of the holes in the main/rear spars thru which you drop two plumb lines.

Tony
 
Tony Spicer said:
Stephen,

Never heard of a "closeout" spar. It's a rear spar. Just look at the entire assembly as a ladder up on edge. The rungs (ribs) will keep the legs (front/rear spars) parallel. Push up on the bottom leg in the center, and the top leg will move up as well. So no, you don't need any support in the center for the main spar. A 2x4 will work just fine for leveling the rear spar. Tap a 1/4-20 hole in the top of the 2x4 and insert a hex head bolt. The head of the bolt will bear on the back of the rear spar. Run a fishline from end to end on the rear spar, then back the bolt out until all the bow is removed. Your plans should show the location of the holes in the main/rear spars thru which you drop two plumb lines.

Tony
Click to expand...

Yeah, I saw that drawing with the vertical fishlines, the only thing that had me confused is the -4 plans don't say anything about a center support that you pointed out, and they had the same type supports for the closeout that the main spar has.

I hear rear spar a lot, but technically the rear spar of an RV is a closeout (where the wing ends), just like a main spar, you don't hear it called the 'forward' spar. It's a descriptor of what the function of the spar is. Technically rear spar is correct because of it's location, and closeout is correct because of it's function.
 
The plans don't say a lot about any of the jigging, except I seem to recall that I had a nice drawing for the fuselage jig for the -6. I think the center support idea came from the RV-ator (it's worth getting 'xx Years of the RVator' for little things that were helpful but not in the plans). Van had suggestions for jigs that were pretty simple but a lot of builders get 'jig-happy' and built amazing jigs from aluminum or steel. But Van's point was always that the jig did not matter; it was just something to hold parts in alignment during assembly. So, jig dimensions and materials are not really critical as long as it's fairly stable and the assembly being worked on can be held in alignment during the assembly process.
 
Makes sense. Yeah, mines nothing fancy, but I was just trying to figure how it works. It's even more complicated for me since my wing kit is already halfway done, and nothing is marked as to where it goes, which wing is right, left, and which side is up down, or inside or out. It's a puzzle.
 
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