F-704 bulkhead spacing

[BJohnson]

I'm getting ready to match drill the F-904H side doublers to the F-704 bulkhead assembly and have a few questions. This will lock in the spacing between the for and aft F-704 assemblies and defines the gap where the wing spar will fit. The instructions say to ensure that this gap is 1.438" exactly. I have blocks and the 2 aluminum spacers that match that. However when I put a clamp on the ends of the spar and measure the tickness, it comes out at 1.447 inches. If I match drill at the 1.438 like the plans state, it seems that the interference will be too great to insert the wing spar when that big day comes.

What have others done here?

 

[plaurence]

I primed my wing spars. Thus the dimesions were greater than Van's. . I machined aluminum spacers to match.

Peter Laurence

 

[Don]

F-704 Spacing

Brice,

I spent a week sweating this point and I didn't find a lot of useful advice. As I recall I measured the spars and added .004 (figuring that would be a really tight fit) and got something very close to Van's recommendation. I made up blocks to fit between the 704 halves based on Van's recommendation and riveted things together.

I'm almost ready to insert the wings - I'd hoped to do them today but it won't happen. It probably will this week. Those blocks are tight so I'm planning to bevel the edge of the spars, per Van's recommendation and liberally apply Boelube to the mating parts and hope for the best. If you want I'll let you know how it goes in a couple of days.

 

[alpinelakespilot2000]

Brice-
I found 3 pieces of 1/2" baltic birch plywood added up to exactly the 1-7/16" that Van's called for. The spars slid right in with just a little Boelube and some up and down motion at the wing tips. I beveled only very slightly and probably didn't even need to. The extra 1/100 that you seem to have isn't going to make a difference in my opinion, so I'd say don't sweat it. I really haven't heard of people having a hard time getting the spars in, though I'm sure there are a couple. Good luck.

BTW: Where are you at in Seattle?

 

[BJohnson]

Thanks all for the comments. No matter how I clamped up the spar assembly, I still measured 1.447 or so, which is about 1/10 greater than the recommendation. So I ended up shiming my blocks with masking take to match the width or slightly greater. I figure the wing bolts can pull out a small oversized gap, but an intereference fit of 1/10 would be tough to overcome when installing the wings. I then matched drilled everything. I guess when it comes time to rivet, if I take out the shims and set the blocks to 1 7/16, the gap could be closed at that time.

Has anyone had any interference inssues installing the wings?

Steve, I live in Federal Way.

Don, good luch on the wing install. How 'bout a report out when it is done.

 

[alpinelakespilot2000]

I have blocks and the 2 aluminum spacers that match that. However when I put a clamp on the ends of the spar and measure the tickness, it comes out at 1.447 inches. If I match drill at the 1.438 like the plans state, it seems that the interference will be too great to insert the wing spar when that big day comes.

Brice-Not to put too fine a point on it, but the difference between 1.438 and 1.447 is about 1/100 of an inch, not the 1/10 of an inch you seem concerned about. If it were the latter I would be concerned too. Again, though, I would'nt be concerned at all if the measurements you provided above are accurate. A layer of tape would definitely take care of it. Good luck though.

 

[BJohnson]

Duh, your right. 0.01 still seems like a lot, but I am probably wringing may hands over nothing.