ARRRRRGH never again!

I just spent HOURS trying to align the wing in my Chipmunk fuselage project. I framed up the wing and fuselage seperately thinking I would insert the wing in the fuselage, jig everything square and glue it in place (per the instructons). Bad plan. any little adjustmente in any one direction would upset everything in the other 5. Now I understand why I see the pictures of the experts building the wing AND the fuselage together in the same jig. According to the Robart Incedence meter and measuring ruler I'm within 1/2 degree incedence and thrust line and square to about 1/16 inch but that is as good as I could get it after a LOT of trying.

I'm working on a Fancherized Twister and will be in the same
position The wing is framed seperately from the fuselage and the fuselage is a sort of trapezoid (as you know) so squaring the thrust line with the wing and stabilizer incedence is going to be a challange. None of the fuselage edges are parallel to the thrust line. Any suggestions would be appreciated.

Use a ruler and pencil and run a reference line parallel with the engine bearers.

>Use a ruler and pencil and run a reference line parallel
>with the engine bearers.
>
>Tom

...yeah, did that
Actually I started with a line that passsed as closely as I could define it through the centerline of the existing wing cutout. The new engine bearer is extended all the way back into the wing cut out parallel to that reference line. The new engine bearers are built as a "crutch" with the balsa divider grain perpendicular to the engine bearer itself. After the crutch was in place and the plywood doubler on I clamped the engine in place with a long straight edge in place of the propeller and drilled the engine mounting holes. That gave me a nice long reference line to make sure the engine is centered on, and square to, the refernce line. So far, so good.

But the actual "jigging" and clamping - holding the sub assemblies (the fuselage and the wing) in alignment in 3 dimensions while they are measured and glued without "dinging" or denting the parts is a bit more problematic. I did end up making some styrofoam "V" blocks for the Chipmunk but that plan had some flaws too: The very fact that the foam is soft enough to be easy on the balsa wood structure also means it easily deforms and doesn't necessarily hold the parts in a rigid alignment.

I think that (for me at least) simple box fuselages are easier to build lighter, stiffer, and straighter than profile fuselages...

First, the thrust line problem--

I process the plane with the wing nearly complete, the best thrustline reference is generally the top of the fuse/engine crutch. install the wing into the fuse before adding the top block. do this upside down on the flat. On the CHip, the top is straight. (JVL Chip)

For squaring, here is what I do.

I have a modular furniture work surface that is 4' square and flat.

Mark a centerline diagonally. THen I geometrically layout a perpendicualr line to that in the rough area of the wing TE. I then ca square blocks with the forward edge on the perpendicular line.

I do the same with a line positioned for the stab TE.

First install the wing--by simply setting the fuse on the Centerline and sliding the whole assembly aft till the wing squares up on the two blocks.

I also place equal height blocks under the wings so the assembly is resting level in roll, on the blocks square, with the fuse on centerlins.

After it is cured, do it again but leave it blocked as for the wing install and slide the stab back against its squaring blocks.

It is best to do the stab after the blocks are installed to keep the fuse from twisting. THis complicates the blocking somewhat but the same process applies.

With the blocks glued down, there is no fiddling with anything, if the wing is touching the blocks, its square as long as the fuse remains on the centerline marks.

Its faster to do this than to write it up.

FWIW