67ccmustang

Hi y'all -
I would like to scratch build a simple replacement wing for a busted up SIG 4*-40.
As an experiment, I would like to make "slide-on" ribs as per full-scale construction. The trouble is, that I can't think of an easy way to accurately cut a square spar-hole through a stack of ribs.

Making good square cutouts in a stack of ribs is always a problem for me.

Another idea was to use an aluminum tube, or possibly a wood dowel, for the main spar. Then I could drill the spar-hole through the ribs. Not sure how well balsa ribs would glue to aluminum.


The 4*40 is already very light. I probably will build this experimental replacement wing very light, with minimal reinforcement, possibly use some functional bracing or cabling (sort of like a flybaby). The rebuilt plane will be very light and not intended for aerobatic - there wouldn't be any additional sheeting or wing reinforcement. (I don't fiberglass-epoxy the center sections of the wing of my non-aerobatic planes to save weight).

Thanks in advance for your thoughts....

-67M

Dsegal

I think you are looking at a lot of work for no likely gain. With a spar going through the center of a rib you will lose the structural benefit of the usual two widely spars, top and bottom, with a shear web to turn them into a strong beam. No one designs models any more with a central spar through the ribs.

Rodney

As Desegal says, a central spar is very weak and not recommended unless you totally sheet the wing. If you do that, the sheeting takes the place of the spar and adds a great deal of structural strength but still not as good as the conventional two spars (one top and one bottom) joined with shear webs.

67ccmustang

Thanks to you all for taking a swing at this one.

Of course it's probably a crack-head idea. But that what makes it fun!

All the kits I built before used the two-spars-and-shear-webs design. For me, the problem with scratch building this way, is that I can't seem to notch out the ribs very neatly to get a good fit to the spars.
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Just looking for some different method to try. I plan on building a flimsy wing, and will use functional external bracing. Not planning to pull any G's with this one!

later,
-67M

BMatthews

You may not plan on doing higher G's but invariably it happens.

Notching for spars is always a fussy job. I've found that you need to cut the notch to fit the actual stock you are using. Never assume that any wood is accurate to the nominal size that it was supposed to be.

Cut the notch or hole slightly smaller than you need and sand or file out to a snug push in fit. For holes in the center of the ribs be sure to make the hole just a HAIR loose in the vertical direction to avoid putting a lot of splitting pressure on the rib but a nice push fit in the fore and aft direction where the longer side grain will carry the SLIGHT pressure.

Stacking and bolting the ribs together is a great way to let you sand the ribs to a nice even sizing and make for a far easier, faster and more accurate way to cut all the spar notches at one time. Better yet is to cut the rib blanks slightly oversize using an oversize template (about 1/64 to 1/32 is fine) and then sandwhich the rough ribs between two accurate plywood templates and sand the ribs down to match the templates. Even with a straight wing be sure to number the ribs as they come off the stack and use them from #1 at one tip to #x at the other. That way any very minor differences are spread out evenly. When done this way and with a light friction push on the spars you can all but build the wing without glue and then just wick on some thin CA to bond it all.

vicman

My Feedback: (10)

I do mine similar to Bruce. All the ribs are lined/stacked up and sanded as one. I also cut a short piece of the material I plan to use as a spar and sand to fit with everything lined up. I also like to use dowel rod for the leading edge and fit it the same way. So far it has worked for me.

Laird SS

In order to sand a rectangular recess for a spar, try gluing a piece of sandpaper to a section of spar material and use that to sand the slot for spar. That's way I used to cut the 1/16 square slots for stingers on stick models about 35 years ago. The idea came from E.T. Packard who started Cleveland Models.

Good luck.

Bruce B.

hummingbird111

anyone have any pictures to post for an example?[]

dreadnaut

My Feedback: (5)

As far a gluing stuff to aluminum. . . CA works if you scuff the aluminum with about 180 sandpaper and ''paint' some accelerator to the al before applying the CA.