All,

I was looking at a set of plans for a cosmic wind - a profile with about a 42 inch span. What I am questioning is that there were two spars 5/16 by 1/4 and the spars twisted as it went further out on the wing.

Is this advisable? I mean would you be stressing the wing and basically building I a warp possibly?     

I would replace them.

Do you mean twisted, like the driveshaft on a '32 Ford that's had its 85 horsepower engine hot-rodded to 200 horsepower?

Or do you mean bent, like a guardrail that stopped a hot-rodded 32' Ford with a powerful engine but with the original mechanical brakes?

And are the two spars placed symmetrically, so that one is twisted clockwise while the other is twisted counter-clockwise?

No matter what, a single 5/16x1/4 spar doesn't have nearly the torsional rigidity to affect the wing of a 42-inch wingspan CL plane.  So there's something else in the wing structure -- either wing sheeting, or possibly the wing covering -- that will completely overpower any twist imparted by the spars.

If the wing has LE sheeting and shear webs, that "D" tube will hold the wing in position once the glue dries, even if individual pieces of wood are held in stress (so be sure it's straight on the building board!)  Even if the wing has no sheeting, it'll be floppy in torsion until you cover it -- then the covering will hold the wing in place (and let the wing be adjusted later, which is nice).

Finally, if there are two spars twisted in opposition, then as long as you choose matched pieces of wood, either by selecting spars that seem evenly matched to you or by cutting them out of a single sheet that does not vary much across its width, (which is overkill but what I would probably do) then they'll cancel each other out.

Post a picture of the plans, or a link, or tell us the name of the designer so we can do a search, but I think you're fine.

All,

I mean twisted. SO the spar starts out in the middle as parallel to the leading edge and trailing edge faces.  like so | | |  - top spar.
                                                                                                                                                                      | | |  - lower spar 
then as it gets to the tip the spars twist, and are not parallel to the leading edge and trailing edge faces  - like so    | \ | - top spar at tip
                                                                                                                                                                      | / |  - lower spar at tip
                                                                                                                                                                       
Hope the diagram  helps

Steam is a friend

Ken

You are correct - the spar twists as it moves out on the wing - the spar twists - it is straight but twists from perpendicular. I will wet the spars and twist them into shape.  I need to get a photograph of the ribs - It was plan that was done by Mike Garmon.

There are two spars, upper and lower  both twist - I use an Adjusto jig so all my ribs are held straight as I build and I can attach both spars without taking the wing off of the jig


Thanks,

Mccoy40