Wing Warp???

Thought I would share a pic of a fix on the wing that I posted earlier on my Magician. I think the wing warp is fixed about as good as it is going to get and will will cover the wing this weekend. Not sure if the fix will be permenant. I took Bruce Hunt's advice in my earlier post. Once I got it straightened out, I cut and glued webbing in between the ribs in the trailing edge. So far, it seems to be holding well.

John, I have a "Twister" wing with the same predicament. Am still not sure what the next step will be, as I have steamed it over a Dutch Oven (24" length segments) under a 'tent', but it returned to its 'unnatural' shape.
Hmmm, maybe that's why they call it that.
Going to steam again, with shims clamped in place to coax it the other way, I'm sure that'll work. I also noticed the crimped copper tubing at the leadouts/bellcrank. Those will be rectified presently!
I will be adding the Trailing Sheet Shear Strips (webs) also.
Thanks for the pic, it made up my mind.

>Thought I would share a pic of a fix on the wing that I
>posted earlier on my Magician. I think the wing warp is
>fixed about as good as it is going to get and will will
>cover the wing this weekend. Not sure if the fix will be
>permenant. I took Bruce Hunt's advice in my earlier post.
>Once I got it straightened out, I cut and glued webbing in
>between the ribs in the trailing edge. So far, it seems to
>be holding well.

John, I could see in this photo that your spar webs have the grain horizontal, and you did the same on the TE. The spar webs should most certainly have vertical grain, and I would suggest the same for the TE. In fact, I did, in my post on that thread, which was above and posted before Bruce's. The objective of the webbing is to prevent spanwise sliding of one spar, relative to the other, as well as preventing the two spars from changing distance apart. Magical bits of balsa, if the grain is going the correct direction. Unfortunately, of little value, if the grain is spanwise. Steve

Steve:

In the June 1992 Model Builder there is a column called Model Design and Techincal stuff by Francis Reynolds where he discusses shear webbing. What he says is that based on mathematical proof the grain should be at an angle between the spars, second best is horizontal and vertical is actually the worst. He then adds that for the size planes we build the difference between the two is small enough to be insignificant.

I always thought vertical was best until I read that, since then I have installed my shear webs cut at a 30deg angle and for overkill reversed the angle on the other side. Hopefully one of the engineers on this site will be able to confirm this or explain why it is false.

When I built my free flight planes, I always used the shear webbing perpendicular to the spars or in a warren truss set up. Never had a wing warp that way. When I went parallel, always warps. So, I agree with Steve on this, vertical webbing. Not all engineers know what they are talking about. Seen many buildings fall down and strange things in cars and on ships. Remember, the top graduates don't work for the lowest bidder.

Hey Steve,

Very interesting comments, espeically when you consider that I AM AN ENGINEER. Cheimcal engineer, that is. Can't say as I remember a whole lot about stress analysis; only took one course that even resembbled that kind of stuff. Spent most of my time in school trying to figure out how to clean the goop out of the good stuff...i.e., distillation and other mass transfer type operations. Now, I spend most of my time at work evaluating what happens when you burn stuff and what kind air pollution it creates. Not much help when it comes to building model airplanes. Ask something about fuel components or mixtures and a chemical engineer might know or be able to find out.....

One thing that I discovered quite some time ago, and as evidenced right here on the forum, it is the "craftsman" in any given endeavor with his many years of hands on experience who probably knows the best answer and the hows and whys to many of the everyday practical problems in his given field of expertise, not the darned engineer who may have designed thing in the first place. Okay....I'll get off of my soap box.

From my extreme lack of engineering knowledge on this subject, it would just make good sense that one might achieve a stronger structure, placing the trailing edge webs with grain of the wood crosswise, i.e., "normal" (got to slip in one those engineering terms) to the direction of the stress. However, with the size of scale encountered with such a small structure, and the small contact area of the 1/16th inch thick webbing strips in this case, and the low compression stregth of balsa wood, I would have to wonder if it would make any real difference. On the other hand, I have seen first hand the significant increase in strenth gained by laying a number of pieces of sheet balsa crosswise for the bottom of a fuselage instead of laying it as one piece with the grain running parallel to the length of the fuse.

As far as it goes on the direction of the grain for the spar...I could reply with easiest answer there is, "that's the way it came in the kit". And, that's the way Jim Silhavy designed it. Having now given it some thought. I would have to say that I am not sure. For example, it would seem that the purpose of the 1/4 x 1/4 top spar is to help primarily to prevent motion in the up and down direction, which is where it would seem that the most stress would be applied in operation, rather than to prevent motion in the front to back direction. And by the way, the Nobler uses a similar type of spar, only with no top cap spar, but with a sheeted leading edge. Finally, and perhaps most significant in the real world, where in the world would one get a piece of balsa wood long (wide) enough to make a one piece spar with the grain running vertically??

In short, the answer still is I don't know, but I'll let you all know how it works out, or not, in this case. Thanks for the comments and hope I didn't turn anybody off with my little tirade here.

Chemical Engineers do make the best "solutions"!