Why does everyone makes shear webs the way they do?

I have a couple more questions:

2. Note that in my other current reality I am a Prof. of engineering, specifically materials eng. with an emphasis on adhesion, gluing and composites and much work with wood. I wonder why everyone makes shear webs the way they do. The standard method is to put the grain running vertically. For shear resistance the better way would be as:

                          wing center
     ______________^__________________top of wing spar
     ///////////////\\\\\\\\\\\\\\\\\\\
     __________________________________  bottom of wing spar

the shear web wood grain should be at 45 degrees and no gap between the shear web and the bottom spar...ASCII being what it is. This would give maximum shear resistance to the standard loading of a HLG and might reduce the problems that folks are seeing with too vigorous a launch when their fingers get hung up on the pegs. Note that there would be minimal shear resistance to shear mode in the case of vigorous outside loops, but then how much is that a problem?

From Don Stackhouse:

Actually, that is a problem. One of the other common major flaws in launching technique is moving the model in an arc during the throw. This results in upward motion during the initial portion of the throw, with a resulting downward load on the wings. The wing has to have significant negative "G" strength to withstand this.

The other reason for keeping the grain vertical is because the main function of a shear web in a built-up wing of this style is NOT to carry the shear load. Yes, the shear load is quite significant and very important, but preventing buckling of the compressively-loaded spar cap is even more important. Keeping the grain of a balsa shear web vertical is the best way to support the spar cap and prevent buckling.

Alternately make the shear web out of 1/64 in. thick 3 ply plywood and run the majority (outside plies) of the grain in the direction shown. That should be about as light as the balsa and much stronger (SWAG). This would work best with a shock absorbing adhesive like the aliphatics and not CA. Just a thought.

As a matter of fact, on the 2-meter Chrysalis the inboard panels use a full box spar, with spruce caps and plywood shear webs, and with the grain of the shear webs running on a +/-45 orientation, just as you mentioned above. The strength and stiffness of the ply is sufficient to handle the buckling problems in this orientation, so we can afford to put more strength into the shear requirements. It's a bit heavier, but does wonderful things for both strength and stiffness. To make all of this practical we also had to develop some entirely new ways to manufacture and install the shear webs. As a result, this will be an extremely easy to build model in this regard.

We're very excited about this model! A lot of other folks are as well, we've been getting a lot of e-mails requesting updates. It shouldn't be too much longer, I see a "light at the end of the tunnel", and it doesn't look at all like the headlight of a train! Keep checking the website, we should have some more info posted there when we're about ready to start shipping them.

Don Stackhouse @ DJ Aerotech
djarotec@bright.net
http://www.bright.net/~djwerks/