more glider design questions

[Bob Chiang]

First of all, thanks Ollie for your comments regarding polyhedral angles for the side arm launched glider I'm working on. The wing is almost finished, and as I begin working on other parts of the model (balsa pod fuselage with carbon tube boom and cruciform tail), I'm coming up with loads of other questions I hope someone can help me with.

I built the wing with a straight center panel, and tapered outer panels. The leading and trailing edges of the outer panels both sweep so that I could keep the spar in a straight line and maintain the same high point on the airfoil. Aerodynamically, should I have kept the trailing edge straight? I haven't joined the panels, so I could still revise it without too much trouble.

I am aware of tail volume coefficient: how do you decide between a longer boom and smaller surfaces, versus shorter boom with larger surfaces? Are built-up tails not suitable for side arm launch gliders?

Why are most wings attached with (a leading edge peg and) a screw through the trailing edge instead of near the spar where the strength is?

If I do join the wing to the pod with a screw near the spar, would there be any advantage to ending the pod under the wing rather than at the trailing edge? Or maybe shaping a streamlined filet/tail cone from spar area to trailing edge?

Thanks in advance,
-Bob

[Ollie]

There is nothing wrong with a straight spar.

There are two advantages and two disadvantages to a long tail boom. The longer tail boom with smaller tail surfaces has less parasitic drag and better yaw and pitch damping. Damping increases as the square of the tail moment arm length and benefits launch height. The disadvantages are more nose weight or a longer nose required to balance and more tail boom flex.

As for wing mounting, a strong wing index is essential to prevent the wing pivoting on a single wing mounting screw. Two well spaced screws or a screw and a peg are the way to go.

I like a streamlined fillet under the wing.