Will dihedral on tail help stabilize a rocket glider

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BABAR

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Back to work on biplane scissor wing glider

Upper and lower wings will be straight and planar, no way to do wing dihedral.

Would putting dihedral on horizontal stabilizer help stabilize?
 
Maybe. You're talking about roll stability in glide? Seems to have worked for the Crusader SW. The original SWT had no dihedral in either surface, but had a pretty big vertical stab for it's size. Maybe that's a way to get around it.

kj
 
Maybe. You're talking about roll stability in glide? Seems to have worked for the Crusader SW. The original SWT had no dihedral in either surface, but had a pretty big vertical stab for it's size. Maybe that's a way to get around it.

kj

I thought the crusader had anhedral on the tail.
 
Maybe. You're talking about roll stability in glide? Seems to have worked for the Crusader SW. The original SWT had no dihedral in either surface, but had a pretty big vertical stab for it's size. Maybe that's a way to get around it.

kj

Sorry, should have been more specific. Yes, I am talking about roll stability in glide.

I get a little confused about "how" the vehicle, in transition from rocket mode in boost to glide mode in descent figures out which orientation of the vehicle is "up". Kind of figured in the Scissor Wing Transport the fact that the wing was only on one "side", which happened to be the "up" side had something to do with it. My BiPlane version will have wing surfaces on the top AND on the bottom, and they will be flat/planar with no dihedral at all. I know I have seen Pod gliders where the vertical stabilizer was on the "down" side of the glider, so I don't think that's a contributing feature, but there is a lot I don't understand.

So I was wondering if putting dihedral on the tail might help out.
 
I thought the crusader had anhedral on the tail.

The fin on the pop-pod points "down" while the two on the glider point "up".

I'm guessing you will have some sort of pup-op elevator on this double swing wing model? That goes a long way into telling the glider which way is up during transition. Good vertical stab area will help it keep that orientation. If it were me, I'd try to have something like the Crusader with good effective tail volume.

kj

estes-1961-crusader-swing-wing-glider.jpg
 
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Upper and lower wings will be straight and planar, no way to do wing dihedral. Would putting dihedral on horizontal stabilizer help stabilize?

Are you going to keep the wings in-line, or use stagger, top-forward or bottom forward?

The tail is usually not as large as the wing, so it's impact at the back end with a much lower aero force, and usually in the downwards direction to trim the wing would not have as much roll authority as the main wing itself which is supporting the majority of the weight near the c.g. of the glider. With the elevators trimmed nose up, the tail is actually a down force not a lifting force, a large dihedral tail would act contrary to rolling stability since it is actually acting like anhedral, I get turned upside down sometimes thinking about it. Just size the vertical tail big enough for directional stability and you should be good. You might be able to add some small wing tips that have a little dihedral over a portion of the wingspan, if that won't interfere with the scissor mechanism, might work for a split scissor where both sides are swept aft during boost and swing forwards for glide.

One idea, is to make some 1/2 or 1/4 smaller scale gliders to try out your wing/tail configurations, and hand toss them to get them balanced, then use them as parasite gliders on something like a Big Bertha to give them a little altitude to see how they glide. When you are happy with the basic wing/tail/balance of the parasite gliders, then you can size them up and figure out how to fold the wings for the full-size scissor wing model.
 
Seconding what Glen said, since the tail force is inverted you need anhedral to promote roll stability. Dihedral in a conventional tail is actually anti-stable and the Crusader design is just a bit whacked. It works because it's a high-wing configuration with the CG located well beneath the wing plane, which provides restoring force (kinda like the ultra forgiving Cessna), enough to overcome the tail's effect.

If you have a zero-dihedral biplane scissor with one wing above and one below, you lose the high-wing benefits and roll stability is gonna be pretty hard. Best hope is large tail volume and significant anhedral. If it shows a stall tip-drop you can play with sanding in some washout to reduce the angle of attack of the dropping wingtips.

A real wild hare idea (not original, i've seen this done) is to release a small weight on a boom that will swing down under the CG at ejection to move the CG downward. If you're sending the pod out the back you can arrange a release clip easily.
 
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