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Unusual Tail Wing Design

Posted: February 25th, 2016, 6:49 pm
by Halo2552
So we had a plane we built from a guide online, used it at regionals, and it worked to win us a medal. Our plane design was the from the guide many people have found online by googling "wright stuff". But we are now looking to go on a more custom route to improve our plane. Our first plan is make cambered wings (Which if anyone has a guide or advice on dimensions of cambered wings, I would appreciate if you shared it). The second thing we noticed is our tail seemed to be kind of small. Maybe it was a problem with it's angle, but I think it wasn't getting enough lift.

So my main question is why not just make a tail that is the max size? Isn't more lift better? Wont that move my center of gravity closer to the center, but also allow me to carry more weight? At the last competition one of the judges said my tail should be 18% the surface area of my main wing, which seemed way to small.

I guess another way to ask this question is what problems would there be with a plane like the "Boomerang Plane" I've never seen one before, so there must be something unfavorable about it.

Re: Unusual Tail Wing Design

Posted: February 26th, 2016, 5:15 am
by bjt4888

You reference "wright stuff" in your post while the boomerang plane is a glider. Is your question meant to be about the elasti launch glider event.

If you give more info regarding your current glider (ex. Exact web link to the plan, longest flight, weight, height of the ceiling where longest flight was accomplished) i can give you very specific help. There are very good kit gliders that will do 22 to 29 seconds in a typical 30 ft gym ceiling height. If your duration is not already on the high end of this range, you should use one of these kits and not build custom.

Brian T.

Re: Unusual Tail Wing Design

Posted: February 26th, 2016, 10:46 am
by jander14indoor
Assuming you are talking about Wright Stuff, be careful about talking to experts who don't have experience with indoor freeflight. The constraints on these planes are sufficiently different that "conventional" wisdom doesn't apply without appropriate adjustment. That 18% comment isn't near correct, for example.

For stability reasons (that I only remember the answers to (and the math/theory is definitely college level engineering)) whenever possible, you are more efficient by adding surface area to the wing and taking it from the tail. And this will typically result in small tails that lift downward and a cg around 20% back from the leading edge of the wing! This is the solution you see in all conventional (wing in front) man-rated planes and most RC planes.
HOWEVER, the rules for indoor planes almost always impose limits on wing area without constraining tail area much. As a result, yes you can get more total lift (won't be quite as efficient) by using a tail as large as the rules allow and moving the cg very far aft and flying with a lifting tail that is well back from the wing. Despite the conventional experts, this CAN be made stable.

So, what do you do. The SO rules don't allow anything as extreme as that boomerang glider (and that is a tough stability solution) but the best planes will have wing and tail as close to the maximum size as you are comfortable without getting tiered by the ES (the added area of an extra mm or chord or span will not offset being second tiered for a construction violation!). It should be a fairly long plane and should have a cg around or behind the rear wingpost. And ALL of this while building to minimum mass.

For more ideas on things to try or focus on, dig around the wiki if you haven't already.

Jeff Anderson
Livonia, MI

Re: Unusual Tail Wing Design

Posted: February 26th, 2016, 12:13 pm
by _deltaV
We have had a lot of success with the dimensions of the aircraft at their limits. From another part of this forum someone suggested 5-6% camber as anything more would cause drag instead of lift. Our plane is fairly long, almost 2', and the CG does sit a little farther aft than what the veterans suggest. The benefit of a large rear stabilizer is that you can change your climb rate and mess with stalling by adjusting your stabilizer. As you may have already read, angling the stabilizer so one tip is higher than the other is one of the ways to get the plane to fly in a circle. The way this works is the lift from the stabilizer acting at an angle offset from lift of the wing causes the plane to turn. The larger your stabilizer, the less dramatic the angle between it and the wings has to be. A third benefit is a larger stabilizer does exactly that: it stabilizes the plane and helps it resist rolling one direction or another. If you use dihedral panels on the wing that also helps a lot in terms of stability, but a large rear stabilizer definitely helps.

Re: Unusual Tail Wing Design

Posted: March 4th, 2016, 4:12 pm
by Halo2552
Brain T, sorry, I should have been specific. I didn't realize division B was also doing Elastic Glider, but I was talking about talking about Wright Stuff. I was just curious how a glider like the one I specified would work if it was paired with a propeller.

Jander14Indoor & dfaris, thank you for the replies, this information is very helpful.