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Thoughts and criticisms on this "tailpennage" concept..

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markaeric

Well-Known Member
Joined
Jul 31, 2015
Messages
346
Location
Wichita
Hello, everyone! I have often come across this forum while searching for stuff online, but never had anything to post until now. I'm hoping to get some of your thoughts on this little concept I've had rattling around in my head the past several days. I don't know if such a thing already exists or if it has at least been discussed, but I can't seem to find anything. If it has, then I'd appreciate it if you would point me in the right direction :)

The premise for the concept is to eliminate empennage but maintain some semblance of tail control surfaces on an otherwise "standard" aircraft layout. It may also allow the horizontal surfaces to be used as elevons. Potential uses would be with high wing ultralight to LSA class aircraft. Well, at least if it's plausible that is :emb:

6aiyTng.jpg

First off, let me apologize for the crude MS Paint drawing, I hope it still gets the point across.

The tail surfaces are stabilator-like, high AR symmetrical airfoils. The horizontal stabilizers start somewhere along the span of the wing at the trailing edge, while the vertical stabilizer near the bottom aft section of the fuselage, with all of them canted towards a single point where they terminate. The logic is that this arrangement would assist in providing some of the much needed structural rigidity without having to beef it all up to the point where you might as well stick a a normal tail on an empennage and call it a day. So it has some inherent structural strength, but there's still plenty of issues, isn't there?

Right off the bat I see that the tail cone and airfoil ends would likely see a variety of considerable loads, though these would seem similar to the thrust and lateral/torque loads on car wheel hub bearings. Maybe the tail cone is less of a concern than the forces at the airfoil ends? A possible solution would be to slip the airfoils over tubing upon which they could longitudinally pivot (with something like a low friction bushing between them) and have those tubes hard mounted at each end. This would eliminate the bearings at the tail cone and probably be more structurally robust. But then that probably leads to a thicker airfoil. Is that a deal breaker? I don't know.

Another issue is torsional stiffness of the airfoils. If flutter was an issue even for aircraft with a chunky empannage, what chance does an airfoil with a large AR have at avoiding it, especially since one end is free? I was wondering if it would be possible to take advantage of any lack of torsional stiffness by anchoring the aft end to the tail cone section, and basically make the airfoil twist/warp, sort of like Kaman does with their helicopter rotors that aren't attached to a conventional rotor head. Of course, the downside here is that the closer the airfoil is to the tail cone, the smaller the pitch changes. Well, that and it might take a bit of muscle to get them twist in the first place, unless you have tabs do the hard work.

Then there's the substantial amount of sweep. I really have no idea if this would be a problem.

I am curious about how well it would work as an elevon. Even if the airfoils had to be chunky for structural reasons, I'd imagine there would be some weight savings and lowered complexity over a standard empennage + tail + aileron configuration.

This post ended up being a bit longer than anticipated, so I think I'll shutup for now :speechles

Any thoughts would be appreciated.

Cheers,
Mark
 
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