stunthanger.com
Building Tips and technical articles. => 1/2 A building. => Topic started by: minnesotamodeler on August 06, 2011, 08:33:11 PM
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Wotcha think of this one? Tiny, tough, fast, stunt/combat trainer.
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I think I'm in love. I want one
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I think I'm in love. I want one
A kit may soon be available. Flight tests first.
there's a story behind its concept; I'll relate it sometime.
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Tis different, I like it. H^^
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A few details: Uses the droopy diamond airfoil; low aspect 18" span wing makes it about impossible to fold it up; extra tall fuselage right at the weakest point (wing LE); upper MM beam extends all the way back over the stab. nothing's unbreakable but this should make it a challenge anyhow.
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Test flown; the "unbreakable" part was fully tested and it passed with flying colors...which is the best flying it did all day. A little redesign is in the works...twitchy and sluggish both, a bad combination. Gonna have to sacrifice some "cute" factor and bring it back a little closer to conventional.
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I thought that tail was kinda odd. Of course, I'm not so sure about the airfoil, either.
What are you planning to change first?
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I thought that tail was kinda odd. Of course, I'm not so sure about the airfoil, either.
What are you planning to change first?
Gonna lengthen the fuselage aft and move the tail feathers back some...push the engine back as close to the wing as I can get and still have minimal room for a tank...increase the span a couple inches, leave the chord alone which will bump up the aspect ratio a tad. Loses some of its "cartoon airplane" look I was striving for, but performance has to come first.
Now I'm trying to decide, do I butcher this one up to try some of the changes or build a whole new one? It's just too cute to cut into, but on the other hand it's too inferior in the air to enjoy flying as is. What to do, what to do...probably both.
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Before you do that, can you fix up the leading edge of the airfoil somewhat? All those sharp edges where you want air to be flowing smoothly would cause turbulence where it doesn't belong, which certainly could account for "sluggish and twitchy at the same time".
If you were up to hot-wire cutting foam, I'd suggest taping on some prosthetic leading edge material with shipping (or plain old scotch) tape. Then if it didn't work, you could take it off easily enough.
OTOH, the stab location could be doing the same thing to you -- it looks like the stab wants to duct the air in a specific direction, which may make elevator response funny. But I don't carry a CFD machine around in my head, so I could be totally off base.
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Tim, the Droopy Diamond airfoil has worked extremely well in several other applications, both stunt and combat (slow speed and high). It's not "just" a diamond airfoil: The diamond-shaped ribs are deliberately spaced far apart to let the covering sag between them, producing a more standard airfoil in cross section between the ribs. Ribs jutting up then serve as "fences" helping direct the airflow. I don't think that's causing any problems on Stumpy since my other designs using it are very successful. see pix.
The stab location on the other hand may well be the culprit...if it were further aft, OR down in line with the wing, it might fly very differently.
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Tim, the Droopy Diamond airfoil has worked extremely well in several other applications, both stunt and combat (slow speed and high). It's not "just" a diamond airfoil: The diamond-shaped ribs are deliberately spaced far apart to let the covering sag between them, producing a more standard airfoil in cross section between the ribs. Ribs jutting up then serve as "fences" helping direct the airflow. I don't think that's causing any problems on Stumpy since my other designs using it are very successful. see pix.
I get it now -- interesting. That means you could do a droopy stretched hex, too, or other "droopy" shapes.
I think you could move the stab back and/or down without losing much, if any, of the looks of the plane.
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Twitchy but sluggish might indicate way too sensitive controls coupled with a too forward cg. I doubt that you would design it that way, but just a thought.
How about moving the tail up? Get it out of wing wash, but retain the "cute". %^@
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Well, l've gone the other way...I cut the tail out this AM and reinstalled it down in line with the wing. Just to see what difference it would make. Haven't tried it yet. Moving the tail up, I guess you mean near the top of the rudder--might be another "trial" to try.
the controls are plainly too sensitive, that's for sure. I foolishly used a Perfect 1/2A alum. BC I had laying around because it was already strung with leadouts, etc. Reminded me why I started using 3" BCs in 1/2As in the first place. And the CG is too far forward I'm pretty sure. Lead on the tail will remedy that, on this one anyhow.
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Pix of the mods. Flew it today, it is much improved but still not where I want it. Not quite as much an adventure flying it now anyway. All I did on this one was move the stab down to inline with the wing, and shorten the nose to move CG back some. Result: More responsive, less twitchy, but still needs more. I'm drawing up another with a little more wingspan and a little longer fuselage aft.
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Try tying the stab into the wing trailing edge (I'd do it with scraps and shipping tape). The gap there is probably making odd things happen.
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Good point, thanks, I'll give that a try next time out.
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I really don't see anything basic with the design that should cause problems. I think you can find a solution to whatever ails it. BW@
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Love the emoticon!
Yah, I think I can fix it too.