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Mar 17, 2009, 07:09 PM
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Vanish's Avatar
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Yippee!

Profile Jet Mashup (SU47ish) - Now Flying :)


Hello all. I've been building my own random pusher jets for awhile and they've always come out interesting and mostly successful. I recently completed outfitting one I cut out last week and took it out tonight to try it out. It has linked ailerons and tailerons for STV.

After some issues with CoG and balance I got it to fly out of my hand perfectly. We're running on rails here. Success, I thought to myself. Alright, let's bank her around and.... woah! Turning is a mess! It is quite difficult to describe the situation, but I'll do my best:

Turning produces an immediate pitch increase and death wobble, where if you continued trying to turn it would stall (much like pushing high alpha flight too far) and then flip upside down.

Where did I go wrong?
Last edited by Vanish; Mar 21, 2009 at 01:17 PM.
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Mar 18, 2009, 10:32 AM
Live to fly... Fly to live
mudman1959's Avatar

Wing Area...


Maybe it does not have enough wing area, or your wing is flexing or twisting when in a turn... Try adding a triangle piece of foam at the wing root to the fuselage on both sides.
Mar 19, 2009, 07:42 AM
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Vanish's Avatar
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No luck with the wing area / wing strength changes. I added a removable KF airfoil front wing section (hey, now it looks more like an F-35) which added lots of strength as as well gave 60% more wing area. Aside from becoming a much floatier plane (instead of fast)...which by the way is an interesting way to change your mind on how you want to fly, I still had turning issues.

Turning produced an almost immediate stall. A left turn was worse than a right. A very slight turn would roll it a little, but it would wobble. A hard turn would stall and flip the plane completely over.

I've verified the controls are set up correctly and that there is no flex in the taileron section of the plane. Will double check motor angle, CG position and might try disabling the linked ailerons, since this is the first time I've tried them.
Last edited by Vanish; Mar 19, 2009 at 08:16 AM.
Mar 19, 2009, 08:08 AM
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Vanish's Avatar
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After reviewing everything, it might just be I went too quick on the build. I hope it stays as nice out as it is now so I can play with it more later, but I've got to get to work. This is the first time I built a plane that didn't fly right out of the gate, so its a good experience.
Mar 19, 2009, 04:07 PM
Sussex, UK
RobinBennett's Avatar
Could it be a lack of yaw stability? There's a lot of vertical area up front, and the fins are quite small (and possibly in turbulence when you pull up elevator to turn)
Mar 20, 2009, 09:18 AM
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Quote:
Originally Posted by RobinBennett
Could it be a lack of yaw stability? There's a lot of vertical area up front, and the fins are quite small (and possibly in turbulence when you pull up elevator to turn)
Maybe. That's an easy thing to test as well, so if my next attempts don't work out I'll give it a shot.

I reviewed all the joints and redid some of them. At first I thought there wasn't any issues with flex due to my ground tests, but after physically pushing on some parts of the plane I disagreed.

Its looking pretty nice out right now, so as long as the wind doesn't pick up I should be able to test at lunch.
Mar 20, 2009, 10:44 AM
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Well, looks like its time to try yaw stability. The fins didn't look small when I was putting it together, about the same ratio as an F15, but now they do.

It's definitely getting better, but still not right. Pulling hard left would give about 40 degrees of left rotation, then a sharp right roll. I'm amazed that I haven't broken anything yet.
Mar 20, 2009, 04:22 PM
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Success! I increased the vertical stabilizer size by about 80% and now it flies, and pretty good, too. I hope the wind backs off a bit for this evening, as I would like to test out the two different wings a bit more. It's still only about 34 degrees outside, but at least it looks nice out.

I do believe that it can fly as two different planes. One a floaty slower flier with the larger KF wing, and two, a faster fighter with the swept forward wing. I was amazed at just how slow I was able to fly it with the larger wing, kept waiting for the stall that never came.

Going to increase the aileron area a bit as the roll was a bit slow.
Mar 21, 2009, 05:48 AM
Sussex, UK
RobinBennett's Avatar
Great!

I suspect the wide, flat nose is providing most of the lift at low speeds, rather than the wing but you won't be able to steer too well at low speeds without rudders.
Mar 21, 2009, 01:18 PM
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I wish I could take the pictures AND fly at the same time!


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