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Problems with Sukoi

Old 08-13-2003, 03:34 PM
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Fighterpilot
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Default Problems with Sukoi

I have a Giant Scale Planes 65" Sukoi ARF. It has a bad tendency to drop the right wing whenever I do a positive G manuever. It will track right when going through a loop, it will drop the right wing if too much elevator is applied and it tends to fly tail down and drop like a brick when power is reduced. It is balanced wing tip to tip, so I do not have a heavy wing.
I'm trying to determine if this could be the result of the aircraft being tail heavy or nose heavy. I've check both elevator halves and there is no differential in their throw. I've looked carefully at the wing and cannot see a warp. Wing and stab are parallel.

I'm ready to tie a wrench to the nose and go take off. If it's worse than I'm nose heavy, if its better, than I'm tail heavy. Then I can make the corrections, if I can get it back on the ground in one piece!
Old 08-14-2003, 02:01 PM
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akflyer
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Default Problems with Sukoi

Sounds tail heavy to me. Does it require much or any down when inverted ???? If it takes no down or just the slightest touch, then I would say its tail heavy. Most planes, for flying the routines, like to be toward the forward CG limit, while they like to be towards or behind the aft CG for 3D flying.

The tail droping when you come off the power is also a good sign it is tail heavy.
Old 08-14-2003, 04:21 PM
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Fighterpilot
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Default Balancing Sukoi

I am of the same opinion and will try additional weight in the nose. I did notice, when closely examining the aircraft, that the rudder is somewhat warped, with the top of the rudder leaning somewhat to left rudder and the bottom (larger part) angeling more toward right rudder. I may trim in some additional left rudder and see if this helps because I trimmed the rudder by looking down from the top and aligning the top of the rudder. This meant that the larger portion of the rudder, the bottom, actually had some right rudder trimmed in.
I'll fly it again soon and post the results.
It is actually a fun airplane to fly with the G-23 gas engine installed in the nose. Very reliable and solid, except for the above described tendency to drop the right wing.
Old 08-14-2003, 04:32 PM
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southern_touch9
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Default Problems with Sukoi

How much does it weigh with the G-23? I was intrested in these planes but I didnt know anything about them so i went with the H9 33% sukhoi (its on its way here now). My suggestion is even though your servos throw the same on the ground they might now throw the same in the air. The airforce over the control surface could be causing one servo to stall. I dont know where the balance is on that plane but if your using a G-23 I would find it hard to beleive that the plane is tail heavy b/c the G-23 is a heavy motor (when compared with a saito 1.50 or 1.80). I know the kit suggested this motor but with the additional weight it could be creating a high wing load. Does the plane have a tendency to snap out with you when you get too slow?
Old 08-14-2003, 08:10 PM
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Fighterpilot
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Default Weight

It doesn't matter what engine you have in the airplane if it needs nose weight to balance anyway. Even with the G-23, I added about 6 oz. to get it to balance at close to 25% of the mean chord. I then took some of the weight out of the nose and the problem didn't change. What I think I'll do is add some more nose weight to the aircraft, get it positively nose heavy. If the problem persist, then I'll remove weight gradually to see if the problem deminishes. Right now, it doesn'e take much up elevator to cause it to drop the right wing.... always the right wing.
One thing I didn't mention is that I can slow the plane down, add power, gradually adding in up elevator and it will fly dumping air on one wing and then the other. This has me confused because if it were too heavy or had a warped wing, it would snap out of this type of flying.
The servos on each elevator half are exactly the same and the two elevator halves are tied together with a wire yoke. I have pressure tested both elevator halves to see if I have a differential in the elevator throw and it doesn't seem to exist.
I'll keep trying the next time I go out and fly it.
Old 08-14-2003, 08:51 PM
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akflyer
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Default Problems with Sukoi

I had this same problem on my Ohio SU 26 with a ZDZ 60. As I played with it I kept taking out throw till I could pull full up at any speed and it would not snap or roll out. This ended up being ~3/8" up and down. I did not think this would be enough to fly the plane but I can still pull 75' diameter loops and it does awsome snaps even with this little bit of throw. The same for my 30% Edge but I can use almost 1/2" before it will start snapping out of a tight loop.
Old 08-14-2003, 10:54 PM
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Fighterpilot
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Default Elevator throw

I've got a lot of experience flying heavily wing loaded warbirds and know what can happen when you horse in too much elevator.
This just doesn't feel that way because I can input the slightest amount of elevator on landing and get the right wing to drop. I will take what you say into consideration and reduce the elevator throw if the other experiments do not work. You might have just nailed the problem.
Thanks for the reply.
Old 08-31-2003, 02:12 AM
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CharlieK
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Default Problems with Sukoi

I have a Goldberg Sukhoi that does this to the left if I really honk on it. I would check #1 the thrust line - if it is aimed up or down when you pull the throttle back the nose will react to the required elevator trim for level flight in an appropriate manner, down thrust will give you a nose up when the power is off. It sounds like the wing drop is probably a difference in the incidence of the wings, at the roots or at the tips. I think my airplane does it because there is a slight amount of difference in where the ailerons sit in neutral, which causes a tip stall under the proper conditions. According to one of the TOC pilots you can test the cg by pulling up 45 degrees and let go of the sticks, the nose should drop slowly after several seconds ( do this right side up and inverted) , if the nose rises you are tail heavy. You can also tell tail heavy by extreme sensitivity on the elevators. If it does the wing drop excessively you can experiment with stall strips near the wing root on the bad side to get the wing root to stall first. These are normally small triangle strips glued to the leading edge in the proper position, the position being determined by flight test .
charliek
if it don't fly I don't mess with it
Old 09-17-2003, 05:41 PM
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Geistware
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Default RE: Problems with Sukoi

While I will not rule out it being tail heavy, the engine could also be setting with some down thrust so that when you slow down and idle back, the tail drops. What happens when you fly inverted? Does it climb?

ORIGINAL: Fighterpilot
it will drop the right wing if too much elevator is applied and it tends to fly tail down and drop like a brick when power is reduced. It is balanced wing tip to tip, so I do not have a heavy wing.

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