Up thrust instead of down thrust???
08-14-2006, 06:05 PM
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Up thrust instead of down thrust???
I was reading the most recent Model Aviation about how to trim your plane for down thrust. I think I have the opposite and need up thrust. Has anyone ever had this?
The plane (GP Super Skybolt, OS FS 91, 13X8 prop, 10 lbs, cg is good) requires up trim to fly level (haven't measured it, but I would say 3/16" to 1/4" deflection up). Does this mean that the engine is always pulling down and therefore need up trim? Being a bi-wing, I know there are incidences interacting, but when the throttle is cut it immidiately heads down, very little float.
Thanks,
The plane (GP Super Skybolt, OS FS 91, 13X8 prop, 10 lbs, cg is good) requires up trim to fly level (haven't measured it, but I would say 3/16" to 1/4" deflection up). Does this mean that the engine is always pulling down and therefore need up trim? Being a bi-wing, I know there are incidences interacting, but when the throttle is cut it immidiately heads down, very little float.
Thanks,
08-15-2006, 10:29 AM
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RE: Up thrust instead of down thrust???
Hi!
More likely (99% sure) that it is nose heavy.
If an airplane dives in a sharp turn (pylon turn) ...it's nose heavy.
Regards!
Jan K
More likely (99% sure) that it is nose heavy.
If an airplane dives in a sharp turn (pylon turn) ...it's nose heavy.
Regards!
Jan K
08-16-2006, 02:33 PM
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RE: Up thrust instead of down thrust???
The incidence between the wings and stab may be slightly negative causing a bit of up trim to be needed. This is not such a bad thing in itself and the plane can fly GREAT that way..... unless the CG or engine thrust is off.
Check the CG first using the dive test. Fly around at about 2/3 throttle or so and get the plane trimmed to fly "hands off" especially on elevator. Then put the plane into about a 45 degree dive and chop the throttle to idle. If the plane begins pulling back up by itself, it is nose heavy. If it keeps going at about the same angle, the CG is good.
Ernie
Check the CG first using the dive test. Fly around at about 2/3 throttle or so and get the plane trimmed to fly "hands off" especially on elevator. Then put the plane into about a 45 degree dive and chop the throttle to idle. If the plane begins pulling back up by itself, it is nose heavy. If it keeps going at about the same angle, the CG is good.
Ernie
08-16-2006, 06:07 PM
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RE: Up thrust instead of down thrust???
I'll try the dive, but my guess it would continue the dive and not pull up. When I first read your reply I thought you said that if it dropped off on a turn, and boy this plane does. To steep of a turn and it falls right off. thanks for the help.
If it was the top wing incidence, how would I change that, by changing the bottom wing? Top wing is soldered wire and would be difficult to alter. thanks
If it was the top wing incidence, how would I change that, by changing the bottom wing? Top wing is soldered wire and would be difficult to alter. thanks
08-17-2006, 07:23 AM
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RE: Up thrust instead of down thrust???
Yea it would be tough to fix the top wing incidence, that's why it's important to watch it during construction. If it is the wing then changing the CG won't help. When you check the CG in flight roll the plane inverted on a upward 45 and see what it does, that's how the TOC flyers do it.
