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Helicopter perfectly trimmed upright but wanders when its inverted?

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Helicopter perfectly trimmed upright but wanders when its inverted?

Old 09-03-2010, 03:00 AM
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Default Helicopter perfectly trimmed upright but wanders when its inverted?

Hi I have a question. I recently started trying out inverted flight and i can hold inverted nose in for a while now. However, I noticed that when my helicopter is upright, my helicopter doesn't wander. However, when its inverted, it likes to wander backwards, so much so that i have to constantly pull back on my right cyclic in order to keep it still. Now this is where it gets confusing. If i were to trim it out inveted, my helicopter would wander when its upright and vice versa. An airplane guy told me that i need to mess with the CG, but i'm not really sure what he was talking about. Any ideas?

Thanks!
Old 09-03-2010, 08:15 AM
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Default RE: Helicopter perfectly trimmed upright but wanders when its inverted?


ORIGINAL: helicub81
If i were to trim it out inveted, my helicopter would wander when its upright and vice versa. An airplane guy told me that i need to mess with the CG, but i'm not really sure what he was talking about. Any ideas?
Your airplane buddy is correct. You have the helicopter trimmed for upright flight, with an incorrect CG. If you were to put the CG in the correct location, the "trimming" needed for upright flight would be minimal and the same would happen for inverted.

Start by stretching the blades of the heli and aligning them legthwise, over the nose, and boom of the heli. Make sure you have the canopy on and some people suggest that you have a half tank of fuel. Grab the heli by the flybar, close to the head. If the heli stays level or slightly nose-down. You are fine. If the heli tilts back, or dips too much forward, then you need to shift some components around.

Out of curiosity, how much trim (or subtrim) do you have right now?

Rafael
Old 09-03-2010, 10:41 AM
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Default RE: Helicopter perfectly trimmed upright but wanders when its inverted?

On my dxi the trim tab for the right cyclic like lateral movement is set to about 1/2 the way back. now that i think about it, it sounds a lot.

The thing is, that when i perfectly center the CG,the heli still tends to wander forwards. Thats why i have so much trim on it.
Old 09-03-2010, 02:19 PM
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Default RE: Helicopter perfectly trimmed upright but wanders when its inverted?


ORIGINAL: helicub81

On my dxi the trim tab for the right cyclic like lateral movement is set to about 1/2 the way back. now that i think about it, it sounds a lot.
Are we talking elevator trim or aileron trim? The way you described it on the above sentence, it seems like you are talking aileron trim.

The thing is, that when i perfectly center the CG,the heli still tends to wander forwards. Thats why i have so much trim on it.
A helicopter with a prefect CG will not wander forward. It will only wander in the direction opposite of the tail rotor, not forward or backward, but sideways. I belive that you might have a few terms confused.

The CG on a helicopter needs to be under and aligned with the main shaft. If the main shaft is not perfectly vertical when held the heli is by the head, then the CG is off. Since there is no way to see a perfectly vertical main shaft, the closest thing is to look for a horizontal tail boom, when holding the heli by the head as I described on my previous post.

Rafael
Old 09-03-2010, 03:25 PM
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Default RE: Helicopter perfectly trimmed upright but wanders when its inverted?

Hm i'll check again. Should I center all the servos before i find the CG?
Old 09-03-2010, 04:05 PM
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Default RE: Helicopter perfectly trimmed upright but wanders when its inverted?

I would definitely remove trim, center the servos and set pitch before doing anything like trimming.
Old 09-03-2010, 05:37 PM
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Default RE: Helicopter perfectly trimmed upright but wanders when its inverted?

u know what.. I found out why my helicopter was behaving like that. My swash wasn't level -_-. Anyways, i haven't taken it inverted yet, but in the upright position, it hovers perfectly.

Thanks for the help!
Old 09-07-2010, 02:12 PM
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Default RE: Helicopter perfectly trimmed upright but wanders when its inverted?


ORIGINAL: helicub81

Hm i'll check again. Should I center all the servos before i find the CG?
Yes, the servos should be centered mechanically and the swash level. After you adjust your CG, the helicopter should need very little to no trimming at all. If it does, then you need to re-check your CG anr/or re-center the servos, and re-level the swashplate.

Rafael
Old 09-07-2010, 03:08 PM
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Default RE: Helicopter perfectly trimmed upright but wanders when its inverted?

yep thanks again for the help

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