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why does my helicopter roll slightly when I apply jaw?

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why does my helicopter roll slightly when I apply jaw?

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Old 06-10-2014, 09:17 PM
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tonyoakden
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Default why does my helicopter roll slightly when I apply jaw?

I'm fairly new to helicopters and have a question. I have a WL922 (micro CP flybarless) which I am gradually mastering. I can hover it OK now and do simple straight and level flight. One thing stumps me a bit though. When I am hovering and try to rotate it on the spot it starts to roll and I need to put in quite a bit of control to stop it rolling. This means it always ends up moving quite a long way of center and does really eccentric circles. I don't get this problem with my flybar 911. I'm wondering what the reason for this is? I think as I remember it if try yawing to the left I need to add some roll to the right to compensate and visa versa. I don't think it's a simple trim issue as the helicopter hovers reasonable stable when I keep it facing away from me and I'm sure I am not accidentally introducing controls when I yaw it. I'm just interested as to whether this is something to do with the flybarless system or some aerodynamic principle I'm not aware of. Anyone know?
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Old 06-11-2014, 08:44 AM
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I'm not sure why it does that but my mCPX did the same thing.....and the weird thing about it....I extended the tail about an inch and it doesn't do it near as bad now. Go figure. One thing I thought was maybe the tail motor wasn't perfectly perpendicular....possibly that small angle caused the roll. Hard to figure....with these heli's every little thing that isn't spot on causes a reaction of some sort it seems.
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Old 06-12-2014, 09:16 PM
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Default Possible explanation that makes sense to me

Originally Posted by tonyoakden View Post
I'm fairly new to helicopters and have a question. I have a WL922 (micro CP flybarless) which I am gradually mastering. I can hover it OK now and do simple straight and level flight. One thing stumps me a bit though. When I am hovering and try to rotate it on the spot it starts to roll and I need to put in quite a bit of control to stop it rolling. This means it always ends up moving quite a long way of center and does really eccentric circles. I don't get this problem with my flybar 911. I'm wondering what the reason for this is? I think as I remember it if try yawing to the left I need to add some roll to the right to compensate and visa versa. I don't think it's a simple trim issue as the helicopter hovers reasonable stable when I keep it facing away from me and I'm sure I am not accidentally introducing controls when I yaw it. I'm just interested as to whether this is something to do with the flybarless system or some aerodynamic principle I'm not aware of. Anyone know?
This is assuming that the main blade rotation is clockwise as seen from above.

While hovering in a fixed heading ( no yaw ) the main blades have ( or should have ) the same pitch ( angle of attack ) while going forward and going backward in each revolution.

When a left yaw is commanded the blade going forward travels a shorter distance while the blade gong backward travel a longer distance so their speed has changed and so does the lift. The left side has less lift and the right side has more lift causing some slight roll to the left.

When a right yaw is commanded the blade going forward has a higher speed than the blade going backward and a slight roll to the right would be observed.

You may now verify if the above is correct on a right yaw and let us know.

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