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Rolling with hard elevator on Yak 102

 
Old 03-04-2009, 09:21 PM
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thaus
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Default Rolling with hard elevator on Yak 102

My Yak 102 rolls when pulling elevator after a vertical down line. I have applied 3 oz. weight to the rising wing so that it now weighs 3 oz more than the other wing. The problem persisted. I have made sure the elevator halves move together and the torque of the servos seems equal. This happens with my low rate throws. The more aggressive the elevator move , the greater the roll. I know I am not applying any aileron.

I believe the problem is wing stall. However the plane will elevator fine. That is, the stalling of each wing seems equal when there is no high G event.

Two theories have been put forth: (1) the leading edge needs to be sharpened and equal at all points, (2) there is incidence difference between the two wings.

Does any one have an opinion?
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Old 03-04-2009, 09:34 PM
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Default RE: Rolling with hard elevator on Yak 102

What method did you use to ensure both elevator halves were matched? Have you checked incidence of every surface? One major reason that you dont see any problem while 3D is because the wings are already stalled. I would NOT touch the leading edges. Does the same wing drop if you try negative input?
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Old 03-04-2009, 11:07 PM
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Default RE: Rolling with hard elevator on Yak 102

I have not tested for roll with negative elevator. I will try that. The elevator halves' movement was matched by taping carbon=fiber tubes to both halves and comparing their throw. I have no incidence meter so I have not checked incidence. The wing root is installed in a 1" cavity in the fuselage, so any incidence adjustment will be extremely difficult.
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Old 03-05-2009, 12:17 AM
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Default RE: Rolling with hard elevator on Yak 102

thaus,

What is the weight of your plane if you don't mind me asking?
Also if one wing has a little off incidence, you can easily fix it with heat gun method.
How much throttle are you carrying it when pulling on the elevator from downline?

I also wouldn't mess with the leading edge, I don't think that would be your problem. Your stab/wing or both incidence can be the problems.

Thank you,
Reza
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Old 03-05-2009, 08:47 PM
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Default RE: Rolling with hard elevator on Yak 102

Resagh,

We are all going to miss your fine counsel. Thanks for your response. I will get an incidence meter. But I do not know how to warp the wing by using a hot gun. Please explain or guide me to some instruction.

You asked what my throttle is on down lines. The answer is idle. I was testing for dynamic balance.
Plane weight is 27.5 #.


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Old 03-06-2009, 12:16 AM
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Default RE: Rolling with hard elevator on Yak 102

You are very welcome, I hope I can help.

Just one more question, you are coming on downline at idle then you pull on the elevator basically pulling making an angle (corner) is that at idle? or when you pull you give it throttle?

Heat gun method is easy, plug the wings to the fuse or have someone hold the root, then grab the wing tip and twist it in the opposite direction that is off, then you will see wrinkles in the wing on top and the bottom, you need to get the heat gun and a glove and take care of those wrinkles. You need to repeat this process to achieve the desired incidence. It works great and unlike some saying, it won't come back unless it is way off!

If your incidence is off or wing has a warp, your airplane trim will be different at half throttle than full throttle. So basically if you trim the plane at full throttle which you should do and then fly the plane at half throttle, you will notice plane wanting to roll to the left or right slightly and will require stick input for level flight.

Another test would be to first make sure the plane is not showing any roll tendency in a full power upline, then do a downline that is perfectly straight at idle, take your hands off the sticks and if plane wanted to roll to one direction that can be an indication of incidence as well.

Hope this helps a little,
Reza

ORIGINAL: thaus

Resagh,

We are all going to miss your fine counsel. Thanks for your response. I will get an incidence meter. But I do not know how to warp the wing by using a hot gun. Please explain or guide me to some instruction.

You asked what my throttle is on down lines. The answer is idle. I was testing for dynamic balance.
Plane weight is 27.5 #.


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Old 03-06-2009, 08:13 AM
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Default RE: Rolling with hard elevator on Yak 102

Resagh, you asked if the throttle is kept at idle through the pull out. The answer is yes. Thanks for the new ideas.

By the way, Composite Arf may not know they need your support service, but they do. If you showed them how helpful you have been to the QQ crowd they may realize what is missing in their own support.
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Old 03-06-2009, 11:15 AM
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Default RE: Rolling with hard elevator on Yak 102

Thank you for your comments. I really appreciate it.
Back to your problem, I really don’t think at that attitude incidence can play a huge roll. I think you may be stalling one wing faster before you actually reach level flight! It’s really hard to say since I am not there to see what’s happening but if you have very little elevator, there is a chance by the time plane is getting close to level flight wing(s) are already stalled. I suggest that you add more throw and try, OR try with a little more throttle, one more thing I would increase the expo on that flight mode for ailerons a lot to ensure that doesn’t make it worse.
Also weigh both wings and see how much apart they are. My wings almost on all my QQ planes have had very close weights so if they are out of balance it is not much.

I would do that before getting a hold of incidence meter since you don’t have one readily available.

Thank you,
Reza

ORIGINAL: thaus

Resagh, you asked if the throttle is kept at idle through the pull out. The answer is yes. Thanks for the new ideas.

By the way, Composite Arf may not know they need your support service, but they do. If you showed them how helpful you have been to the QQ crowd they may realize what is missing in their own support.
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