I have made a balsa glider with following specification:

Aerofoil : Clark X

Dihedral Wing (2m)

Pusher Configuration .

Rudder and Elevator

I m facing a problem of thrust torque , As I increase throttle, bird goes leftwards . So to correct this i trimmed my rudder to rightwards . Now it goes straight in power but as i off the throttle , Bird turns to rightward .And the problem is i have to change its rudder trim according to the throttle level.Kindly suggest me how can i reduce the motor torque effect on my bird.



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Two solutions that will work.

1 Easy to do. Use a mixer to feed in rudder correction with throttle input. Only problem is that the torque is not linear with throttle stick position.

2 This is harder to do depending on how the motor is mounted. Shim the motor to make the thrust line push the plane to the right as power is applied. Start at about 2 to 3 degrees right thrust and try it without the rudder correction. Increase or decrease as necessary. It should work well over a range of throttle settings.

Let us know how it works.

Is there anyway to check the thrust line of my bird, Can i hang my Bird on CG and check the thrust line by applying throttle, so in the direction nose is turning that may be my thrust line . Or is there any other way to check this factor .
I think i can change the motor mounting angle to left or rightwards to make the thrust line straight with straight rudder.

Well it's usually easier to make some length and alignment measurements.

Suspending the plane - not recomended:

Hanging the plane and running up the motor can be unsafe depending on how much power your motor is putting out, and will not really tell you how the plane flies. Without air moving over all the flying surfaces you won't have any dihedral yaw roll coupling to counter the torque. Remember the torque causes the plane to roll and turn. Using rudder trim works because it causes a correction yaw and the dihedral makes the yawed plane roll so as to counter the torque. So you really want to generate a thrust yaw to counter the motor torque.

Even if the thrust line is straight with the fuselage / rudder, the torque will cause it to roll and turn, so you need the thrust angle to counteract the torque.

  I usually use the prop as a sort of sighting device. If you look down on the fuselage from the top with the prop horizontal (assumes 2 bladed prop) it should be at 90 degrees to the longitudinal axis of the fuselage. If you want to be more precise I will send you a simple measuring procedure.

Thanks for info , i will be very glad to you , kindly send me that measuring procedure . It may help me a lot .

Clarification needed here Viky. The rudder trim causes yaw relative to airflow which the dihedral will cause to create a roll. For a front motor mount (tractor configuration) you will want right thrust to yaw right.

On a pusher configuration with the motor behind the CG, you will need left thrust but it will still cause a right yaw.

Measurement procedure up loaded


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