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Home✈️Aircraft🚁HelicopterBeginners Corner › Need help with rudder flight control issue
11-01-2013 09:32 PM  5 years ago
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Lillian, AL, United States

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Need help with rudder flight control issue
Hello all,

I am the proud but frustrated owner of an Align T-Rex 450. I am also new to the sport of
rc heli flying, approximately 5 months. As Newbies are prone to do, I had a very hard tail first
landing that resulted in me replacing the tail boom and support struts, landing skids, etc. I have not
been able to fly my 450 since the crash due to a tail rotor control actuation problem.

I will try to explain my problem: When I increase the throttle to near 50% and the heli gets light on
it's skids the heli will start to yaw (piro) in one direction or the other (which is normal)Let's say
to the left. When I move the rudder stick slightly to the right to oppose the yaw the heli goes into
a rapid right piro. Then when I make a rudder input to the left to oppose the right piro that I induced
the heli goes into a piro to the left. These piros are so rapid that the heli is unflyable.

I brought the heli inside to investigate the problem. I found that the tail rotor was moving in the correct
commanded direction when rudder inputs were made, but it then "froze" in that position instead of returning
to the neutral position commanded by the heading lock system when I moved the rudder stick back to the rudder
centered position. I found that, using the rudder stick, I could move the tail rotors from their centered
positions progressively out to their end points and they would stay in their last commanded position instead
of returning to center after I centered the rudder stick. By the way the tail rotor control linkages all moved
smoothly through out their full range of travel. There is no binding or resistance at all.

I suspected that the problem might be in the Heading Lock mode of the gyro or perhaps the gyro itself. I unplugged
the motor power wires then powered up the heli. I rotated the heli's nose left and right by hand to varify that the
Heading Lock was working, heading lock pitched the tail rotor blades in the correct direction in response to
me yawing the heli left and right. I also installed a new rudder servo to eliminate it as a possible source
for the problem. I borrowed and installed a friends spare gyro to see if my original gyro was the culprit. The
test results were the same with the newly installed gyro, the heading lock feature worked correctly by moving the
tail rotor blades to counter the left and right yaw that I induced by rotating the heli's nose with my hand.

This is a real head scratcher for me, I'd appreciate any help that my fellow heli drivers can give me on this.


Larry Osborne
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11-01-2013 09:36 PM  5 years ago


Brewerton, New York

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Is the gyro in rate mode or HH?Bill Whittaker
11-02-2013 12:18 AM  5 years ago


A little to the right and down!

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Hi Larry,

You didn't mention if it was a torque tube or belt drive tail.

My guess would be that if it's belt drive you may have put the twist in the belt in the wrong direction and the tail is turning the wrong way.

Take a look and see if this helps.
If it ain't broke, go fly some more!
11-03-2013 02:13 AM  5 years ago



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Your heading lock doesn't effect your yaw direction in any way.

It seems you have the system revesed in your tx. When you give input from your tx does it move in the right direction?

I know you said it RESPONDS in the right direction, but is it following your tx?
When I increase the throttle to near 50% and the heli gets light on
it's skids the heli will start to yaw (piro) in one direction or the other (which is normal)Let's say
to the left.
No its not normal. I can take off with my pinky finger on the collective and it rises straight up. Hovers hands off.

How is your mechanical setup? Make sure you have no revo mixing in your tx too. If the belt is wound wrong yes it would **** things to hell but you would notice something like that. Right?

It sounds so much like you have bad end points or sub trim or trim in their and its telling the gyro it wants a constant rate of rotation.

Anyways hope the bugs get out.

Can you post a pic of your linkage setup etc. What radio do you use?

Miniature Aircraft - OS power - Futaba electronics
11-03-2013 05:03 PM  5 years ago

rrKey Veteran


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First off, the behavior you are seeing on the bench with the tail "sticking" is normal operation with a gyro in heading hold mode. The tail will only properly center itself after moving the rudder stick if it (the gyro) is rate mode.

99%of the time, if a heli goes into a hard piro as soon as it gets light or you move the rudder stick, it's because the gyro sense, and possibly direction as well, is set backwards. If the tail drive is failing, it will always piro opposite the direction of the main rotor. If the piro will happen either way, it's a control problem.

11-04-2013 03:58 AM  5 years ago


Cedar Rapids, IA

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Answered your question in depth in your other post:

Offered explanations, troubleshooting, and setup information for you to go on.

It helps if you post once, instead of starting multiple threads in different spots here on RR.

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
12-05-2013 09:18 PM  5 years ago


brilliant ohio

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well you need to set the tail in rate mode but you will need to fly in HH mode and you will need to set gyro to at least 50% and before you do anything you need to make sure that tail blades are going the right way and if it is belt or shaft driven belt drive must be going to the belt inside the air frame will be a gear will be horizontal and be on its side you will need to turn the belt to the right or clockwise to make the tail blades go in the correct direction witch will be counterclockwise then you can set up
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