Turn Coordinator - Speed error
 

Hi !

Frow what I have understood, a turn coordinator works thanks to the torque applied on its side (yawing).
This force is redirected at 90 degrees which makes it bank on the side (precession).
This bank is then calibrated by a spring to indicate if we are yawing at rate 1 turn (or not).

By reading the Oxford manual I came threw something I can't understand.
It says that if the gyro is underspeeding, it will underturn.

I would have thought that if the gyro underspeeds, its rigidity would decrease.
And as the rigidity decreases the precession would increase (and thus increase the indicated turn rate).

Thanks for your explanation.

Precession is always 90º. I think the cause of the underturn would be that the decrease in rigidity means the spring is out of calibration and provides too much resistance.

The way was explained to us back in the day when others had the same thought - a spinning wheel resists force application, a stationary wheel doesn't, a wheel spinning slower than optimal is somewhere in between the two, so more prone to being pushed around by the changing attitude of the aircraft therefore under reading. Likewise an over speeding gyro will over read as it resists the changing attitude