Flying Model Helicopters

Model Helicopter Gyros Explained
By Jeff Barrington - Mid Devon Heli Club

The purpose of the gyro is to stabilize the tail, without it the model would be almost unflyable. Early gyros had a motor and two flywheels inside and at the time worked quite well but they are no match compared to piezo gyros, which have no motor but use an electronic sensor.

Piezo Gyros
Modern piezo gyros have never been so good and are no longer an expensive alternative but an essential part of the radio system. Modern peizo gyros can cost anything from £40 to £300. So how much should you spend and which one should you buy?

Well at the lower end of the scale the gyro will be single rate adjusted on the gyro itself and will not have pilot authority, while at the top of the range it will probably be dual rate in both normal and heading lock mode (sometimes called heading hold or AVCS), selectable from the transmitter, and it will also have full pilot authority.

Modern piezo gyros have a very fast response, and will need a servo, which can keep up with the gyro output. Servo speed is measured by the number of seconds it takes for the servo to turn 60 degrees so a digital servo with a speed of 0.12s/60 to 0.08s/60 is the ideal but you will have to pay around £60 to £125 for it.

Gyro Gain
The best way to adjust gyro gain is to turn it up until the tail wags in forward flight then turn it down a little. You should be able to get near 100% gain, if you cant then try changing the length of the rudder servo arm, there is no point spending serious money on a good gyro and then only using 50% gain.

Pilot Authority
On a standard gyro when you input a rudder command the gyro will try to correct the tail back to the centre, the higher the gain on the gyro, the less tail authority you will have.
With pilot authority the gyro gain decreases as you input commands so you can have 100% gyro gain and still have full tail authority.

Heading Lock
With the gyro in normal mode the tail will weathercock to some extent so when flying circuits or hovering in to wind the tail will tend to follow the line of the model. In heading lock mode the tail stays wherever you put it, so it is quite easy to fly the model sideways or backwards at speed without losing the tail position. The only downside to heading lock mode is that you have to steer the tail all the time as it will not naturally follow the model, and if you enter a manoeuvre, say a loop, with the tail offline it will stay offline throughout the manoeuvre. If you are not sure which mode the gyro is in, with the radio on and without the engine going, move the rudder control fully to one side, if heading lock is selected the servo will stay at one end until you move the stick back to the other side.

Mixing Makes
I have used Futaba, JR, and CSM gyros on JR radio systems with no problems at all but I would advise the use of a matching rudder servo in the case of JR or Futaba, as they would have been designed to work with their own servo.

This page has been contributed by Jeff Barrington
Web Site: Mid Devon Heli Club