A form of simple flight controller that works on principle of a gyroscope developing forces used to measure change in attitude.  Typically employs feedback loops with adjustable gains to match the responsiveness of a heli and keep the tail direction predictable. There are two types of gyro: rate mode and heading hold, and some flight controllers may employ both modes in the same device.   An example — an RC pilot Tx instructs the on-board gyro how fast to turn the tail of a heli in a particular direction, then the gyro with its feedback mechanisms implements the instruction.  Also used in flight stabilizers for fixed wing RC planes.  More sophisticated flight controllers combine gyros with accelerometers.