FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsMedium
A technician is comparing two gyroscopic turn instruments installed in a light twin. One instrument's gimbal is mounted with the gyro spin axis canted approximately 30 degrees from the horizontal. What advantage does this canted mounting provide compared to a standard turn-and-slip indicator?
- AIt increases the gyro's rotational speed for faster erection after power-up
- BIt allows the instrument to double as a backup attitude indicator during vacuum failure
- CIt allows the gyro to sense both roll rate and yaw rate, giving an earlier indication of a turn
- DIt eliminates the need for an inclinometer or slip ball entirely
Show answer & explanationAnswer & explanation
Correct answer: C. It allows the gyro to sense both roll rate and yaw rate, giving an earlier indication of a turn
The turn coordinator's gimbal is canted about 30° so the gyro is sensitive to roll rate about the longitudinal axis as well as yaw rate about the vertical axis, allowing it to display the initial roll into a turn before a steady turn rate is established, unlike the turn-and-slip indicator which only senses yaw rate.
Why the other options are wrong
- A. Gimbal angle does not affect gyro rotational speed, which is set by the electric motor or air jet.
- B. Turn coordinators do not display pitch/bank attitude like an attitude indicator.
- D. Both instruments still use a separate inclinometer/slip indicator to show coordination.
Turn Coordinator vs Turn-and-Slip Indicator
A turn coordinator uses a gyro canted about 30° to sense both roll and yaw rate, giving earlier turn indication, while a turn-and-slip indicator's gyro spin axis is horizontal and senses only yaw rate.
- Turn coordinator gimbal canted ~30° from horizontal
- Senses roll rate plus yaw rate, shown as a miniature airplane symbol
- Turn-and-slip indicator uses a needle and senses only yaw rate about vertical axis
Memory trick: Tilt the gyro 30° to catch the roll before the turn.