A gyroscope is a device consisting of a wheel or disc mounted to spin rapidly about an axis free to alter direction; by maintaining its spin axis regardless of aircraft orientation it provides stability to aircraft. Mounted on gimbals, the spinning wheel operates as a vital navigational instrument that measures angular velocity to determine direction the aircraft is headed and to monitor orientation during flight, thereby keeping aircraft stable in instrument flight.
A mechanical gyroscope is a spinning top suspended by gimbals that allows aircraft to roll and pitch around it; the data is supplied to the pilot whenever the plane rolls or pitches. Used in both commercial and general aviation, the gyroscopic effect further detects engine-axis change during takeoff, completing the suite of functions that make the gyroscope indispensable for safe operation aloft.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is a gyroscope in aviation?
A gyroscope is a device used for measuring or maintaining orientation and angular velocity. A wheel or disk is free to rotate about one or both of two axes perpendicular to each other and to the axis of spin.
In aviation, a gyroscope is a sensor that measures the rotation rate of an aircraft with respect to an inertial frame, thereby delivering a stabilized positional reference for flight instruments. Mechanically, it is a wheel or disc mounted on gimbals so the wheel can spin rapidly around an axis that is free to change direction. This spinning wheel resists tilting except about its spin axis and therefore maintains orientation irrespective of movement in the aircraft. Because the gyroscope captures subsequent changes in orientation when rotated, it provides the datum for attitude indicators, turn coordinators and heading indicators, and it simultaneously supplies feedback to autopilot systems. Whether electrically driven, vacuum driven or powered by a pneumatic source, the device measures angular velocity and enables gyroscopic flight instruments to display aircraft orientation relative to the horizon, making the gyroscope a vital navigational instrument in aviation.
How is a gyroscope used in aircraft?
Gyroscopic flight instruments are used in most general aviation aircraft and in older commercial aircraft. These instruments include attitude indicators, heading indicators, and turn coordinators, each built around a spinning gyro that senses rotation about the aircraft's pitch, roll, and yaw axes. Elmer Sperry put gyroscopes to work stabilizing and navigating aircraft. Honeywell gyroscopic systems later refined the technology, supplying navigation systems for aircraft and stabilization systems for gunsights, bombsights, and radar platforms. Inside the cockpit, the attitude indicator contains a set of weights intended to keep the miniature airplane horizon level with gravity, while the heading indicator - called a directional gyro - allows pilots to read the aircraft's orientation without the errors of a magnetic compass.
Laser ring gyros, MEMS sensors, and mechanical gyros combine to fix the position of the aircraft and guarantee very accurate navigation. They are vital components of systems used in all kinds of aerospace applications. Turn coordinators measure pitch and bank, attitude indicators are vacuum powered, the datum is used to measure aircraft orientation, and the pivot is aligned with the aircraft centerline so the instruments reflect the true angular difference during flight. Gyrocompasses complement or replace magnetic compasses, giving stable references for ships, aircraft, and spacecraft, while inertial navigation systems rely heavily on accelerometers and gyroscopes to stabilize and orient scientific instruments and cameras. Modern MEMS sensors are mostly found on unmanned aircraft, but the same principle guides commercial airliners that use an inertial navigation system to navigate vehicles ranging from airplanes to drones and self-driving cars.
How does a gyroscope work on a plane?
Gyroscopic instruments work by using the inherent property of gyroscopes to create a datum and deviation from this datum is measured and displayed to the pilot. Gyro instruments operate on the principle of gyroscopic inertia, the conservation of angular momentum that keeps a spinning gyro wheel fixed in space unless an external torque is applied. This rigidity in space allows the gyro to maintain a constant reference direction inside the aircraft, so the airplane symbol remains fixed while the disc, attached to a gyroscopic gimbal, moves to reveal pitch and bank changes. As the aircraft manoeuvres, turns, acceleration and deceleration impose torques on the gyro, causing precession. Friction within the gyro also contributes to this precession, so the instrument slowly drifts and must be periodically re-caged or corrected. During take-off, the sudden change in the axis of rotation of the engines creates a gyroscopic effect that makes the nose veer to one side and the pilot must counteract this force with rudder input to keep the aircraft straight.
The attitude indicator contains a set of weights that sense gravity and gently drive the gyro toward level flight, while the outer gimbal, possessing one degree of rotational freedom, allows the instrument to tilt with the aircraft. Deflection movement is translated to movement of a needle or card on the instrument's face, giving the pilot an immediate visual cue. With this information, an airplane's autopilot can keep the plane on course, holding heading and attitude without pilot input.
I learned that a gyroscope on a plane works by exploiting the inflexibility in spatial orientation of a whirling impeller set in gimbals. Each comprised a gyroscope whose rotation body exhibited inflexibility in place that rejected any effort to alter its position so the device kept its axes fixed while the jet moved, banked, or rose around this constant mark. Because the devices accurately mirrored our every motion the orientation signal delivered a stable reference even when the view outside the windscreen was not clear.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
What are the characteristics of a gyroscope in aircraft?
The characteristics of a gyroscope are rigidity in space and precession, the two fundamental properties that allow a gyroscope to serve flight instruments. Of these, rigidity in space is the principal characteristic that makes the gyro suitable for attitude instruments. When the wheel spins at high speed it becomes rigid and resists tilting or turning in any direction other than around its spin axis. Because of this rigidity the gyro does not move regardless of the aircraft's attitude, so the aircraft symbol and the aircraft itself fly around the fixed axis of the artificial-horizon gyroscope while the gyro remains rigid in its case.
The rotor is deliberately built with great weight or density for its size and must spin at a high rate to maximize rigidity. Weight concentrated around the periphery of the wheel increases the angular momentum. While attitude indicators exploit rigidity, rate instruments like turn coordinators exploit precession: when the aircraft rotates about one of its axes the gyro processes proportionate to the rate of rotation, thereby providing rate-of-turn information.
Gyroscopic flight instruments are either pneumatically or electrically driven. Many general-aviation aircraft pair pneumatic attitude indicators with electric rate indicators to achieve redundancy. Any single power failure will not deprive the pilot of the ability to safely conclude the flight.
What are the different planes of a gyroscope?
A gyroscope has three planes. Mechanically, the arrangement is built from supporting rings known as gimbals. The inner gimbal, mounted inside the outer gimbal, possesses two degrees of rotational freedom. The outer gimbal adds one more where the spin rotor itself supplies the third. Each gimbal allows the spin axis to precess in its own direction, whereas frictionless bearings present in the gimbals keep the central rotor isolated from external torques. A tied gyroscope has freedom in three planes at right angles to each other, but its motion is constrained by some external force like a spring or dash-pot and as a result it shows movement rather than position.
What are the types of gyroscopes?
The types of gyroscope are detailed below.
- Mechanical gyroscope
- Ring laser gyroscope
- MEMS gyroscope
- Fiber-optic gyroscope
- Laser ring gyroscope
- Optical gyroscope
- Light-based gyroscope
A mechanical gyroscope is a traditional type, dependent on the ball bearing. It holds a gyro wheel that remains rigid in space, giving stability. Gyroscopes within instruments are vacuum driven, but modern installations replace mechanical gyroscopes with laser gyros. Within light-based gyroscopes, laser-ring and fiber-optic gyroscopes operate based on Sagnac effect. A ring laser gyroscope has a ring as part of the laser, while a fiber-optic gyroscope passes light from an external laser through a fiber-optic cable. Both are next-generation technology, yet laser-ring gyroscopes are expensive and intricate, so they are found on certain high-end aircraft that need to fix the position of the aircraft. A MEMS gyroscope gives adequately good performance for many avionics tasks. Its advancement has led to smaller, lighter units now serving in the turn coordinator found on aircraft. Across these types, most commercial airliners use an inertial navigation system that combines whichever gyro technology best meets accuracy, cost, and weight requirements.
