Automatic heading correction for directional gyroscopes

1. A navigation system for a rotorcraft having a heading and an airspeed, the navigation system comprising:

a directional gyroscope configured to determine the heading of the rotorcraft during flight by rotating in a vertical plane and being oriented in space in a constant direction, the directional gyroscope having a magnetic heading correction mode, a nonmagnetic manual heading correction mode and a nonmagnetic automatic heading correction mode;

a magnetic field sensor operably coupled to the directional gyroscope and operable to generate magnetic north-based signals;

a heading correction input operably coupled to the directional gyroscope and operable to generate manual signals upon actuation thereof; and

a global positioning system sensor operably coupled to the directional gyroscope and operable to generate track-based signals;

wherein, in the magnetic heading correction mode, the directional gyroscope receives the magnetic north-based signals from the magnetic field sensor for heading corrections;

wherein, in the nonmagnetic manual heading correction mode, the directional gyroscope receives the manual signals from the heading correction input for heading corrections;

wherein, in the nonmagnetic automatic heading correction mode, the directional gyroscope receives the track-based signals from the global positioning system sensor for heading corrections; and

wherein, when the directional gyroscope is not in the magnetic heading correction mode, the directional gyroscope automatically transitions from the nonmagnetic manual heading correction mode to the nonmagnetic automatic heading correction mode responsive to the airspeed exceeding a predetermined airspeed threshold between 10 knots and 30 knots and automatically transitions from the nonmagnetic automatic heading correction mode to the nonmagnetic manual heading correction mode responsive to the airspeed falling below the predetermined airspeed threshold.

2. The navigation system as recited in claim 1 further comprising a speed processor operably coupled to the directional gyroscope and the speed processor operable to determine whether the airspeed exceeds the predetermined airspeed threshold and operable to transition the directional gyroscope between the nonmagnetic manual heading correction mode and the nonmagnetic automatic heading correction mode.

3. The navigation system as recited in claim 1 further comprising a compass card mechanically linked to the directional gyroscope that indicates the heading of the rotorcraft during flight.

4. The navigation system as recited in claim 1 further comprising a compass card digitally linked to the directional gyroscope that indicates the heading of the rotorcraft during flight.

5. The navigation system as recited in claim 1 further comprising:

a vertical gyroscope configured to determine a true vertical direction, a horizon plane and angles of inclination relative thereto; and

a turn rate gyroscope configured to determine a turn rate of the rotorcraft.

6. The navigation system as recited in claim 1 further comprising a navigation display operably coupled to the directional gyroscope and operable to indicate the heading of the rotorcraft during flight.

7. The navigation system as recited in claim 1 wherein, in the nonmagnetic automatic heading correction mode, the directional gyroscope periodically receives the track-based signals from the global positioning system sensor to automatically perform heading corrections.

8. A method of navigating a rotorcraft having a heading and an airspeed, the method comprising:

rotating a directional gyroscope in a vertical plane such that the directional gyroscope is oriented in space in a constant direction to determine the heading of the rotorcraft during flight;

receiving magnetic north-based signals from a magnetic field sensor for heading corrections by the directional gyroscope when the directional gyroscope is in a magnetic heading correction mode;

receiving manual signals responsive to actuation of a heading correction input for heading corrections by the directional gyroscope when the directional gyroscope is in a nonmagnetic manual heading correction mode; and

receiving track-based signals from a global positioning system sensor for heading corrections by the directional gyroscope when the directional gyroscope is in a nonmagnetic automatic heading correction mode;

wherein, when the directional gyroscope is not in the magnetic heading correction mode, automatically transitioning the directional gyroscope from the nonmagnetic manual heading correction mode to the nonmagnetic automatic heading correction mode responsive to the airspeed exceeding a predetermined airspeed threshold between 10 knots and 30 knots and automatically transitioning the directional gyroscope from the nonmagnetic automatic heading correction mode to the nonmagnetic manual heading correction mode responsive to the airspeed falling below the predetermined airspeed threshold.

9. The method as recited in claim 8 further comprising rotating a vertical gyroscope mounted within a gimbal having two degrees of freedom about a vertical axis to determine a true vertical direction, a horizon plane and angles of inclination relative thereto.

10. The method as recited in claim 8 further comprising rotating a turn rate gyroscope mounted in a gimbal with a rotational axis in-line with a pitch axis of the rotorcraft and with the gimbal having a degree of freedom around a roll axis of the rotorcraft to determine a turn rate of the rotorcraft.

11. The method as recited in claim 8 further comprising rotating a compass card linked to the directional gyroscope that indicates the heading of the rotorcraft during flight.

12. The method as recited in claim 8 further comprising providing periodic alerts to perform the manual heading corrections when the directional gyroscope is in the nonmagnetic manual heading correction mode.

13. The method as recited in claim 8 wherein receiving track-based signals from the global positioning system sensor for heading corrections by the directional gyroscope further comprises receiving periodic track-based signals from the global positioning system sensor to automatically perform the heading corrections.

14. The method as recited in claim 8 further comprising indicating the heading of the rotorcraft on a navigation display.

15. A rotorcraft having a heading and an airspeed, the rotorcraft comprising:

a directional gyroscope configured to determine the heading of the rotorcraft during flight by rotating in a vertical plane and being oriented in space in a constant direction, the directional gyroscope having a magnetic heading correction mode, a nonmagnetic manual heading correction mode and a nonmagnetic automatic heading correction mode;

a navigation display operably coupled to the directional gyroscope and operable to indicate the heading of the rotorcraft;

a magnetic field sensor operably coupled to the directional gyroscope and operable to generate magnetic north-based signals;

a heading correction input operably coupled to the directional gyroscope and operable to generate manual signals upon actuation thereof; and

a global positioning system sensor operably coupled to the directional gyroscope and operable to generate track-based signals;

wherein, in the magnetic heading correction mode, the directional gyroscope receives the magnetic north-based signals from the magnetic field sensor for heading corrections;

wherein, in the nonmagnetic manual heading correction mode, the directional gyroscope receives the manual signals from the heading correction input for heading corrections;

wherein, in the nonmagnetic automatic heading correction mode, the directional gyroscope receives the track-based signals from the global positioning system sensor for heading corrections; and

wherein, when the directional gyroscope is not in the magnetic heading correction mode, the directional gyroscope automatically transitions from the nonmagnetic manual heading correction mode to the nonmagnetic automatic heading correction mode responsive to the airspeed exceeding a predetermined airspeed threshold between 10 knots and 30 knots and automatically transitions from the nonmagnetic automatic heading correction mode to the nonmagnetic manual heading correction mode responsive to the airspeed falling below the predetermined airspeed threshold.

16. The rotorcraft as recited in claim 15 further comprising a speed processor operably coupled to the directional gyroscope and the speed processor operable to determine whether the airspeed exceeds the predetermined airspeed threshold and operable to transition the directional gyroscope between the nonmagnetic manual heading correction mode and the nonmagnetic automatic heading correction mode.

17. The rotorcraft as recited in claim 15 further comprising a compass card mechanically linked to the directional gyroscope that indicates the heading of the rotorcraft during flight.

18. The rotorcraft as recited in claim 15 further comprising a compass card digitally linked to the directional gyroscope that indicates the heading of the rotorcraft during flight.

19. The rotorcraft as recited in claim 15 further comprising:

a vertical gyroscope configured to determine a true vertical direction, a horizon plane and angles of inclination relative thereto; and

a turn rate gyroscope configured to determine a turn rate of the rotorcraft.

20. The rotorcraft as recited in claim 15 wherein, in the nonmagnetic automatic heading correction mode, the directional gyroscope periodically receives the track-based signals from the global positioning system sensor to automatically perform heading corrections.