ION Technical Content
Offset Course Guidance
| Abstract: | The digital avionics onboard the MH-60K and MH-47E helicopters of the Army Special Operation Aircraft (SOA) include a digital computer interfaced to navigation sensors and multi-function displays (MFDs). This system devel-oped by Lockheed Martin under the SOA contract permits the pilot to fly a flight plan by maneuvering the helicopter so the flight director cues shown on the MFD are nulled or, in the case of the MH-47E, by coupling to the autopi-lot. The horizontal situation display (HSD) on an adjacent MFD significantly improves situational awareness by showing the helicopter position relative to the desired ground track. The flight crew can insert a flight plan as a sequence of waypoints into the onboard computer prior to takeoff. The avionics mission management function will automati-cally sequence from one flight plan leg to the next at the proper time during the mission. The Army requested that the SOA avionics be upgraded to include an offset course guidance mode which would permit the flight director or autopilot to be used to fly a parallel course that is offset a specified distance from the original flight plan. The two basic applications of this new mode are: 1) formation flight where the follower aircraft are offset laterally relative to the lead aircraft, and 2) obstacle avoidance such as a sudden storm cell in the path of the original flight plan. These two objectives de-mand a wide range of offset distances (the requirement is offset values from 0.0 to 99.9 NM). One approach for adding the offset course guidance mode is to compute a second set of waypoints corresponding to the offset course. This approach would have required major modifications to the mission management software. A simpler approach was devised based on the concept of a "shadow aircraft" which did not require any modifications to the mission management software. The shadow aircraft is defined such that using the flight director or autopilot to force the shadow aircraft to track the original flight plan causes the (true) aircraft to fly the desired offset course. The Army favored the second approach since it met their objectives of low cost and low risk while providing the capability to fly the offset course as easily as flying the original flight plan. This paper describes the offset course guidance design and simulated performance. In addition to the shadow aircraft concept, the design description includes the solu-tion for constructing and transitioning to the offset course in the case of large offset distances. The paper contains trajectory plots generated by a closed loop simulation that demonstrate the capability of the resulting design to smoothly capture and accurately track the offset course. Also described is another simulator called the Desk Top Trainer (DTT) which simulates the cockpit displays. It was used to validate the design and fine tune the human interface. |
| Published in: |
Proceedings of the 54th Annual Meeting of The Institute of Navigation (1998) June 1 - 3, 1998 The Adams Mark Hotel Denver, CO |
| Pages: | 657 - 666 |
| Cite this article: | Hutton, Maurice F., "Offset Course Guidance," Proceedings of the 54th Annual Meeting of The Institute of Navigation (1998), Denver, CO, June 1998, pp. 657-666. |
| Full Paper: |
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