FACTORS AFFECTING HANDLING QUALITIES OF LIFT-FAN AIRCRAFT DURING STEEP TERMINAL AREA APPROACHES

摘要

The XV-5B lift-fan aircraft was used to explore the factors affecting handling qualities in the terminal area. A 10° ILS approach task was selected, to explore these problems. Three major phases of the approach were considered:(1) interception of the glide slope at 457.2 m (1,500 ft), (2) glide slope tracking, (3) deceleration along the glide slope to a spot hover. Variations in airplane deck angle, deceleration schedule, and powered-lift management were studied to assess their effects on handling qualities. The overall descent performance envelope was identified on the basis of such operational limitations as fan stall, maximum comfortable descent rate, and controllability restrictions. The "collective-lift" stick provided precise glide slope tracking capability through direct control of fan lift, but the pilot tended to "chase" glide slope if engine power (throttle) was modulated. The pilot preferred a deck-parallel (to elide slope) attitude for which he used powered lift (collective) to control glide slope and pitch attitude (stick) to keep the angle of attack near zero, which minimized his workload. This technique also provided a greater angle-of-attack margin from fan stall. Workload was reduced when the deceleration schedule was delayed until the aircraft was well established on the glide slope, since thrust vector changes induced flight path disturbances.