Factors Affecting Handling Qualities of a Lift‐Fan Aircraft During Steep Terminal Area Approaches

Abstract

The XV-5B lift-fan aircraft was used to explore the factors affecting handling qualities in the terminal area. A 100 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 glide 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 fron 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. SUMMARYThe XV-5B lift-fan aircraft was one of four NASA V/STOL research vehicles recently used to explore the factors affecting handling qualities in the terminal area. The objectives of the program were to define the limitations of powered-lift VTOL aircraft that prevent full exploitation of their low-speed capabilities, and to develop operationally feasible techniques for performing simulated precision instrument landing approaches. A 100 ILS approach task was selected as representing a typical steep-angle approach with which 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 "collectivelift" stick provided precise glide-slope tracking capability (to within ±6.1 m (20 ft) 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 glide 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 delaye...

Control of V/STOL aircraft

“…These results show that only Level 2 flying qualities can be achieved at best, and that degradation to Level 3 occurs in moderate turbulence. Flight experience with the Do-31* 14 ', the Kestrel* 25 ', and the XV-5B* 26 ' agrees with these findings. To achieve further improvement in precision approach and hover flying qualities, all these results indicate that some form of attitude stabilisation is required.…”