TERMINAL AREA APPROACH OPERATIONS

The XV-5B demonstrated that lift-fan aircraft are capable of performing steep simulated instrument approaches with up to 20° flight-path angles. Once more, lack of an integrated powered-lift flight control system was the primary cause of adverse handling qualities and operational limitations. The SSTOVLF’s integrated powered-lift system must provide decou­pled flight path control for glide slope tracking where a sin­gle controller, such as a throttle-type lever is used for direct flight-path modulation while airspeed and/or angle-of-attack are held constant. Simulator evaluations of such systems have indicated significant improvements in handling qualities and reductions in pilot workload, an integrated powered-lift sys­tem a must in a single-piloted SSTOVF.

Evaluations of the XV-5B’s ability to perform simulated instrument landing approaches along a 10° glide slope revealed that pilots preferred to approach with a deck-parallel attitude (near-zero angle-of-attack) instead of using deck-level attitude (near 10° angle-of-attack) instead of 15°. Fan-stall boundary and random aerodynamic lift disturbances were cited as the causes.

SSTOVLF designers should encourage the development of lift – fans with increased angle-of-attack capability which would enhance Instrument Meteorological Conditions (IMC) oper­ational capability and improve safety.

All pilots that flew the XV-5 (the "XV-5 Fan Club”) were of the unanimous opinion that the conversion handling qualities of the Vertifan were completely unsatisfactory for IMC oper­ations. Trying to contend with the large power changes, atti­tude and altitude displacements, and abrupt airspeed changes while trying to fly instruments with the XV-5’s "manual” con­trol system was too much to handle. The enhanced operational flexibility requirement laid on the SSTOVLF requires that it have full IMC operational capability.