Appendix: Lessons from Flight-Testing the XV-5 and X-14 Lift Fans

Note: The following compilation of lessons learned from the XV-5 and X-14 programs is excerpted from a report prepared by Ames research pilot Ronald M. Gerdes based upon his extensive flight research experience with such aircraft and is of interest because of its reference to Supersonic Short Take-Off, Vertical Landing Fighter (SSTOVLF) studies anticipat­ing the advent of the SSTOVLF version of the F-35 Joint Strike Fighter:[1457]

The discussion to follow is an attempt to apply the key issues of "lessons learned” to what might be applicable to the prelim­inary design of a hypothetical Supersonic Short Take-off and Vertical Landing Fighter/attack (SSTOVLF) aircraft. The objec­tive is to incorporate pertinent sections of the "Design Criteria Summary” into a discussion of six important SSTOVLF pre­liminary design considerations to form the viewpoint of the writer’s lift-fan aircraft flight test experience. These key issues are discussed in the following order: (1) Merits of the Gas – Driven Lift-Fan, (2) Lift-Fan Limitations, (3) Fan-in-Wing Aircraft Handling Qualities, (4) Conversion System Design, (5) Terminal Area Approach Operations, and (6) Human Factors.

MERITS OF THE XV-5 GAS-DRIVEN LIFT-FAN

The XV-5 flight test experience demonstrated that a gas-driven lift-fan aircraft could be robust and easy to maintain and oper­ate. Drive shafts, gear boxes and pressure lubrication systems, which are highly vulnerable to enemy fire, were not required with gas drive. Pilot monitoring of fan machinery health is thus reduced to a minimum which is highly desirable for a single – piloted aircraft such as the SSTOVLF. Lift-fans have proven to be highly resistant to ingestion of foreign objects which is a plus for remote site operations. In one instance an XV-5A wing – fan continued to produce substantial lift despite considerable damage inflicted by the ingestion of a rescue collar weight. All pilots who have flown the XV-5 felt confident in the integrity of the lift-fans, and it was felt that the combat effectiveness of the SSTOVLF would be enhanced by using gas-driven lift-fans.