XV-15 litho - NASA's History Office

Flight Envelope Expansion
With the initial hover/low-speed/low-altitude evaluation and the 40-by 80-foot
wind tunnel test completed and all identified technical issues addressed, authorization
was provided by the Government to initiate Phase I of the Contractor
Flight Test activity. This phase involved the initial venture into the full flight
capabilities of the XV-15 TRRA. It became apparent that the Government
Project Office and the Ames Airworthiness and Flight Safety Review Board
(AFSRB) had a conservative view on the approach to envelope expansion. Bell,
on the other hand, having had more recent experience in the development of new
flight vehicles was anxious to more aggressively explore the flight capabilities of
the XV-15. The directives from the Ames TRRA Project Office prevailed and
Bell was required to accept the more cautious approach to envelope expansion.
Expansion would be performed in small airspeed and nacelle angle increments
and a thorough analysis of the test data would be conducted prior to the next
configuration and airspeed test condition.
The first flight of XV-15 N703NA (the aircraft available at Bell for the
Contractor Flight Tests) occurred on April 23, 1979, at the Bell Flight Test
Center, Arlington Municipal Airport, Texas. The Bell pilots assigned to the envelope
expansion were Ron Erhart and Dorman Cannon, and the Bell test director
was Shep Blackman.
In mid June, when the XV-15 had explored flight regimes from the helicopter
mode to a nacelle angle of 60-degrees, LTC Dan Dugan, the NASA/Army
project pilot, made an evaluation flight. In his report to the Ames AFSRB, he
recommended that the envelope expansion be continued, and permission was
granted.
After a total of 15 hours of flight testing and more than three months of expanding
the flight envelope with carefully planned incremental steps, a major milestone
was reached when, on July 24, 1979, the first full in-flight conversion from
helicopter-to-airplane mode was accomplished. During that initial airplane mode
flight lasting about 40 minutes, the crew evaluated climbs, descents, turns, accelerations,
and decelerations and reached an airspeed of 160 knots. The Bell flight
crew and test engineers were quite pleased with the results and envelope expansion
in the airplane mode continued.
The success of the Phase I effort now opened the door for the Proof-of-Concept
Flight Tests, Phase II of the contractor’s XV-15 flight activity. This phase of the
flight program involved a closer examination of the flight characteristics of the
XV-15 and of the performance and operation of its systems. It also presented an
opportunity for the Bell test pilots to train the Government flight crew and permitted
an initial Government evaluation of the XV-15.
In accordance with the Project Plan, the completion of the Proof-of-Concept
phase was to be conducted at a Government test site. Because of the level of risk
associated with the flight test of a low-time research aircraft, it was decided that
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