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THE XV-15 TILT ROTOR RESEARCH AIRCRAFT _
Daniel C. Dugan (M)
NASA-Ames Research Center
Ronald G. Erhart (M)
Bell Helicopter Textron
Laurel G. Schroers
Aeromechanics Laboratory
U.S. Army Research and Technology Laboratories (AVRADCOM)
INTRODUCTION
The XV-15 Tilt Rotor Research Aircraft Program is a
joint NASA/Army program to develop and evaluate tilt rotor
technology for civil and military applications. Navy par-
ticipation in the program began one year ago as a result of
their interest in the tilt rotor concept. The XV-15 evolved
from the XV-3 "Convertiplane" of the 1950's (fig. I). _
Although the XV-3 successfully demonstrated the concept and
was able to perform conversions between the helicopter and
airplane modes, it was very limited by deficiencies in per-
formance, aeroelastic stability, and handling qualities.
After a design competition, Bell Helicopter Textron was
awarded a contract in 1973 to build two tilt rotor research
aircraft.
The potential of the tilt rotor concept can be illus-
trated by comparing various VTOL concepts in terms of hover
and cruise performance (fig. 2). It is difficult to surpass
the hovering capability of the helicoptez, given its low
disc loading. However, the highly twisted blades of the
tilt rotor provide hovering performance that compares favor-
ably, even though its disc loading is somewhat higher than
that of the helicopter. The blades provide efficiency that
the helicopter is denied because the helicopter rotor must
provide both thrust and lift in forward flight. Considering
cruise performance (fig. 3), the tilt rotor is also promis-
ing because of its speed and yet it retains the benefits
that are derived from much lower disc loadings than other
concepts. It combines some of the better features of both ::
helicopters and airplanes and can be superior to either in i
some areas, including fuel efficiency and noise levels.
Before discussing the design characteristics of the
aircraft, a brief review of the program chronology is
appropriate. _ _
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