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research facility that utilizes two Yamaha R-50 remotely piloted helicopters, Fig 2. The facility
is dedicated to flight testing of advanced control algorithms on helicopters. The facility is
dedicated to flight testing of advanced control algorithms on helicopters. The helicopters are
fully instrumented for flight control research, and will be used to demonstrate the NN based
flight control architecture, described later.
Tiltrotor Handling Qualities Application
This section details an application of a NN based adaptive controller architecture to the
XV-15 tiltrotor aircraft. The primary objective is to provide the pilot with consistent handling
qualities throughout all modes of flight. It requires only an approximate linear model at a single
operating point. The architecture is based on the inversion of the linear model, augmented with
an adaptive NN.
Tiltrotor aircraft combine the hover performance and control of a helicopter with the
cruise speed and efficiency of a turboprop airplane. As shown in Fig 3, tiltrotor aircraft feature
wing tip mounted prop-rotors that can be rotated from a vertical orientation for take-off and
landing to a horizontal position for efficient fixed-wing-borne flight for high speed cruise. The
successful XV-15 tiltrotor research aircraft led to the V-22, Osprey, which has begun low rate
serial production for the U.S. Marines and Air Force. Experience with both the XV-15 and V-22
led Bell Helicopter Textron International to commit to design and development of the first civil
tiltrotor, the BB-609. Tiltrotor aircraft represent the first major new aircraft type to enter
production since the supersonic transports of the 1970’s.
Tiltrotor aircraft hold the promise of revolutionizing short-range air transportation. The
military application, exemplified by the V-22, has a clear requirement for high cruise speeds and
long ranges combined with vertical take-off and landings on board ships or into small clearings.
Similarly, the six to nine passenger BB-609 shows immediate promise in search and rescue,
resource development, utility, medical and executive transport roles. In the future, large tiltrotor
transports, serving as regional airliners, promise to relieve growing conventional airport
congestion by replacing commuter aircraft, and freeing up runway slots for larger jet transports.
Such regional transport tiltrotors achieve this air-transportation-system capacity increase by
operating into airport sites other than the active conventional runway and into urban vertiports
located near commercial and population centers such as seen in Fig 3.
The flight mechanics of a tiltrotor present both opportunities and challenges to the
designer. Prop-rotor movement from the vertical, helicopter mode position toward the
horizontal, airplane mode position rapidly accelerates the aircraft while orienting prop-rotor
thrust to its optimum position. Conversely, up and aft movement of the prop-rotors, required to
prepare for a vertical landing, provides the drag needed to decelerate but at the same time
produces a generally undesirable additional lift which the pilot must counteract with appropriate
flight path control.
The shift between helicopter and airplane flight modes necessitates a change in control
strategy. In helicopter mode, thrust is used for vertical control while pitch attitude is used for