A new challenge to industry and the government
alike is the trend toward highly compressed schedules
for rotorcraft uninhabited aerial vehicle (RUAV)
development and system fielding. Current RUAV
proposals and development programs are on 6- to
9-month schedules, in contrast to the 6- to 10-year
schedules common to most recent piloted rotorcraft
systems. This year, the Army/NASA Rotorcraft
Division launched a new initiative: COntrol and
Simulation Technologies for Autonomous Rotorcraft
(COSTAR) which seeks to develop key enabling
technologies for the control and simulation of
RUAVs.
The COSTAR initiative refines technologies
originally developed for manned rotorcraft for
application to the RUAV problem, and seeks to
increase technology integration sufficiently to realize
the desired reduction in design cycle time. Key
elements of COSTAR include accurate flight-mechanics
modeling using system identification
(CIFER), control system design optimization for
multiple objectives (CONDUIT), and real-time
workstation-based simulation (RIPTIDE). COSTAR
technologies are central to three ongoing cooperative
projects, in which university and industry RUAV
developers have teamed with the Army/NASA
Rotorcraft Division's Flight Control Technology
Group.
In one such cooperative activity, Army/NASA
personnel worked under direct contract to Northrop
Grumman, supporting development of the U.S.
Navy's Vertical Takeoff UAV (VTUAV) (figure 1).
Ames personnel participated in flight testing, followed
by extensive system identification of the
aircraft dynamic models (using CIFER), and flight
control analysis/optimization (using CONDUIT).
Ames was also responsible for developing the
detailed flight control preliminary design, including
the determination of a comprehensive set of "Aeronautical
Design Standard-33 (ADS-33) like" design
requirements for use in CONDUIT. This close
working relationship resulted in a successful autonomous
flight of the demonstrator aircraft. The Flight
Control Technology Group is currently under contract
to Northrop Grumman to support system
identification of forward flight models, and flight
control law optimization for the full flight envelope.
Another joint venture involves model identification,
control system design, and flight testing of a
fully instrumented model-scale unmanned helicopter
(a Yamaha R-50 with 10-foot-diameter rotor). In
conjunction with Carnegie-Mellon University, the
CIFER system identification techniques developed
for full-size helicopters were applied to the R-50. An
accurate, high-bandwidth, linear state-space model
was derived for the hover condition. A conclusion of
this study was that small helicopters seem to be
particularly well suited to identification, in part
because of the dominance of the rotor in their
dynamics. This is illustrated by the exceptionally
clean frequency-sweep time responses shown in
figure 2. The R-50 was shown to be dynamically
similar to a scaled UH-1H, although the R-50 is
proportionally heavier. Preliminary control system
designs have been studied using CONDUIT, and
evaluated using the RIPTIDE simulation environment
for remotely piloted operations.
Army/NASA personnel and technology have also
been instrumental in Kaman Aerospace's development
of the Broad-area Unmanned Responsive
Resupply Operations (BURRO) aircraft for the U.S.
Marine Corps. The BURRO program adapts the
existing K-MAX piloted external-lift helicopter for
remotely piloted flight and autonomous way-point
navigation. CIFER was used to identify linear math
models for unloaded and loaded flight at hover and
at 50 and 80 knots; this is the first time that system
identification has been used to extract a coupled
aircraft-plus-slung load model. The resulting linear
models were used to design and tune a flight control
system in the CONDUIT environment-19 design
parameters were tuned to meet 41 handling-quality
and performance specifications, which were based
on the ADS-33 manned rotorcraft requirements. This
work led to a successful flight demonstration of the
K-MAX BURRO UAV for the Marine Corps. Follow-on
work will expand the range and capabilities of the
demonstrator aircraft.
Point of Contact: M. B. Tischler
(650) 604-5563
mtischler@mail.arc.nasa.gov
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