There is considerable interest in the potential of
active rotor control as a means of improving rotor-craft
loads, vibration, noise, and performance by
using various approaches including individual blade
control, on-blade controls, and active twist. Smart
materials and actuators figure prominently in many of
these approaches, but at present this technology is
limited with respect to actuation force and displacement
capability, as well as maturity level of the
underlying technologies.
With these considerations in mind, the U.S. Army
Aeroflightdynamics Directorate (AFDD) investigated
alternative technologies for individual blade control
surface actuation, and solicited proposals under the
Small Business Innovative Research (SBIR) program.
The Heliflap TM is an electromagnetic actuator
and trailing-edge control surface developed for
helicopter rotor active-control applications. It is a
rugged, compact system with no external linkages
and no moving parts except the flap itself. It has
excellent force, deflection, and frequency characteristics,
as well as good power and thermal dissipation
characteristics. The flap amplitude and frequency are
controlled by modulation of the electrical current to
the actuators. The net installed weight for the non-optimized
prototype is 9.6 pounds. The design and
development of the Heliflap has been completed
including bench testing and preliminary whirl testing
on a full-scale OH-58 helicopter rotor (figure 1) at
rotor speeds up to 81% of normal operations and at
low collective pitch settings.
Test results compare favorably with design
predictions from the Heliflap analytical model. Bench
testing demonstrated 35.6 foot-pounds static torque
for 100 amperes, ±8-degree deflections, and operation
from 0-37 hertz. Whirl testing of the 6- by
24-inch prototype at 81% nominal rotor speed
demonstrated ±6-degree deflections at 21 hertz
(4.4 times per rotor revolution) requiring a total
average electrical power of 220 watts. The actuator
appears to be well suited for active control for rotor
vibration reduction and may have significant potential
for application to rotor primary flight control as
well. A comparison of test results with computer
predictions of the actuator performance is shown in
figure 2.
Point of Contact: B. Wellman/R. Ormiston
(650) 604-3645/5835
bwellman@mail.arc.nasa.gov
rormiston@mail.arc.nasa.gov
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