Comparative Bench Test Assessment of Medium Authority On-blade Actuation Technologies

Trailing Edge (TE) servo flaps embedded in the outer portion of a rotor blade have been proposed for both primary flight control and higher harmonic controls. The flight control application requires large 1/rev flap displacements on the order of ±15°. Higher harmonic control applications require less flap displacement, but greater bandwidth. Higher harmonic active control of vibration and acoustics can generally be achieved with small flap deflections of approximately ±1° or less. However, rotor power reduction appears to benefit from medium deflections, on the order of +5° to +10° at 2/rev through N+1/rev frequency content. Research at Bell Helicopter has been conducted to explore actuation methods that are capable of medium flap deflections up to N+1/rev frequencies to enable performance improvements, in addition to vibration and noise benefits. Three medium authority on-blade actuation approaches are developed against a common set of requirements generated for a Bell model 430 rotor blade with a TE flap. Actuator technologies investigated include one electromagnetic and two flexible membrane pneumatic actuator configurations, including a pneumatic muscle and pneumatic diaphragm. Each actuator is fabricated and bench tested against a common set of conditions to provide a side-by-side comparison of key performance metrics and to gain practical experience. Test results indicate that all three actuation approaches have sufficient stroke, torque and bandwidth potential for the medium authority on-blade application. The electromagnetic linear motor and drive mechanism approach is mechanically complex and heavy relative to the pneumatic approaches. The pneumatic muscle approach is light and compact, but its linear output requires additional mechanisms to connect to the flap and remain within the blade contour. The pneumatic diaphragm approach is powerful and compact, and connects to the flap in a mechanically simple way, with the lowest installed mass of the three configurations. Both flexible membrane pneumatic actuators have great promise for the medium authority on-blade actuation application.