Trailing-edge flaps provide a means to dynamically alter aerodynamic characteristics of rotorcraft such as primary flight control and secondary vibration control. While the development of several novel technologies has been explored, many practical implementation barriers exist, particularly for full-scale helicopters. Some of these include force-displacement characteristics of actuators, bandwidth limitations, life cycle concerns, and the ability to operate in the harsh rotary and vibratory environment of rotorcraft. Using these drawbacks as motivation to investigate alternative approaches to on-blade active control, a unique pneumatic actuation system has been developed and tested. Pneumatic Artificial Muscles (PAMs) with high force-to-weight ratios were employed in a prototype device that was designed and evaluated on the bench-top under simulated loads and in a wind tunnel under true aerodynamic loading. The design is based on size and performance estimates of the UH-1 with a flap centered near 0.75R. Experimental measurements show that half peak-to-peak deflections of 10 degrees are achievable at 5 Hz (1/rev) with Mach 0.56 loading, while deflections of greater than 6 degrees can be sustained up to 21 Hz (4/rev). This indicates that the flap actuation system is properly scaled for performance in two frequency ranges required for advanced rotor control. Hence, this research has taken the first step in validating the feasibility of pneumatic artificial muscles for full-scale rotorcraft applications.
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