Wind Tunnel Testing of a Helicopter Rotor Trailing Edge Flap Actuated via Pneumatic Artificial Muscles

Abstract

An active trailing edge flap system, actuated utilizing Pneumatic Artificial Muscles (PAMs), is developed in this study. PAMs were chosen as the actuation method because of several attractive properties, including: high specific work and power output, an expendable operating fluid (air), and robustness. Because of their performance, PAM are a potential enabling technology for a variety of next-generation aerospace systems. The actuation system developed here is sized for a full-scale active rotor system for a Bell 407 scale helicopter. This system is designed to produce large Trailing Edge Flap (TEF) deflections (±20°) at the main rotor rotation frequency (1 rev−1) to create large amplitude thrust variations that enable primary control of the helicopter. Additionally, the TEF actuation system is designed to produce smaller magnitude deflections at higher frequencies, up to 5 rev−1 ( N + 1 rev−1), to provide vibration mitigation capabilities. The PAMs are mounted antagonistically in the root of each blade. A bell crank and linkage system transfers the force and motion of these actuators to a trailing edge flap on the outboard portion of the rotor. A reduced span wind tunnel test model of this system was fabricated and tested in the Glenn L. Martin Wind Tunnel at the University of Maryland at wind speeds of up to M = 0.3, which is the maximum test wind speed of the facility. The test article consisted of a 1.55 m long outboard section of a Bell 407 rotor blade cantilevered from the base of the tunnel with a 0.86 m, 15% chord plain flap that was driven by the PAM actuation system. Testing over a wide range of aerodynamic conditions and actuation parameters demonstrated the considerable control authority and bandwidth of the system at the aerodynamic load levels available in the tunnel. Comparison of quasi-static experimental results shows good agreement with analytical predictions made using a simple system model.