A novel active trailing edge flap system nominally sized for a 35-ft (10.7-m)-diameter four-bladed rotor was developed and whirl tested. The pneumatic artificial muscle actuators employed have several attractive properties, including large forces and displacements, excellent specific work, and robustness. Two pneumatic artificial muscles weremounted antagonistically in the blade root and were connected to an outboard trailing edge flap via bell cranks and linkages. The system was sized to produce flap deflections at frequencies up to 5/rev (N+1/rev) for vibration reduction, as well as large 1/rev deflections for primary rotor control. A quasistatic model of system performance was developed and used to determine the best available actuator geometry and to optimize the kinematics of the linkage system. A subspan, vacuum chamber whirl test rig was developed for testing under full-scale centrifugal, inertial and simulated aerodynamic loading. The performance of the system under a range of operating conditions was evaluated. Large output flap deflections under full-scale loading show the promise of this actuation system.