Abstract: An unmanned aerial vehicle (UAV) having a toroidal fuselage and a rotor assembly including counter-rotating rotors coaxially mounted with respect to the toroidal fuselage incorporates ancillary aerodynamic structures aerodynamically configured and mounted in combination with the toroidal fuselage to provide a nose-down pitching moment to counteract the nose-up pitching moment generated by airflow over the toroidal fuselage during forward translational flight of the UAV. The ancillary aerodynamic structures have a cambered airfoil profile to provide high lifting forces.

Abstract: An active noise control (ANC) system for a helicopter that is operative to effectively nullify one or more high frequency vibrations emanating from the main transmission gearbox thereof at the gearbox/airframe interface, thereby significantly reducing the interior noise levels of the helicopter, that is design optimized to minimize the number of actuators required, and that is design optimized to minimize contamination forces arising from operation of the system actuators. The ANC system includes modified transmission beams that are mechanically stiffened to function as rigid bodies with respect to the one or more of the high frequency vibrations, a plurality of actuators disposed in combination with the modified transmission beams, a plurality of sensors disposed in combination with the modified transmission beams in a collinear, spaced apart functional correlation with respective actuators, and controllers interconnecting individual actuators with respective functionally correlated sensors.

Abstract: A helicopter (10) is roll vibration resistant having cantilever spring (40) supported masses (42) located at extreme outboard locations (30). The spring portion (40) extends substantially horizontally and is rigidly secured to rigid structure (28). This vibration absorber (34) is tuned to the forced frequency established by the normal rotor (14) RPM times the number of rotor blades (16).