Abstract: A flight control system for a helicopter having a main rotor and a tail rotor is provided. The flight control system includes an automatic rotor speed control being configured to transition the main rotor and the tail rotor between a high speed and a low speed based upon a plurality of received information without requiring any pilot action, the plurality of received information comprising height above ground level, knot indicated air speed, outside air temperature, barometric altitude, pressure altitude, density altitude, and an engine operational status.

Abstract: A transmission is provided wherein selected configurational parameters of interacting spur gearing are modified to abate the vibration levels thereof due to the effects of differential thermal expansion of the gearbox housing. The chordal addenda of the gear teeth of the interacting spur gearing are extended by a predetermined amount, based upon the computed relative radial displacement of the centerlines thereof due to the differential thermal expansion effects, to provide modified interacting spur gearing having increased outside diameters. Such modified spur gearing provides an effective centerline spacing for the transmission such that the interacting spur gearing thereof has an operating contact ratio greater than the design contact ratio at engine start up.