Abstract: A transmission system for a hybrid aircraft is driven by a plurality of driveshafts and drives a translational propulsion system. Each driveshaft is mounted to a pinion gear which mesh with an upper and lower counter-rotating gear. The upper and lower counter-rotating gears drive a respective upper and lower rotor shaft which powers a counter-rotating rotor system. A first angle is defined between a first and a second driveshaft while a second angle is defined between the second and a third driveshaft. The angle between the driveshafts are a whole number multiple of the formula: &thgr;=(CP/R)*(180/&pgr;). By so angularly locating the driveshafts, proper meshing of the pinion gears and the upper and lower counter-rotating gears is assured and tolerances are less stringent as the support structure is effective designed around optimal location of the driveshafts for gear meshing rather than vice versa.

Abstract: A transmission system for a hybrid aircraft is driven by a plurality of driveshafts and drives a translational propulsion system. Each driveshaft is mounted to a pinion gear which mesh with an upper and lower counter-rotating gear. The upper and lower counter-rotating gears drive a respective upper and lower rotor shaft which powers a counter-rotating rotor system. A first angle is defined between a first and a second driveshaft while a second angle is defined between the second and a third driveshaft. The angle between the driveshafts are a whole number multiple of the formula: &thgr;=(CP/R)*(180/&pgr;). By so angularly locating the driveshafts, proper meshing of the pinion gears and the upper and lower counter-rotating gears is assured and tolerances are less stringent as the support structure is effective designed around optimal location of the driveshafts for gear meshing rather than vice versa.

Abstract: A translational propulsion system for a hybrid UAV includes a pusher prop mounted to the rear of the aircraft with its rotational axis oriented substantially horizontal. The pusher prop is mounted to a driveshaft assembly which transmits power from a coaxial transmission to drive the pusher prop. The driveshaft assembly includes a shaft which defines an axis of rotation. The shaft is mounted to the transmission through a crown spline assembly and is supported by a single bearing. The crown spline and the inherent slop in the bearing accommodates angular deflection and misalignment. The length of the shaft is selected such that the force on the crown spline is less than an allowable level.