Minimum Weight Design of a Two Speed Dual Clutch Offset Compound Gear Transmission for Rotorcraft Applications

This paper develops a design code for sizing the major components of a two speed, dual clutch OCG transmission for rotorcraft applications. Furthermore, this design code is integrated into a single main rotor helicopter sizing model to assess any overall system-level performance benefits offered by the two speed transmission. The results of this study show that the two speed variant will always be heavier that the single speed baseline for a given maximum design payload. The results also show that the combined weight of multiple smaller OCG units placed upstream from the combiner stage are significantly lighter than a single OCG located after the combiner. Finally, the results also show that, despite the added weight due to the OCG transmission, the best two speed variant achieved a 20% increase in flight range compared to the single speed baseline carrying the same maximum payload. Hence, the added weight and complexity of the two speed OCG transmission looks like it can indeed "buy it's way onboard".