A MAIN POWER SYSTEM FOR SHAFT-DRIVEN HEAVY LIFT HELICOPTERS

摘要

A study was conducted to optimize a geared power system for a heavy lift helicopter (HLH), and to determine specific areas requiring maximum development effort, specific weights, and complexity. The power transmission concept explored here uses multiple gas generators, conventionally installed, and gas-coupled to a peripherally-driven remote turbine of the lift and cruise fan type. The remote turbine is co-axially mounted to a speed-reducing gearbox which is also co-axial with the rotor. This concept is known as the tur¬bine integrated geared rotor (TIGR). Two speed-reducing gearbox configurations are considered. The first uses an integrated rotor hub/ring gear in which the large diameter rotor hub required for HLH has an internal ring gear as its inner surface with the main hub mounting bearings above and below the gear. The second speed-reducing gearbox has the rotor hub segregated from the gearbox. The configurations are extremely compact and necessarily affect many adjacent systems performing essential functions for HLH. Accordingly, a three-part program of design, analysis, and comparative evaluation was undertaken which included the effect on adjacent systems and the resulting HLH aircraft.nThe design for this power transmission concept encompasses the transmission; rotor hub, rotor blade retention, ar-ticulation, and control; affected portions of the fixed and rotating controls; affected portions of the hydraulic and electrical systems; affected portions of aircraft struc¬ture; accessory and tail rotor drive provisions; tail rotor drive by hypercritical shafting; and the power plant.nThe analysis phase includes manufacturing technology, weight, efficiency, stress, deflection, dynamic behavior, reliability, maintainability, cost, and development time.nThe comparative evaluation of the mechanical drive systems includes parametric analysis to define total aircraft, comparison of performance of identical missions by total aircraft, comparison of total aircraft, and evaluation.nThe results show the TIGR concept to be superior to conventional multiple engine/transmission practice for HLH with respect to the essential factor of reliability. The segre¬gated rotor hub with fixed ring gear was found superior to a rotating ring gear integral with the rotor hub. The TIGR concept is compatible with present conceptions of HLH air¬craft.nNo maximum effort development areas were found. The fact remains, however, that interactions between the closely juxtaposed rotor, gearing, and turbine may introduce prob-lem areas that cannot be predicted by paper studies alone. It is recommended, therefore, that this novel concept be investigated by power system testing concurrent with addi-tional studies for better HLH definition.