1181. Influence of Mechanical Transmission Concepts on a Navy Type A Operational Aircraft Weight

Paper

Abstract

Current requirements envisioned for Type ‘A’ V/STOL are placing unique demands on design ingenuity. The usual demands on cost, reliability, maintainability, etc., are complicated by a variety of conflicting mission and special performance requirements.
– Range and endurance requirements suggest the need for highly efficient fuel consumption concepts such as turboprop designs.
– Vertical takeoff and landing requirements demand high thrust efficient power plants.
– Engine out emergency landing requirements necessitate propulsive system interconnect for power transfer.
– Planned Navy Vertical Support Ships place stringent size limitations in terms of weight and spotting factors.
Numerous other requirements such as dash mach number, cruise altitude and alternate mission capability further complicate the design task.
Studies to date indicate that the most efficient balance in terms of cost/size/weight/ilities will be obtained by a concept employing a common propulsive system for both vertical lift and cruise. The common propulsive system implies a configuration with at least two thrust generators (fans, propellers or jet thrust) and some sort of thrust vectoring (deflector nozzles, tilt nacelles, tilt wing, etc .).
One of the most significant factors in the development Type ‘A’ V/STOL is the power transmission concept employed to transfer power the engine to the thrust generators and the attendant system interconnect necessitated by engine out emergency landing requirements. A transmission system cannot amplify the horsepower output of the engines nor contribute any lifting thrust. Therefore, the transmission weight must be considered dead weight necessary to achieve the desired thrust balance. Elementary rules of design dictate that this dead weight must be held to a minimum and it will be a prime driver in the gross weight of the aircraft.
The most prominently mentioned power transmission scheme is the traditional mechanical design involving gears, shafts, clutches and bearings. This paper addresses the weight, size and to some extent, the complexity for a variety of Type ‘A’ V/STOL mechanical transmission configurations. Although the paper emphasizes the mechanical transmission weight and size, overall aircraft characteristics are summarized for the various configurations to illustrate how the transmission weight influences the total aircraft weight. Growth sensitivities and transmission system design criteria effects are also addressed.