Abstract
Abstract Geared contra-rotating open rotors have the potential to further reduce fuel consumption relative to geared turbofans, but require a more-complex speed-reducing transmission system to drive the propellers. Hitherto, the preliminary design for such transmission systems has been reported independently of the overall engine modeling or has been limited by many predetermined engine constraints. This has restricted the feasible design space of the transmission systems. A simple transmissions preliminary design approach is needed that does not involve complicated mechanical assessments and can be integrated with engine preliminary design studies. This paper presents a novel design framework for sizing a double-helical differential planetary gearbox for a contra-rotating open rotor. An up-to-date methodology is proposed for the design of maximum load capacity gears for this application based on the power-transmitted, durability, and space envelope requirements. The methodology was validated with published data, demonstrating only very minor differences in geometry dimensions. Parametric analyses have been made to assess the impact of the design assumptions on gearbox dimensions. The framework also enables the identification of feasible torque ratios between the output shafts of the speed-reducer and the contra-rotating propellers driven by them. The impact of the torque ratio on the size of the gearbox has been analyzed for equal propeller rotational speeds and different speed ratios between the output shafts. This study shows that potential torque ratios lie between 1.1 and 1.33, with the higher ratios enabling more compact gearboxes having four or five planet gears.
Highlights
The sustainable economic growth of the aerospace industry requires innovative solutions
The upgraded methodology proposed in this paper for the sizing of the differential planetary gearbox (DPGB) is deemed to be validated and appropriate for the Contra-Rotating Open Rotor (CROR) application using a gearbox arrangement similar to the one in reference [26]. 5.2 Parametric Assessments of the Gearbox Preliminary Design
This paper provides a framework to calculate the dimensions of a differential planetary gearbox to comply with the transmitted power and durability requirements of a contra-rotating open rotor
Summary
The sustainable economic growth of the aerospace industry requires innovative solutions. The Contra-Rotating Open Rotor (CROR) is one of these architectures with the potential for improving propulsive efficiency as it benefits from low specific thrust and presents the capability to reduce the propeller speed and loading to maintain a high stage efficiency. The contribution of this paper is the development of a design framework for the planetary gears in a CROR, incorporating the engine performance requirements into the preliminary design of the transmission system. The transmission system and the CROR share a common preliminary design variable that is the torque ratio (TR) between the contra-rotating propellers, i.e. between the output shafts of the speed-reducer. The engine core includes a two-spool gas generator and a low-pressure system (the propulsor) comprising a free-power LPT driving co-axially mounted contra-rotating propellers through a transmission system that enables the LPT and the propellers to run at their optimum speeds and efficiencies. Propeller rotational speeds are a design parameter of the engine model and are inputs to the preliminary design of the transmission system
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