Tiltrotor Propulsion Configuration with Clutched Thrust Fan
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Tiltrotor aircraft face limitations in forward airspeed due to proprotor aeroelastic instability, and existing propulsion systems with combined engine and thrust fan configurations result in parasitic power losses, residual thrust, and increased complexity, requiring custom-designed engines and compromised performance.
Innovation Solution
A propulsion configuration that separates the engine core power from the thrust fan using a combined gearbox with clutches to allow independent operation of rotor systems and thrust fans, enabling optimal rotational speeds and reducing power losses, while allowing for flexible component placement and maintenance access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the bypass fan is rigidly connected to the power output shaft and always rotates during engine operation, then the engine can provide both thrust and mechanical shaft power, but parasitic power loss occurs due to drag from the rotating bypass fan when thrust is not required
Solution Approach 1:
The propulsion system is segmented into independent components: the engine core can operate independently to provide shaft power, while the bypass fan is separated and only engaged when thrust is required. This segmentation allows the engine to deliver mechanical power without the parasitic drag of a continuously rotating bypass fan.
Solution Approach 2:
The bypass fan is designed with variable geometry and can be dynamically adjusted or retracted. During shaft-power-only operation, the bypass fan is positioned to minimize drag or stopped entirely, while during thrust mode, it is deployed to provide the necessary bypass airflow for propulsion.
2Adaptability or versatility
If the bypass fan always rotates during engine operation, then the engine can maintain operational flexibility, but significant parasitic power loss results from the drag of the rotating bypass fan when bypass airflow is not required
Solution Approach 1:
The propulsion system separates the engine core from the bypass fan, allowing independent operation. The engine core can deliver full shaft power without the bypass fan consuming power, while the bypass fan is only activated when thrust is needed, maximizing available power in each operational mode.
Solution Approach 2:
The bypass fan's operational parameters (rotation speed, geometry, or position) are dynamically changed based on flight conditions. During shaft-power mode, the bypass fan is stopped or positioned to minimize drag, thereby maximizing the power available from the engine core.
3Device complexity
If a combined engine and thrust fan configuration is used, then component integration is achieved, but heavy aft placement results from component placement requirements
Solution Approach 1:
The engine core and bypass fan are separated into independent units. This allows the bypass fan to be positioned optimally for aerodynamic efficiency and weight balance, rather than being constrained by a combined configuration that forces heavy aft placement.
4Device complexity
If inlet guide vanes are used to limit the thrust fan, then component integration is maintained, but unwanted thrust is produced and engine power is robbed, resulting in degraded aircraft performance in shaft mode
Solution Approach 1:
The system separates the engine core from the bypass fan, eliminating the need for inlet guide vanes to limit thrust fan operation. During shaft-power mode, the bypass fan is completely isolated from the engine output, allowing full engine power to be delivered to the shaft without any power being robbed by unwanted thrust production.
5Productivity
If large air inflow is directed into the engine and thrust fan, then propulsion efficiency is maintained, but filtration options are limited, thereby shortening engine life
Solution Approach 1:
The engine core and bypass fan are separated, allowing independent airflow paths. The engine core can be equipped with its own dedicated filtration system optimized for protecting the engine, while the bypass fan has its own airflow path that does not compromise engine filtration or life.
Data Source
AI summary
A tiltrotor aircraft having a propulsion configuration that divorces the engine core power from the thrust fan, using a combined gearbox with a plurality of clutches to couple and decouple one or more rotor systems and one or more thrust fans. The aircraft can be operable for vertical takeoff and landing (VTOL) in a helicopter mode, forward flight in a proprotor mode, and high-speed forward flight in an airplane (jet) mode. The propulsion configuration provides shaft horsepower (SHP) to rotors for VTOL flight, while also providing SHP to the thrust fan for high speed flight. Allowing the rotor and the thrust fan to be clutched on and off, sequentially, enables transition from rotor-borne VTOL flight to wing-borne thrust fan flight, and back.