Aircraft Engine Windmilling Speed Control via Electric Motor
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Solution Overview
Problem
In multi-engine aircraft operations, a turbofan blade-off event often forces engine shutdown, leading to uncontrollable and drag-inducing 'dead' engines with vibration issues due to windmilling, which existing systems fail to effectively manage during flight.
Innovation Solution
A method involving a turbofan engine with an electric motor/generator system that allows the engine to windmill, determining and maintaining a desired windmilling speed to avoid critical shaft speeds, and using motor/generators to control shaft speed to minimize vibration and resonance, thereby reducing drag and extending flight duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine is shut down after a blade-off event, then the engine stops producing thrust, but the windmilling engine creates vibration issues and drag on the aircraft
Solution Approach 1:
The patent changes the operational parameter of the windmilling engine from uncontrolled free rotation to controlled rotation at a specific RPM range (50-100% of normal operating RPM). The electric motor/generator applies electrical braking torque to reduce the windmilling speed from potentially dangerous high speeds to a controlled range that minimizes vibration and drag while maintaining engine controllability throughout the flight.
Solution Approach 2:
The patent replaces the purely mechanical windmilling system with an electro-mechanical control system. The electric motor/generator, which normally serves as a starter, is repurposed to provide electrical braking control during emergency shutdown scenarios, substituting uncontrolled mechanical windmilling with controllable electro-mechanical speed regulation.
2Ease of operation
If the engine is allowed to windmill freely after shutdown, then the engine remains simple to operate, but the uncontrollable windmilling creates vibration and drag issues
Solution Approach 1:
The patent makes the electric motor/generator multi-functional by using it both as a starter motor during normal engine starting and as a braking device during emergency shutdown scenarios. This eliminates the need for separate braking mechanisms, maintaining ease of operation through existing system components while addressing vibration and drag problems.
Solution Approach 2:
The system uses its own electric motor/generator component to control its own windmilling speed after shutdown, rather than requiring external braking systems. The engine's existing electrical system provides the braking torque needed to control the windmilling speed, making the system self-sufficient and maintaining operational simplicity.
3Object-generated harmful factors
If the electric motor/generator is used to control shaft speed, then vibration and drag are reduced, but the system complexity increases
Solution Approach 1:
The patent utilizes the existing electric motor/generator that is already part of the engine's starter system. By programming the Flight Management System to control this existing component in braking mode during emergency shutdown, the patent avoids adding new hardware complexity while achieving vibration and drag reduction through speed control.
Solution Approach 2:
The system employs feedback control where the Flight Management System monitors the engine's windmilling speed and adjusts the electric motor/generator braking torque accordingly to maintain the desired RPM range (50-100% of normal operating RPM). This closed-loop control minimizes vibration and drag while using existing system components, thereby limiting the increase in overall system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces vibration-related component failures, minimizes drag, and extends the operational range and controllability of the aircraft by efficiently managing engine speed and energy usage during emergency shutdowns.
Implementation Method 1
operating the electric motor/generator to rotate the shaft at said desired windmilling speed
Implementation Method 2
operating the electric motor/generator change a speed of the shaft to avoid said at least one shaft speed to be avoided
Data Source
AI summary
A method of emergency operation of an aircraft turbofan engine during an aircraft flight is provided. The engine includes a fan shaft with a fan, and an electric motor/generator mounted for rotation therewith. The method includes shutting down the engine while allowing the engine to windmill, operating the electric motor/generator to rotate the shaft at a determined windmilling speed which is desired for the fan shaft, and operating the engine at the desired windmilling speed for substantially a remainder of the aircraft flight.