Starter Generator Lock Feature for APU Windmilling Control
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Solution Overview
Problem
Aircraft auxiliary power units (APUs) face challenges during flight due to windmilling, where ambient air drives generator components without lubrication, leading to undesired rotation and complications in electrical energy control, making it difficult to start the APU.
Innovation Solution
A sensor detects windmilling and triggers a lock feature by supplying AC power to the starter generator's stator, limiting rotation by reversing the polarity, preventing continuous rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the APU inlet duct remains open during flight to allow air flow, then the gas turbine engine components can be cooled and lubricated, but ambient air drives the compressor and turbine rotors to rotate undesirably (windmilling)
Solution Approach 1:
The patent applies preliminary anti-action by using a sensor to detect windmilling conditions and then activating a lock feature that applies a counteracting force to prevent rotor rotation. The lock feature, when engaged, creates a mechanical constraint that opposes the windmilling torque generated by ambient air flow through the inlet duct, thereby preventing undesired rotation while maintaining the inlet open for cooling and lubrication.
2Use of energy by moving object
If the generator components are allowed to rotate freely during windmilling, then the mechanical energy from air flow can be converted to electrical energy, but this generates uncontrolled electrical energy that complicates aircraft electrical grid control
Solution Approach 1:
The patent applies the taking out principle by removing the generator from the windmilling path through the lock feature. When windmilling is detected, the lock feature disengages the generator rotor from the turbine output shaft, effectively extracting the generator from the energy conversion path. This prevents ambient air flow from driving the generator and generating uncontrolled electrical energy, while allowing the turbine to continue rotating for cooling and lubrication purposes.
3Adaptability or versatility
If the APU is started during flight with the inlet duct open, then the aircraft can maintain operational flexibility, but windmilling makes the startup process more challenging and less reliable
Solution Approach 1:
The patent applies preliminary action by detecting windmilling conditions before APU startup and pre-engaging the lock feature to prevent rotor rotation. The sensor monitors the rotational state of the turbine components, and when windmilling is detected prior to startup attempts, the control system activates the lock feature in advance. This preliminary locking action eliminates the windmilling interference before the APU startup sequence begins, ensuring reliable startup while maintaining the inlet open for operational flexibility.
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
Significantly reduces undesired rotation caused by windmilling, ensuring proper lubrication and control of electrical energy generation, facilitating safe APU startup during flight.
Implementation Method 1
supplying AC power to the starter generator's stator, limiting rotation by reversing the polarity
Data Source
AI summary
An APU has a gas turbine engine and a starter generator to be selectively driven by the gas turbine engine. A sensor senses windmilling of components associated with the starter generator. A lock feature limits rotation within the starter generator when windmilling is sensed. A method of operation is also disclosed.