Turbofan In-Flight Relight via Accessory Drag Control
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Solution Overview
Problem
Current systems for in-flight relighting of turbofan engines are complex and inefficient, as they require additional power sources and mechanisms to overcome parasitic drag and achieve relight speed, especially in small turbofans with low inertia.
Innovation Solution
The method involves disconnecting accessory loads from the high-pressure shaft to eliminate parasitic drag, utilizing windmill rotation and ram air to rotate the high-pressure shaft to a desired relight speed, and optionally employing electromagnetic braking to control rotor speed for optimal relighting, without the need for additional power transfer mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If accessory loads are connected to the high-pressure shaft during relighting, then the generator can provide electrical power, but parasitic drag increases making relight difficult
Solution Approach 1:
The accessory loads are segmented into essential and non-essential categories. During relighting, non-essential loads are disconnected from the high-pressure shaft to eliminate parasitic drag, while essential loads (such as the generator for ignition system power) remain connected. This segmentation allows the system to manage the trade-off between power availability and drag reduction.
Solution Approach 2:
Parasitic drag is extracted by selectively disconnecting specific accessory loads from the high-pressure shaft during the relighting process. The system identifies and isolates the drag-causing elements while maintaining the generator connection for essential electrical power needs, thereby resolving the contradiction between power availability and drag reduction.
2Reliability
If additional power transfer mechanisms are used to achieve relight speed, then relight can be achieved, but system complexity increases
Solution Approach 1:
The system uses itself to achieve relight by utilizing the windmill effect of the running engine to drive the high-pressure shaft to the required speed. This self-service approach eliminates the need for external power transfer mechanisms like shaft power transfer arrangements, thereby maintaining reliability while reducing complexity.
Solution Approach 2:
The patent replaces complex mechanical power transfer mechanisms with a simpler aerodynamic solution - the windmill effect. Instead of using mechanical shafts and gears to transfer power, the system relies on air flow through the engine to rotate the high-pressure shaft, substituting a mechanical system with a more efficient and simpler aerodynamic one.
3Device complexity
If windmill effect alone is used to rotate the high-pressure shaft, then system simplicity is maintained, but relight may not be achieved in small turbofans with low inertia
Solution Approach 1:
The system applies local quality by adjusting the drag characteristics at specific locations - disconnecting accessory loads from the high-pressure shaft during relighting. This creates a localized reduction in parasitic drag that compensates for the low inertia of small turbofans, allowing the windmill effect to achieve sufficient rotation speed for reliable relight while maintaining overall system simplicity.
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 simplifies the relighting process by eliminating parasitic drag and allowing windmill power to achieve relight speed, extending the in-flight relight envelope and ensuring efficient engine relighting without additional energy inputs, even in challenging conditions like rapid descent.
Implementation Method 1
permitting ram air to rotate the high pressure shaft
Implementation Method 2
the generator electrically driving an accessory load
Implementation Method 3
the engine having at least one electromagnetic bearing apparatus
Data Source
AI summary
The method and apparatus for in-flight relighting of a turbofan engine involve in one aspect selectively controlling an accessory drag load on one or more windmilling rotors to permit control of the windmill speed to an optimum value for relight conditions.