Auxiliary Power Unit Mechanical Coupling for Aircraft Taxiing Thrust
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Solution Overview
Problem
Existing aircraft propulsion systems face inefficiencies in providing thrust during taxiing operations and starting the engine, particularly in terms of fuel efficiency and mechanical power distribution between high and low pressure spools.
Innovation Solution
A propulsion system incorporating an auxiliary power unit (APU) with a reduction gearbox mechanically coupled to both high and low pressure spools, allowing the APU to supply rotational power to both spools and include a clutch for disengagement, along with a continuously variable transmission to vary rotational speed, enabling efficient thrust generation and engine starting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the APU supplies rotational power to both high pressure spool and low pressure spool simultaneously via reduction gearbox and shafting system, then sufficient thrust for taxiing is provided without starting main engines, but device complexity increases due to additional mechanical coupling components
Solution Approach 1:
The patent combines the functions of starting the high pressure spool and driving the low pressure spool into a single APU system. The APU is mechanically coupled to both spools through a reduction gearbox and shafting system, allowing one power source to perform multiple functions that traditionally required separate systems (pneumatic starter for HP spool and separate drive for LP spool).
Solution Approach 2:
The APU serves multiple functions: it acts as a pneumatic starter for the high pressure spool, provides mechanical power to rotate the low pressure spool for propulsor-driven taxiing, and can operate independently of the main engines. This multi-functionality eliminates the need for dedicated pneumatic starting systems and separate taxiing arrangements.
2Loss of energy
If the reduction gearbox and shafting system are used to couple APU to both spools, then fuel consumption is reduced during taxiing, but manufacturing complexity increases
Solution Approach 1:
The system uses the propulsor (propeller or fan) driven by the low pressure spool to generate thrust during taxiing operations. This self-service approach eliminates the need for external pushback equipment or additional thrust-reversal systems, as the same propulsor used for flight propulsion provides taxiing thrust when driven by the APU.
3Adaptability or versatility
If the clutch is used to mechanically disengage the APU from the spools, then operational flexibility is improved, but device complexity increases
Solution Approach 1:
The clutch mechanism enables dynamic reconfiguration of the power transmission path. It allows the APU to be selectively engaged or disengaged from the high pressure spool and/or low pressure spool based on operational requirements. This dynamic capability provides flexibility for different flight phases, maintenance modes, and emergency procedures while maintaining a relatively simple mechanical implementation.
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 configuration provides sufficient thrust for taxiing without starting the main engines, reduces fuel consumption, and allows for efficient engine starting, eliminating the need for pneumatic starters and minimizing drag during taxiing.
Implementation Method 1
the APU is a thermodynamic machine configured to generate mechanical power from fuel
Implementation Method 2
an auxiliary power unit (APU) comprising a reduction gearbox mechanically coupled to both the high pressure spool and the low pressure spool
Data Source
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AI summary
A propulsion system for an aircraft, comprising a gas turbine engine (20) having a high pressure spool (24) and a low pressure spool (26), wherein the low pressure spool (24) is operative to drive a propulsor (28); and an auxiliary power unit (APU) (22) mechanically coupled to both the high pressure spool (26) and the low pressure spool (24), wherein the APU (22) is operative to supply rotational power to both the high pressure spool (26) and the low pressure spool (24).