Helicopter APU Power Transfer Architecture
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Solution Overview
Problem
Current auxiliary power units (APU) in helicopters remain switched off during flight and represent a useless load, as they do not contribute effectively to propulsive or non-propulsive power, and their power supply capacity is not optimized, especially in scenarios like engine failure or asymmetric operation.
Innovation Solution
An optimized energy transfer method where the drive shaft of the auxiliary engine is connected to the main engines, allowing power generated by the auxiliary engine to be added to the main engines, with power matching and conversion to mechanical, electrical, or hydraulic power, and thermal energy recovery from main engine exhaust gases to fuel the auxiliary engine, enabling it to participate in propulsive and non-propulsive power supply and balancing engine asymmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the APU group remains switched off during flight to simplify operation, then ease of operation is improved, but the power supply capacity and energy optimization are worsened
Solution Approach 1:
The APU is designed to perform multiple functions: it can operate independently to provide non-propulsive power (electrical, mechanical, hydraulic, pneumatic) and can also connect to main engines to provide propulsive power. This multi-functionality allows the APU to remain switched off during normal flight (simple operation) while being capable of activating when needed to enhance power supply capacity.
Solution Approach 2:
The system dynamically adjusts the APU's operational state based on flight conditions. The APU can be switched on or off, and its power output can be adjusted, allowing it to transition from a static 'off' state to an active power-providing state when engine failure or asymmetric operation occurs, thus optimizing power supply capacity without compromising operational simplicity during normal conditions.
2Power
If the APU group is activated during flight to increase power supply capacity, then power is improved, but device complexity increases
Solution Approach 1:
The APU system is integrated with the main engine systems through shared power transmission components (reduction gearbox, accessory gearbox, shafts). This merging allows the APU to contribute to propulsive power by connecting to existing main engine infrastructure rather than requiring completely separate systems, thus increasing power supply capacity while limiting the increase in overall system complexity.
Solution Approach 2:
The reduction gearbox and accessory gearbox serve as intermediary components that facilitate power transfer between the APU and the helicopter's power distribution system. These intermediaries enable the APU to provide power without requiring direct integration with all subsystems, thereby managing system complexity while enhancing power supply capacity.
3Weight of moving object
If the APU provides propulsive power to reduce main engine load, then weight of moving object is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The system adjusts operational parameters (power output, shaft speed, torque) of the APU and main engines to achieve optimal power distribution. By dynamically changing these parameters, the system can balance the power contribution between APU and main engines, allowing reduction in main engine size while managing the precision requirements through active parameter control rather than fixed design specifications.
4Loss of energy
If thermal energy recovery from exhaust gases is implemented to fuel the auxiliary engine, then fuel consumption is reduced, but device complexity increases
Solution Approach 1:
The system converts the harmful waste heat from main engine exhaust gases into a useful resource by using it to preheat air for the APU combustion chamber. This thermal energy recovery reduces the fuel needed by the APU while utilizing an otherwise wasted energy stream, thus reducing fuel consumption while adding only the necessary thermal exchange infrastructure.
Solution Approach 2:
Instead of discarding the thermal energy in the exhaust gases, the system recovers this energy through heat exchangers that transfer heat from the exhaust stream to the APU intake air. This recovery process reduces fuel consumption by providing preheated air to the APU combustion chamber, converting a discarded resource into a beneficial contribution.
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 solution optimizes the use of available motorization on a helicopter by enhancing propulsive power, reducing the load and dimensions of main engines, and improving power density, while also reducing fuel consumption through thermal energy recovery, allowing the APU to contribute effectively during flight and in engine failure scenarios.
Implementation Method 1
a heat exchange is carried out between the exhaust gases of each main engine and the air at the compression outlet of the auxiliary engine in order to recover at least in part the thermal energy of the exhaust gases exhaust and to reinject the air thus heated upstream of the combustion of the gases of the auxiliary engine
Implementation Method 2
fuel is injected into the chamber and combustion of the fuel/air mixture provides energy gases. These hot gases are expanded in the turbine
Data Source
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Figure 3~4
Figure 5
AI summary
The aim of the invention is to optimize the entirety of the drive power available in a helicopter by using an auxiliary motor to supply power to the equipment and accessories of the helicopter that are connected to the engines. In an example of an optimized power transfer architecture for implementing the invention, the main engines (1, 1') and the APU group (8), as an auxiliary motor, comprise a gas generator (2; 81) connected, for the main engines (1, 1'), to the gearboxes (6) and accessory boxes (7) of mechanical, electric, and/or hydraulic power sockets, and connected, for the APU group (8), to at least one power conversion member (83, 84, 11). The power conversion member (83, 84, 11) of the APU group (8) is connected to the equipment and accessories via the gearbox (6) and/or via the accessory box (7) of the main engines (1, 1').