Multi-Engine Hybrid Aircraft Propulsion Assembly with Redundant Start
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Solution Overview
Problem
Existing propulsion systems in twin-engine or multi-engine aircraft, such as helicopters, lack redundancy for starting engines in standby mode and result in significant electrical draw when not operating in Single Engine Operative (SEO) mode, leading to inefficiencies and reliability issues.
Innovation Solution
A hybrid propulsion assembly with two engines, each equipped with a gas generator and a free turbine, featuring high-power and low-power electric machines that can be coupled to the gas generator or free turbine during different phases to optimize engine start and electrical generation, reducing reliance on the gas generator for efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single high-power electric machine is used to start the gas generator, then the starting function is achieved, but redundancy for engine restart in standby mode is insufficient
Solution Approach 1:
The single high-power electric machine is segmented into two separate electric machines: a first high-power electric machine coupled to the gas generator for starting, and a second high-power electric machine coupled to the free turbine for generating electrical energy. This segmentation provides functional redundancy and resolves the reliability-complexity contradiction by distributing functions across multiple specialized components.
Solution Approach 2:
The patent merges the starting function and electrical generation function into a coordinated system where two electric machines work together - one dedicated to starting the gas generator and the other to generating electricity from the free turbine, while both can contribute to engine restart in standby mode, achieving reliability through functional integration.
2Reliability
If the gas generator is kept in standby mode for quick restart, then engine restart capability is improved, but electrical draw increases when not in SEO mode
Solution Approach 1:
The free turbine is configured to automatically drive the second high-power electric machine to generate electrical energy during normal operation, which can then be used to maintain the gas generator in standby mode without excessive electrical draw from external sources. The system serves itself by using waste energy from the free turbine to support the standby function.
Solution Approach 2:
The patent recovers electrical energy that would otherwise be wasted by coupling the second high-power electric machine to the free turbine. This recovered electrical energy is used to maintain the gas generator in standby mode, reducing the net electrical draw and resolving the contradiction between reliability and energy consumption.
3Adaptability or versatility
If electric machines are coupled to both gas generator and free turbine, then functional versatility is improved, but device complexity increases
Solution Approach 1:
Each electric machine is assigned a specific primary function and coupling configuration: the first high-power electric machine is primarily coupled to the gas generator for starting, while the second high-power electric machine is primarily coupled to the free turbine for electrical generation. This localized functional assignment reduces complexity while maintaining overall system versatility through coordinated operation.
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
The system enhances engine start reliability, optimizes power consumption, and reduces electrical draw by utilizing electric machines to generate power from the free turbine, thereby improving overall propulsion assembly efficiency and reducing mass.
Implementation Method 1
one of the first or of the second electric machine being able to be coupled to the gas generator and to set the gas generator in rotation during a start phase of the engine
Implementation Method 2
a free turbine driven in rotation by a gas stream generated by the gas generator
Implementation Method 3
The gases burnt due to the combustion are then discharged at high speed. A first expansion then occurs in the gas generator turbine, during which the latter extracts the energy necessary to drive the compressor
Data Source
AI summary
A propulsion assembly for a hybrid aircraft including a first and a second engine each having a gas generator and a free turbine, a main rotor coupled to the free turbine of the first and second engines, the first engine including a first electric machine and a second electric machine of lower power than the first electric machine, one of the first or of the second electric machine being able to be coupled to the gas generator and to set the gas generator in rotation during a start phase of the engine, and being further able to be coupled to the free turbine in order to generate electrical energy after the start phase, the other of the first or of the second electric machine being coupled to the gas generator only.