Aircraft Propulsion Assembly With Offset Fan and Differential Gear
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Solution Overview
Problem
Conventional turbojet engines with a turbine connected directly to the fan have limited by-pass ratios due to peripheral tip speed constraints, and distributing propulsion across multiple fan modules complicates production and increases noise, while exposing the gas generator to foreign body ingestion.
Innovation Solution
A powerplant configuration featuring a twin-spool gas generator with a main fan on the longitudinal axis and an auxiliary fan with an offset axis, driven by a differential gear system incorporating a bevel gear, simplifying the design and increasing by-pass ratio without compromising integration or noise levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a turbine is connected directly to the fan, then the structure is simple, but the by-pass ratio is limited due to peripheral tip speed constraints
Solution Approach 1:
The propulsion system is divided into multiple independent fan modules (main fan and offset fans) driven by separate turbines through transmission systems. This segmentation allows each fan-turbine pair to operate independently, enabling higher by-pass ratios without being constrained by the peripheral tip speed of a single large fan, while maintaining manageable structural complexity through modular design
Solution Approach 2:
Transmission systems (including differential gear systems and bevel gears) are introduced as intermediary mechanisms between the turbines and offset fans. These intermediaries enable power transmission to fans positioned at different locations and orientations, allowing the system to achieve high by-pass ratios through distributed fan configuration while maintaining a relatively simple overall architecture
2Productivity
If multiple fan modules are distributed, then the by-pass ratio increases, but production becomes complex
Solution Approach 1:
The propulsion system is divided into standardized modular units (turbine-transmission-fan assemblies) that can be manufactured independently and assembled together. This modular segmentation enables parallel production processes and simplifies quality control, reducing overall production complexity while achieving high by-pass ratios through the combination of multiple modules
Solution Approach 2:
The differential gear system combines multiple power transmission functions into a single integrated mechanism that drives both the main fan and offset fans. This merging of transmission functions reduces the total number of separate components and simplifies the manufacturing process compared to having entirely separate drive systems for each fan
3Productivity
If offset fans are used, then the by-pass ratio increases, but noise increases due to jet shearing
Solution Approach 1:
The differential gear system merges the exhaust flows from multiple turbines into a coordinated output that drives the fan assembly in a unified manner. This coordinated operation reduces turbulent shearing between separate jet streams, thereby reducing noise while maintaining the high by-pass ratio benefits of the distributed fan configuration
Solution Approach 2:
The system converts what would normally be harmful separate jet streams into a beneficial coordinated flow pattern. By using the differential gear system to synchronize the offset fans, the previously noisy separate exhaust plumes are merged into a more unified flow, reducing turbulence-induced noise while preserving the high by-pass ratio
4Device complexity
If the gas generator is exposed, then the structure is simple, but it becomes vulnerable to foreign body ingestion
Solution Approach 1:
The offset fans are positioned and oriented such that their housings and intake structures physically shield the gas generator inlet from foreign objects. This nested arrangement, where the fan assembly envelops or covers portions of the gas generator, provides passive protection against foreign body ingestion while maintaining the overall structural simplicity of the propulsion system
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 enhances propulsive efficiency by optimizing fan and turbine operation independently, reducing noise, and protecting the gas generator from foreign body ingestion while maintaining acceptable ground clearance.
Implementation Method 1
driven by a differential gear system incorporating a bevel gear
Implementation Method 2
differential gear system incorporating a bevel gear
Implementation Method 3
at least one main fan arranged upstream of the gas generator on the longitudinal axis and driven in rotation by the gas generator
Data Source
AI summary
The present invention relates to a powerplant of an aircraft including at least one twin-spool gas generator of longitudinal axis (XX), at least one main fan arranged upstream of the gas generator on the longitudinal axis (XX) and driven in rotation by the gas generator, the main fan being shrouded with a main fan housing; and at least one auxiliary fan with axis (XY, XY′) offset relative to the longitudinal axis (XX) and driven by the gas generator, the auxiliary fan being shrouded with an auxiliary fan housing, the gas generator including at least one low-pressure compressor and a low-pressure turbine connected by a low-pressure shaft, the low-pressure turbine driving in rotation the main fan and the auxiliary fan via at least one power transmission system including a differential gear system incorporating a bevel gear.