Direct Drive Aft Fan Engine Boundary Layer Thrust
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Solution Overview
Problem
Traditional aircraft engines with forward-mounted fans face challenges in reducing drag and optimizing thrust production, particularly when mounted in the tail region, as they do not effectively utilize the boundary layer air for thrust generation.
Innovation Solution
A direct drive engine configuration with multiple fans positioned in the fuselage and tail section, featuring a long shaft connecting the turbine engine core to the fans and a gearing system, including bevel gears, to drive the fans and optimize airflow through an aerodynamic sleeve, allowing air from the boundary layer to be drawn into the fan inlet flowpath for enhanced thrust.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a traditional forward-mounted fan engine configuration is used, then the engine structure is simple and easy to manufacture, but the drag is high and thrust production is not optimized
Solution Approach 1:
The fan is repositioned from the traditional forward-mounted position to the tail region of the aircraft, changing the spatial dimension of the engine configuration. This dimensional change allows the fan inlet to access boundary layer air from the fuselage, optimizing thrust production while reducing drag.
Solution Approach 2:
The engine is divided into separate functional components: a turbine engine core and a fan assembly connected by a long shaft. This segmentation allows the fan to be positioned independently in the tail region while the engine core remains in a conventional position, resolving the conflict between manufacturing simplicity and aerodynamic optimization.
2Object-affected harmful factors
If the fan is mounted in the tail region to reduce drag, then drag is reduced and thrust production is optimized, but the engine structure becomes complex with a long shaft and gearing system
Solution Approach 1:
A long shaft acts as an intermediary mechanical connector between the turbine engine core and the fan assembly. This intermediary component transmits rotational power over the distance required to position the fan in the optimal tail region location, enabling drag reduction while maintaining structural connectivity.
Solution Approach 2:
The direct mechanical connection between engine core and fan is replaced with a geared connection system. Bevel gears at the fan hub provide the mechanical interface, allowing rotational power transmission while accommodating the spatial separation and enabling independent optimization of both engine core and fan positions.
3Use of energy by moving object
If boundary layer air is utilized for thrust generation, then thrust production is enhanced and energy efficiency improves, but the shaft must be disposed in the fan inlet flowpath creating potential flow interference
Solution Approach 1:
The shaft is nested within the fan inlet flowpath rather than being positioned outside it. This nesting arrangement allows the shaft to occupy the central region of the flowpath without creating external flow interference, while still enabling access to boundary layer air for enhanced thrust generation.
Solution Approach 2:
An aerodynamic sleeve is introduced as an intermediary component between the shaft and the fan inlet flowpath. The sleeve is at least partially disposed in the fan inlet flowpath and includes an aerodynamic profile that minimizes flow interference while allowing the shaft to remain in position for boundary layer air utilization.
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 reduces drag and engine power requirements by efficiently utilizing boundary layer air for thrust production, improving aircraft performance and reducing the energy needed to fly at given air speeds.
Implementation Method 1
the turbine core driving the fan rotation by expanding gasses compressed within a compressor section across a turbine section
Implementation Method 2
Rotation of the fan drives air along a bypass flowpath around the turbine core and generates thrust
Implementation Method 3
the sleeve includes an aerodynamic profile relative to an expected direction of fluid flow through the fan inlet flowpath
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An aircraft engine includes a gas powered turbine core (130). A first fan (150) is connected to the turbine core (130) via a shaft (134). The fan (150) is positioned aft of the turbine (130). A second fan (150) is connected to the first fan (150) via a geared connection (170).