Flapping Hinge Fan Blade for Unducted Engine Lift Dissymmetry
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Solution Overview
Problem
Unducted fan assemblies in gas turbine engines experience dissymmetry of lift due to off-axis airflow from crosswinds or high angles of attack at low speeds, leading to high one-per-revolution loads and structural challenges.
Innovation Solution
Integration of a mechanical flapping hinge into the fan blades allows axial movement, altering the effective angle of attack and reducing lift dissymmetry, with the option to lay back during shutdown to minimize drag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an unducted fan assembly is used to generate thrust, then thrust generation efficiency is improved, but dissymmetry of lift occurs due to off-axis airflow from crosswinds or high angles of attack
Solution Approach 1:
The fan blade is designed with a flapping hinge that allows the blade to dynamically adjust its angle of attack in response to asymmetric airflow conditions. The hinge enables the blade to flap upward on the high-lift side and downward on the low-lift side, automatically balancing the lift distribution across the fan assembly during crosswind or high angle of attack operations.
2Power
If the fan blade operates at high angle of attack during low speed flight, then thrust generation is improved, but dissymmetry of lift increases due to off-axis airflow
Solution Approach 1:
The flapping hinge enables the fan blade to dynamically respond to asymmetric aerodynamic forces by adjusting its flapping angle. During high angle of attack operations, the blade automatically flaps to equalize lift distribution, reducing the magnitude of one-per-revolution loads while maintaining effective thrust generation at low speeds.
3Device complexity
If the fan blade is fixed in position, then structural simplicity is maintained, but drag increases during shutdown due to exposed blade area
Solution Approach 1:
The flapping hinge provides passive aerodynamic adjustment capability without complex actuation systems. During shutdown, the blade naturally flaps to a reduced-exposure position, minimizing drag from exposed blade area. The mechanism maintains structural simplicity while enabling dynamic position adjustment through pure aerodynamic forces.
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 flapping hinge reduces 1P loads and dissymmetry of lift, enhancing structural integrity and reducing drag during operation and shutdown, while maintaining efficient thrust generation.
Implementation Method 1
a flapping hinge integrated into the fan blade or coupled to the fan blade, with at least a portion of the fan blade rotatable about the flapping hinge
Data Source
AI summary
An engine defining a longitudinal axis includes: a turbomachine; a fan drivingly coupled with the turbomachine, the fan being a forward thrust fan and having: a hub; a plurality of fan blades, the plurality of fan blades comprising a first fan blade; and a flapping hinge integrated into the first fan blade or coupled to the fan blade, at least a portion of the first fan blade moveable about the flapping hinge to define a variable angle with the longitudinal axis.