Variable-Pitch Fan Blade Center of Gravity Design
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Solution Overview
Problem
Turbine engine blades tend to rotate into an unfavorable 'flat' position during failure of the pitch change mechanism, leading to increased drag and potential loss of control, and existing solutions like heavy counterweights or flyweights are either mass-penalty or space-constrained.
Innovation Solution
The design positions the center of gravity of each blade on or near a fictitious plane perpendicular to the pivoting axis, allowing aerodynamic forces to guide the blade into a minimum drag 'feathered' position in case of failure, eliminating the need for heavy counterweights or flyweights, thus reducing weight and optimizing space usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy eccentric counterweights are used to ensure blade return to feathered position, then reliability is improved, but weight increases significantly
Solution Approach 1:
The patent extracts the heavy counterweights from the system and replaces them with a blade geometry design where the center of gravity is positioned on the rotation axis. This eliminates the need for separate counterweight components while maintaining the feathered position return function through aerodynamic forces alone.
Solution Approach 2:
The blade design allows itself to return to the feathered position automatically through aerodynamic forces when the pitch change mechanism fails. The center of gravity positioning on the rotation axis enables the blade to self-correct without requiring external counterweights or additional active control systems.
2Weight of moving object
If flyweights are attached to bevel gears, then mass is reduced through compounding effects, but space constraints prevent integration into the rotor
Solution Approach 1:
The patent removes the flyweights from the pitch control mechanism entirely and replaces them with a blade geometric design. This extraction eliminates the space occupation issues while achieving the same feathered position return function through the center of gravity positioning on the rotation axis.
Solution Approach 2:
Instead of adding mass (flyweights) to the pitch control mechanism to achieve feathered position return, the patent inverts the approach by positioning the center of gravity on the rotation axis and using aerodynamic forces. This inversion eliminates the need for additional components in the limited space.
3Weight of moving object
If blades are positioned to return to feathered position without counterweights, then weight is reduced, but control precision during failure may be compromised
Solution Approach 1:
The patent applies local quality by precisely positioning the center of gravity of each blade at a specific location (on the rotation axis) rather than using a general mass addition approach. This localized precision in center of gravity positioning ensures reliable feathered position return without requiring heavy counterweights.
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 prevents blades from assuming a 'flat' position during pitch change mechanism failure, reduces weight and axial/radial space usage, and allows for a higher bypass ratio and improved propulsive efficiency, reducing specific fuel consumption and increasing the bypass ratio.
Implementation Method 1
allowing aerodynamic forces to guide the blade into a minimum drag 'feathered' position in case of failure
Implementation Method 2
the blade has a tendency to rotate around the pivoting axis Y (in the direction of the arrow A) under the influence of centrifugal forces Fc applied to it
Data Source
AI summary
A fan of a turbine engine, the fan including a fan disk provided with blades on its periphery, the blades being pivotally mounted on the disk around a pivoting axis and having a center of gravity, and a pitch change mechanism for the blades, each blade being configured so that its center of gravity is positioned on or at a small distance from a fictitious plane which passes through the pivoting axis of the blade and which is perpendicular to the axis of revolution of the fan when the blade is in a minimum drag position.