Variable-Pitch Fan Blades Using Spring Bias Against Centrifugal Twist
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Solution Overview
Problem
Existing gas turbine engines with variable pitch fan blades rely on counterweights to bias blades to a high pitch or feathered condition in case of hydraulic system failure, which adds weight and complexity, and there is a need for a more efficient mechanism to ensure blade positioning in such scenarios.
Innovation Solution
A spring mechanism is introduced to provide a spring twisting moment that counters centrifugal twisting moments on fan blades, potentially eliminating or reducing the need for counterweights, and ensures blades are in a feathered position during failures, using torsion springs or cam and gear configurations to apply torque in the opposite direction of centrifugal forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If counterweights are used to bias fan blades to high pitch or feathered condition in case of hydraulic system failure, then blade positioning reliability is improved, but device complexity and weight increase
Solution Approach 1:
The patent extracts the essential function of counterweights (biasing blades to feathered position) and implements it through a spring mechanism alone, eliminating the need for heavy counterweight components while maintaining the same safety function during hydraulic system failure
Solution Approach 2:
The patent replaces the traditional mechanical counterweight system with a spring-based mechanism that uses elastic potential energy storage and release to achieve the same blade biasing function, thereby reducing mechanical complexity and weight
2Reliability
If counterweights are used to bias fan blades to high pitch or feathered condition, then blade positioning in failure mode is improved, but weight of the fan assembly increases
Solution Approach 1:
The patent removes the heavy counterweight components from the fan assembly while retaining the essential function of biasing blades to feathered position through a spring mechanism, directly reducing the weight of the moving object
Solution Approach 2:
The patent uses lightweight spring elements that can be replaced if needed, substituting for heavy permanent counterweights, thereby reducing the overall weight of the fan assembly while maintaining the same safety function
3Device complexity
If spring mechanism is used to counter centrifugal twisting moment, then weight and complexity are reduced, but the mechanism must reliably maintain blade position under varying operational conditions
Solution Approach 1:
The patent employs a spring mechanism that dynamically adapts to varying operational conditions through elastic deformation, automatically adjusting the biasing force on fan blades in response to changes in centrifugal forces during different flight regimes
Solution Approach 2:
The spring mechanism changes its mechanical properties (force-displacement relationship) based on operational parameters, providing appropriate blade biasing force across different rotational speeds and flight conditions while maintaining reliability
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 spring mechanism reduces weight and complexity by minimizing or eliminating counterweights, while ensuring reliable blade positioning, enhancing operational efficiency and safety in case of hydraulic system failures.
Implementation Method 1
a spring mechanism operably associated with each fan blade of the plurality of fan blades, the spring mechanism of each respective fan blade operable to create a spring twisting moment on the respective fan blade that is counter to a centrifugal twisting moment of the respective fan blade
Implementation Method 2
The counterweights produce a twisting moment on the propeller blades when the propeller blades are rotating such that the twisting moment on the propeller blades bias the blades to the high pitch or feathered condition
Data Source
AI summary
A gas turbine engine includes a turbomachine comprising a compressor section, a combustion section, and a turbine section arranged in serial flow order. A fan defining a fan axis and comprising a plurality of fan blades is rotatable about the fan axis. A pitch change mechanism is operable with the plurality of fan blades to control a pitch of the plurality of fan blades. A counterweight is connected to each respective fan blade. A spring mechanism is operably associated with each fan blade of the plurality of fan blades to create a spring twisting moment on the respective fan blade that is counter to a centrifugal twisting moment of the respective fan blade.