Variable-Pitch Propeller Counter-Weight Layout for Lower Blade Stress
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Solution Overview
Problem
Existing counter-weight arrangements in variable pitch propeller assemblies exert bending forces on blades, leading to high local stresses and increased mass, which is disadvantageous in aircraft design.
Innovation Solution
A double counter-weight arrangement is designed where the first and second counter-weights are aligned such that a line between their centers of mass is perpendicular to the propeller blade's longitudinal axis, canceling out bending forces and reducing stress, while maintaining the ability to bias blades towards a feathered position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single counter-weight arrangement is used to bias blades towards feathered position, then reliability is improved, but bending stress and blade mass increase
Solution Approach 1:
The single counter-weight arrangement is divided into two separate counter-weights (first and second counter-weights) positioned at different locations on the propeller blade. This segmentation allows each counter-weight to contribute to the feathering bias while distributing the bending forces, thereby reducing the peak bending stress on the blade structure.
Solution Approach 2:
The counter-weights are positioned in different spatial dimensions along the blade span. The first counter-weight is located at a first radial position while the second counter-weight is located at a second radial position, creating a three-dimensional distribution that optimizes both the feathering moment and stress distribution across the blade.
2Strength
If blade mass is increased to account for bending stress, then strength is improved, but weight increases which is disadvantageous
Solution Approach 1:
By segmenting the counter-weight function into two separate masses distributed along the blade, the bending moments are distributed more evenly through the blade structure. This reduces the peak stresses that would otherwise require excessive strengthening and additional mass.
Solution Approach 2:
The dual counter-weight arrangement creates a balanced system where the gravitational and centrifugal forces on the two counter-weights work together to produce the desired feathering moment while counterbalancing each other's bending effects, reducing the overall structural reinforcement needed.
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 double counter-weight arrangement reduces bending stress on propeller blades, allowing for lighter blade construction and maintaining control in the event of actuator failure.
Implementation Method 1
The counter-weight arrangements provide a torsional force to the blades, biasing the blades towards a feathered position when the propeller is spinning as a result of centrifugal forces.
Data Source
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Figure 5
AI summary
A variable pitch aircraft propeller assembly (52) comprising: a plurality of propeller blades (1) and at least one counter-weight arrangement (30) mounted on a propeller blade (1). The counter-weight arrangement (30) comprises: a first counter-weight (38) and a second counter-weight (42). The counter-weights (38, 42) are arranged such that when the propeller blade (1) is in fine pitch, the counter-weights (38, 42) are in a first position with respect to the plane of rotation (7) of said propeller blade (1), and when the propeller blade (1) is substantially feathered, the counter-weights (38, 42) are in a second position with respect to the plane of rotation (7) of said propeller blade (1). The counter-weights are aligned such that a line drawn between the centre of mass of the first counter-weight (38) and the centre of mass of the second counter-weight (42) is substantially perpendicular to a longitudinal axis of the propeller blade (1).