Variable-Pitch Propeller Assembly With Balanced Counter-Weights
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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 with first and second counter-weights aligned symmetrically on either side of the propeller blade, canceling out bending forces and reducing stress, while maintaining the ability to bias blades towards a feathered position using a common actuator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a single counter-weight arrangement is used to provide torsional force, then blade pitch control is achieved, but bending force creates high local stresses requiring increased blade mass
Solution Approach 1:
The single counter-weight arrangement is segmented into two separate counter-weights positioned on opposite sides of the propeller blade. Each counter-weight provides a portion of the required torsional force, while their symmetric arrangement causes the bending forces to cancel each other out, eliminating high local stresses and the need for increased blade mass.
Solution Approach 2:
The counter-weights are positioned asymmetrically in terms of their individual force contributions but symmetrically in terms of their spatial arrangement. The line connecting the centers of mass of the two counter-weights is perpendicular to the longitudinal axis of the blade, creating a balanced configuration that provides torsional force while canceling bending moments.
2Reliability
If counter-weight arrangements are positioned to maximize torsional bias, then feathered position control is improved, but bending stress on blades increases
Solution Approach 1:
The torsional bias function is segmented between two counter-weights positioned on opposite sides of the blade. This segmentation allows each counter-weight to be optimized for providing torsional force while their opposite positioning ensures that bending forces cancel out, maintaining reliability without increasing stress.
Solution Approach 2:
The second counter-weight acts as a counterweight to the first counter-weight, specifically counterbalancing the bending force generated by the first counter-weight. This anti-weight principle allows the system to achieve maximum torsional bias while the opposing bending moments cancel each other out.
3Strength
If blade mass is increased to withstand bending stress, then structural strength is improved, but aircraft design performance deteriorates
Solution Approach 1:
By segmenting the counter-weight arrangement into two balanced components, the bending stress that would require increased blade mass is eliminated. The symmetric positioning of the two counter-weights creates equal and opposite bending moments that cancel out, allowing the blade to maintain its original optimized mass while withstanding the reduced stress.
Solution Approach 2:
The bending force, which was originally a harmful effect requiring increased blade mass, is converted into a beneficial self-balancing mechanism. The symmetric arrangement of the two counter-weights ensures that the bending forces they generate are equal and opposite, automatically canceling each other out and eliminating the need for mass increase.
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 designs and ensuring aircraft controllability even in actuator or connection failures.
Implementation Method 1
These 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
Implementation Method 2
The counter-weights are aligned such that a line drawn between the center of mass of the first counter-weight and the center of mass of the second counter-weight is substantially perpendicular to a longitudinal axis of the propeller blade
Data Source
AI summary
A variable pitch aircraft propeller assembly includes: a plurality of propeller blades and at least one counter-weight arrangement mounted on a propeller blade. The counter-weight arrangement comprises: a first counter-weight and a second counter-weight. The counter-weights are arranged such that when the propeller blade is in fine pitch, the counter-weights are in a first position with respect to the plane of rotation of said propeller blade, and when the propeller blade is substantially feathered, the counter-weights are in a second position with respect to the plane of rotation of said propeller blade. The counter-weights are aligned such that a line drawn between the center of mass of the first counter-weight and the center of mass of the second counter-weight is substantially perpendicular to a longitudinal axis of the propeller blade.