Propeller Pitch Change System Rectilinear Outer Race
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Solution Overview
Problem
Existing propeller pitch change systems face challenges with increased loads due to high horsepower, leading to high contact stresses and size limitations that complicate maintenance and assembly, particularly with roller bearings, and more complex systems with self-aligning spherical bearings are needed to mitigate these issues.
Innovation Solution
A pitch change system featuring a yoke assembly with offset pitch trunnions and bearing assemblies having a rectilinear outer race and spherical inner race, which reduces contact stresses through spacers and allows for axial movement and rotation, accommodating high loads while minimizing the physical envelope and facilitating maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If roller bearing size is increased to reduce contact stress, then contact stress is reduced to acceptable levels, but the roller becomes too large to pass through the hub blade retention opening
Solution Approach 1:
The bearing assembly is segmented into multiple smaller rollers that work together, allowing them to pass through the hub blade retention opening while collectively supporting the high loads. This segmentation enables the system to achieve the required load capacity without individual rollers becoming oversized.
Solution Approach 2:
The bearing assembly utilizes a nested configuration where multiple rollers are arranged within a compact space, allowing them to be contained within the hub assembly and pass through the retention opening while maintaining the necessary load-bearing capacity.
2Power
If self-aligning spherical bearings are used to avoid sizing limitations, then the system can accommodate high horsepower, but the system becomes complicated with multiple linkages
Solution Approach 1:
The bearing assembly merges the functions of multiple spherical bearings into a single integrated unit that combines the self-aligning capability with the pitch change mechanism. This consolidation maintains the horsepower capacity while reducing the number of separate linkages and components required.
Solution Approach 2:
The bearing assembly is designed as a multi-functional component that simultaneously provides self-aligning capability, supports high radial and axial loads, and interfaces with the pitch change mechanism. This universal design eliminates the need for separate specialized components for each function.
3Force
If larger roller bearings are used to handle high loads, then load capacity is sufficient, but maintenance and assembly become difficult
Solution Approach 1:
The bearing assembly is segmented into multiple smaller, standardized rollers that can be individually replaced or serviced. This segmentation allows maintenance personnel to work with smaller, more manageable components while maintaining the overall load capacity of the assembly.
Solution Approach 2:
The bearing assembly uses standardized, locally-optimal roller dimensions that are sized for ease of handling and replacement, while the overall assembly configuration ensures adequate load distribution. This local optimization of component size improves maintainability without sacrificing load capacity.
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 system effectively manages high horsepower loads, reduces maintenance demands, and minimizes the physical size of the pitch change system, enabling efficient operation and assembly by distributing loads effectively and accommodating blade and pitch trunnion tolerances.
Implementation Method 1
Each of the bearing assemblies includes a generally rectilinear outer race and a spherical inner race inside diameter to receive a pitch trunnion pin
Implementation Method 2
Axial moment of the yoke assembly and movement of the pitch trunnion pin is accommodated by the bearing assemblies
Implementation Method 3
The pitch trunnion is offset from the blade axis such that as the yoke assembly transits axially along the axis, the pitch trunnion is rotated about the blade axis to effectuate a pitch change in the blade assembly
Data Source
Figure 1
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AI summary
A pitch change system (50) includes a yoke assembly (52) which receives a pitch trunnion (70) that extends from each propeller blade assembly (56). Each pitch trunnion (70) is received within a respective bearing assembly (56) mounted in the yoke assembly (52). The bearing assemblies (56) are mounted between a forward yoke plate (66) and an aft yoke plate (62). A spacer (66) is mounted between each adjacent bearing assembly (56) to position and restrain each bearing assembly (56). Each spacer (66) includes an extension (67) which retains the adjacent bearing assembly (56) on a pitch trunnion pin (70) in a direction generally parallel to axis (A). Each of the bearing assemblies includes a generally rectilinear outer race (68) and a spherical inner race (72) inside diameter to receive the pitch trunnion pin (70). The rectilinear outer race (68) reduces contact stresses to acceptable levels for high load applications yet permits blade installation without actuator disassembly.