Propeller Blade Retention Using Variable Radius Bearing Races
Solution Overview
Problem
Modern propeller blade retention systems using composite materials face challenges with weight reduction and ease of maintenance due to the lack of preloading and complex designs, leading to large and heavy retention mechanisms.
Innovation Solution
A bearing arrangement with a 'gothic arch' configuration of inner and outer bearing races and a method of installing bearing balls between these races to retain the propeller blade, allowing for preloading and easier maintenance, while minimizing clearance to enhance retention and reduce stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If bearing races are designed with large clearance to accommodate misalignment, then ease of assembly is improved, but retention stiffness and load capacity deteriorate
Solution Approach 1:
The patent changes the geometric parameters of the bearing races by introducing variable radius profiles with relief regions. The inner race has a first radius in the loading region and a second, larger radius in the non-loading region, creating controlled clearance zones. This parameter variation allows the bearing to accommodate misalignment while maintaining load-bearing capacity through the strategically positioned relief regions that prevent stress concentrations.
2Ease of manufacture
If bearing races are designed with uniform radius to simplify manufacturing, then manufacturing complexity is reduced, but stress concentrations increase under variable loads
Solution Approach 1:
The patent applies local quality by creating non-uniform radius profiles in specific regions of the bearing races. The inner race features a first radius in the loading region where high stress occurs and a second, larger radius in the non-loading region. This localized variation in geometric quality optimizes stress distribution under variable loads while maintaining manufacturability through defined relief regions that eliminate stress concentrations.
3Strength
If preloading mechanisms are added to retention systems, then load capacity is improved, but device complexity and weight increase
Solution Approach 1:
The patent implements preliminary action through the preloaded bearing arrangement where the bearing races are designed with inherent preload characteristics. The variable radius profiles and relief regions create a preloaded condition that optimizes load capacity from the outset. This preliminary structural configuration eliminates the need for complex external preloading mechanisms, maintaining simplicity while achieving the desired load-bearing performance.
Data Source
AI summary
A propeller assembly includes a hub and a blade installed in the hub. A bearing arrangement retains the blade in the hub and includes an outer bearing race at the hub including a first outer race radius and a second outer race radius different from the first outer race radius, connected by an outer relief. The bearing arrangement further includes an inner bearing race at the blade including a first inner race radius and a second inner race radius different from the first inner race radius, connected by an inner relief. A plurality of bearing balls are installed between the inner race and outer race thereby retaining the blade at the hub.