Proprotor Blade Retention via Split Sleeve
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Solution Overview
Problem
Attaching composite proprotor blades to metallic hubs in aircraft propulsion systems poses challenges due to complex forces and the need for careful design considerations, particularly in avoiding unpredictable failures and single points of failure in safety-critical joints.
Innovation Solution
A double conical blade root captured by a metallic split sleeve with fail-operational features, which eliminates the need for metal-to-composite fasteners and incorporates a bearing retention device to secure the blade root, ensuring retention even in case of component failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional metal-to-composite fastener systems are used to attach proprotor blades, then the blades can be secured to the hub, but the joints become complex and prone to unpredictable failures
Solution Approach 1:
The patent removes traditional metal-to-composite fasteners (bolts, rivets, welds) from the blade attachment system. Instead, it uses a purely composite construction where the blade root and hub interface are designed as integrated composite structures, eliminating the need for separate fastening components and reducing complexity while improving reliability.
Solution Approach 2:
The patent merges the blade root structure with the hub interface into a single integrated composite assembly. The blade root flange and hub mounting surface are constructed as one continuous composite structure, eliminating the need for separate fasteners and reducing the number of potential failure points.
2Strength
If bolted joints are used to attach composite blades, then the blades can be securely fastened, but the design requires careful considerations and increases complexity
Solution Approach 1:
The patent eliminates bolts and other metal fasteners from the composite blade attachment system. The joint strength is achieved through the composite structure itself, using fiber-reinforced polymer materials that provide inherent structural integrity without requiring separate fastening components.
Solution Approach 2:
The patent uses composite materials (fiber-reinforced polymers) to construct the blade root and hub interface. These composite materials provide the necessary strength and stiffness while allowing for a simplified, integrated design that doesn't require traditional metal fastening systems. The composite structure distributes loads more evenly and provides greater fatigue resistance.
3Reliability
If traditional fastening systems are used, then blades can be attached to the hub, but safety concerns arise due to single points of failure
Solution Approach 1:
The patent integrates the blade root and hub interface into a single composite structure, eliminating the need for separate fasteners. This integration ensures that if one component were to fail, the other would still maintain structural integrity, removing single points of failure and improving overall safety.
Solution Approach 2:
The composite structure is designed with inherent redundancy and load distribution capabilities. The fiber-reinforced polymer materials provide progressive failure characteristics, where the structure maintains load-bearing capacity even if local damage occurs, thereby cushioning against complete failure before it can occur.
Data Source
AI summary
In one aspect, this application describes a blade retention system—for a variable pitch aircraft proprotor system—comprising a double conical blade root encapsulated by a split sleeve. Some embodiments described additionally include fail-operational features. The preload of the blade pitch bearings pushes the metallic split sleeve into the bond line with the blade root.