Propeller Hub Backup Retaining Members for Blade Escape Prevention
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Solution Overview
Problem
The existing propeller hubs for turbomachines with variable pitch blades face significant structural damage due to high centrifugal forces when the polygonal ring fractures, as the blades can escape and cause extensive damage if not retained properly.
Innovation Solution
A propeller hub design incorporating a polygonal ring with backup retaining members that pass through openings in the ring, featuring enlarged heads with bearing surfaces and dovetail-shaped bases for secure retention, which engage with the rotor element to absorb radial forces in case of ring fracture or deformation, preventing blade escape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the polygonal ring is used to hold the blades, then the blades can be retained during normal operation, but the structure becomes vulnerable to fracture under high centrifugal forces
Solution Approach 1:
The retention system is segmented into multiple independent backup retaining members distributed around the polygonal ring, rather than relying on a single continuous ring structure. Each backup retaining member independently engages with the rotor element through the openings in the ring, providing distributed load bearing capacity that reduces stress concentration and prevents catastrophic failure if one member fails.
Solution Approach 2:
The backup retaining members are pre-installed and positioned to engage with the rotor element before the polygonal ring can fail under centrifugal load. The bearing surfaces of these backup members are designed to contact the exterior surface of the ring at critical stress points, providing a cushioning effect that prevents blade escape even if the main polygonal ring fractures.
2Reliability
If backup retaining members are added to prevent ring fracture, then blade retention reliability improves, but device complexity increases
Solution Approach 1:
The backup retaining members serve multiple functions: they act as structural reinforcement elements during normal operation, provide emergency retention capability if the polygonal ring fails, and distribute centrifugal loads across multiple engagement points. This multi-functionality justifies the added complexity by providing both primary and backup retention mechanisms through the same components.
Solution Approach 2:
The backup retaining members are nested within the existing hub structure, passing through openings in the polygonal ring and engaging with the rotor element. The dovetail-shaped bases of these members are integrated into the rotor element's geometry, allowing them to be incorporated into the existing design without requiring separate complex assembly structures.
3Strength
If the backup retaining members have enlarged heads with bearing surfaces, then the ability to absorb radial forces improves, but the manufacturing complexity increases
Solution Approach 1:
The backup retaining members feature localized enlarged heads with bearing surfaces at specific critical locations where they contact the polygonal ring exterior surface. This local reinforcement provides high radial force absorption capacity precisely where needed during failure events, while the rest of the member structure remains relatively simple for manufacturing.
Solution Approach 2:
Instead of making the entire backup retaining member structure complex to achieve high strength, the design inverts the approach by keeping the member geometry simple and concentrating the complexity only in the localized bearing surface area. The enlarged head is a straightforward machining feature that can be added to standard member geometries without requiring complex forming or assembly processes.
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 backup retaining members effectively limit damage by retaining the polygonal ring and blades, even in the event of fracture, thereby reducing the risk of extensive structural damage to the turbomachine.
Implementation Method 1
In operation, the blades of the propeller are subjected to very high centrifugal forces, as high as 30 000 daN, which forces are transmitted to the polygonal ring.
Data Source
AI summary
A hub for a propeller having variable pitch blades for a turbine engine, for example for a propfan turbine engine. The propeller hub includes: a polygonal ring having substantially radial cylindrical housings distributed about a central axis of the ring for receiving the blades; a rotor element for the turbine of the turbine engine; a supporting flange attached to the ring so as to connect the ring to the rotor element; and a plurality of backup retaining members linked to the rotor element, and each of which includes at least one bearing surface opposite an outer surface of the ring with a radial spacing.