Variable Pitch Propeller Blade Fixing Device
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Solution Overview
Problem
Existing solutions for fixing blades with variable pitch in non-streamlined turbomachines, such as open rotors, face issues with high centrifugal stress damage and vibration-induced premature deterioration, particularly when using titanium alloys, due to the limitations of thread-based coupling methods.
Innovation Solution
A device featuring a cylindrical foot with a hub and complementary engagement elements, allowing axial insertion and locking, which resists high centrifugal stress through large surface contact areas and provides a shrunk-fit mounting to prevent vibrations, using materials like titanium alloys for the foot and steel for the internal bearing parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If thread-based coupling methods are used to fix the foot into the internal part of the bearing, then the assembly is easier to manufacture, but the structure becomes vulnerable to high centrifugal stress damage and cracking
Solution Approach 1:
The invention extracts the threads from the titanium alloy foot structure and relocates them to a separate steel locking ring. This removes the vulnerable threaded connection from the titanium foot, eliminating the risk of stress concentration and cracking in the blade support structure while maintaining the ease of threaded assembly.
Solution Approach 2:
The steel locking ring acts as an intermediary component between the titanium alloy foot and the bearing internal part. It mediates the connection by providing a robust threaded interface that can withstand high centrifugal stresses, while the titanium foot itself remains free of threads and stress concentration points.
2Device complexity
If the foot is inserted into the internal part of the bearing without shrinking means, then the assembly is simpler, but vibrations are generated causing premature deterioration
Solution Approach 1:
The locking ring serves a dual function: it provides the threaded connection for assembly and simultaneously creates the shrinking fit by its interference fit with the bearing internal part. The structure serves itself by using the same component for both connection and vibration prevention functions.
3Reliability
If large resting surfaces are used to transmit stress, then the stress transmission is more reliable, but the assembly size increases
Solution Approach 1:
The invention applies local quality by concentrating the stress transmission function in specific localized areas: the bearing surfaces and the locking ring contact surfaces. The majority of the foot structure remains compact and lightweight, with only the necessary contact areas providing the large resting surfaces for stress transmission.
Data Source
AI summary
The invention relates to a device (12) for a non-streamlined propeller (6, 7) with blades (10) having variable pitch of a turbomachine (1), the device comprising a support (15) intended to support a blade (10) and including a cylindrical foot (17), a bearing comprising a radially internal annular section (20) and a radially external annular section (21) capable of pivoting with respect to each other, the foot (17) being mounted in said internal section (20) of the bearing. The device comprises a hub (27) mounted in the foot (17), said hub (27) including a rim (29) comprising a face (30) coming to bear on the radially internal annular section (20) of the bearing, the hub (27) and the foot (17) of the support (15) comprising complementary engagement elements (18, 28) interacting with a locking component (23).