Contra-rotating Propeller Radial Arm Tilt
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Solution Overview
Problem
Counter-rotating propeller systems in aircraft turbomachines face mechanical challenges due to axial offset, leading to increased mass and size, as well as significant casing elongation to accommodate propeller overhang and rolling bearings, which is costly and inefficient.
Innovation Solution
The counter-rotating propeller system design tilts the connecting arms of the second propeller radially outward, bringing the blades closer to the casing, reducing the axial length and overhang, and shifting the center of mass towards the casing, allowing for a shorter casing extension and reduced bearing spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the propeller is axially offset from the casing extension, then the propeller can be positioned correctly in the turbomachine, but the casing extension must be significantly lengthened to accommodate the overhang and provide bearing guidance
Solution Approach 1:
The connecting arms are inclined at an angle relative to the axial direction, introducing a radial component to the propeller support geometry. This dimensional change allows the propeller to be supported closer to the casing extension while maintaining proper axial positioning, effectively reducing the required axial length of the casing extension by utilizing radial space instead.
2Reliability
If the casing extension is lengthened to support the propeller overhang, then acceptable bearing guidance can be provided, but the overall mass and size of the system increase
Solution Approach 1:
By inclining the connecting arms, the support structure utilizes radial dimension to reduce axial dimension requirements. This allows bearing guidance to be achieved with a shorter casing extension, thereby reducing the overall mass of the support structure while maintaining reliability.
3Length of moving object
If the connecting arms are inclined radially outward, then the propeller blades can be brought closer to the casing, but the structural design becomes more complex
Solution Approach 1:
The connecting arms are designed with a specific inclination angle parameter that optimizes the balance between reducing axial length and maintaining manufacturing feasibility. By carefully selecting and controlling this angular parameter, the design achieves compact dimensions while keeping the structural design within reasonable manufacturing complexity limits.
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The present invention relates to a system of contra-rotating propellers (30) for an aircraft jet engine, including: - a free power turbine (32); - a first propeller (7) and a second propeller (9), contra-rotating, the former being placed in a predetermined direction relative to the latter, each one including a hub (48a, 48b), an outer ferrule (56a, 56b), as well as coupling arms (60a, 60b) linking the two; and - a casing (42) inserted between the free turbine (32) and the propellers, the latter being arranged in the predetermined direction relative to the casing and the turbine being arranged in the opposite direction relative to said same casing, the latter having a casing extension (46) in the given direction, rotatably supporting the hub (48b) of the propeller (9). According to the invention, the coupling arms (60b) extend in said opposite direction, radially towards the outside.