Aircraft Rotor Blade Root with Separate Force Paths
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing rotor blade connections in aircraft propellers and rotors suffer from inefficient distribution of tensile, bending, and torsional forces, leading to suboptimal mechanical resistance and fatigue due to multiaxial stresses, particularly when using composite materials.
Innovation Solution
A rotor blade design featuring a hollow torsion box, anchoring device, and cylindrical sleeve system that independently absorbs and transfers these forces, allowing for optimized component dimensions, mass, and mechanical strength without compromising operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single rotational linkage with ball bearings is used to connect blade and hub, then the blade can rotate about pitch axis, but the tensile, bending and torsional stresses are not properly distributed leading to suboptimal mechanical resistance
Solution Approach 1:
The connection system is segmented into separate functional components: a cylindrical sleeve for rotational movement, a stop for tensile force bearing, and a profiled portion with undercut shapes for bending and torsional force resistance. This segmentation allows each component to be optimized for its specific function, improving overall mechanical resistance while maintaining manageable complexity.
Solution Approach 2:
The blade root connection system is designed as a multi-functional assembly where the cylindrical sleeve provides rotational guidance, the stop handles tensile forces, and the undercut shapes resist bending and torsional moments. This multi-functionality within a single integrated structure improves mechanical resistance without requiring multiple separate devices.
2Ease of manufacture
If removable fasteners are used to attach profiled portion to cylindrical sleeve, then the profiled portion can be easily removed or replaced, but the fasteners bear most of the tensile, bending and torsional stresses leading to fatigue
Solution Approach 1:
The fastening function is extracted from the load-bearing function. Removable fasteners are used solely for assembly and disassembly, while the permanent undercut shapes in the cylindrical sleeve provide the load-bearing connection. This separation allows easy maintenance while ensuring reliable stress distribution through the robust undercut geometry.
Solution Approach 2:
The undercut shapes are designed beforehand to distribute and cushion the tensile, bending, and torsional stresses across multiple contact surfaces. This pre-designed stress distribution prevents concentration of forces on single fasteners, reducing fatigue risks while maintaining ease of assembly through removable fastening mechanisms.
3Reliability
If non-removable retention system with undercut shapes is used, then the profiled portion is securely retained on cylindrical sleeve, but the blade cannot be easily removed or replaced
Solution Approach 1:
The retention system merges removable and non-removable features: permanent undercut shapes provide secure retention and load bearing, while removable fasteners enable easy assembly and disassembly. This combination achieves both high reliability through the undercut shapes and ease of manufacture through the removable fastening mechanism.
4Strength
If composite materials are used for profiled portion, then the blade has good mechanical properties, but the connection to cylindrical sleeve becomes more complex requiring special retention systems
Solution Approach 1:
The connection system is designed with local quality considerations for composite materials. The undercut shapes are positioned to match the grain orientation and strength characteristics of the composite layup. This localized optimization allows secure retention of composite blades without requiring overly complex connection systems, as the undercut geometry is tailored to the specific composite structure.
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 system effectively distributes and absorbs tensile, bending, and torsional forces, enhancing mechanical resistance and reducing the risk of failure, while facilitating assembly and disassembly, and improving the lifespan of the blades.
Implementation Method 1
one or more ball bearings arranged between the hub and the blade root to guide the blade's rotation about a pitch axis
Implementation Method 2
The blade root also includes a translational stop relative to the hub to restrain the blade from centrifugal force during propeller rotation
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
The present invention relates to a blade (1) for an aircraft rotor, comprising a hollow cylindrical sleeve (2), a stop (7) fixed to said cylindrical sleeve (2), a profiled portion (3), an anchoring device (5), and a hollow blade body (4) and torsion box (6) integral with said profiled portion (3). Said anchoring device (5) and said blade body (4) are positioned inside said cylindrical sleeve (2). Said anchoring device (5) surrounds said stop (7) to form a stop for said profiled portion (3) parallel to a longitudinal axis (AXL, Fig. 4) of said blade (1). Said hollow torsion box (6) is integral with said profiled portion (3) and comprises a bearing area in contact with an internal wall of said cylindrical sleeve (2), allowing the transfer of bending stresses to said blade (1).