Friction Welded Raceways for Rotorcraft Propulsion Assemblies
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Solution Overview
Problem
Current rotorcraft propulsion assemblies face issues with corrosion, structural integrity, and stress concentrations due to the use of conventional steel for masts and raceways, leading to frequent replacements and reduced performance under cyclic loading.
Innovation Solution
A propulsion assembly with a raceway having a tapered inner surface friction welded to a mast, forming an integral mast-raceway structure, using corrosion-resistant steel for the mast and high-strength steel for the raceway, eliminating the need for fasteners and enhancing structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional steel is used for the mast to form an integral raceway through induction hardening or carburizing, then the raceway can be formed with case hardened surface, but the mast tends to corrode in areas such as the hub spline requiring more frequent replacement
Solution Approach 1:
The mast is divided into two separate components: a corrosion-resistant steel mast and a separate raceway component. This segmentation allows each component to be optimized for its specific function - the mast for corrosion resistance and the raceway for hardness - without compromising either property.
Solution Approach 2:
The invention uses composite construction by combining corrosion-resistant steel for the mast with hardened steel for the raceway. This composite approach allows the structure to exhibit both corrosion resistance and hardness simultaneously, resolving the contradiction between these two properties.
2Reliability
If stainless steel is used for the mast to mitigate corrosion, then corrosion resistance is improved, but integral raceways require a case hardened surface that cannot be sufficiently achieved with stainless steel
Solution Approach 1:
By separating the mast from the raceway, the invention allows the raceway to be made from a different material (hardened steel) that can achieve the necessary case hardened surface, while the mast remains as corrosion-resistant stainless steel.
Solution Approach 2:
The invention combines stainless steel for the mast with hardened steel for the raceway, creating a composite structure that achieves both corrosion resistance and case hardened surface properties that cannot be obtained from a single material.
3Reliability
If a lower mast formed from conventional steel with integral raceway is welded to an upper mast formed from stainless steel, then both corrosion resistance and case hardened surface are achieved, but the mast assembly includes a circumferential weld line through which the torque path must travel, resulting in reduced structural integrity
Solution Approach 1:
Instead of welding two mast sections together, the invention segments the mast into a separate corrosion-resistant steel mast and a separate raceway component. This eliminates the circumferential weld line and its associated structural integrity issues while maintaining both corrosion resistance and case hardened surface properties.
Solution Approach 2:
The raceway is extracted from the mast structure as a separate component rather than being integral to the mast. This extraction eliminates the need for circumferential weld lines and allows the torque path to travel through the solid mast structure without interruption.
4Ease of manufacture
If nonintegral raceways are used with mast threads, nuts and other fasteners, then the raceway can be attached to the mast, but structurally compromising stress concentrations are created especially when experiencing induced cyclic loading during flight
Solution Approach 1:
The invention replaces mechanical fastening systems (threads, nuts, and other fasteners) with a friction fit mechanism. The raceway is retained on the mast through friction generated by the tapered surfaces, eliminating stress concentrations associated with mechanical fasteners while maintaining ease of assembly.
5Ease of manufacture
If nonintegral raceways are used, then the raceway can be attached to the mast, but more parts are required thereby increasing the weight of the propulsion assembly and introducing additional stress points during operation
Solution Approach 1:
The invention merges the raceway attachment function into the mast structure itself through the friction fit mechanism. By eliminating the need for separate fasteners and using the tapered surfaces already present in the mast-raceway interface, the design reduces the number of parts and overall weight while maintaining secure attachment.
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 solution reduces weight, minimizes stress concentrations, and enhances structural integrity by forming a seamless, corrosion-resistant integral structure that withstands loads and cyclic stresses without the need for additional fasteners or weld lines, thus improving the durability and reliability of rotorcraft propulsion systems.
Implementation Method 1
The tapered inner surface of the raceway is friction welded to the tapered outer surface of the mast at the raceway receiving station to form a tapered friction weld line
Data Source
AI summary
A propulsion assembly for a rotorcraft includes a raceway having a tapered inner surface and a mast configured to receive the raceway at a raceway receiving station. The mast has a tapered outer surface at the raceway receiving station. The propulsion assembly includes a mast bearing assembly having a plurality of bearings facing the mast to engage the raceway. The tapered inner surface of the raceway is friction welded to the tapered outer surface of the mast at the raceway receiving station to form a tapered friction weld line.