Rotorcraft Mast Raceway Press-Fit Without Threaded Fasteners
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Solution Overview
Problem
Current rotorcraft propulsion assemblies with nonintegral raceways face challenges such as structurally compromising stress concentrations, increased weight, and additional stress points due to the requirement of mast threads, nuts, and other fasteners.
Innovation Solution
A propulsion assembly design featuring a mast with an internal ledge, a raceway station, and an external ridge, where a nonintegral raceway forms a press fit joint with the mast, utilizing a nonuniform normal force to axially bias the raceway toward the external ridge, thereby securing it without fasteners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nonintegral raceways are used with fasteners (mast threads, nuts, and other fasteners), then the raceway can be secured to the mast, but stress concentrations and structural integrity are compromised
Solution Approach 1:
The raceway and mast are merged into a single integrated structure where the raceway is formed as a continuous, seamless part of the mast body. This eliminates the need for separate fasteners, threads, and connection components, thereby removing stress concentration points and preserving structural integrity while reducing the total number of parts in the propulsion assembly.
Solution Approach 2:
The mast is segmented into distinct functional zones including the raceway station with internal ledge and external ridge features. This segmentation allows the raceway to be positioned precisely within the mast structure at the raceway station, creating optimized load paths and stress distribution without requiring external fastening mechanisms.
2Ease of repair
If nonintegral raceways are used with multiple parts, then the raceway can be independently replaced, but the weight of the propulsion assembly increases
Solution Approach 1:
The raceway is merged with the mast to form a unified structure, eliminating the need for separate raceway components, fasteners, and connection hardware. This integration dramatically reduces the total weight of the propulsion assembly while maintaining the capability for raceway replacement through controlled material removal and regeneration processes.
Solution Approach 2:
The design enables selective removal of the raceway portion of the mast while preserving the main mast structure. The raceway can be discarded and replaced with a new raceway section or regenerated through additive manufacturing or other restoration techniques, providing ease of repair without the weight penalty of traditional multi-part assemblies.
3Strength
If integral raceways are used with case hardened steel alloys, then the raceway can bear high loads, but corrosion resistance decreases and replacement frequency increases
Solution Approach 1:
The mast is designed with local quality variations where the raceway station features (internal ledge, external ridge) provide localized structural characteristics. The raceway portion can be made from materials optimized for load-bearing while the rest of the mast maintains corrosion-resistant properties, or the entire structure uses corrosion-resistant materials with localized hardening treatments applied only where needed for load-bearing capacity.
Solution Approach 2:
The propulsion assembly utilizes composite material construction where the mast and raceway are formed from materials that combine the desirable properties of both load-bearing strength and corrosion resistance. This may involve using stainless steel or other corrosion-resistant alloys with surface treatments, coatings, or heat treatments that provide the necessary hardness and load-bearing capability while maintaining overall corrosion resistance.
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
This design enhances the structural integrity of rotorcraft propulsion assemblies by minimizing weight, reducing stress points, and allowing for independent replacement of the raceway, while maintaining high load-bearing capabilities.
Implementation Method 1
The internal ledge is configured to generate a nonuniform normal force between the mast and the nonintegral raceway along the raceway station that axially biases the nonintegral raceway toward the external ridge
Implementation Method 2
A nonintegral raceway is receivable by the raceway station to form a press fit joint between the mast and the nonintegral raceway
Data Source
AI summary
A propulsion assembly for a rotorcraft. The propulsion assembly includes a mast having an internal ledge, a raceway station and an external ridge with at least a portion of the raceway station positioned axially between the internal ledge and the external ridge. A nonintegral raceway is receivable by the raceway station to form a press fit joint between the mast and the nonintegral raceway. A mast bearing assembly includes a plurality of bearings configured to engage an outer surface of the nonintegral raceway. The internal ledge is configured to generate a nonuniform normal force between the mast and the nonintegral raceway along the raceway station that axially biases the nonintegral raceway toward the external ridge, thereby securing the nonintegral raceway at the raceway station.