Shaft Cap Design for Ram Air Fan Stability
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Solution Overview
Problem
At lower flight speeds or when on the ground, the ram air pressure is insufficient to provide adequate airflow across the heat exchangers in aircraft environmental control systems, necessitating the use of a fan to enhance heat removal, which can be inefficient and weight-intensive.
Innovation Solution
A ram air fan assembly featuring a shaft cap with a circular and conical design that connects to a tie rod, allowing for secure and balanced rotation without additional supports, reducing weight and complexity, and enabling efficient airflow through the elimination of unnecessary components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional supports are added to the shaft cap to ensure stable rotation, then reliability improves, but device complexity and weight increase
Solution Approach 1:
The shaft cap is divided into multiple functional segments: a circular portion for tie rod connection, a conical portion for shaft connection with interference fit, and a pilot portion for alignment. This segmentation allows each portion to perform its specific function efficiently without requiring additional supporting components, thus improving reliability while maintaining simplicity.
Solution Approach 2:
Multiple functions are merged into a single shaft cap structure. The circular portion connects to the tie rod, the conical portion connects to the shaft, and the pilot portion provides alignment - all within one integrated component. This merging eliminates the need for separate supports while ensuring stable rotation, resolving the contradiction between reliability and complexity.
2Weight of moving object
If the shaft cap design is simplified to reduce weight, then manufacturing cost decreases, but manufacturing precision requirements increase
Solution Approach 1:
The conical portion of the shaft cap employs an interference fit design with specific dimensional parameters. By carefully controlling the cone angle and diameter tolerances, the design achieves a precise fit between the shaft cap and shaft without requiring additional heavy reinforcement structures. This parameter optimization reduces weight while maintaining the necessary manufacturing precision for reliable operation.
Data Source
AI summary
A shaft cap to connect between a shaft and a tie rod on a rotative assembly includes a circular portion with a central opening for connecting to the tie rod; a conical portion extending out from the circular portion at a slope; and a pilot around the outer edge of the conical portion. The pilot includes an outer lip to connect to an end of the shaft, an inner portion to connect to the inner circumference of the shaft and an undercut portion between the outer lip and the inner portion.