Nested Actuator Rod Assembly for Fail-Safe Blade Pitch Control
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Solution Overview
Problem
Actuator rods in pitch control systems, such as those for helicopter tail rotors, are prone to fatigue failure due to cyclic loads, lacking an intrinsic fail-safe mechanism, which can lead to loss of yaw control if they fail.
Innovation Solution
The actuator rod assembly consists of a tubular outer rod and an inner rod, keyed at their ends to prevent rotation, with a lock nut and tensioning mechanism to maintain compression in the outer rod, and an indicator washer for easy failure detection, allowing continued operation and easy repair.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-piece actuator rod is used, then the structure is simple and easy to manufacture, but it lacks fail-safe mechanism and is prone to fatigue failure
Solution Approach 1:
The actuator rod is divided into an outer rod and an inner rod as separate components. The inner rod can move independently within the outer rod, creating a segmented structure that provides fail-safe capability while maintaining manufacturing simplicity.
2Reliability
If the actuator rod is designed with fail-safe mechanism, then reliability is improved, but the structure becomes more complex
Solution Approach 1:
The inner rod is nested within the outer rod, with the inner rod's second end positioned inside the outer rod's hollow interior. This nesting arrangement provides fail-safe mechanism through independent movement capability while minimizing structural complexity.
3Reliability
If the inner rod is allowed to move freely, then fail-safe capability is provided, but alignment and rotation control become problematic
Solution Approach 1:
The inner and outer rods are keyed to each other at their respective second ends to prevent relative rotation. This preliminary constraint ensures proper alignment is maintained while still allowing the inner rod to move axially for fail-safe operation.
Solution Approach 2:
A bearing is provided at the second end of the outer rod to guide and support the inner rod, preventing lateral movement while allowing axial movement. This intermediary component maintains alignment without restricting the fail-safe movement capability.
Data Source
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AI summary
An actuator rod assembly (106) for a blade pitch control system is provided herein. The actuator rod assembly (106) includes a tubular outer rod (42) and an inner rod (44). The outer rod (42) has a first end (46) and a second end (48). The inner rod (44) has a first end (50) and a second end (52) and extends through the tubular outer rod(42). The inner rod (44) is tensioned against the tubular outer rod (42) so as to place the outer rod (42) in compression.