Concentric Control Tubes for Rotor Blade Pitch Actuation
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Solution Overview
Problem
Rotary-wing aircraft with dual or counter-rotating rotor systems face challenges in controlling upper rotor blades due to the complexity and weight issues associated with long control rods prone to buckling, which complicates the sizing and weight reduction of the upper rotor control shaft.
Innovation Solution
The implementation of a rotor control system using a plurality of concentric control tubes within the rotor shaft, allowing for pitch changes in rotor blades through translation along the rotor axis, which reduces the risk of buckling and enables a lighter upper rotor shaft by allowing larger diameters and incorporating sliding bearings for enhanced stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If long control rods are used in the upper rotor control system, then pitch control is achieved, but the control rods are prone to buckling and add weight to the control system
Solution Approach 1:
The patent divides the single long control rod into multiple shorter control tubes arranged concentrically. Each control tube is a separate segment that translates axially to control blade pitch. This segmentation eliminates the buckling problem of long control rods while maintaining the pitch control function through coordinated translation of the multiple shorter tubes.
Solution Approach 2:
The patent implements a nested configuration where multiple control tubes are arranged concentrically within the rotor control shaft, with each control tube positioned inside the others or in a nested pattern. This nesting allows all control tubes to fit within the limited space of the rotor shaft while enabling independent translation of each tube to achieve pitch control.
2Reliability
If control rod diameter is increased to prevent buckling, then buckling resistance improves, but the upper rotor control shaft diameter must increase adding weight
Solution Approach 1:
By segmenting the control system into multiple shorter control tubes, each tube has sufficient buckling resistance without requiring excessive diameter. The multiple tubes can be arranged concentrically to fit within a compact rotor shaft diameter, avoiding weight increase while maintaining reliability.
Solution Approach 2:
The patent transitions from a single-dimensional solution (one long control rod) to a multi-dimensional arrangement (multiple control tubes in concentric positions). This spatial arrangement in multiple dimensions allows the control system to achieve both buckling resistance and compact size, reducing the overall rotor shaft diameter and weight.
3Reliability
If multiple control tubes are used instead of long control rods, then buckling risk is reduced, but the control system complexity increases
Solution Approach 1:
The nested concentric arrangement of control tubes within the rotor shaft provides a compact and organized structure. This nesting simplifies the overall layout compared to alternative configurations, as all control tubes are contained within the existing rotor shaft envelope and can be actuated through coordinated translation along the same axial path.
Data Source
AI summary
A rotor assembly includes a rotor shaft rotatable about a rotor axis and a plurality of rotor blades operably connected to the rotor shaft. A rotor control assembly has a plurality of substantially concentric control tubes extending through the rotor shaft. Each control tube of the plurality of control tubes is operably connected to a rotor blade of the plurality of rotor blades such that movement of one or more of the control tubes of the plurality of control tubes along the rotor axis effects a pitch change in one or more rotor blades of the plurality of rotor blades. A method of controlling pitch of a plurality of rotor blades of a rotor assembly includes locating a plurality of concentric control tubes inside of a rotor shaft of the rotor assembly capable of changing a pitch of one or more of the rotor blades.