Counter-rotating Rotor Hub Shaft Fairing De-rotation System
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Solution Overview
Problem
The counter-rotating, coaxial rotor system in rotary-wing aircraft experiences significant aerodynamic drag due to dual rotor hubs and the interconnecting main rotor shaft, leading to increased power consumption and reduced low-observability benefits, especially during hover and low-speed maneuvers where friction causes the shaft fairing to rotate undesirably.
Innovation Solution
A de-rotation system is implemented, which includes a belt-driven mechanism and a drive cone assembly with beveled cones to maintain the shaft fairing's position relative to the airframe, preventing it from rotating freely with the rotor shafts, and an active control system using a variable torque generator to adjust the shaft fairing's position throughout flight profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the shaft fairing is mounted to rotate freely on the bearing arrangement, then the shaft fairing can align with the relative wind during low speed maneuvering, but the shaft fairing rotates in unison with the main rotor system during hover and low speed maneuvers due to frictional forces, increasing drag and reducing low-observability benefits
Solution Approach 1:
A de-rotation system is introduced as an intermediary mechanism between the shaft fairing and the rotating rotor system. This system includes a fairing de-rotation mechanism that actively counteracts the rotation of the shaft fairing caused by frictional forces on the bearing arrangement, preventing the fairing from rotating in unison with the rotor while still allowing it to align with the relative wind during maneuvering.
Solution Approach 2:
The de-rotation system applies a preliminary counteracting torque to the shaft fairing through the bearing arrangement to prevent the harmful rotation that would otherwise occur due to frictional forces. By applying this anti-action in advance, the system maintains the fairing's alignment with the airframe during hover and low-speed maneuvers, reducing drag and preserving low-observability benefits.
2Object-generated harmful factors
If the shaft fairing is prevented from rotating freely, then drag is reduced and low-observability benefits are maintained, but the shaft fairing cannot align with the relative wind during low speed maneuvering
Solution Approach 1:
The de-rotation system is designed with dynamic characteristics that allow it to adapt to different flight conditions. During hover and low-speed maneuvers, the system actively prevents rotation to reduce drag. During low-speed maneuvering, the system allows controlled alignment with the relative wind while maintaining prevention of unison rotation, providing the necessary adaptability across different operational regimes.
3Object-generated harmful factors
If a de-rotation system is added to control shaft fairing position, then drag is reduced and low-observability is improved, but device complexity increases
Solution Approach 1:
The de-rotation system is integrated with the existing bearing arrangement and rotor hub structure, allowing these components to serve multiple functions. The bearing arrangement not only supports the shaft fairing but also accommodates the de-rotation mechanism. The fairing structure itself serves both aerodynamic and low-observability functions while being part of the de-rotation system, reducing the need for separate dedicated components.
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 de-rotation system reduces drag, maintains low-observability benefits, and enhances maneuverability by ensuring the shaft fairing remains stationary relative to the airframe, even during low-speed maneuvers, thereby improving the aircraft's performance and efficiency.
Implementation Method 1
friction force between the belts and pulleys of the de-rotation system
Implementation Method 2
frictional forces acting on the bearing arrangement may tend to cause the shaft fairing to undesirably rotate
Data Source
Figure 1A~1C
Figure 2A
Figure 2B
AI summary
A rotor hub fairing system includes an upper hub fairing, a lower hub fairing and a shaft fairing therebetween. The rotor hub fairing system is attached to the counter-rotating, coaxial rotor system through a bearing arrangement such that the shaft fairing may be positioned at an azimuthal position about the main rotor axis of rotation relative the airframe by a de-rotation system. The de-rotation system controls the position of the shaft fairing about the axis of rotation such that the shaft fairing is prevented from rotating freely in unison with either shaft as may otherwise result during some flight regimes.