Planetary De-rotation System for Shaft Fairing Drag Reduction
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Solution Overview
Problem
The counter-rotating, coaxial rotor system in rotary-wing aircraft experiences increased aerodynamic drag due to the exposed interconnecting main rotor shaft, which also leads to undesirable rotation of the shaft fairing during flight, increasing drag and reducing low-observability benefits.
Innovation Solution
A de-rotation system incorporating a shaft fairing mounted for rotation about an axis of rotation, with a planetary gear set to control the position of the shaft fairing, ensuring it remains aligned with the airframe and minimizing drag by maintaining a stable azimuthal position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the shaft fairing is mounted for rotation to align with relative wind during low speed maneuvering, then the low-observability benefit is improved, but aerodynamic drag increases during high speed flight
Solution Approach 1:
The shaft fairing is mounted for rotation about the axis of rotation, allowing it to dynamically adjust its orientation based on flight conditions. During low speed maneuvering, the fairing can rotate to align with the relative wind for low-observability benefits, while during high speed flight, it maintains a fixed alignment with the airframe to minimize aerodynamic drag.
Solution Approach 2:
A planetary gear set is introduced as an intermediary mechanism between the shaft fairing and the rotor system. This gear set controls the rotational position of the shaft fairing, enabling it to maintain alignment with the airframe during high speed flight while preventing unwanted rotation during low speed maneuvering.
2Adaptability or versatility
If the shaft fairing is allowed to rotate freely to maintain alignment with relative wind, then adaptability to different flight conditions is improved, but aerodynamic drag and power consumption increase
Solution Approach 1:
The shaft fairing mounting allows for controlled rotation about the axis of rotation, providing adaptability to different flight conditions. The planetary gear set enables the fairing to rotate into alignment with the relative wind during low speed maneuvering while maintaining fixed alignment during high speed flight, optimizing adaptability without excessive energy loss.
Solution Approach 2:
The system changes the operational parameters of the shaft fairing based on flight conditions. During low speed maneuvering, the fairing is allowed to rotate to change its angular position relative to the airframe. During high speed flight, the planetary gear set constrains the fairing to maintain a fixed angular position, changing the parameter from variable to fixed to reduce drag.
3Object-affected harmful factors
If a planetary gear set is added to control shaft fairing position, then aerodynamic drag is reduced by maintaining alignment, but device complexity increases
Solution Approach 1:
A planetary gear set is introduced as an intermediary mechanism to control the rotational position of the shaft fairing. This gear set reduces aerodynamic drag by preventing unwanted rotation and maintaining alignment with the airframe during high speed flight, while allowing controlled rotation during low speed maneuvering.
Solution Approach 2:
The planetary gear set is designed to automatically control the shaft fairing position based on the rotational environment between the upper and lower rotor hubs. The system self-regulates the fairing's orientation without requiring external control mechanisms, reducing the overall complexity despite the addition of the gear set.
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 effectively reduces aerodynamic drag and maintains low-observability benefits by stabilizing the shaft fairing's position, minimizing power consumption and maintaining alignment regardless of rotor RPM variations.
Implementation Method 1
a planetary gear set configured to control a position of the shaft fairing about the axis of rotation
Data Source
AI summary
A fairing system according to an exemplary aspect of the present disclosure includes, among other things, a shaft fairing mounted for rotation about an axis of rotation and a planetary gear set configured to control a position of the shaft fairing about the axis of rotation.