Propeller Blade Pitch Control for Cyclical Load Mitigation
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Solution Overview
Problem
Propellers operating in non-uniform flow fields experience sinusoidal thrust load variations (1P load) due to angular inflow, leading to increased structural weight and drag as control surfaces react to these moments, necessitating a reduction in 1P load to achieve weight savings and smaller control surfaces.
Innovation Solution
A blade pitch control mechanism featuring an actuation shaft with a spherical member and a rotatable yoke that adjusts propeller blade pitch by translating the yoke's rotation about a perpendicular axis, allowing each blade to change pitch in response to flow forces, thereby mitigating cyclical loading and reducing moments on the propeller shaft and airframe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control surfaces are enlarged to counter the 1P load moment, then the aircraft's ability to counter propeller load varies, but aircraft drag increases and structural weight increases
Solution Approach 1:
The patent extracts the 1P load counteracting function from the aircraft control surfaces and transfers it to the propeller blade pitch control system. By actively adjusting blade pitch to counter sinusoidal thrust variations, the control surfaces no longer need to be oversized to handle propeller loads, thereby reducing aircraft drag while maintaining the ability to counter 1P loads through the propeller system itself
Solution Approach 2:
The patent introduces an intermediary control system between the propeller blades and the hub, using pitch control mechanisms actuated by hydraulic or electric actuators. This intermediary system actively modulates blade pitch in response to detected 1P load variations, providing a direct counteracting mechanism that eliminates the need for oversized control surfaces
2Reliability
If control surfaces are enlarged to counter the 1P load moment, then the aircraft's ability to counter propeller load varies, but structural weight increases
Solution Approach 1:
The patent extracts the 1P load counteracting function from the aircraft control surfaces and transfers it to the propeller blade pitch control system. By actively adjusting blade pitch to counter sinusoidal thrust variations, the control surfaces no longer need to be oversized to handle propeller loads, thereby reducing control surface weight while maintaining the ability to counter 1P loads through the propeller system itself
Solution Approach 2:
The patent implements dynamic pitch control where blade pitch angles are continuously adjusted in response to detected 1P load variations. This dynamic adaptation allows the propeller system to actively counteract load moments, replacing the need for statically oversized control surfaces and enabling weight reduction in the control surface structure
3Force
If blade pitch is dynamically adjusted to counter 1P load, then cyclical forces and moments are reduced, but device complexity increases
Solution Approach 1:
The patent implements periodic pitch control where blade pitch angles are modulated at the fundamental frequency (1P) of the sinusoidal thrust variation. Sensors detect the periodic load variations and actuators apply corresponding periodic pitch adjustments, creating a synchronized control system that effectively counteracts cyclical forces while using simple harmonic motion principles
Solution Approach 2:
The patent employs feedback control where sensors mounted on the propeller hub or aircraft structure detect 1P load variations, and this information feeds back to pitch control actuators. The actuators adjust blade pitch in real-time based on detected load conditions, creating a closed-loop system that reduces cyclical forces while using straightforward sensor-actuator feedback architecture
Data Source
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AI summary
A blade pitch control mechanism for a propeller assembly (10) includes an actuation shaft (24) having a spherical member (28) located at a propeller axis (22). A yoke (40) is located around the spherical member (28) and is rotatable thereon about a yoke tilt axis (62) substantially perpendicular to the propeller axis (22). The yoke (40) includes a plurality of propeller blade attachments (44), each receptive of a propeller blade (14). The plurality of blade attachments (44) are configured such that rotation of the yoke (40) about the yoke tilt axis (62) results in rotation of each propeller blade (14) about a blade pitch change axis (48).