Cyclic Pitch Phase Adjustment for UPR Noise Mitigation
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Solution Overview
Problem
Aircraft noise mitigation, particularly from unducted propulsive rotors (UPRs), is challenging due to constraints on rotor RPM, blade pitch, and air speed, which affect noise levels both on the ground and in the cabin, and adjusting these parameters to reduce noise is undesirable as it causes noticeable tonal changes.
Innovation Solution
A noise mitigation system that uses a cyclic pitch mechanism with an adjustable phase schedule applied to rotor blades, a positioning and attitude system, and a processor to determine the position of ground points and adjust the blade pitch to minimize noise levels by ensuring the azimuthal interval with the lowest blade pitch coincides with the entry point of ground points into the rotor plane, thereby reducing noise without altering propulsive thrust.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If rotor RPM is adjusted to reduce noise, then noise level is reduced, but tonal changes become noticeable to people on the ground
Solution Approach 1:
The patent applies local quality by implementing azimuthal variation in blade pitch angle rather than uniform pitch throughout the rotor disk. The pitch schedule is designed to be lower at specific azimuthal positions where ground points are predicted to enter the rotor plane, creating localized noise reduction in those directions while maintaining higher pitch (and thus thrust) at other positions. This resolves the contradiction by reducing noise at specific locations without requiring overall RPM reduction that would cause noticeable tonal changes.
Solution Approach 2:
The patent applies dynamics by making the blade pitch angle time-varying through the rotor rotation cycle. The cyclic pitch mechanism dynamically adjusts the pitch angle based on the azimuthal position and predicted ground point entry timing. This dynamic pitch modulation allows the system to reduce noise when ground points are approaching the rotor plane while maintaining propulsive thrust during other portions of the rotation cycle, thereby resolving the contradiction between noise reduction and thrust maintenance.
2Object-affected harmful factors
If blade pitch is reduced to minimize noise at ground points, then noise level is reduced, but propulsive thrust is compromised
Solution Approach 1:
The patent applies local quality by implementing azimuthal variation in blade pitch angle rather than uniform pitch throughout the rotor disk. The pitch schedule is designed to be lower at specific azimuthal positions where ground points are predicted to enter the rotor plane, creating localized noise reduction in those directions while maintaining higher pitch (and thus thrust) at other positions. This resolves the contradiction by reducing noise at specific locations without requiring overall RPM reduction that would cause noticeable tonal changes.
Solution Approach 2:
The patent applies periodic action by implementing a cyclic pitch schedule that varies blade pitch periodically throughout the rotor rotation cycle. The pitch angle is modulated according to the azimuthal position, with lower pitch values applied periodically when ground points are predicted to enter the rotor plane, and higher pitch values applied during other portions of the rotation. This periodic modulation maintains average thrust while reducing noise at specific moments in the rotation cycle.
3Object-affected harmful factors
If cyclic pitch schedule phase is adjusted to reduce noise at predicted ground point entry, then noise level is reduced, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by using a positioning and attitude system to predict in advance when ground points will enter the rotor plane, before the actual noise mitigation action is required. The processor receives position and attitude data, calculates predicted entry times and azimuthal coordinates, and pre-determines the optimal phase adjustment for the cyclic pitch schedule. This preliminary prediction and planning allows the system to prepare the pitch schedule in advance, reducing the need for complex real-time control adjustments and thereby managing system complexity while achieving noise reduction.
Solution Approach 2:
The patent applies feedback by using the positioning and attitude system to continuously monitor the aircraft's position, attitude, and velocity, and feeding this information back to the processor. The processor uses this feedback data to calculate predicted ground point entry positions and adjust the cyclic pitch schedule phase accordingly. This feedback mechanism enables adaptive noise mitigation that responds to changing flight conditions, managing complexity through systematic use of available sensor data rather than requiring overly complex control algorithms.
Data Source
AI summary
A noise mitigation system for an aircraft comprises a cyclic pitch mechanism arranged to apply a cyclic pitch schedule to rotor blades of an unducted propulsive rotor (UPR) under control of a processor. The processor receives input data corresponding to the position and attitude of the UPR, the position of one or more ground points stored in a memory and the velocity of the aircraft. If the processor determines that a ground point will enter the plane of the UPR, a control signal is output to the cyclic pitch mechanism as necessary to adjust the phase of the cyclic pitch schedule such that the azimuthal position of the ground point on entry to the plane of the UPR lies within an azimuthal interval over which the blade pitch of the cyclic pitch schedule is below its average value, thus reducing noise in the direction of the ground point.