VTOL Propeller Noise Reduction via Asymmetric Blade Counts
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Solution Overview
Problem
Aircraft rotorcrafts, particularly all-electric and hybrid-electric aerial vehicles, face significant noise challenges due to propeller noise, with existing strategies mainly focusing on rotor blade design, which do not effectively mitigate the constructive interference of noise signatures from multiple rotors operating at the same operating point, leading to higher sound pressure levels.
Innovation Solution
The implementation of a system and method involving multiple propellers with different geometries, such as varying blade counts and operating conditions, to spread noise energy across the spectrum, reducing peak sound pressure levels and perceived annoyance by ensuring each propeller delivers equivalent thrust at predetermined RPMs, and dynamically adjusting RPMs to maintain a desired noise signature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If multiple rotors operate at the same operating point, then the control system is simplified, but the noise signature increases due to constructive interference
Solution Approach 1:
The patent applies asymmetry by configuring rotors with different blade counts (e.g., one rotor with 3 blades and another with 5 blades) so that they rotate at the same RPM but generate different blade passage frequencies. This asymmetric configuration prevents constructive interference of noise signatures while maintaining synchronized rotation for simplified control.
2Ease of operation
If multiple rotors operate at the same RPM, then the control system is simplified, but peak sound pressure levels increase due to constructive interference
Solution Approach 1:
The patent employs asymmetric rotor blade counts (e.g., 3-blade and 5-blade configurations) that rotate at the same RPM, creating different blade passage frequencies that prevent constructive interference and reduce peak sound pressure levels while maintaining control simplicity.
3Ease of manufacture
If all propellers have the same geometry, then manufacturing is simplified, but noise reduction effectiveness is reduced
Solution Approach 1:
The patent applies local quality by giving different propellers distinct geometric characteristics (different blade counts, pitch distributions, or airfoil sections) tailored to their specific positions and noise reduction requirements, rather than using identical geometries throughout the system.
Data Source
AI summary
Disclosed is an aerial vehicle having a reduced noise signature. The aerial vehicle may be a vertical take-off and landing (VTOL) aerial vehicle. The aerial vehicle comprises an airframe and a plurality of rotors operatively coupled with one or more motors. The plurality of rotors may comprise a first, second, third, and fourth rotor. Each of the first, second, third, and fourth rotors may be arranged in a single plane and oriented to direct thrust downward relative to the airframe. In certain aspects, at least two of the plurality of rotors employ a different geometry to generate a targeted noise signature.