Propeller Unloaded Tip Zone Reduces Noise and Drag
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Solution Overview
Problem
Conventional propeller designs generate high noise due to strong tip vortices, which is a challenge for unmanned aircraft systems (UASs) and eVTOL aircraft operating in urban settings, as they need to reduce sound levels while maintaining efficiency.
Innovation Solution
A propeller design with an unloaded tip zone, where the beta angle decreases near the tip to reduce the angle of attack, creating a double break propeller that minimizes lift and tip vortex strength, thereby reducing noise and induced drag while maintaining high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional propeller design maintains constant angle of attack over blade span for maximum lift to drag ratio, then propeller efficiency is improved, but noise increases due to strong tip vortices
Solution Approach 1:
The propeller blade is designed with different angle of attack characteristics in different regions: the root section maintains a constant angle of attack for maximum lift-to-drag ratio and efficiency, while the tip section transitions to a decreasing angle of attack that creates an unloaded tip zone with negligible lift. This local differentiation allows the efficient loading of the blade root while minimizing tip vortex generation, thereby resolving the contradiction between propeller efficiency and noise reduction.
2Object-generated harmful factors
If propeller tip is unloaded to reduce tip vortex strength and noise, then noise is reduced, but lift is decreased requiring higher RPM to compensate
Solution Approach 1:
The propeller blade is segmented into two functional zones: a loaded root zone that generates the majority of the lift and thrust, and an unloaded tip zone that minimizes vortex generation. By concentrating the lifting function in the root section and allowing the tip section to be aerodynamically unloaded, the design achieves noise reduction while maintaining sufficient total lift through optimized root section loading and increased RPM.
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
This design significantly reduces noise levels and mechanical power required, allowing UASs to operate more quietly and efficiently, enhancing their acceptance in populated areas.
Implementation Method 1
the propeller blade is formed with a beta angle that reduces in value toward the blade tip to lower an angle of attack so that a lift coefficient prior to the tip becomes zero or less
Implementation Method 2
Aero dynamic forces acting on the blade generate the rotational motion required to spin the propeller
Data Source
AI summary
The present disclosure provides a rotating propeller design that maintains a high efficiency and reduces noise. The design provides an unloaded tip zone of positive lift starting prior to an end of the tip with negligible, if any, positive lift that is counterintuitive to the purpose of a propeller. The unloaded tip zone decreases the strength of a tip vortex and reduces induced drag. The result is a significant reduction in noise while maintaining substantially high mechanical efficiency, even with an optional increase in RPM to compensate for the reduced lift without requiring a longer propeller. At least one propeller design can break the beta angle from the propeller hub with a different beta angle at a first location from the hub and then also break the beta angle at a second location further from the hub into the unloaded tip zone to form a double break propeller.