Sigmoid Propeller Blades Reduce Cavitation and Engine Load

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Solution Overview

Problem

Conventional propeller designs suffer from early cavitation due to lift generation and complexity, leading to increased production costs and limited efficiency improvements, despite minor variations in blade shape and twist.

Innovation Solution

A propeller design featuring blades with a sigmoid cross-section, comprising two arcuate concave faces with different radii of curvature, where the first face faces rearwards and the second face forwards, optimizing blade area and reducing engine load, and optionally twisting for increased efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If conventional propeller blades with curved outer profile and twist are used, then thrust generation is improved, but cavitation occurs early and production complexity increases

Engineering Contradiction:

Improvethrust generationVSAvoidcavitation

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The patent inverts the conventional blade design by using straight edges instead of curved profiles and eliminating twist. The sigmoid cross-section with straight edges and different radii of curvature on concave faces achieves thrust generation through a fundamentally different geometric approach, avoiding the lift-induced pressure differences that cause cavitation in conventional designs.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes key geometric parameters of the blade cross-section from conventional curved profiles with uniform radius to a sigmoid shape with straight edges and two different radii of curvature. This parameter change fundamentally alters the flow characteristics and pressure distribution, reducing cavitation while maintaining thrust generation capability.

Inventive Principle:

Principle #35Parameter changes

2Power

If conventional propeller blades with twist and skew are used, then thrust distribution is improved, but manufacturing complexity and cost increase

Engineering Contradiction:

Improvethrust distributionVSAvoidproduction complexity

Core Design Contradiction:

PowerVSEase of manufacture

Solution Approach 1:

The patent inverts the conventional approach by eliminating twist and skew from the blade design. Instead of using curved profiles with varying geometry along the blade length, the invention employs straight edges and a consistent sigmoid cross-section, dramatically simplifying manufacturing while maintaining effective thrust distribution through the different radii of curvature on the concave faces.

Inventive Principle:

Principle #13The other way round (Inversion)

3Power

If conventional propeller designs are used, then basic thrust is generated, but efficiency improvements are limited

Engineering Contradiction:

Improvethrust generationVSAvoidefficiency

Core Design Contradiction:

PowerVSProductivity

Solution Approach 1:

The patent achieves efficiency improvements by fundamentally changing the geometric parameters of the blade cross-section. The sigmoid shape with straight edges and two different radii of curvature creates more favorable flow characteristics and pressure distribution, enhancing thrust generation efficiency compared to conventional curved profiles with uniform geometry.

Inventive Principle:

Principle #35Parameter changes

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 enhances efficiency and reduces engine load, thereby extending engine life while minimizing cavitation and production complexity.

Implementation Method 1

Under Newton's first law, action and reaction are equal and opposite, and hence the fluid applies an equal and opposite force to the screw, propeller, etc. which reaction force is transmitted to the body and in turn drives the body through the fluid.

Methodology Applied

Scientific EffectNewton's first law (action and reaction):

Implementation Method 2

The shape of the blades tends to generate lift, and the resulting pressure differences can lead to early cavitation.

Methodology Applied

Scientific EffectPressure differences:

Data Source

PatentUS8221086B2Propeller

Publication Date: 2012.07.17 AXIOM WATER PROPELLERS

AI summary

A propeller has a hub 1 with a pair of blades 3 extending therefrom. Each blade 3 has a root, a tip, a first blade portion 10a extending between the root and tip and a second blade portion 10b extending between the root and tip adjacent and substantially parallel to said first blade portion 10a. The first and second blade portions 10a, 10b each have an arcuate concave face 11a, 11b, the radius of curvature of the concave face 11a of said first blade section 10a being greater than the radius of curvature of the concave face 11b of the second blade section 10b. The concave faces of said first and second portions 10a, 10b facing in substantially opposite directions such that, in use, said concave face 11a of said first blade portion 10a faces rearwards and said concave face 11b of the second blade portion 10b faces forwards.