Blade Airfoil Modification for Negative Stall Angle

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Solution Overview

Problem

Conventional aircraft blade airfoils are not optimized for delivering aerodynamic forces in both positive and negative angles of attack, leading to inefficient mechanical power usage and suboptimal performance during hovering flights, as they are designed primarily for positive angles of attack.

Innovation Solution

The method involves modifying the airfoils by increasing the radius of the initial leading edge circle and modifying the intermediate segment to enhance the negative stall angle of attack, allowing the blade to deliver aerodynamic forces effectively in both directions without degrading performance at positive angles of attack.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If the blade is designed with conventional airfoils optimized for positive angles of attack, then the aerodynamic force delivery in positive direction is improved, but the negative stall angle of attack remains limited and power consumption increases in reverse direction

Engineering Contradiction:

Improveaerodynamic force deliveryVSAvoidmechanical power consumption

Core Design Contradiction:

ForceVSUse of energy by moving object

Solution Approach 1:

The patent applies asymmetry by modifying only specific portions of the airfoil (leading edge radius and intermediate segment) while maintaining the overall airfoil shape. This selective asymmetric modification allows the blade to achieve improved negative angle of attack performance without completely redesigning the airfoil, thus reducing power consumption in reverse direction while preserving positive direction aerodynamic force delivery

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent changes geometric parameters of the airfoil, specifically increasing the leading edge radius and modifying the intermediate segment coordinates. These parameter changes directly affect the flow separation characteristics, enabling the blade to operate effectively at negative angles of attack with reduced power consumption while maintaining performance at positive angles

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the blade operates at negative angles of attack with conventional airfoils, then reverse aerodynamic force can be delivered, but the stall angle of attack is reached prematurely causing flow separation and turbulence

Engineering Contradiction:

Improvebidirectional aerodynamic force deliveryVSAvoidaerodynamic performance stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies preliminary action by pre-modifying the airfoil geometry (increasing leading edge radius and adjusting intermediate segment) before the blade encounters negative angles of attack during operation. This pre-adjustment ensures that when the blade operates in reverse, the modified geometry already prevents premature flow separation, maintaining reliable aerodynamic performance across the full range of angles including negative angles

Inventive Principle:

Principle #10Preliminary action

3Use of energy by moving object

If the leading edge radius is increased and intermediate segment is modified, then the negative stall angle of attack is extended improving reverse performance, but the airfoil geometry changes may affect positive angle performance

Engineering Contradiction:

Improvepower consumption in reverse directionVSAvoidaerodynamic force at positive angles

Core Design Contradiction:

Use of energy by moving objectVSForce

Solution Approach 1:

The patent applies local quality by making modifications only to specific local regions of the airfoil (leading edge radius and intermediate segment) rather than changing the entire airfoil geometry. This localized modification approach ensures that the changes primarily affect negative angle of attack performance while minimizing impact on positive angle performance, thus extending power consumption benefits without sacrificing forward thrust capability

Inventive Principle:

Principle #3Local quality

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 modification enables the blade to deliver reverse aerodynamic forces at negative angles of attack with reduced power consumption, improving the anti-torque device performance and flight safety of hybrid helicopters by extending the stall limit and optimizing power usage.

Implementation Method 1

starting from a threshold angle of attack of the blade, referred to as the 'stall' angle of attack, air streamlines become separated from the blade, particularly at its leading edge or at its trailing edge

Methodology Applied

Scientific EffectFlow separation: Flow Separation

Data Source

PatentUS11225316B2Method of improving a blade so as to increase its negative stall angle of attack

Publication Date: 2022.01.18 EUROCOPTER FRANCE SA

AI summary

A method of improving a blade and also an improved blade and a advancement propeller including the improved blade. The radius of the initial leading edge circle of each airfoil of the blade is increased, and its leading edge is moved away from a pressure side half-airfoil towards a suction side half-airfoil, thereby modifying the airfoil of each cross-section of the blade and modifying the camber of each airfoil. Consequently, the absolute value of the negative stall angle of attack of the blade is increased, thus making it possible to increase the aerodynamic performance of the blade under a negative angle of attack compared with a blade that is not modified, and without significantly degrading its aerodynamic performance under a positive angle of attack.