Rotorcraft Blade Tip Airfoil Camber for Hover Drag Reduction

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Solution Overview

Problem

Conventional aerodynamic profiles for rotorcraft blades experience significant aerodynamic drag and stall issues during hovering and low-speed flights due to shock waves forming at the free end of the blade, leading to reduced performance.

Innovation Solution

The method involves modifying the aerodynamic profiles by displacing the leading and trailing edges in the extreme spanwise zone, increasing the camber and modifying the average line to delay shock wave formation, thereby reducing drag and improving airflow acceleration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If the blade operates at high blade pitch angles during hovering flight, then the aerodynamic force is increased, but aerodynamic drag increases rapidly due to shock wave formation and boundary layer separation

Engineering Contradiction:

Improveaerodynamic forceVSAvoidaerodynamic drag

Core Design Contradiction:

ForceVSLoss of energy

Solution Approach 1:

The invention applies different camber values to different radial positions of the blade. Specifically, the mean line is positioned at a first camber value in a first radial region (near the hub) and at a second camber value in a second radial region (toward the tip), where the second camber value differs from the first. This local differentiation allows the blade to optimize lift generation near the hub while reducing drag from shock waves near the tip during hovering flight.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the geometric parameter of the airfoil's mean line position (camber) along the radial span of the blade. By varying the camber value from the first radial region to the second radial region, the invention modifies the airflow characteristics and delays shock wave formation, thereby reducing aerodynamic drag while maintaining lift generation.

Inventive Principle:

Principle #35Parameter changes

2Force

If the camber is increased near the leading edge, then the positive stall angle is increased and aerodynamic force is enhanced, but shock wave formation occurs more readily at high speeds

Engineering Contradiction:

Improveaerodynamic forceVSAvoidshock wave formation

Core Design Contradiction:

ForceVSObject-affected harmful factors

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention applies camber modification selectively to specific radial regions rather than uniformly across the entire blade span. By applying the mean line positioning strategy primarily to certain radial zones, the invention achieves sufficient aerodynamic force enhancement without excessively increasing shock wave formation tendencies across the whole blade.

Inventive Principle:

Principle #16Partial or excessive action

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 enhances the aerodynamic performance of the blade during hovering and low-speed flights by delaying stall incidence and reducing aerodynamic drag, while maintaining performance in other flight phases.

Implementation Method 1

a specific phenomenon related to air compressibility and the formation of shock waves near the leading edge of the airfoil, close to the free-swinging tip

Methodology Applied

Scientific EffectShock wave: Shock Wave

Implementation Method 2

These shock waves form on the upper surface of the airfoil and cause boundary layer separation

Methodology Applied

Scientific EffectBoundary layer separation: Boundary Layer

Data Source

PatentEP3984883B1Method for improving the aerodynamic performance of blades of a hovering rotorcraft by movement of the leading edge of the aerodynamic profiles of these blades

Publication Date: 2023.02.15 EUROCOPTER FRANCE SA

Figure 1~2
Figure 3~4
Figure 5

AI summary

The present invention relates to a method for improving a blade at an extreme area of said blade in terms of its span, as well as to such an improved blade and a rotor comprising said improved blades. A displacement of said leading edge (5) of said airfoils (10) located at said extreme area is made from said upper surface half-airfoil (11) to said lower surface half-airfoil (21), then said leading edge sections (12, 22) of said two half-airfoils (11, 21) are modified to connect said leading edge (5) to said intermediate sections (13, 23) of said two half-airfoils (11, 21). Subsequently, the manufacturing of said blade according to said modified airfoils (10) is carried out. As a result, the negative camber of said aerodynamic profiles (10) of said blade is thus increased, allowing the aerodynamic performance of said blade to be improved in hovering flight.