Blade Airfoil Modification for Negative Stall Angle
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Solution Overview
Problem
Conventional aircraft blades with cambered airfoils are optimized for positive angles of attack, leading to inefficient operation at negative angles of attack, particularly in hybrid helicopters, where the second advancement propeller requires more mechanical power to deliver reverse aerodynamic forces during hovering flight.
Innovation Solution
The method involves modifying the airfoils by increasing the radius of the leading edge circle and modifying the intermediate segment to enhance the negative stall angle of attack without degrading positive stall performance, allowing the blade to deliver aerodynamic forces in both directions with reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If cambered airfoils are used to optimize positive angle of attack performance, then positive thrust is improved, but negative angle of attack performance deteriorates
Solution Approach 1:
The patent applies asymmetry by modifying only one half-airfoil (typically the suction side) while leaving the other half-airfoil unchanged. This creates an asymmetric airfoil configuration that is optimized for negative angles of attack while preserving acceptable performance at positive angles of attack. The asymmetric modification allows the blade to deliver aerodynamic forces efficiently in both forward and reverse directions.
Solution Approach 2:
The patent applies local quality by making modifications only to specific regions of the airfoil - particularly the leading edge and intermediate segment of one half-airfoil - while leaving other regions unchanged. This localized modification approach allows optimization for negative angle of attack without degrading the overall aerodynamic performance of the blade across its entire operating range.
2Reliability
If the leading edge radius is increased to improve negative stall angle, then negative angle of attack performance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by providing a detailed method for determining the initial leading edge circle and intermediate segment coordinates before actual manufacturing. The method includes calculating geometric parameters, determining control points, and establishing the airfoil geometry in advance through computational procedures. This preliminary design phase ensures that the complex leading edge geometry can be manufactured accurately by providing precise guidance for toolpath generation and fabrication processes.
3Power
If the airfoil geometry is modified to enhance negative stall angle, then aerodynamic performance at negative angles is improved, but positive stall performance may degrade
Solution Approach 1:
The patent applies local quality by modifying only the leading edge and intermediate segment of one half-airfoil while leaving the terminal segment and the other half-airfoil unchanged. This localized modification ensures that the changes primarily affect negative angle of attack performance while preserving the aerodynamic characteristics that contribute to positive stall performance. The selective modification approach prevents degradation of positive angle performance.
Solution Approach 2:
The patent applies asymmetry by creating an asymmetric airfoil configuration where one half-airfoil is modified and the other remains unchanged. This asymmetric design allows the blade to be optimized for reverse aerodynamic force delivery while maintaining acceptable performance in forward flight, thereby resolving the contradiction between improving reverse thrust and preserving forward thrust capability.
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 improves aerodynamic performance under negative angles of attack while maintaining performance at positive angles, reducing power requirements for the second advancement propeller and optimizing the anti-torque device, thereby enhancing flight safety and efficiency.
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. This separation can lead to the blade stalling aerodynamically
Data Source
AI summary
A method of determining an initial leading edge circle for airfoils of a blade and 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 determined and then 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.