Swept Rotor Blade Outboard Section for Transonic Drag Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Medium and large rotorcraft face inefficiencies and increased noise and vibrations due to transonic flow phenomena as rotor blade tips approach Mach 1, which are not adequately addressed by existing solutions such as thin airfoils and swept back tips limited to 10% of the blade radius.
Innovation Solution
Designing rotor blades with a swept portion that occupies at least 20% of the blade length, featuring varying sweep angles and thicker airfoils, to optimize lift distribution and reduce drag and noise across different flight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If rotor blade tips operate at high angular velocity to generate required lift from limited disc area, then lift generation is improved, but transonic flow phenomena occur causing noise, vibration and efficiency loss
Solution Approach 1:
The patent applies different geometric properties to different sections of the rotor blade. The outboard 10% of the blade radius features thin airfoils with reduced tip lift coefficients and swept-back tips to handle transonic flow, while the inboard sections maintain conventional thicker airfoils for optimal lift generation. This local differentiation allows the blade to operate efficiently across the entire span without uniform compromises.
Solution Approach 2:
The patent modifies aerodynamic parameters in the outboard section of the blade, specifically reducing the tip lift coefficient and implementing sweep angles. These parameter changes delay the onset of transonic flow effects and reduce shock wave formation, thereby decreasing noise and vibration while maintaining lift generation capability.
2Object-generated harmful factors
If thin airfoils and swept back tips are used in outboard 10% of blade radius to delay transonic effects, then noise and vibration are reduced, but rotor efficiency decreases and blade area must increase
Solution Approach 1:
The patent concentrates the sweep and thin airfoil modifications to only the outboard 10% of the blade radius, while the remaining 90% of the blade maintains optimized conventional geometry. This localized approach minimizes the impact on overall rotor efficiency while achieving noise reduction at the critical transonic tip region.
3Force
If blade width is increased or additional blades are added to delay transonic effects, then lift generation is improved, but rotorcraft empty weight increases
Solution Approach 1:
The patent modifies aerodynamic parameters (sweep angle, airfoil thickness, lift coefficient) in the outboard section to delay transonic effects, allowing the existing blade geometry and rotor configuration to maintain lift generation capability without requiring increased blade width or additional blades, thereby avoiding weight penalties.
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
The solution significantly improves rotor efficiency, reduces noise and vibrations, and increases maximum take-off weight while maintaining or reducing rotor size and weight, achieving higher hover efficiency and propulsive efficiency without increasing blade area or adding more blades.
Implementation Method 1
As any section of a rotor travels above Mach 0.7 and approaches Mach 1, transonic flow phenomena limit the maximum section lift, create shock waves, substantially increase rotor noise level
Implementation Method 2
create shock waves, substantially increase rotor noise level
Data Source
AI summary
Blades for rotorcraft are designed and/or implemented with rotor blades having a swept portion that occupies at least 20-40% of a length of the blade. Forward and aft sweeps are contemplated, with up to 20° or more of sweep. The swept portion preferably has a thickness ration of at least 10-20% at R80, and can have a tapered planform with a relatively outboard section having a smaller chord than a relatively inboard section. Contemplated design methods include optimizing or otherwise designing the rotor blade planform and lift distribution along the blade for efficiency in various flight conditions without taking into account the detrimental effects of high Mach numbers, and then using sweep angle, airfoil thickness and transonic airfoil shaping to maintain the lift distribution, low drag and low noise level at real Mach numbers at the various blade stations at the various flight conditions.