High Lock-Number Rotor Blades Eliminate Lead-Lag Dampers
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Solution Overview
Problem
Traditional rotor designs for aircraft are heavy, costly, and noisy due to their mass and chord width, and require lead-lag dampers to maintain in-plane frequencies below 1/rev, which limits their efficiency and flexibility.
Innovation Solution
The use of high Lock-number blades with a stiff-in-plane and soft-out-of-plane configuration, achieved by reducing yoke stiffness and adding tip weights, allowing blades to move relative to the yoke, thus eliminating the need for dampers and reducing mass, weight, and noise, while maintaining in-plane frequencies above 1/rev.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If traditional rotor designs with fewer, larger blades are used, then the rotor provides sufficient lift, but the rotor mass and inertia increase, leading to higher noise, higher cost, and requirement for dampers
Solution Approach 1:
The rotor is segmented into multiple smaller blades (5 or more) instead of using fewer larger blades. Each blade is narrower with reduced chord width, which reduces individual blade mass and overall rotor inertia while maintaining total lift capability through increased blade count
Solution Approach 2:
The Lock number parameter is increased to greater than 6 by changing blade geometry (reducing chord length c) and distributing lift across more blades. This parameter change enables lighter blades with reduced inertia while maintaining aerodynamic performance and eliminating the need for dampers
2Ease of manufacture
If the number of blades is increased to reduce rotor mass, then material cost and noise are reduced, but the chord width of each blade must be reduced
Solution Approach 1:
The total lifting surface is segmented into multiple narrower blades. By dividing the rotor into 5 or more blades with reduced chord width, the material required per blade decreases, reducing manufacturing cost while the increased blade count compensates for individual blade area reduction
Solution Approach 2:
Instead of increasing blade area in the chord dimension (width), the solution moves to another dimension by increasing the number of blades (radial distribution). This dimensional shift allows each blade to be narrower while maintaining total lifting capability
3Stability of the object's composition
If dampers are added to traditional rotors to control in-plane frequency, then stability is maintained, but device complexity and mass increase
Solution Approach 1:
Instead of adding dampers to control in-plane frequency as in traditional designs, the invention inverts the approach by designing blades with Lock number > 6 that naturally achieve in-plane frequency above 1/rev without dampers. The frequency control is built into the blade design itself rather than added as a separate control mechanism
Solution Approach 2:
The dampers are completely removed from the rotor system. By extracting the damper components and redesigning the blades with high Lock number, the system achieves frequency control through blade geometry alone, eliminating the need for separate damping mechanisms
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 configuration results in a lighter, quieter, and more cost-effective rotor system with reduced loads and mass, enabling increased blade count without the need for dampers, enhancing aircraft performance and reducing overall aircraft mass.
Implementation Method 1
The Lock number represents the ratio of aerodynamic forces, which act to lift the blade, to inertial forces
Implementation Method 2
The centrifugal force developed by the rotor blade is greater than the sum of the gravitational force acting on the rotor blade and the lift of the rotor blade
Data Source
AI summary
An aircraft rotor assembly has a central hub and a plurality of rotor blades coupled to the hub for rotation with the hub about an axis, each blade having a Lock number of approximately 5 or greater. A lead-lag pivot for each blade is formed by a flexure coupling the associated blade to the hub. Each pivot is a radial distance from the axis and allows for in-plane lead-lag motion of the associated blade relative to the hub, each pivot allowing for in-plane motion from a neutral position of at least 1 degree in each of the lead and lag directions. Elastic deformation of the flexure produces a biasing force for biasing the associated blade toward the neutral position, and the biasing force is selected to achieve a first in-plane frequency of greater than 1/rev for each blade.