Rotor Assembly With High Lock-Number Blades and Flexures
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional rotor designs for aircraft are heavy, leading to increased mass and inertia, which affects lift, noise, vibration, and cost, and require additional components like dampers to manage lead-lag motions, whereas high Lock-number blades with reduced mass and stiffness could provide a lighter, quieter, and more efficient rotor system.
Innovation Solution
The implementation of a rotor assembly with high Lock-number blades and flexures connecting the blades to the hub, allowing for lead-lag motions without the need for dampers, achieving a stiff-in-plane and soft-out-of-plane configuration with an in-plane frequency above 1/rev, reducing mass and load while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional 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 and vibration
Solution Approach 1:
The rotor system is segmented into multiple smaller blades instead of fewer larger blades. The patent describes a rotor assembly with three or more blades, where each blade has reduced mass and chord width. This segmentation allows the total lift to be distributed across multiple blades while reducing the mass of each individual blade and the overall rotor system.
Solution Approach 2:
The patent changes key parameters of the blade design, including increasing the number of blades, reducing chord width, and optimizing blade mass distribution. These parameter changes result in higher Lock numbers (greater than 10) while maintaining sufficient lift capability and reducing rotor mass.
2Device complexity
If fewer, larger blades are used to achieve sufficient lift, then the rotor structure is simpler, but the lead-lag motions require additional dampers and complexity
Solution Approach 1:
The patent extracts and eliminates the need for lead-lag dampers by designing blades with inherent structural characteristics that naturally control lead-lag motions. The flexible root construction and optimized blade geometry allow the blades to self-regulate their lead-lag behavior without requiring separate damping components.
Solution Approach 2:
The blade design incorporates self-regulating features where the blade's own flexibility and aerodynamic characteristics control lead-lag motions. The blade root flexibility and mass distribution create natural damping effects that eliminate the need for external dampers.
3Force
If larger chord width blades are used, then each blade generates more lift, but the blade noise increases and material cost increases
Solution Approach 1:
The total aerodynamic force requirement is segmented across multiple blades with smaller chord widths. Instead of relying on a few large blades, the patent uses three or more blades where each contributes to the total lift, resulting in reduced individual blade noise and material usage.
Solution Approach 2:
The patent describes how multiple blade passages create a higher frequency noise pattern that coalesces into a less offensive sound. The periodic passage of multiple smaller blades through the air generates a higher frequency noise spectrum compared to fewer larger blades.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An aircraft rotor assembly (217) has a central hub (221) and a plurality of rotor blades (215) coupled to the hub (221) for rotation with the hub (221) about an axis (242), each blade (215) having a Lock number of approximately 5 or greater. A lead-lag pivot for each blade (215) is formed by a flexure (219) coupling the associated blade (215) to the hub (221). Each pivot is a radial distance from the axis (242) and allows for in-plane lead-lag motion of the associated blade (215) relative to the hub (221), 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 (219) produces a biasing force for biasing the associated blade (215) 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 (215).