Bearingless Rotor Blade Assembly for High-Speed Aircraft
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Solution Overview
Problem
Conventional rotary-wing aircraft face limitations in forward airspeed due to stall conditions of retreating blades and increased aerodynamic drag from counter-rotating, coaxial rotor systems, which complicate fairing system integration and degrade lift/drag ratios at high speeds.
Innovation Solution
A bearingless rotor system with a flexbeam assembly featuring a first and second beam in back-to-back orientation with a pitch shaft channeled between, extending to an outboard rotor blade station, where the beams morph into a rotor blade spar, surrounded by an aerodynamic skin that minimizes torsional stiffness, allowing direct pitch input and reducing the need for bulky torque tubes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a counter-rotating, coaxial rotor system is used to increase forward airspeed, then lift balance between advancing and retreating blades is improved, but aerodynamic drag increases significantly
Solution Approach 1:
The invention extracts and eliminates the bearing assembly from the rotor hub, replacing it with a bearingless configuration where the rotor hub rotates directly on the main rotor shaft. This removal of the bearing assembly reduces the structural complexity and aerodynamic drag of the rotor system, enabling higher forward airspeeds while maintaining lift balance through the counter-rotating coaxial configuration.
Solution Approach 2:
The rotor hub in this invention serves multiple functions simultaneously: it acts as both the rotation support structure and the fairing interface, eliminating the need for separate bearing assemblies. This multi-functional design reduces the number of components and minimizes aerodynamic drag, directly addressing the energy loss problem while maintaining the speed advantage.
2Strength
If a thick inboard airfoil section is used in conventional flexbeam rotor systems, then structural strength is improved, but fairing system integration becomes complicated and lift/drag ratio degrades
Solution Approach 1:
The invention applies local quality by using a thin airfoil section at the inboard portion of the rotor blade where it interfaces with the fairing system, while maintaining sufficient structural strength through the flexbeam assembly's torsional flexibility and the outrigger blade structure. This localized thin section simplifies fairing integration and improves the lift/drag ratio without compromising overall structural integrity.
Solution Approach 2:
The invention changes the airfoil section parameter from thick to thin at the inboard portion, which directly simplifies the fairing system integration and improves the lift/drag ratio. The structural strength is maintained through alternative means including the flexbeam assembly's torsional properties and the distribution of loads through the rotor hub and main rotor shaft configuration.
3Ease of operation
If a bulky torque tube is used to provide pitch input, then pitch control is achieved, but device complexity and weight increase
Solution Approach 1:
The invention extracts and eliminates the bulky torque tube structure, replacing it with a direct pitch control mechanism where the pitch shaft connects directly to the flexbeam assembly at the rotor hub. This removal of the torque tube reduces device complexity and weight while maintaining effective pitch control through the simplified direct connection path.
Solution Approach 2:
The pitch shaft serves as an intermediary element that directly transmits pitch control inputs from the rotor hub to the flexbeam assembly, eliminating the need for a bulky torque tube. This intermediary approach maintains pitch control functionality while significantly reducing structural complexity and weight.
Data Source
AI summary
A bearingless rotor system includes a flexbeam assembly having a first beam and a second beam arranged in a back-to-back orientation with a pitch shaft channeled therebetween. The beams morph into a rotor blade spar at an outboard rotor blade station. The outboard section of the flexbeam assembly receives the full pitch input from the pitch shaft while the most inboard section of the flexbeam assembly is essentially fixed in pitch by a blade attachment to a rotor hub assembly. The flexbeam assembly twist versus span is essentially linear from the most inboard to the most outboard rotor blade stations. The outboard rotor blade station, being attached to the outboard section of the flexbeam assembly, thereby also defines the pitch input equivalent from the outboard rotor blade station to the rotor blade tip.