Coaxial Rotor Tip Clearance Measurement Using Optical Emissions
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Solution Overview
Problem
Conventional coaxial helicopters with counter-rotating rotors face challenges in measuring tip clearance effectively due to the close proximity of blades, which increases drag and degrades performance, especially during high-speed flight, as traditional laser tracking systems are impractical for in-flight deployment.
Innovation Solution
A tip clearance measurement system using divergent laser beams emitted by laser diodes on one rotor blade, detected by a photodiode on the opposing blade, with a flight computer calculating clearance based on emissions and azimuth calculations, and optionally including a third emitter for additional positioning data, communicated via RF transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large spacing between blades is used in conventional coaxial helicopters, then tip clearance measurement becomes easier, but drag increases and performance degrades in forward flight
Solution Approach 1:
The patent replaces mechanical measurement systems with an optical measurement system using laser beams and photodetectors. This allows accurate tip clearance measurement without requiring large blade spacing, as the optical system can function effectively in the close-proximity configuration needed for reduced drag.
2Loss of energy
If rigid rotors with close spacing are used for high speed flight, then drag is reduced, but tip clearance measurement becomes more difficult and critical
Solution Approach 1:
The patent employs an optical measurement system that uses laser beams and photodetector arrays to measure tip clearance non-contactly. This system can accurately measure the small clearances between rigid rotors in close proximity without being affected by the high-speed rotation or vibration, solving the measurement difficulty associated with drag-reduced configurations.
Solution Approach 2:
The patent introduces an intermediary optical measurement system consisting of laser beams, beam expanders, and photodetector arrays positioned in the gap between the rotors. This intermediary system enables indirect measurement of tip clearance without requiring physical contact or large spacing, allowing accurate measurement in the close-proximity high-speed configuration.
3Measurement precision
If conventional laser tracking systems are used for tip clearance measurement, then measurement accuracy is achieved, but the system becomes impractical for in-flight deployment
Solution Approach 1:
The patent divides the measurement system into separate components: laser emitters mounted on one rotor, beam expanders positioned in the gap, and photodetector arrays on the opposing rotor. This segmentation allows each component to be compact and optimized for its specific function, enabling the overall system to be deployed on flying rotors rather than requiring a fixed ground-based tracking system.
Solution Approach 2:
The patent creates a dynamic measurement system where lasers are mounted on one rotating rotor and photodetectors on the opposing rotor. The system continuously measures clearance throughout the rotation cycle, adapting to the dynamic conditions of flight. The measurement system rotates with the blades rather than remaining fixed, enabling in-flight deployment and continuous monitoring.
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
Enables accurate tip clearance measurement between counter-rotating rotors, providing real-time data for pilots to avoid unacceptable clearance margins, thereby improving flight performance and safety by alerting pilots to potential clearance issues.
Implementation Method 1
A tip clearance measurement system uses a laser tracker adapted for in-flight operation in a coaxial counter-rotating helicopter. The system uses a single laser mounted on one of the rotors and a photodiode on the other rotor to measure tip clearance.
Implementation Method 2
The system uses a single laser mounted on one of the rotors and a photodiode on the other rotor to measure tip clearance.
Data Source
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AI summary
An aircraft is provided and includes an airframe, first and second main rotors rotatably supported on the airframe to rotate about a rotational axis in opposite directions, first and second emitters disposed on an emitter blade of the second main rotor, each of the first and second emitters being configured to emit an emission toward a detector blade of the first main rotor, a detector disposed on the detector blade of the first main rotor, the detector being configured to detect the emissions of the first and second emitters and a flight computer which determines a clearance between the first and second main rotors in accordance with detections of the emissions by the detector.