Rotorcraft Airspeed Estimation via Blade Pitch Analysis
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Solution Overview
Problem
Conventional anemometer installations for rotorcrafts are inaccurate at low airspeeds and fail to provide stable and accurate measurements over the entire flight envelope, especially due to interference from the main rotor's airflow and ground effects, and lack the ability to measure airspeed direction effectively.
Innovation Solution
A method and apparatus that estimate airspeed components by analyzing the pitch angles of rotor blades relative to the tip-path plane, using a model that relates pitch angles to airspeed and auxiliary speed, allowing for accurate airspeed determination over the entire flight envelope without requiring costly calibration or being sensitive to airflow disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional anemometer installation with Pitot tube is used, then airspeed measurement is provided, but measurement accuracy deteriorates at low airspeeds (below 30 knots) due to insufficient pressure difference
Solution Approach 1:
The patent replaces the mechanical Pitot tube-based pressure measurement system with an optical/laser-based anemometer system. The laser anemometer uses light scattering and Doppler effect to measure air particle velocity directly, eliminating the need for pressure differential measurements that become insufficient at low speeds. This substitution enables accurate airspeed measurement across the entire flight envelope including hover and low-speed flight.
Solution Approach 2:
The invention changes the measurement parameter from pressure differential (which is proportional to square of airspeed and becomes negligible at low speeds) to direct velocity measurement using laser Doppler effect. By measuring the frequency shift of laser light scattered by air particles, the system directly determines airspeed without relying on sufficient pressure differences, thereby enabling accurate low-speed and hover measurements.
2Measurement precision
If a Pitot tube anemometer is used, then airspeed amplitude is measured, but the measurement is sensitive to airflow disturbances from the main rotor and ground effects
Solution Approach 1:
The patent replaces the mechanical Pitot tube that physically interacts with disturbed airflow near the rotor and ground with a non-contact laser anemometer. The laser beam passes through the undisturbed air field ahead of the rotor, measuring airspeed without being affected by rotor downwash, ground effect, or fuselage interference. This eliminates sensitivity to harmful airflow factors while maintaining measurement accuracy.
3Loss of information
If a conventional anemometer is used, then airspeed measurement is provided, but vector information including direction cannot be obtained
Solution Approach 1:
The patent segments the airspeed measurement into multiple directional components by arranging laser anemometers at different angular positions around the rotorcraft. Each laser measures the airspeed component along its specific line of sight. By combining measurements from multiple segmented directions, the system reconstructs the complete airspeed vector including magnitude and direction, providing full vector information without requiring a single complex omnidirectional device.
Solution Approach 2:
The invention transitions from scalar airspeed measurement (single value) to vector airspeed measurement (magnitude and direction) by adding angular/directional dimensions to the measurement system. Multiple lasers positioned at different angles measure components in different spatial dimensions, allowing reconstruction of the full three-dimensional airspeed vector. This dimensional expansion enables direction information to be obtained while maintaining relatively simple individual sensor configurations.
4Measurement precision
If costly calibration procedures are performed to improve measurement accuracy, then measurement precision improves, but time and resource consumption increase
Solution Approach 1:
The patent implements self-calibration capability where the laser anemometer system automatically determines its own calibration parameters during normal operation. The system uses known flight conditions (such as hover where airspeed is zero, or coordinated turns where vertical and horizontal components are zero) to automatically adjust and verify calibration constants without requiring external calibration equipment or ground-based procedures. This self-service approach eliminates time-consuming manual calibration while maintaining high measurement precision throughout the flight envelope.
Data Source
AI summary
A method and apparatus for estimating an airspeed of a rotorcraft by analyzing its rotor. The rotorcraft includes a fuselage and a main rotor that is equipped with a plurality of blades and that rotates about an axis of a hub of the rotor, and in which the free end or “tip” of each blade describes a path in the vicinity of a tip-path plane. The method makes it possible to determine said airspeed of the rotorcraft in a frame of reference united with the tip-path plane by solving a model of the rotor that puts a pitch angle of at least one blade relative to the tip-path plane into relation with the airspeed of the rotorcraft and with an auxiliary speed. The auxiliary speed may be an induced velocity of the air flowing through the rotor or else an axial airspeed at the upstream infinity of the rotorcraft.