Rotocraft Airspeed Measurement Using Beam-Scanning Laser Anemometry
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Solution Overview
Problem
Conventional anemometric systems for rotary-wing aircraft, such as helicopters, become inoperative during low-speed maneuvers and lack of local wind data during takeoff in uninstrumented areas, leading to safety concerns and payload limitations, with existing alternative methods being complex and limited to flight tests or high-performance military use.
Innovation Solution
A method and system utilizing a beam-scanning Doppler laser anemometry device with continuous scanning and anomaly detection, employing a cone with an apex angle greater than 60°, and spectral analysis to differentiate between useful and parasitic signals, ensuring accurate airspeed measurement even in the presence of obstacles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional anemometric systems (Pitot tube probes) are used for rotary-wing aircraft, then the system structure is simple, but the system becomes inoperative during low-speed maneuvers and stationary flight
Solution Approach 1:
The patent replaces the mechanical Pitot tube system with an optical laser-based Doppler anemometry system. The laser beam scans through the air mass and measures Doppler frequency shifts from atmospheric particles, providing airspeed measurements without mechanical contact with the airflow, thus maintaining operation during low-speed and stationary flight maneuvers.
Solution Approach 2:
The patent introduces atmospheric particles as an intermediary medium. The laser beam does not directly measure air flow but instead measures the Doppler shift from light scattered by atmospheric particles that are carried along with the air mass, enabling indirect but reliable airspeed measurement in all flight conditions.
2Measurement precision
If laser beam scanning is used to measure airspeed, then accurate measurement is achieved, but parasitic echoes from obstacles degrade measurement accuracy
Solution Approach 1:
The patent extracts and separates the useful Doppler signal from parasitic echoes through spectral analysis. By analyzing the frequency spectrum of the received signal, the system identifies and isolates the Doppler frequency component corresponding to atmospheric particles from other frequency components caused by parasitic reflections from obstacles.
Solution Approach 2:
The patent implements a feedback mechanism where the measured Doppler frequency is continuously compared with expected values based on the scanned cone geometry and aircraft motion. When parasitic echoes are detected through spectral analysis, the system can identify and exclude these anomalous measurements, maintaining accuracy through continuous validation and correction.
3Loss of information
If three fixed laser beams are used to measure the three components of air speed vector, then complete airspeed information is obtained, but the device complexity increases
Solution Approach 1:
The patent uses periodic scanning of a single laser beam along a conical path instead of maintaining three fixed simultaneous beams. The beam systematically scans through different spatial directions in a periodic manner, collecting velocity information along the cone generator during rotation, thereby obtaining complete airspeed vector components through time-sequential measurements.
Solution Approach 2:
The patent transitions from a static three-beam configuration to a dynamic single-beam scanning system that adds the time dimension. By scanning the beam along a cone and measuring Doppler frequencies at different angular positions and times, the system reconstructs the three-dimensional airspeed vector from a sequence of one-dimensional measurements.
4Device complexity
If conventional anemometric systems are used during takeoff in uninstrumented areas, then no additional equipment is needed, but payload must be limited due to lack of wind data
Solution Approach 1:
The patent enables the rotary-wing aircraft to perform self-measurement of local wind conditions during takeoff operations. The laser Doppler anemometry system directly measures the air mass velocity relative to the aircraft, providing local wind information without requiring external anemometers or ground-based instruments, thus eliminating payload limitations.
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 airspeed measurement at low speeds and on the ground, enhancing pilot safety and payload optimization by providing precise wind data, reducing the impact of obstacles and parasitic echoes on measurement accuracy.
Implementation Method 1
This device is based on the measurement of the frequency shift, by Doppler effect, between a laser beam emitted into the atmosphere and the beam backscattered by the particles naturally present in the volume of air probed.
Implementation Method 2
measurement of the frequency shift, by Doppler effect, between a laser beam emitted into the atmosphere and the beam backscattered by the particles naturally present in the volume of air probed
Data Source
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AI summary
The invention relates to a method for determining the speed vector (I) relative to the surrounding air of a rotocraft (HL) equipped with a beam scanning Doppler laser anemometry device to measure (Step 1) a set of projections (Vm) of said speed vector (I) in at least four non-coplanar directions, comprising the following steps: - detecting (Step 2) any anomaly of at least one element from the set of measured projections (Vm), from a comparison relative to a first threshold (S1), of a deviation between the measurements (Vm) and the measurements anticipated (Vp) from a predetermined model depending on values of beam scanning parameters of the anemometry device; and - reducing (Step 3) the effect of a detected anomaly by invalidating measurements corresponding to said anomaly, and computing the components of the speed vector from valid measurements.