Rotorcraft Anemometer Tail Fin Placement for Low-Speed Accuracy
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Solution Overview
Problem
Rotorcraft anemometers face challenges in accurately measuring airspeed, especially at low speeds due to aerodynamic disturbances from rotors, leading to unreliable measurements and the need for complex and expensive calculation systems.
Innovation Solution
An omnidirectional anemometer, referred to as a drift anemometer, is installed at the top of the tail fin, with a correction rule applied to account for aerodynamic effects from the main rotor, using affine functions calibrated during test flights to provide accurate airspeed measurements across various speed thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an anemometer is installed on a rotorcraft to measure airspeed, then airspeed information is provided to the pilot, but the measurements become unreliable at low speeds due to aerodynamic disturbances from rotor rotation
Solution Approach 1:
The patent relocates the anemometer from conventional positions (nose or fuselage) to the tail fin, utilizing a different spatial dimension and location that is less affected by rotor downwash. This dimensional relocation allows the anemometer to measure airspeed in a region where airflow is less disturbed by main rotor rotation, improving measurement reliability at low speeds and during hover operations
Solution Approach 2:
The tail fin acts as an intermediary structure that protects the anemometer from direct exposure to rotor-induced turbulent airflow. By positioning the anemometer on the tail fin, which extends into the wake region, the device benefits from the tail fin's ability to modify and smooth the airflow pattern, reducing the impact of rotor turbulence on measurements
2Measurement precision
If complex calculation systems are used to compensate for rotor effects on anemometer measurements, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent extracts the anemometer from the main fuselage structure and relocates it to the tail fin, separating the measurement function from the disturbed airflow region. This extraction eliminates the need for complex computational compensation algorithms by placing the sensor in a location where rotor-induced disturbances are naturally minimized, thereby reducing system complexity while maintaining measurement accuracy
3Reliability
If the anemometer is positioned to avoid rotor downwash, then measurement reliability improves, but the device may be exposed to other aerodynamic disturbances from the tail rotor or fin structure
Solution Approach 1:
The patent applies local quality by specifically positioning the anemometer on the tail fin in a location that optimizes protection from main rotor downwash while minimizing exposure to tail rotor and fin-induced disturbances. The tail fin's geometry and the anemometer's specific placement create a localized measurement environment with favorable airflow characteristics, filtering out harmful aerodynamic factors while preserving measurement accuracy
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
This approach enables reliable and relevant airspeed measurements for rotorcraft at low speeds and hovering conditions, reducing the impact of rotor-induced aerodynamic disturbances and eliminating the need for complex systems, while maintaining accuracy at higher speeds.
Implementation Method 1
The anemometers traditionally used in aeronautics commonly implement at least one Pitot tube. Such anemometers make it possible to deduce the airspeed of the aircraft from the measurements supplied by the Pitot tube(s) of the static pressure of the air and of the total pressure of the air surrounding the anemometer.
Implementation Method 2
LORAS type anemometers use a pair of Pitot tubes mounted to rotate and placed head to tail with respect to each other, so that said LORAS type anemometers can measure the longitudinal component and the lateral component of the speed- air.
Implementation Method 3
optical anemometers, such as LIDAR anemometers (after the English acronym LIght Detection and Ranging), make it possible to measure the airspeed of an aircraft by sequential emission/reception at a given frequency of a LASER light beam
Implementation Method 4
ultrasonic anemometers, such as for example the anemometer described by document US Pat. No. 4,031,756 (HONEYWELL), make it possible to measure the airspeed of an aircraft by transmission/reception of ultrasonic waves
Data Source
Figure 1~2
AI summary
The present invention relates to a method for calculating and displaying the current airspeed (TAS) of a rotorcraft (1). At least one omnidirectional airspeed indicator is mounted on the top of a tail fin (7) of the rotorcraft. The current airspeed (TAS) of the rotorcraft (1) operating at speeds less than or equal to at least one airspeed threshold (S1, S2) of the rotorcraft (1) is calculated by correcting the measurements (V1) provided by the airspeed indicator (10) mounted on the top of the tail fin (7) according to the effects produced by the airflow generated by the rotation of a main rotor (2) equipping the rotorcraft (1) on the airflow velocity characteristics measured by the tail fin airspeed indicator (10). To this end, a correction rule calibrated during a test flight is advantageously applied to correct the measurements provided by the airspeed indicator (10) mounted on the top of the tail fin (7).