Miniature multihole airflow sensor for lightweight aircraft over wide speed and angular range

TL;DR

The paper tackles safe, accurate estimation of airspeed, AoA, and AoS for lightweight UAVs operating near stall. It introduces a compact, integrated nine-hole multihole pressure probe with an embedded PCB, leveraging differential pressure sensing to infer flow features without external tubing. Calibration employs a multivariate polynomial regression aided by a preprocessing step that decouples airspeed via a scaling factor $q$, and design optimization identifies a cone-tip probe with 1.2 mm hole spacing, achieving MAEs of 0.44 m/s for speed and 0.163°/0.156° for AoA/AoS, respectively, with RMSEs around 0.22° for angles and 3.6% for speed. Outdoor validation on an EasyGlider4 confirms competitive performance against a pitot tube and enhanced decoupling during stall and yawing maneuvers. The 9 g, public-domain sensor enables safe, near-stall operation for small UAVs and provides a path toward reliable low-speed aerodynamic state estimation in agile platforms.

Abstract

An aircraft's airspeed, angle of attack, and angle of side slip are crucial to its safety, especially when flying close to the stall regime. Various solutions exist, including pitot tubes, angular vanes, and multihole pressure probes. However, current sensors are either too heavy (>30 g) or require large airspeeds (>20 m/s), making them unsuitable for small uncrewed aerial vehicles. We propose a novel multihole pressure probe, integrating sensing electronics in a single-component structure, resulting in a mechanically robust and lightweight sensor (9 g), which we released to the public domain. Since there is no consensus on two critical design parameters, tip shape (conical vs spherical) and hole spacing (distance between holes), we provide a study on measurement accuracy and noise generation using wind tunnel experiments. The sensor is calibrated using a multivariate polynomial regression model over an airspeed range of 3-27 m/s and an angle of attack/sideslip range of +-35°, achieving a mean absolute error of 0.44 m/s and 0.16°. Finally, we validated the sensor in outdoor flights near the stall regime. Our probe enabled accurate estimations of airspeed, angle of attack and sideslip during different acrobatic manoeuvres. Due to its size and weight, this sensor will enable safe flight for lightweight, uncrewed aerial vehicles flying at low speeds close to the stall regime.

Figures (8)

• Figure 1: Miniature integrated 3D airflow sensor: (A) The fixed-wing UAV used for validation flights with the multihole pressure probe mounted on the right wing. (B) The multihole pressure probe consists of a 3D-printed structure and sensor-PCB, joined by silicone sleeves that ensure an airtight seal. The integrated design eliminates traditional tubing between the structure and the sensors, significantly reducing weight and complexity.
• Figure 2: Comparison of multihole pressure probes on mass and measurement range: Existing sensors (red, full line) are unsuitable for small uncrewed aerial vehicles (UAVs) due to their weight or airspeed range. Our approach (green, hatched line) satisfies those requirements.
• Figure 3: Design of the multihole pressure probe:(A) Printed circuit board (PCB) with five differential pressure sensors (1-5). Each sensor is connected to two holes, measuring differential pressure. Data is transmitted via a connector in the back (right side). (B) Complete probe with colour-coded internal pathways. (C) Side view, showing the static holes at the side (yellow). Front holes are placed at a 45$^\circ$ angle. (D) Front view, displaying pairs of holes (e.g., left-right or up-down) that are connected to the same differential pressure sensor. (E) Isometric view, showing only the static hole for enhanced readability.
• Figure 4: Design parameter optimisation:(A) Four different hole spacings between 0.4 mm and 1.2 mm are explored with cone and sphere tip shapes, resulting in eight different designs. (B) All probes were manufactured through Stereolithography resin printing. (C) A robotic arm was used to rotate the probes at different angles of attack and sideslip against an open wind tunnel (brown panel, Windshape Ltd)
• Figure 5: Results of the design parameter optimisation: (A) Differential pressures at 3 m/s airspeed, averaged over time (1.4 s / 70 samples), are plotted as a function of AoA and AoS. Each of the five pressure sensors records the pressure difference between a pair of ports. The distribution is aligned with the direction of the hole pair of the corresponding sensor, enabling estimation of AoA and AoS. (B) Comparison of all tested hardware configurations with respect to measurement resolution across velocity and angular ranges. Each point or triangle represents a distinct hardware design, with its performance compressed into a single metric according to the procedures outlined in Table \ref{['tab:compare_res_noise']}. Statistically significant differences, as determined by independent t-tests, are marked with asterisks. The results show that conical tips yield significantly higher velocity measurement resolution compared to spherical tips, while hole spacing has no significant impact. (C) Comparison of hardware designs in terms of noise generation. Conical tips produce significantly lower speed noise compared to spherical tips.