Hélice

Résumé

thumb|Hélice de navire En mécanique, l’hélice est un dispositif formé de plusieurs pales disposées régulièrement autour d’un axe. Lorsque son axe entre en rotation, ce système décrit des hélices dans un fluide en avançant perpendiculairement au plan de rotation, grâce aux pales orientées suivant un certain angle de calage qui prennent appui sur le fluide. Une hélice peut donc être motrice (transfert d’énergie vers le fluide : avion) ou réceptrice (récupération d’énergie depuis le fluide : turbine, éolienne ou aérogénérateur). Le profil et le calage des pales sont optimisés pour l’utilisation prévue. Application : appareil de traction, compression, propulsion, sustentation, dispositif de mesure. Histoire Le premier type d’hélice est la vis d’Archimède qui fait son apparition vers 200 av. J.-C. ans en tant qu’outil de pompage et d’irrigation. Cette même vis devait servir comme mode de propulsion pour des engins amphibies destinés à se déplacer avec la même aisance en eau l

Source officielle

https://fr.wikipedia.org/wiki/H%C3%A9lice

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vignette|alt=|Rotors de turbines à vapeur de la centrale nucléaire de Philippsburg. Une turbine est un dispositif rotatif convertissant partiellement l'énergie interne d'un fluide, liquide (comme l'

thumb|Hélice d'un F4U Corsair En aéronautique, une hélice est un type d'hélice aérienne qui tourne grâce au mouvement rotatif imprimé directement ou indirectement par un moteur et qui, en accélérant v

Le profil d'un élément aérodynamique est sa section longitudinale (parallèle au vecteur vitesse). Sa géométrie se caractérise par une cambrure (inexistante s'il est symétrique), une épaisseur et la

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Design and development of the efficient anguilliform swimming robot- MAR

Peter Eckert, Auke Ijspeert, Anouk Looijestijn

Propulsion of swimming robots at the surface and underwater is largely dominated by rotary propellers due to high thrust, but at the cost of low efficiency. Due to their inherently high speed turning motion, sharp propeller blades and generated noise, they also present a disturbance to maritime ecosystems. Our work presents a bio-inspired approach to efficient and eco-friendly swimming with moderate to high thrust. This paper describes the concept, development and experimental validation of the novel anguilliform robot MAR. With 15 elements making up the 0.5 m long propulsive section and driven by a single, speed-controlled brushless DC motor (BLDC), the robot creates a smooth continuous traveling wave for propulsion. Steering and autonomy are realized by an actuated head with integrated batteries that serves as a front-rudder. Almost neutral buoyancy paired with individually actuated pectoral fins furthermore enable submerged swimming and diving maneuvers. MAR accomplished high thrusts at a moderate power consumption in first performance tests. The achieved maximum velocity and the speed related efficiency (defined as the achieved speed over the power consumption m Ws(-1)) did not fulfill the expectations in the first tests (in comparison to commercial rotary thrusters), which can be largely attributed to the spatial limitations and an imperfect test setup. Nevertheless, the potential towards highly efficient and high thrust propulsion is visible and will be further investigated in future efforts.

IOP PUBLISHING LTD2020

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A Morphing Cargo Drone for Safe Flight in Proximity of Humans

Mir Alikhan Bin Mohammad Feroskhan, Dario Floreano, Przemyslaw Mariusz Kornatowski, William John Stewart

Delivery drones used by logistics companies today are equipped with unshielded propellers, which represent a major hurdle for in-hand parcel delivery. The exposed propeller blades are hazardous to unsuspecting bystanders, pets, and untrained users. One solution to provide safety is to enclose a drone with an all-encompassing protective cage. However, the structures of existing cage designs have low density in order to minimize obstruction of propeller airflow, so as to not decrease efficiency. The relatively large openings in the cage do not protect hands and fingers from fast rotating propellers. Here we describe a novel approach to safety and aerodynamic efficiency by means of a highdensity cage and morphing arms loosely inspired by the box turtle. The drone cage is made of a dense and lightweight grid. When flying in proximity of humans, the arms and propellers are retracted and fully sealed within the cage, thus making the drone safe and also reducing the total footprint. When flying at cruising altitude far from people and objects, the arms and propellers extend out of the protective grid, thus increasing aerodynamic efficiency by more than 20%.

2020

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An origami-inspired cargo drone

Dario Floreano, Przemyslaw Mariusz Kornatowski, Stefano Mintchev

Multicopters stand to revolutionize parcel delivery because of their capability to operate in areas with unsuitable road infrastructure and precisely maneuver in cluttered environments. However, current multicopters for delivery can be dangerous for people, and are difficult to store and transport. Safety issues arise because users are exposed to unshielded spinning propellers. Transportation to the place of deployment and storage is often impaired by the large size that is required for heavy lifting. This paper addresses these limitations by proposing the integration of a quadcopter into a foldable protective cage. The cage provides an all-round protective structure that physically separates the propellers from the environment, ensuring the safety of people. The drone and the cage can be easily folded with a single movement, significantly reducing its size for ease of storage and transportation. This design has been validated with a quadcopter that can lift parcels up to 500 g and reduce its storage volume by 92% when folded.

2017

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