Aerial robots capable of locomotion in both air and water would enable novel mission profiles in complex environments, such as water sampling after floods or underwater structural inspections. The design of such a vehicle is challenging because it implies significant propulsive and structural design trade-offs for operation in both fluids. In this paper, we present a unique Aquatic Micro Air Vehicle (AquaMAV), which uses a reconfigurable wing to dive into the water from flight, inspired by the plunge diving strategy of water diving birds in the family . The vehicle's performance is investigated in wind and water tunnel experiments, from which we develop a planar trajectory model. This model is used to predict the dive behaviour of the AquaMAV, and investigate the efficacy of passive dives initiated by wing folding as a means of water entry. The paper also includes first field tests of the AquaMAV prototype where the folding wings are used to initiate a plunge dive.

Robotic vehicles that are capable of autonomously transitioning between various terrains and fluids have received notable attention in the past decade due to their potential to navigate previously unexplored and/or unpredictable environments. Specifically, aerial-aquatic mobility will enable robots to operate in cluttered aquatic environments and carry out a variety of sensing tasks. One of the principal challenges in the development of such vehicles is that the transition from water to flight is a power-intensive process. At a small scale, this is made more difficult by the limitations of electromechanical actuation and the unfavorable scaling of the physics involved. This paper investigates the use of solid reactants as a combustion gas source for consecutive aquatic jump-gliding sequences. We present an untethered robot that is capable of multiple launches from the water surface and of transitioning from jetting to a glide. The power required for aquatic jump-gliding is obtained by reacting calcium carbide powder with the available environmental water to produce combustible acetylene gas, allowing the robot to rapidly reach flight speed from water. The 160-gram robot could achieve a flight distance of 26 meters using 0.2 gram of calcium carbide. Here, the combustion process, jetting phase, and glide were modeled numerically and compared with experimental results. Combustion pressure and inertial measurements were collected on board during flight, and the vehicle trajectory and speed were analyzed using external tracking data. The proposed propulsion approach offers a promising solution for future high-power density aerial-aquatic propulsion in robotics.

Many insects are well adapted to long-distance migration despite the larger energetic costs of flight for small body sizes. To optimize wing design for next-generation flying micro-robots, we analyse butterfly wing shapes and wing orientations at full scale using numerical simulations and in a low-speed wind tunnel at 2, 3.5 and 5 m s 21. The results indicate that wing orientations which maximize wing span lead to the highest glide performance, with lift to drag ratios up to 6.28, while spreading the fore-wings forward can increase the maximum lift produced and thus improve versatility. We discuss the implications for flying micro-robots and how the results assist in understanding the behaviour of the butterfly species tested.

Despite significant research progress on smallscale aerial-aquatic robots, most existing prototypes are still constrained by short operation times and limited performance in different fluids. The main challenge is to design a vehicle that satisfies the partially conflicting design requirements for aerial and aquatic operation. In this paper we present a new class of aerial-aquatic robot, the Sailing Micro Air Vehicle, 'SailMAV'. Thanks to a three-part folding wing design, the SailMAV is capable of both flying and sailing. The robot design permits long and targeted missions at the water interface by leveraging the wind as movement vector. It simultaneously offers the flexibility of flight for rapidly reaching a designated area, overcoming obstacles and moving from one body of water to another, which can be very useful for water sampling in areas with many obstacles. With a total wingspan of 0.96 m, the SailMAV employs the same wing and actuation surfaces for sailing as for flying. It is capable of water surface locomotion as well as takeoff and flight at a cruising speed of 10.8 ms −1. The main contributions of this paper are (i) new solutions to the challenges of combined aerial and aquatic locomotion, (ii) the design of a novel hybrid concept, (iii) the development of the required control laws, and (iv) the demonstration of the vehicle successfully sailing and taking off from the water. The presented work can inform the design of hybrid vehicles that adapt their morphology to move effectively.

experience tradeoffs in propulsion, structural design, and vehicle configuration. [1][2][3] Superhydrophobic surfaces show great potential in providing performance benefits for aerial-aquatic robots as a passive drag reduction technique. Such surfaces do not add complexity or significant additional mass to the vehicle nor do they need actuators to display the desired properties on the vehicle they are applied to. In addition, superhydrophobic surfaces can exhibit self-cleaning properties, preventing dirt or contaminants dissolved in water to adhere to the robot's surface, providing corrosion and fouling resistance. [4] This paper examines the application of superhydrophobic surfaces in drag reduction, which small unmanned aerial-aquatic vehicles (UAAVs) can utilize to minimize their power consumption and improve their mission capabilities when transitioning between air and water.Superhydrophobic surfaces are defined as surfaces with which, when laid flat, a drop of water forms an angle larger than 150 . [5] Superhydrophobicity is achieved by producing a surface topology, which enables gas to be trapped in surface voids preventing the liquid from penetrating. This is referred to as the Cassie-Baxter state. [6] The required surface topology must have roughness in the micrometer range or smaller, with surfaces consisting of nanometer scale structures typically achieving higher contact angles. These can also be combined, forming surfaces that have nanometer scale roughness on top of micrometer scale structures, with the purpose of minimizing the contact area of the water with the surface, known as the Lotus state. [7] The use of superhydrophobic surfaces for drag reduction is a developing field that is recently gaining traction. [8] So far, the focus of the research in the field has been primarily on micro-channel flow and less research has been carried out on external hydrodynamics over 3D geometries. As such, questions remain about the fundamentals of drag reduction over these surfaces, especially in the turbulent regime. [8] For the laminar flow through a micro-channel up to 40% reduction in pressure drop was found when the walls were made superhydrophobic by etching a series of square wave patterns onto them. [8] Another channel flow study found no drag reduction for laminar flow but up to 50% drag reduction in the turbulent flow regime. [9] These experiments also showed a large reduction in drag with