Unmanned Systems Technology 006 | ECA Inspector Mk2 USV | Antenna systems | Northwest UAV NW-44 | Unmanned ground vehicles | Navigation systems | Lunar X challenge

24 Dossier | ECA Inspector Mk2 USV The water jet’s input coupling, with its supporting bearing, attaches the engine adapter (which is a flange assembly specific to the selected engine type) to the water jet’s integral reduction gearbox that can be matched to the power units’ input speed – 3600-4000 rpm for Steyr SE 236 engines, for example – eliminating the need for a separate marine gear set. The reduction box uses robust wide-faced, ground helical gears. Next in line come the intake body and grate, which prevents large items of debris being sucked in, then the impeller and its casing, and then the stator with its vanes that remove the swirl given to the water flow by the impeller. After that come the steering bowl, which is the fixed structure in which the steering nozzle moves, then the steering nozzle itself and the thrust reverser bucket which, when deployed, splits the flow into backward-angled jets. With a diameter of 245 mm, the impeller is of axial flow design and delivers high thrust over the vessel’s entire speed range and offers high resistance to cavitation (the formation and collapse of water vapour bubbles that could damage low-pressure impeller surfaces) at low speeds. The reverse bucket features a split duct operated either by 12 V dc actuator or a hydraulic alternative, with follow-up control managed by a position- sensing control box. Installation options are a simple transom mounting and, as in the Inspector Mk2’s case, in an insert that forms an integral part of the hull structure. The Inspector Mk2’s compact dimensions and weight of less than 5 tonnes keep it compliant with French road transport rules for towing, so the complete system fits on a single trailer. This also makes it compatible with the boat-handling systems of most of the surface ships likely to operate it, Clavier points out. Other key requirements included high levels of stability despite large variations in weight distribution, and great accuracy in positioning and steering control for applications such as underwater survey work. This demanding set of requirements for a small vessel presented a significant naval architectural challenge, leading ECA to partner with Orion Naval Engineering, based in Canéjan, near Bordeaux in France. “We designed this boat together to be able to integrate a lot of payloads,” Clavier says, “but stability was a very big issue because if you have to put, say, 500 kg on the aft deck to operate another ROV then stability is a major challenge.” Solving that problem involved compromises to come up with the correct positions of the major masses within the boat, such as the engines and the fuel tank, and optimising ballast capabilities. As well as coping with the extreme fore- to-aft weight distribution changes that occur during daughter vehicle launch and recovery operations, the requirement also called for high levels of stability during high-speed runs tracking surface targets and at the low speeds typical of underwater survey work. ECA solved this low-speed issue by developing a novel, and now patented, bow keel arm, which is deployed when the arm pivots down into the water along a slot built into the bow. Usable at speeds of up to 10 knots, the keel has a symmetrical profile and, positioned ahead of the boat’s bow wave, it significantly enhances stability at low speeds. Rather than simply deploying weight and a hydrodynamic surface, however, it normally carries a sensor such as a side-scan sonar. Other payloads that the bow keel arm can accommodate include a multi-beam echo sounder and acoustic modems to enable communications with UUVs and so on; in its above-deck position it can support other sensors and effectors such as podded electro-optical systems or loudspeakers. The mechanical and hydrodynamic February/March 2016 | Unmanned Systems Technology One of the underwater vehicles that the Inspector Mk2 can launch and operate is the K-Ster C, an expendable mine-disposal ROV Its dimensions, and weight of less than 5 tonnes, allow the system to comply with French road transport rules and to fit on a single trailer