Unmanned Systems Technology 009 | Ocean Aero Submaran S10 | Simulation and testing | Farnborough report | 3W-110xi b2 TS HFE FI | USVs | Data storage | Eurosatory/UGS 2016 report

25 neutral” stage, then the electric thruster is activated in reverse to flood the vehicle, making it neutrally buoyant, followed by the addition of a little extra ballast to take the buoyancy slightly below neutral. The S10 then uses its electric thruster and ruddervators to dive to the selected depth; it takes eight minutes to submerge to 10 m. As in a conventional submarine, compressed air is retained in tanks to expel the ballast water and enable the S10 to return to the surface. With so much of the vehicle flooded, protecting the electrical, electromechanical and electronic systems from the water proved a challenge, Childress says. For example, the processor stack has eight boards, consisting of the main processor and a number of controller boards that manage the solar panels, operate the servos for the ruddervators, command sail deployment and adjustment, submerging and surfacing, navigation and comms, and so on. Ocean Aero designs its own electronics boards but has them populated and finalised by DigiKey. They are housed in a clear pressure tube with a circular cross-section, through the top of which all the signal and power wiring must pass without letting water in. “We destroyed several sets of processor boards getting that right!” Childress recalls. Ocean Aero is in discussion with Prevco for high- performance pressure tubes to protect the electronics of future deeper diving versions such as the S200. The S10’s computers are protected against more than water, however, as the software is written in-house in the C++ language and is proprietary and therefore secret. As a sealed-processor boat, customers will not have access to the code, which in any case features encryption and cut-offs, which are parts of the code to which other modules attach but which can be removed without affecting functionality. On a wing and a sail The wing sail – a concept proven in racing yachts – can pivot on the mast axis to change its angle with respect to the centreline of the boat to set its angle of incidence, and features the equivalent of the flap on an aircraft wing that changes the camber of the wing as a whole to adapt it to different wind speeds, equivalent to trimming a fabric sail. Made from GRP ribs with a Kevlar outer skin, the wing sail is light, tough and very stiff, providing an ability to resist flexing, which is very important for its efficiency. A traditional fabric sail was never considered because managing the autonomous folding and unfolding of the sail for the transition between surface and subsurface operations is very difficult. There are also major performance benefits to be had from using wing sails over fabric sails, Childress says, particularly when sailing into the wind. “If you design a rigid wing sail correctly, you can get about 1.5 times the power that you can from a cloth sail,” he says. “They can create a higher pressure against the wind because of their rigidity and because of their shape, and they hold that shape. They create a lot of lift, identical to the way an airplane wing creates lift.” As well as generating more power per unit area, this shape-holding rigidity also enables the boat to sail closer to the wind, wind direction being a fundamental limit on the courses any sailing vessel can set. While no sailing boat can sail directly into the wind, the more efficient its sails, the less it is limited by wind direction. Deployment and retraction Control of the sail wing’s flap, the sail’s rotation about the mast axis and the raising and lowering process are all handled by one mechanism, for which Ocean Aero as applicant and Vance McClure and Chris Todter as inventors are seeking patent protection, along with the vessel’s overall concept. The patent describes a deployment mechanism that includes an actuator and linkage that pivots on the wing or wing and keel assemblies simultaneously between the deployed and retracted configurations. It also includes a drive mechanism to rotate either the wing and flap together so that the flap angle relative to the wing is constant, or to change the flap angle relative to the wing with the wing angle of incidence held constant. There are both electrical and electro-hydraulic versions of the drive mechanism. Unmanned Systems Technology | August/September 2016 An S10 prototype folded for transport. The flap folds back against the wing sail with the chords of the two aerofoils parallel to fit into the slot