Unmanned Systems Technology 015 | Martin UAV V-Bat | William Sachiti | Sonar Systems | USVs | Desert Aircraft DA150 EFI | SeaCat AUV/ROV | Gimbals

28 V-Bat’s critical transition mechanism, the ducted tail section of the UAV constitutes the other. While a typical aeroplane tail arrangement would feature an elevator and rudder as the main tools for thrust vectoring, the V-Bat forgoes them in favour of its unique ducted fan design, which integrates eight controllable vanes arranged radially about the longitudinal axis. As mentioned, the vanes take commands from the autopilot and navigation sensors regarding roll, pitch and yaw to provide control authority during autonomous take-off and landing, and lateral and longitudinal stability during waypoint-based active flight operations via a map display on the user interface and a data link (as well as providing restoring moments to re-align the aircraft during strong winds). The vanes operate independently of each other using COTS digital servos, to control the airflow through the duct. “Mechanically, it is very simple,” Jones says. “This scale of UAV can be fraught with single points of failure, and simplicity of design means less likelihood of exposing such points.” Both wings are fitted with an aileron for added roll authority in high-speed flight. These take the form of cut-out slots hinged onto the main section of its wing, and each is operated by a digital servo, although Jones notes that this feature exists mainly to save using the control vanes during high-speed rolling manoeuvres, and that the ailerons could be omitted from a future version to make the V-Bat’s overall design even simpler. The use of a ducted fan is also intended to provide other advantages. For example, the basic safety level achieved by having a shroud around the propeller protects people against the fan blades. This is also the critical factor in enabling the V-Bat to launch and land close to ground or ship structures, or with flight crew members nearby. Jones and McAuliffe add that this, along with the craft’s short assembly time, enables more efficient manned/ unmanned vehicle teaming, as a single helicopter pad can be used. V-Bats and manned helicopters could ‘queue’ to use the launch area one by one with no need to spend time clearing any ancillary helicopter equipment (for refuelling or maintenance checks). Also, the duct (and its four landing struts) provides a stable base for landing, particularly when compared with a historical tail-sitter design that would sit, launch and land on its tail fins. Each landing strut beneath the duct takes the shape of a curved ‘spring foot’ to provide shock absorbency as the craft hits the ground. Each foot is fitted with a coiled spring, the material of which may vary on the iteration of the V-Bat being tested – although Martin UAV is also iterating designs for the struts themselves, working with steel, aluminium and fibreglass components to identify their relative merits. “Choosing that part depends on how robust you need the absorbency to be on landing,” Jones explains. “If you want landing to be totally autonomous then you probably want it to be more forgiving. But if you’re happy to conduct what we call ‘hand landings’ – where the Bat hovers down gently and a flight deck officer literally just walks up, takes hold of a wing or support strut and eases it down – it doesn’t make any real difference what you’ve chosen for the landing springs.” If the V-Bat should be off-balance when landing and there are no personnel present to catch it in time, it is designed to tip over safely onto one of its wings before toppling onto the front landing skid under the nose section, or straight down onto the skid. That avoids any direct impacts on the duct, fuselage or nose that could damage the powertrain, payload or avionics. Tip-over landings during flight testing August/September 2017 | Unmanned Systems Technology Dossier | Martin UAV V-Bat The V-Bat uses a twin-blade propeller, the edges of which are shielded from causing or receiving damage from its surroundings by the shroud of the duct. The propeller and its cowling also provide cooling for the engine The radial stator rail holds the eight control vanes critical to the V-Bat’s control during flight and transition phases