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

30 Dossier | Martin UAV V-Bat Following fuel preparation, which occurs concurrently with the inflow and reflecting phase inside the resonance tube, the fuel vapour and the reflection of the pressure wave are injected back into the combustion chamber in a time window specifically intended to avoid fuel losses via the exhaust port. That avoids the fuel scavenging losses that can occur with two- stroke engines without notably increasing the size or weight of the design. New engine Before version 5, the V-Bat had used a carburetted 3W International engine with 170 cc displacement. As development proceeded in an increasingly defence- oriented direction, however, the engineering team aspired to a more ‘military-grade’ engine, making the Hirth 4201’s smaller packaging, direct fuel injection and 183 cc attractive qualities. The core engine measures 24 x 14.5 cm and weighs 5.7 kg including the exhaust system, sensors. The wiring harness, with the ECU, ignition system and fuel supply system add a further 600 g. Engine control uses an integrated throttle servo from Volz, while Hirth’s ECU (based on a Triject ECU with modified software) receives commands from the autopilot to actuate the throttle commands and operate the capacitor discharge ignition system. A carbon-Kevlar motor mount isolates the vibration from the powertrain in one axis to prevent it reaching the payload and causing image distortions or damage over time. The control arms running up the sides of the motor mount enable the engine to pivot without risking the propeller hitting the duct. The team’s selection of a direct drive system from the crankshaft to the fan with a rigid connection results in the engine being able to run to 2000-6600 rpm, with 3500-4500 given as the cruising rpm range, although that varies according to the running fuel weight. Take-off rpm varies between 5600 and 6100 rpm. The V-Bat also integrates Hirth’s permanent magnet and inner rotor- type starter/generator designed for UAV installations. The starter/generator comes with an integrated data link for remote monitoring of power output and operating temperature. The generator weighs 1670 g, and can produce up to 2 kW from 4000 rpm. It comes with dual redundant regulator modules that, along with the internal temperature control function in the generator, provide safeguards against overloading the system. Martin UAV says the starter/generator was a key addition that prompted it to switch from the 3W International engine to the 4201. The generator provides power to the various onboard systems, from the autopilot to the avionics and servos, while also charging the batteries. If the generator should cease running, power switches to the batteries, providing enough power for the V-Bat to land safely, should the user wish to avoid continuing a potentially lengthy mission without a functioning generator. The system uses lithium-polymer batteries, the capacity of which the company prefers not to divulge. In addition to providing a back-up source of electricity in the event of generator failure, the batteries act as power source for ground checks and starter power. Martin UAV has also entered into a deal with NWUAV to develop a custom solution around an existing core for fuel injection and heavy fuel capability, with custom mufflers and other improvements, to support heavy-fuel engine testing in Autumn 2017, according to aerodynamics lead engineer Zach Hazen. Production supervisor Aaron Hendrickson adds “The NWUAV powertrain additions are likely to be tested on an eighth and possibly ninth iterations of the V-Bat when the system is trialled later this year.” Fuel tank The fuel tank is built between the wings as a direct part of the lower fuselage (using the pre-existing cubic outer hull and epoxied bulkheads) and takes up almost all of this section of the aircraft. The standard maximum fuel capacity is given as 23 lb, although there are options down to a 20 lb fuel capacity if shorter endurance or heavier payload is required. The V-Bat’s modular nature allows users to swap out the lower fuselage section for different fuel tank sizes. Hirth also supplied two electric pumps on each V-Bat to ensure fuel delivery is handled effectively in both horizontal and vertical flight, with a single fuel line running from the tank to the twin pump rail. “You have to make sure the fuel senders can grab the dregs when the craft is in vertical orientation,” Jones says. In addition to the standard EO/IR camera for day and night operations, the V-Bat has been tested to carry and August/September 2017 | Unmanned Systems Technology Twin mufflers, connected to the two cylinders of the Hirth 4201 and fastened to the V-Bat’s undercarriage, provide noise damping for the UAV engine