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64 and the company’s Sean Hilbert told UST that it has had more than 20 years’ experience of producing two-stroke engines for the powersports market, and that its new aero division is benefiting from “deep design expertise” that comes partly from the company’s founders’ automotive engine background. Hilbert noted that Cobra’s new UAV- oriented two-stroke, the A33, overcomes the usual compromises between outright power, noise and efficiency, and that it has two operational modes – power, primarily for take-off, and efficiency for cruising, including loitering, when fuel efficiency and typically lack of noise are the primary considerations. The switch between ‘power’ and ‘efficiency’ modes is made by the engine control system, and there are two characteristics that determine each mode. The first is a guillotine-type slide valve that alters the height of the exhaust port and thus exit area. Working in conjunction with that is an exhaust port bypass valve, which bypasses the baffling that minimises noise in the efficiency mode. Hilbert told us that the A33, a recently developed 33 cc two-stroke with an air- cooled single cylinder and reed valve induction, has successfully implemented this technology. He quoted 1200-1300 kW power output at 5000 rpm in efficiency mode compared with 2400 kW at 8500 rpm in power mode. He added that the A33 saves 1 g per minute fuel consumption in the former mode. Robert Alger, US defence electronics specialist at SRC, provided an update regarding the company’s GBSAA (Ground Based Sense And Avoid) product, which it is currently providing to the US Army and is a response to the key challenge of preventing UAVs from colliding with one another and other aircraft. The GBSAA system includes the firm’s LSTAR (V)3 ground-based air surveillance radar, a three-dimensional (range, bearing and speed) radar providing 360 º surveillance with a range of about 27 nautical miles (50 km). The overall GBSAA system architecture which is being fielded by the US Army includes two radars, and accompanying software to warn of a collision and to advise safe avenues of manoeuvre to avoid collisions. It is planned that future releases of the GBSAA system will incorporate ADS-B to enable integration with the FAA’s Next Generation Air Transportation System (NextGen). The US Army procured the GBSAA radar system in order to provide a sense- and-avoid capability to help UAVs fly safely from their operating bases to their training areas, which may not necessarily be linked by an accompanying air corridor. The first GBSAA system is already operational in Fort Hood in Texas, and Alger said that over the next 18 months other GBSAA systems will be installed, at Fort Riley in Kansas, Fort Stewart in Georgia, Fort Campbell in Tennessee and Fort Bragg in North Carolina. A further six sites could also be provided by the system, but that will depend on funding. The GBSAA radar system could also be mounted on a transportable tower or on a vehicle as a palletised payload. SRC’s subsidiary, Gryphon Sensors, is designing an as-yet-unnamed radar that will be free of export restrictions for US proprietary technology to international customers. The software will also have a different design but will offer similar functionality. Available radio spectrum is an ever- present problem for UAV operators. As the number of UAVs increases, so does pressure on the radio spectrum, with operators requiring RF bandwidth for the vital communications links needed to operate their aircraft safely, and to receive data and imagery gathered by the aircraft’s payloads. Help is at hand though in this respect from Access Spectrum, a company which has bought a block of exclusive, unencumbered radio spectrum in the 700 MHz section of the UHF range – specifically 757-758 MHz in the lower channel, with the upper channel covering 787-788 MHz – for use across much of the continental US, Alaska, Hawaii and the Gulf of Mexico. Access Spectrum is making segments of this available for purchase by commercial users, John Vislosky told us. Companies buying segments will receive the exclusive rights to them in specific geographical areas for voice, data and commercial UAV operations. For UAV operations, this specifically relates to small UAVs weighing less than 55 lb (25 kg) for line-of-sight and beyond-line-of-sight operations. Summer 2015 | Unmanned Systems Technology SRC’s LSTAR 3D radar has a range of about 50 km