<p>Engine selection</p><p> From initial research it was found that many aircraft of similar size and weight used two strokes and rotary engine to power three aircraft(uav engine pdf)</p><p> Looking specifically at uav engines used in the past, the main brands that appear are Rotax now known as Bombardier Recreational Products (BRP), UAV Engines Limited (UEL) and Herbranson</p><p> Looking at rotax many engines have been discontinued and therefore limit the effective use of them, one that would be feasible is the Rotax 122 which produces 15 horsepower capacity 124.8cc and weighs 12kg (made up couldn’t find it anywhere) but in unrestricted form with a power value power increases to 30hp(details: http://www.brp- powertrain.com/en/desktopdefault.aspx/tabid-225/362_read-331/ official wedsite)</p><p> UAV limited has a few compatiable engines with ar-731 and the ar-741, both produce 38 horsepower from 208cc with the 731 wieghing 9.9kg and the 741 weighing 10.7kg (http://www.uavenginesltd.co.uk)</p><p> Herbrandson produce opposed twin two strokes engines that produce 25.5 horsepower from 290cc and weigh 7.7kg (http://www.herbrandsonengines.com)</p><p> And limbach produce a 20hp engine from 274cc which weighs 7.2kg (pdf)</p><p> When comparing the use of these engine and there equivalent aircrafts we found three examples that closes match see Israel Harpy(below), Rq-7 shadow(pdf and link below),Rq-2a (link below)</p><p> The required achievements of these aircraft closely match the mission profile we were given.</p><p> Therefore by using these as an example we evaluated the use of the ar-741 and later the ar- 731</p><p> Initially we went with the ar-741 due to limitation in finding data on the ar-731 </p><p> Reasons behind choosing these engines over the two strokes:</p><p> They use less oil</p><p> Produce more power for the same weight</p><p> Have no radial vibration which allow for ease of taking picture and limit the use of lock nuts and fasteners on the rest of the aircraft, reduce the need for rubber mounts for the electronics.</p><p> It is also more fuel efficient and produces less pollution due to it being a fore stroke not a two stroke where the exhaust and inlet values are sometimes both open resulting in loses. </p><p> Takes up a smaller space because the rotor displaces circularly rather than up and down http://www.vectorsite.net/twuav_10.html [10.3] ISRAELI MBD HARPY / ELBIT TACTICAL UAVS * The MBD missile division of IAI sells another UAV, the "Harpy", which is an antiradar loitering attack drone. It patrols over a battlefield, waiting for somebody to turn on a radar, and then dives into it, destroying it with a blast-fragmentation warhead. The Harpy is in service with the Israeli Defense Forces, as well as Turkey, India, China, Taiwan, and the Republic of Korea. </p><p>The Harpy is a delta-winged machine with finlets on the wingtips. It weighs 135 kilograms (300 pounds), and is 2.7 meters (8 feet 10 inches) long with a span of 2.1 meters (6 feet 10 inches). It is powered by a UAV Engines Limited (UEL) AR731 rotary engine, with 28 kW (37 HP), driving a pusher propeller. Maximum speed is roughly 185 KPH (115 MPH / 100 knots), and endurance is about six hours. Although the Harpy is clearly different in appearance to the Boeing BRAVE 200, the two UAVs are conceptually similar in many ways, and the Harpy has a similar launch scheme. 18 Harpies are carried by a truck, with each UAV in its own sealed container. Three trucks make up a battery, which also includes a mission control center. A Harpy can be fueled, programmed, and tested inside its container, which is then opened for launch by RATO booster. After launch, the UAV makes its way to its patrol area, following navigational waypoints provided by the command center, and then flies circuits, waiting for a radar to turn on. On finding a radar, it dives into it almost vertically, detonating before impact to ensure maximum damage to the radar site. If the radar is turned off and the Harpy loses target lock, the UAV returns to its patrol. If no radar is spotted by the time the Harpy is running low on fuel, the UAV will self-destruct. An improved "Harpy 2" AKA "Harop" was introduced in 2009. It featured wingtip extensions to improve endurance, canard foreplanes, and a longer, bulbous nose to accommodate an imaging system. It is unclear if the Harop is intended for the antiradar mission. The UAV Engines Limited AR741 Wankel engine - from http://www.uavenginesltd.co.uk/ Design Features:  Exceptionally high power-to- weight ratio.  Economical fuel consumption.  Low cross sectional area.  Low levels of vibration.  Long life Background:  The UAV Engines AR741 has an outstanding power-to-weight ratio, combined with much longer life and better SFC, than any alternative engine.  It has been developed from the mature UAV Engines AR731 target drone engine, to meet the needs of small surveillance-type UAVs.  The UAV Engines AR741 engine has successfully completed a 150 hour FAR-33 type endurance test. AAI RQ-7 Shadow http://www.designation-systems.net/dusrm/app2/q-7.html</p><p>RQ-2A</p><p>Upgraded to a rotary after using a two stroke single http://www.designation-systems.net/dusrm/app2/q-2.html</p>