Unmanned Systems Technology 017 | AAC HAMR UAV | Autopilots | Airborne surveillance | Primoco 500 two-stroke | Faro ScanBot UGV | Transponders | Intergeo, CUAV Expo and CUAV Show reports

64 boxer in the One 100 impacting on the performance of the UAV, or in particular on its control system or payload operation. “During development of the 500 we will get some idea of the impact of the vibration on the UAV from the sensors on the craft – the autopilot measures the vibration to which it is subject – and we will make any adjustment as is necessary,” Smat adds. He is confident that no major development in this respect will be needed. He notes that the key to the durability of the engine, and in particular its ability to cope with the power level and the loading on its main bearings, is the integrity of its crankshaft joint and the stiffness of its crankcase, which to that end is very well ribbed. The crankshaft runs in four main bearings, with a fifth bearing immediately behind the propeller drive hub. That fifth bearing is the axial support bearing, and is a sealed, grease-lubricated ball bearing, since unlike the unsealed ball main bearings flanking the two crank chambers it does not come into contact with the pre-mix oil. The crankcase consists of front, centre and rear sections, which are machined by VM Motor from billet 7075 T651 aluminium alloy. The split lines correspond to the central axis of each cylinder pair (perpendicular to the crankshaft axis). Thus the two main bearings supporting the (individual) crankpins for the front pair of cylinders are housed in the front and centre sections. The centre section also carries the forward main bearing for the rear cylinder pair. This general arrangement, together with the use of (un-split) roller bearings, is possible given that the crankshaft is formed as separate front and rear sections. The adjoining ends of the two sections of crankshaft are formed in the manner of a dog clutch, in this case having an interference fit. In addition, a screw is threaded into the front section, and this passes through the rear section into its first web. From the other side of the web a securing, self-locking K-nut is fitted using a special tool. Smat remarks that a pre-war roller bearing Mercedes Grand Prix engine used the same concept. The crankshaft is driven by I-section steel con rods and, says Smat, “We made the optimisation calculations for the form of the big end and small end to minimise December/January 2018 | Unmanned Systems Technology The Primoco 500 is air-cooled The finned cylinder head