Unmanned Systems Technology 016 | Hydromea Vertex AUV | Power management systems | Unmanned Space Vehicles | Continental CD-155 turbodiesel | Swift 020 UAV | ECUs | DSEI 2017 Show report

58 The cranktrain The steel crankshaft is machined in- house from a forging supplied by an outside contractor and is then sent out for induction hardening and fillet rolling of its journals. It is flat plane with counterbalanced webs, and runs in plain main and big-end bearings. The con rods are machined in-house from C70-grade steel forgings that are then sent out for cracking. The cracked big end is attached by a pair of bolts. The little end is bronze bushed while an uncoated, superfinished piston pin runs directly in the piston bores. The pin is through-drilled and has tapered ends to save weight. It is retained by round wire C-clips. While these are free to rotate within their groove, the spring pressure applied to it and the low operating speed of the engine mean that in practice they don’t. The aluminium piston is a 4032 (12% silicon) casting. It has an all-over (including the crown) manganese phosphate surface treatment that offers improved running-in behaviour and some protection against wear damage at start-up, especially in the piston pin bore and piston ring grooves. It also promotes adhesion of the graphite- impregnated low-friction piston skirt coating, which reduces bore wear and piston skirt fatigue. This piston incorporates a steel top ring carrier such that the ring is carried within a steel band, whereas the other two rings both run directly in a phosphate-coated aluminium groove. The steel oil control ring is two-piece, having an energising coil spring running in a groove at the back of it. The steel spring acts uniformly around the whole of the circumference, enabling the ring to twist and conform to the shape of the bore. Transmission The drive to the gearbox is at what would be considered in the automotive world the rear of the crankshaft, with the timing drive by chain at the front. The crankshaft projects through the front engine cover to connect to a torsional vibration damper. That damper powers an ancillary belt drive operating the water pump and alternator. Thielert’s original aircraft engine had a clutch between the crankshaft and the gearbox, whereas the CD-155 has in its place a ‘dual-mass flywheel’. This acts like a conventional flywheel but dampens any violent variation of torque or revolutions that could cause an unwanted vibration by accumulating stored energy in two flywheel half-masses, damped by connecting springs. In the CD-155, the inner side of the October/November 2017 | Unmanned Systems Technology The CD-155’s made-in-house crankshaft The CD-155’s cylinder head with plenum attached