Unmanned Systems Technology 013 | AutonomouStuff Lincoln MKZ | AI systems | Unmanned Underwater Vehicles | Cosworth AG2 UAV twin | AceCore Neo | Maintenance | IDEX 2017 Show report

58 Con rod and piston assembly The steel con rods are crankshaft-guided. The crankpins carry caged needle roller bearings. The cages are split for assembly, with each rod having a two- bolt cap secured by fasteners without nuts. There are, however, additional (undisclosed) measures to assist alignment. “Alignment is crucial given the use of a roller bearing,” notes Heath. The big-end and small-end rollers run directly in the respective con rod bore, the big-end bearing split-caged for assembly. The piston pin is an uncoated steel production, through-drilled with a chamfer at each end to minimise weight (in the light of FEA). The piston is a billet production made from an undisclosed aluminium alloy. It has a long skirt relative to four-stroke practice given its role in port operation. There are scallops in the skirt around the pin bore for lightening, even on the blind end. Given the skirt area, the piston is DLC coated to minimise friction and enhance wear. That coating is all over its exterior since that approach is more straightforward than masking the crown, where the thin layer of DLC plays no role. The piston grooves are, however, masked during the coating process. The piston carries three identical 1.5 mm high rings. Heath remarks, “The piston rings are conventional but detail development has been required to allow them to cope with the marginal lubrication of a heavy-fuel, two-stroke engine as well as providing sufficient heat transfer from the piston for piston and small-end durability.” Intake and exhaust A front engine cover forms an air chamber ahead of the intake window controlled by the rotary valve; that chamber is fed through an air filter. Having no structural function, the cover is a carbon composite production for lightness. The rotary valve is bolted to its adjacent web, using six fasteners with careful shimming for clearance. It is spring steel, and its front face has a Xylan anti-scuff coating, which helps it seal against the adjacent bulkhead, in which is the intake window. April/May 2017 | Unmanned Systems Technology Cosworth AG2 twin Compression-ignition UAV engine Horizontally opposed twin 54 x 53 mm = 242.8 cc Naturally aspirated Diesel, JP5 or JP8 fuel Aluminium structure Linerless Three main bearings, roller Steel crankshaft, two pins Steel con rods Light alloy pistons; three rings Rotary valve Common rail direct injection Engine management system Undisclosed compression ratio Maximum rpm, 5250 Data sheet Main structure: in-house Bore coating: Capricorn Crankshaft: in-house Rotary valve: Micrometric Pistons: in-house Rings: Mahle Koenig Piston pins: Pankl Con rods: undisclosed Custom bearings: undisclosed Other bearings: INA Fasteners: Unbrako Fasteners: Pankl Fuel injectors: undisclosed Fuel rail and high-pressure pump: in-house Engine management system: in-house Fuel pressure sensor: TE Engine speed sensor: McLaren Applied Technologies Data acquisition: in-house Oil pump: undisclosed Air filter: ITG Electrical generator: Sullivan UAV Exhaust: in-house Fluid lines: St Gobain Metals: Smiths Metals RP bureau: Graphite RP bureau: LPE Some key suppliers to this engine The AG2 is horizontally opposed with 180 º phased crankpins for balance