Unmanned Systems Technology 033 l SubSeaSail Gen6 USSV l Servo actuators focus l UAVs insight l Farnborough 2020 update l Transforma XDBOT l Strange Development REVolution l Radio telemetry focus

So although each valve has two seals – one on each side of its cylindrical section – the valve is designed with the knowledge that it will experience some marginal level of leak. The company sees this as a valid trade-off; in exchange, the seals are subjected to a minimum of friction, which reduces their associated wear and parasitic losses, and allows the valve to spin freely. The two valves rotate parallel with the crankshaft, with the timing factory- set by a belt drive on the engine’s front and a quadrangular push-fit interlock connecting the two valves as a shaft at 90 º to each other. Six-cycle two-stroke The way in which this engine operates and scavenges is not to be confused with a conventional two-stroke’s crankcase compression. The traditional two-stroke will forgo valving (aside from reeds or other systems on the throttle) because it relies on the piston as a pump to carry out internal pressure changes and dynamic fluid movements. Most often, the piston moves upwards (lowering crankcase pressure) to draw fuel and air into the crankcase, and when it thrusts downwards it pushes the fuel-air mixture out of the crankcase, through transfer ports up into the cylinder. In the REVolution, however, the supercharger provides a persistent feed of high-pressure air directly into the cylinder, with a flow rate of 6188 litres/ minute at peak power, eliminating the need for the piston to act as a pump. Instead, the piston acts solely as a valve for the intake air, shutting off the feed from the supercharger at key moments. With the exhaust port positioned slightly higher than the intake port, the piston leaves the exhaust open for combustion gases to escape when needed. When it needs to be closed off, to catch and compress the intake air, the REV shuts off this passage, as per Krzeminski’s earlier recommendation. The added element of having a rotary valve in the exhaust port creates a ‘six- cycle, two-stroke’ operation, with six stages or events taking place during each revolution of the crankshaft: exhaust, cylinder flush, cylinder charging, injection, compression, and power. These stages are defined by the relative positions of the piston and the REV, with the latter driven by a belt and gears on the front of the block (and initial start-up provided by a standard 12 V starter). In the initial, exhaust, phase the piston thrusts from top dead centre (TDC), opening the exhaust port. At this stage the REV’s passage is lined up with the exhaust passage, allowing combustion gas to exit freely, as it would in a conventional two-stroke. However, the difference becomes noticeable as the crank angle goes THE NEW FUEL SUPPLY UNIT The compact all-in-one solution ready to feed your engine: • Integrated suction filter • Integrated bleeding system • Integrated check valve • Integrated pressure regulator • Flow rates up to 4.0L/min • Working pressure up to 10bar • Brushless motors with integrated electronic All engineered and manufactured according to the highest standards.