Very closely based on the Norton engine, the MidWest engine nevertheless took things a stage further. The lubrication system became a semi-total-loss system whereby Silkolene 2-stroke oil was directly injected into the inlet tracts and onto the main roller bearings, but the oil that fed the bearings became an oil-mist within the rotor-cooling air, and around 30% of the oil was recovered and returned to the remote oil tank. Unlike the Nortons, the rotor-cooling air was forced in by a belt-driven centrifugal pump and then dumped overboard as it was considered too hot for ideal volumetric efficiency. Instead, ambient-temperature combustion air was inducted into the engine separately. Early Midwest engines had simple Tillotson carburettors, but these proved unsatisfactory, and later engines were fitted with fuel injection. This gave the advantage both of excellent fuelling, and avoided any need for carb heat. The engine gave maximum power at 7,500 rpm, but a 2.96:1 reduction gearbox gave a maximum propeller rotation of an efficient 2,500 rpm. Unlike the Hewland's gearbox, where the output shaft and propellor flange was below the crankshaft, the MidWest's gearbox had its output shaft higher than the eccentric shaft. This feature allowed a larger propeller and better prop clearance, while raising the height of the engine's thrust line, and reducing downward visibility over the nose very slightly.
Diamond Aircraft
bought MidWest and transferred the engine rights to Austro Engine, a company founded in 2007 and located in Wiener Neustadt. Diamond discontinued production of the MidWest twin-rotor engine, but for a period they continued with the single-rotor model, mainly for the motor glider market. Diamond then designed and produced two replacement models, both single-rotor Wankel engines: the Austro Engine AE50R and the Austro Engine AE75R. These new designs feature liquid cooling with forced-air rotor cooling, metered oil lubrication pumped to the main bearings and to the rotor tips, with partial oil recovery, dual ignition, and electric starting. They also have electronic fuel injection.
Power outputs
The Norton road bikes and racing bikes and the Midwest engines all used identical rotors. While both the Norton Classic and the Commander produced a maximum output of 85 bhp, the Midwest AE110 could produce up to 110bhp. The Norton racing bike, the JPS Norton RCW588, had an even greater output of over 130bhp. The Midwest engine could in theory have had a similar output to the RCW588, but the designers opted for a lower figure in the interests of longevity and reliability.
