Gulliver's Engines

Shrinking full-scale engines to pocket size is no small feat. A running quarter-scale model of a 1937 Harley Knucklehead V-Twin. An electric motor in the base starts the engine. The fuel tank sits where the generator would in the full-sized version. For size reference, adjusting the pushrods takes a pair of /32-in. open-end wrenches. The overhead-valve Knucklehead engine was built from 1936 to 1947 and is the progenitor of today's Harley aircooled V-Twins. The Aurora V8 engine-block tool is built in several sections to prevent back locks and to let a wax form be removed in one piece without damaging it. Above: a wax positive of an Aurora cylinder head and a finished investment casting. Above: Nancy Warner holds an Aurora engine block. Also shown are a crankshaft, camshaft, connecting rod and piston, valve, distributor cap, and fuel-injection manifold. The quarter-scale 1913 Gnome Monosoupape (single-valve) rotary is 9-in. diameter and spins a 24-10 prop at 2,400 rpm. The Gnome is unusual in that its cylinders rotate with the prop while the crankshaft remains fixed. Nine separate cams stacked together actuate poppet exhaust valves. Air, oil, and fuel flow though a hollow crankshaft. Induction is through ports in the cylinder bases. Extra inlet air enters the exhaust valves because the valves remain open 90° after top-dead-center of the intake stroke. Both full and quarter-scale Gnomes have no throttle — they run wide open at all times. (A “blip switch” in the aircraft let a pilot momentarily interrupt the ignition for landing.) Gnomes were noted for having the highest horsepower-to-weight ratio of anything flying at the time. The nine-cylinder engine produced 160 hp and gave the Nieuport 28 fighter a top speed of 122 mph. Gyroscopic forces induced by the rotating cylinder heads made flying the plane “interesting.” Castor oil was used in a total-loss oiling system, which bathed the plane and pilot in the hot, sticky stuff. The model uses the same oiling system. Valve split keepers in Aurora engines