FILENAMES: Bucherer-1.jpg Bucherer-2.jpg Bucherer-3.jpg DESCRIPTION: These are diagrams of an unusual rotary engine for an airplane. Posted by Nick Müller . The following description was provided: ================================================================= Hypocycloidal crank: A "new" invention by Randall Wiseman. Patent grantend April 2003 US Patent 6,510,831 This invention isn't as new as the patent suggests. Bucherer from Cologne Germany has built a rotory engine in 1908 that used a crank equal to WIseman's invention. Technical data: Air-cooled four cylinder engine bore 80 mm stroke 182 mm output 29.4 kW (40 HP) case speed 1000 RPM crankshaft speed 2000 RPM Note, that this was a rotary engine. In the time before and during WW 1, engineers thought that rotary engines would be superior due to the better cooling that was achieved by fixing the crank shaft to the frame and letting the engine rotate. Bucherer added a gear that let the case rotate with half the normal speed (thus the two numbers for RPM). That's quite interesting, because all the rotary engines had a terrible drawback. The gyroscopic effect made them hard to fly, especialy during take-off. At this moment the rudders didn't have enough air stream. With rudder left, the nose went up (or down, depending on direction of rotation). This lead to many crashes. Bucherers unique design was the hypocycloidal crank. His intent was to eliminate the side forces to the piston coming from the connection rods (between TDC and BTC). Well, it just reduced the forces, because the Coriolus forces still remained, as the engine was a rotary engine. Another goal of his construction was to increase the bore/stroke ratio. 80/182mm is quite impressive. In these times, long strokers were considered to be better. If you look at Fig 94, you might be puzzled how 8 cylinders and a hypocycloidal crank fit. At a first glance, 2 cylinders would be the maximum (per crank pin). But Bucherer's engine hat 8 cylinders, spaced 45 degrees apart. The trick is to replace the single crank pin with a (conventional looking) crank shaft who's center line is in line with the small gear wheel's center line. One more thing to note about rotary engines worth noteing is their incredible oil consuption. 250 .. 300 gramms per HP/hour equals modern engines gas consuption! To Fig 93.: a: connection rod b: bearing for small gear wheel d: small gear wheel g: big inner gear wheel Pictures scanned from: Flugtechnische Bibliothek Band 1 "Flugmotoren" by H. Dorner & W. Isendahl; second printing; Richard Carl Schmid & Co. / Berlin; 1916