output power. Wankel engines in auto racing are operated at speeds up to 10,000rpm, but so are four-stroke reciprocating piston engines with relatively small displacement per cylinder. In aircraft, they are used conservatively, up to 6500 or 7500rpm. Chamber volume and displacement Chamber volume In a Wankel rotary engine, the chamber volume is equivalent to the product of the rotor surface and the rotor path . The rotor surface is given by the rotor tips' path across the rotor housing and determined by the generating radius , the rotor width , and the parallel transfers of the rotor and the inner housing . Since the rotor has a trochoid ("triangular") shape, sinus 60 degrees describes the interval at which the rotors get closest to the rotor housing. Therefore, The rotor path may be integrated via the eccentricity as follows: Therefore, For convenience, may be omitted because it is difficult to determine and small: A different approach to this is introducing as the farthest, and as the shortest parallel transfer of the rotor and the inner housing and assuming that and . Then, Including the parallel transfers of the rotor and the inner housing provides sufficient accuracy for determining chamber volume. Displacement In a Wankel rotary engine, the eccentric shaft needs to make three full rotations (1080°) per combustion chamber in order to complete all four cycles of a four-cycle engine. Since a Wankel rotary engine has three combustion chambers, all four cycles of a four-cycle engine are completed within one full rotation of the eccentric shaft (360°). This is different from a four cycle piston engine, which needs to make two full rotations per combustion chamber in order to complete all four cycles of a four cycle engine. Therefore, in a Wankel rotary engine, the chamber volume has to be doubled in order to obtain the displacement : , with being the number of rotors per engine. The Wankel rotary engine's displacement is equivalent to a piston engine's displacement . Examples KKM 612 (NSU Ro80) e=14 mm R=100 mm a=2 mm B=67 mm i=2 Mazda 13B-REW (Mazda RX-7) e=15 mm R=103 mm a=2 mm B=80 mm i=2 Licenses issued NSU licensed the Wankel engine's design to companies around the world, in various different forms, with many companies implementing continual improvements. In his 1973 book Rotationskolben-Verbrennungsmotoren, German engineer Wolf-Dieter Bensinger describes the following licensees, in chronological order, which is confirmed by