Wolfgang Seidel, of Germany, designed and built several custom radial engines. The ST540, ST770 and ST996 were among the smaller series of radial engines that were used in 1/5-scale and 1/4-scale model aircraft. These engines varied in size from approximately 8 inches to 11 inches in diameter.
The ST770 is a 7-cylinder 70cc (4.17 cubic inch) radial engine with a speed range or 1,000 to 6,000 revolutions per minute (rpm), using a 26-10 propeller. Its maximum speed is 6,300 rpm. It burns methanol with castor oil mixed in for lubrication and is capable of producing 4.0 horsepower. Completed in 1992, this engine is 10″-wide, 12″-high, and 10″-long.