Wolfgang Seidel custom designed and built several radial engines. The ST 540, ST 770 and ST 996 were among the smaller series of radial engines that were used in one-fifth scale and one-fourth scale model aircraft. In the late 1990s, Seidel designed a larger series of radial engines that are commonly used in the larger one-quarter scale or smaller one-third scale model aircraft.
The ST 1426, designed and built in 1998/1999, is the largest engine in the series, and perhaps the largest model airplane engine commercially sold. It is a 14-cylinder, two-row 364 cc (22.2 cubic inch) radial that is 14 inches in diameter, weighing 28 pounds and turning approximately 4,000 revolutions per minute.