At the time Cox developed the first Cox engines, they were used in control line and free flight model planes as there was no market for throttled radio control engines back then. Radio control, although first developed in the 1890s it was not available for model airplanes until the 1950s and did not become economically viable for small model planes until the mid-1970s and even then was for the modelers who could afford it. It was certainly out of reach of the hands of most children.