On 28 October 1908 he successfully conducted the first motor-flight over German soil in a motorised triplane aircraft of his own construction at Magdeburg.
Although successful, Grade monoplanes did not become as famous as many contemporary European designs, and for this reason comparatively few were built.
In 1921 he established an automobile company called "Grade Automobilwerke AG", which produced small, 2 seater personal cars.
After the Nazi takeover in 1933 Grade tried, without success, to develop a new Volksflugzeug and in 1934 he undertook research projects for the German aircraft manufacturers.
[3] On May 14, 1939 he re-flew his original monoplane from 1909, then 30 years old, at Berlin Tempelhof Airport for about 550 metres to celebrate his sixtieth birthday.