Clayton Folkerts designed the "Mono Special" NX/NR500W while working for the Mono-Aircraft Corporation. The aircraft was a strut-braced mid-winged conventional geared aircraft with a slender tapered tail and undersized wheels and fairings.

 

 

In 1930, for the American Cirrus Derby, pilot John Livingston was hired, but Stub Quimby flew in his place after an illness. The team did not win any earnings. In the 1930 National Air Races, Quimby placed fourth in the 650 Cubic inch class at 142 mph.

 

 

In the 1933 American Air Races, the aircraft was renamed the Folkerts SK-1, with modified lift struts and addition of wheel pants. The aircraft won first place twice in the 350 cubic inch class, and third in the 500 cubic inch class piloted by Harold Neumann, and fifth piloted by Marcellus King. During the 1933 International Air Races, Roy Ligget and Roy Hosler won two fifths and one fourth at a speed of 170 mph.

 

 

In the 1934 Pan American Air Races, the aircraft was renamed "Matilda". In the 1935 National Air Races, with a modified headrest fairing, the aircraft raced as the "Fordon-Neumann Special" and placed second at 187 mph.

 

Folkerts SK-1