The Nieuport 21 was a variant of the successful Nieuport Type 17 fighter, but with a less powerful engine and enlarged ailerons. The standard Nieuport 17 was powered by an 110hp Le Rhône engine, but on the Type 21 that was replaced by an 80hp Le Rhône 9C. Different sources suggest two reasons for this change - either that the new aircraft was designed as a fighter-trainer, or that it was produced to escort high altitude bombers and the change of engine was to save weight and improve high altitude performance. This second alternative would be supported by the increased size of the ailerons, intended to improve manoeuvrability in the thinner air at altitude. It is also possible that the less powerful engine was adopted because of a shortage of the 110hp Le Rhône.
Whatever the original purpose for the Nieuport 21 was, it soon ended up serving as a standard fighter. It was undergoing testing by mid June 1916 and was in service by 1 August, but soon after that the French abandoned day bombing and the new fighter probably lost its original purpose.
The type was recorded as the Nieuport 21 in a list of official designations of 1 September 1916, and saw some service with front-line fighter escadrilles. It was used by the Escadrille Lafayette (the American volunteer unit), where it was one of the aircraft flown by Sergent Raoul Lufbery.
The Nieuport 21 was also used by the RNAS, which had at least five of the type, the Russian Air Service and by the American expeditionary force. The Americans received 181 aircraft, with the last batch arriving in January 1918. They were used a training aircraft for the American units based in France.
Engine: Le Rhône 9C
Span: 26ft 9.25in
Length: 19ft 0.33in
Height: 7ft 10.5in
Empty weight: 772lb
Maximum take-off weight: 1,168lb
Max speed: 94mph at sea level
Climb Rate: 8m 45s to 6,560ft
Service ceiling: 17,220ft
Endurance: 2 hours