Grahame-White Type 21 / G.W.21
 
The 1917 Grahame-White Type 21 (G.W.21) was sometimes mistaken for the Type 20, despite considerable differences, this single-seat scout biplane was quite an improvement on the concept, with its unbalanced rudder, slab-sided fuselage, closer wings and the I-shaped interplane struts. It was powered by a rotary Le Rhone engine and tested with both two- and four-bladed propellers.
 
Other similar aircraft by larger manufacturers were already in production and the G.W.21 remained a prototype.