F.Mason The British Fighter since 1912 (Putnam)
Grahame-White Type 21
Clearly representing an attempt to refine the Type 20, the Grahame-White Type 21 appeared early in April 1917, powered by an 80hp Le Rhone engine driving a four-blade propeller. Most readily visible change was the use of I-form interplane and cabane struts with prominent spacer fairings at their extremities.
In almost every respect, however, the design differed in detail; the fuselage, instead of being formed to almost circular section, was a plain, flat-sided, wooden box-girder, only faired with rounded top decking; the fin and rudder were enlarged , although the latter was now no longer balanced; the front pair of undercarriage struts was mounted further forward - directly behind the engine, and a small, faired headrest was incorporated immediately aft of the cockpit. The previous design’s large wing gap was retained, as was the unusually large number of bracing wires.
In all likelihood the wings were of reduced thickness, for the Type 21 returned a speed of 107 mph at sea level, a not unreasonable performance on only 80 horsepower, although there is no evidence that any armament was ever carried.
There appeared to be little inherently disagreeable about the Type 21, except that it flew about a year later than other scouts of similar capabilities; and, apart from a possible training role, it could have contributed little to meeting the needs of the fighting Services.