P.Lewis The British Fighter since 1912 (Putnam)

1916 saw the appearance of another hopeful scout design from Grahame-White, the Type 20 single-seat biplane with the 80 h.p. Clerget. The machine embodied a neat, circular-section fuselage to which were fitted wings set with a pronounced gap. No progress was made with the Type 20.
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   Despite its lack of success in obtaining orders for its previous scout designs, the Grahame-White Company tried once again with the Type 21 which was completed in April, 1917. The machine was a single-seat biplane, powered by an 80 h.p. le Rhone, in which every effort had been made to streamline the airframe and cut down drag. Single I-type interplane and centre-section struts braced the wings, to which ailerons were fitted to all four tips. Despite its attributes, which included a top speed of 107 m.p.h., the Grahame-White Type 21 was not adopted.

F.Mason The British Fighter since 1912 (Putnam)

Grahame-White
  
   One of the lesser-known contenders for consideration as a single-seat scout was the Grahame-White Type 20 single-bay biplane which is believed to have flown in mid-1916.
   Characterized by unusually thick, staggered wings with large gap, the Type 20 was of all-wood construction, the slim fuselage being formed to circular section. The tail unit comprised a fixed fin and balanced rudder, but no tailplane was fitted forward of the balanced elevator. Ailerons were fitted on both upper and lower wings, hinged to the rear spars. The twin V-strut twin-wheel undercarriage was raked forward, presumably so as to dispense with a landing skid.
   Power was provided by an 80hp Clerget 7Z seven-cylinder rotary engine within a narrow-chord oil-sling ring, this engine being licence-built by Gwynnes Ltd of Hammersmith. Also considered as an alternative to this engine was the 80hp Le Rhone.
   With a top speed probably between 80 and 90 mph (without armament fitted), it is unlikely that this little aeroplane excited much serious attention at the War Office or Admiralty and, as far as is known, underwent no official trials; its development, therefore, was probably very shortlived.

J.Bruce British Aeroplanes 1914-1918 (Putnam)

Grahame-White Type 20

  THE Grahame-White type number 19 was allotted to the Breguet V, ten of which, powered by the 250 h.p. Rolls-Royce engine, were built by the Grahame-White company under licence. The next true Grahame-White type was the Type 20, a small single-seat scout, powered by the 80 h.p. Clerget 7Z engine, which appeared in 1916.
  The fuselage was faired to a circular cross-section throughout its length, and the pilot’s cockpit was directly under the centre-section; the main fuel tank was immediately behind the cockpit. There was no tailplane, only a balanced elevator reminiscent of that of the Morane-Saulnier Type G monoplane which the Grahame-White company had built under licence as their Type XIV. An alternative power-unit for the Type 20 was the 80 h.p. Le Rhone.
  The single-bay wings were, for 1916, of unusually thick section and were rigged with a very large gap.