wing. The forward propeller position, together with the tailless wing configuration, gave the rear gun turret an outstanding field of fire. Despite its performance and flyability in other respects rivalling its conventional competitor the Hawker Hart it was not accepted for production. Associated with the Mk. V was a complementary Mk. VI design for a pusher variant with front-mounted gun turret, and the intention was to fly a mixed squadron with front-firing machines leading and rear-firing machines behind, but the Pterodactyl programme was cancelled before any order for the Mk, VI had been received. At the time of cancellation, wind tunnel models of a Mk. VII four-engined reconnaissance seaplane had been tested, and a proposal for a Mk. VIII transatlantic airliner was being worked on. After World War II, Hill helped develop the similar NRC tailless glider in Canada. Returning to England, he developed the aero-isoclinic wing and helped Short Brothers develop the Short SB.1 and SB.4 tailless swept-wing test aircraft. Design characteristics Hill's Pterodactyl designs were all intended to handle safely without any definite stall point, allowing reliable recovery without loss of altitude even by inexperienced pilots. The characteristic wing was of moderately tapered and swept planform, with reverse taper at the root to improve pilot vision. The wing was "washed out", having a slight twist which reduced the angle of incidence progressively towards the tips, providing a near-stationary overall centre of pressure and ensuring that the aircraft was stable in pitch. Thus, no horizontal stabiliser was needed and the craft was tailless, allowing the fuselage to be relatively short. Early examples used a patented system in which the wingtips pivoted to act as slab elevons providing control in pitch and roll, while later types had more conventional elevons in the wing trailing edge. Yaw stability was generally achieved by vertical fins, and control by vertical rudders, but the exact arrangement varied between types and even during the flight testing of individual machines. The Mk. I differed in having horizontal "electroscope rudders" on the trailing edge, inboard of the movable wingtips, which acted to provide differential drag. The IA had no vertical surfaces but small fixed fins were added to the IB. Aircraft Pterodactyl Glider, built by G T R Hill and his wife in 1926; later fitted with Bristol Cherub engine in cooperation with the Air Ministry and test-flown at Farnborough. Pterodactyl I First Westland-built example, a braced