In an attempt to provide a replacement for the Magister, Miles flew the M.18 with a 97kW de Havilland Gipsy Major engine in December 1938. While the fuselage was similar to that of the Magister, the square cut thick wing and tail surfaces were new. A decision against production was reached by the Air Ministry, but a further three M.18s were built, the second having a 112kW Blackburn Cirrus Major III engine.
The first prototype M.18, U-0222, flew for the first time on 4 December 1938. The M.18 had nothing in common with the M.14 Magister. It started with a 150 hp Gipsy Major III engine, tandem open cockpits and a tailwheel undercarriage. During its time, U-0222 had the forward cockpit removed and a fixed nosewheel undercarriage installed.
Initially the wingspan remained at 31 ft but this was subsequently reduced to 22 ft 2 in. U-0222 was also flown with an experimental Jameson engine and as a glider.
The second prototype, U-0224, was officially tested as HM545. As a result, it was ordered into production for the RAF. That order was then reversed, in favour of the DH82 Tiger Moth. But in 1942, the M.18 was again ordered into immediate large-scale production, again to be cancelled.
Only two other M.18s were built, U-0238, fitted with an enclosed cabin, and U-0236 / JN703 which, as M.18HL, was fitted with a specially designed wing to ascertain the coefficient of lift obtained by the employment of very large slotted flaps used in conjunction with slats along the whole of the wing leading edge. The machine was extensively tested by the RAE who measured a maximum coefficient of lift of 3.
All Aero 