The Miles M.28 Mercury was a British aircraft designed to meet the need for a training and communications plane during the Second World War. It was a single-engined monoplane of wooden construction with a twin tail and a tailwheel undercarriage with retractable main units.

Originally, the M.28 had been planned as a replacement for the Whitney Straight and Monarch, but this was shelved when war broke out.

In 1941, the project was revived in response to a requirement for a training and communications aircraft. The design was produced as a private venture by Ray Bournon using Miles' normal wooden construction. The resulting machine introduced several features not found on trainers: retractable undercarriage and trailing edge flaps amongst others. In the communications role, the M.28 had four seats and a range of 500 miles (800 km).

The prototype first flew on 11 July 1941 ^[1] and proved easy to fly, with light controls and a short landing run. Owing to Miles' heavy commitment to war-production, however, only six aircraft were built, of slightly varying specifications, the last being the Mercury 6 which first flew in early 1946.^[2] Examples of the type were operated in the United Kingdom, Denmark, Germany, Switzerland and Australia.

• M.28 Mark I: First prototype – Two seat trainer, powered by 130 hp (97 kW) de Havilland Gipsy Major I engine.^[3]
• M.28 Mark II: Three seat trainer (with dual controls) powered by 140 hp (100 kW) de Havilland Gipsy Major IIA. One built 1942. Re-engined with 140 hp Blackburn Cirrus Major II and then with a 150 hp (110 kW) Cirrus Major III post-war.^[4]
• M.28 Mark III: Three seat trainer with triple controls for two students and one instructor, powered by 150 hp Cirrus Major 3 and with revised wing section. One built (PW937).^[5][6]
• M.28 Mark IV: Four seat communications aircraft powered by 145 hp (108 kW) Gipsy Major IIA. One built 1944.^[4]
• M.28 Mark V: Post-war four-seater powered by Cirrus Major III. Square rear windows. One built 1947.^[7]
• M.28 Mark VI: Post war four-seater powered by Cirrus Major III. Round rear windows. One built 1946.^[7]

Data from Miles Aircraft since 1925^[8]

General characteristics

• Crew: one
• Capacity: 2 or 3 passengers
• Length: 24 ft 0 in (7.32 m)
• Wingspan: 30 ft 8 in (9.35 m)
• Height: 8 ft 4 in (2.54 m)
• Wing area: 162 sq ft (15.1 m²)
• Aspect ratio: 5.8
• Airfoil: root: NACA 23018; tip: NACA 2412
• Empty weight: 1,658 lb (752 kg)
• Gross weight: 2,500 lb (1,134 kg)
• Fuel capacity: 24 imp gal (29 US gal; 110 L) fuel
• Powerplant: 1 × Blackburn Cirrus Major III 4-cylinder air-cooled inverted in-line piston engine, 150 hp (110 kW)
• Propellers: 2-bladed fixed-pitch propeller

Performance

• Maximum speed: 159 mph (256 km/h, 138 kn)
• Cruise speed: 152 mph (245 km/h, 132 kn)
• Stall speed: 46 mph (74 km/h, 40 kn) flaps down
• Range: 408 mi (657 km, 355 nmi)
• Endurance: 2 hours 45 minutes
• Rate of climb: 840 ft/min (4.3 m/s)
• Time to altitude: 10,000 ft (3,048 m) in 14 minutes
  
• Take-off distance to 50 ft (15 m): 1,344 ft (410 m)
• Landing distance from 50 ft (15 m): 942 ft (287 m)

Aircraft of comparable role, configuration, and era

• Bücker Bü 181
• Nord NC.850
• Percival Proctor