Savoia-Marchetti SM.85 - Design and Development

Design and Development

The SM.85 was part of a programme by the Regia Aeronautica to produce a twin-engine monoplane dive bomber based on the theories developed over the previous 20 years by the American General Billy Mitchell, which were enthusiastically adopted by Colonel Amedeo Mecozzi (who also developed the Breda Ba.64 and its derivatives) for attack aircraft.

The resulting aircraft, constructed of wood, had a wing set in an upper-middle configuration, a rectangular cross-section fuselage, retractable undercarriage and a fixed tailwheel, and was powered by two Piaggio P.VII C.35 engines. The wings, made totally of wood, had three longerons, with fabric covering. The aircraft was designed to give the pilot the best possible forward view, with a transparent panel built into the cockpit floor.'

The SM.85's useful payload was 1,150 kg (2,540 lb), including the possibility of fitting a 12.7 mm (0.5 in) machine gun with 300-500 rounds. The aircraft was capable of also using its flaps as airbrakes for diving attacks, a notable characteristic of this aircraft. The bombload was carried in a parallelogram-shaped section mounted under the fuselage. The SM.85 was capable of carrying a 500 kg/1,100 lb bomb (or an 800 kg/1,760 lb bomb, the heaviest weapon in the Italian aviation arsenal, but only on very short range missions).

At maximum payload, with a 4,000 kg (8,820 lb) takeoff weight, the climb rate was 20 min to 5,000 m (16,400 ft), but freshly started engines did not produce their theoretical maximum power and the aircraft was usually much slower than this. The takeoff needed 433 m (1,421 ft), and the landing 415 m (1,362 ft). Ceiling was 6,000-6,500 m (19,690-21,330 ft) and 756–827 km (470-514 mi) range. Maximum speed was 367 km/h ( mph) at 4,000 m (13,123 ft). The fuel capacity was 1,078 L (285 US gal), contained in four self-sealing fuel tanks. At the maximum payload with a 500 kg (1,100 lb) bomb, it was incapable of taking off with a full fuel load (around 730 kg/1,610 lb), so this was used only on ferrying missions.

The first prototype was tested in December 1936, and in spite of its insufficient speed and the disappointing rates of climb, the Regia Aeronautica felt there was sufficient room for development and ordered the SM.85 into production. Despite some improvements, critical deficiencies continued to be experienced during test flights by the Reparto Sperimentale Volo a Tuffo. These revised aircraft were disappointing as dive bombers in almost every aspect, with the most serious problems encountered being frequent uncontrollable spins, extremely slow climb rate after a dive, and instability during the dive.

Production of the aircraft was halted, and the 34 produced up to that time were organised as 96° Gruppo Tuffatori (96th Independent Dive-Bomber Group).