The Savoia-Marchetti S.M.81 Pipistrello (bat) was a development of the Savoia-Marchetti S.M.73 18-pagsenger airliner which had first flown in prototype form on 4 June 1934. Like the airliner from which it was derived, the S.M.81 was a three-engine cantilever low-wing monoplane with fixed tailwheel landing gear. First flown in early 1935, it was available in some numbers by the time that Italy invaded Abyssinia (Ethiopia) on 3 October 1935. Here in addition to its dedicated bomber role, it was used also for reconnaissance and transport. The next operational use of the type came during the Spanish Civil War, with S.M.81s being among the first aircraft provided in support of General Franco, and others served in Spain a little later as components of the Aviazione Legionaria.
By the time Italy became involved in World War II about 100 remained in service with the Regia Aeronautica, but although it was already completely outdated the S.M.81 was to be found wherever Italian forces were fighting. Because of its low speed and vulnerability to attack, it was used primarily for second-line duties, but with the protection of darkness many found important use as night bombers, particularly in North Africa. Some remained in service at the time of the Italian surrender, continuing in operation with the Aeronautica Cobelligerante del Sud, and a few survived the war to serve for five or six years with the post-war Aeronautica Militare Italiana. A total of approximately 534 S.M.81s had been built and flown with a variety of powerplants including the 650 hp (485 kW) Gnome-Rhôene 14K or similarly powered Alfa Romeo 125 RC.35, the 900 hp (671 kW) Alfa Romeo 126 RC.34, and the 700 hp (522 kW) Piaggio P.X RC.35. Under the designation S.M.81B a single experimental twin-engine prototype had been flown under the power of two 840 hp (626 kW) Isotta Fraschini Asso XI RC engines, but no production examples followed.
Savoia-Marchetti S.M.81 - The production version and flown with a variety of powerplants including the 650 hp (485 kW) Gnome-Rhôene 14K or similarly powered Alfa Romeo 125 RC.35, the 900 hp (671 kW) Alfa Romeo 126 RC.34, and the 700 hp (522 kW) Piaggio P.X RC.35 radial engines, with the latter being the most common (534 built).
Savoia-Marchetti S.M.81B - A single experimental aircraft using only two 840 hp (626 kW) Isotta Fraschini Asso XI RC engines. Performance was disappointing an no further development or production took place (1 built).
Three-engine bomber, transport aircraft, 535 built.
Experimental twin-engine prototype, one built.
Specifications (Savoia-Marchetti SM.81)
* Crew: 6
* Length: 18.3 m (58 ft 5 in)
* Wingspan: 24 m (78 ft 9 in)
* Height: 4.3 m (14 ft 7 in)
* Wing area: 92.2 m² (1,001 ft²)
* Empty weight: 6,800 kg (AR.125 engines) (13,900 lb)
* Loaded weight: 9,300 kg (19,000 lb)
* Max takeoff weight: 10,505 kg (20,500 lb)
* Powerplant: 3× Piaggio P.X RC.15 (or Alfa Romeo 125 RC.35, 126 RC.34 or Gnome-Rhône 14K) radial engines, 522 kW (670 hp) each
* Maximum speed: 320-347 km/h (211 mph)
* Range: 2,000 km ferry range, 430 km with 2,000 kg and 640 km endurance with the same load, max practical combat range 1,500 km. (1,240 mi)
* Service ceiling: 7,000 m (23,000 ft)
* Wing loading: 101 kg/m² ()
* Power/mass: 4.9 hp/kg ()===Performance when fitted with Alfa Romeo 125 engines===
* Maximum speed 340 km/h at 4,000 m
* Cruise speed 260 km.
* Minimum speed 110 km/h.
* 1,000 m (3,280 ft) in 4 min 15 s
* 3,000 m (9,840 ft) in 11 min 48 s
* 5,000 m (16,400 ft) in 20 min 36 s
* 6 × 7.7 mm (.303 in) Breda-SAFAT machine guns
* Up to 2,000 kg (4,409 lb) of bombs