In 1935, the SM.81 Pipistrello (Bat) made its debut and marked a definite step forward in the development of military aviation. The excellent overall qualities of this aircraft were first tested in the Ethiopian campaign and then in the Spanish Civil War. The SM.81s success in combat directly transformed into a series of orders that eventually led to the production of 534 SM.81s. However, as in the case of other combat planes produced in that same period, the Spanish Civil War did not provide very reliable proof of what subsequent needs were to be. The SM.81, clearly out of date by the outbreak of World War II, remained in service for the duration of hostilities, operating on almost all fronts, although it was gradually phased out to play a secondary role as a transport.
The SM.81’s direct predecessor was the SM.73, a commercial airplane, whose prototype appeared on 6/4/34, and which was an immediate commercial success.
It was this aircraft that provided the basis for the construction formula that was to remain virtually unchanged in SIAI Marchetti’s later production, a three-engine, low-wing monoplane with a wood and metal structure and wood and fabric covering. The military version was presented toward the end of the year and was subjected to a whole series of operational tests by the Regia Aeronautica before going into mass production.
As in the case of the civilian version, the fitting of several types of engines was also planned for the SM.81, and each of the engines characterized a particular version of the aircraft. These included the 680 hp Piaggio IX, 700 hp Piaggio X, 680 hp Alfa Romeo, 900 hp Alfa Romeo and the 1,000-hp Gnome Rhone 14K engines. Defensive armament consisted of 6 – 7.7mm machineguns, a pair in the retractable ventral position, a pair firing rearward from the back of the cockpit and two in lateral positions in the fuselage. Normal bomb load was 2,000 lbs, but the maximum load was 4,415 lbs of bombs.
The prototype of an experimental version, the SM.81bis was produced with two 840-hp Isotta-Fraschini Asso in-line liquid cooled engines, and with substantial modification to the nose, by which the third engine was occupied by a bombardier. This variant was not followed up.
The SM.81 went into service early in 1935 and made its military debut in Africa that same year. After the experiences of the Spanish Civil War, the appearance of the stronger and more reliable SM.79 consigned the older SM.81 to a secondary role. At the beginning of World War II, the SM.81 was gradually withdrawn from front-line service in national territory and was used mainly on the African and Russian fronts as transport aircraft. After the Armistice, only four SM.81s were left in southern Italy. The others that remained went in the north to form part of two groups of transport planes in the air force of the pro-axis forces.
The SM.81 with the 670 hp Piaggio X engines had a maximum speed of 211 mph at 3,281 ft; a service ceiling of 22,966 ft; and a range of 1,243 miles. With the 680 hp Alfa Romeo engines, the maximum speed was 211 mph at 13,210 ft; service ceiling of 23,000 ft and a range of 1,200 miles.
Article by JDG