Power
From the outset, the SM.81 would be powered by a variety of powerplants. A series of Alfa Romeo, Gnome-Rhone and Piaggo radial piston powerplants were installed in some number by the end of her production run. Alfa Romeo supplied their 125 RC.35 and 126 RC.34 series engines of 580- to 900-horsepower while Piaggo's P.X RC.15 and P.IX RC.40 of 670- to 700-horsepower were both utilized. Gnome-Rhone's contribution was its 14K series engine of 650- to 1,000-horsepower. One distinct SM.81bis model even fielded just two Isotta-Fraschini Asso XI inline engines of 840 horsepower for evaluation purposes. The nose of this aircraft was appropriately revised to cover the missing area caused by removal of the nose engine and became a bombardiers position. The type was not furthered.
The production breakdown for each engine type was as follows: Alfa Romeo 125 RC.35 in 192 examples; Piaggo P.IX RC.40 in 140 examples; Gnome-Rhone 14K in96 examples; Alfa Romeo 126 RC.34 in 58 exampes; Piaggo P.X RC.15 in 48 examples.
At the time of her inception, the SM.81's performance was excellent. She could top speeds of over 200 miles per hour with a ceiling nearing 23,000 feet and a range equal to 1,200 miles. However, by the time of World War 2, these specs were wholly inadequate and she became a sitting duck to the new generation of enemy fighters on the prowl.
The SM.81 in Action
The SM.81 saw her combat debut in the Second Italo-Abyssinian War of 1935-1936, a conflict pitting the forces of the Kingdom of Italy against the forces of the Ethiopian Empire, resulting in the latter's conquer and annexation into the Italian East Africa colony. The platform served well in the reconnaissance, bomber and transport role, making her an important facet of the Italian war machine for the near future and netted orders for further production examples. The SM.81 was also fielded by the Aviazone Legionaria during the upcoming Spanish Civil War of 1936-1939. Italian dictator Benito Mussolini even made use of one converted SM.81 as his personal transport - this aircraft receiving the unfortunate name of "Taratuga" (or "Tortoise").
By the time of World War 2, the 1930s roots of the SM.81 were becoming painfully obvious. Despite her robust internal construction and design (she reportedly held up very well to enemy gunfire, able to absorb a great deal of punishment), the type was well slower than newer contemporary bomber models and made for easy fighter fodder. As such, production of the SM.81 was halted in March of 1938 and the type was relegated to second-line duties and night time bombing. The appearance of the more powerful Savoia-Marchetti SM.79 "Sparrowhawk" in 1936 also helped to doom the SM.81 to lesser roles. Of the 534 examples already delivered, 304 were still in service with the Regia Aeronautica, though many outside of Italy. In time, these active service SM.81s were quickly converted for the troop carrier role to help extend their usefulness in the war effort. Despite their age, the SM.81 was still fielded in limited yet aggressive bombing roles from 1940 on, now centering on targets in East Africa.
From then on, the type was placed into action strictly along the African and Eastern Fronts. Their impressive rebirth as troop transports forced production to resume once again in early 1943. About 80 additional aircraft (designated as SM.81/T) were produced before the Italians surrendered to the Allies in September of 1943, but by this time, nearly all of the active SM.81s were removed from service with just four remaining in Southern Italy. In parts of Axis-controlled Northern Italy, Italian SM.81s still fought on in some number, making up of two pro-axis air force groups. After the war, some SM.81s survived to be used a little longer, eventually seeing the series retired in whole by 1950.
The SM.81 was produced in only two distinct marks - the SM.81 base production bomber/transport and the SM.81/T when production was resumed. The SM.81Bwas a "one-off" experimental twin-engine prototype that was dropped from consideration due to poor performance specs. Beyond Italy, the SM.81 made it into the inventories of the Taiwan (the Republic of China) and Spain. The three delivered to Taiwan only to be lost in training accidents by early 1938.
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