Forerunner of the SM.81 bomber that fought
in Ethiopia, Spain, and in the Second World War, the SM.73 three-engined
transport was produced in 1934. The prototype was powered by 600 h.p.
Gnome-Rhone 9 Kfs radial engines driving wooden airscrews (four-bladed on the
nose engine, two-bladed on the outboard units), and featured the tall tail
surfaces of the SM.71. The SM.73 went into production with a revised, longer
fuselage, 700 h.p. Piaggio Stella IX R.e. nine-cylinder radials driving
three-blade variable-pitch metal airscrews, and a lower, broader vertical tail
assembly. As the SM.73P it entered service with Ala Littoria; as well as
S.A.B.E.N.A., the Belgian airline; and C.S.A., the Czechoslovakian state
airline.
The SM.73, weighing 12,760 lb. empty and
20,460 lb. loaded, had an all-wood cantilever wing and fabric-covered welded
steel tube fuselage and tail group. Wheel spats were filled, open on early models,
later fully-enclosing. Eighteen passengers and a crew of four were
accommodated, plus up to 800 lb. of baggage in the bottom of the fuselage.
Maximum speed was 205 m.p.h. at 13,120 fl., cruising speed 174 m.p.h., and
landing speed 56 m.p.h. Service ceiling was 24,272 fl. and maximum range 994
miles. The SM.73 climbed to 6560 ft. in 10 min., to 13,120 ft. in 20 min., and
to 19,680 ft. in 33 min. On two engines, maximum speed was 168 m.p.h. and
service ceiling 14,432 ft. Dimensions were: span 78 ft. 8 2/3 in., length 57
ft. 2 3/4 in., height 15 ft. 1 in., and wing area 1000.7 sq. ft.
With Italy's entry into the war, the
SM.73's of Ala Lilloria came under the management of the Commando Servizi Aerei
Speciali (C.S.A.S.) as military transports. Thirteen formed the 605a and 606a
Squadriglie of the 1480 Gruppo "T", based at Reggio Calabria. These
were used for varied duties, including the supply of troops and equipment to
North Africa. In many ways the Italian counterpart of the German Junkers Ju
52/3m, the SM.13 was one of the earliest transports to serve efficiently on
European air routes. A few were built by S.A.B.C.A. in Belgium.
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