Design
The SM.82's fuselage was of mixed-construction, with welded-steel tube framework, with 22 frames and four longerons, skinned with metal forward, and plywood and fabric elsewhere. The wings were constructed almost entirely of wood, having three T-section spars, and 42 ribs in each. The flaps were made from a single piece of wood, while the ribs were of light and flexible poplar. The skin was of fabric-covered plywood, doped to be water-resistant. The ailerons (+13/-28°) occupied about half of the wing's trailing edge while Handley Page slats occupied the leading-edge. The tail had a conventional spruce structure and a plywood skin, while the rudder and elevators were a fabric-covered metal framework.
Inside, there were two levels. The upper level held seats for 32. The lower level was used for freight or to carry bombs when used in the bombing role, with two large duralumin bomb bay doors. The floor was made of wood, with nine detachable panels, that helped with the accommodation (through the bomb bay doors) of heavy loads. The cockpit held four: two pilots, with the first (on the left) with an armoured seat, a mechanic and an engineer/gunner.
Internal equipment comprised a radio-transmitter (AR8 and AR350), a fire extinguisher system, an electrical generator. The instruments included altimeters, thermometers, compass, clock, and a Telefunken P63N radio goniometer.
The SM.82 was fitted with three 641 kW (860 hp) Alfa Romeo 128 RC.18 radial engines with aluminium and steel three-blade constant speed propellers 3.6 m (11 ft 9 in) in diameter. These engines were the ultimate evolution of the license-built Bristol Pegasus.
The aircraft had six self-sealing fuel tanks in each wing, three between the second and third spar, with a total of 1,276 L (337 US gal). Between the first and second spar there were another three fuel tanks with 653 L (173 US gal). Another tank in the nose, with 167 L (44 US gal) of 100 octane fuel (rather than 87) for the electric generator. The total weight of fuel amounted to 4,403 kg (9,707 lb), plus 136 L (36 US gal) of oil.
The SM.82 had both defensive and offensive armament. For offensive purposes it could carry a very wide range of ordnance, up to 4,000 kg (8,820 lb).
- 4 × 800 kg (1,760 lb)
- 8 × 500 kg (1,100 lb)
- 8 × 250 kg (550 lb)
- 27 × 50 kg (110 lb) or 100 kg (220 lb) bombs
- 25 × 100 kg (220 lb) cluster bombs, each containing 56 bomblets, though these were rarely used.
Control over bomb release was in the retractable ventral bombardier's gondola, equipped with a Jozza bombsight and also fitted with a rear-facing 7.7 mm (.303 in) Breda machine gun. Accommodation for the bombardier was far from ideal, being cramped, unheated, unpressurized, and not connected to the oxygen system. The 1 mm steel structure was also highly vulnerable to enemy fire.
For protection, only the first pilot's seat was armoured, while the self-sealing fuel tanks were proofed, theoretically, against 12.7 mm (.50 in) rounds, but did not have Carbon dioxide pressurization to prevent explosions if they were hit by tracer, incendiary or explosive rounds. No other armour was fitted. All this made it extremely vulnerable to enemy fire.
The main defensive weapon was a Caproni-Lanciani rotating dorsal turret, armed with a Scotti 12.7 mm (.50 in) machine gun with 350 rounds. This weapon was theoretically more powerful and lighter than the Breda-SAFAT, but reliability was a concern, and projectile dispersion was so wide as to reduce the theoretical range of 400 m (1,310 ft) to around 200 m (660 ft) in practice. Additional 7.7 mm (.303 in) Breda-SAFAT machine guns were mounted in each side and in the bombardier's gondola, with four 215-round magazines each. The gondola's machine gun was of little use given the cramped accommodation, and was often not fitted, even in the SM.82 equipped for the bombing role. German machine-guns were used in the Luftwaffe versions, with the 13 mm (.51 in) MG 131 in the turret. 7.92 mm (.312 in) MG 17s were used in some aircraft.
The SM.82's performance was modest, with a cruising speed only 250 km/h (160 mph) at 3,000 m (9,840 ft), even without the bombardier's gondola under the nose (which added more drag), it was slow, while its silhouette was large and easy to spot. The ceiling was seldom over 5,000 m (16,400 ft). This left the SM.82 well inside the operational altitude of most fighters of the time, as well as the effective range of heavy and medium anti-aircraft guns. In comparison the B-17 had a ceiling of 6,000-9,000 m (19,690-29,530 ft), almost out of range of both German 88 mm (3.46 in) AA and FW 190 fighters.
In operation, when faced with a fighter opposition, the SM.82 suffered a devastating loss rate. On 24 November 1942, three Beaufighters downed seven SM.82s, a 100% loss. Later on 10 April 1943, 10 out of 20 in formation were downed by a single pass of a P-38 Lightning squadron. At altitude, the SM.82 was almost a fixed target for both flak and fighter opposition.
Read more about this topic: Savoia-Marchetti SM.82
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