Savoia-Marchetti SM.84 - Design

Design

Basically it was an enhanced SM.79, with more modern solutions and systems It shared the basic design of a three-engine mixed construction monoplane as the SM.79. Wood was used for the wings, supported by three spars. Steel tubing was used as a skeleton for the fuselage, covered by metal (forward), fabric and wood. The new fuselage housed a crew of five to six, with the pilots sitting side-by-side. Behind them there were a radio-operator and flight engineer. They enjoyed a large windscreen and eight windows in the fuselage.

The armour was much improved compared to the almost nonexistent protection fitted to the SM.79; it was said there was a total of 700 kg (1,540 lb) fitted, however it is unclear if this also included the self-sealing fuel tanks, bullet-proofed up to 12.7 mm (.50 in) rounds. One noticeable difference was the twin tail, which gave a better field of fire to the dorsal gun, and helped to cope with the greater power and weight compared to the SM.79.

Armament was similar to the Cant Z.1007, rather than the SM.79. There was a dorsal Caproni-Lanciani Delta turret, with a 12.7 mm (.50 in) Scotti machine gun, and 350 rounds. Another Scotti was in the ventral gondola. Other two Scotti were in the flanks with six 120-round belts. It was a theoretical improvement, though Scotti machine guns, even with a slightly higher rate of fire, were much less reliable than the Breda. Another disadvantage was the inability of the turret to fire directly forward, through the propeller's blades, so the aircraft had no defence from frontal attacks.

The bomb bay was in the middle of fuselage. Horizontally mounted, the aircraft could carry two 500 kg (1,100 lb), three 250 kg (550 lb), 10 100 kg (220 lb), or 10 50 kg (110 lb) bombs. Outside the fuselage it was possible to mount two 500 kg (1,102 lb) or 800 kg (1,760 lb) bombs, or two torpedoes, or even smaller bombs like eight 100 kg (220 lb) or 50 kg (110 lb) (but really weighing of 130 kg/290 lb and 70 kg/150 lb). Generally, the aircraft carried only one torpedo or around 1,000 kg (2,200 lb) of bombs. The aiming apparatus was a Jozza U3, fitted in the bombardier's nacelle, just below the cockpit. It was retractable when not in use, to reduce drag.

An OMI camera was fitted in the fuselage, while in the tail section it was possible to mount one of three different cameras, like the AGR.90 or 91.

Three Piaggio P.XI RC.40 engines, giving 746 kW (1,000 hp) at 4,000 m (13,120 ft) were fitted. There were 16 self-sealing fuel tanks inside the wing and the fuselage, six for the central engine (1,070 L/283 US gal) and five for each wing engine (1,095 L/289 US gal). Total fuel load was 3,260 L (860 US gal), which was less, despite the more powerful engines, than previous Italian bombers. It was possible, however, to mount another three fuel tanks: two of 415 L (110 US gal) in the fuselage, and one of 2,500 L (661 US gal) in the bomb-bay.

With these engines, at full load the SM.84 was capable of:

• 400 km/h (250 mph) at 1,000 m (3,280 ft).
• 418 km/h (260 mph) at 2,000 m (6,560 ft).
• 437 km/h (272 mph) at 3,000 m (9,840 ft).
• 456 km/h (283 mph) at 4,000 m (13,120 ft).
• 467 km/h (290 mph) at 5,000 m (16,400 ft).
• 450 km/h (280 mph) at 6,000 m (19,690 ft).

Climb rates to:

• 1,000 m (3,280 ft) in 2 min 32 sec.
• 2,000 m (6,560 ft) in 5 min 25 sec.
• 3,000 m (9,840 ft) in 8 min 2 sec.
• 4,000 m (13,120 ft) in 10 min 54 sec.
• 5,000 m (16,400 ft) in 14 min 48 sec.
• 6,000 m (19,690 ft) in 19 min 18 sec.

The maximum practical ceiling was 8,200 m (26,900 ft). At 5,500 m (18,050 ft) and 397 km/h (247 mph), it had 5 hour 17 minutes endurance, and a range of 2,040 km (1,270 mi). As was expected, the performance of the SM.84 was superior to the SM.79.