Caproni Ca.135 - Design

Design

The Ca.135 was to be built at Caproni's main Taliedo factory in Milan, which is why the type had a designation in the main Caproni sequence, rather than in the Caproni-Bergamaschi Ca.300 series. However, the project was retained at Ponte San Pietro and the prototype, completed during 1934-35, (a long construction time for the period), was first flown on 1 April. The project chief was Cesare Pallavicino of CAB (Caproni Aereonautica Bergamasca).

Although the new bomber was in the "century series" of Caproni aircraft, it resembled the Caproni Ca.310, with its rounded nose, two engines, low-slung fuselage and wings with a very long chord. Several versions were fitted with different engines and some had noticeable performance differences.

The prototype was powered by two 623 kW (835 hp) (at 4,000 m/13,123 ft) Isotta Fraschini Asso XI.RC radial engines initially fitted with two bladed wooden propellers. It had a length of 14.5 m (48 ft), a wingspan of 18.96 m (62.2 ft), and a wing surface of 61.5 m2 (662 sq ft). It weighed 5,606 kg (12,360 lb) empty and had a 2,875 kg (6,340 lb) useful load. Structurally, it was built of mixed materials, with a stressed-skin forward fuselage and a wood and fabric-covered steel-tube rear section; the wings being of metal and wood, using fabric and wood as a covering. The wings were more than ⅓ of the total length, and had two spars of wooden construction, covered with plywood and metal. The strength coefficient was 7.5. The tail surfaces were built of wood covered with metal and plywood. The fuel system, with two tanks in the inner wings, held a total of 2,200 L (581 US gal).

The Ca.135's fuselage shape was quite different from, for example, that of the Fiat BR.20. If the latter resembled the American B-25 Mitchell, the Ca.135, with its low fuselage more resembled the American B-26 Marauder. Its long nose accommodated the bomb-aimer (bombardier) and a front turret (similar to the Piaggio P.108 and later British bombers). The front part of the nose was detachable to allow a quick exit from the aircraft. It also had two doors in the cockpit roof, giving the pilots the chance to escape in an emergency. The right-hand seat could fold up to assist entry to the nose.

A single 12.7 mm (0.5 in) in a turret in mid-fuselage, was manned by the co-pilot. A seat for the flight engineer was later fitted. The wireless operator's station, in the aft fuselage, was fitted with the AR350/AR5 (the standard for Italian bombers), a radiogoniometer (P63N), an OMI AGR.90 photographic-planimetric machine or the similar AGR 61. The aircraft was also equipped with an APR 3 camera which although not fixed, was normally operated through a small window. The wireless operator also had a 12.7 mm (0.5 in) machine gun in the ventral position. All this equipment made him very busy; as a result, an extra man was often carried. The aircraft had very wide glazed surfaces in the nose, cockpit, and the central and aft fuselage; much more than in other Italian aircraft.

The aircraft was fitted with three machine guns, of 12.7 mm (0.5 in) calibre in the turrets, and a 7.7 mm (0.303 in) calibre gun in the nose. All had 500 rounds, except the 7.7 mm (0.303 in) which had 350.

Bombload, like most Italian bombers, was less than impressive in terms of total weight, but was relatively flexible, depending on the role - from anti-ship to close air support:

• 2 × 800 kg (1,760 lb) bombs (the heaviest in the Regia Aeronautica), plus 2 × 50 kg (110 lb), and 2 × 31 kg (68 lb), for a total of 1,862 kg (4,105 lb)
• 2 × 500 kg (1,100 lb) + 4 × 100 kg (220 lb) + 2 × 31 kg (68 lb), total nominal 1,462 kg (3,223 lb)
• 4 × 250 kg (550 lb)
• 8 × 100 kg (220 lb) + 8 × 50 kg (110 lb) + 4 × 31 kg (68 lb), total 1,324 kg (2,919 lb)
• 16 × 50 kg (110 lb) + 8 × 31 kg (68 lb), total 1,048 kg (2,310 lb)
• 24 × 31 kg (68 lb), 20 kg (40 lb), 15 kg (33 lb), or 12 kg (26 lb).
• 120 × 1 kg (2 lb) or 2 kg (4 lb) bomblets
• 2 × torpedoes (never used, but hardpoints were fitted)

The aircraft had a better bomb capacity than most of its contemporaries (the SM.79 could carry: 2 × 500 kg/1,100, 5 × 250 kg/550 lb, 12 × 100 kg/220 lb or 50 kg/110 lb bombs, or 700 × 1–2 kg/2-4 lb bomblets).