In 1939, the Regia Aeronautica (Italian Air Force) initiated its R Plan, or 3,000 airplanes, a campaign to quickly increase its strength with modern aircraft. By that time, Regia Aeronautica had been involved in wars on two continents, and its equipment had been depleted and had not kept up with technological advances.
As a part of this plan, a competition for a modern medium bomber was announced in 1939. CRDA submitted its Z.1015 for this competition. The Z.1015 was basically an all-metal version of the Z.1007, a three-engine medium bomber with a wooden airframe. The Z.1007 had first flown in 1937 but had not yet entered military service by 1939.
Regia Aeronautica requested Zappata's proposal be modified to incorporate greater strength: the design ultimate load factor was to be increased from 7.0 to 10.0. Zappata determined that such a change would require significant re-engineering and increased weight, and countered with a proposal for a new two-engine aircraft, the Z.1018.
The three engines of the Z.1007 had a combined power output of 2,237 kW (3,000 hp), whereas the two engines proposed for the Z.1018 Alfa Romeo 135 RC.32 had a combined output of 2,088 kW (2,800 hp). Thus its performance would be comparable to the proposed Z.1015 with simpler construction, possible lower weight, and reduced maintenance.
Zappata proposed three variants of the basic aircraft, using different wing planforms:
High-speed bomber, equipped with a wing of 50 m² (532 ft²) area;
Higher-capacity bomber, equipped with a wing of 63 m² (678 ft²) area;
High-altitude bomber, equipped with a wing of 72 m² (775 ft²) area.
The new design also offered the possibility of carrying an internal torpedo, which would have been impossible with the Z.1015 fuselage layout.
The new design also offered the possibility of a floatplane version (designated Z.514), using the floats from the Z.506 (the 500 designations were for floatplanes while the 1000 designations were for landplanes).
On 23 February 1939, the Regia authorized production of 32 Z.1018 aircraft, but stipulated an ultimate load factor of 9.0, and also demanded construction of a prototype, and further required that production deliveries begin before the end of the year. This would have been an extraordinarily rapid development schedule, so CRDA objected. The proposed engines had not yet been certificated, and its counter-rotating version had not yet been developed.
Construction of the first prototype was authorized on 7 April 1939. In July 1939, Regia requested that the design be altered to use the new Daimler-Benz DB 601 water-cooled inline engine instead of the planned radial engine.
The aircraft, in its definitive form (as the Leone I) was a two-engine medium bomber, with a single tail, retractable undercarriage, and metallic structure. It had duralumin structure, a skin of light alloy, and a crew of four or five. The contours of the slim fuselage were designed for aerodynamic benefit. As with the Z.1007, the two pilots were in tandem, not side-by-side. Only the first pilot had a complete set of controls, while the copilot had limited visibility and only few instruments.
Its wing was straight-tapered, with rounded wingtips. The low wing incorporated two structural spars. The wing was metal-covered forward and fabric-covered aft. In spite of efforts to reduce the airframe weight, the empty weight of the prototype was comparable to the three-engine Z.1007.
Engines for the Z.1018 prototype were Piaggio P.XII-RC.35 air-cooled radials with 18 cylinders in two rows, rated at 895 kW (1,200 hp) for takeoff and 1,007 kW (1,350 hp) at 3,500 m (11,480 ft) altitude, at 2,050 rpm. Their dry weight was 930 kg/2,050 lb (940 kg/2,070 lb with oil), and they used 87 octane fuel. Propellers were metal three-blade variable-pitch Alfa Romeos.
Using this powerplant, CANT engineers calculated a top speed for the Z.1018 of 524 km/h (326 mph) at 4,500 m (14,764 ft), with a takeoff run of 354 m (1,160 ft), landing run of 462 m (1,518 ft), and a climb to 4,000 m (13,120 ft) in 7 minutes 32 seconds (14 minutes 4 seconds to 6,000 m/19,685 ft).
Design fuel capacity was 3,300 L (870 US gal) in wing-mounted self-sealing fuel tanks. A possible modification was offered - a 500 L (130 US gal) auxiliary fuel tank in the aft fuselage. Calculated endurance with standard tanks was about three hours, for 1,335 km (830 mi) range (using calculated maximum cruise speed). Endurance and range using economical cruise speeds are not available, but should have been better. For example, the Savoia-Marchetti SM.79 Sparviero could boost its range from 1,750 km (1,090 mi) at 350 km/h (220 mph) to 2,300 km (1,430 mi) at 260 km/h (160 mph).
Proposed armament was twelve 100 kg (220 lb) bombs carried in the internal bomb bay. Wing hardpoints were provided capable of carrying 1,000 kg (2,200 lb) each. Two such external weapons could be carried, since the calculated payload (difference between empty weight and maximum operating weight) was 2,700 kg (5,950 lb). For comparison, the Fiat BR.20 and Savoia-Marchetti SM.79 both had a 3,600 kg (7,940 lb) payload, and the CANT Z.1007 payload was over 4,000 kg (8,820 lb).
This calculated Z.1018 payload was barely enough for takeoff with full fuel and crew (2,800 kg/6,1703 lb), so it would not allow for any weapon load. A possible explanation is that the prototype was never flight-tested at its maximum capacity including weapon load.
Defensive armament for the Z.1018 consisted of four machine-guns:
Breda-SAFAT (12.7 mm/.5 in) in a Caproni-Lanciani belly turret;
Scotti (12.7 mm/.303 in) in an upper turret;
(Two) Breda-SAFAT (7.7 mm/.303 in) in fuselage side openings.
In addition, a fixed Breda-SAFAT (7.7 mm/.303 in) machine gun was mounted in the right wing, to be used for ground attack or straight-ahead defense. Ammunition to be provided was 350 rpg for each 12.7 mm (.5 in) gun and 500 rounds for each 7.7 mm (.303 in) gun. The upper turret was troublesome to install, and was finally mounted in a partially retracted position, which prevented a full field of fire.
The added weight of these guns adversely impacted the aircraft's performance. In addition, in retrospect the inclusion of a fixed forward-firing gun on a fast bomber appears to have been unnecessary.
Other systems on board were oxygen cylinders, radios, fire extinguishers and a photographic machine.
The first prototype flew on 9 October 1939. By the end of 1939, this aircraft had logged only 10 hours of flight, due to the unreliable engines. This was not sufficient to adequately evaluate the design, so in March 1940, the engines were replaced with Piaggio P.XII radial engines with three-blade propellers, with improved engine nacelles and propeller spinners.
On 25 May 1940, the prototype flew to Guidonia Montecelio for flight testing. The program was well behind the original schedule at that point; Regia had planned on placing the first 32 machines of the type in service by the end of 1939. Instead, Mario Stoppani and then Adriano Mantelli only flew the prototype. Stoppani made the delivery flight; Mantelli performed the flight tests. He reported an overall good impression, but not outstanding.
In December 1940, Regia Aeronautica specified that the Z.1018 be constructed with a double tail, but in May 1942 the requirement was changed back to the originally envisioned single tail. During this period, Regia also required the addition of dive brakes, increased armament, engine type changes and several other changes.
In the meantime, the test activity continued. The prototype was tested with the P.XII engines, and thanks to the absolute lack of military systems on board, it reached good speeds: at 4,200 m (13,780 ft), the Z.1018 reached 514 km/h (319 mph), equalling the Reggiane Re.2000 that was also undergoing flight evaluation there.
This aircraft had replaced the engines, but the Piaggio P.XII also suffered problems (in fact they were affected for years by many problems).
The verdict of Mantelli was not encouraging: the 'future bomber' Leone was not enough of an improvement to justify its replacing the CANT Z.1007, which was already in production for Regia Aereonautica. A measure of the delays which this program suffered is given by the fact that, in spite of pressures caused by the war being waged at that time, it had taken six months to complete the proof-of-concept aircraft, and a true prototype would still have to be constructed in order to verify the adequacy of the basic design.
Finally, the configuration of this aircraft was fixed, almost 2 years after its first-projected entry into service.
The final Z.1018 configuration is considered by some to be the most attractive of all the Italian aircraft, with its line so slim and well shaped.