Between 10/38 and 4/39, Sergio Stefanutti designed the SAI.7 as a high-performance touring plane for the civil market. Undoubtedly one of the best looking aircraft ever designed, the SAI.7 possessed exceptionally clean lines, was of wooden construction with plywood skin. The SAI.7 was the first Ambrosini airplane with retractable landing gear, in this instance of the fully-retractable tail wheel type with wide-track main units that swung inward and upward into the roots of the cantilever low-set wing. The first two aircraft were completed in 7/39 with a windscreen design that extended right to the nose for a very clean entry, and were entered in the Avio Raduno del Littorio competition that started a few days after the machines made their maiden flights.
The aircraft were too under developed to win the competition, but nonetheless put in a very credible performance that included a maximum speed of 251 mph with a 280 hp air-cooled Hirth HM 508D inverted-Vee engine. One aircraft took a class closed-circuit speed record over 61.2 miles with a speed of 244 mph.
The high speed/power ratio of the SAI.7 caught the imagination of the Italian air force which saw considerable possibilities in the concept of a lightweight interceptor that could be built in large numbers without drawing on the country’s strategic stockpile of aluminum alloys. Little was done about the military potential of the SAI.7 in the short- term, however, and it was 1941 before Stefanutti began work on a fighter trainer derived from the SAI.7 with the Hirth engine being replaced by a 280 hp Isotta-Fraschini Beta RC.10 inverted-Vee engine. The fuselage and wingspan were increased and the faired racing windscreen was replaced by a conventional stepped windscreen at the front of a more heavily framed cockpit enclosure with two rearward sliding sections for access, and the landing gear was modified with a fixed tail wheel. These changes increased the maximum take-off weight, but the maximum speed was reduced only slightly to 248.5 mph. By the time the first of an eventual 10 SAI.7 fighter trainers appeared, the increasingly difficult military position in which Italy found itself was reflected in the emphasis on combat aircraft rather than trainers; and so further work on the fighter trainer variant was abandoned until after the war when it was revived and led to the S.7 and Supersette trainers.
Throughout this process Stefanutti and the Italian air ministry had not lost sight of the SAI.7’s potential for development into a lightweight fighter. In 1942 Ambrosini evolved the SAI.107 as an experimental fighter for full evaluation of this potential. The new type was essentially a single-seat derivative of the fighter trainer was a considerably more powerful engine in the form of a 540 hp Isotta-Frashini Gamma RC.35 IS inverted-Vee engine driving a two bladed propeller. This prototype recorded a maximum speed of 348 mph and confirmed that a viable interceptor was possible. Stefanutti then proceeded to the design of a fighter with full operational equipment including armament. This was the SAI.207 that otherwise differed from the SAI.107 only in its more powerful engine driving a three-bladed propeller. Flight trials began in 1942, and in the course of these, the first SAI.207 recorded a dive speed of 596 mph at 9,845 ft, corresponding to Mach .86.
The Italian air ministry ordered Ambrosini to begin work on a pre-production batch and placed an order for 2,000 production aircraft. In the event only 13 of the pre-production aircraft were completed, three of them being allocated to the 3rd Stormo Caccia Terrestre during 7/43 for operational trials. Italy secured an armistice with the Allies just two months later.
Production of the SAI.207 had meanwhile been cancelled in favor of its SAI.403 Dardo (dart) derivative. This essentially was a more sophisticated version of the SAI.207 with the same type of stressed-skin wooden construction, but which had fully retractable landing gear rather than the 207’s combination of retractable main gear and fixed tailwheel. In addition, changes included a revised tail unit with a variable-incidence tailplane, greater ammunition capacities, and an upgraded power plant in the form of the 750 hp Isotta-Fraschini Delta RC.21/60 Serie I-IV driving a three-bladed Piaggio constant-speed propeller.
The three variants of the SAI.403 planned were the Dardo-A lightweight interceptor with armament restricted to two 12.7mm machine guns, the Dardo-B general-purpose fighter with two 20mm cannon and two 12.7mm machine guns, and the Dardo-C long-range fighter with 2 20mm cannon and provision for two 39.6 US gallon drop tanks supplementing the internal fuel capacity from the 79.25 US gallon of the Dardo A/B to 108.3 US gallon. The first SAI.403 flew late in 1942 and revealed exceptional performance, including a maximum speed of 404 mph at 23,620 ft. This resulted in the termination of the SAI.207 in favor of 3,000 of the SAI.403 to be produced. None of these fighters had been delivered before the Italian armistice with the Allies and the closing of the program.
|Powerplant||One Isotta-Fraschini Delta RC.40 inverted-Vee engine|
|Cruising Speed||304 mph|
|Max Speed||398 mph at 14,765 ft|
|Max Ceiling||39,370 ft|
|Armament||(2) 20mm cannon and (2)12.7mm machine guns|
Article by JDG
Wings: Midway to Hiroshima – CD-ROM (Discovery Channel Multimedia: Wings)
Elke Weale, Combat Aircraft of World War Two, Bracken Books, 1985.
Complete Book of World War II Combat Aircraft (Documents of History)