AMBROSINI S.S.4

A prewar design, the S.5.4 all-metal canard (tail-first) interceptor was the result of a totally different approach by Ambrosini's able designer. In 1938 Ing. Stefanutti had examined the flight characteristics of the unorthodox layout with the S.S.3 two-seat pusher monoplane, built at Guidonia by S.C.A. (Stabilimento Costruzioni Aeronautiche). The arrangement consisted of a fixed forward lifting surface with slotted elevator, and an aft-positioned cantilever wing incorporating normal ailerons and twin fins and rudders. The S.S.3, nicknamed Anitra (Duck), featured a fixed tricycle landing gear with steerable nosewheel. Power was supplied by a C.N.A. II bis flat-twin engine of 38 h.p. Numerous successful test flights demonstrated the efficiency of the arrangement, although performance was naturally limited by the low power available. Maximum speed was only 87 m.p.h., but the S:S.3 remained stable at a minimum speed of 34 m.p.h. Ceiling was 13,120 ft. Span was 41 ft. 11 in., length only 19 ft. 8 in., and height 6 ft. 7 in.

The canard layout offered many advantages for fighter aircraft, among them improved visibility, concentrated forward-firing armament, and the elimination of slipstream drag effects through the use of a pusher airscrew. Accordingly, Ing. Stefanutti developed the Ambrosini S.S.4 fighter, which flew for the first time in May, 1939. Handling qualities proved more than satisfactory in extensive tests at Guidonia during 1940-41, stability being particularly good. The steerable tricycle landing gear, fully retractable on the S.S.4,  was a factor contributing to the excellent take-off and landing qualities. Unfortunately, the S.S.4 was destroyed in a landing accident caused by the failure of its 960 h.p. Isotta Fraschini Asso XI R.C.40 engine. Although a further prototype was ordered immediately, the more easily developed wooden fighters were given priority, and the S.S.4 was finally abandoned in 1942.

Maximum speed had proved to be 355 m.p.h. Span was 40 ft. 5 in., length 22 ft. 1 1/2 in., and height 8 ft. 1 3/4 in. The armament consisted of one 30-mm. cannon and two 20-mm. cannon, all mounted in the nose. Loaded weight was 5400 lb. The Ambrosini S.S.4 canard design preceded that of the Kyushu J7Wl and Curtiss XP-55 fighter prototypes developed near the end of the war, as well as that of the Henschel Projekt 75, which was never built. In addition to its promise as an interceptor, the S.S.4 was considered suitable for the alternate role of dive bomber.