Ambrosini SS 4

The single-seat S.S.4 monoplane fighter designed by Ing Sergio Stefanutti was tail-first configuration with a retractable nosewheel undercarriage. Built by the Societa Aeronautica Italiana Ing A Ambrosini it was of all-metal construction and powered by a 960hp liquid-cooled 12-cylinder Isotta-Fraschini Asso XI R.C.40 engine driving a three-bladed variable-pitch pusher propeller.

With a 960-hp Isotta Fraschini Asso XI 12-cylinder liquid--cooled engine, the S.S.4 was capable of a maximum speed of 540 kph (335 mph) at 5000 m (16,400 ft) and was to have been armed with two 20-mm and one 30-mm can-non.

The sole prototype was first flown on 7 March 1939, but was destroyed during its second flight on the following day when the starboard aileron separated, the wing developed a high amplitude oscillation and the aircraft entered a dive and crashed at Guidonia.

Although. the Italian Air Ministry ordered another prototype, pressure of other projects caused the fighter to be abandoned. No further development was undertaken.

Manufacturer's estimates:

Engine: Isotta-Fraschini Asso XI R.C.40, 960hp
Take-off weight: 2446 kg / 5393 lb
Empty weight: 1800 kg / 3968 lb
Wingspan: 12.32 m / 40 ft 5 in
Length: 6.74 m / 22 ft 1 in
Height: 2.48 m / 8 ft 2 in
Wing area: 17.50 sq.m / 188.37 sq ft
Max. speed: 540 km/h  / 336 mph