Flown in 1925, the S20 was an unequal-span single-bay biplane of mixed construction with a 300 hp Skoda HS 8Fb water-cooled engine with Lamblin strut-type radiators on the front undercarriage legs, armament comprising two synchro¬nised 7,7-mm Vickers machine guns.
Designed by Alois Smolik, the S-20 had a steel tube framed fuselage as well as fin , rudder and elevator fabric-covered. Wood-framed wings were covered by fabric, and a sheet metal plated cowling. Whereas the upper wing of the first prototype had no gap above the fuselage, the series model introduced a narrow gap and an inverted-vee cabane, the upper fuselage decking being recontoured to improve view from the cockpit.
In 1926, the Š 20 was the winning contender in a contest for a new fighter for the Czechoslovak Air Force, and a total of 105 was to be built for that service. The Š 20 took fourth place at the International Air Meeting in Zurich in 1927, the type serving with all three air regiments of the CzAF.
Ten examples were exported to the Latvian Air Force (as the Š 20L) with interchangable ski u/c in 1925, one experimental model was completed with a slimmer fuselage (as the Š 20R, also called S-20M). Another was fitted with a Walter¬built Bristol Jupiter air-cooled radial of 480 hp (as the Š 20J). This led to S-31 fighter. The Š 20J model attaining an altitude of 28,543 ft (8700 m).
S.20
Engine: Hispano Suiza 8 Fb, 300 hp
Wingspan: 9.70 m
Length 7.44 m
Empty weight: 728 kg
Maximum speed: 256 kph
Service ceiling: 7200 m
Range: 528 km
S.20
Engine: Skoda HS 8 Fb, 300 hp
Wingspan: 9.70 m
Length: 7.44 m
Empty weight: 728 kg
Climb to 5 00 m: 13 min 50 sec
Service ceiling: 7200 m
Range: 528 km
Š.20
Engine: 1 x 300 hp kW V-8 Skoda HS 8 Fb
Max speed, 160 mph (257 km/h)
Range, 328 mls (528 km)
Empty weight, 1,631 lb (740 kg)
Loaded weight, 2,315 lb (1 050 kg)
Span, 31 ft 6 in (9,60 m)
Length, 24 ft 4 9/10in (7,44 m)
Height, 8 ft 4.75 in (2,56 m)
Wing area, 198.06 sq.ft (l8,40 sq.m).
Armament: two synchro¬nised 7,7-mm Vickers machine guns
Š.20J
Engine: Walter¬built Bristol Jupiter, 480 hp
Max altitude: 28,543 ft (8700 m)
Š.20L
Undercarriage: ski/wheel
Š 20R / Š.20M
All Aero 