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Letov S-31

The Letov Š-31 was a fighter aircraft produced in Czechoslovakia in the early 1930s in a number of variants.

All of the aircraft had metal tubular framing and fabric covering with a metal engine cowling.

The first flight of the definitive and highly altered Š.231 version was on March 17, 1933.

After testing at the Czechoslovak flight facility at Prague-Lethany, modifications were undertaken to improve the machine’s performance.

It entered production the following year and began equipping Czech fighter units in June 1936.

The machines however did not remain in frontline fighter status with the Czechoslovak Air Force until the German occupation of Czechoslovakia in 1939.

The sole Š.331 and 22 out of 24 produced Š.231s were sold to representatives of the Spanish Republican government.

Reports of their combat record in the Spanish Civil War are vague, but at least three machines survived the war and were used by victorious Nationalists.

The operational performance and ultimate fate of the Š.331 is unrecorded.

While the Š.31, Š.131, Š.231, and Š.431 had engines of 480 to 680 hp, the Š.331 had a 670 kW (900 hp) Walter K.14 engine, giving it outstanding performance for an aircraft of the early 1930s.

In May 1935, the aircraft established a new Czechoslovak altitude record of 10,650 m (34,941 ft).



Initial version with Walter-built Bristol Jupiter (33 built)


Racing version with BMW-built Pratt & Whitney Hornet (three built)


Main production version with Walter-built Bristol Mercury engine


Version with Walter K.14 engine (one built)


Version with Armstrong Siddeley Tiger engine (one built)





7.85 m (25 ft 9 in)


10.06 m (33 ft 0 in)


3 m (9 ft 10 in)

Wing area

21.5 m2 (231 sq ft)

Empty weight

1,243 kg (2,740 lb)

Gross weight

1,715 kg (3,781 lb)

Fuel capacity

200 l (53 US gal; 44 imp gal) main fuselage tank


100 l (26 US gal; 22 imp gal) centre-section gravity tank


1 × Walter Mercury V-S2,

9-cylinder air-cooled radial piston engine,

412 kW (553 hp)


2-bladed fixed-pitch propeller


Maximum speed

348 km/h (216 mph, 188 kn) at 5,000 m (16,404 ft)

300 km/h (190 mph; 160 kn) at sea level

Cruise speed

310 km/h (190 mph, 170 kn)


450 km (280 mi, 240 nmi)

Service ceiling

9,300 m (30,500 ft)

Absolute ceiling

9,750 m (31,988 ft)

Time to altitude

5,000 m (16,404 ft) in 8 minutes 13 seconds

Wing loading

82.5 kg/m2 (16.9 lb/sq ft)


0.245 kW/kg (0.149 hp/lb)



Two fixed forward-firing 7.7 mm (0.303 inch) machine guns mounted in fuselage nose,


One similar weapon in pod beneath each lower wing,


Six small bombs at hardpoints beneath lower wings.








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