Flight, November 1934

THE FOURTEENTH PARIS AERO SHOW

THE EXHIBITS DESCRIBED

A Fast Fighter

   The Letov S.231, although a biplane of more conventional form, is also very fast, as, with the Gnome-Rhone "Mistral Major" of 880 h.p., the top speed is 405 km.p.h. (251 m.p.h.). The armament consists of two pairs of large-calibre machine guns in each bottom wing outside the airscrew disc. The general construction is of welded steel tubes, and, on the whole, the machine appears both solid and strong. Each undercarriage wheel is carried on a single strut which is braced to the fuselage by three wires. These legs take the compression by an outwards movement against a shock-absorbing unit inside the fuselage. The wing bracing is by N-struts at the tips and streamline wires on the front spar only.
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Flight, January 1935

CZECHOSLOVAKIA "MULTI-GUN" FIGHTER
Bristol "Mercury" Engine in Letov S.231

   DURING 1933 the Vojenska Tovarna Na Letadla built a high performance single-seater fighter, equipped with four machine guns, and using a Bristol "Mercury" IV S.2 engine, known as the type S.231. The "Mercury" IV S.2 has since been replaced by a later mark of the "Mercury," the VIS, and a Siddeley "Tiger III" (610 h.p.) and Gnome Rhone 14 Kfs. (900 h.p.) have been fitted experimentally. Unusually complete wind tunnel tests were made with models of the fuselage of the aircraft to determine the best shape to provide efficient cooling for the engine.
   The machine is a staggered biplane of unequal span with dihedral on the bottom wings only. Struts of a modified "N" formation, braced with wires, carry the centre section of the top plane above the fuselage. Two duralumin spars of rectangular section, ribs of pressed duralumin sheet and fittings of high-grade steel are used for the wing structure. Ailerons of duralumin, aerodynamically and statically balanced and mounted on ball bearings, are fitted on the bottom wing only.
   Steel tubular construction is used for the fuselage, which is rectangular in shape. The forward portion is rigidly braced and fastened with bolts and rivets, and the rear portion is of welded chrome molybdenum steel tubes braced with steel wires. Metal panelling and fabric fairs the fuselage to an oval section. The engine mounting is of welded steel tubes and is joined to the fuselage by four bolts. An adjustable tail plane is fitted and the tail surfaces are statically and aerodynamically balanced. Controls are of conventional type, the rudder bar being adjustable.

Single-strut Undercarriage

   An original single strut type of undercarriage is employed, each of the two struts being braced by three streamline steel wires. Pantof oleo pneumatic shock absorbers are carried within the fuselage, and Dunlop wheels and brakes are fitted.
   The prototype S.231 is fitted with a Bristol "Mercury" IV S.2 engine (560 h.p. at 16,000 ft.), cowled with a low drag ring in several easily detachable parts. When later marks of the "Mercury" engine are fitted, a combined exhaust collector and cowling ring will toe used. The main petrol tank is in the fuselage and a small gravity tank is carried in the centre section of the top plane. A sheet metal oil radiator is mounted beneath the fuselage and fitted with adjustable shutters. Either a Viet or a Walter Mechano starter is used for the engine.
   An easily adjustable seat is provided for the pilot. This seat is designed to accommodate a back type parachute which fills the back of the seat in a similar manner to that in which seat pack parachutes fit into the pilots' seats of most British fighters. Armament consists of four "outboard" machine guns mounted with their ammunition boxes in the lower planes. Electrical, wireless, oxygen, navigating and signalling equipment is carried.
   The performance figures given in the accompanying table were obtained when the machine was fitted with a "Mercury" IV S.2 engine using a wooden airscrew. With the Gnome Rhone 14 Kfs. "Mistral Major," in which form the machine was shown at Paris this year, the top speed is claimed to be about 250 m.p.h., the climb to 16,400 ft. taking six minutes.

LETOV S.231
Bristol "Mercury" IV S.2 (560 h.p. at 16,000 ft.)
   Span 33 ft. (10,06 m)
   Length 25 ft. 9 in. (7,85 m)
   Height 9 ft. 10 in. (3 m)
   Wing area 232 sq. ft. (21,5 m2)
   All up weight 3,594 lb. (1 630 kg)
   Maximum speed at 16,400 ft. (5 000 m) 216 m.p.h. (348 km/h)
   Maximum speed at ground level 186 m.p.h. (300 km/h)
   Climb to 16,400 ft. (5 000 m) 8 min
   Ceiling 30,500 ft. (9 300 m)