Built as a low-risk back-up to the advanced PZL P.37 Los, the LWS Zubr (Bison) bomber had its origin in a design for an airliner that the Polish national airline had rejected as too old-fashioned. Unlike the all-metal Los, the Zubr was built of all sorts of materials. As production began, engines were changed from 336kW (450hp) Twin Wasps to 507kW (680hp) Bristol Pegasuses, which caused different stresses on the airframe. Many weaknesses soon became apparent and cracks were dealt with by fixing on wooden patches. Inevitably the prototype fell apart, unfortunately while carrying prospective Romanian purchasers. The ‘improved’ LWS.6 with the same engines and a twin tail weighed more because of its extra strengthening — so much more that they were unable to carry bombs. The Luftwaffe put the survivors into use as unarmed trainers.
The LWS-6 Żubr (PZL.30 Żubr) was a Polish twin-engined medium bomber, produced by the LWS factory before World War II. A short series was used for training only, because it was inferior to the PZL.37 Łoś design.
Fifteen LWS-6 aeroplanes were delivered to the Polish Air Force in 1938-1939. From the beginning they were considered obsolete, and were assigned to training units. In use they revealed several faults – for example, the undercarriage retracted on some planes during landing. However, there was only one crash in a military aviation, without fatal injuries. Reportedly, they flew with the undercarriage fixed in the open position later. As training aircraft they had their armament removed. The Żubr was inferior to its counterpart the PZL.37 Łoś, developed at the same time. For a similar price, it was of now obsolete design, slower, with inferior performance, and a much smaller bomb load.
During the Invasion of Poland in 1939, Żubrs were not used in combat. Several were destroyed on the ground, along with many other training aircraft. The Germans captured several LWS-6, including the twin-tailfin prototype, and used them for blind flying training until at least 1942 (among others, in Blindflugschule Schleissheim). Ironically, the Luftwaffe service of this bomber was longer than the Polish one.
The Soviets captured four aircraft after their invasion on Poland and next used them in communication aviation.
Apart from the Polish Air Force, Romania showed an interest in the Żubr prototype in 1936, and wanted to buy 24 planes. However, after the prototype crash on November 7, 1936 over Michałowice with two Romanian officers on board, they ordered the PZL.37 Łoś instead (the factory published a cover-up story, that the crash was caused by one of Romanians opening the door during flight).
The aircraft was conventional in layout, high-wing cantilever monoplane, of mixed construction (metal and wood). The fuselage was rectangular in cross-section, made of a metal frame, covered with metal (upper fuselage) and canvas (sides and bottom), front part was made of duralumin. Wings were of wooden construction, plywood covered. There was a crew of four: pilot, commander-bombardier, radio operator and a rear gunner. The bombardier was accommodated in a glazed nose, with a forward machine gun turret and a significant pointed “beard” below. The pilot’s canopy was above a fuselage, offset to the left. The rear gunner operated an upper turret, elevating to a working position. The main undercarriage retracted into engine nacelles. The plane was powered by two Bristol Pegasus VIII radial engines, normal power: 670 hp (500 kW), take-off power: 700 hp (522 kW). Bombs were carried in a bomb bay in the fuselage, the maximum load was 660 kg.
Specifications (LWS-6)
General characteristics
Crew: four (pilot, commander-bombardier, radio operator, rear gunner)
Length: 15.40 m (50 ft 6 in)
Wingspan: 18.50 m (60 ft 8 in)
Height: 4 m (13 ft 2 in)
Wing area: 49.5 m² (532.6 ft²)
Empty weight: 4,788 kg (10,533 lb)
Loaded weight: 6,747 kg (14,843 lb)
Useful load: 1,959 kg (4,319 lb)
Max. takeoff weight: 6,876 kg (15,127 lb)
Powerplant: 2 × Bristol Pegasus VIII 9-cylinder air-cooled radial engine, 700 hp (522 kW) each
Performance
Maximum speed: 341 km/h (212 mph)
Cruise speed: 280 km/h
Range: 750-1250 km (466-776 mi)
Service ceiling: 6,700 m (21,975 ft)
Rate of climb: 408 m/min (6.8 m/s) (1,338 ft/min)
Wing loading: 129 kg/m² (26.4 lb/ft²)
Armament
2 × 7.7 mm Vickers F machine guns in nose turret
2 × 7.7 mm Vickers F machine guns in upper rear turret
1 × 7.7 mm Vickers F machine gun in underbelly
660 kg (1,450 lb) of bombs
