LWS-6 Żubr

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The LWS-6 Żubr (PZL.30 Żubr) was the Polish twin-engine medium bomber, produced in a small series in the LWS factory before the World War II.

Contents

1 Development
2 Use
3 Technical design

3.1 Specifications

3.1.1 General characteristics
3.1.2 Performance

3.2 Armament

4 Operators
5 Related content

Development

It was initially designed in the PZL in the early-1930s as a passenger plane (main designer was Zbyslaw Ciolkosz). Since the Polish Airlines LOT bought Douglas DC-2 planes instead, the project was converted to a bomber aircraft, with a projected bomb load 1,200 kg. It was developed as an alternative less-advanced design, in case the modern bomber design, PZL.37 Łoś would fail. The first prototype, designated PZL.30 flew in March 1936 (only three months before PZL.37 prototype).

The plane was accepted for a limited production in the LWS state factory in Lublin, with a name LWS-6 Żubr (in Polish - the wisent). It was planned to produce 16 aircraft for the Polish Air Force. After a crash of the PZL.30 prototype on November 7, 1936, caused by a weak construction of a wing, the aircraft was strengthened. Due to increased weight, it had much less bomb load, than expected. An improved prototype was made with a double tail fin, and flown in the end of 1937. The serial variant, however, returned to a single tail fin configuration, but it was enlarged. A series of 15 aircraft was built in 1938. The factory continued works upon Zubr development and in 1939, there were developed a lighter wing of a steel construction and a refined fuselage, but they were not built due to war.

There was also proposed a seaplane torpedo bomber variant LWS-5 in 1937, but it was rejected by the Polish naval aviation due to its low payload. Works upon the prototype were canceled in 1938.

In many sources there is an erroneous designation LWS-4 used for Zubr, but in fact it was a designation of a light fighter project.

Use

15 produced LWS-6 planes were given to the Polish Air Force in 1938-39. Just from the beginning, they were considered as too obsolete to equip combat units, and were moved to training units. They revealed several faults as well - for example, an undercarriage retracted on some planes during landing. Reportedly, they flew with an undercarriage fixed in open position later. As training machines, these planes eventually carried no armament. Żubr appeared as much inferior, than its counterpart PZL.37 Los, developed at the same time. For a similar price, it had older construction, worse speed, handling and, especially, much lower bomb load.

During the Polish September Campaign in 1939, Żubr's were not used in combat. Several planes were bombed by the Germans in air bases, along with many other training aircraft. The Germans captured several LWS-6, including twin tailfin prototype, and used them for training until at least 1942 (among others, for blind flying training). Ironically, the Luftwaffe service of this needless bomber was longer, than the Polish one.

Apart from the Polish Air Force, also Romania showed an interest in Żubr prototype in 1936, and wanted to buy 24 planes. However, after the prototype crash on November 7, with two Romanian officers onboard, Romania resigned from this plane (it later ordered PZL.37 Łoś).

Technical design

The aircraft was conventional in layout, high wing, mixed construction (metal and wood), covered with metal (upper fuselage), canvas (fuselage) and plywood (wings). Fuselage was rectangular in cross-section. The crew consisted of four: pilot, commander-bombardier, radio operator and a rear gunner. The bombardier was accommodated in a glazed pointed nose, with a forward machine gun turret. The pilot's canopy was above a fuselage, offset to the left. The rear gunner operated an upper turret, elavating 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), maximum: 700 hp (522 kW). Bombs were carried in a bomb bay in the fuselage, a maximum load was 660 kg.

Specifications

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General characteristics

Crew: 4
Length: 15.40 m ( ft)
Wingspan: 18.50 m ( ft)
Height: 4 m ( ft)
Wing area: 49.5 m² ( ft²)
Empty: 4,788 kg ( lb)
Loaded: 6,747 kg ( lb)
Maximum takeoff: 6,876 kg ( lb)
Powerplant: 2 x Bristol Pegasus VIII, 670-700 hp (500-522 kW)

Performance

Maximum speed: 341 km/h (212 mph)
Range: 750-1250 km
Service ceiling: 6,700 m ( ft)
Rate of climb: 6.8 m/s ( ft/min)
Wing loading: 129 kg/m² ( lb/ft²)
Power/mass:

Armament

2× 7.7 mm Vickers F machineguns in nose turret
2× 7.7 mm Vickers F machineguns in upper rear turret
1× 7.7 mm Vickers F machinegun in underbelly station
bombs: 660 kg

Operators

Germany, Poland, Romania.