LWS-4 Zubr

LWS-4 (PZL-30) Żubr
Description
Role	Medium bomber
Crew	4
First Flight	March 1936
Entered Service	1938
Manufacturer	LWS
Dimensions
Length	15.40 m	in
Wingspan	18.50 m	in
Height	4 m	in
Wing area	49.5 m²	ft²
Weights
Empty	4,788 kg	lb
Loaded	6,747 kg	lb
Maximum takeoff	6,876 kg	lb
Powerplant
Engines 2 x	Bristol Pegasus
Power 2 x	Pegasus VIII
	670-700 hp	kW
Performance
Maximum speed	341 km/h	mph
Combat range	750 km (with bombs)	miles
Ferry range	1,250 km	miles
Service ceiling	6,700 m	ft
Rate of climb	6.8 m/s	ft/min
Wing loading	136 kg/m² (with bombs)	lb/ft²
Power/Mass	hp/lb	kW/kg
Armament
Guns	5 x 7.7 mm machine guns: 2 in nose turret 2 in rear upper turret 1 in underbelly station
Bombs	660 kg	lbs

The LWS-4 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.

Development

It was initially designed in the PZL in the early-1930s as a passenger plane. 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 tradtional design, in case the modern bomber design, PZL.37 Los 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 factory in Lublin, with a name 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, the aircraft had much less bomb load, than expected. An improved prototype, designated LWS-6, was made with a double tail fin, and flown in the end of 1937. The serial variant, however, received a designation LWS-4 and returned to a single tail fin configuration. A series of 15 aircraft was built in 1938. There was also proposed a hydroplane variant LWS-5, but was rejected by the naval aviation due to its mass and low useful weight.

Use

The produced 15 LWS-4 planes were given to the Polish Air Force. Just from the beginning, they were considered as too obsolete, and moved to training units. They revealed several faults as well - for example, an undercarriage retracted on some planes while landing. As training machines, these planes carried no armament. Żubr showed 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. The Germans captured several LWS-4 and the single LWS-6, and used them for training until at least 1942 (among others, for blind flying training). Ironically, the German service of this needless bomber was longer, than the Polish one.

Apart from the Polish Air Force, also the 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 Los).

Technical design

The aircraft was conventional in layout, mixed construction (metal and wood), metal- and canvas-covered, with high wings. The crew consisted of four: pilot, commander-bombardier, radio operator and a rear gunner. The bombardier was accommodated in the glazed pointed nose, with a forward machine gun turret. The pilot's canopy was offset to the left. The main undercarriage retracted into the engine nacelles. The plane was powered by two Bristol Pegasus VIII radial engines (normal power: 670 hp, maximum: 700 hp). The bombs were carried in a bomb bay in the fuselage, a maximum load was 660 kg.

pl:LWS-4 Żubr