The LWS-6 Zubr (PZL.30 Zubr) 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 Los 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. Reportedly, they flew with the undercarriage fixed in the open position later. As training aircraft they had their armament removed. The Zubr was inferior to its counterpart the PZL.37 Los, 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.

Info: Wikipedia
http://en.wikipedia.org/wiki/LWS-6_%C5%BBubr

Profile: Spafi
http://www.spafi.org/resources/category/19