Bartel BM-4
| Bartel BM-4 | |
|---|---|
 |
|
| BM-4 at exhibition in Poznan, 1929 | |
| Role | Primary trainer aircraft |
| Manufacturer | Samolot, PWS |
| First flight | 20 December 1927 |
| Introduction | 1929 |
| Retired | 1939 |
| Primary user | Polish Air Force |
| Produced | 1928–1932 |
| Number built | ~75 |
The Bartel BM-4 was a Polish biplane primary trainer aircraft used from 1929 to 1939 by the Polish Air Force and Polish civilian aviation, manufactured in the Samolot factory in Poznań. It was the first plane of Polish design put into production.
The aircraft was designed by Ryszard Bartel in the Samolot factory in Poznań. It was a development of the Bartel BM-2, which did not advance beyond the prototype stage. Thanks to a lower weight than the BM-2, it could use lower-powered engines, so its performance was actually improved. Its performance was also superior to the Hanriot H.28, used by the Poles and licence-built by Samolot. The BM-4 prototype was flown on 20 December 1927 in Poznań. It had good handling and stability and was resistant to spinning. A distinguishing feature of all Bartels was an upper wing of a shorter span, because lower and upper wing halves were interchangeable (i.e. the lower wingspan included the width of the fuselage).
The first prototype was designated BM-4b and was fitted with 90 hp Walter Vega radial engine. The second prototype, flown on 2 April 1928, was designated BM-4d and fitted with the Polish experimental 85 hp WZ-7 radial engine, then refitted with 80 hp Le Rhône 9C rotary engine and redesignated BM-4a. The BM-4a became a production variant, because the Polish Air Force had a store of Le Rhône engines. 22 aircraft were ordered and built in 1928–1929. This variant had a cowled engine which made it different from all other BM-4s with radial engines.
Next several variants remained experimental. The BM-4c with a 125 hp Lorraine-Dietrich 5Pb radial engine, built as a one-off in 1928, was supposed to be used for long-distance flights to advertise the engines, but was finally used as the factory's aircraft. Three BM-4a's were converted to BM-4e of 1930 with the Polish experimental 85 hp Peterlot radial engine, the BM-4f of 1931 with the Polish experimental 120 hp Skoda G-594 Czarny Piotruś radial engine, and the BM-4g of 1931 with 100 hp de Havilland Gipsy I inline engine. The last one competed against the RWD-8 in a search for a standard trainer aircraft, but was not selected. After tests in 1932, all three were converted back with Le Rhône engines.
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