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The Bartel M.5 was a Polish intermediate trainer that was based on the earlier Bartel M.2, and entered production just before the Samolot company that had developed it went bankrupt.
The Bartel M.2 was designed by Ryszard Bartel soon after he was appointed as chief designer of the Samolot company. It was an unequal span biplane of largely wooden construction which was produced as a private venture by the company. Only one flying prototype was built, but it became the basis of the Bartel M.4 and Bartel M.5.
By early 1927 the Department of Aeronautics had issued two requirements for new training aircraft, one for an intermediate trainer and one for a primary trainer. The company developed the Bartel M.4 as the primary trainer, and the Bartel M.3 as an intermediate trainer, which would be powered by war surplus Austro-Daimler, Spa and Hispana-Suiza engines of 200-300hp. The M.3 was submitted to the Department of Aeronautics, which awarded it with a development contract, but Bartel then suggested that they should use an alternative design instead. This was based on the M.4, which was itself only just approaching the prototype stage. The M.4 was smaller but heavier than the M.2 but used the same general construction methods. The Department agreed, and the M.3 was replaced by the Bartel M.5.
The M.5 was structurally similar to the M.4, with a largely wooden framework (apart from the use of steel tubes in the tail), mainly covered in plywood although with some parts of the wing and tail using fabric and metal alongside the cockpit. All four wing panels were interchangeable. Each also carried a storage compartment near the root, which could be used for fuel tanks in the upper wing and to carry luggage in the lower wing. The M.5 was larger than the M.4, with a wider wingspan and longer fuselage, and was around 1,000lb heavier. It was also significantly faster although the service ceiling was similar.
Work on the first prototype of the M.5 began in November 1927. The static test airframe was tested in July 1928 and pasted its tests. The prototype M.5a, powered by a 220hp Austro-Daimler six-cylinder inline water cooled engine made its maiden flight on 27 July 1928 (well before the M.4 had entered service). Service acceptance trails started at the end of August and the type was ordered into production. A number of changes were made on the second prototype, including a new fuel system and the use of a 220hp Spa six-cylinder inline water-cooled engine. This made its maiden flight on 15 March 1929 as the BM 5b. A series of radiators were tested, and an underslung radiator was found to be most effective. Both of these versions were accepted and an order was placed for 40 aircraft.
In February 1929 the M.5 was tested as a possible fighter trainer. The first prototype was given skies instead of wheels, but it proved to be too stable, and couldn’t be spinned, making it useless as a fighter trainer. Instead Samolot was ordered to produce a dedicated fighter trainer, which became the M.6
Both the Austro-Daimler powered BM 5a and Spa powered BM 5b entered production in 1929 and deliveries of the first batch of 40 began in the autumn of 1929.
In the summer of 1929 the second prototype was given a 300hp Hispano-Suiza eight cylinder radial engine and made its first flight as the BM 5c on 29 July 1929. A batch of twenty BM 5cs were ordered, although delivery was delayed by a fire at the factory which also helped push the firm into insolvency.
Although there were officially three variants of the BM 5, the engines of all three were interchangeable, and several were swapped over in service.
All three of the original versions used war surplus engines, but the supply of these engines soon ran out. In order to keep the BM 5s flying Bartel produced a conversion kit to allow it to use a 220hp Wright/ Skoda J/5 Whirlwind air-cooled radial engine. The prototype was produced at P.Z.L, as were the twenty conversion kits. The actual conversion took place at Delbin.
The majority of BM 5s went to the training centre at Deblin where they were used as intermediate trainers. Some of the converted BM 5ds were still in use when the Germans invaded in 1939.
In the early 1930s the Polish Navy bought five of the BM 5cs, and converted them into twin float float planes. Three of these aircraft were still in service at the end of 1936.
BM 5a
Engine: Austro-Daimler six-cylinder inline water cooled engine
Power: 220hp
Crew: 2
Span: 36ft 9in
Length: 25ft 7.5in
Height: 10ft 5.5in
Empty Weight: 1,998lb
Loaded Weight: 2,852lb
Maximum Speed: 101.9mph at sea level, 93.8mph at 6,561ft
Cruising Speed:
Climb rate: 8m 9s to 3,280ft
Ceiling: 10,662ft