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Bartel BM-4
 
Bartel-4-01
BM-4a
 
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. The Bartel BM-4 performance was superior to the BM-2, and also to the Hanriot H.28, used by the Poles and licence-built by Samolot.
 
Wooden construction biplane, conventional in layout. Fuselage rectangular in cross-section, plywood covered (engine section - metal covered). Rectangular two-spar wings, plywood and canvas covered. Crew of two, sitting in tandem in open cockpits, with individual windshields. Cockpits with dual controls, instructor's at rear. Fixed landing gear, with a rear skid.
 
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 first prototype BM-4b was given to the king of Afghanistan Amanullah Khan during his visit to Poland in 1928. 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.
 
Bartel-4-02
B-4all
 
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.
 
Bartel-4-03
BM-4h
 
The second series variant became BM-4h, with 120 hp de Havilland Gipsy III or 120 hp Walter Junior 4 inline engines. Like late BM-4a's, they had a rounded tailfin and a modified undercarriage. Due to the Samolot factory's closure in 1930, the BM-4h was developed at the PWS (Podlaska Wytwórnia Samolotów) and built there in 1932 in a series of about 50 aircraft.
 
Bartel-4-04
BM-4b
 
BM-4a's were used in the Polish Air Force from 1929 - in pilots' school in Bydgoszcz. 6 burnt in September 1929 in the Samolot factory. BM-4h's were used in the Polish Air Force from 1932, in schools in Bydgoszcz and Dęblin. They only partly replaced Hanriot H.28s and were themselves replaced with the RWD-8. They had military numbers starting with 33.
 
In 1936 the Polish Air Force handed over their remaining 23 BM-4h's to civilian aviation - most to regional aero clubs, some to the Ministry of Communication. They received registrations SP-BBP - BBZ and from a range SP-ARB to ARZ. Several survived until the German invasion of Poland in September 1939. Several were used as liaison aircraft during the campaign. None survived the war.
 
Bartel-4-05
BM-4 at exhibition in Poznan, 1929
 
Variants:
 
BM-4a
Engine: Le Rhône 9C, 80 hp / 60 kW nominal power.
Propeller: Two-blade wooden 2.55 m diameter.
Wingspan: 10.175 m (33 ft 5 in)
Wing area: 25 m2 (270 sq ft)
Length: 7.22 m (23 ft 8 in)
Height: 2.93 m (9 ft 7 in)
Empty weight: 538 kg (1,186 lb)
Gross weight: 359 kg (791 lb)
Fuel tank (fuselage): 89.5 lt
Wing loading: 31.6 kg/m2 (6.5 lb/sq ft)
Power/mass: 0.101 kW/kg (0.0615 hp/lb)
Maximum speed: 125 km/h (78 mph; 67 kn) at sea level
Cruising speed: 110 km/h (68 mph; 59 kn)
Stall speed: 57 km/h (35 mph; 31 kn)
Endurance: 3 hours
Service ceiling: 2,820 m (9,252 ft)
Rate of climb: 1.9 m/s (370 ft/min)
Time to altitude 1,000 m / 3,281 ft: 9 min 42 sec
Crew: 2
 
BM-4b
Engine: Walter Vega, 90 hp take-off power, 85 hp nominal power.
Propeller: Two-blade wooden 2.55 m diameter.
Fuel tank (fuselage): 89.5 lt
 
BM-4c
Engine: Lorraine-Dietrich 5Pb, 125 hp take-off power, 110 hp nominal power.
Propeller: Two-blade wooden 2.55 m diameter.
Fuel tank (fuselage): 89.5 lt
 
BM-4d
Engine: Avia WZ-7, 85 hp take-off power, 80 hp nominal power.
Propeller: Two-blade wooden 2.55 m diameter.
Fuel tank (fuselage): 89.5 lt
 
BM-4e
Engine: Peterlot, 85 hp take-off power, 80 hp nominal power.
Propeller: Two-blade wooden 2.55 m diameter.
Fuel tank (fuselage): 89.5 lt
 
BM-4f
Engine: Skoda G-594 Czarny Piotruś, 120 hp take-off power, 100 hp nominal power.
Propeller: Two-blade wooden 2.55 m diameter.
Fuel tank (fuselage): 89.5 lt
 
BM-4g
Engine: de Havilland Gipsy I, 100 hp take-off power, 90 hp nominal power.
Propeller: Two-blade wooden 2.55 m diameter.
Fuel tank (fuselage): 89.5 lt
 
BM-4h
Engine: de Havilland Gipsy III, 120 hp nominal power or Walter Junior 4, 120 hp take-off power, 110 hp nominal power.
Propeller: Two-blade wooden 2.55 m diameter.
Fuel tank (fuselage): 89.5 lt
 
Bartel-4-06
BM-4a1
 
Bartel-4-07

 

Bartel-BM4-ld-01
 
Bartel-BM4-ld-02
 
 
 
 


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