When it became clear that series production of the DB 601 E engine was far behind schedule, the Messerschmitt team had to resort temporarily to the readily available DB 601 A engine of 1100 hp instead. On 26th January 1939, the new airframe went through a series of flight tests. On that day Messerschmitt Bf 109 V22 (W.Nr. 1800, registered as D-IRPQ) took to the air for the first time, with test pilot Dipl. Ing. Heinrich Beauvais at the controls. The machine featured a new supercharger air intake scoop intended for the F-series and was powered by the older DB 601 A engine. The second prototype to be flown was the Bf 109 V23 (W.Nr. 1801, D-ISHN), fitted with one of the still-experimental DB 601 E units. Finally, the Bf 109 V24 (W.Nr. 1929) and V25 (W.Nr. 1930, D-IVKC) incorporated all the distinctive external features of the Bf 109 F, which included the modified fuselage and new wings with rounded wingtips4.
Flight test results were promising and the RLM placed an order for a pre-production batch of 15 Bf 109 F-0s. They were to be delivered to the Luftwaffe in the period between November 1939 and April 1940. However, due to Hitler’s decision to curtail development work on all combat aircraft designs, completion of the first batch of ‘Friedrichs’ was delayed until June 1940 – February 19415. Four more Bf 109 F-0s were assembled between March and June 19416. Most of them subsequently served as test-beds. At least five of these aircraft were converted standard Bf 109 E-3 airframes (W.Nr. 5601 through 5605). Messerschmitt Bf 109 F-0, W.Nr. 5601, was earmarked for “further constructional development” (Weiterentwicklung des Baumusters); it was powered by a DB 601 A engine and featured wings identical to that of the Bf 109 E variant. Bf 109 F-0, W.Nr. 5602, was used to test the new radiator systems intended for the F-series. It was lost during trials at Rechlin (the Luftwaffe’s main testing ground for new aircraft designs).
The first prototype of the definitive series-production Bf 109 F-1 was the Bf 109 F-0, W.Nr. 5603 (coded CE+BP) powered by a DB 601 N engine. This powerplant was an upgraded DB 601 A, rated at 1,175 hp. It ran on 96-octane C3 fuel (the octane number of the Luftwaffe’s standard B4 fuel was 87). Upon completing the tests the aircraft was returned to the Messerschmitt plant, where it was later used to develop the Me 309, being subsequently fitted with a new landing gear and nose wheel. Another Bf 109 F-0, W.Nr. 5604 (coded VK+AB), was used for testing the wing slats and radiator flaps. Messerschmitt Bf 109 F-0, W.Nr. 5605 (VK+AC), fitted with the standard wings of an E variant, served as a test-bed for the engine cooling system; it was also experimentally fitted with several different types of supercharger air intake.
The major difference between the ‘Friedrich’ and its predecessor was the onboard armament. The twin wing-mounted 20 mm MG FF/M cannons of the E variant were replaced by a single 15 mm Mauser MG 151 cannon installed between the engine cylinder banks and firing through the hollow propeller shaft. The new cannon, despite its smaller calibre, gave more firepower. This was due to the considerable increase in the rate of fire – from 530 rds/min to as many as 700! Furthermore, the increased muzzle velocity (1020 m/sec, compared to the previous 718 m/sec) gave the new weapon greater accuracy. Nevertheless, the process of preparing the MG 151 cannon for mass production was handicapped by numerous delays, as was the case with the DB 601 E engine. This left the Messerschmitt team with no option but to initiate production with the DB 601 N engine and the MG FF/M cannon.
Messerschmitt Bf 109 F-1
The Bf 109 F-1 was the first series-production ‘Friedrich’. In accordance with the aircraft production program issued on 1st April 1939, production was to begin as early as June 1940 with machines being manufactured by the Messerschmitt plant at Regensburg, the Arado plant at Warnemünde and the WNF plant at Wiener-Neustadt. It was estimated that 1072 aircraft of the type would have been constructed by March 1942.
The Messerschmitt Bf 109 F-1 was powered by a Daimler-Benz DB 601 N engine. It was a 12-cylinder, inverted-vee, inline engine with a displacement of 3390 cm³. It developed a maximum output of 1,175 hp. Maximum rpm at take-off/emergency power was 2600 at a boost pressure of 1.35 ata. “Climb and Combat Power”7 at 5400 meters was 1060 hp at 2400 rpm and 1.3 ata. Continuous power rating was 950 hp at 2300 rpm and 1.2 ata. The DB 601 N was similar to the earlier DB 601 A; its higher power was attained through the use of higher-octane C3 fuel and higher compression ratios. Its production continued until October 1939. The engine drove a VDM 9-11207A three-bladed metal propeller of constant speed type, with a diameter of 9 ft 10 in (3000 mm). The aircraft was equipped with a lever for manual adjustment of the propeller pitch in case the constant speed governor failed.
The oil tank of 56.5 litre capacity (it was normally filled with 50 litres of ‘Intava 100’, ‘Rotring’ or ‘Aero Shell mittel’ oils) was moved on top of the engine reduction gear’s housing. The oil had to be changed every 8-10 hours of engine running time. The oil cooler was built into the lower cowling. Airflow through it was automatically regulated by means of a thermostat and a hydraulically operated cooling flap. The engine was cooled by a mixture of water and ethylene glycol (in 1:1 proportion), together with 1.5% of Schutzöl 39 anti-corrosion additive. The coolant mixture was stored in two header tanks with a total capacity of 35 litres, located on either side of the engine. The underwing radiators were installed behind the main spar and fitted with flaps to regulate the airflow. The split flaps located behind the radiators were operated via hydraulic actuators and thermostatically controlled.
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