The Messerschmitt Bf109F "Franz"

Late in 1940, based upon lessons learned in the Battle of Britain, Willy Messerschmitt's Augsburg design team reworked their notorious Bf109. Previously, it had been the finest fighter in the world, but its supremacy was seriously challenged by the British Spitfire. The result was the F series: aerodynamically streamlined, making it faster, and far more maneuverable than the previous E, or "Emil" series. The Franz variant was short lived, however, as the need for more heavily armed bomber interceptors grew.

More extensive aerodynamic improvements necessary to take full advantage of the increased power available from later Daimler Benz engines were initiated in the spring of 1940. A standard Bf 109 E airframe was fitted with a 880 kW (1200 HP) Daimler Benz DB 601 E-1 engine housed in an entirely redesigned cowling. The supercharger air intake was redesigned and positioned further out from the engine cowling to increase the ram effect, the airscrew spinner was enlarged, and the diameter of the airscrew was reduced by some 15 cm (6 inch). Shallower underwing radiators were fitted, incorporating boundary layer by-passes and the raced tailplane was replaced by a cantilever structure. This experimental machine was flown for the first time on July 10, 1940, at Augsburg-Haunstetten, and subsequently served as the first prototype of the BF 109 F-series.

The BF 109 E embedded all the modifications included on the experimental machine and also an extensively redesigned wing which was tested on two further E frames. The new wing featured rounded tips and slightly increased span. The slotted ailerons were replaced by Frise-type surfaces, and plain flaps of reduced area replaced the slotted flaps that had been standard on all previous models. In addition, a retractable tail wheel was fitted. The first pre-production BF 109 F-0 fighters were delivered to Luftwaffe test centers for evaluation late in 1940. these were powered by the Daimler Benz dB 601 N engine which also powered the majority of the BF 109 F-1 production batches, and an armament of two MG 17 machine guns and one MG FF cannon was carried.

The first BF 109 F-1 fighters were delivered to operational units in January 1941, but in February three earlier production machines were lost in temporarily inexplicable circumstances. In each case the pilot announced over the radio that his engine was vibrating violently, and immediately thereafter his aircraft dived out of control, the pilot having no time to bail out. A few weeks later a forth accident where the tail assembly of a BF 109 F-1 broke off in midair. Upon examination it was discovered that all the screws on the tail assembly / fuselage joint had been torn out. This could only have been caused by tremendous vibrations for which the engine could not be held responsible as it was found to have suffered damage only in the crash. Suspicion then fell on the tail spar since the rivets between the ribs and the elevators were all loose, missing or broken. Prolonged investigations ascertained that when the bracing struts of the BF 109 E tail assembly were omitted on the BF 109 F and stronger but less ribbing used, the proportions of the rigidity to the strength of the member was altered. The result was that the tailplane had a frequency of oscillation which, at certain rpm, was overlapped by the engine , and resultant sympathetic vibrations tore out the tail spars.

Within a few months of the service debut of the BF 109 F-1, in July 1941, a well-known German fighter pilot, Peter Pingel, was forced down over Britain. His BF 109 F-1 being virtually intact. This aircraft was subsequently repaired enabling the British test pilots to ascertain its handling characteristics and performance.

The BF 109 F-2 differed from the initial production model in having the engine mounted MG FF replaced by a 15 mm MG 151 which substantially increased fire power because of its higher velocity and better trajectory. However, there were conflicting opinions among the leading German fighter pilots concerning the armament of the BF 109 F. Adolph Galland considered the reduced number of guns to be a retrogressive step, while Werner Mölders favored this light armament. Later, the BF 109 F-1/R1 was to appear with a 20 mm MG 151 cannon mounted in a gondola under each wing; but while this improved the fighter's effectiveness as a bomber destroyer, it adversely affected the machines power of maneuver and reduced its potency fighter-versus-fighter combat.

The BF 109 F.2/Z had GM-1 power boosting equipment, and the BF 109 F-2/Trop was a tropicalized version for use in North Africa. Both the BF 109 F-1 and BF 109 F-2 production models were intended to have the Daimler Benz dB 601 E engine of 955 kW (1300 HP), but delivery delays had necessitated the installation of the Daimler Benz dB 601 N, and was not until the BF 109 F-3 appeared on the production lines early in 1942 that the Daimler Benz dB 601 E was installed. With this engine the BF 109 F-3 could attain a maximum speed of 628 km/h (390 mph) at 6700 m (22000 feet). Normal cruising range was 710 km (440 miles) at 500 km/h (310 mph) at 5000 m (16500 feet), and the service ceiling was 11300 m (37000 feet). Empty and loaded weights were 1964 kg (4330 lb) and 2746 kg (6054 LB) respectively, and the wing loading had risen to 34.8 LB/sq feet. The BF 109 F-4 had the engine-mounted 15 mm MG 151 cannon replaced by a 20 mm MG 151, and the BF 109 F-4/B and BF 109 F-4/trop were fighter-bomber and tropicalized versions respectively. The BF 109 F-4/R1 could have a GM-1 power boosting system in place of the additional 20 mm cannon underwing, and it was intended to fit four RZ 65 air-to-air or air-to-ground rocket missiles on underwing racks, but this armament was never perfected for operational use. The BF 109 F-5 was primarily for long-range reconnaissance duty, carrying a 66 Imperial gallon drop tank and the BF 109 F-6 was another reconnaissance variant which, generally unarmed, had a RB 50/30, RB 20/30 or RB75/30 camera in place of the radio.

Several BF 109 F-series airframes were utilized for experimental purposes. One BF 109 F-1 was fitted with boundary layer fences for comparison purposes with the leading-edge slots; one was fitted with an elongated wing for high-altitude trials, and another had a vee-type (butterfly) tail assembly and two others had single and twin nose wheels
A total of 2628 BF 109 E and BF 109 F fighters was produced in 1941, and of this total some 60 per cent was produced by the Erla plant at Leipzig-Mockau (683) and the WNF factories at Drelitzsch and Wiener Neustadt (836).