The Messerschmitt Bf 109F Friedrich
Externally the Bf 109F had many aerodynamic improvements over the E series.
On later aircraft the left hand exhaust was fitted with a metal shield to stop exhaust fumes from entering the supercharger intake. The canopy stayed essentially the same as that of the E-4 although the handbook for the F stipulated that the forward, lower triangular panel to starboard was to be replaced by a metal panel with a port for firing signal flares. A two-piece, all metal armour plate head shield was added to the hinged portion of the canopy, although some lacked the curved top section. A bullet-resistant windscreen could be fitted to the windscreen as an option. A boundary layer duct allowed continual airflow to pass through the airfoil above the radiator ducting and exit from the trailing edge of the upper split flap. The lower split flap was mechanically linked to the central 'main' flap, while the upper split flap and forward bath lip position were regulated via a thermostatic valve which automatically positioned the flaps for maximum cooling effectiveness.
In 1941 'cutoff' valves were introduced which allowed the pilot to shut down either wing radiator in the event of one being damaged; this allowed the remaining coolant to be preserved. The valves were only delivered to frontline units as kits, the number of which, for unknown reasons, was limited. Other features of the redesigned wings included new leading edge slats, which were slightly shorter but had a slightly increased chord, and new rounded, removable wingtips which changed the profile of the wings and increased the span slightly over that of the E series. The redesigned wing made the internal mounting of guns impractical, so armament was revised.
The armament of the Bf 109F consisted of the two MG 17 above the engine plus a Motorkanone cannon firing through the propeller hub: The early F versions were equipped with the MG FF/M cannon, the F-2 got the 15 mm MG 151, and from F-4 on the 20 mm MG 151/20 was used. Only after a lack of spare parts, did he accept an F. Later on, an attachment of underwing 20 mm cannons addressed the issue of fire-power, but at a price to performance.