HISTORY
June 2023
new aircraft on the production line were
equipped with separation valves as standard,
which, given the date of the regulation, would
involve aircraft from the F-4 version on. The
claim from the same source that the shortage
of these kits and the high demand for them led
to a race by groundcrew to cannibalize these
items from shot down and damaged aircraft
seems to be a reasonable one, where most of the
Bf 109F-2s produced and part of the F- 4 (as well
as all Bf 109 Es still in service) did not have these
valves. Even the Bf 109F-4s produced had them
as standard from the second half of July 1941 at
the earliest, and possibly even later. The use
of these valves cannibalized from aircraft that
were no longer combat capable makes sense.
A claim regarding the stopping of the installation
of these valves in the Bf 109G is probably also
erroneous. These valves are, for example,
documented on a British captured Bf 109 G-2
carrying the W.Nr. 10639.
Photo: SDASM
OIL COOLERS
The oil cooler was located as in the Bf 109E,
under the engine. Like the coolant radiators, it
was a new design, developed for use with the
DB 601E engine and was already installed in the
Bf 109F-1 powered by the DB 601N. The Fö 699B oil
cooler (9-6130A – Vogt) had a frontal area of 590
cm2 , the two-position control flap at the outlet
of the cooler (outlet edge) was hydraulically
opened and automatically controlled by
a thermostat. It had only two positions, closed/
open, the difference between the two positions
was 4 cm. The control hydraulics were not
connected to the aircraft's hydraulic system as
such, but used oil from the engine's oil pan. This
amounted to 35 liters of oil (and 8 liters of air)
in the DB 601N engine, and 36.8 liters of oil and
6 liters of air for the DB 601E. The Bf 109F-4/Z
and part of Bf 109 F-4 Trop production were fitted
with the new Fö 870 radiator (9-6150 Vogt). It had
a frontal area of 650 cm2 and a depth of 250 mm.
Vogt also states that the first F-4/Z still had the
original smaller radiator Fö 699B) with a frontal
area of 590 cm2. The hydraulic system of the
Bf 109F was expanded compared to the Bf 109E
and, in addition to retraction of the main landing
gear, also controlled the retraction of the
tailwheel and the regulating flaps of the coolant
radiators.
Bf 109 F-0 PH+BE already had oval wingtips, but the intake turbocharger had a rectangular cross-section,
characteristic of the Bf 109 F-1 produced by the WNF factory.
Photo: SDASM
was updated. The coolant radiators had
a completely new design compared to those of the
Bf 109E series of aircraft, which not only ensured
a higher efficiency of the cooling system, but was
also simpler to manufacture. The manufacturing
complexity of the new radiators was said to be
50% that of the older Bf 109 radiators. Aluminum
alloys were used extensively in the construction
of the new radiators. Although the new radiators
were larger, with a frontal area of 0.334 m2
compared to the Bf 109E's 0.292 m2, they were
logically more efficient due to the cross fall,
and they were also aerodynamically more
advantageous due to the fact that they were
embedded deeper into the wing. The air flow was
regulated by two hydraulically opening flaps on
the trailing edge of the wing, the opening and
relative position of which were automatically
controlled by a thermostat. At the same time,
when the flaps were extended, the flap on the
front of the radiator opened. If necessary, the
pilot could bypass the automatic the automatic
feature and set the coolers manually with a lever
in the cabin. The cooling system was filled with
75 liters of a mixture of glycol and water, two
separate overflow tanks of the cooling system,
each with a volume of 5 liters, were located on
the sides of the engine block (on the sides of the
crankcase). In the Bf 109E, the U-shaped coolant
overflow tank was located on the front of the
engine block.
The cooling system of the Bf 109E and the first
Bf 109Fs was extremely sensitive to damage,
most often by gunfire. Any interference with
the radiator or other part of the cooling system
meant a rapid loss of coolant, followed by
engine seizure. This was a problem common
to all fighters powered by liquid-cooled inline
engines. The P-51 Mustang, for example, had
a large underbody radiator which was extremely
susceptible to damage and a single lucky shot
meant an almost immediate engine seizure and
a total loss of the aircraft. Splitting the cooling
system between two radiators, one under each
wing, offered a theoretical advantage. But this
was not the case with the Bf 109E and Bf 109F-1
and F-2, where the cooling system was a singlecircuit affair with one pump. In February and
March 1941, a design modification of the system
was successfully tested on the test Bf 109E,
consisting of the introduction of separation
valves (Kühlerabschaltventile), which, in the
event of damage to one of the radiators, enabled
the pilot to close it and separate it from the other
part of the cooling circuit. This modification
(Kühlerabschaltung) was introduced into
series production on July10, 1941 by regulation
Änderungsmotteilung I 181. The earlier claim
(Prien/Rodeike) that these valves were supplied
as retrofit kits for previously produced aircraft
has no basis in any known regulation and
appears that such sets were actually never
produced and delivered to units. To the contrary,
Bf 109 F-4 od 10. (Jabo)/JG 2 in France during the summer of 1942. The aircraft sports reinforcing stringers
on the rear fuselage. The photo shows the typical position of the open landing flaps and the combined glycol
cooler and landing flaps.
INFO Eduard
9