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

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