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Spitfire Mk.V - Technical development

In the end of 1940, the new aircraft were arriving at the units
in their nal weapon and equipment conguration as full-ed-
ged, fully functional combat aircraft. Earlier manufactured
airplanes were continuously upgraded with the installation of
armor and more modern equipment to meet the standards of
the newly manufactured Spitres. However, during the same
time, the modernized Bf 109 versions were arriving at the Ger-
man Luftwae ghter units. The Spitres were able to keep up
the pace with Bf 109E-7 quite successfully when they appeared
in the fall 1940, but with the arrival of Bf 109F-1 and F-2 in the
end of 1940 and beginning of 1941, the tables turned in favor
of the Germans. In order to counter the growing German tech-
nical supremacy, the Spitres’ performance had to be improved
rapidly.
A traditional way to increase the aircraft performance is to in-
stall the more powerful engine. The rst attempt to develop a
more powerful Spitre version was the project Improved Spit-
re, later renamed Superiority Spitre, launched as early as the
beginning of 1939. The prototype with the factory designation
Type 330 and military one as Spitre Mk.III was ready for its
maiden ight in March 1940. It was designed by modifying the
standard Spitre Mk.I serial number N3927. The airframe was
modied by installing a new Rolls-Royce Merlin RM 2SM engi-
ne, the future Merlin XX, featuring a single-stage, two-speed
compressor with the maximum output of 1,320 hp (1,037 kW).
In order to accommodate Merlin XX, the engine bearers were
strengthened and the nose lengthened by four inches.
The wingspan was shortened to 9.30 meters by removing the
wingtips and shortening the ailerons while the internal design
remained unchanged. During the ight trials, the prototype
apparently never reached the calculated maximum airspeed of
644 kph at 6,400 meters, the maximum recorded speed is said
to be 620 kph which was still an outstanding improvement in
comparison to Mk.I performance. Air Ministry demanded that
the large-scale production of Spitre Mk.III was accelerated,
however there was a serious obstacle to this eort due to the
complicated development of Merlin XX and teething troubles
with its large-scale production. In the fall 1940, the available
engines were utilized for Hurricane Mk.II and Deant Mk.II up-
grades and they were also installed in Bristol Beaughter Mk.II,
Avro Lancaster B Mk.I, Mk.III and Mk.IV and Handley Page Hali-
fax Mk.Il and Mk.V. There were none left for Spitres and the
idea of an accelerated, large-scale Spitre Mk.III production
was silently swept under the table. The smaller series of photo-
-reconnaissance Spitres PR Mk.III was manufactured under the
same designation, mostly by converting Spitres Mk.I.
Merlin 45
Once the Merlin XX installation proved to be more and more
complicated, in the end of 1940 Rolls-Royce company oered
a feasible and fast solution in the form of parallelly developed
and easier to manufacture engine Merlin RM5S later marked
Merlin 45. It featured a one-stage, single-speed compressor op-
timized for high altitudes, its output at 5,400 meters was 1,210
hp (902 kW), some sources state rather optimistic, and to tell
the truth, less probable output of 1,440 hp (1,074 kW). Merlin
45 had the same dimensions as Merlin III powering Spitres Mk.I
and its design enabled Merlin III upgrade to Merlin 45 standard
by replacing the compressor. This facilitated the simple insta-
llation into the current Spitre Mk.I and II airframes and the
conversion of the already manufactured aircraft as well. RR
company promised to supply 300 Merlin 45 by March 1, 1941
and further 200 by April 1.
The rst airframe to receive the new engine, modied from
Merlin XX, was supposedly Spitre Mk.I K9788 on December 26,
1940, in Boscombe Down. It was followed by PR Mk.III X4334,
converted into the photo-reconnaissance version from Spitre
Mk.I, which took to the air on January 13, 1941, from the Rolls
Royce factory airport in Hucknall. Spitre Mk.I N3053, too tes-
t-own on February 13, 1941, in Hucknall, was another conver-
sion. Right after both airplanes were own over to Boscombe
Down for further testing. The ight trials recorded the maxi-
mum speed of 593 kph at 6,100 meters was recorded during
the ight trials, climbing time to this altitude was 6 min and
12 seconds and the operational ceiling 11,590 meters. The trial
also discovered the problems with the constant-speed propel-
lers De Havilland when oil in their control system was freezing
at high altitudes. There were troubles with the Mk.II oil cooler
as well as it was not ecient enough for the more powerful
engine. Even though this was considered an interim solution, as
the Spitre Mk.III production was still being planned, the order
SPITFIRE Mk.V HISTORY
In the course of 1940, the Spitre Mk.I large scale production at Supermarine company has been ne-tuned so it
could meet the Air Ministry orders, supply the RAF Fighter Command combat units with the new aircraft and re-
plenish the combat losses. The situation was similar at Castle Bromwich Aircraft Factory in Birmingham which after
some initial organizational problems reliably supplied the ghter squadrons with license-built, and, compared to
Mk.I, slightly improved Spitres Mk.II.
HISTORY
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December 2025
Info EDUARD