The Messerschmitt Me 262 was the first operational jet
fighter in the world. Its Jumo 004 turbojet powerplants and swept wing made it
one of the most extraordinary designs of World War II. The Me 262A-1a achieved
an incredible top speed for its time of 870 km/h (497 mph) at an altitude of
6000 meters (19,685 feet), nearly 200 km/h faster than the North American P-51
Mustang. The Me 262 also employed the deathly firepower of four nose- mounted
MK-1 08 30 mm cannon. Its operational service, however, was hampered by the
unreliability of its engines and its weak undercarriage.
The first serial-produced Me 262A-1a (Werknummer
1300061VI+AF) took off on its maiden flight on 28 March 1944. The first Me 262s
were allocated to Erprobungskommando 262, a special fighter evaluation unit of
the Luftwaffe under the command of Hauptmann (Captain) Werner Thierfelder, on
19 April 1944 at Lechfeld airfield in Bavaria.
Leutnant (Lieutenant) Alfred Schreiber scored the first
victory with the Me 262, and the first victory ever of a jet-powered fighter,
when he shot down a Mosquito on 26 July 1944. The Blitzbomber (literally
"lightning bomber") version received the designation Me 262A-2a. The
Me 262A-2a had the upper two MK-108 cannons removed and a pair of ETC 503
Wikingerschijf ("Viking ship") bomb racks mounted on the nose undersurface.
The Me 262A-2a could carry either two SC-250 blast bombs or two SD-250
fragmentation bombs.
A total of 1,433 Me 262s were built, assembled at Leipheim
(Kuno I and Kuno IT), Schwabisch Hall-Hessental, Obertraubling near Regensburg,
Neuburg/Donau-Bruck, Eger, Kahla, and Brandenburg-Bliest. Messerschrnitt AG
made wide use of concentration camp prisoners and forced labor supplied by the
Waffen SS-owned Deutsche Erd- und Steinwerke GmbH (German Earth and Stone Works
Company) to keep Me 262 production at a rapid pace. Nearly 53,000 prisoners and
forced laborers were employed in the manufacture of parts, components, and
final assembly.
Czechoslovakia became the only other country in the world to
use the Messerschmitt jet fighter operationally. The Avia company at Cakovice
began building the Me 262 from components left behind in the country after the
end of World War II. The type received the designation S-92. A total of seven
S-92 and three CS-92 trainers were built, the last S- 92 being accepted on 24
September 1948. The S-92 became a training aircraft in 1949. Most S-92s and
CS-92s were phased out of service after 1951 and subsequently scrapped.
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The jet propelled Me 262 introduced in the last year of the
war was 100 mph faster than contemporary piston-engine fighters and well armed
with four 30mm cannons. [1] In a head-on attack, its 350 yards per second
closing rate was too fast to allow accurate aiming or to allow optimum use of
its short-ranged armament. To overcome this, German Jet pilots used the
"roller coaster" attack. Approaching from astern at about 6000 ft
above the bombers, the jets pushed over into a shallow dive starting about 3
miles away. They quickly built up speed such that the escorts could not follow
them. Diving down until they were about a mile behind and 1500 ft below, they
pulled up sharply to bleed off speed, leveling off at 1000 yds astern in
position to deliver an attack.
[1]Later in the war, the Germans introduced the Mk 108 30mm
heavy cannon capable of firing 600 11-ounce high explosive rounds per minute.
Three hits with this weapon were usually sufficient to bring down a Flying
Fortress. On the other hand it was a low velocity weapon and its effective
range was shorter than the 20-mm cannon forcing German pilots to fly even
closer to get hits.
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"I passed one that looked as if it was hanging
motionless in the air (I am too fast!). The one above me went into a steep
right-hand turn, his pale blue underside standing out against the purple sky.
Another banked right in front of the Me's nose. Violent jolt as I flew through
his airscrew eddies. Maybe a wing's length away. That one in the gentle
left-hand curve! Swing her round. I was coming from underneath, eye glued to
the sight (pull her tighter!). A throbbing in the wings as my cannon pounded
briefly. Missed him. Way behind his tail. It was exasperating. I would never be
able to shoot one down like this. They were like a sack of fleas. A prick of
doubt: is this really such a good fighter? Could one in fact, successfully
attack a group of erratically banking fighters with the Me 262?"
Johannes Steinhoff, Luftwaffe fighter ace.
The Junkers Jumo 004 was the world's first turbojet engine
in production and operational use, and the first successful axial compressor
jet engine ever built. Some 8,000 units were manufactured by Junkers in Germany
during late World War II, powering the operational Messerschmitt Me 262 fighter
jet and the Arado Ar 234 reconnaissance / bomber jet, along with prototypes
including the Horten Ho 229 aircraft. Variants of the engine were produced in
Eastern Europe for years following the war.
The first prototype 004A, which was constructed to run on
diesel fuel, was first tested in October 1940, though without an exhaust
nozzle. It was benchtested at the end of January 1941 to a top thrust of 430
kgf (4,200 N; 950 lbf), and work continued to increase the output, the RLM
contract having set a minimum of 600 kgf (5,900 N; 1,300 lbf) thrust.
Vibration problems with the compressor stators, originally
cantileverd from the outside, delayed the program at this point. Max Bentele,
as an Air Ministry consulting engineer with a background in turbocharger
vibrations, assisted in solving the problem. The original aluminium stators
were replaced with steel ones in which configuration the engine developed 5.9
kN (1,300 lbf) in August, and passed a 10-hour endurance run at 9.8 kN (2,200
lbf) in December. The first flight test took place on March 15, 1942, when a
004A was carried aloft by a Messerschmitt Bf 110 to run up the engine in
flight. The 004 used an eight-stage axial-flow compressor, with a number of
axial combustion chambers (made from sheet steel), and a one-stage turbine with
hollow blades.
On July 18, one of the prototype Messerschmitt Me 262s flew
for the first time under jet power from its 004 engines, and the 004 was
ordered into production by the RLM to the extent of 80 engines.
The initial 004A engines built to power the Me 262
prototypes had been built without restrictions on materials, and they used
scarce raw materials such as nickel, cobalt, and molybdenum in quantities which
were unacceptable in production. Franz realized that the Jumo 004 would have to
be redesigned to incorporate a minimum of these strategic materials, and this
was accomplished. All the hot metal parts, including the combustion chamber,
were changed to mild steel protected by an aluminum coating, and the hollow
turbine blades were produced from folded and welded Cromadur alloy (12%
chromium, 18% manganese, and 70% iron) developed by Krupp, and cooled by
compressed air "bled" from the compressor. The engine's operational
lifespan was shortened, but on the plus side it became easier to construct.
Production engines had a cast magnesium casing in two halves, one with
half-sections of stator assemblies bolted to it. The four front stators were
constructed from steel alloy blades welded to the mount; the rear five were
pressed steel sheet bent over the mount and welded on. Steel alloy compressor
blades dovetailled into slots in the compressor disk and were fixed by small screws.
The compressor itself was mounted to a steel shaft with twelve set screws. Jumo
tried a variety of attach compressor blades, beginning with solid steel, later
hollow sheet metal ones, welded on the taper, with their roots fitted over
rhomboidal studs on the turbine wheel, to which they were pinned and brazed.
The first production model of the 004B weighed 100 kg (220
lb) less than the 004A, and in 1943 had passed several 100 hour tests, with a
time between overhauls of 50 hours being achieved.
Later in 1943 the 004B version suffered turbine blade
failures which were not understood by the Junkers team. They focused on areas
such as material defects, grain size and surface roughness. Eventually, in
December, blade-vibration specialist Max Bentele was once again brought in
during a meeting at the RLM headquarters. He identified that the failures were
caused by one of the blades` natural fraquencies being in the engine running
range. His solution was to raise the frequency, by increasing the blade taper
and shortening them by 1 millimeter, and to reduce the operating speed of the
engine[6] from 9,000 to 8,700 rpm.
It was not until early 1944 that full production could
finally begin. These setbacks were the principal factor delaying the
Luftwaffe's introduction of the Me 262 into squadron service.
Given the lower-quality steels used in the 004B, these
engines typically only had a service life of some 10–25 hours, perhaps twice
this in the hands of a skilled pilot.[citation needed] Another shortcoming of
the engine, common to all early turbojets, was its sluggish throttle response.
Worse, it was fairly easy to inject too much fuel into the engine by throttling
up too quickly, allowing heat to build up before the cooling air could remove
it. This led to softening of the turbine blades, and was a major cause for
engine failures. Nevertheless, it made jet power for combat aircraft a reality
for the first time.
The exhaust area of the 004 featured a variable geometry
nozzle, which had a special restrictive body nicknamed the Zwiebel (German for
onion, due to its shape when seen from the side) which had roughly 40 cm (16
inch) of fore-and-aft travel to vary the jet exhaust's cross-sectional area for
thrust control, as the active part of a pioneering "divergent-convergent"
nozzle format.
One interesting feature of the 004 was the starter system,
which consisted of a Riedel 10 hp (7.5 kW) 2-stroke motorcycle engine hidden in
the intake, and essentially functioned as a pioneering example of an APU for
starting a jet engine. A hole in the extreme nose of the intake diverter body
contained a pull-handle for the cable which "turned-over" the piston
engine, which in turn spun up the turbine. Two small gasoline/oil mix tanks
were fitted within the upper perimeter of the annular intake's sheet metal
housing for fueling the Riedel two-stroke mechanical APU unit.
The Jumo 004 could run on three types of fuel:
J-2, its standard
fuel, a synthetic fuel produced from coal.
Diesel oil.
Aviation gasoline;
not considered desirable due to its high rate of consumption.
Costing RM10,000 for materials, the Jumo 004 also proved
somewhat cheaper than the competing BMW 003, which was RM12,000, and cheaper
than the Junkers 213 piston engine, which was RM35,000. Moreover, the jets used
lower-skill labor and needed only 375 hours to complete (including manufacture,
assembly, and shipping), compared to 1,400 for the BMW 801.
Production and maintenance of the 004 was done at the
Junkers works at Magdeburg, under the supervision of Otto Hartkopf.[11]
Completed engines earned a reputation for unreliability; the time between major
overhauls (not technically a TBO) was thirty to fifty hours, and may have been
as low as ten, though a skilled flyer could double the interval.[12] (The
competing BMW 003's was about fifty.) The process involved replacing turbine
blades (which suffered the most damage, usually from ingesting stones and such,
later known as fodding) and rebalancing the rotors; the starter and governor
would also be examined and replaced as needed. Combustors required maintenance
every twenty hours, and replacement at 200.
Between 5,000 and 8,000 004s were built; at the end of the
Second World War, production stood at 1,500 per month. The Fedden Mission, led
by Sir Roy Fedden, postwar estimated total jet engine production by mid-1946
could have reached 100,000 units a year, or more.
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