Arado Ar 240
Encyclopedia
The Arado Ar 240 was a German
twin-engine multi-role heavy fighter
aircraft developed for the Luftwaffe
during World War II
by Arado Flugzeugwerke
. Its first flight was in 1940, but problems with the design hampered development and it remained only marginally stable through the prototype
phase. The project was eventually cancelled, with the existing airframe
s used for a variety of test purposes.
responded. Messerschmitt's response, the Me 210
, was a totally new design, but thanks to Messerschmitt's experience with the Zerstörer ("Destroyer") concept, it would be able to enter service quickly. Arado's design was considerably more ambitious for the smaller firm, a dream project of Arado's chief designer, Walter Blume, since the mid-1930s. While it would take some time before deliveries of the Arado design could begin, the Reichsluftfahrtministerium
(German War Ministry, RLM) was nevertheless interested enough to order prototypes of both designs.
Prior to this point, Arado had invested heavily in several lines of basic research. One was the development of the "Arado travelling flap
" which offered excellent low-speed lift performance. Another was ongoing work into the design and construction of pressurized
cockpit
s, which dramatically lower pilot fatigue for any flight above about 4,500 m (14,760 ft). Finally, they had also invested in a technically advanced remote-control defensive gun system, which they had been experimenting with for several years. The system used a gunsight located in the rear cockpit, operated by the navigator
/gunner
, which had optics on both the top and bottom of the aircraft allowing aim in any direction. The gunsight was hydraulically connected to well-streamlined "pancake"-shaped turret
s on the top and bottom of the aircraft. For the Ar 240 design, the Arado engineers combined all this research into a single airframe.
For outright performance, they used as small a wing as reasonable, thereby lowering parasite drag
(at the expense of greater lift-induced drag
). Normally this would make the plane have "impossibly high" landing speeds, but this was offset by the use of a huge travelling flap and leading edge
slats
for high low-speed lift. When the flaps were extended, the upper portion of the aileron
s would remain in place while the lower portion extended rearward, essentially increasing the wing area.
The Daimler-Benz DB 601
inline engine
s were conventionally installed and equipped with a three-blade fully adjustable propeller
. The radiator
s were somewhat unique however, quite similar to those fitted to the Junkers Ju 88
which pioneered them, consisting of an annular block located in front of the engine, but with the Ar 240 partially covering each of them in an oversized propeller spinner, with the air entering through a large hole in the front of the spinner and exiting out the cowl
flaps. As with the Jumo inline-powered versions of the Ju 88, this made the plane look as if it was mounting a radial engine
, and the Ar 240, like later Jumo inline-powered fighter aircraft from the Focke-Wulf firm (the Fw 190 D, Ta 152 and twin engined Ta 154) also benefitted from the simpler setup of an annular radiator just forward of the engine.
The fuel cell
s in the wings were provided with a newly developed self-sealing
system that used thinner tank liners, allowing for more fuel storage. The liners could not be easily removed as they stuck to the outer surface of the tank, so in order to service them, the wing panelling had to be removable. This led to a complex system for providing skinning stiff enough to be handled in the field, complicating construction and driving up weight.
As with all German multi-use aircraft designs of the era, the aircraft was required to be a credible dive bomber
. The thick wing panelling wasn't suitable for piercing for conventional dive brake
s, so a "petal"-type brake was installed at the extreme rear of the fuselage
which opened to the sides when activated. When closed the brake looked like a stinger, extending beyond the horizontal stabilizer
and twin fins
.
Finally, the cockpit was fully pressurized. This would not have been easy if the armament had to be hand-operated by the gunner, as it would have required the guns to penetrate the rear of the cockpit canopy. However, the remote control system allowed for them to be located in turrets in the unpressurized rear of the fuselage.
All of this added weight combined with the small wing led to a very high wing loading
of 330 kg/m² (221 lb/ft²), compared to an average of about a 100 for a single-seat fighter.
.
The handling was thought to be the result of the ailerons being too small given the thick wing, so the second prototype was modified to have larger ones, as well as additional vertical fin area on the dive brakes to reduce yaw. In addition small radiators were added to the gear legs to improve cooling at low speeds, when the gear would normally be opened. Ar 240 V2, KK+CD, first flew on 6 April 1941, and spent most of its life at the factory in an experimental role.
Ar 240 V3 followed, the first to be equipped with the FA 9 rear-firing armament system, developed jointly by Arado and DVL, armed with a 7.92 mm (.312 in) MG 81Z machine gun
. Ar 240 V4 was the first to include an operational dive brake, and flew on 19 June 1941. Ar 240 V5 and V6 followed in December and January, including the upgraded FA 13 system using two 13 mm (.51 in) MG 131 machine gun
s in place of the MG 81Z for a considerable boost in firepower.
The Ar 240's excellent performance quickly led to the V3, V5 and V6 being stripped of their armament, including the defensive guns, and used as reconnaissance
aircraft over England
, where no other two-seater could venture by 1942.
Ar 240B: Proposed version
Ar 240 C-1: Heavy fighter version.
Ar 240 C-2: Night fighter
version.
Ar 240 C-3: Light bomber
version.
Ar 240 C-4: High-altitude reconnaissance version. The project was abandoned in favour of the Ar 440.
Ar 440: Improved variant with the fuselage stretched by 0.9m (35.5 in) and powered by the 1,900 hp (1,417 kW) DB 603G, the production aircraft would have had two 2,000 hp (1,491 kW) DB 627A/B engines. Prototype converted from a prototype Ar 240, total of four built in 1942. The type did not enter production and the programme was cancelled in 1943.
Nazi Germany
Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...
twin-engine multi-role heavy fighter
Heavy fighter
A heavy fighter is a fighter aircraft designed to carry heavier weapons or operate at longer ranges. To achieve acceptable performance, most heavy fighters were twin-engined, and many had multi-place crews....
aircraft developed for the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
by Arado Flugzeugwerke
Arado Flugzeugwerke
Arado Flugzeugwerke was a German aircraft manufacturer, originally established as the Warnemünde factory of the Flugzeugbau Friedrichshafen firm, that produced military hydroplanes during the First World War.-History:...
. Its first flight was in 1940, but problems with the design hampered development and it remained only marginally stable through the prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
phase. The project was eventually cancelled, with the existing airframe
Airframe
The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...
s used for a variety of test purposes.
Design and development
The Ar 240 came about as the response to a 1938 request for a much more capable second generation heavy fighter to replace the Messerschmitt Me 110, which was becoming outdated. Both Arado and MesserschmittMesserschmitt
Messerschmitt AG was a famous German aircraft manufacturing corporation named for its chief designer, Willy Messerschmitt, and known primarily for its World War II fighter aircraft, notably the Bf 109 and Me 262...
responded. Messerschmitt's response, the Me 210
Messerschmitt Me 210
The Messerschmitt Me 210 was a German heavy fighter and ground-attack aircraft of World War II. The Me 210 was designed to replace the Bf 110 in heavy fighter role; design started before the opening of World War II. The first examples of the Me 210 were ready in 1939, but they proved to have poor...
, was a totally new design, but thanks to Messerschmitt's experience with the Zerstörer ("Destroyer") concept, it would be able to enter service quickly. Arado's design was considerably more ambitious for the smaller firm, a dream project of Arado's chief designer, Walter Blume, since the mid-1930s. While it would take some time before deliveries of the Arado design could begin, the Reichsluftfahrtministerium
Reich Air Ministry
thumb|300px|The Ministry of Aviation, December 1938The Ministry of Aviation was a government department during the period of Nazi Germany...
(German War Ministry, RLM) was nevertheless interested enough to order prototypes of both designs.
Prior to this point, Arado had invested heavily in several lines of basic research. One was the development of the "Arado travelling flap
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
" which offered excellent low-speed lift performance. Another was ongoing work into the design and construction of pressurized
Cabin pressurization
Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...
cockpit
Cockpit
A cockpit or flight deck is the area, usually near the front of an aircraft, from which a pilot controls the aircraft. Most modern cockpits are enclosed, except on some small aircraft, and cockpits on large airliners are also physically separated from the cabin...
s, which dramatically lower pilot fatigue for any flight above about 4,500 m (14,760 ft). Finally, they had also invested in a technically advanced remote-control defensive gun system, which they had been experimenting with for several years. The system used a gunsight located in the rear cockpit, operated by the navigator
Navigator
A navigator is the person on board a ship or aircraft responsible for its navigation. The navigator's primary responsibility is to be aware of ship or aircraft position at all times. Responsibilities include planning the journey, advising the Captain or aircraft Commander of estimated timing to...
/gunner
Air gunner
An air gunner a.k.a. aerial gunner is a member of an air force aircrew who operates flexible-mount or turret-mounted machine guns or autocannons in an aircraft...
, which had optics on both the top and bottom of the aircraft allowing aim in any direction. The gunsight was hydraulically connected to well-streamlined "pancake"-shaped turret
Gun turret
A gun turret is a weapon mount that protects the crew or mechanism of a projectile-firing weapon and at the same time lets the weapon be aimed and fired in many directions.The turret is also a rotating weapon platform...
s on the top and bottom of the aircraft. For the Ar 240 design, the Arado engineers combined all this research into a single airframe.
For outright performance, they used as small a wing as reasonable, thereby lowering parasite drag
Parasitic drag
Parasitic drag is drag caused by moving a solid object through a fluid medium . Parasitic drag is made up of many components, the most prominent being form drag...
(at the expense of greater lift-induced drag
Lift-induced drag
In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is a drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars...
). Normally this would make the plane have "impossibly high" landing speeds, but this was offset by the use of a huge travelling flap and leading edge
Leading edge
The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one....
slats
Leading edge slats
Slats are aerodynamic surfaces on the leading edge of the wings of fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a result of angle of attack and speed, so by deploying slats an aircraft can fly at slower...
for high low-speed lift. When the flaps were extended, the upper portion of the aileron
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
s would remain in place while the lower portion extended rearward, essentially increasing the wing area.
The Daimler-Benz DB 601
Daimler-Benz DB 601
|-See also:-Bibliography:* Mankau, Heinz and Peter Petrick. Messerschmitt Bf 110, Me 210, Me 410. Raumfahrt, Germany: Aviatic Verlag, 2001. ISBN 3-92550-562-8.* Neil Gregor Daimler-Benz in the Third Reich. Yale University Press, 1998-External links:...
inline engine
Inline engine (aviation)
In aviation, an inline engine means any reciprocating engine with banks rather than rows of cylinders, including straight engines, flat engines, V engines and H engines, but excluding radial engines and rotary engines....
s were conventionally installed and equipped with a three-blade fully adjustable propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
. The radiator
Radiator (engine cooling)
Radiators are used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine....
s were somewhat unique however, quite similar to those fitted to the Junkers Ju 88
Junkers Ju 88
The Junkers Ju 88 was a World War II German Luftwaffe twin-engine, multi-role aircraft. Designed by Hugo Junkers' company through the services of two American aviation engineers in the mid-1930s, it suffered from a number of technical problems during the later stages of its development and early...
which pioneered them, consisting of an annular block located in front of the engine, but with the Ar 240 partially covering each of them in an oversized propeller spinner, with the air entering through a large hole in the front of the spinner and exiting out the cowl
Cowling
A cowling is the covering of a vehicle's engine, most often found on automobiles and aircraft.A cowling may be used:* for drag reduction* for engine cooling by directing airflow* as an air intake for jet engines* for decorative purposes...
flaps. As with the Jumo inline-powered versions of the Ju 88, this made the plane look as if it was mounting a radial engine
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...
, and the Ar 240, like later Jumo inline-powered fighter aircraft from the Focke-Wulf firm (the Fw 190 D, Ta 152 and twin engined Ta 154) also benefitted from the simpler setup of an annular radiator just forward of the engine.
The fuel cell
Fuel tank
A fuel tank is safe container for flammable fluids. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled or released into an engine...
s in the wings were provided with a newly developed self-sealing
Self-sealing fuel tank
In aviation, self-sealing fuel tank is a fuel tank technology in wide use since World War II that prevents fuel tanks primarily on aircraft from leaking fuel and igniting after being damaged by enemy fire....
system that used thinner tank liners, allowing for more fuel storage. The liners could not be easily removed as they stuck to the outer surface of the tank, so in order to service them, the wing panelling had to be removable. This led to a complex system for providing skinning stiff enough to be handled in the field, complicating construction and driving up weight.
As with all German multi-use aircraft designs of the era, the aircraft was required to be a credible dive bomber
Dive bomber
A dive bomber is a bomber aircraft that dives directly at its targets in order to provide greater accuracy for the bomb it drops. Diving towards the target reduces the distance the bomb has to fall, which is the primary factor in determining the accuracy of the drop...
. The thick wing panelling wasn't suitable for piercing for conventional dive brake
Dive bomber
A dive bomber is a bomber aircraft that dives directly at its targets in order to provide greater accuracy for the bomb it drops. Diving towards the target reduces the distance the bomb has to fall, which is the primary factor in determining the accuracy of the drop...
s, so a "petal"-type brake was installed at the extreme rear of the fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
which opened to the sides when activated. When closed the brake looked like a stinger, extending beyond the horizontal stabilizer
Tailplane
A tailplane, also known as horizontal stabilizer , is a small lifting surface located on the tail behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed wing aircraft such as helicopters and gyroplanes...
and twin fins
Vertical stabilizer
The vertical stabilizers, vertical stabilisers, or fins, of aircraft, missiles or bombs are typically found on the aft end of the fuselage or body, and are intended to reduce aerodynamic side slip. It is analogical to a skeg on boats and ships.On aircraft, vertical stabilizers generally point upwards...
.
Finally, the cockpit was fully pressurized. This would not have been easy if the armament had to be hand-operated by the gunner, as it would have required the guns to penetrate the rear of the cockpit canopy. However, the remote control system allowed for them to be located in turrets in the unpressurized rear of the fuselage.
All of this added weight combined with the small wing led to a very high wing loading
Wing loading
In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing. The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly,...
of 330 kg/m² (221 lb/ft²), compared to an average of about a 100 for a single-seat fighter.
Testing and evaluation
Technical specifications were first published in October 1938, followed by detailed plans later that year. In May 1939, the RLM ordered a batch of six prototypes. The first Ar 240 V1 prototype, DD+QL, took to the air on 25 June 1940, and immediately proved to have poor handling in all axes, and it also tended to overheat during taxiingTaxiing
Taxiing refers to the movement of an aircraft on the ground, under its own power, in contrast to towing or push-back where the aircraft is moved by a tug...
.
The handling was thought to be the result of the ailerons being too small given the thick wing, so the second prototype was modified to have larger ones, as well as additional vertical fin area on the dive brakes to reduce yaw. In addition small radiators were added to the gear legs to improve cooling at low speeds, when the gear would normally be opened. Ar 240 V2, KK+CD, first flew on 6 April 1941, and spent most of its life at the factory in an experimental role.
Ar 240 V3 followed, the first to be equipped with the FA 9 rear-firing armament system, developed jointly by Arado and DVL, armed with a 7.92 mm (.312 in) MG 81Z machine gun
MG 81 machine gun
The MG 81 was a German belt fed 7.9 mm machine gun, used in flexible installations in World War II Luftwaffe aircraft, replacing the older drum magazine-fed MG 15....
. Ar 240 V4 was the first to include an operational dive brake, and flew on 19 June 1941. Ar 240 V5 and V6 followed in December and January, including the upgraded FA 13 system using two 13 mm (.51 in) MG 131 machine gun
MG 131 machine gun
The MG 131 was a German 13 mm caliber machine gun developed in 1938 by Rheinmetall-Borsig and produced from 1940 to 1945...
s in place of the MG 81Z for a considerable boost in firepower.
The Ar 240's excellent performance quickly led to the V3, V5 and V6 being stripped of their armament, including the defensive guns, and used as reconnaissance
Aerial reconnaissance
Aerial reconnaissance is reconnaissance that is conducted using unmanned aerial vehicles or reconnaissance aircraft. Their roles are to collect imagery intelligence, signals intelligence and measurement and signature intelligence...
aircraft over England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
, where no other two-seater could venture by 1942.
Variants
Ar 240 A-0: Four pre-production aircraft.Ar 240B: Proposed version
Ar 240 C-1: Heavy fighter version.
Ar 240 C-2: Night fighter
Night fighter
A night fighter is a fighter aircraft adapted for use at night or in other times of bad visibility...
version.
Ar 240 C-3: Light bomber
Light bomber
A light bomber is a relatively small and fast class of military bomber aircraft which were primarily employed before the 1950s. Such aircraft would typically not carry more than one ton of ordnance....
version.
Ar 240 C-4: High-altitude reconnaissance version. The project was abandoned in favour of the Ar 440.
Ar 440: Improved variant with the fuselage stretched by 0.9m (35.5 in) and powered by the 1,900 hp (1,417 kW) DB 603G, the production aircraft would have had two 2,000 hp (1,491 kW) DB 627A/B engines. Prototype converted from a prototype Ar 240, total of four built in 1942. The type did not enter production and the programme was cancelled in 1943.