The Arado Ar 240 was a 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 airframes used for a variety of test purposes.
The Ar 240 came about as the response to a 1938 request for a much more capable 2nd generation heavy fighter to replace the Messerschmitt Me 110, which was becoming outdated. Both Arado and Messerschmitt responded. Messerschmitt's response, the Me 210, was essentially a cleaned up version of the 110 with more power, and would be able to enter service quickly. Arado's design was considerably more ambitious, 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 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 cockpits, which dramatically lower pilot fatigue for any flight above about 15,000ft. 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 turrets on the top and bottom of the aircraft. For the Ar 240 design, the Arado engineers combined all of this research into a single airframe.
For outright performance they used as small a wing as reasonable, thereby lowering 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 ailerons would remain in place while the lower portion extended rearward, making the entire wing grow longer.
The Daimler-Benz DB 601 engines were conventionally installed and equipped with a four blade fully-adjustable propeller. The radiators were somewhat unique however, consisting of an annular block located in front of the engine in an oversized propeller spinner, with the air entering through a large hole in the front of the spinner and exiting out cowl flaps. This made the plane look as if it was mounting a radial engine, and this part of the design was so successful that it was used on most German designs for the rest of the war.
The fuel cells 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 breaks, so a "petal" type break was installed at the extreme rear of the fuselage which opened to the sides when activated. When closed the break 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 them to stick through 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 330kg/m², compared to say 100 for a single-seat fighter.
Technical specifications were first published in October 1938, followed by detailed plans later that year. In May 1939 the RLM ordered a run of six prototypes. The first Ar 240 V1 prototype, DD+QL, took to the air on June 25th, 1940, and immediately proved to have terrible handling in all three axis, and also tended to overheat during taxing.
The handling was thought to be the result of the aeilerons 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 breaks 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 April 6th, 1941, and spend most of its life at the factory as a test plane.
V3 followed, the first to be equipped with the FA 9 rear-firing armament system, developed jointly by Arado and DVL, armed with a 7.92mm MG 81Z twin machine gun. V4 was the first to include an operational dive brake, and flew on June 19th, 1941. V5 and V6 followed in December and January, including the upgraded FA 13 system using two 13mm MG 131s 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.
Weapons on the A-0 Model:
MG 17 machine gun, MG 81 machine gun
Arado Ar E.654
Weapons on the C-0 Model:
MG 151 machine gun, MG 131 machine gun, and up to nearly 4000lbs of bombs.
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