Arado Ar 240

Arado Ar 240
Type:	Destroyers, high-speed bombers, high-altitude fighters, scouts, night fighters
Design country:	German Empire
Manufacturer:	Arado Flugzeugwerke GmbH
First flight:	May 10, 1940
Commissioning:	only troop trials
Number of pieces:	14th

The Arado Ar 240 was a destroyer and high-speed bomber made by Arado Flugzeugwerke in the early 1940s. It was commissioned directly by the Technical Office of the Reich Aviation Ministry (RLM) without a tender and was intended to serve as a progressive addition to the Messerschmitt Me 210 , which was being developed at the same time .

The aircraft was designed as a destroyer , high-speed bomber , high altitude fighter, reconnaissance aircraft and night fighter. A special constructive feature was the patented "Arado Wanderflügel", which was a further development of the Fowler flaps . These lift aids with great depth became necessary because the construction was optimized for high speed with a minimal wing area, which inevitably brought a relatively high wing loading with it.

history

The starting point for the development of the Ar 240 was the efforts of the Technical Office of the RLM to develop another design as a destroyer and high-speed bomber in addition to the Me 210. This should be more advanced than the Messerschmitt design. The aim was to achieve the smallest surfaces, smallest cross-sections and thus minimum air resistance. The Ar 240E was to have a fuselage cross-sectional area of ​​1.42 m², only slightly larger than that of a Messerschmitt Bf 109 with 1.05 m². The engine arrangement and design should also be aerodynamically optimized. With the installation of dive brakes, a pressurized cabin and a weapon turret planned at the same time , however, a significant increase in weight and thus a critical surface load of up to 390 kg / m² was to be expected.

That is why the use of auxiliary wings to increase lift was of crucial importance. After an initially planned so-called “fan aileron”, the “Arado moving wing” was finally used. This was a piece of the wing profile, with the fixed front wing already terminating at the rear before the end of the profile. The remaining part of the profile protruded with its front part under the fixed part of the profile and could be moved and pivoted backwards.

In the summer of 1939, the construction of two prototypes began, which were completed within 13 months. The planes did not have any military installations, as the remote-controlled weapon turrets were not yet available. The flight tests of these defensive weapons were carried out within three months of 1940 in a converted Messerschmitt Bf 110  C-1. However, due to icing problems, the development of the associated periscopes was delayed, and the optics became blind, especially during dives. The problem was finally solved by overpressure filling with pre-dried air. The visual range monitoring by the optics of the periscope sight was not yet optimally solved, as even with 1.6x magnification of the image the shooter could not capture his target early enough.

The first flight of the Ar 240 V1 took place on May 10, 1940, followed by the V2 two months later. Both aircraft showed extremely poor flight characteristics in the subsequent tests. As a result, the fuselage was first lengthened and the cabin moved forward from the area of ​​the center wing into the nose tip. With these changes, testing of the Ar 240 V3 began in spring 1941, but the lateral stability still proved to be too low. As a remedy, additional auxiliary fins were provided on the top and bottom of the "tail rump" (dive brakes). To remedy the likewise inadequate lateral stability, the V3 was given the new "moving wing" ailerons. In this condition it was handed over to the Air Force for troop trials in the summer of 1941 . Because of the unreliability, both the remote-controlled and the rigid weapons were removed and the machine was used as a reconnaissance aircraft, whereby it could evade any attack by a fighter because of the high speed it could achieve.

The Ar 240 V4 was built as a dive bomber and received DB-603A engines for the first time , while the first three prototypes were still equipped with the DB 601 . The V5 and V6 took off on their maiden flights in October 1942 and were supposed to be the two model machines for the A-0 pilot series. The flight characteristics could be significantly improved by using a new profile with a larger thickness reserve . The AGO works in Oschersleben were intended to build 40 more Ar 240 A- 0s . The production facility and the material cutting were already 80% complete when Erhard Milch stopped the entire series and had the material scrapped. Only four machines were built as pilot series A-01 to A-04, another four machines were changed in many details as prototypes V7 to V10.

The A-01 and A-02 were used with Jagdgeschwader 5 (Eismeergeschwader), while the third machine was used with the 2nd squadron of long-range reconnaissance group 122 (2. (F) / 122) in Italy . This machine carried out a single reconnaissance flight in July 1943 and had to be written off after a crash landing. The A-04 was also used in Italy, but shortly afterwards ordered back to Arado. This was followed by modifications to the prototype of the Ar 440 , the whereabouts of the machine are unknown.

The following V7 and V8 were prototypes for the Ar 240B equipped with DB-605 engines. The troop trials yielded very poor results, so that further changes were necessary. V9 (destroyer) and V10 (night fighter) were prototypes for the C series, they received a wing with a wing span increased from 14.30 m to 16.60 m and DB-603A engines. V11 and V12 were planned as further prototypes of the C series; a completion cannot be proven. Testing of the C series began in spring 1943, but without any urgency on the part of the RLM. With the exception of the high speed of 700 km / h, the troop evaluation of the machines was so poor that the construction program was ordered to be discontinued. All other planned variants (D, E, F) remained only project drafts. A total of only 14 machines were built (V1 to V6, A-01 to A-04, V7 to V10).

construction

The fuselage of the Ar 240 was designed in four parts in smooth sheet metal - shell construction, the pressurized cabin had a double wall with a film layer, which should provide an automatic seal in the event of bullets. The three-part wing had two spars and a continuous middle section. The automatic slats only opened when the Fowler flaps (" moving wings ") were extended. The in-flight adjustable tailplane fin was also adjusted when the Fowler flaps were operated. The hot air de-icing of the wings and the tail unit was carried out using Kärcher ovens. Elevator and rudder were fully weight balanced.

It was controlled electrically by servomotors . The retractable single-leg buckling struts of the tail wheel landing gear had double tires. The engines were equipped with ring coolers and oil coolers underneath, as well as automatically adjustable propellers. The rotating arms were operated hydraulically, loading was done electrically / pneumatically. A rubber dinghy was carried as special equipment in the central hull, which could be triggered by an emergency puller.

Technical data (Arado Ar 240C)

Parameter	Data
crew	2
length	13.45 m
span	16.59 m
height	3.95 m
Total mass	10,700 kg
drive	two V12 engines DB 603A each with 1,750 PS (1,287 kW) starting power
Top speed	670 km / h at 7,000 m
Service ceiling	9,800 m
normal range	2,090 km
Armament	six MG 151 , two remote-controlled EDL 131 Z turrets with two MG 131 each

Illustrations

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  Supervision of a model; aft of the cockpit, the upper rear gun and the periscope aiming device

• 

  View from below with belly mount including aiming device. The landing light is located under the left engine / landing gear pod, which can also be used without the landing gear extended

• 

  The Plexiglas pane reaching far down and the open propeller hubs, optimized aerodynamics

literature

• Rüdiger Kosin: The development of the German fighter aircraft. Bernard & Graefe, 1990, ISBN 978-3-7637-6100-5 .
• Armin Kranzhoff: The Arado airplanes: from biplanes to jet airplanes. Series Die deutsche Luftfahrt , Vol. 31 Bernard & Graefe, 2000 ISBN 3-7637-6122-5 .
• Gerd W. Heumann: The way to the Arado 240. Flug Revue December 1963.

Web links

Commons : Arado Ar 240  - collection of images, videos and audio files

• More information and pictures

Individual evidence

1. ↑ Gerd W. Heumann: The way to Arado 240. FR 12/63, p. 34.