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Junkers Ju 87 "Stuka"
Development

The Ju 87's principal designer, Hermann Pohlmann, held the opinion that any dive-bomber design needed to be simple and robust. This led to many technical innovations, such as the retractable undercarriage being discarded in favour of one of the Stuka's distinctive features, its fixed and "spatted" undercarriage. Pohlmann continued to carry on developing and adding to his ideas and those of Dipl Ing Karl Plauth (Plauth was killed in a flying accident in November 1927), and produced the Ju A 48 which underwent testing on 29 September 1928. The military version of the Ju A 48 was designated the Ju K 47.

After the Nazis came to power, the design was given priority. Despite initial competition from the Henschel Hs 123, the Reichsluftfahrtministerium (RLM, the German aviation ministry) turned to the designs of Herman Pohlmann of Junkers and co-designer of the K 47, Karl Plauth. During the trials with the K 47 in 1932, the double vertical stabilisers were introduced to give the rear gunner a better field of fire. The main, and what was to be the most distinctive, feature of the Ju 87 was its double-spar inverted gull wings. After Plauth's death, Pohlmann continued the development of the Junkers dive bomber. The Ju A 48 registration D-ITOR, was originally fitted with a BMW 132 engine, producing some 450 kW (600 hp). The machine was also fitted with dive brakes for dive testing. The aircraft was given a good evaluation and "exhibited very good flying characteristics".

Ernst Udet took an immediate liking to the concept of dive-bombing after flying the Curtiss Hawk II. When he invited Walther Wever and Robert Ritter von Greim to watch Udet perform a trial flight in May 1934 at the Jüterbog artillery range, it raised doubts about the capability of the dive bomber. Udet began his dive at 1,000 m (3,300 ft) and released his 1 kg (2.2 lb) bombs at 100 m (330 ft), barely recovering and pulling out of the dive. The chief of the Luftwaffe Command Office, Walther Wever, and Secretary of State for Aviation Erhard Milch, feared that such high-level nerves and skill could not be expected of "average pilots" in the Luftwaffe. Nevertheless, development continued at Junkers. Udet's "growing love affair" with the dive bomber pushed it to the forefront of German aviation development. Udet went so far as to advocate that all medium bombers should have dive-bombing capabilities, which initially doomed the only dedicated, strategic heavy bomber design to enter German front-line service during the war years — the 30 meter wingspan He 177A — into having an airframe design (due to Udet examining its design details in November 1937) that could perform "medium angle" divebombing missions, until Reichsmarschall Hermann Göring exempted the He 177A, Germany's only operational heavy bomber, in September 1942 from being given the task of such a mismatched mission profile for its 30-meter wingspan airframe.

The design of the Ju 87 had begun in 1933 as part of the Sturzbomber-Programm. The Ju 87 was to be powered by the British Rolls-Royce Kestrel engine. Ten engines were ordered by Junkers on April 19, 1934 for £20,514, two shillings and sixpence. The first Ju 87 prototype was built by AB Flygindustri (sv) in Sweden and secretly brought to Germany in late 1934. It was to have been completed in April 1935, but, due to the inadequate strength of the airframe, construction was not completed until October 1935. However, the mostly complete Ju 87 V1 W.Nr.c 4921 (less non-essential parts) took off for its maiden flight on 17 September 1935. The aircraft originally did not carry any registration, but later was given the registration D-UBYR. The flight report, by Hauptmann Willy Neuenhofen, stated the only problem was with the small radiator, which caused the power plant to overheat.

The Ju 87 V1, powered by a Rolls-Royce Kestrel V12 cylinder liquid-cooled engine, and with a twin tail, crashed on 24 January 1936 at Kleutsch near Dresden, killing Junkers' chief test pilot, Willy Neuenhofen, and his engineer, Heinrich Kreft. The square twin fins and rudders proved too weak; they collapsed and the aircraft crashed after it entered an inverted spin during the testing of the terminal dynamic pressure in a dive. The crash prompted a change to a single vertical stabiliser tail design. To withstand strong forces during a dive, heavy plating was fitted, along with brackets riveted to the frame and longeron, to the fuselage. Other early additions included the installation of hydraulic dive brakes that were fitted under the leading edge and could rotate 90°.

The RLM was still not interested in the Ju 87 and was not impressed that it relied on a British engine. In late 1935, Junkers suggested fitting a DB 600 in-line engine, with the final variant to be equipped with the Jumo 210. This was accepted by the RLM as an interim solution. The reworking of the design began on 1 January 1936. The test flight could not be carried out for over two months due to a lack of adequate aircraft. The 24 January crash had already destroyed one machine.

The second prototype was also beset by design problems. It had its twin stabilizers removed and a single tail fin installed due to fears over stability. Due to a shortage of power plants, instead of a DB 600, a BMW "Hornet" engine was fitted. All these delays set back testing until 25 February 1936. By March 1936, the second prototype, the V2, was finally fitted with the Jumo 210Aa power plant, which a year later was replaced by a Jumo 210 G (W.Nr. 19310). Although the testing went well, and the pilot, Flight Captain Hesselbach, praised its performance, Wolfram von Richthofen told the Junkers representative and Construction Office chief engineer Ernst Zindel that the Ju 87 stood little chance of becoming the Luftwaffe's main dive bomber, as it was underpowered in his opinion. On 9 June 1936, the RLM ordered cessation of development in favour of the Heinkel He 118, a rival design. Udet cancelled the order the next day, and development continued.

On July 27, 1936, Udet crashed the He 118 prototype, He 118 V1 D-UKYM. That same day, Charles Lindbergh was visiting Ernst Heinkel, so Heinkel could only communicate with Udet by telephone. According to this version of the story, Heinkel warned Udet about the propeller's fragility. Udet failed to consider this, so in a dive, the engine oversped and the propeller broke away. Immediately after this incident, Udet announced the Stuka the winner of the development contest.

Despite being chosen, the design was still lacking and drew frequent criticism from Wolfram von Richthofen. Testing of the V4 prototype (A Ju 87 A-0) in early 1937 revealed several problems. The Ju 87 could take off in just 250 m (820 ft) and climb to 1,875 m (6,152 ft) in just eight minutes with a 250 kg (550 lb) bomb load, and its cruising speed was 250 km/h (160 mph). However, Richthofen pushed for a more powerful engine. According to the test pilots, the Heinkel He 50 had a better acceleration rate, and could climb away from the target area much more quickly, avoiding enemy ground and air defences. Richthofen stated that any maximum speed below 350 km/h (220 mph) was unacceptable for those reasons. Pilots also complained that navigation and powerplant instruments were mixed together, and were not easy to read, especially in combat. Despite this, pilots praised the aircraft's handling qualities and strong airframe.

These problems were to be resolved by installing the Daimler-Benz DB 600 engine, but delays in development forced the installation of the Jumo 210 Da in-line engine. Flight testing began on 14 August 1936. Subsequent testing and progress fell short of Richthofen's hopes, although the machine's speed was increased to 280 km/h (170 mph) at ground level and 290 km/h (180 mph) at 1,250 m (4,100 ft), while maintaining its good handling ability.

Sources:
WikiPedia
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
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