Profile Publications No. 135 The Dewwoitine 520.

Top: The D.520-01 on its second flight, 8th October 1938: note underwing radiator. Centre: Note new Jin and rudder in this view o f D.520-01 over Toulouse in mid-November 1938: also the propeller spinner. Bottom: The second prototype in Feb­ruary 1939 note machine-gun “baths" under the wings. (Photos: S.A.) Aeronautique in January 1937. Designated D.520, the number referring to the required speed, this second proposal embodied awing of reduced span and provision for the future installation of the 1,200 h.p. engine underdevelopment by Hispano-Suiza. In the meantime the Air Ministry issued anew technical programme coded A.23, of 12th January 1937. Though the S.T.Ae. agreed that the D.520 was likely to meet its requirements no prototype order was placed for the aircraft, the M.S.405 having been chosen shortly beforehand to re-equip the fighter units and orders calling for 67 of these having been placed in November 1936. In spite of this further set-back, Emile Dewoitine, who from March 1937 had been appointed deputy managing director of the Societe Ncitionale deConstructions Aero- nautiques du Midi (SNCAM) which had absorbed his own plant, decided to carry on with the detail drawing of two D.520 prototypes and a structural test cell, which were initiated in late 1937. His initiative was not regularised until 3rd April 1938, by Air Ministry contract No. 513/8. At that stage the first prototype was not far from completion, desig­nated D.520-01. Slightly delayed by minor modifications resulting from the examination of a full-scale wooden mock-up by S.T.Ae. on 27th June 1938, the first prototype made its maiden flight on 2nd October of that year, with Marcel Doret at the controls, from Toulouse- Francazal airfield. For the preliminary trials the 12Y21 engine drove a two-bladed wooden airscrew and the cockpit canopy was removed. The first flight tests proved rather disappointing, the maximum speed not exceeding approximately 480 km/h (300 m.p.h.) due to the excessive drag of the underwing coolant radiators. Their efficiency was also low, causing engine overheating: and the first step was to replace them with a single radiator under the fuselage, at the same time increasing fin and rudder area slightly to improve lateral stability. After a wheels-up landing on its eighth flight on 28th November, the D.520-01, practically undamaged, was re-engined with a I2Y29 powerplant and fitted with a “jet” exhaust manifold replacing the former separate pipes. These modi­fications allowed the Dewoitine to attain its quoted speed of 520 km/h indeed, on 7th February 1939, Leopold Galy reached a speed of 825 km/h (506 m.p.h.) in a power dive. Bearing the inaccurate designation D.520 No. I painted on its fin, and the serial F-317 underwing, the second prototype Hew for the first time on 28th January 1939. Main differences between this machine and the 01 were a completely redrawn tail, aback­ wards-sliding canopy, new undercarriage shock absorbers and the fitting of a provisional armament of one II.S.404 20 mm. cannon firing through the airscrew hub and two machine guns located in gondolas under the wings. Immediately taken on charge by C.E.M the.A., second prototype was flown by Capitaine Rozanoff at 527 km/h (326 m.p.h.) at 5,000 m. (16,400 ft.) and climbed to 8,000 m. (26.240 ft.) in 13 minutes 45 seconds. When it was re-engined with a 12Y3I powerplant in place of its original 12Y29 (and, incidentally, repainted in stan­dard fighter camouflage with its correct designation D.520-02) it recorded the following performance: maximum speed, 550 km/h (341 m.p.h.) at 5,200 m. (17,060 ft.) climb to 8,000 m. (26,240 ft.) 12 minutes 53 seconds. The third prototype was essentially similar to the second, the only changes being the replacement of the Hispano-Suiza supercharger on the engine by one Top: D.520-02 at C.E.M .A., Villacoublay, late in February 1939. Centre: D.520-02 with correct fin markings, flown by C.E.M.A. at Orleans-Bricy in March 1940, in standard camou­flage. Bottom: The second production aircraft. 4
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