Editing Dewoitine D.520 (section)

==Design==
===Overview===
[[File:D.520 Le Bourget Cckpit01.jpg|thumb|Gunsight and instrument panel from the D.520 on display at Le Bourget]]
The Dewoitine D.520 was a French [[fighter aircraft]], intended to be a capable contemporary of types such as the [[Messerschmitt Bf 109]] and [[Supermarine Spitfire]]. An all-metal structure was used, except for fabric-covered ailerons and tail surfaces. The wing, even if single-spar, was a solid and rigid unit with a secondary spar and many reinforced parts. The inwardly retracting undercarriage had a broad {{cvt|2.83|m}} track, and was fitted with wide, low-pressure tyres.<ref>Danel and Cuny 1966, pp. 225, 226.</ref>

The D.520 was designed to be maintained easily with many inspection panels, a rare feature for its time. Recharging the D.520 ammunition was swift and easy; the machine gun magazines required five minutes each and three minutes for the {{cvt|20|mm|3}} cannon. To fill the machine gun ammunition boxes took 15 minutes, while five minutes were needed to empty it as the cartridges were not expelled. The D.520's cockpit was set well back in the fuselage, aft of the trailing edge of the wings. This gave the pilot good downward visibility, but the long nose in front of him was a drawback when taxiing on the ground.<ref name="Jackson p. 15.">Jackson 2003, p. 15.</ref>

A [[self-sealing fuel tank]] with a capacity of {{cvt|396|L}} was mounted between the engine and cockpit, along with two wing tanks which, combined, carried another {{cvt|240|L}}, for a total of {{cvt|636|L}};<ref>Danel and Cuny 1966, p. 228.</ref> this was considerably more than the contemporary Bf 109E, Spitfire I and early Italian fighters, each with about {{cvt|400|L}} fuel capacity. The ferry range was from {{cvt|1300|to|1500|km}} at {{cvt|450|km/h}} which, from June 1940, allowed D.520s to escape to North Africa when France fell.<ref name="Gigli-Cervi"/>

===Engine===
The [[Hispano-Suiza 12Y]]-45 engine was an underpowered, older design, with {{cvt|850|CV|kW hp}} at takeoff at 2,400 rpm, or {{cvt|935|CV|kW hp}} emergency power at 2,520 rpm and at a height of {{cvt|1900|m}}.<ref>Danel and Cuny 1966, p. 248.</ref> The Hispano engine had some advantages over some later engines; for example, its weight was only {{cvt|515|kg}}, compared to the {{cvt|620|kg}} of the [[Rolls-Royce Merlin]] III. Development of the engine had not been straightforward, and had delayed production.<ref name="Danel 5 6"/> According to an aviation author, it was alleged by American aviator [[Charles Lindbergh]] that secret negotiations were conducted between Dewoitine and [[Daimler-Benz]] during 1939 to obtain the DB.601 engine for the D.520, but that these did not come to fruition due to the war.<ref name="Danel 5"/>

Fuel was fed via six [[Solex Carburetor|Solex]] S.V. 56 carburettors mounted on an inlet manifold which directed compressed air from the supercharger to the engine cylinders; the 12Y-45 and -49s fitted to production D.520s used either [[octane rating|92 or 100 octane]] fuel.<ref>Danel and Cuny 1966, pp. 72, 245, 303.</ref> The -45 drove an electrically operated [[Ratier Type 1606M]] three-bladed, {{convert|3|m|ft|-diameter|adj=mid}}, variable-pitch propeller, while D.520s from No. 351 were fitted with the 12Y-49 {{cvt|960|CV|kW hp}} engine driving a [[Chauvière type 3918]] pneumatically operated propeller, {{cvt|3|m}} in diameter.<ref>Danel and Cuny 1966, pp. 227, 228.</ref>

By 1940 a version of the 520D was flying with a Rolls-Royce Merlin X engine. [[Ernest Hives]] stated that agreement had been reached with the French Government for the manufacture of the Merlin in France. ("The Merlin in perspective" - A Harvey-Bailey -Rolls-Royce Heritage Trust, p130)

===Fire suppression system===
The D.520 had a fire-suppression system with a fire extinguisher activated from the cockpit. The engine was started by a simple but effective system, operating with compressed air. A Viet 250 air compressor charged several air bottles (one with a 12-litre capacity, as well as another eight litre tank, three smaller one litre units were matched to the weapons). The 12-litre air bottle was used for the brakes and later, for the Chauvière propeller's constant speed adjustment. The small air bottles provided up to 12 seconds at {{cvt|9000|m}} or 20 seconds at low level, before the Viet air compressor recharged them. The pilot had a complete set of cockpit instruments, and a ten-litre oxygen bottle located in the fuselage just behind his seat, with either a Munerelle or Gourdou oxygen regulator system mounted on the right instrument panel.<ref>Danel and Cuny 1966, pp. 226–227, 236–237.</ref> Equipment included a ''[[Radio Industrie Type Rl 537]]'' radio-receiver set, an OPL RX 39 [[reflector sight]] (less effective than the Revi system), a height-adjustable seat, and a sliding canopy with large, clear panels.<ref>Danel and Cuny 1966, pp. 236, 238, 250.</ref> Except over the long nose, the pilot's view was good, since he was seated quite high over the forward fuselage; however, no rear-facing mirrors were fitted.

===Armament===
[[File:Dewoitine 520 ON040.jpg|thumb|A D.520 after crash landing]]
Production-standard armament consisted of a {{cvt|20|mm|3}} HS.404, which had an ammunition capacity of 60 rounds, firing through the propeller hub, and four belt-fed MAC 1934 M39 {{cvt|7.5|mm|3}} machine guns in the wings, with 675 rounds per gun.<ref name="Danel and Cuny 1966, p. 249"/> The MAC 1934 machine guns had a high [[rate of fire]] of 1,200 rounds per minute (rpm), while the HS.404 had an effective rate of fire of 600 rpm and was accurate up to {{cvt|500|m}}; the ammunition capacity meant that the machine guns could be fired for a total of 30 seconds, while the cannon had ten seconds' worth of ammunition.

In combat, the MS.406 had only a pair of {{cvt|7.5|mm|3}} machine guns and was, therefore, at a disadvantage when the HS.404 had used up its ammunition, while a D.520 could continue to fight effectively because it had four fast-firing machine guns (over 80 rounds/sec), with 20-plus seconds of ammunition still available. The D.520 had provisions for two BE33 "illuminating bombs", useful for nocturnal interception missions, but these were seldom used because French fighters rarely flew nighttime missions.<ref>Danel and Cuny 1966, p. 236.</ref>

===Flight performance===
Although employing a modern design philosophy for its time, the D.520 was considered more difficult to fly than the older MS.406.<ref name="Gigli-Cervi">Gigli-Cervi, Alessandro. "D.520, la tecnica" (in Italian). ''Aerei nella Storia,'' W.Ward editions, Parma n.7/99, pp. 26–33.</ref><ref>Danel and Cuny 1966, pp. 256–257, 327.</ref> Captain [[Eric Brown (pilot)|Eric Brown]], commanding officer of the [[Royal Aircraft Establishment]]'s Captured Enemy Aircraft Flight, tested the D.520 at [[RAE Farnborough]], saying that "It was a nasty little brute. Looked beautiful but didn't fly beautifully. Once you get it on the ground, I was told not to leave the controls until it was in the hangar and the engine stopped. You could be taxiing toward the hangar and sit back when suddenly it would go in a right angle."<ref name="Thompson with Smith p. 239.">Thompson with Smith 2008, p. 239.</ref>

The handling changed according to the amount of fuel carried; using the fuselage tank alone, fuel consumption had no appreciable effect on handling because the tank was at the [[centre of gravity]], but with full wing tanks, directional control was compromised, especially in a dive. The flight controls were well harmonized and the aircraft was easy to control at high speed. The maximum dive speed tested was {{cvt|830|km/h}} with no buffeting and excellent stability both in the dive (depending on fuel load) and as a gun platform.