By William Pearce

The state-owned French aircraft manufacturer SNCAM (Société nationale des constructions aéronautiques du Midi or National Society of Aircraft Constructors South) was formed in March 1937 when the Dewoitine firm was nationalized. Many Dewoitine personnel, including the company’s founder, Émile Dewoitine, continued to work for SNCAM. As a result, aircraft designed and built at SNCAM continued to bear the Dewoitine name.

Wind tunnel model of the Sud-Est SE 580 complete with contra-rotating propellers.

In 1940, SNCAM began studies of a new fighter aircraft. The aircraft was based on a continuing design evolution that started with the Dewoitine D.520 production fighter and progressed through the D.551/552 pre-production fighters. SNCAM’s new fighter design was designated M 580.

The M 580 aircraft was a tractor design with conventional undercarriage. However, the power plant was unusual in that it utilized two Hispano-Suiza 12Z engines coupled in tandem and driving a coaxial contra-rotating propeller (similar to the Arsenal VB 10). The M 580 was designed by Robert Castello and Jacques Henrat, who had been very involved with previous Dewoitine fighter designs. Before much design work was completed, SNCAM was absorbed into SNCASE (Société nationale des constructions aéronautiques du Sud-Est or National Society of Aircraft Constructors Southeast) in late 1940.

With the SNCASE (often referred to as Sud-Est) takeover and the German occupation of France, the M 580 design languished during the war. Under Sud-Est, the aircraft was redesignated SE 580. Wind-tunnel tests were conducted in 1943, and the SE 580 design was changed to incorporate a new engine then under development. Gone was the tandem V-12 engine configuration, and in its place was a single 24-cylinder Hispano-Suiza 24Z engine. With much of France liberated in 1944, two SE 580 prototypes were ordered by the Ministère de l’Air (French Air Ministry). The Marine Nationale (French Navy) was interested in a navalized version designated SE 582 and ordered two prototypes in early 1945.

The SE 580 with open cowling revealing the 24-cylinder, 3,600 hp (2,685 kW) Hispano-Suiza 24Z engine.

Work on the SE 580 prototype was started first. The aircraft was of all-metal construction with fabric-covered control surfaces. The aircraft’s structure, especially the wings, followed basic Dewoitine design principals used in their earlier fighter aircraft. The SE 580 featured dive recovery flaps positioned under the wing and outside of the fully retractable main landing gear. Another unusual feature was that the incidence of the aircraft’s horizontal stabilizer was adjustable.

The smooth flow of the aircraft’s fuselage was interrupted by a large hump behind the cockpit. This structure housed the scoop that directed air through a radiator positioned horizontally in the aircraft’s rear fuselage. Cooling air entered a large opening just behind the cockpit, traveled down through the radiator, and exited the fuselage via a ventral flap. The intake also incorporated a slot for boundary layer air bleed. The radiator’s location in the center of the aircraft offered some inherent protection that was further enhanced by rear armor plating to protect against enemy fire.

Three fuselage fuel tanks and one fuel tank in each wing held a total of 660 gallons (2,500 L). A drop tank under the fuselage held an additional 79 gallons (300 L) of fuel. The SE 580’s Hispano-Suiza 24Z engine was an H-24 that was forecasted to produce 3,600 hp (2,685 kW). The 24Z would turn an 11.5 ft (3.50 m) diameter, six-blade, contra-rotating propeller.

The supercharger intakes and numerous exhaust stacks interrupt the otherwise clean lines of the SE 580’s fuselage. The dorsal radiator scoop created a large blind spot for the pilot. One must wonder how cleanly air would flow into the scoop after being disrupted by the canopy.

The SE 580’s armament was quite substantial and consisted of a 30 mm cannon mounted between the engine’s upper cylinder banks and firing through the propeller hub. Each wing housed two 20 mm cannons and four 7.5 mm (or three 12.7 mm) machine guns. A hardpoint under each wing could accommodate a 1,102 lb (500 kg) bomb. A photo reconnaissance version would accommodate a vertical camera in the central fuselage.

The SE 580 had a 52.0 ft (15.86 m) wingspan and was 42.7 ft (13.0 m) long. The aircraft had an empty weight of 11,228 lb (5,093 kg) and a gross weight of 17,919 lb (8,128 kg). The SE 580 had a top speed of 373 mph (600 km/h) at sea level and 465 mph (749 km/h) at 30,512 ft (9,300 m). Its landing speed was 88 mph (141 km/h). The SE 580 could climb to 19,685 ft (6,000 m) in just over six minutes and had a theoretical ceiling of 44,619 ft (13,600 m). The aircraft’s maximum range was 1,709 miles (2,750 km).

By 1946, construction of the first SE 580 prototype was well underway, and a Hispano-Suiza 24Z engine was installed in the airframe. Unfortunately, problems with the 24Z engine resulted in its cancellation. The Arsenal 24H was selected as the replacement engine. The 4,000 hp (2,983 kW) 24H was also a 24-cylinder engine in an “H” configuration but had many differences when compared to the 24Z. The 24H was heavier and had a different propeller location; it used a single rotation, 12.1 ft (3.70 m) diameter, five-blade propeller. These differences required numerous, complex changes to the SE 580. The longer propeller was located 5.12 in (130 mm) lower on the engine and required changes to the aircraft’s landing gear and wings to maintain acceptable ground clearance. Wind-tunnel tests indicated further wing changes would be needed and that the engine had to be moved forward. In light of all the required changes, budgetary cutbacks, Sud-Est’s preoccupation with other projects, and the emergence of jet aircraft, the SE 580 was cancelled in 1947.

This rear view of the SE 580 shows the large radiator housing behind the cockpit. Note the cooling air exit flap under the fuselage.

SE 582 development trailed behind that of the SE 580; the French Navy was more interested in the Sud-Ost SO.8000, and Sud-Est was more focused on the SE 580. Changes needed to navalize the aircraft included incorporating an arrestor hook and folding wings. Construction of the SE 582 was limited to components that were shared with the SE 580, but it does not appear that any substantial part of the SE 582 was ever completed. The SE 582 had the same basic specification as the SE 582, except it was 712 lb (323 kg) heavier, at a gross weight of 18,631 lb (8,451 kg).

When Sud-Est abandoned the SE 580/582, the possibility of SNCAC (Société nationale des constructions aéronautiques du Centre or National Society of Aircraft Constructors Center) taking over the projects was discussed. However, the status of aviation could not be changed—the SE 580 and 582 were outdated, and existing aircraft already matched their performance. The first SE 580 prototype was never completed.

SE 580 was a large aircraft, and its predicted performance equaled, but not bettered, existing aircraft then in service. Lack of available information about the aircraft, combined with its unique configuration and engine have made the SE 580 a curiosity for many aviation enthusiasts.

Sources:
– Les Avions de Combat Francais 1944-1960 I – Chasse-Assaut by Jean Cuny (1988)
– Les Avions Dewoitine by Raymond Danel and Jean Cuny (1982)
– http://www.secretprojects.co.uk/forum/index.php/topic,4110.0.html
– http://www.aviationbanter.com/showthread.php?t=76826