The Heinkel He-274 was not associated with the “Amerikabomber” project.
The Amerikabomber project, led by the German Ministry of Aviation, aimed to develop a long-range bomber for the Luftwaffe capable of reaching the United States, particularly New York City, from Germany – a journey totaling about 11,600 km (7,200 mi).
This idea was first considered in 1938, but it wasn’t until early 1942 that detailed plans for such a bomber were presented to Reichsmarschall Hermann Göring. Despite various proposals, the project was ultimately shelved due to its high costs, diminishing resources and production capabilities, and technical impracticalities.
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During World War II, the Heinkel He-274, was engineered specifically for high-altitude bombing missions and featured pressurized cabins for the crew. However, the advancement of Allied forces through Northwest Europe led to the abandonment of its prototypes at a French factory where they were under construction. Post-war, these aircraft were completed by the French and repurposed for high-altitude research.
Back Ground
On November 17, 1938, Ernst Heinkel, head of Heinkel aviation, proposed to the RLM to use two He-177 bomber prototypes, V3 and V4, for testing. He wanted to fit them with four separate Junkers Jumo 211 engines.
This was different from the RLM and Luftwaffe High Command’s preference for paired Daimler-Benz DB 601 engines. They required heavy bombers to have dive-bombing capabilities, a concept Heinkel opposed.
In April 1939, Heinkel’s engineering team proposed a high-altitude version of the He 177. This aircraft, designed with a reduced crew of three, featured a pressurized nose compartment for the pilot and bombardier/forward gunner, and a separate pressurized tail gun section. By December 1940, they developed the He 177A-2 high altitude bomber.
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It had a four-person crew and two pressurized compartments, powered by regular A-series DB 606 engines. The defense was scaled down to three remote gun turrets and one MG 131 machine gun in the tail. The A-2 model was even considered for pioneering in-flight refueling, potentially extending its range to 9,500 km (5,900 mi).
From 1940 to late summer 1941, Heinkel worked on cockpit pressurization for the A-2 and the A-4, which differed only in its DB 610 engines. By late 1941, the A-4’s pressurized cockpit, resembling the standard He 177A-series cockpit, was ready for testing and development.
By October 1941, Heinkel had developed a more advanced “He 177H” specification for a high-altitude heavy bomber. This design evolved from the A-2 and A-4 models with coupled engines. The goal was to carry a 2,000 kg (4,410 lb) bomb load over a range of 3,000 km (1,895 mi).
He-177 Based Bomber
For the first time since November 1938, the RLM considered a four-engine setup for the He 177-based bomber. The options included BMW 801 or DB 603 engines, with the latter using a Heinkel-specific design also applied in the He 219. This model followed the reduced-armament defense strategy of the A-2 and A-4.
In May 1942, alongside his request to Generalmajor Eccard Freiherr von Gablenz about aircraft suitability for the Amerikabomber competition, Generalfeldmarschall Erhard Milch also discussed the He 177 and its He 274 development with von Gablenz. Von Gablenz expressed that neither of these Heinkel “heavy bomber” designs met the range requirements for the new contract’s demands.
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The early He 177A-0 pre-production prototypes, rebranded as He 177 V10 and V11, were designated for high-altitude trials. They aimed to test the A-4 pattern pressurized cockpit at altitude.
However, only the V11 underwent the required research, reaching 9,200 m (30,200 ft) on August 9, 1943. Testing continued until October of that year, but both V10 and V11 were grounded in April 1944.
In February 1943, the same month the RLM officially recognized the Heinkel He 277 heavy bomber design, Heinkel’s engineering team began working on it as their Amerikabomber contract contender.
Consequently, the RLM ordered a halt to further work on the coupled-engined He 177A-2 and A-4 designs. The four-engined He 177H high-altitude design proposal gained significance, especially after Reichsmarschall Hermann Göring’s August 1942 criticism of the He 177 A-series’ engine problems with the DB 606 and 610 “power systems.”
This led to three parallel programs for four-engined heavy bomber designs at Heinkel, running from February 1943 to April 20, 1944.
He-274 Engines
The He-177 Greif’s “paired” engine concept was replaced with four separate liquid-cooled Daimler-Benz DB 603A 12-cylinder inverted-vee engines, each with a TK 11 turbocharger and housed in its own nacelle.
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This engine type, also used in high-performance aircraft like the Do-335 Pfeil and Me-410 fighters, He-219 Uhu night fighter, and Ta-152C high-altitude interceptor, featured a front ring radiator similar to the He-219’s.
This design mimicked the look of an air-cooled radial engine. Additionally, the cylinder exhausts heated a system that provided cabin warmth and de-iced the wings.
The He-274 showcased impressive high-altitude performance. At sea level, its top speed was 232 knots, which increased to 323 knots at 33,300 feet.
Aerodynamic Efficiency
This was around 20 knots faster than a B-29 Superfortress at the same altitude, even though the B-29 had nearly double the horsepower. The He-274 had a landing speed of 112 mph, which was relatively high for a large aircraft, due to its aerodynamic efficiency.
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The He-274 featured an advanced structure for its time. Its four-man crew operated from a single pressurized cabin.
The aircraft’s aluminum airframe had a twin-wall design with expanding rubber sealant, and the cockpit glass was a hollow-sandwich type. The cabin pressurization system maintained a consistent atmospheric pressure, equivalent to 8,202 feet, up to the aircraft’s ceiling of 46,916 feet.
With a bomb capacity of up to 4¼ tons, the He-274’s speed and ceiling were affected, but it was primarily valued for reconnaissance. Defensively, it had a single forward-firing MG 131 13mm machine gun and two twin FDL 131Z remote-control turrets with the same weapon. The aircraft’s main defense was its ability to operate at high altitudes.
The Allies anticipated the development of aircraft like the He-274. The Westland Welkin, a high-altitude interceptor, could operate up to 44,000 feet.
He-274 The Difference
The He-274 differed significantly from the He 177 A in several ways. It replaced the twin coupled “power system” engine arrangement with four independent DB 603A-2 fully unitized engines.
These engines, cooled by annular radiators similar to those on the Heinkel He 219 night fighter, were integrated into each engine’s setup.
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The aircraft featured an extended rear fuselage with a twin tail fin empennage and a pressurized, double-glazed cockpit that closely resembled the He-177A’s “Cabin 3” nose. It also had a longer wingspan and a simpler main undercarriage with a single oleo strut per side and twinned wheels, replacing the He-177A’s more complex four-strut system.
The He-274’s high-altitude cockpit, while externally similar to the He-177A, included a pressurized compartment for four crew members. This compartment used double walls of heavy-gauge alloy, hollow sandwich-type glazing, and inflatable rubber seals, maintaining a pressure equivalent to 2,500 m (8,200 ft) at high altitudes.
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The aircraft’s defensive armament was minimal, consisting of a single forward-firing 13 mm MG 131 machine gun and remotely controlled dorsal and ventral gun turrets, each with two MG 131s.
The dorsal turret had a Plexiglas domed rotating sighting station, while the ventral turret was aimed from the rear of the ventral Bola gondola. The chosen powerplants were Daimler-Benz DB 603A Kraftei unitized engines with He-219 style annular radiators and added DVL-designed TK 11 turbochargers for improved high-altitude performance.
He 274 Scrapped
Work on the He-274 V1 and V2 prototypes began in 1943, intended to be constructed in France by SAUF at Suresnes. However, they weren’t completed on time. In July 1944, as Allied forces approached, the nearly finished He-274 V1 was at Suresnes for flight testing. Heinkel personnel had to evacuate, and orders were issued to destroy the prototype. The damage to He-274 V1 was minor, and repairs began after the Allies took over.
The He 274 V1 was fixed by Ateliers Aéronautiques de Suresnes (AAS) and used by the French Air Force for high-altitude research, renamed AAS 01A. The He-274 V2 was completed as AAS 01B, featuring Heinkel-Hirth 2291 turbochargers instead of the TK 11 units.
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The V2 flew on December 27, 1947, two years after AAS 01A. By then, AAS had merged into the French aviation conglomerate SNCASO. Both AAS 01 versions of the He-274 were scrapped in late 1953. They had been used as “mother ships” for launching early French jet and rocket test aircraft like the Sud-Ouest SO.4000 M.1.
The Leduc 0.10 and Leduc 0.16 also had their initial tests launched from these prototypes. The less powerful, French-designed SNCASE SE.161 Languedoc airliner later took over this role for further high-speed aerodynamic research prototypes.
