Heinkel He 274

The Heinkel He 274 was a four-engine bomber designed during World War II as a high altitude variant of the Heinkel He 177 for the German Luftwaffe. Normally a major new version would be numbered by adding 100 to the original model number, but the He 277 was yet another different version of the He 177, which was itself being developed as early as September 1943 into the He 177B four engined bomber, four prototypes of which were converted from He 177A airframes with all-new wings, over the 1943-44 winter season at Heinkel's southern factories near Vienna. The main differences between the He 274 and the He 177 was the abandoning of the twin coupled engine arrangement in favor of four independent turbocharged units, an extended fuselage with a modified wingspan, a twin tail empennage tail surface unit, and a more conventional set of twin-wheel main gear units, abandoning the cumbersome four-strut main gear system of the He 177A.

Originally designated He 177H on October 11, 1941, the He 274 was a high-altitude development of the He 177A-3. The He 274 dispensed with coupled engines in order to provide room for the installation of DVL exhaust driven TK 11B turbo-superchargers. The He 274 featured a pressurized compartment for a crew of four, this employing double walls of heavy-gauge alloy, hollow sandwich-type glazing and inflatable rubber seals, a pressure equivalent to that at 2,500 m (8,200 ft) being maintained at high altitude. Defensive armament was restricted to a single forward-firing 13 mm (.51 in) MG 131 machine gun and remotely-controlled dorsal and ventral gun turrets each containing a pair of 13 mm (.51 in) MG 131s and directed from a slightly offset plexiglass dome in the roof of the flight deck or the rear of the ventral Bola gondola. First envisioned as being fully in the He 177's eventual line of development as the He 177H ("H" likely an abbreviation for "Höhe", meaning high-altitude in German), the growing incompatibility of parts led to the redesignation to He 274. By 1941, Heinkel was engrossed by other urgent projects that left the company seriously short of detail design capacity. The He 274 project was therefore reassigned to SAUF at Suresnes, France.

Construction of the two prototypes, the He 274 V1 and V2 did not commence until 1943. They were to have been built in France by SAUF at Suresnes, France, but the prototypes were never completed in time. The He 274 V1 was being readied for flight testing at Suresnes in July 1944 when the approach of Allied forces necessitated the evacuation of Heinkel personnel working on the project. Minor difficulties had delayed the flight testing and transfer of the aircraft to Germany, and orders were therefore given to destroy the virtually completed prototype. Only minor damage was actually done to the airframe of the He 274 V1, and repairs were begun after the Allied occupation. The He 274 V1 was repaired by Ateliers Aéronautiques de Suresnes and used by the Armée de l'Air (French Air Force) for several years as a high-altitude research plane. It was renamed the AAS 01A. The He 274 V2 was eventually completed as the AAS 01B, complete with the TK 11 turbochargers, and eventually flew exactly two years (on December 27, 1947) after the AAS 01A. By this time, the AAS organization had been absorbed into the French SNCASO aviation conglomerate.. Both of the AAS 01 completed and airworthy versions of the He 274 were eventually broken up in late 1953, after serving as "mother ships" for aerial launching of a number of early French advanced jet and rocket test aircraft.

Operators

• Template:FRA
  • French Air Force
• Template:Country data Germany
  • Luftwaffe