Heinkel He 274

He 274

Manufacturer: Heinkel
First flight: December 1945
Primary users: Luftwaffe Armée de l'Air
Number built: 2
Developed from: Heinkel He 177
Variants: Heinkel He 277

The Heinkel He 274 was a German Luftwaffe heavy bomber developed during World War II, purpose-designed for high-altitude bombing with pressurized crew accommodation.

He 177 ancestry

On 17 November 1938 the owner of the Heinkel aviation firm, Ernst Heinkel, requested permission from the RLM that two of the requested eight prototype airframes for the nascent He 177 heavy bomber project, specifically the V3 and V4 airframes, be set aside for a trial installation of four separate powerplants. Herr Heinkel had forseen that a individually-engined version of his bomber would someday be preferred, quite unlike the requested fitment of the coupled pairs of Daimler-Benz DB 601 inverted V12 engines, each known as a DB 606, which ended up being fitted to all of the eight He 177 V-series prototypes at the request of the RLM, and the Luftwaffe High Command, with the concerned government agencies citing the desire for a dive-bombing capability be present even with a heavy-bomber sized offensive warplane, something Ernst Heinkel vehemently disagreed with.

By April of 1939, interest in developing a high-altitude version of the He 177 had arisen, and on April 27, 1939, the first proposal for such an aircraft was presented to Herr Heinkel by his firm's engineering staff. The aircraft was intended to have a reduced crew manifest of three people, with a fully pressurized nose compartment for the pilot and bombardier/forward gunner, and separate pressurized tail gun emplacement. The result, in December 1940, was the specification for the He 177A-2 high altitude bomber design, with a four person crew manifest (pilot, bombardier, forward gunner and tail gunner) in the two specified pressurized compartments, and powered by the regular A-series pair of DB 606 coupled engines. The defensive armament had been reduced to a trio of Ferngesteuert-Lafette FL 81Z remote gun turrets, each with a twin-barrel MG 81 armament installation each in an upper nose mount, forward dorsal and (as part of the Bola casemate-style gondola under the nose) forward ventral location each, and a single MG 131 machine gun in an He 177A-1-style, pressurized manned flexible tailgun emplacement.

The Heinkel firm had been working on practical cockpit pressurization methods and hardware for both the A-2, and slightly later A-4 versions (identical to the A-2, except for the fitting of a pair of the later DB 610 coupled engine "power systems") from 1940 through the late summer of 1941, when the DB 610-powered A-4's pressurized cockpit in provisional form, almost identical in external appearance to the standard "Cabin 3" He 177A-series production cockpit, was ready for tests and development.

By October 1941, a more developed "He 177H" specification for a high-altitude Heinkel-designed heavy bomber had emerged from the proposed A-2 and A-4 coupled-engine designs, with the intent of carrying a 2,000 kg (4,410 lb) bombload over a maximum range of some 3,000 km (1,895 mi), and accepted by the RLM for the first time, a individual four-engine installation was being considered for any He 177-based bomber airframe, with a quartet of either BMW 801 or DB 603 engines among the choices of powerplants being specified, with the same sort of reduced-armament defensive weapon format as the A-2 and A-4 were intended to have.

A pair of the early He 177A-0 pre-production prototypes were redesignated the He 177 V10 and V11 for the purposes of high-altitude trials, and were to be the first to test the A-4 pattern pressurized cockpit design at altitude, but only the V11 was actively used for the needed research, and managed to achieve an altitude of 9,200 m (30,200 ft) with complete success on August 9, 1943, with further tests continuing through October of that year, before both the V10 and V11 were grounded in April 1944.

In February 1943 any further work on the coupled-engined A-2 and A-4 designs was halted by order of the RLM, as the four-engined He 177H high-altitude design had gained in importance from that time, evidenced by Reichsmarschall Hermann Goering's derisive "welded-together engines" complaints in August 1942, regarding the He 177 A-series unending engine problems from the choice of the DB 606 and 610 "power systems" for the A-series operational aircraft.

Development

The first proposal for what would become the He 274 started with six examples of what had been known as the He 177H, which were requested from Heinkel as early as mid-October 1941, all to have four individual engines, and intended to use what were essentially production He 177A-3 fuselages mated to longer-wingspan, four-engined wings. These proposed aircraft were shortly thereafter officially given the project number 8-274 by the RLM, and due to the heavily preoccupied Heinkel factory design offices and aircraft manufacturing facilities, this new "He 274" high-altitude bomber was to have its prototypes built in France by the Societe des Usines Farman (SAUF) firm in Suresnes.

Two He 274 prototypes were ordered built in France by the Farman Brothers and four pre-production prototypes by Heinkel at its Rostock-Marienehe facility. SAUF at Suresnes, began their prototype development.

Work on the requested half-dozen He 274 prototype airframes was leveraged off Heinkel aircraft production at AIA Breuget, Toulouse where French factories produced Heinkel components and Junkers aero engines. French production facilities at Toulouse for Heinkel aircraft were severely damaged by Royal Air Force(RAF) air raids on the night of 5/6 March 1944 and again by the US Eighth Air Force on 25 June 1944. This frustrated completion of the French prototypes as the design work on what would emerge as the Heinkel-designed entry in the Amerika Bomber competition, the He 277, was slowly progressing at the Heinkel-Sud facility in Vienna. The "Typenblatt" drawings for the never-completed He 277, with a heavy design influence for the fuselage's geometry from the smaller Heinkel He 219 night fighter, however show that it had also adopted many features from the He 274, especially its twin tail empennage design.

Characteristics

Major differences between the He 274 and the He 177 A were abandonment of the twin coupled engine arrangement in favor of four independent DB 603 A-2 engine units, an extended fuselage with a pressurized double glazed cockpit, longer wingspan, a twin tail fin empennage and a more conventional set of twin-wheel main undercarriage, abandoning the cumbersome four-strut main gear system of the He 177A.

The He 274 dispensed with coupled engines, providing room for the installation of DVL exhaust driven TK 11B turbo-superchargers.

The He 274 also 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. Largely unneccessary defensive armament was restricted to a single forward-firing 13 mm (.51 in) caliber MG 131 machine gun and remotely-controlled dorsal and ventral Fernbedienbare Drehlafette FDL 131Z gun turrets each containing a pair of MG 131s and with the dorsal turret operated from a slightly offset plexiglass domed sighting station in the roof of the flight deck, with the ventral unit aimed from the rear of the ventral Bola gondola. The powerplants selected were the same Daimler-Benz DB 603A Kraftei "power-egg" unitized engine installations, complete with their He 219-style annular radiators, that were placed on the wings of the He 177B prototypes, but with the added TK 11 turbochargers, one per engine, for better power output at high altitude.

The significance of this design is that had this aircraft entered production and been used in operations over England it would have been impossible for Allied fighters to intercept over the target, owing to its extreme high altitude performance.

Abandoned prototypes

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 not 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(AAS) 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 Hirth 2291 turbochargers.

Eventually the V2 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 (Société nationale des constructions aéronautiques du sud-ouest, or commonly, Sud-Ouest) 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

France
French Air Force
Germany
Luftwaffe

Specifications (He 274 V1)

General characteristics

Crew: 4 (pilot, second-pilot/navigator/bomb-aimer, and two gunners)
Length: 23.80 m (78 ft 1¼ in)
Wingspan: 44.19 m (145 ft 0 in)
Height: 5.50 m (18 ft 0½ in)
Wing area: 170.00 m² (1,829.86 ft²)
Empty weight: 21,300 kg (46,958 lb)
Max takeoff weight: 38,000 kg (83,776 lb)
Powerplant: 4x— Daimler-Benz DB 603A 12-cylinder inverted-vee engine, 1,750 PS (1,726 hp; 1,287 kW) each

Performance

Maximum speed: 580 km/h at 11,000 m (360 mph at 36,090 ft)
Range: 3,440 km (2,137 mi)
Service ceiling: 14,300 m (46,920 ft)
Rate of climb: 237 m/min (780 ft/min)

Armament

5 x 13mm MG 131 machine guns, one in nose, and twin guns in single dorsal and ventral Fernbedienbare Drehlafette FDL 131Z remotely-operated gun turrets
up to 4,000 kg (8,818 lb) of disposable stores in two internal bomb bays

Related development

Heinkel He 177

Comparable aircraft

Heinkel He 277

Bibliography

Jane's fighting aircraft of World War II. Studio Books, 1989.
Green, William. Warplanes of the Third Reich. London: Macdonald and Jane's Publishers Ltd., 1970 (4th Impression 1979). ISBN 0-356-02382-6.
Griehl, Manfred and Dressel, Joachim. Heinkel He 177-277-274, Airlife Publishing, Shrewsbury, England 1998. ISBN 1-85310-364-0.
Gunston, Bill & Wood, Tony. Hitler's Luftwaffe. London: Salamander Books Ltd., 1977. ISBN 0-86101-005-1.

Heinkel He 274 Pictures and Heinkel He 274 for Sale.

Living Warbirds: The best warbirds DVD series.

Source: WikiPedia