View source for Heinkel He 274

{{short description|Prototype bomber aircraft by Heinkel}}
{{use dmy dates|date=August 2022}}
{{Infobox aircraft
  |name =He 274
  |image =File:He 274 43936449.jpg
  |caption =Heinkel He 274
  |type =High-altitude [[heavy bomber]]<br>[[Parasite aircraft]] [[mother ship]] (post-war French service)
  |national_origin=
  |manufacturer = [[Heinkel]]
  |designer =
  |first_flight =December 1945
  |introduction =
  |retired =
  |status =
  |primary_user =[[French Air Force]]
  |more_users =
  |produced =
  |number_built = 2
  |developed_from =[[Heinkel He 177]]
  |variants =[[Heinkel He 277]]
}}

The '''Heinkel He 274''' was a [[Nazi Germany|German]]  [[heavy bomber]] aircraft with pressurized crew accommodation developed during [[World War II]], designed for high-altitude bombing. Due to the Allied advance through Northwest Europe, the prototypes were abandoned at the factory in [[German-occupied France]] where they were being built. They were completed after the war by the French and used for high-altitude research.

== Background ==
{{main|Heinkel He 177}}
On 17 November 1938, the owner of the [[Heinkel]] aviation firm, [[Ernst Heinkel]], requested permission from the [[Reich Air Ministry|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 [[Junkers Jumo 211]]<ref>{{cite web |url=http://www.lexikon-der-wehrmacht.de/Waffen/He177.htm |title=Lexikon der Wehrmacht - Heinkel He 177, He 177B-Reihe |publisher=lexikon-der-wehrmacht.de |access-date=April 22, 2012}}</ref> powerplants.<ref name="GriehlDresselp14">Griehl & Dressel 1998, p. 14</ref>  Heinkel had foreseen that an 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 — weighing some 1.5 tonnes apiece — which ended up being fitted to all of the eight He&nbsp;177 V-series prototypes at the request of the RLM, and the [[Oberkommando der Luftwaffe|Luftwaffe High Command]], with the concerned government agencies citing the desire for a dive-bombing capability to be present even with a heavy-bomber-sized offensive warplane, something Ernst Heinkel vehemently disagreed with.{{Cn|date=January 2021}}

By April 1939, interest in developing a high-altitude version of the He 177 had arisen, and on 27 April 1939, the first proposal for such an aircraft was presented to Heinkel by his firm's engineering staff.<ref name="GriehlDresselp176">Griehl & Dressel 1998, p. 176</ref> The aircraft was intended to have a reduced crew of three, 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 (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 machine gun|MG 81]] armament installation each in an upper nose mount, forward dorsal and (as part of the ''Bola'' casemate-style [[Gondola (airplane)|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.<ref name="GriehlDresselp227">Griehl & Dressel 1998, p.227</ref>  The A-2 version had even been considered for a pioneering [[in-flight refueling]] capability, possibly using [[Junkers Ju 290|Ju 290]] maritime patrol aircraft as the tankers. With in-flight refueling, the range of the A-2 would have been extendable to some 9,500&nbsp;km (5,900&nbsp;mi) of total flight distance.<ref>{{cite book |title=Heinkel He 177-277-274 |author1=Griehl |author2=Manfred and Dressel, Joachim |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, England |isbn= 9781853103643|pages=57 & 58 |url=https://books.google.com/books?id=WOe9Kt76zVcC |access-date=March 29, 2012}}</ref>

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 engines) 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.{{Cn|date=January 2021}}

By October 1941, a more developed "He 177H" specification for a high-altitude Heinkel-designed heavy bomber<ref name="GriehlDresselp177">Griehl & Dressel 1998, p. 177</ref> had emerged from the proposed A-2 and A-4 coupled-engine designs, with the intent of carrying a 2,000&nbsp;kg (4,410&nbsp;lb) bombload over a maximum range of some 3,000&nbsp;km (1,895&nbsp;mi), and accepted by the RLM for the first time since the rejection of Dr. Heinkel's initial November 1938 request for two of the early He 177 V-series prototype airframes to get them, an individual four-engine installation was being considered for any He&nbsp;177-based bomber airframe, with a quartet of either [[BMW 801]] or [[DB 603]] [[Kraftei|unitized]]-installation engines — the DB 603 powerplants being unitized in a Heinkel factory-specific design also used for the [[He 219]] — 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.{{Cn|date=January 2021}}

In conjunction with his request for help from ''Generalmajor'' [[Eccard Freiherr von Gablenz]] in May 1942, concerning the suitability of aircraft for the ''[[Amerikabomber]]'' contract competition as that proposal first appeared, ''Generalfeldmarschall'' [[Erhard Milch]] also received von Gablenz's opinion on the He 177 and its He 274 development, with von Gablenz stating that neither of these Heinkel "heavy bomber" designs had anywhere near the range to conduct a mission approaching the demands of the new contract.<ref>{{cite book |last1=Griehl |first1=Manfred |last2=Dressel |first2=Joachim |title=Heinkel He 177 - 277 - 274 |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, UK |isbn=1-85310-364-0 |page=191 }}</ref>

A pair of the early He&nbsp;177A-0 pre-production prototypes were renamed 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. Only the V11 was used for the needed research and managed to achieve an altitude of 9,200&nbsp;m (30,200&nbsp;ft) on 9 August 1943. Further tests continued through October of that year, before the V10 and V11 were grounded in April 1944.<ref name="GriehlDresselp179">Griehl & Dressel 1998, p.179</ref>

In February 1943, the same month by which the RLM's first mention of any official status had occurred for design work on an entirely separate, [[Heinkel He 277]]-named heavy bomber design to be paid to Heinkel's engineering shops by them, and becoming the Heinkel firm's ''Amerikabomber'' contract contender, any further work on the coupled-engined He 177A-2 and A-4 designs was halted by order of the RLM.<ref>{{cite book |last1=Griehl |first1=Manfred |last2=Dressel |first2=Joachim |title=Heinkel He 177 - 277 - 274 |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, UK |isbn=1-85310-364-0 |page=179 }}</ref> The four-engined He&nbsp;177H high-altitude design proposal had gained in importance from that time, evidenced by ''Reichsmarschall'' [[Hermann Göring]]'s derisive [[Heinkel He 177#Engine difficulties|"welded-together engines" complaints]] in August 1942, regarding the He 177 A-series unending engine problems from the choice of the 1.5 tonne-weight apiece DB 606 and 610 "power systems" for the A-series operational aircraft. This resulted in a trio of parallel programs under development by the Heinkel engineering shops for four-engined heavy bomber designs, from February 1943 to 20 April 1944.<ref>{{cite book |last1=Griehl |first1=Manfred |last2=Dressel |first2=Joachim |title=Heinkel He 177 – 277 – 274 |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, UK |isbn=1-85310-364-0 |page=203 }}</ref>

== Development ==
The first proposal for what would become the He 274 started with six airframe orders for what had been known as the He 177H, which were requested from Heinkel as early as mid-October 1941, all to have four engines in stretched production He 177A-3 fuselages.<ref name="GriehlDresselp180">Griehl & Dressel 1998, p.180</ref> The main production version had been lengthened by 160&nbsp;cm aft of the wing's trailing edge for better stability and also used for the A-5 subtype — mated to longer span, four-engined wings.<ref>{{cite book |last1=Griehl |first1=Manfred |last2=Dressel |first2=Joachim |title=Heinkel He 177 - 277 - 274 |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, UK |isbn=1-85310-364-0 |pages=46, 54 }}</ref>  These proposed aircraft were shortly thereafter officially given the airframe project number '''8-274''' by the RLM; due to the busy 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 ''[[Farman Aviation Works|Societe des Usines Farman]]'' (Farman Brothers) in [[Suresnes]]. Two He 274 prototypes were ordered built in [[France]] by the Farman Brothers and four pre-production prototypes by the Heinkel's ''Heinkel-Nord'' headquarters at its Rostock-Marienehe (today's Rostock-Schmarl) facility. Farman at Suresnes, began their prototype development.{{Cn|date=January 2021}}

Work on the requested half-dozen He 274 prototype airframes was leveraged{{clarify|date=April 2014}} off Heinkel aircraft production at [[Breguet Aviation|AIA Breguet]], [[Toulouse]] where French factories produced Heinkel components and [[Junkers]] aviation 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 design work in Germany and Austria had already begun by February 1943 on what had emerged as the Heinkel entry in the trans-Atlantic ''[[Amerikabomber]]'' strategic heavy bomber design competition, the newer [[Heinkel He 277]]. While the RLM-designated ''8-277'' airframe's design work had been progressing at the ''Heinkel-Sud'' facility in [[Vienna]] from before that time, [http://forum.axishistory.com/download/file.php?id=305484&mode=view general arrangement "Typenblatt" the drawings] for the never-completed He 277, with a design influence for the fuselage's geometry from the smaller [[Heinkel He 219]] night fighter, show that it had also adopted many features from the He 274, especially its [[twin tail]].<ref>{{cite book |last1=Griehl |first1=Manfred |last2=Dressel |first2=Joachim |title=Heinkel He 177 - 277 - 274 |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, UK |isbn=1-85310-364-0 |page=159 }}</ref> The Heinkel entry for the ''Amerika Bomber'' competition was itself cancelled on 20 April 1944, with not one airframe completed.<ref>{{cite book |last1=Griehl |first1=Manfred |last2=Dressel |first2=Joachim |title=Heinkel He 177 – 277 – 274 |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, UK |isbn=1-85310-364-0 |page=203 }}</ref>

== Characteristics ==
Major differences between the He 274 and the [[He 177 A]] were abandonment of the twin coupled "power system" engine arrangement in favor of four independent [[DB 603]]A-2 fully unitized engines, cooled by annular radiators nearly identical in appearance to those on the similarly-powered [[Heinkel He 219]] night fighter as an integral part of each "unitized" engine's installation, an extended rear [[fuselage]] with a twin [[Vertical stabilizer|tail fin]] [[empennage]], a [[pressurized]] [[double glazed]] [[cockpit]] of nearly identical external appearance to the 177A's standard "Cabin 3" nose, a longer [[wingspan]], and a more conventional, single [[oleo strut]]-per-side set of twinned-wheel main undercarriage, abandoning the cumbersome four-strut main gear system of the He 177A, needed for the earlier design's pair of larger-diameter, four-blade propellers.{{Cn|date=January 2021}}

The He 274's advanced, high-altitude cockpit, despite its external resemblance to that of the He 177A, comprised a [[Cabin pressurization|pressurized compartment]] for a crew of four employing double walls of heavy-gauge alloy, hollow sandwich-type glazing and inflatable rubber seals. This cockpit maintained a pressure at high altitude equivalent to that at {{cvt|2500|m}}. Largely unnecessary defensive armament was restricted to a forward-firing {{cvt|13|mm}} caliber [[MG 131 machine gun]] and remotely controlled [[Anatomical terms of location#Dorsal and ventral|dorsal and ventral]] ''Fernbedienbare Drehlafette'' FDL 131Z [[gun turret]]s each containing a pair of MG 131s machine guns and with the dorsal turret operated from a slightly offset [[Plexiglas]] domed rotating sighting station in the roof of the flight deck as most A-series He 177s were, with the ventral unit aimed from the rear of the ventral ''Bola'' gondola. The engines used were the same type of  [[Daimler-Benz DB 603]]A ''Kraftei'' "[[power-egg]]" unitized engine installations, complete with their He 219-style annular radiators that were placed on the wings of the quartet of ordered [[Heinkel He 177#Further development-the Heinkel He 177B|He 177B]] prototypes, but for the He 274, added [[Deutsche Versuchsanstalt für Luftfahrt|DVL]]-designed TK 11 [[turbochargers]], one per engine, for better power output at high altitude.{{Cn|date=January 2021}}

== Abandoned prototypes ==
Construction of the two [[prototype]]s, 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 [[Allies of World War II|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.{{Cn|date=January 2021}}

The He 274 V1 was repaired by ''[[Ateliers Aéronautiques de Suresnes]]'' (AAS) and used by the ''[[French Air Force|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''', completed with the alternate choice of Heinkel-[[Hirth]] 2291 turbochargers, in place of the TK 11 units used by the He 274 V1's engines.{{Cn|date=January 2021}}

Eventually the V2 flew exactly two years (on 27 December 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.<ref name="GriehlDresselp207">Griehl & Dressel 1998, p.207</ref> Both of the AAS 01 completed and airworthy versions of the He 274 were eventually broken up in late 1953, after serving as "[[mother ship]]s" for aerial launching, in the manner of a [[composite aircraft|composite]] or [[parasite aircraft]], of a number of early French advanced jet and rocket test aircraft like the unpowered [[SNCASO SO.4000#Design and development|Sud-Ouest SO.4000 M.1]], almost always launched from a strut-braced, above-fuselage position.<ref>{{cite book |last1=Griehl |first1=Manfred |last2=Dressel |first2=Joachim |title=Heinkel He 177 - 277 - 274 |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, UK |isbn=1-85310-364-0 |pages=208–209 }}</ref>  The [[Leduc 0.10]] and [[Leduc 0.10#0.16|Leduc 0.16]] also each had their first aerial tests from atop the pair of surviving He 274 prototypes.<ref>{{cite book |last1=Griehl |first1=Manfred |last2=Dressel |first2=Joachim |title=Heinkel He 177 - 277 - 274 |year=1998 |publisher=Airlife Publishing |location=Shrewsbury, UK |isbn=1-85310-364-0 |page=207 }}</ref> The slightly less powerful, French designed four-engined [[SNCASE Languedoc#Operational history|SNCASE SE.161 ''Languedoc'']] airliner design took over this "mother ship" role later in the 1950s, for further air launch duties with French high-speed aerodynamic research prototypes.{{Cn|date=January 2021}}

==Operators==
* {{FRA}}
** [[French Air Force]]

==Specifications (He 274 V1)==
{{Aircraft specifications/switch
|plane or copter?=plane
|jet or prop?=prop
|ref={{citation needed|date=April 2013}}
|crew=4 (pilot, second-pilot/navigator/bomb-aimer and two gunners)
|capacity=
|length alt=23.80 m
|length main=78 ft 1¼ in
|span alt=44.19 m
|span main=145 ft 0 in
|height alt=5.50 m
|height main=18 ft 0½ in
|area alt=170.00 m<sup>2</sup>
|area main=1,829.86 ft<sup>2</sup>
|airfoil=
|empty weight alt=21,300 kg
|empty weight main=46,958 lb
|loaded weight alt=
|loaded weight main=
|useful load alt=
|useful load main=
|max takeoff weight alt=38,000 kg
|max takeoff weight main=83,776 lb
|more general=
|engine (prop)=[[Daimler-Benz DB 603]]A
|type of prop=12-cylinder inverted-vee engine
|number of props=4
|power alt=1,750 PS
|power main=1,726 hp; 1,287 kW
|power original=
|max speed alt=580 km/h
|max speed main=360 mph
|max speed more=at 11,000 m (36,090 ft)
|cruise speed alt=
|cruise speed main=
|never exceed speed alt=
|never exceed speed main=
|stall speed alt=
|stall speed main=
|range alt=3,440 km
|range main=2,137 mi
|ceiling alt=14,300 m
|ceiling main=46,920 ft
|climb rate alt=4 m/s
|climb rate main=780 ft/min
|loading alt=
|loading main=
|thrust/weight=
|power/mass alt=
|power/mass main=
|more performance=
|guns= 5 × 13 mm [[MG 131 machine gun|MG 131]] machine guns, one in [[nose gunner|nose]] and twin guns in single dorsal and ventral ''Fernbedienbare Drehlafette'' FDL 131Z remotely operated gun turrets
|bombs=up to {{convert|4000|kg|lb|0|abbr=on}} of disposable stores in two internal bomb bays
|avionics=
}}

==See also==
{{Aircontent|
|related=* [[Heinkel He 177]]
|similar aircraft=
* [[Heinkel He 277]], Heinkel's ''Amerikabomber'' contract contender
|lists=
* [[List of World War II military aircraft of Germany]]
* [[List of military aircraft of Germany]]
* [[List of WW2 Luftwaffe aircraft prototype projects]]
|see also=
}}

==References==
{{Reflist}}

==Sources==
{{Refbegin}}
* ''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}}.
* Marchand, Alain & Carbonel, Jean-Christophe. ''Heinkel He 274 et Junkers Ju 488, Les bombardiers stratégiques allemands développés en France durant l’Occupation''. Paris: Éditions Artipresse, Airprofils n°6, 2011 {{ISBN|978-2-919-23102-7}}

{{Refend}}
{{commons category|Heinkel He 274}}
{{Heinkel aircraft}}
{{RLM aircraft designations}}

[[Category:1940s German bomber aircraft]]
[[Category:Heinkel aircraft|He 274]]
[[Category:Four-engined tractor aircraft]]
[[Category:Aircraft first flown in 1945]]
[[Category:Four-engined piston aircraft]]
[[Category:Twin-tail aircraft]]