He-177 Story

Pictured the He-177 V-8 prototype in flight.

Nazi Germany created the concept of carpet bombing when bombers of Legion Kondor bombed the town of Guernica for two hours in April 1937. In one sense precision bombing was not an option. German bomb sights of the time were not gyro stabilised. These early sights included the Carl Zeiss Lotfernrohr 3 or the BZG-2. 

One of the most secret military inventions in World War 2 was a gyro stabilised, calculating bomb sight, called the Norden Bomb Sight. Eventually espionage delivered the Norden Bomb Sight's secrets to Germany. It's features were incorporated to Germany's Lotfernrohr 7, but prior to this the most precise and effective means to bomb any small target was dive bombing.

From his time in USA as a Hollywood stunt pilot Ernst Udet had become infatuated with the Curtis Goshawk Helldiver and Goering obtained two for him to display in Germany. This obsession led to development first of the Ju-87 Stuka tactical dive bomber but also later medium bombers like the dornier Do-17 dive bomber. 

To dive-bomb a target the entire aircraft must be dived at it's target. After releasing the bomb the aircraft itself must be hauled out of the dive placing huge structural strain on the aircraft, requiring aircraft to be built with incredible strength and a heavy structure. Pilots are also prone to pass out as they haul the aircraft back to level flight so like the autopilot iof a Ju-87 Stuka, german dive bombers were fitted with primative autopilots able to perform this recovery with an unconsious pilot.


Bombers which Nazi Germany used for the Battle of Britain were created to satisfy what is known as the bomber A specification. This specification was largely dictated to satisfy Generaloberst Ernst Udet's demand for dive bomber performance. Requirements which governed use of aircraft were built around the Truppenfuhrung concept, to destroy enemy lines of communication and headquarters in the battlefield. This concept was spelled out in service regulation 10, published in 1934. Prior to this the main guide had been a manual of directives for the conduct of operational air war published in 1926 based on WW1 experience. These were both documents concerned with tactical support of ground forces and these influenced bombers like the Ju-88 and Dornier Do17.[1] 

In 1934 however Chief of General Staff General Walther Wever had a different more strategic vision and wanted an aircraft capable of reaching the Urals, with a 1,000kg (2,204 lb) bomb load. It also had to fly 5,000km (3,107 mi) with that bomb load at a speed not less than 500 km/h (311 mph) at altitude. His vision however was hampered by the lack of suitable engines for a long range bomber.[2] This is when Heinrich Hertel of Heinkel's company took an interest in 1936. He proposed coupling two DB601 engines through a gearbox driving a single propellor. This engine would become the 2,700hp DB606. This engine was already proving itself in the long range reconnaisance He-119 aircraft. The He-119 set speed and distance records in November 1937, notably a sustained 504.98 km/h (313.79 mph) over 1,000km (540nm).[3]  

Hertel proposed the He-177 as a Ural Bomber. General Wever welcomed the proposal and it was designated Heinkel Projekt 1041 Bomber A. Wever however was killed in an air crash in in June 1936 and Goering who had been jealous of Wever's independence appointed his own yes man, Ernst Udet to replace Wever at the Reich Air Ministry Technical Office. Udet was obsessed with dive bombing and tactical air support as it was the novel concept which he had brought back with himself from America.



RLM Projekt 1041
 
Reichs Luft Ministerium (RLM) which governed aircraft development in Germany granted the He-177 a further designation which finally gave the aircraft it's lasting name, type number "8-177". The Luftwaffe high command (OKL) in November 1937 also stipulated for Heinkel's Projekt 1041 that it meet stringent requirements for "medium" dive bombing roles. Once He-177 development was underway OKL subsequently placed a new requirement demanding diving ability up to 60 degrees angle. The wings however were not stressed to the new requirement and RLM tests in 1942 found that the wings were a third below strength estimates. In reality the wings were strong, but subjected to diving requirements not demanded when the type was first designed. Ironically after the initial production batch of He-177 A-0 aircraft the type's dive brakes were omitted.

Hertel left the Heinkel company in March 1939. Heinkel's new chief designer, Siegfried Gunter continued to develop the He-177 "Grief" (Griffon) but now had to sort out engine problems and satisfy the dive bombing requirement too. After Wever's death Ural Bomber specifications became redefined as the Algiers Bomber, for a bomber able to bomb Algiers, North Africa and return. These also included a dive bombing capability. 

The requirement for high speed demanded as little airframe drag as possible. An aircraft layout with just two propellers was desirable, however it also required engines producing at least 2,000 horsepower per propeller. Had such an engine been available in 1940 the He-177 might have been a hugely successful bomber and superior to British bombers of the day. At that time however, no such engine existed. To obtain maximum engine horsepower with least frontal drag, it was decided to build with two engines one behind the other on a common crankshaft. This would make the He-177 a four engined aircraft with just two propellors, housed on two engine nacelles.

For the early models of He-177 it was decided to pair a couple of Daimler Benz DB601 engines more commonly used on the Messerschmitt Bf-109 fighter. Configured together, these became the DB606 engine. Later He-177 used the DB610 engine.

The primary cause of problems for the DB606 engine was oil foaming by the oil pumps. When oil foamed it lost any value as an engine coolant, leading to overheating and fires in exhaust manifolds. When hot oil did pool in a hot exhaust manifold it often resulted in uncontrollable fires. Many instances especially in early models of He-177, engine fires could not be stopped and wing spars were burned through before crews could abandon their aircraft. Luftwaffe Air Marshal Erhard Milch knowingly ordered production and service deployment of several aircraft types with known defects and this was also the case with He-177A that they were simply put into production before technical problems were solved.

A common cause of engine fires for the DB606 was the pooling of crankcase oil in a shared exhaust manifold. This was often caused by exhaust blowback carrying foamed oil into the manifold. Through poor mechanical linkages, for example one engine's power setting was often retarded before the other engine's. Great difficulties arose trying to co-ordinate power settings on both engines.

At high altitude, the oil tended to foam due to poorly designed oil pumps. Foaming oil circulated in the engines, failing to provide proper lubrication. Lack of adequate lubrication resulted in the disintegration of the connecting rod bearings which often burst through the engine crankcase, puncturing the oil tanks which poured their contents on to the hot exhaust pipe collector.

Goering became enraged at Heinkel's ongoing failures with the He-177 which led to a severe break down in Heinkel's relationship with Goering. This breakdown delayed and stymied development of the promising He-277 which Heinkel himself had much prefered to develop over the He-177. Possibly this was one of the factors why Germany lost the war through an inability to develop a true offensive strategic bomber force.


The He-177 A V-1 (first prototype)

Early models of He-177 had also suffered from instability in pitch and yaw. This was later overcome with the He-177 A-3 / A-5 model by lengthening of their fuselages. Later models also acquired redesigned DB 610 engines overcoming the earlier engine fire nightmares. With such improvements a large fleet of early He-177 A-0 and A-1 airframes were surplus and became a pool of airframes for conversion to the He-277 B-5. This conversion process began late in 1943 at Heinkel's factory in Vienna. Some sixteen were claimed built, however He-277 prototype number run as high as V26.

Most He-177 prototypes were assigned to Dipl.Ing Carl Franke of Eprobungstelle E-2 at Reichlin. Three crashed prototypes were replaced by three new airframes creating further confusion as to their identities. Replacement airframes may in fact have become He177B V-101 to V104, in which case may have involved conversion of He177 A-04 ("DL+AR"), A-06 ("DL+AT") & A-08 ("DL+AV") early pre-production airframes. 

 He-177 A-V1
  fuselage code/stkz "CB+RP"
 Destroyed landing 3 Oct 1941
 He-177 A-V2  fuselage code/stkz "CD+RQ" In flight break up from flutter 27 June 1940
 He-177 A-V3  fuselage code/stkz "D-AGIG" Destroyed in crash 24 April 1940
 He-177 A-V4 
 Break up flutter in dive trials 8 Jun 1941, crashed into sea off Ribnitz.
 He-177 A-V5  fuselage code/stkz "PM+OD" Crashed low level flight from simultaneous engine fire on both wings.
 He-177 A-V6  fuselage code/stkz "BC+BP" Destroyed 18 Dec 1943 (Allied bombing?)
 He-177 A-V7  Assigned weapons testing with IV/KG40
 He-177 A-V8  Testing of engines and flaps



Evolution of He-177 Versions

In November 1942 the troubled He-177 evolved from the A-O & A-1 model with a 1.6m lengthening to the fuselage. This change immediately created a much more stable aircraft known as the A-3 still using the 2,700hp DB606 engine.

The He-177 A-5 emerged with more powerful 2,950hp DB610 engines. The A-6 version was to have been a pressurised high altitude version. Prototypes of the A-6 were ultimately converted to He-277 aircraft. The He-177 A-7 ordered for delivery by Japan had much longer wingspan and at least one example was captured by US forces and flown to USA as a prize aircraft for further study.



The Russian website wingspalette: http://wp.scn.ru/en/ww2/b/446/21/0 features this example.

Other airframes manufactured for the A-7 variant however were abandoned and readily converted to the He-277.









[1]
The Luftwaffe:Creating the Operational Air Wing, 1918-1940, James S Corum 1997, p.129.

[2]
Hooten, Luftwaffe at War, Gathering Storm. 2007 p.33

[3] Ernst-Heinrich Hirschel, Horst Prem, Gero Madelung, Aeronautical Research in Germany: from Lilienthal until today, Volume 147, Springer 2004, p.215
   
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