He 177 and 277 performance difference

What exactly was the performance difference between the He177 and 277?

Was the reason for having 2 engines solely the requirement that it be capable of dive bombing?

Had coupling to engines together on one propellor been tried on any other aircaft previously?

[Primoz]

It had been tried on the Heinkel He 119 (double engine, single prop).

[Graham Boak]

The coupled-engine concept was an intrinsic part of the He 177 design from the start: the structural strengthening for dive-bombing came later.

Had there been no other differences, then the four-engined configuration of the He 277 would have had more drag, thus giving a lower top speed and poorer payload/range characteristics.

[Propellerhead]

No Nonny the dive bombing requirement was not the only reason for a twin airscrew layout. It also needed high level speed to satisfy requirements for a Ural bomber.

When Heinkel's chief designer, Siegfried Gunter developed the He-177 "Grief" (Griffon) he was obliged to meet specifications for a bomber 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 the bomb load at a speed not less than 500 km/h (311 mph) "at altitude".

RLM however suggested to heinkel as early as 18 November 1938 that he should also produce prototypes for a more conventional four engined layout as an insurance policy against failure of the DB 606 engine. This became the He-177H and later from May to August 1943 as the He-177B.

The He-177H later developed into the He-274. The He-274 however sported greater span wings and abandoned the He-177A undercarriage arrangement (like two petals retracting sideways to a rear retracting twin wheel bogie for He-274). When Hitler urgently required a Strategic bomber at a conference in Obersalzberg on 23 May 1943, the He-274 design was too different to be mass produced quickly on existing He-177A production lines so the He-177B design was developed into the He-277.

Hitler demanded a bomber which could bomb Britain day and night. The only way to achieve this was with very great altitude. the He-277 B-5 and B-6 were intended to overfly England at 49,200 feet, well beyond any interception. They were intended it appears to carry one very large 2.5 tonne bomb externally, outside the bomb bay, or 6 tonnes of small bombs internally.

The He-177A by comparison had ralatively low service ceiling and performance much like the Lancaster.

[Graham Boak]

There's something a bit odd about this dive-bombing story. The He177 ended up structurally weak for the conventional role: had it been strengthened for dive bombing there should have been no problems in this respect. The time taken from initiation of design to first flight does not seem particularly protracted by the standards of the time: stopping to redesign would have extended this.

Further, the suggestion that it was the RLM that desired a traditional back-up goes against the conventional story that Heinkel tried to force this option through against RLM opposition.

Are we looking at yet another myth that has been accepted as history, or perhaps even two?

[Propellerhead]

Originally Posted by Graham Boak

There's something a bit odd about this dive-bombing story. The He177 ended up structurally weak for the conventional role: had it been strengthened for dive bombing there should have been no problems in this respect. The time taken from initiation of design to first flight does not seem particularly protracted by the standards of the time: stopping to redesign would have extended this.

Further, the suggestion that it was the RLM that desired a traditional back-up goes against the conventional story that Heinkel tried to force this option through against RLM opposition.

Are we looking at yet another myth that has been accepted as history, or perhaps even two?

I suspect there is an aspect of myth that Goering prevented the He-277. Udet definitely hampered and obstructed it via his influence at OKL.

Goering did issue a decree against further development of the He-177A in 1942. This cancelled the twin propeller He-177 A4 high altitude aircraft, but that aircraft was reborn as the He-177 A6/R1 six of which were built as prototypes.

However, there was no cancellation of the He-177 H project in France. Nor was subsequent development of the He-177 A5, nor He-177 A7 prevented.

Heinkel Projekt 1041 Bomber A had originally been encouraged by Weaver. RLM granted it the type number "8-177". In November 1937 just one day after RLM gave it the 8-177 designation, meddling by Luftwaffe's high command (OKL) stipulated that it also meet requirements for "medium" dive bombing roles.

Once the design was frozen, under pressure from Udet, OKL changed it's mind stipulating that the He-177 now be capable of dive bombing at a steeper 60 degree angle not forseen in design planning. In 1942 this oversight came to light after midair break ups of V2 and V4 were investigated. There was something of a witch hunt by Goering looking for someone to blame for difficulties.

Ironically after the initial pre-production run of He-177 A-0 aircraft, dive brakes were omitted from production aircraft.

Heinkel himself dispised the He-177A and wanted to put the traditional bomber into production. The "back up" was originally known as the He-177 H with a traditional four engined lay-out. RLM opposed it's development on grounds that Heinkel had insufficient production capacity. In October 1941 Heinkel persuaded RLM to allow him to work on the He-177 H in France. he was granted permission in 1942 to develop two prototypes near Toulouse in France with the Farman brothers. He was also granted consent to build four pre-production prototypes at Rostock Marienehe.

Prior to becoming the He-277 B-5 it was also designated as the He-177 A8.

[Graham Boak]

That's the familiar story. But, if it is true, why wasn't the He177 strong enough to do dive-bombing missions? Why did it fail to meet the structural requirements for conventional missions?

If Heinkel hated it so much, why was it ever built? Surely it was Heinkel who pushed the entire twin-engine principle? Not that there was anything wrong with the principle, although there were considerable problems with the DB606 and the detail design of the He177 installation. The later DB610 does not seem to have been anywhere near as troubled, but by then the dog had been given a bad name - and Germany could no longer afford a strategic bomber programme (not that it ever could, probably).

Heinkel's comments have the ring of self-justification after the event. After it had failed, he wanted to wash his hands of it and be seen as the one who had it right all along. OK, but had he not been pushing it in the first place it would never have been built. A prime cause of the failure of the He177 was lack of adequate attention in the design stages, not something Heinkel would have wished to highlight. Blaming the OKL - and the dead Udet - was mightily convenient.

Obviously there is something in the traditional story, but not in the black-and-white way it is told. Yes, Udet did have an obsession with divebombing, but there is no suggestion that this carried over to other 4-engined bombers like the Me264. Was it even a requirement of the twin-engined Bomber B programme?

[Propellerhead]

The dive bombing role was an impromptue requirement not forseen by Heinkel when he submitted the design.

The dive bombing requirement first emerged from the final inspection of the Projekt 1041 mock-up on November 5, 1937, the same day that Projekt 1041 was officially designated the He 177 by the RLM, when Ernst Heinkel and Ernst Udet conversed after the inspection, about the future usage of Heinkel's design. Udet stated the OKL's requirement for the He 177 design to be able to execute moderate diving attacks, something Ernst Heinkel told Udet it would never be capable of doing.*

* Griehl & Dressel 1998, pg.9

Heinkel resented this and hated the requirement. The twin engined layout was for speed in meeting the fast Ural Bomber requirement. Not for dive bombing.

Goering was severely embarassed by engine development and flutter problems with the He-177A. Goering instituted a witch hunt like investigation by Oberst Petersen, later involved with trans oceanic Fw200 operations. Petersen's report identified causes for crashes and ongoing problems with the He-177A. Much of the problems he lay at the feet of poor servicing and maintenance rather than the design itself.

Various aircraft trials were carried out for Obst Petersen during August 1942. The initial production version of the Greif, the He 177 A-1, demonstrated a tendency for instability in the yaw and pitch axes that would have led to poor bombing accuracy in action. Petersen recommended a stretch of the fusellage to restore stability.*

* Griehl & Dressel 1998, p.46 & 54

During his investigations the strength of the wings were also reassessed and it was discovered that they had never been built to meet Udet's dive bombing requirements and Heinkel was correct in saying they could not be built to cope with dive bombing. In September 1942 Goering ordered the abandonment of Udet's dive bombing requirement for the He-177. According to Griehl & Dressel, during Goering's decision from September 1942, he also mandated work to commence on the conventionally powered He-177B.

[Graham Boak]

That Heinkel disapproved of any dive-bombing requirement does not read across to the earlier blanket statement that he despised the He177A. He may have come to hate it later, after the effect of its failure and faults, but that's not how things began.

That Heinkel did no work to make the aircraft suitable counters the comment that the delays and problems with the aircraft can be blamed on the dive bombing requirement. They are to be laid at the foot of the Heinkel works. Not that the delays were actually particularly unreasonable for that class of aircraft at the time.

There has been statements that the Rechlin studies came up with 250 modification needed on the aircraft, including one to stop leaking fuel draining onto hot exhaust pipes when at landing angles of attack. That is not entirely compatible with poor maintenance, although such there clearly was. For that, much of the blame must lie with Daimler Benz, but in the end Heinkel was the prime contractor, to use modern parlance.

[Propellerhead]

Erhard Milch was perhaps part of the problem too for he had a reputation for pressuring aircraft manufacturers to rush aircraft into production before they were truly ready.

Many of the delays with the He-177A stemmed from attempts to correct engine problems and in particular a technical fix for foaming oil. There was a significant pause in development flying in which the aircraft was grounded waiting for a fix to the engines.

It was during this time in late 1940 that Heinkel began pressing for a conventional engine layout with DB 603 engines.

Ironically the He-177B had problems of it's own because with all four propellers spinning the same way it encountered significant torque issues and required development of a twin finned tail.