He-177/277/274

[KJ_Lesnick]

This is a quick rehash, and revolves around a couple of things centering around the Heinkel He 177 (as well as the He-177B/277 and He-274), and some WHIF's revolving around them.

From what I remember, the initial requirements for the He-177 dictated the following...

• Top speed of at least 311 mph/500 kph
  
• The ability to carry out shallow/moderate-angle dives (glide-bombing)
  
• Specified range with payload (not sure what the initial spec called for, but it ultimately carried 13227 lbs/6000 kg internal)
  

At this point my questions are as follows...

• Was the aircraft always expected to release bombs in shallow/moderate dives?
  
• Was the aircraft designed to release bombs in level flight normally with the provision for shallow dives?
  

From the initial descriptions the latter seems to be the case, but I don't know (hence the question).

From what I gather: The maximum speed requirements (and possibly a desired speed of more like 550 kph/342 mph), the range and payload dictates (and possibly the ability to accelerate to a reasonably high speed in the glide-bombing attack), lead to the decision to use two engines for the following reasons...

• The drag produced by four nacelles, each with a carburetor intake, oil cooler, and radiator would produce more drag than two
  
• two huge propellers were either more efficient than four moderately sized ones overall in terms of either net-thrust, or greater surface area impinged upon by slipstream from four propellers.
  

...which would allow more speed for the same overall horsepower (The projected increase was approximately 3% over a four engine design).

This then lead to the DB606 propulsion system, which effectively consisted of...

• 2 x DB-601's connected in such a way that they normally run as one, driving the propeller
  
• The engines could be decoupled and operate separately
  

...as well as the decision to use a surface evaporative cooling scheme similar to the He-100 with the hope that it would eliminate all cooling drag?

My questions at this point are...

• Who dictated the twin-propeller requirement: Heinkel or the RLM?
  
• Would it have been acceptable for Heinkel to simply "eat" the 3% speed difference and still meet the 311 mph maximum speed on four propellers?
  
• Was the 3% figure based on installation drag with a normal radiator, or with the surface evaporative cooling?
  

Next, as the plane was being developed, a decision was made based on the statistical analysis from the Spanish Civil War on the use of level-bombing, and dive-bombing lead to the conclusion that the aircraft's requirements should be modified to allow a dive-angle as high as 60-degrees.  Something that Ernst Heinkel allegedly said it would never be capable of doing.

• Why was such accuracy demanded of such a large aircraft?  These planes were designed predominantly to destroy railway yards, harbors and docks, aircraft construction factories, and whole cities in massed raids
  
• Did they factor in the accuracy increase of glide-bombing compared to level bombing?
  
• Where would I go to be able to find accurate data on dive-bombing, glide-bombing, and level-bombing accuracy from aircraft with speeds from around 300-450 mph (basically propeller-era designs)?
  

The higher dive-angles produced a considerably higher dive speed which might very well have required an increase in the dive-speeds, as well as the strength to pull high g-loads once the bombs came off, the effects appeared to have the following results (as far as I know)...

• A heavier structure
  
• Either less fuel capacity, or a lower fuel-fraction owing to the heavier fuselage
  
• The landing-gear had to be beefed up producing an overly complicated structure that may have had a variety of problems (I think)
  
• The flaps had to be re-designed (which I take little issue with as they seemed overly complicated)
  

... and this had the results of producing a slower climb-rate, poorer acceleration, a lower top-speed, and less range.  The firewalls were also removed and that made fire-spread very fast.

Though the engine was controversial, and posed a great deal of trouble in the first 130 aircraft to enter production service for the following reasons

• The engine did run hot, even hotter than the DB-601 due to the central exhaust system, and the natural soot and grease deposits if they got hot enough could ignite
  
• The engine did have a tendency to leak a bit of oil, which only aggravated things
  
• The cowling they fit was tight and this was good for drag, but bad for cooling and this meant the engine ran uncomfortably hot
  
• The placement of the engine against the spar, and the poorly arranged electrical wiring positions made electrical fires possible
  

The engine had been used on other aircraft, though it was mentioned that a poorly designed oil pump could cause foaming and deprive the engine of lubrication, this could result in a disintegration and fire. 

While the He 119 and Me 261 used these without incident, my questions are: Why didn't they have the same problem?

• The Me-261 and He-119 seemed to have lower cruise altitudes: Was the thinner air a factor on its own, or just at high temp?
  

All that out of the way, I was thinking how would the design have compared to the actual aircraft provided the following things were different

• The aircraft had four engines with surface evaporative cooling
  
• The aircraft was designed for shallow/moderate angle glide-bombing attacks
  

[maxmwill]

While this may not seem to be part of the seeder discussion, it might shed some light on the 177's flight characteristics.

There was an article in recent issue of Aeroplane(I think, either that or Flypast), authored by Eric "Winkle" Brown, in which he flew the 177 after the war and lived to tell the tale.

It is quite informative as to answering such questions as, can it actually dive bomb at all?" and others.

[Rheged]

Winkle Brown was not at all happy flying the 177, and reckoned it a very fragile aircraft.  I think that this was the aircraft he said should carry a maximum payload of "....a VERY SHORT  verbal message......".

[KJ_Lesnick]

maxmwill

While this may not seem to be part of the seeder discussion, it might shed some light on the 177's flight characteristics.

There was an article in recent issue of Aeroplane(I think, either that or Flypast), authored by Eric "Winkle" Brown, in which he flew the 177 after the war and lived to tell the tale.

I have a book which was about Luftwaffe planes he flew, that one came up.

It is quite informative as to answering such questions as, can it actually dive bomb at all?" and others.

Yeah, it actually could: Since it was fairly heavily based on g-limits, it required one to know the aircraft's weight at all times, but it could be done.  The early issues with the tail coming off was due to flutter (they also put a larger tail on to reduce control loads), and not due to an inherently weak design.

I'm not sure if Brown knew that at the time he strapped into it: He said the controls were uncomfortably light for such a big aircraft, and the known g-limits, and the fact that he'd heard of the plane coming unglued gave it the feel of being very big, and very weak (not a good mix), he described it as one of the (few) german designs he did not like.

[rickshaw]

Ernst Heinkel always believed that the production of the He177 was too rushed.  When they discovered that the engine bearers were too short and that forced the fuel and oil lines around too tight corners, which lead to them fracturing under the vibrations of the engine, which in turn lead to foaming oil and leaking fuel, which in turn lead to engine fires which burnt through the main wing spar in minutes, he wanted to halt production and redesign them.  Goring and Milch refused and so the aircraft kept falling out of the sky.   There was nothing inherently wrong with the aircraft design, it was just badly built.

[KJ_Lesnick]

rickshaw

Ernst Heinkel always believed that the production of the He177 was too rushed.  When they discovered that the engine bearers were too short and that forced the fuel and oil lines around too tight corners, which lead to them fracturing under the vibrations of the engine, which in turn lead to foaming oil and leaking fuel

So this was the design specifics and not inherent to the DB606

[ysi_maniac]

Fw-200 Condor + He-177 Greiff (Nose, tail, wings, and engines)

[NARSES2]

Very nice  Got a slight Junkers look about it

[ysi_maniac]

What if Greif's issue with coupled engine were solved with tandem engines (as suggested by GTX)?

[ysi_maniac]

In order to fix the problem with cooling... what about installing deeper annular radiators?