He277: Promising? Or further development of a bad apple?

[Matt308]

The He177 met with little success due to numerous design issues resulting in few operation sorties for its designed long rang bombing mission. While these design issues (hydraulics, fuel system, engine gearbox, etc) plagued the aircraft to its end, the airplane's mission was constantly being changed to unrealistic expectations.

Heinkel also developed the He274 and He277. My understanding is that Goering did not want the He277, and Heinkel pursued its development as the He177B. Below is the pic of the He-277 with four engines. A design change to address the engineering concerns with dual engines coupled through a common gearbox. I have seen the He274 with only two engine nacelles, but with dual vertical stabilizers.

What was the primary difference between the He177 and He274?

Was the He277 a derivative of the He177? He274? Both?

And given the multiple He177 engineering issues that were not related to the dual coupled engine design, was Heinkel pursuing a bombing solution that had been overtaken by events?

[DerAdlerIstGelandet]

Well the 277 I believe was a step in the right direction. They corrected the problems with the He-177 on it and got rid of those damn coupled engines.

[Henk]

Yup Adler the He-277 were a way better design than the He-177. Just too late though. I think the He-274 were tested by the French government.

[V-1710]

The He-177 biggest issue was the coupled Daimer-Benz engines. Going to 4 conventional engines certainly solved that problem. Didn't Heinkel want to go with 4 engines early in the program?

[DerAdlerIstGelandet]

The He-177 was not a bad design, as V-1710 said and I said in an earlier post it was the coupled engines that caused the most problems. They were not very reliable and would catch on fire easily.

The He-274 and He-277 corrected the problems of the He-177 but were too late to do anything. The He-274 was flown by the French after the war.

[Matt308]

So what pics do I have of a He177 (ie two engine nacelles) with dual vertical stabs? I was under the impression it was the He274. I'll try and post them too.

[Matt308]

It's small, but all I have. Is this just an early He177 prototype?

[Smokey]

It's the Heinkel He 274 according to LuftArchiv.de

LuftArchiv.de - Das Archiv der Deutschen Luftwaffe im 2.Weltkrieg

[Matt308]

Right! With the bigger pic I can see the other engine nacelle behind No.1 engine. Thanks Smokey.

[Gnomey]

I agree with what has been said if the engines had been uncoupled like in the 277 and 274 then it would of been fine, however the modifications came to late and too few were made to make an impact.

[Henk]

Yes Adler it was those coupled engines on the He-177 that made the fuel boil and thus were easy to catch fire, well I have a few pics of the He-274 and He-277, but will post them a bit later.

[V-1710]

Actually, it wasn't boiling fuel that would set a Daimler-Benz 610 on fire. The problem was with it's basic configuration. As it was double inverted V-12's, the two center cylinder banks shared a common exhaust manifold. This manifold, while getting very hot with 12 cylinders exhausting into it and poor airflow around the outside of it, was also prone to having oil leaking on it due to it being positioned low and in the center of the nacelle. If enough oil collected on the exhaust manifold to start a fire, it wasn't long before the fuel lines would catch fire, and at that point it was all over. The Allison V-3420 didn't have this problem, as the cylinder banks were not inverted, and there was enough space between the center banks for separate manifolds and adequate air flow. You know, the He-117 probably would have been a great plane with a pair of V-3420's!

[Matt308]

V-1710,

Wasn't another problem the timing of the gearbox between the coupled engines? Improper timing resulting in shear stress on the gears and resultant timing failures compounding ability to maintain symetric power application?

[V-1710]

Didn't hear about that being a problem, but it certainly sounds like it could have been an issue. Early in the He-177's testing, oil foaming due to improperly sized oil pumps resulted in connecting rod failures, which not only resulted in total engine failure, but also fire would result as the hot oil coming out of the busted crankcase and oil tanks would invariably land on the hot exhaust manifolds. Another design factor that made engine fires so disastrous on the He-177 was due to the fact that the back of the engines were very close to the wing spar. Not only did this create a 'rats nest' of leaking fuel and oil lines (another potential cause of fire) it also meant that an engine fire could rapidly result in structural damage to the wing.

[delcyros]

Original question belongs to whether or not this plane was promising.
I tend to disagree. The He-277 (and to a lesser degree the He-274) were technically interesting planes, worth mentioning. But by their time, the Luftwaffe had other needs than strategical bombers. Fighter and tactical bombers were urgently needed. They already developed V-1 and V-2, which to some degree could substitute the role of a strategical bomber for much lower costs. With the numerical superiority of first class piston A/C the allied had in this stage of war in mind, a new strategical bomber design is only justified in case it is either very fast (requiring jet propulsion) or flying extremely high or both.