Germany goes for centrifugal flow turbojet engines? (1 Viewer)

[z42]

Since we've lately had quite a few threads about all the mistakes (or however you wish to characterize it..) the Germans made and what they could (should?) have done better, here's another one: Should they have gone for centrifugal flow turbojet engines instead of axial flow?

Yes, axial flow eventually won out, with much smaller diameter being a big win. (Though to this day many turboprop engines have a number of axial stages followed by a final centrifugal one). But, the centrifugal ones are simpler. So by going for centrifugal designs they could have had something in service sooner?

And while we're at it, target a bit more thrust than the historical Jumo 0004 / BMW 003, enabling single engine fighters from the get-go. Maybe something that looks a bit like the Ta 183, with a nose intake? Performance doesn't have to be as good as the Me 262, even a top speed of 800 km/h should be enough to outclass any prop fighter. More important to have something reasonably reliable in service sooner. And which doesn't flameout when you give the throttle lever a stern look.

 

[tomo pauk]

Yes, axial flow eventually won out, with much smaller diameter being a big win. (Though to this day many turboprop engines have a number of axial stages followed by a final centrifugal one). But, the centrifugal ones are simpler. So by going for centrifugal designs they could have had something in service sooner?

Seems also that centrifugal engines were lighter. Being simpler should mean that it is easier to make them en masse (prerequisite being that the air-cooled turbine blades are also in the place).

Should they have gone for centrifugal flow turbojet engines instead of axial flow?

Going with centrifugal flow would've probably meant that they have a less of a rocky start wrt. both development and mass production.

 

[MIflyer]

I suspect that centrifugal engine turbine wheels were less sensitive to the type of alloy used, having more material to add strength. On the other hand they likely would have used more material than the individual blades.

 

[bf109xxl]

Since we've lately had quite a few threads about all the mistakes (or however you wish to characterize it..) the Germans made and what they could (should?) have done better, here's another one: Should they have gone for centrifugal flow turbojet engines instead of axial flow?

It's not a mistake. It's rather a bad luck. The Germans had a chance to jump over the period of fascination with centrifugal compressors straight into the future - powerful jet engines with axial compressors (RR Avon class). But they could not find a solution to the aerodynamic problems, although they were close - the Jumo 012 could become a breakthrough. In early 1947, German engineers completely redesigned the Jumo 012 (012B) and achieved a very good result. All they had to do was to replace the manager - Scheibe with Brandner - and involve H.-J.Schröder as a leading mathematician. It took about a year and a half, which could have been saved with a rational choice of personnel. And I'm not sure they would have succeeded with centrifugal compressors - they would have needed more time to gain experience.

 

[GrauGeist]

Germany had the opportunity to field a true Jet-powered fighter well before the Me262 in the form of the He280, which was powered by centrifugal flow jet engines.
The HeS8 produced enough power to enable the He280 to perform well, though the fighter was intended to have a pair of HeS30 engines.

However, the RLM, once again, screwed itself by interfering with development and ordered Heinkel to develop the HeS011 instead.

Adding to the RLM's idiocy, the HeS30 development, which held a great deal of promise, was set back by infighting and eventual cancellation due to Schelp's favoring the Axials of BMW and Junkers.

*had* the RLM backed the HeS engine development (HeS3/HeS8/HeS30) early on AND not interfered, it is more than likely the HeS30 would have been ready for production sooner than late 1942 and the He280 would have been in the skies two years before the Me262.

 

[z42]

I suspect that centrifugal engine turbine wheels were less sensitive to the type of alloy used, having more material to add strength. On the other hand they likely would have used more material than the individual blades.

AFAIU centrifugal flow jet engines all have axial flow turbines, only the compressor is centrifugal. (Now I'm sure someone will prove me wrong by digging up a diagram of some jet engine with a centrifugal turbine )

 

[bf109xxl]

AFAIU centrifugal flow jet engines all have axial flow turbines, only the compressor is centrifugal. (Now I'm sure someone will prove me wrong by digging up a diagram of some jet engine with a centrifugal turbine )

 

[SaparotRob]

Ask and ye shall receive.

 

[bf109xxl]

 

[bf109xxl]

Since we've lately had quite a few threads about all the mistakes (or however you wish to characterize it..) the Germans made and what they could (should?) have done better, here's another one: Should they have gone for centrifugal flow turbojet engines instead of axial flow?

Ohain unsuccessfully tried to bring the engine with centrifugal compressor to an acceptable state, but by early 1942 the thrust remained at 550 kg. HeS 10 was designed, but its thrust would not exceed 900 kg, which was also insufficient. Heinkel himself counted on the engine with axial compressor (HeS 30), but this development also failed.
I am very impressed by the number of different projects of the Germans, which at that time was clearly unacceptable.

 

[MIflyer]

I do recall an article that said that the Germans concentration on axial flow jet engines was a mistake because it was too early for that type design. I thought that was a bit odd, since axial flow was a better approach in the long run. But after dealing with centrifugal cooling turbines used in aircraft air cycle systems I came to appreciate that while it was not a sure thing with turbines turning at 75,000 RPM, you had a bit more latitude in the turbine wheel design when the centrifugal approach was used. And aside from that, almost every major power had at least some experience with building exhaust driven turbosuperchargers of that design.

 

[GrauGeist]

Heinkel himself counted on the engine with axial compressor (HeS 30), but this development also failed.

The HeS30 did not fail, it's thrust-to-weight ratio of 2.20, was unmatched until 1947 and was operating reliably in late summer 1942.

The RLM cancelled the project in favor of the BMW003 and Jumo004.

The HeS011 engine that the RLM did want, was too complex and was not fully developed by war's end.

The HeS30 was a huge missed opportunity. It's weight was half that of the Jumo004 with twice the output and did not require exotic metals.

 

[marathag]

The HeS30 was a huge missed opportunity. It's weight was half that of the Jumo004 with twice the output and did not require exotic metals.

Heinkel centrifugal compressor? Even better if made for a turboprop.
Germany didn't really need fast jets.

They needed something just fast enough to keep up, and a bit ahead of the Allies, while doing it on Kerosene.

But Ernst wasn't as good a Nazi as his main competitor, Willy.

 

[GrauGeist]

Heinkel centrifugal compressor? Even better if made for a turboprop.
Germany didn't really need fast jets.

They needed something just fast enough to keep up, and a bit ahead of the Allies, while doing it on Kerosene.

But Ernst wasn't as good a Nazi as his main competitor, Willy.

The He280's HeS8 engines operated on kerosene.

And it was faster than any Allied aircraft in service at the time (and several years after, too)

 

[z42]

Even better if made for a turboprop.
Germany didn't really need fast jets.

They needed something just fast enough to keep up, and a bit ahead of the Allies, while doing it on Kerosene.

I agree, sort of. They didn't need to push the jet concept to the limit. Something like 100 km/h faster than the late-war prop fighters would have been plenty. So in that sense the Me 262 was overkill (whereas the He 162 was just 'too cheap' to be a good fighter, regardless of how fast it was or wasn't).

That being said, I'm not sure the early 1940'ies turbine technology was good enough that they could produce a turboprop fighter with the required performance advantage over the Allied props? A jet engine would provide more 'legroom' in that even a fairly primitive engine could provide the required thrust.

 

[z42]

I do recall an article that said that the Germans concentration on axial flow jet engines was a mistake because it was too early for that type design. I thought that was a bit odd, since axial flow was a better approach in the long run.

It seems Frank Whittle was also of the opinion that axial flow was the better long-term option, but he decided to go for a centrifugal compressor design because it was easier to make it work (source: some interview video with Eric Brown, IIRC). That's sort of the premise of this thread, could the Germans have had jets in service a couple of years earlier had they made the same decision? Axial is better long term, but centrifugal ought to be plenty enough to outclass piston fighters, which is what is required for the initial generation(s).

 

[z42]

I am very impressed by the number of different projects of the Germans, which at that time was clearly unacceptable.

I'm not sure. On one hand, yes once you have a basically functional engine design, it makes sense to concentrate resources on that to get it out of the door ASAP, and then further improve it. OTOH, considering how new jet engine technology was at the time it made sense to have a multitude of different projects to explore the design space. Where's the 'optimal' balance?

 

[z42]

The HeS30 was a huge missed opportunity. It's weight was half that of the Jumo004 with twice the output and did not require exotic metals.

HeS30 does indeed look very impressive on paper. But hard to say they wouldn't have ran into similar issues that subsequently seriously delayed the 003 and 004?

Further, lack of exotic materials might imply a seriously limited lifespan for the hot parts? Unless they had invented something like film cooling?

In any case, considering how promising it was, canceling it was arguably a big mistake.

 

[bf109xxl]

I'm not sure. On one hand, yes once you have a basically functional engine design, it makes sense to concentrate resources on that to get it out of the door ASAP, and then further improve it. OTOH, considering how new jet engine technology was at the time it made sense to have a multitude of different projects to explore the design space. Where's the 'optimal' balance?

Distributing resources across many projects is a guaranteed lose-lose. Concentration of efforts on a small number of the most promising ones is certainly a very risky step, but it gave a chance, if not to win, then to lose on more honorable conditions.
With some luck with personnel selection, the Germans could achieve a much higher level of perfection of jet engines with axial compressor - e.g., with the mentioned Jumo 012. This engine German engineers completed later in the USSR. All the necessary arrangements for this could have been made three or four years earlier in the Reich.

 

[bf109xxl]

HeS30 does indeed look very impressive on paper. But hard to say they wouldn't have ran into similar issues that subsequently seriously delayed the 003 and 004?

It is possible that due to its low weight, the HeS 30 would have a very short service life (just a hypothesis). In any case, this axial compressor engine is proof that the use of a centrifugal compressor did not offer an unquestionable advantage at that time.