Germany goes for centrifugal flow turbojet engines?

[bf109xxl]

Again with the hostile response. Calm it down. You get defensive whenever anyone questions what you say, you don't provide what you expect others to do and you call everyone names when they counter your points or call them out. Play nice.

This is coming from a man who was constantly provoking me with his rudeness. ))) And as soon as he received the same coin in return, he immediately started talking about my hostility.
Stop preaching, better look for some numbers to argue your unsubstantiated statements.

 

[MIflyer]

It is a totally new independent design, having V-1710 at the initial design stage.

Nope! Nope! Nope! Read the definitive work on the P-47, Warren Bodie's extensively researched book, "Thunderbolt!" It was based on the P-43 which was based on the P-35 which was based on Seversky's two seat sportplane. After the P-43 showed promise Republic abandoned its initial P-47 concept, a lightweight fighter using a V-1710 and enlarged the P-43 with the same arrangement but a R-2800 instead of a R-1830, to make the P-47. FACTS!

 

[Shortround6]

Nope! Nope! Nope! Read the definitive work on the P-47, Warren Bodie's extensively researched book, "Thunderbolt!" It was based on the P-43 which was based on the P-35 which was based on Seversky's two seat sportplane. After the P-43 showed promise Republic abandoned its initial P-47 concept, a lightweight fighter using a V-1710 and enlarged the P-43 with the same arrangement but a R-2800 instead of a R-1830, to make the P-47. FACTS!

I guess it depends on what "enlarged with the same arrangement" means

So if I take a P-35 and scale it up 13.1% I get a P-47 I can drop a R-2800 into ?
Off course the gross weight clean about doubles but what the heck,
Wait a minute, if I multiply the wing span by 1.13 (difference in percentage of the wing span) then by 1.13 again (13% longer cord ) I only get 280 sq ft of wing area, not 300 sq ft.
Is my math wrong or did they 'tweak' the outline just a bit?
Of course the fuselage got about 33% longer (just under 27ft to just over 36ft)

I am so confused

 

[DerAdlerIstGelandet]

I'm sick of the constant bickering, insults, and childishness exhibited by some. It ruins the discussion.

I'm seeing a common denominator here, and in several threads.

Patience is wearing thin…

 

[z42]

The problem with the Germans was that while they sank money and resources into advanced projects like rockets and jets and missiles and cool stuff that everyone believes meant they were more advanced than everyone else, we forget that the Germans didn't get some of the basics right. Had they concentrated on these, perhaps they might have been able to have lasted longer - of course it is to our benefit that they didn't.

No objection there. Nazism needed to be utterly crushed, and it was good that it was. Not that Soviet communism was much better, but alas..

They never got a 2,000 hp plus engine into production and service, their advanced four engined heavy bomber programme Bomber A was a failure, resulting in one of the worst aircraft of the war, the He 177, their replacement fast bomber programme Bomber B was also a failure because they couldn't get their 2,000 hp plus engine to work, which meant that aircraft of pre-war vintage were kept on in service for far longer than they should have been. The He 111 was still in the Luftwaffe's frontline in 1945, equating to the RAF relying on the AW Whitley, or the USAAF relying on the B-18 Bolo in that time.

The Me 262 and He 162 were highlights, but were troubled because of their unreliable engines and the reliance on forced labour for their manufacture.

Yes, and no. I'm not sure a 2000 hp engine, per se, would have been that necessary. The Allied heavy bomber fleets that flattened Europe were using ~1200 hp engines, and the arguably best piston fighter of the war, the Mustang, didn't have a 2000 hp engine either. The Allied 2000 hp engine equipped planes certainly helped, but honestly I don't think the air war would have been lost without them either. But the goal of powerful next generation piston engines is perhaps instructive of the German engine development effort flailing in all kinds of directions instead of focusing on improving their basic engines (605/603/213), which still had plenty of potential left in them.

As for the jets, yes it was very early days for jet propulsion and they suffered from all kinds of problems. However, I'd also argue that jets represented one of the few ways that could have allowed the LW to face the onslaught of Allied air power from say late 1943 onwards. Incrementally better piston engine aircraft weren't going to cut it anymore.

The cost of the way in which the Third Reich was run was directly responsible for Germany's failures. The fostering of internal squabbling, currying favour, self-promotion and outright sabotage of competitors' plans was no way to run things during a war footing, but that's how they did it.

This is, generally, how dictatorships work. The strongman at the top stays at the top by playing the various factions against each other and have them compete in bootlicking. It's inherent in how the entire system works. Nazism, fascism, communism, it's all the same.

Democracies may seem weak and impotent, endlessly debating things in public. But once they decide to act, they are immensely powerful.

There might be a lesson here for the modern world as well..

 

[Marcel]

bf109xxl and nuuumannn can you both tone down the personal attacks? It's not helping and I might have to step in here which I don't want to do.

 

[bada]

Rubbish. The compressor blades were made of poor quality metals and flame outs caused by the engines shedding fan blades or blades disintegrating is widely recorded.

Must say this is the first time i ever read of poor compressor blades. Would be nice to add some official figures and quotes.

...they did have a foot in the past. The Riedel starter motor was one of these. Relying and small piston engines with their own fuel supply for starting means the engines cannot be started in the air and it seems like a bit of a waste of weight. Surely an electric or even cartridge starter, like the British engines would have been a better option. The Riedel was started by a ring pull starter that was done by guys on the ground standing in front of the engines, the rung protruded out of the bullet and had to be pulled to engage the starter for each engine.

Ok, this is like a comment by someone that totally missed the starter buttons inside the cockpit. The riedel could be fired-up from the cockpit, it wasn't done on the ground to not overload the batteries, just like the BWM801 were started with an APU and the Db's by cranks (or apu's) for the same reason.... The riedel was actually a very good idea as the 004's spool time at start sequence was high, meaning it needed to run for a long time before combustion was able to run the 004 by it's own power. An electric starter would burn out directly, not even commenting the "cardridge" part

Another peculiarity was the fuel management of these engines. Thrust and fuel flow was managed manually by the pilot based on instrument readings, which meant the pilot had to keep a keen eye on fuel flow and engine temp gauges to move the power levers and the zwiebel, the variable thrust cone located in the exhaust nozzle, which was driven mechanically by a long shaft that extended aft to the thrust chamber. By 1945 this was relatively simplistic because there were already mechanical and electric fuel control devices fitted to piston engined aircraft, not to mention constant speed propellers, which equated to varying thrust output, rather than controlling the zwiebel, whose operation should have been automatic and keyed into the fuel control system, rather than manually actuated by the pilot.

Love this part, comparing apples to patotoes (not even oranges).
Having such a remark done when the engines used in their airplanes were still "carburated" without any automatic engine management devices is very funny.
But yes, the 004 was fuel pressure sensitive (unlike the 003 that had a fuel auto-regulator) and it wasn't easy for the pilots to unlearn their reflexes gained on internal combustion engines (jerking the throttle).
The fuel flow management was indeed manual, like in any engine, it's called the throttle Some engines are more sensible than others, my old CR500 from 30 years ago was the perfect example of it, once you learned how to use it, there is no problem anymore.
The onion was automatic , auto regulated, no pilot input needed.

The germans redrew the 004A so it could be easily mass produced, that gave the 004B , that's the reason they were able to build more than 5000 of them, meanwhile the british built theirs in a small shack and for the same period, build 120 of them , all versions included.

Was the 004B a bad engine? 50/50 yes and no. it did it's job, not so badly as mainstream historians want to picture it, but it could be better, with better logistics especially.
it was a war-tool, build for a role and to be thrown away, could it be better, yes, the 004D would be much better, but it never came to operational status.

anyway, in42, the Hirth had much more potential and faster (easier) development curve than the 003/004, but stupid administration and oversized ego's got it put aside....


Nice Vid of original 004 in action:

View: https://www.youtube.com/watch?v=FPazuFQZE3o

KR

 

[Zmauky]

Just one small addition.
Even today, it is a rule not to buy a car that is a new model for the first few years until the "childhood diseases" of a complicated technological system are sorted out.
And jet engines were also new as a technology (in serial production). We can argue whether the German engines worked for 20 or 25 hours, but the Allied side also had initial problems. The P-80 did not fly on engines that were good for 200 hours of operation - in fact, the first XP-80 ate itself and the tests in England were stopped because one crashed (due to the engine) and not to mention the death of R.Bong. So ....

 

[z42]

Just one small addition.
Even today, it is a rule not to buy a car that is a new model for the first few years until the "childhood diseases" of a complicated technological system are sorted out.
And jet engines were also new as a technology (in serial production). We can argue whether the German engines worked for 20 or 25 hours, but the Allied side also had initial problems. The P-80 did not fly on engines that were good for 200 hours of operation - in fact, the first XP-80 ate itself and the tests in England were stopped because one crashed (due to the engine) and not to mention the death of R.Bong. So ....

All the combatants rushed immature systems into service during WWII. Germany obviously much more than most, but the others had their fair share of botched introductions (*cough* Sabre *cough*).

 

[nuuumannn]

Must say this is the first time i ever read of poor compressor blades. Would be nice to add some official figures and quotes.

I'm not near my sources right now, but it is a known factor that compressors failed in the Jumo 004. When I'm near my info I'll dig it out.

Ok, this is like a comment by someone that totally missed the starter buttons inside the cockpit. The riedel could be fired-up from the cockpit, it wasn't done on the ground to not overload the batteries,

Looks like I missed that part of the rating course on the 262! Maybe I was asleep during that part... Ah, that is an interesting oversight, I wasn't aware the Riedel could be started from the cockpit. I was under the impression it was ground start only.

Love this part, comparing apples to patotoes (not even oranges).

Why? Power management between gas turbines and pistons is the same! Fuel flow is governed by mechanical fuel controls linked to the power levers in both types of engine. Automatic fuel management systems certainly existed, remember the Germans developed the Kommandogerat. As for the throttle, not the same role as automatic fuel control, fella, I think it's you getting mixed up here. Even modern electronic engine management systems in modern aircraft require power levers or throttles. A C-130J cockpit, note the four power levers.

_ADP8893

 

[nuuumannn]

Yes, and no. I'm not sure a 2000 hp engine, per se, would have been that necessary.

Hmm, that's a bit like saying, we don't need to develop gas turbines because piston engined aircraft are doing okay, thanks. Regardless of whether current aircraft were using lower power outputs, all the major powers including the Germans worked on 2,000 hp plus engines, but not all of them worked. Let's put it this way, the Germans hinged the next generation of their aircraft development on them, the Jumo 222 was to power the Bomber B but they couldn't get it to work successfully. If they had, do you think that they would have relied solely on lower powered engines? The Brits shoehorned a Griffon onto the Spitfire and that worked out pretty well for them, the Mk.XIV had terrific gains over its contemporaries.

As for the jets, yes it was very early days for jet propulsion and they suffered from all kinds of problems. However, I'd also argue that jets represented one of the few ways that could have allowed the LW to face the onslaught of Allied air power from say late 1943 onwards. Incrementally better piston engine aircraft weren't going to cut it anymore.

That's right and gas turbines kind of rendered engine developments redundant, but in wartime, you cannot simply end one production line and begin another without major disruption to supply lines and so forth.

This is, generally, how dictatorships work. The strongman at the top stays at the top by playing the various factions against each other and have them compete in bootlicking. It's inherent in how the entire system works. Nazism, fascism, communism, it's all the same.

Democracies may seem weak and impotent, endlessly debating things in public. But once they decide to act, they are immensely powerful.

There might be a lesson here for the modern world as well..

Now I agree with you on that. As you have pointed out, yes, that is how dictatorships work, which is why they don't work, just like Nazi Germany. You can't run a war like that. Germany proved it. As for the modern world, Yes, Yes, Yes...

bf109xxl and nuuumannn can you both tone down the personal attacks? It's not helping and I might have to step in here which I don't want to do.

Sorry Marcel. I will no longer engage in discussion with him. It's easier.

 

[bf109xxl]

Sapienti sat.

 

[z42]

Here's an article that made the rounds recently about why jet engines are expensive.

Why it's so hard to build a jet engine

Civilization's toughest technical challenges are those that require extraordinary (and constantly improving) performance to be delivered at a low cost.

www.construction-physics.com

The author is not an authoritative source on jet engines, but still, it's a decent enough overview. In particular it has some nice graphs nicked from a paywalled article describing TBO, specific fuel consumption, etc. as a function of time. And it shows a somewhat smooth and steady rate of improvement, with no evident low-hanging fruits. Or to put it another way, every advance was the result of a lot of $$$, blood, and sweat. So perhaps we shouldn't assume that the Germans, or anyone else for that matter, could have made dramatic advancements in time to make an impact during WWII. Biggest advancement is perhaps recognizing the potential earlier and start funding R&D at a higher level sooner?

 

[tomo pauk]

Here's an article that made the rounds recently about why jet engines are expensive.

Modern and powerful jet engines are indeed expensive. But more expensive than the piston engines of the similar power - I don't think so.

Yes, we cannot directly compare the jets and 'pistons', but still. Eg. Dobrynin VD-4K of 4300 HP + the cost of the turbo + cost of 3 blowdown turbines vs. General Electric T64-100 turboshaft of the similar power?
Expensive materials required to make the VD-4K (2065kg + the turboes) vs. the expensive materials to make 327 kg light T64? Price for the complete engines?

The author is not an authoritative source on jet engines, but still, it's a decent enough overview. In particular it has some nice graphs nicked from a paywalled article describing TBO, specific fuel consumption, etc. as a function of time. And it shows a somewhat smooth and steady rate of improvement, with no evident low-hanging fruits. Or to put it another way, every advance was the result of a lot of $$$, blood, and sweat. So perhaps we shouldn't assume that the Germans, or anyone else for that matter, could have made dramatic advancements in time to make an impact during WWII. Biggest advancement is perhaps recognizing the potential earlier and start funding R&D at a higher level sooner?

Sometimes, it depends a lot on the path taken. One path might offer the savings of both the material, coin and time vs. another path.
With radial compressors, Germans were trying to go away from the beaten path, while the centrifugal compressors were using the accumulated knowledge from the compressors used on piston engines. For the pressure ratio of, say, 6:1, making two compression stages with centrifugal compressors should've been faster, easier and cheaper than making the required pressure ratio with 6-8 stages of radial compressors.
Granted, earlier and better support by the RLM should've changed a lot wrt. the German jet engines.

 

[GrauGeist]

Ok, this is like a comment by someone that totally missed the starter buttons inside the cockpit. The riedel could be fired-up from the cockpit, it wasn't done on the ground to not overload the batteries, just like the BWM801 were started with an APU and the Db's by cranks (or apu's) for the same reason.... The riedel was actually a very good idea as the 004's spool time at start sequence was high, meaning it needed to run for a long time before combustion was able to run the 004 by it's own power. An electric starter would burn out

I must have missed this earlier.

The Riedel starter was most certainly pull started on the Jumo004 engines. The switches seen on the Me262's panel were for starter ignition on/off and the pull start cable was concealed behind the nose-cone.

The BMW003 was configured differently, as to where the Riedel relied on an electric starter.

 

[10020070122]

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.

Originally, the HeS 8 was supposed to be a substitute for the HeS 30. It was made extremely compact in an attempt to mimic an axial engine, leaving virtually no room for further improvement—so its thrust ceiling was only around 600 kp.

 

[spiralcopter]

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.

The chief advantage of an axial-flow compressor is that the air flows in a straight line through it, as opposed to turning ninety degrees. This makes it very easy to stack multiple axial stages in a row. The J79 in a Phantom (and many other planes) is a good example. There are no fewer than seventeen stages of axial compressor, one feeding to the next.

By contrast, because of the ninety degree airflow turn, it's really only practical to put two centrifugal flow compressors in series.

The reason that axial flow compressors weren't really helping the German jet engine designs of the 1940s is that they weren't pushing the pressure ratios above what could be achieved with a centrifugal flow design. Look up the overall pressure ratios for a Jumo 004 and a Derwent; they're both in the neighborhood of 4:1. That's pretty low by modern standards; most fighter engines are in the neighborhood of 25:1, while airliner engines are higher still often exceeding 30:1 on newer designs. For pressure ratios that high, there isn't a debate whether centrifugals or axial compressors are better. Axials are the only way to practically achieve it.

But for the very modest pressure ratios of WWII jet engines, the axial doesn't really give any benefits, and indeed there is a case to be made for the centrifugal compressor since it's shorter, less prone to stalling, and more resistant to foreign object ingestion.

 

[Shortround6]

Quite true.
The axial compressor was actually harder to design. Getting each stage to play nicely with each other turned out to be a problem.
For the engine in the above photo there is a row of curved blades fixed to the outer casing called stators. Air did a crapload of zigs and zags though the compressor. As seen the inner surface of the compressor grows in size to help match the compression.
With an axial compressor if things are not done right you can get one stage to stall which screws up everything after that stage, Knowing that the compressor as whole stalled (and the stall may occur at different speeds) is fairly simple. Know which stage started things is harder and fixing it is the really hard part. A little more twist on the blades or a little less? different airfoil? is it the rotating blades or the fixed blades? Is the problem all in one stage or did the stage before it start things?
In 1948 none of the existing axial flow compressors were hitting 6:1 according to the figures released to the public.
French had an experimental low bypass ratio jet.

with 16 stages, Not sure in the entire compressor offered 4:1 compression or if the rear 12 stages offered 4:1 on top of the 1.6:1 from the 1st 4 stages. 36% of the total airflow by-passed the 2nd stage and the combustion chambers and turbine to be mixed with the hot gasses at the rear.
A lot of people had ideas but getting them to work or work better than small/lighter/simpler engines was the problem.
This French engine was a bit smaller than an Allison J-33 but it was about 500lbs heavier, and about 2/3rds as powerful (without after burners) and only offered about 12% less fuel burn.
Later versions of the J-35 (axial) went from 4:1 to 5.5:1 compression but that took several more years.

 

[Airborne2001]

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.

This reminds me of the how the Italian government handled liquid cooled inlines, and how when they finally brought them back into consideration for the military they ended up botching the A.38 by forcing Fiat to invert it based on the DB 600 series.