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

[bf109xxl]

No it wasn't, the British engines were more reliable and were demonstrating greater time between overhaul than the German engines, this is well known.

All of the Jumo 004's problems had nothing to do with the compressor. The Germans were forced to save alloying additives (nickel, first of all), as a result, the heat resistance of materials for the hot part of the engine was insufficient. The limiting factor was the combustion chambers, the next was the turbine blades - even hollow air-cooled turbine blades did not provide the required material durability. If the Germans had enough skilled workers to produce the hot part of the engine from suitable materials, the reliability of their engines would not differ from that of the British. Under nickel shortage conditions, the Germans could use any type of compressor with exactly the same result. German engineers chose the most promising type of compressor and created quite good engines, as the further development of jet engines showed. The centrifugal compressor was a temporary dead-end solution.

Any report on the Me 262 will tell you that its engines were excessively unreliable.

Except it had nothing to do with the compressor.

 

[marathag]

It does when your aircraft are grounded because your engines have a time between overhaul of less than a quarter of that of your opposition. A grounded jet fighter with unserviceable engines is as useless as no jet fighter at all.

Jet engines, while requiring very close tolerances and exotic metals, the same can be said about High Inline Vees.

You can't use garbage 1020 steel for the rotating parts, but very good, very strong, expensive alloys, and need high heat resistant alloys for the valves, different alloys for the camshafts rather than just chilled Iron. And balancing all those rotating bits is an art and a science at this time

In comparison, considering what alloys were set aside for reciprocating, could be redirected for the turbines instead.

Jet engines can be build cheaper than inlines, and faster as well.
And at the end of the game, they run on kerosene or low grade gasoline, no high octane fuels needed.

People forget that if an reciprocating engine was run at WEP levels for long, they would need to be pulled apart as well.

So what if an engine has a 20 hour life, when they are cheaper and faster to build?have more spares

All Engines are consumables at the very high HP we are talking about.

 

[z42]

Jet engines, while requiring very close tolerances and exotic metals, the same can be said about High Inline Vees.

You can't use garbage 1020 steel for the rotating parts, but very good, very strong, expensive alloys, and need high heat resistant alloys for the valves, different alloys for the camshafts rather than just chilled Iron. And balancing all those rotating bits is an art and a science at this time

In comparison, considering what alloys were set aside for reciprocating, could be redirected for the turbines instead.

Jet engines can be build cheaper than inlines, and faster as well.

Our contemporary view of things might be skewed by very cheap car engines vs astronomically expensive turbines for aerospace and power generation. But that's probably largely an effect of the markets they're targeted at, I suspect you could make a pretty cheap turbine if you were prepared to make some sacrifice in fuel efficiency and power/weight.

The WWII German experience was that the BMW 003 & Jumo 004 were about 10000-12000 RM in materials cost vs about 35000-50000 for 605/213/801 piston engines. Similarly build time was around 375 hours for the jets (Jumo, IIRC the BMW figures where similar) vs about 1500 hours for the above piston engines. Also, jet production required less skilled labor than the high end piston engines.

And at the end of the game, they run on kerosene or low grade gasoline, no high octane fuels needed.

Yes. Further, if turbines had been available earlier, they could have built more FT plants instead of Bergius ones, as FT ones are much less capital intensive and well suited for diesel and turbine type fuels. As well as skipping all those expensive iso-octane plants.

People forget that if an reciprocating engine was run at WEP levels for long, they would need to be pulled apart as well.

So what if an engine has a 20 hour life, when they are cheaper and faster to build?have more spares

All Engines are consumables at the very high HP we are talking about.

IIRC sometime mid war the Germans were pulling apart their piston aviation engines at something like 25 hour intervals anyway. In addition to the well publicized valve issues, lack of the silver-lead-indium bearings the Allies used necessitated fairly frequent replacement of bearings (insufficient bearing lubrication on the 605 didn't help either, of course).

 

[z42]

We already have steampunk and dieselpunk, can we have turbinepunk as well?

 

[tomo pauk]

<snip>

Excellent points there.

 

[Shortround6]

Maybe if the Germans had spent more money on the jet engines they would have lasted longer?
It is tough to build both cheap and long lasting.

On the other had it took the Allies a while to get their jet engines to last, or at least go longer without inspection tear downs.

The Axial flow compressor needed a lot work come out ahead of the centrifugal compressors.
The German axial flow compressors were heavy (so were the British and American designs) and they actually didn't compress very well. The early allied axial compressors also didn't compress air very well.
On very basic terms the engine designer had choice of using a long skinny, heavy compressor the compressed the air at a 3:1 ratio or bit more, or a short/fat light compressor that gave a 4:1 compression ratio.
Theory says that the Axial compressor can be improved or at the least just add more stages (making it longer and heavier) while the Centrifugal compressor was hitting it's limit (or had less room for improvement) stacking centrifugal stages was a lot harder. Designers could stack a few axial stages in front of the centrifugal stage but that came a bit later in practice. Idea and drawings have existed earlier. A lot of people had drawings years before working hardware was built.

Germans had bet on the wrong horse for WW II (even a longer WWII). The Centrifugal compressor came out of the starting gate faster, it held it's lead for several years and the Axial compressor didn't catch up until the late 40s or very early 50s. By 1953-56 the Axial was far in the lead and the centrifugal had collapsed on side of the race course being seen to by the vets while the glue wagon was en route.
But the bet isn't what would be the best commercial engine in the mid 1950s or best military engine in the mid 50s. The bet is what would be the best military engine in 1944-45-46.

The difference in compression ratio is big as that governs both power and fuel economy.

Both Britain and the US were working on axial flow compressors and in fact an Axial Meteor may have been the 3rd Meteor to fly (by 4 days) on Nov 13th 1943. Plane was later lost due to engine failure thought to been the fault of compressor over speeding.

A real "what if" consideration

 

[peceed]

The HeS30 addressed and improved on the HeS8's issues and was performing reliably by Fall of 1942.
It's development had been delayed several times due to typical infighting, which seemed to be a typical condition within the German aircraft industry, existing at both the design level and with the RLM itself.

It is surprising to me that in such circumstances a "double HeS30" was not proposed as a higher thrust class engine, convincing officials that such an operation was a simple equivalent of multiple cylinders in piston engines.

It is sort of wonder that the US turbos worked as well as they did as there was certainly a lot of room for blaming the other guy.

There was a lot of experimental engines with integrated turbos and they failed.
The universal turbocharger was simply supposed to maintain atmospheric pressure on the ground, leaving no room for excuses. This setup theoretically worked with any engine and allowed the aircraft to take off on its own compressor (in case of turbo failure), effectively providing the two-stage compressor system necessary at high altitude in a simple way.
But as you correctly point out, it still resulted in poor performance.
A well-made turbocharger should provide a pressure ratio of 3.5-4:1, minimal charge heating, and save at least half the exhaust thrust at altitude.
Paired with a supercharger with a hydraulic clutch, it could completely unload the engine at takeoff up to 15-20k ft.

Seems many (most?) contemporary turboprop engines tend to have a number of axial stages, followed by a final centrifugal compressor stage.

Small axial compressors lose their aerodynamic efficiency, and the last stages tend to be the smallest ones.

The P-47 was derived from a TWO SEAT aircraft.

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

 

[yulzari]

New concepts tend to first emerge as modelled upon existing methods but using the new idea.

Axial compressors leveraged off steam turbines and centrifugal compressors off centrifugal superchargers. Both being existing methods. The engineering being limited by the ever moving limits of metallurgy and alloy constituents available in industrial quantities in competition with other uses. What was possible in 1943 was not possible on 1938 and what was available to the Allies was not necessarily available to the Axis.

One has to consider decisions in the light of their period contexts.

Myself, in the early days, would have leveraged off the existing centrifugal compressors as a passably mature compression technology with room to improve. The tricky bit being stopping the burning end from melting. Making a turbo jet from an internal combustion engine turbo and a length of pipe with fuel injected is simple enough but the back end goes all white hot and droopy/ dribbley in less than a minute.

One reason we got steam engines before internal combustion engines was the ease of combustion and low thermal loads on materials. These could have done a working, if grossly inefficient, job in Roman times but there was enough water and animal power to meet the demands of the day. Once we got deep mines and centralised power factories water power initially took the load but was scarce and variable so there was a market for enterprising steam power entrepreneurs to service, thus worth the investment. It all had to come together as a whole. Turbojets etc. would not have (literally) taken off until there was the materials and a market. Once there was a serious large aero engine demand then there was somewhere to market the turbojet. Bright engineers had sketched out assorted quasi jet turbines in principle since the eighteenth century at least. Materials and engineering had advanced enough to make a working, if not economic, turbojet by the end of the nineteenth century but there was nowhere to sell it to until the 1930s establish a large powerful aero engine market.

I only say all of this to highlight that centrifugal or axial compressors are not one better than another but alternatives dependent upon the needs and engineering available for a particular customer, time and place. I believe that the Germans followed their cultural engineering bias in choosing the option with the most potential. The British chose in the same manner in choosing the pragmatic option that stood the best chance of entering service soon. The Germans did a sterling job under their reduced circumstances and the axial was the best choice but rendering them service reliable required the Soviets some years and total redesigns to get their copy German axials up to a reliable service standard. When offered sample centrifugal service standard jet engines they grabbed the chance and got them into service quickly. The USA used copy British centrifugal jets also for many early years.

I conclude that the Germans would have got a service reliable jet engine faster had they gone for the pragmatic centrifugal engine even though the axial would out perform it a few years later, ie a few years too late. A classic example of the best driving out the good. But then, by 1942, it was a matter of how slowly they could lose rather than how fast they could win.

 

[Shortround6]

Here is kind of a classic what if?
What if the US government had allowed General Electric Lynn MA and General Electric Schenectady NY to talk to each other during 1941-44?
Lynn had the Whittle project and Schenectady had the long term axial flow turboprop project starting in July 25th 1941 (no it won't be ready for Midway).
sharing combustion chamber problems, turbine problems and lubricating problems might have speeded things up.

On the subject of reliability, Douglas got two J35 engines for the XB-43 bomber in Nov 1944. one of the engines failed in a ground test with most of the compressor blades coming off. The next 10 engines also had problems so it was not until May 17th 1946 ( 1 1/2 years) that the prototype XB-43 first flew.

 

[SaparotRob]

I wonder if they will ever get jet engines to work.

 

[Shortround6]

I wonder if they will ever get jet engines to work.

They are just a passing fad.
I am waiting for steam powered aircraft.

 

[nuuumannn]

They are just a passing fad.
I am waiting for steam powered aircraft.

That's old hat, mind you, they look kinda cool.

Europe 205

I'm still waiting on the upcoming airship resurgence everyone keeps going on about...

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[nuuumannn]

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. 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.

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. We can be thankful that German attempts to develop nuclear weapons did not progress much further than building a pile in a university in Berlin because of this attitude.

 

[nuuumannn]

Jet engines, while requiring very close tolerances and exotic metals, the same can be said about High Inline Vees.

You can't use garbage 1020 steel for the rotating parts, but very good, very strong, expensive alloys, and need high heat resistant alloys for the valves, different alloys for the camshafts rather than just chilled Iron. And balancing all those rotating bits is an art and a science at this time

In comparison, considering what alloys were set aside for reciprocating, could be redirected for the turbines instead.

Jet engines can be build cheaper than inlines, and faster as well.
And at the end of the game, they run on kerosene or low grade gasoline, no high octane fuels needed.

People forget that if an reciprocating engine was run at WEP levels for long, they would need to be pulled apart as well.

So what if an engine has a 20 hour life, when they are cheaper and faster to build?have more spares

All Engines are consumables at the very high HP we are talking about.

And yet here we are. German jet engines were notoriously unreliable and part and component supply was not forthcoming to sustain a wartime economy under the pressures the Germans were facing.

While those early gas turbines were relatively simple, the jet engine relies on heat to run efficiently and while the power outputs of those early engines was low by comparison to the gas turbine's potential, the premise was there and it was abundantly clear to all involved even at the time that gas turbines would eventually overshadow recip engines in performance and complexity. To believe what was available was all that was required is setting a ridiculously low bar because of the potential of what the gas turbine offered. There was no way that they would remain as simple as you claim, everyone involved in their development could see that.

 

[nuuumannn]

All of the Jumo 004's problems had nothing to do with the compressor.

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.

While the engines (Jumo 004 and BMW 003) were well designed and conceived, they certainly did have their issues and were hampered because of the state of war. Here is a British engineer's impression of the German engines based on his examination of examples captured by the British in 1944:

"Both engines were in good condition and I was impressed with the quality of the design right down to the very neat petrol engine starter mounted in the "bullet" [the Riedel starter motor] of the compressor air intake. Both engines were straight through axial compressor designs. I particularly recall the hollow air cooled alloy turbine blades of the Jumo engine, which the manufacturer had to resort to because of the effectiveness of the Allied blockade in preventing supplies of nickel from reaching Germany. The short service life of these low alloy turbine blades may have been one of the factors which led to fires in the Me 262 aircraft."

It is interesting to analyse the German engines from a technical standpoint, the Jumo and the BMW were relatively simple in design, which was a virtue in that they did work - the issues that affected them were not necessarily design related, although design compromises were made because of Germany's faltering industry that did affect their reliability. By the standards of 1945 technology, 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.

A Riedel starter motor inside the cowl of a Jumo 004 without the bullet. The pull starter cable is visible.

_DSC2018_s

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.

A Jumo 004 on display at the Musee de l'Air, Paris. Note the ring pull for the starter motor in the extremity of the nose bullet and the extension shaft halfway along the engine's flank that operated the zwiebel in the exhaust shroud. The removed oval cover on the front engine cowl was for the fuel port for the starter motor. It ran on standard 87 octane fuel.

Musee de l'Air 56

Nevertheless, the German engines were great designs.

 

[bf109xxl]

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.

Firstly, again we are talking about poor quality materials, and secondly, these cases were not a serious problem, unlike the burnout of combustion chambers or turbine blades. That was also caused by poor quality materials and flawed assembly due to low skilled labor. Even the more reliable compressor did not solve the main problem of German jet engines. And problems with the axial compressor were not critical.

"Both engines were in good condition and I was impressed with the quality of the design right down to the very neat petrol engine starter mounted in the "bullet" [the Riedel starter motor] of the compressor air intake. Both engines were straight through axial compressor designs. I particularly recall the hollow air cooled alloy turbine blades of the Jumo engine, which the manufacturer had to resort to because of the effectiveness of the Allied blockade in preventing supplies of nickel from reaching Germany. The short service life of these low alloy turbine blades may have been one of the factors which led to fires in the Me 262 aircraft."

TURBINE BLADES!!! Not a word about compressor problems.

It is interesting to analyse the German engines from a technical standpoint, the Jumo and the BMW were relatively simple in design, which was a virtue in that they did work - the issues that affected them were not necessarily design related, although design compromises were made because of Germany's faltering industry that did affect their reliability. By the standards of 1945 technology, 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.

Not a word about compressor problems.

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.

Not a word about compressor problems.

Nevertheless, the German engines were great designs.

The Germans had at least two jet engines that were superior to ALL Allied jet engines of the war. Fortunately, the Germans were unlucky and these engines were not brought to the required perfection during the war, although there was every chance to do it.
The discussion about the type of compressor for German engines is completely pointless, as the main problem was in heat resistant materials. The Germans did not have the necessary metals, the Soviets had metals, but they had neither technological developments nor fundamental understanding of heat-resistant alloys, while the British had both technology and metals.

 

[nuuumannn]

Okay Sonny Jim, back in your box. The point of my post was not a direct riposte to your post, except the first line, so you can cool off for a bit. It was merely to discuss the engines and some of their details.

Firstly, again we are talking about poor quality materials, and secondly, these cases were not a serious problem, unlike the burnout of combustion chambers or turbine blades. Th at too was caused by poor quality materials and flawed assembly due to low skilled labor. Even the more reliable compressor did not solve the main problem of German jet engines. And problems with the axial compressor were not critical.

Problems with the compressor blades were not critical? Are you kidding me? Shedding fan blades is critical, VERY critical. Yes they were a serious problem! Where are you getting this rubbish from! There were dozens of Me 262s found abandoned at airfields and road sidings around Germany devoid of engines because there were insufficient serviceable ones! Clearly you need to do some more reading and stop living in a fantasy world.

TURBINE BLADES!!! Not a word about compressor problems.

The quote was designed to illustrate what the British thought of the engine in that they were impressed with its quality. I can tell the difference between a turbine and a compressor as I work on gas turbine engined aircraft as a job, but the conceptual design on both are the same since you want to split hairs. like I said in the beginning, my post was not a direct counter to what you said, except the first line.

Not a word about compressor problems.

Ditto, not meant to be. Again, READ!

The Germans had at least two jet engines that were superior to ALL Allied jet engines of the war.

Again, rubbish. You live in a dream world. I have just pointed out why they were not superior - they were smart but very much contemporary to what was being developed elsewhere. Britain had already built axial flow engines, the centrifugal engines were faster in development and it was decided to put them into Britain's first jets because of expediency, there was a war on and getting results as quickly as possible was the order of the day in Britain. Had the British had the time they would have also put axial engines into their aircraft, one of the Meteor prototypes had axial flow engines fitted, but the decision was made to put the centrifugal flow engines into mass production first because they were simpler, but of course if you had done some reading you might have known this before you make such silly statements.

 

[nuuumannn]

Fortunately, the Germans were unlucky and these engines were not brought to the required perfection during the war, although there was every chance to do it.

The Germans were not "unlucky". The Germans were masters of their own destiny. They were forced to make compromises because of the mess they had started. The Me 262 and the He 162 and their engines were rushed into service and both suffered deficiencies because of this. There was a war on and this led to severe compromises as factories were being bombed, leading to shortages in materials and time. Luck had nothing to do with it.

I fear you are one of those guys who believe that everything the Germans did in WW2 was better than everyone else. what do you call them...?


View: https://www.youtube.com/watch?v=hYTQ7__NNDI

 

[bf109xxl]

Problems with the compressor blades were not critical? Are you kidding me? Shedding fan blades is critical, VERY critical. Yes they were a serious problem! Where are you getting this rubbish from!

I'm sick of your meaningless verbal drivel. Give me the numbers. The combustion chambers burned out in 15 hours. How many hours before compressor problems started? What was the probability of compressor blade failure in German engines? I'm not interested in generalities, just relevant figures.

There were dozens of Me 262s found abandoned at airfields and road sidings around Germany devoid of engines because there were insufficient serviceable ones! Clearly you need to do some more reading and stop living in a fantasy world.

What was the percentage of engines that failed due to compressor failure rather than burnout of combustion chambers or turbine blades?

The quote was designed to illustrate what the British thought of the engine in that they were impressed with its quality. I can tell the difference between a turbine and a compressor as I work on gas turbine engined aircraft as a job, but the conceptual design on both are the same since you want to split hairs. like I said in the beginning, my post was not a direct counter to what you said, except the first line.

In other words, it was completely meaningless in the context of this discussion.

Ditto, not meant to be. Again, READ!

Try to think before you try to write nonsense again.

Again, rubbish. You live in a dream world. I have just pointed out why they were not superior - they were smart but very much contemporary to what was being developed elsewhere. Britain had already built axial flow engines, the centrifugal engines were faster in development and it was decided to put them into Britain's first jets because of expediency, there was a war on and getting results as quickly as possible was the order of the day in Britain. Had the British had the time they would have also put axial engines into their aircraft, one of the Meteor prototypes had axial flow engines fitted, but the decision was made to put the centrifugal flow engines into mass production first because they were simpler, but of course if you had done some reading you might have known this before you make such silly statements.

Stupidity again. The Germans did not need any centrifugal compressors - they had quite reliable axial compressors. AND NO COMPRESSORS WOULD AVOID MAJOR PROBLEMS WITH HEAT-RESISTANT MATERIALS. Is that so hard to understand?

The Germans were not "unlucky".

So you also don't know the history of German engine development.

The Germans were masters of their own destiny.

Of course, they were "Übermenschen", they never made a mistake and all their failures were planned ones.

 

[nuuumannn]

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.