Centrifugal vs axial compressors in WW2 jets

[wuzak]

On another thread davparlr remarkd:

And I think putting all their eggs into the axial flow design was a mistake. I believe that if they had pressed the much simpler centrifugal flow design that they could have had a single 4-5000 lb thrust engine, straight wing fighter fielded in late '43, in time to affect the air war over Germany. Possibly, such engine installed into a P1101 type fighter could have been in production by early '45, pre-dating the F-86/Mig 15 by 2 years.

SR6 followed that up with the following:

The Axial flow design was NOT easier to get into service quickly, the British had a least one if not more axial programs and the US and 2 or 3 programs, even allocating them to engineering firms with extensive steam turbine experience resulted in spotty results. In part because the US imposed some rather restrictive secrecy rules which prevented companies from talking to each other (although a few of them could talk to a "parent/partner" company in England) which meant a lot of the same problems had to solved a number of times independently.
The Axial compressor ( the rest of the "stuff" ie, combustion chambers and power turbines are pretty much interchangeable between the two types) was very hard to sort out. The early axial flow compressors (everybody's) were heavy, complex, and had lower compression ratios and efficiency than the centrifugal compressor. By the late 40s and very early 50s this had flipped and new axial compressors were showing much better performance than the centrifugals but that is several years too late.

Firstly, the Germans first flying jet engines used centrifugal compressors. And they used radial inflow turbines. These were the Heinkel-Hirth HeS 3. This was replaced by the HeS 6, which worked but was deemed to be too heavy and was cancelled. The next development was the HeS 8 (109-001), which was delayed by problems and didn't produce the expected thrust. It was cancelled in favour of axial flow projects that Heinkel had also been working on.

So, there was some effort in Germany towards making a centrifugal flow jet engine. These did not have the performance of the contemporary BMW and Jumo engines. Not sure that they were any more reliable, either.

Partly on the RLM's instructions, Heinkel's class II jet engine featured a "diagonal" compressor - a cross between an axial and centrifugal compressor, which did not work as well as either.

I have serious doubts as to whether Germany could have produced a 4000-5000lb static thrust jet using a centrifugal compressor, certainly before the Me 262 became operational.

Back to the British.
The RAE and AA Griffiths had been running test axial flow compressors since the mid 1930s. This was work towards their first complete engine, a turbo-prop, which was to be made by Metropolitan Vickers. When Whittle demonstrated his jet, the decision at MV was to drop the turbo-prop in favour of a new jet. The was the F.2.

The F.2 did have reliability problems - these appear to be mainly in the combustion chamber, which caused hot spots in the turbine and turbine failure. The solution was to use several smaller combustion chambers like those used in the centrifugal types. This change was made in 1943, resulting in even more thrust.

The F.2 gave more thrust than the contemporary Welland or (early mk) Derwent, was somewhat heavier but also more fuel efficient.

One wonders if the reliability issues that the F.2 was experiencing would have been overlooked if Britain had been in a similar position to Germany in 1943/44?

Another British axial flow egine was the Armstrong-Siddeley ASX. This didn't run until sometime in 1945, and was abandoned in favour of the Metrovicks F.9 Sapphire.

In the US the only axial jet project I am aware of is the Lockheed L-1000 project.

 

[Shortround6]

Two American programs were the Westinghouse program and the General Electric program. Northrop also was working on an axial design.

During the war years the Army and Navy had contracted for the development of seven turbo-props, five turbo jets, three pulse jets. There were also several ramjet design studies.

The Westinghouse 19A is claimed to be the 2nd Axial jet engine to run outside of Germany on March 19th 1943. This lead to the 19XB (J30) under flight test Sept 28th 1944 ( Under/In a Martin Marauder), the 9.5 or J32 first run in June 1944 and the larger J34 first run in April 1945 and in early models could reach 3000lbs thrust.

GE had been contracted to build a turbo-prop, design work started July 25th 1941 on the TG-100 with a 14 stage axial compressor. First test run Dec 23rd 1943. Much of what was learned was used on the TG-180 (J-35) which was first run on April 21 1944 although it doesn't make it to flight test until May of 1946.

 

[fastmongrel]

And they used radial inflow turbines.

a "diagonal" compressor - a cross between an axial and centrifugal compressor, which did not work as well as either.

.

Never heard of these 2 types of jet engine have you got anymore details wuzak

 

[wuzak]

Never heard of these 2 types of jet engine have you got anymore details wuzak

The radial in-flow turbine is the type of turbine used on modern turbochargers. The GE turbos used axial turbines, as did most of the jets of WW2.

Basically the radial in-flow turbine works like the centrifugal compressor, but the opposite way.

A schematic of the Heinkel-Hirth system

A picture of the HeS 3 trubine and exhaust

The diagonal flow compressor has the air flow moving diagonally along its length. A centrifugal compressor turns the air 90° to its axis, while the axial compressor has air that flows parallel to the axis (for each stage). The diagonal compressor is somewhere in between.


Item 2 in this diagram is the diagonal compressor.
http://img441.imageshack.us/img441/2386/109011a0.jpg

In these two pictures it is the set of blades ahead of the 3 stage axial compressor.
http://upload.wikimedia.org/wikipedia/commons/8/8d/Heinkel-Hirth_HE_S_011_USAF.jpg
http://img185.imageshack.us/img185/5249/heinkelhirthhes001view7.jpg

The diagonal compressor was used on the HeS 011.

 

[delcyros]

The Westinghouse 19A is claimed to be the 2nd Axial jet engine to run outside of Germany on March 19th 1943. This lead to the 19XB (J30) under flight test Sept 28th 1944 ( Under/In a Martin Marauder), the 9.5 or J32 first run in June 1944 and the larger J34 first run in April 1945 and in early models could reach 3000lbs thrust.

Would You mind to shed more light on this SR?
I have read conflicting data to that in that the J30 -which run earlier- was certified in the first series production version J-30 WE-20 for 150 hour benchtests not earlier than sept. 1945 (on a static thrust rating of 1,550lbs and rev limited to 17,000rpm) and that in april 1945, the J34 was projected, but the first engine wasn´t completed before 1946 and was first trialed on an airplane in 1947.

There were a couple of challanges to be overcome with axial jet engines:

[+] compressor stall caused by rotors
[+] compressor stall caused by air duct and boundary layer seperation
[+] burn out of turbine blades (requiring an accelerator valve of the fuel gouvernor)
[+] exhoust nozzle needle controll for optimum performance in a given range of altitudes / engine speed
[+] technical reliability
[+] ability to relight in flight (Seems trivial but THIS WAS A BIG CONCERN. -the primary reason to give early jet A/C so large wing areas and good low speed handling -that if engine was lost during take off/landing it doesn´t critically effect the survivability of the pilot)

the first jet engine which adressed most of these points -to my knowledge- was the BMW-003A1. The BMW- jet engine project took longer than Junkers -004 but it was a more matured design. Lighter and smaller, better thrust-weight ratio, 150 hours certified lifetime for the hot turbine section (the compressor section had a significantly larger lifetime), an accelerator valve to prevent the burn out of the turbine blade due to rapid throttle changes (AFAIK, this was the first jet engine, whiches throttles could be less gingerly advanced and returned without fear of damaging the engine), good altitude performance with very few documented compressor stalls (could be relighted in flight) and overrew capability for increased thrust. There was one aspect which was not included, an automatic exhoust jet needle controll such as employed by Junkers, requiring the operator to controll this aspect.


Radial compressor jet engines like those mentioned previously were probably better suited for the low thrust ratings concerned in ww2 but required more machining, milling and higher grade steel ressources.

The requirement to produce only jet engines with spare free charakteristics would preclude the idea that the Luftwaffe could have fielded a working 4000 to 5000lbs jet engine in time for ww2, be it radial or axial design. As I mentioned previously, this requirement set back the whole jet engine project by approx. 1.5 years. Many of the issues encountered historically really just need to be adressed in order to be able to move beyond this low thrust rating to higher performance engines.

 

[wuzak]

There were a couple of challanges to be overcome with axial jet engines:

[+] compressor stall caused by rotors
[+] compressor stall caused by air duct and boundary layer seperation

These seem, to me, to be the only points that apply to axial jets only, though I'm not sure that the second one is unique to axial jets either.


Whereas the following seem to be general gas turbine concerns.

[+] burn out of turbine blades (requiring an accelerator valve of the fuel gouvernor)
[+] exhoust nozzle needle controll for optimum performance in a given range of altitudes / engine speed
[+] technical reliability
[+] ability to relight in flight (Seems trivial but THIS WAS A BIG CONCERN. -the primary reason to give early jet A/C so large wing areas and good low speed handling -that if engine was lost during take off/landing it doesn´t critically effect the survivability of the pilot)

Axial flow compressors were being tested in the UK, Germany and, probably, the US before the war. They could, and did, run compressors without the combustors and turbines to test them. So while they weren't building gas turbines they were ironing out the compressor problems and improving them.

 

[wiking85]

How much and what kinds of raw materials would the Germans have needed to make their without restrictions on materials? I've read that the V-2 rocket nozzles consumed major heat resistant metals that would have been used with the jet engines like nickel, so had the V-2 project not been followed through on, then the jet program wouldn't have had to restrict itself and would have been further along. Is there any truth to that?

 

[Shortround6]

Would You mind to shed more light on this SR?
I have read conflicting data to that in that the J30 -which run earlier- was certified in the first series production version J-30 WE-20 for 150 hour benchtests not earlier than sept. 1945 (on a static thrust rating of 1,550lbs and rev limited to 17,000rpm) and that in april 1945, the J34 was projected, but the first engine wasn´t completed before 1946 and was first trialed on an airplane in 1947.

I am not sure how much more light you want. First ground "test" or first run is not type test or certification test.

The Westinghouse 19A used a different compressor than the 19B ( 6 stages instead of 10 and there were more than likely other changes as well, both combustion chambers and turbine section design did not stay static during the development period.) Apparently only 6 of 19A engines were built. A 19A was test flown under neath a Corsair for the first time Jan 21 1944. The 6 stage compressor offered NO advantage over a centrifugal compressor however (pressure ratio and thus fuel consumption being no better than centrifugal engines under development at the same time. The 19A had been intended as a "booster" engine.
A contract for 500 19XB engines had been placed in Jan of 1944 (essentially off the drawing board) and while the J-30 WE-20may or may not have been certified for 150 hours in Sept of 1945 the XFD-1 Phantom Prototype first flew with two J30s in Jan of 1945. There were a number of problems with the engine even several years later that kept the Phantom from reaching the hoped for performance. Contract was cut to 190 engines right after V-J day. Many American programs were cut, slashed, dropped and then re-instated and cut again during late 1945 and 1946/47. Research, development and deployment was nowhere near the wartime pace until the cold war really got going in 1948.
Most sources say the Vought XF6U-1 first flew Oct 2 1946 with a J34 engine. Granted that is only a few months from 1947. The J-34 may have taken a while to fully develop but wound up being a fairly reliable and long lived, or long used engine ( many jets gave a LOT trouble in their first few years) being manufactured until 1962 and in use in flying aircraft until the 1980s. Unfortunately Westinghouse's follow up engines were not as good or introduced nothing new, being little more than scaled up J-34s which was NOT good enough to compete with P&W and GE's newer, more sophisticated engines.

 

[nuuumannn]

though I'm not sure that the second one is unique to axial jets either.

Compressor surge was/is an issue that affects all gas turbines. Modern centrifugal compressors in use in turboprop and turboshaft engines have bleed valves specifically to handle compressor surge at low power settings; these are nominally controlled by electronic engine control units - depending on the sophistication of the engine system. The early incarnation of the Rolls-Royce Avon was prone to excessive compressor surge and had big blow-off valves fitted to the compressor casing, but it was found that mating the more efficient compressor unit of the (by then) Armstrong Siddeley Sapphire to the Avon hot section produced a better and more reliable engine.

Getting back to the original thread subject; I suspect the German firms were under considerable pressure to get working aircraft and engines in service and reliable as quickly as possible, which would have meant that priority would have had to have been placed on certain technology and advances, although the resources were not necessarily there to take advantage of these advanced concepts. Add to that Allied bombing and you have an industry unable to meet the expectations of the equipment being developed, or the demands of the high command.

 

[delcyros]

Shortround6, thanks for Your memo. I am interested in these periods jet engines and just keep notes on the topic, so Your input is greatly appreciated.
What the american jet engine project demonstrates, in my mind, is that the pace of progress was really rapid in this timeframe.
When we think about it the J30 took considerable time to mature but was more efficient than either BMW-003 or JUMO-004 when finished. The J-34 was an awesome compact engine but by the time all problems were ironed out, it was already on the edge of becomeing obsolete in comparison to more powerful engines aviable.

Getting back to the original thread subject; I suspect the German firms were under considerable pressure to get working aircraft and engines in service and reliable as quickly as possible, which would have meant that priority would have had to have been placed on certain technology and advances, although the resources were not necessarily there to take advantage of these advanced concepts. Add to that Allied bombing and you have an industry unable to meet the expectations of the equipment being developed, or the demands of the high command.

That´s a correct assessment. But to be fair, the option of the RLM to prefer the JUMO-004 was dictated primarely by it´s low risk charakteristics. It was a working jet engine capable to be manufacturerd in the thousends (as poor as it goes but nevertheless). The best class I engine would have been the HeS-030 (RLM called it 109-006) with smaller frontal diameter than either BMW- or JUMO engine, a very good spec. fuel consumption and excellent thrust to power ratio. But then again, in 1941, JUMO and BMW already had engines with the same net thrust power flying, while the HeS-030 was still very much a developmental engine, which still had lots of spare elements buildt into it and many problems yet in fornt of it. Instead of supporting a third engine of this class, Schelp ordered Müller (axial compressor project) and v. Ohain (radial compressor project) to merge for the HeS011 project and it´s diagonal compressor layout. A failure to decide between radial and axial compressor in my mind. I guess that the HeS030 should have been developed further, with a 2 stage turbine and another two compressor stages, as proposed by Müller, who hoped that this design could develop around 1200kp on just under 500kg weight.
That would certainly entail less developmental risk than the complex diagonal layout of the HeS011.
But then again, jet engines were still very much in their infancy and nobody knew for sure which direction was the best in this timeframe.

I guess we all agree that 4000 to 5000lbs jet engines, placed in series production within ww2 are beyond any realistic possibility.
The LW likely developmental path has been well documented in sources:
890Kp JUMO-004B3/4 engines in late 1944 and early 1945 (historical)
930kp JUMO-004D4 engines in early 1945 to mid 1945 (historical)
1000kp (1200kp with reheat) JUMO-004E1 engines in mid 1945 to the end of 1945. (benchtested, scheduled for mass production in mid 1945)

similarely for BMW:
800Kp BMW-003A engines in late 1944 (historical)
800Kp (920 Kp with overrew) BMW-003A2/E1 egines in early 1945 (historical)
1000 Kp (1150Kp with overrew) BMW-003D engines in mid 1945 (benchtested, scheduled for production)
-the BMW-003 was added with an afterburner only in the SU and has been excluded here-

HeS011 (benchtested, flighttested), JUMO-012 (as well as the downscaled -012 derivate called JUMO-004H) (assembled) and BMW-018 (part assembly or assembled, sources vary) were still developmental and should be treated with caution. They are listed according to their developmental stage.

 

[nuuumannn]

But to be fair, the option of the RLM to prefer the JUMO-004 was dictated primarely by it´s low risk charakteristics.

That's essentially what I mean, but yes indeed I agree with your post and thanks for the like!

 

[davparlr]

I guess we all agree that 4000 to 5000lbs jet engines, placed in series production within ww2 are beyond any realistic possibility.

This is true for the axial flow engine but definitely not for the centrifugal flow engine. While low level development activity had been going on with the British jet for quite a while, serious government involvement did not occur until many years after the Germans started their government funded jet engine development, yet the British, and Americans had 4-5000 lb thrust engines running in 1944 and, since 83 production P-80s were delivered by the end of July, '45, there certainly was production J-33s in ww2. I think the Germans, with their multi-year head start with government money could easily beaten this by a year or more if they had stuck with the centrifugal flow engines.

The axial engines are much more complex to develop due to their multiple compressor stages. The Jumo had eight stages of compressors, each stage consisted of a compressor and a stator for a total of sixteen sub-stages. Each sub-stage has to be specifically designed to operate with different airflow characteristics including different velocities, pressures, temperatures, and incidence angles and must be finely tuned to operate efficiently over the entire operational RPM range and variable initial airflow values. In addition, each blade of compressor and stator must be manufactured to tight tolerances to prevent leakage; this is a lot of components. The centrifugal compressor on the other hand has, effectively, only one stage consisting of one moving part, a much easier design and manufacturing problem. In addition, the axial engine has a much longer shaft that can induce vibration problems and could require multiple bearings. The centrifugal engine is much shorter and less problems in these areas, and it tends to be more robust.

 

[wuzak]

This is true for the axial flow engine but definitely not for the centrifugal flow engine.

I disagree.

The Metrovicks F.2/4 "Beryl" had tested at about 4000lb static thrust sometime in 1944. But like the centrifugal flow engines it was a prototype, and not a production engine.

I think the Germans, with their multi-year head start with government money could easily beaten this by a year or more if they had stuck with the centrifugal flow engines.

Von Ohain's team at Heinkel did stick with the centrifugal engine - for a while. But they weren't getting the improvements that Whittle and Halford were. In some respects they were going backwards. The HeS 6 was overweight and did not have the required performance improvement over the HeS 3. The HeS 8 was the first turbojet officially supported by the RLM (as the 109-001), but its performance never met targets, and it was only ably to muster about 1500lb static thrust. The HeS 8 was abandoned in 1943 - it had well and truly been overtaken by the BMW 003 and Jumo 004, and even by the HeS 30 (109-006), which was itself abandoned so that Heinkel could work on the class II turbojet - the HeS 011.

By the end of the war there were a few class II projects in hand (the HeS 011, Daimler Benz 109-007), as well as class III and class 4 (BMW 018, target of over 7000lb static thrust).

The axial engines are much more complex to develop due to their multiple compressor stages. The Jumo had eight stages of compressors, each stage consisted of a compressor and a stator for a total of sixteen sub-stages. Each sub-stage has to be specifically designed to operate with different airflow characteristics including different velocities, pressures, temperatures, and incidence angles and must be finely tuned to operate efficiently over the entire operational RPM range and variable initial airflow values. In addition, each blade of compressor and stator must be manufactured to tight tolerances to prevent leakage; this is a lot of components. The centrifugal compressor on the other hand has, effectively, only one stage consisting of one moving part, a much easier design and manufacturing problem. In addition, the axial engine has a much longer shaft that can induce vibration problems and could require multiple bearings. The centrifugal engine is much shorter and less problems in these areas, and it tends to be more robust.

At the end of the day the main problems exhibited by German turbojets was in the combustion chambers and turbines. And this was due largely to materials not being able to withstand the temperatures, with air cooled turbine blades being developed as a result.

AA Griffiths wrote a paper on an axial flow gas turbine engine in 1926. He showed mathematically how the compressor should be designed, as opposed to previous attempts. He included a case study of an engine with a multi-stage compressor, a single stage turbine to drive the compressor and a single stage "free" turbine to drive a propellor. A model engine based on his thesis was built and tested by 1928.

While the British found it easier to develop the centrifugal flow compressor, it doesn't follow that the Germans did. Von Ohain's original engine used a centrifugal flow compressor and radial in-flow turbine because it was simple, cheap and easy to make for a proof-of concept. Not that he thoughtthat the centrifugal compressor was the way of the future.

 

[delcyros]

yet the British, and Americans had 4-5000 lb thrust engines running in 1944 and, since 83 production P-80s were delivered by the end of July, '45, there certainly was production J-33s in ww2. I think the Germans, with their multi-year head start with government money could easily beaten this by a year or more if they had stuck with the centrifugal flow engines.

Correct me if I am wrong but I don´t think that the americans had any 4000 to 5000lbs jet engines running in 1944. Even in 1945 their best engine was the I40/J33 which made 3,850lbs until Allison uprated it in late 1945 to 4,000lbs on the bench. All P80A1 had only 3,850lbs rating and the uprated engine was not delivered before 1946. The british had the R.B.41 Nene which offered the required thrust rating but first benchtests were late in 1944 (oct, IIRC) and the engine was far from production ready in 1944 and still looked around for a suitable platform (Vampire and P80 got them as experimental fits in mid/late 1945, with the P80 beeing badly damaged due to a Nene engine failure) and finally missed ww2 by a good margin.
The germans may have had a headstart but they needed to invent new cooling techniques due to the spare free requirements. Without them, just go along with the JUMO-004A, which was benchtested to 1000kp thrust rating in 1941 or the JUMO-004C, which eventually was a classical -004A with afterburner added (1200kp). They couldn´t do that, hence they reverted to the derated JUMO004B (1944), the slightly improved JUMO004D (1945) and the afterburner aequivalent JUMO-004E (1945).

I fully agree that the axial compressor layout was more complicated than the radial layout but nothing fundamentally new. It inherited a lot experiences from axial compressor layouts in steam turbine propulsion (both navy steam turbines and electric power generation plants).

 

[davebender]

How much and what kinds of raw materials would the Germans have needed to make their without restrictions on materials?

Germany had plenty of nickel until mid 1944 when Finland changed sides. Chromium was in short supply for the entire war.

1943 Chromium requirements per engine.
27.41kg DB605
21 lbs Jumo 004A jet engine.

It's readily apparent that raw material shortages had little to do with decision not to mass produce Jumo 004A engine during 1943.

 

[wiking85]

Germany had plenty of nickel until mid 1944 when Finland changed sides. Chromium was in short supply for the entire war.

1943 Chromium requirements per engine.
27.41kg DB605
21 lbs Jumo 004A jet engine.

It's readily apparent that raw material shortages had little to do with decision not to mass produce Jumo 004A engine during 1943.

The V-2 took a lot of nickel for its nozzle, so the 'extra' went to that in 1944. Also I think they expected that the jet engines, being a new technology, would see more attrition than the more proven piston engines. I agree that it was a matter of priorities rather than anything else. If they had used all the DB603 raw materials that would have been saved by not producing the ME210/410, then there would have been a significant amount of nickel and other metals for Jumo.

BTW what raw materials were needed? IIRC Molybenium, Coblat, Chromium, and Nickel, but what about Tungsten and Copper?

Edit:
https://en.wikipedia.org/wiki/Junkers_Jumo_004

The initial 004A engines built to power the Me 262 prototypes had been built without restrictions on materials, and they used scarce raw materials such as nickel, cobalt, and molybdenum in quantities which were unacceptable in production.

I think the last two were the real issue.

 

[davebender]

I'm no metallurgist but I know alloy metals can substituted to some extent when making high temperature steel. For example we have this quote:
http://www.ww2aircraft.net/forum/engines/jumo-004-a-12983-3.html

"In 1936, when development work on the Jumo 004 started, a high-temperature Krupp steel known as P-193 was available. This material, which contained Ni, Cr, and Ti, could be given good high-temperature strength by means of solution treating and precipitation hardening. Krupp developed an improved version of P-193 known as Tinidur. It was of the same type as Nimonic 80, which was used in British Gas turbines from 1942 but contained over 50 percent iron (which was replaced by Ni in Nimonic 80) and this caused a rapid drop in creep strength at 1080F (compared to 1260F for Nimonic 80). While Krupp knew that Tinidur could be improved by increasing the Ni content from 30 to 60 percent, there was a recognition that Ni would not be available. The Ni content was therefore left at 30 percent. Similarly, work on cobalt-based alloys was also shelved due to a shortage of cobalt." (Journal of Engineering for Gas Turbines and Power, October 1997, Vol. 119)

Albert Speer provides considerable detail concerning Nickel imports from Finland so we can dismiss talk of a nickel shortage. Nickel ore was piling up at Petsmo faster then Germany cared to transport it to the Ruhr.

So why wasn't Jumo 004A engine placed into mass production with turbine blades made from Nimonic 80 alloy which relies largely on Nickel? There must be reason(s) besides shortage of alloy metals.

 

[davparlr]

I disagree.

The Metrovicks F.2/4 "Beryl" had tested at about 4000lb static thrust sometime in 1944. But like the centrifugal flow engines it was a prototype, and not a production engine.

Yes, I kinda overlooked the Metrovick engine. According to Kay, the Beryl certainly ran at 3500 lb/thrust in 1943 and could possibly have been in production by 1945 (my limited opinion).

Von Ohain's team at Heinkel did stick with the centrifugal engine - for a while. But they weren't getting the improvements that Whittle and Halford were. In some respects they were going backwards. The HeS 6 was overweight and did not have the required performance improvement over the HeS 3. The HeS 8 was the first turbojet officially supported by the RLM (as the 109-001), but its performance never met targets, and it was only ably to muster about 1500lb static thrust. The HeS 8 was abandoned in 1943 - it had well and truly been overtaken by the BMW 003 and Jumo 004, and even by the HeS 30 (109-006), which was itself abandoned so that Heinkel could work on the class II turbojet - the HeS 011.

There is no doubt that Heinkel's early engine work was hampered by secrecy and poor engineering. His engine was much more complicated than those of Whittle and Halford but it is difficult to believe that Germany did not have the capability to engineer compressor designs equivalent to the Brits.

By the end of the war there were a few class II projects in hand (the HeS 011, Daimler Benz 109-007), as well as class III and class 4 (BMW 018, target of over 7000lb static thrust).

It is inescapable to come to the conclusion that the Germans had some serious problems with their engine design work when the British, and the Americans even earlier than the Brits, were able to run 4000-5000 lb thrust engines in 1944. The Americans, using British technology was running the J-33 in early '44 and was in production in early '45. The Germans never came close to being able to do this. It is my opinion that the centrifugal engine was easier to engineer and manufacture (a whole lot less parts) and was also easier to increase thrust levels. Doubling thrust was simply increasing the size and could be done with relatively inexperienced engineers. GE began work on a 3-4000 lb thrust engine in June, 1943 and the engine was run at 4000 lbs thrust in February, 1944, doubling the thrust of the previous engine. This engine went on to become one of the most robust engines ever built and was in production until 1959 and was in military use much longer (The USAF was still using them when I was in the AF in 1970, and some are still flying today).

At the end of the day the main problems exhibited by German turbojets was in the combustion chambers and turbines. And this was due largely to materials not being able to withstand the temperatures, with air cooled turbine blades being developed as a result.

This is true, but at the beginning of the day there was a lot of complex engineering and manufacturing that needed to be done before they even got to the end of the day.

While the British found it easier to develop the centrifugal flow compressor, it doesn't follow that the Germans did. Von Ohain's original engine used a centrifugal flow compressor and radial in-flow turbine because it was simple, cheap and easy to make for a proof-of concept. Not that he thoughtthat the centrifugal compressor was the way of the future.

Yes, and I think that was a mistake.

Correct me if I am wrong but I don´t think that the americans had any 4000 to 5000lbs jet engines running in 1944. Even in 1945 their best engine was the I40/J33 which made 3,850lbs until Allison uprated it in late 1945 to 4,000lbs on the bench. All P80A1 had only 3,850lbs rating and the uprated engine was not delivered before 1946.

According to Antony Kay's book "Turbojet History and Development 1930-1960, Vol. 2", the GE I-40 (J33) was run at 4000 lb thrust in February, 1944. Ray Wagner in his "American Combat Planes" along with E.T. Wooldridge,Jr.'s "The P-80 Shooting Star" stated the YP-80's engine was also 4000 lb thrust, but, although they are reliable books, I not as sure. Of course 3,850 lbs is certainly in the 4000 lb range.

The british had the R.B.41 Nene which offered the required thrust rating but first benchtests were late in 1944 (oct, IIRC) and the engine was far from production ready in 1944 and still looked around for a suitable platform (Vampire and P80 got them as experimental fits in mid/late 1945, with the P80 beeing badly damaged due to a Nene engine failure) and finally missed ww2 by a good margin.

I cannot argue this point. The J33 took one year to go from test bench to production. Of course this also applies to German engines which were not even at the test bench stage.

 

[davparlr]

Merry Christmas. "Peace on earth and good will to all"

 

[fastmongrel]

An excuse to post one of my favourite pictures the Meteor F1 with Metrovick F2 engines