Which country designed the best engines for WWII?

davparlr said:

I have always had the opinion that the Germans made an error by abandoning the centripetal compressor too soon. Each axial flow compressor stage and associated stator stage has to be designed to unique varied airflow parameters and made to work as compared to the much simpler centripetal compressor which has only one stage to design to. Had the Germans pursued the simpler design they may have had a very capable fighter a couple of years earlier and kept their cities clear of the upcoming bomber formations and escorts. Had the Germans installed more reliable 2500-3000 lb thrust engines in the Me 262 in Jan 1944, the outcome of the war could have been altered, certainly extended.

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DO-17 ramjet and pulse jets that is whatt they should have put efford in. Far less complex.

Snautzer01 said:

DO-17 ramjet and pulse jets that is whatt they should have put efford in. Far less complex.

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Pulse jets use a staggering amount of fuel.

but they would have gotten them much earlier in the war. That would have been dangerous.

With Schmidt now working for Argus, the pulsejet was perfected and was officially known by its RLM designation as the Argus As 109-014. The first unpowered drop occurred at Peenemünde on 28 October 1942 and the first powered flight on 10 December 1942.

Pulsejet - Wikipedia

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Pulse jets tended to take the aircraft apart with vibration. Not too bad if you figured the airframe was only going last a few hours before crashing (flying bomb).
But trying to beef up the airframe enough to last 30-50 hours was going to bring a weight penalty and/or a maintenance penalty.

Snautzer01 said:

but they would have gotten them much earlier in the war. That would have been dangerous.

With Schmidt now working for Argus, the pulsejet was perfected and was officially known by its RLM designation as the Argus As 109-014. The first unpowered drop occurred at Peenemünde on 28 October 1942 and the first powered flight on 10 December 1942.

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Pulse jets are also very noisy and have pulsating thrust. And, yes, they are very thirsty, with thrust sfcs in the neighborhood of 2 lbf/lbm-hr. Going alongside of airframes being shaken apart, human beings -- a category into which all WW2-era pilots fell -- are not immune to degradation by vibration. They may have been dangerous, but the question is to whom.

Shortround6 said:

Pulse jets tended to take the aircraft apart with vibration. Not too bad if you figured the airframe was only going last a few hours before crashing (flying bomb).
But trying to beef up the airframe enough to last 30-50 hours was going to bring a weight penalty and/or a maintenance penalty.

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Not to mention the pilots.

Pulsejet vibration has not been a problem in model flying. Heat is the greatest problem as the tube glows red hot and must rely of airflow for cooling. Ground running with the engines used for models has to be limited to about 10 sec to prevent damage. Pulsejets used for models are generally about 21 inches long with about two inch chamber tapering to one inch tube. There is a you tube video of two guys flying two jet models controlline at the same time in the same circle. If interested, find Brodaks dueling jets.

Shortround6 said:

Everybody forgets that there are 3 basic sections to a jet engine.
The compressor is just one.
However if you get the the burner section and the turbine right then you can design/build engines of either type.
However if your burner section or turbine is not right it doesn't matter what type of compressor you are using.

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I need to be a bit picky here. The jet engine does indeed have three "components" and each one has its own development issues but I want to expand on the compressor component comparing the axial to the centrifugal compressors. The axial compressor typically has separate stages each consisting of compressor blades and stator blades. We could say the stators are a stage in itself as all calculations are similar and designs are unique, but I'll combine them here for simplicity. The compressor function is to take ambient air and compress it, increasing pressure but also changing velocity and increasing temperature. This is accomplished by the design of both the compressor blades and the stator. Each stage, including stator, must be carefully designed to ensure compressor stalling does not occur over the ambient operation range, including changes in inlet velocity and pressure, and that the output is compatible with the next stage. Each stage sees a different environment than the stage before it. This analysis and design must be repeated for every stage including stator. All of the design work and manufacturing must be very precise. In WW2 up to early 50s stator blades were fixed. When variable stator blades became available, J79-GE-1, much more powerful and efficient engines became available (Turbojet History and Development1930-1960, vol 2M Kay). Modern engines have many compressor stages, 15 on the TF-33. Mucho analysis and design work.

It is intuitively obvious that the centrifugal engine design is much simpler. There is only one analysis for compressor and stator design (some design had two sided compressors but the same design was effective for both sides). There are much fewer problems to overcome. Also, centrifugal jet engines are much shorter coupled between turbine and compressor. When you are transferring 3,000 hp or higher (much), the shorter the shaft the less the problems.

As stated, burner design had it's own issues which had to be addressed, but was common to all designs.

Also, turbine design, while similar aerodynamically to the compressor, kind of a reverse design, was very difficult due to the heat environment. Metal had to be developed along with cooling designs to make it operational. This is again, independent of compressor design.

All in all, I think if Germany had put money into the centrifugal compressor, they would have had a solid 2-3k lb thrust engine a couple of years before the axial engine, couple that with Germany's advanced airframe designs and Germany gets a lot tougher.

But, as Shortround6 says, it all has to come together.

Analysis of centrifugal compressors is quite difficult, probably more so than the analysis of axial-flow compressors. Design of the diffuser for centrifugals is especially difficult. Centrifugals also scale down better, both mechanically (small axials are more susceptible to foreign object damage) and thermodynamically (achievable efficiencies with axials drop off faster as size drops than it does it with centrifugals). During the 1930s and 1940s it was easier to design a centrifugal of acceptable efficiency and operating range than to do so with an axial, partly as there was quite a bit of experience with centrifugal compressors in superchargers, but also because centrifugal compressors were more common in industrial use.

In small sizes, centrifugals may demonstrate better efficiencies than axial flow machines, both because of manufacturing limitations but also because of fluid mechanics.

Considering the development of axial and centrifugal for the Germans raises the question of why the RAE left jet development in the hands of Griffith so long. He seems to have demonstrated a remarkable capability of making pretty models but not actually producing a working engine.

For those who are not familiar, Griffith started jet development in the UK in 1926, and built the first experimental axial compressor in 1928. It was not until 1938 that he decided to actually try to build an engine, and the design was hopelessly complex and didn't work. In 1939 he was finally convinced to use a compressor/stator arrangement, and then immediately putting into another bizarre Heath Robinson concept, and then making yet another that had a 17-stage compressor, 8-stage turbine and another 5-stage turbine for the propeller drive!

If not for Whittle pressing ahead with the design Griffith dismissed as useless because it was centrifugal, the allies would not have had jets during the war and would have been behind just about everyone after it - even France was doing well with the Atar courtesy of the BMW team.

Most of Griffith's time during the 1930s was as a researcher, not an engine designer.

He and Haynes Constant started working with Metropolitan Vickers to develop a turboprop in 1938. This had an axial compressor, but not a contra-rotating one.

This turboprop was redesigned as a pure jet after Whittle demonstrated his engine. By that time Griffith had moved to Rolls-Royce. The jet Metrovicks F.2 first ran in 1941, and was more powerful than the contemporary Whittle jet. The F.2 flew in a Meteor prototype a few months after the W.2 did.

Most of the issues with the F.2 concerned the combustion chamber(s) and the turbine.

Also, Metropolitan Vickers was thought to be slow and steady with development.

The F.2 line of development would lead to the F.9, which would become the Armstrong-Siddeley Sapphire.

My point is that someone, especially Tizard, should have realized the importance of putting this into the hands of someone who was going to drive development rapidly. Griffith simply wasn't, and no one else was selected to do so.

In contrast, Whittle ran himself off his feet and into a hospital bed. Sad, but absolutely required for the task.

Seems to me that a proper book about the early (1930s-50s) development of British jet engines is yet to be written.

As I understood it, when Whittle got involved with "jets" the idea was for another engine to drive the compression stage, which then just had a combustion chamber and tailpipe. It was Whittle who calculated that the compressor could be driven by turbine blades in the exhaust stream, which is what we now know as a jet engine. Is that not correct?

pbehn said:

As I understood it, when Whittle got involved with "jets" the idea was for another engine to drive the compression stage, which then just had a combustion chamber and tailpipe. It was Whittle who calculated that the compressor could be driven by turbine blades in the exhaust stream, which is what we now know as a jet engine. Is that not correct?

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Wasn't that the design of the Caproni C.C. 2?

SaparotRob said:

Wasn't the design of the Caproni C.C. 2?

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I dont know, but I dont really know much at all, apart from what I posted. I only read one article, which was on "the net" and I cant find anymore. As I remember it, at the time the idea that a "jet" could be sustainable and have a useful residual thrust wasnt considered to be practical or even possible, so the idea was to use an engine to drive the compressor and the jet pipe to provide more thrust than a propeller could at high speed. Maybe someone who has read more can put me right?

The Russians used a "motorjet" in the I-250.

pbehn said:

As I understood it, when Whittle got involved with "jets" the idea was for another engine to drive the compression stage, which then just had a combustion chamber and tailpipe. It was Whittle who calculated that the compressor could be driven by turbine blades in the exhaust stream, which is what we now know as a jet engine. Is that not correct?

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In a word - No

This is retyped from a book that I photocopied aeons ago that I have lost the cover from - the chapter is called early jets

Reaction propulsion was discussed as early as the seventeenth century, and numerous devices were patented during the First World War. In 1921 a Frenchman named Charles Guillaume patented a complete axial flow turbojet in very nearly its modern form. There was one difference: Guillaume's patent drawings, in addition to showing the expected compressor, combustion chamber, and turbine, also show, protruding from the front of the engine, a very large manual starting crank. One wonders how aeronautical engineers would have streamlined that. Guillaume's concept, although the same configuration as a turbojet, was never built and did not have the valid scientific assumptions that made the turbojet practical so to say that he "invented" the turbojet in any meaningful sense is absurd.

Like the water turbine or the steam turbine, the gas turbine has remote origins. Mediaeval Europe knew the gas turbine as a "smoke jack" installed in a chimney: rising hot smoke turned a windmill like turbine geared to a cooking spit. The first design for an internal combustion gas turbine proper is attributed to John Barber in England, who was granted a patent in 1791. The idea of the gas turbine was kicked around for most of the nineteenth century, but with little attention and no serious development. The impetus for gas turbine development came, quite naturally, from the success of the steam turbine.

Despite the hundreds of designs only three proposals were subjected to serious full scale experimentation before World War one: the constant volume design of the German engineer Hans Holzwarth and the similar constant pressure designs by Rene Armengaud/Charles Lemale in France and by Sanford Moss in the United States.

The first Holzwarth gas turbine was constructed between 1906 and 1908 and "operated on the explosion cycle without precompression." Based on the results obtained with the experimental engine, a second gas turbine with a nominal rating of 1,000 h.p. was built and tested, between 1909 and 1913. This, however, gave a nett output of only about 200 h.p. This second gas turbine employed a small centrifugal compressor, ten water cooled explosion combustion chambers (essentially pulse jets with exhaust valves) and a two stage Curtis turbine wheel with water cooled nozzles.

Meanwhile, in 1901, two remarkably parallel, although completely separate, constant pressure internal combustion gas turbine projects were started; that of Sanford Moss, which was conceived at the University of California, begun at Cornell, and extensively developed in the General Electric laboratories and that of Armengaud and Lemale in Paris.

The efforts of Armengaud and Lemale were probably the first elaborate gas turbine experimental work. Charles Lemale had applied for a gas turbine patent in 1901. He and Rene Armengaud began actual operation of a gas turbine in France in 1903. The turbine operated at constant combustion pressure using petroleum fuel which was ignited by a glowing platinum wire.

The promise shown by the first Armengaud-Lemale experiments led to the construction of a larger turbine during 1905-6. This employed a centrifugal compressor with twenty-five impellers in series arranged in three casings, all on the same shaft. Auguste Rateau and Armengaud jointly designed an internal water-cooling system for the entire compressor. The compressor delivered about 2,150 c.f.m. of air at a compression ratio of approximately 3:1; ran at 4,000 rpm, required 328 h.p., at an efficiency of 65 to 70 percent depending upon load. It used a single pear shaped carborundum-lined combustion chamber into which petrol was injected and atomised. Combustion was continuous at a temperature of 1,800° C. A convergent-divergent water jacketed (for cooling) nozzle was fabricated integrally with the combustion chamber which exhausted through a two stage impulse turbine, the disc and blades of which were also provided with internal cooling water passages. The water used to cool the compressor, nozzle, and the turbine was passed through coils downstream from the turbine itself, where the hot cooling water was converted into steam in the exhaust. This steam was exhausted, via separate nozzles, onto the same turbine. By injection of the lower temperature steam, turbine running temperatures were reduced to 400°C.

The engine produced about 300 h.p. nett versus 500 h.p. designed. It was, however, grossly inefficient, burning 3.9 lb. of petrol per brake horsepower hour, compared to 0.5 lb. petrol per brake horsepower hour for contemporary piston engines.

Simultaneously Sanford Moss in the United States was conducting almost identical, although totally independent, experiments on internal combustion gas turbines.

Moss invented his gas turbine while in the thermodynamics and hydrodynamics classes of Prof. Frederick G. Hesse at the University of California in 1895. Moss submitted a master's thesis on gas turbine design, including a proposal for a turbine powered locomotive, to the University of California in 1900. In 1901, Moss began gas turbine research in the Sibley College Laboratory of Cornell University. It took a year of concentrated effort just to get a continuous combustion chamber in stable operation.

Moss's Cornell experiments were not successful. As with many other experimental gas turbines, the power for compression was more than the turbine power. Except for the historical fact that the combustion chamber actually operated the turbine wheel, the experiment was a flat failure.

In June of 1903 Moss went back to General Electric, for whom he had previously worked as a steam turbine draftsman, and continued to pursue his gas turbine research. As was rapidly becoming customary at G.E., their investigations into the various elements of internal combustion gas turbine design were the most thorough and comprehensive to that time. Extensive experiments were begun in the fall of 1903 on centrifugal compressor design, and a 1904 patent application in Moss's name demonstrated theoretically the relation between the velocity of flow of a compressible fluid and diffuser shape. Essentially, Moss showed that for flow velocities below the local speed of sound in a compressible fluid (gas), compressor diffuser design could be treated "just as with an incompressible fluid" (water, for example), and that divergent diffuser passages were appropriate.

On the basis of Moss's theory G.E. began successful development of centrifugal compressors. Moss also performed fundamental investigations of energy conversion in nozzles, using compressed air, steam, or the products of internal combustion as his working medium.

General Electric experiments continued until 1907, when fuel consumption was 4 lb. of kerosene per net hp/hr compared to good oil engines using 1 lb. of oil per net hp/hr. No way then seemed open to do better, and so the gas turbine part of the research was stopped. Moss continued at GE first on centrifugal compressors and the piston engine turbo-supercharger research and development program.

After 1920, Glenn B. Warren joined GE concentrating on steam turbine problems, especially on materials resistant to high temperature creep and vibration, turbine blade and disc design, and, significantly, nozzle design. In all of these areas, G.E. made major progress during the 1920s and 1930s, and this progress played a basic role in their ultimate capacity to adopt and develop the turbojet. In May 1941 GE accepted a US Army contract to build Whittle engines under licence and the first GE engine was run ten months later on 18 March 1942. The Bell XP-59 flew with a GE engine in October 1942.

Several other gas turbine projects, deserve mention. About 1908 A. Barbezat supervised construction of a turbine of the Karavodine "explosion" system. The mode of operation of the Karavodine combustion chamber was identical to that of the "pulse jet" as used later in the German V-1 flying bomb.

Hugo Junkers, professor of mechanical engineering at Aachen Technical University (and soon to be of aircraft fame), together with Otto Mader, worked before the First World War on a free-piston engine, a system in which crank-less opposed pistons are used to produce exhaust gas to run a turbine.

Of the hundreds of gas turbine proposals current in 1900, few were developed, and only those of Holzwarth, Armengaud and Lemale, and Moss, seriously. Most of the projects were terminated outright so the first gas turbine revolution proved largely abortive. Ironically, its most successful results were centrifugal superchargers and turbo-superchargers for piston aircraft engines.

In England in 1926, A. A. Griffith wrote a report for the RAE proposing a new aerofoil theory of axial compressors. Griffith argued that the design of the blading of the compressor should be approached through aerofoil theory in order to get the maximum transfer of energy with minimal losses (the same as lift and drag, respectively). The converse of the same argument would be valid for turbines.

An appendix to that paper applied the new theory to the design of a hypothetical turboprop engine. During 1927 the Aeronautical Research Council authorised a small single-stage test rig which was built and tested under Griffith's supervision yielding stage efficiencies of better than 90 percent.

Griffith continued to develop his axial flow compressor ideas, and in November 1929 submitted a memorandum to the ARC containing a design study for a very complex contra-rotating, contra-flow, 500 h.p. turboprop engine. In his proposal, Griffith sought an engine fully competitive with contemporary piston engines in power, weight, and fuel consumption. Construction was approved but the Depression resulted in cancellation. Griffith eventually designed the Rolls Royce Avon engine.

Another document with history of other early gas turbines, covering other early pioneers is the recently released Gas Turbine Handbook : Principles and Practices which can be found and downloaded at Gas Turbine Handbook : Principles and Practices

From the second book

Note: A radial aircraft engine is NOT a "rotary". Those are altogether different. A V-12 Merlin is NOT an in-line engine.