Which country designed the best engines for WWII?

[swampyankee]

A question that's bugged me for years: why did the Merlin and Griffon have opposite rotation?

 

[wuzak]

Standardisation.

I believe that the Society of British Aircraft Constructors (SBAC) had pushed for standardisation of engine rotation, presumably because it simplified propeller production. The Merlin was built before standardisation, the Griffon after.

Some say that as, originally, a naval engine the Griffon's rotation was changed compared to the Merlin for safety reasons. But as far as I can tell, the Griffon's torque reaction would have caused a single engine aircraft to swing towards the island on an aircraft carrier, not away.

 

[Shortround6]

Hmmmm, Bristol has a lot to answer for

 

[fastmongrel]

And the fact that it is an English magician!

Merlin the Magician was Welsh. Myrddin ap Ambrosius.

 

[Ryanjames17]

I found the answer to why the RR griffin was oposet the rotation to other engines one time, I can tell you it was in something that also explains why the reduction in RPM from 3000 to 2750.

 

[swampyankee]

Standardisation.

I believe that the Society of British Aircraft Constructors (SBAC) had pushed for standardisation of engine rotation, presumably because it simplified propeller production. The Merlin was built before standardisation, the Griffon after.

Some say that as, originally, a naval engine the Griffon's rotation was changed compared to the Merlin for safety reasons. But as far as I can tell, the Griffon's torque reaction would have caused a single engine aircraft to swing towards the island on an aircraft carrier, not away.

So the Merlin was opposite to the majority of its contemporaries or were British engines evenly split between clockwise and counter-clockwise rotation?

 

[Shortround6]

It looks like RR used a right hand rotation and Bristol Used left hand?

 

[pbehn]

Standardisation.

I believe that the Society of British Aircraft Constructors (SBAC) had pushed for standardisation of engine rotation, presumably because it simplified propeller production. The Merlin was built before standardisation, the Griffon after.

Some say that as, originally, a naval engine the Griffon's rotation was changed compared to the Merlin for safety reasons. But as far as I can tell, the Griffon's torque reaction would have caused a single engine aircraft to swing towards the island on an aircraft carrier, not away.

Hard to say for sure because the Griffon as an engine may have come after standardisation but the Griffon was evolved from the type R and that was from the Buzzard. I have read somewhere about a naval requirement for rotation but that doesn't seem to be conclusive. As for the name of the Merlin, well they were birds not mythical magicians and we are lucky one didn't end up as a Hobby or even a Subbuteo.

 

[Shortround6]

There is a story that when first being tested they broke two Griffon crankshafts in less than ten hours each. A junior engineer (supposedly) noticed that they were trying to run a Merlin style crankshaft ( throws for the connecting rods laid out in identical fashion) backwards. They made a mirror image crankshaft and........no more broken crankshafts.

 

[wuzak]

Hard to say for sure because the Griffon as an engine may have come after standardisation but the Griffon was evolved from the type R and that was from the Buzzard. I have read somewhere about a naval requirement for rotation but that doesn't seem to be conclusive. As for the name of the Merlin, well they were birds not mythical magicians and we are lucky one didn't end up as a Hobby or even a Subbuteo.

The Griffon I was a detuned R.

The Griffon II owed nothing to the Griffon I, R and Buzzard, save the bore and stroke.

As I said earlier, the naval requirement doesn't make sense to me, as the Griffon's rotation would swing the aircraft towards the island of a carrier, the Merlin's away.

 

[Ryanjames17]

The Griffon I was a detuned R.

The Griffon II owed nothing to the Griffon I, R and Buzzard, save the bore and stroke.

As I said earlier, the naval requirement doesn't make sense to me, as the Griffon's rotation would swing the aircraft towards the island of a carrier, the Merlin's away.

i think your right on the naval requirement, i found it one time and it was something stupid too.

 

[Dan Fahey]

My opinion was the Allison 1710 was the BEST Liquid Cooled Engine..!
Far easier to maintain and operate and lasted longer between rebuilds.
It down fall was a lack of thinking !

Here the German and British built over all better packages.

US and Allies had the logistical advantage of better Fuels and Oils.

The US never approached WW2 as desperate as all the other combatants.

Hence the delay of the Mustang and better tanks and other war material.
Think the US Navy was far more attentive than US Army.

 

[Reluctant Poster]

My opinion was the Allison 1710 was the BEST Liquid Cooled Engine..!
Far easier to maintain and operate and lasted longer between rebuilds.
It down fall was a lack of thinking !

Here the German and British built over all better packages.

US and Allies had the logistical advantage of better Fuels and Oils.

The US never approached WW2 as desperate as all the other combatants.

Hence the delay of the Mustang and better tanks and other war material.
Think the US Navy was far more attentive than US Army.

The USN continued to lead the way after WWII. While the newly minted USAF was wasting money on the Hughes Falcon missile the Navy was purchasing the Sidewinder and Sparrow, which the USAF eventually adopted. The USAF century series fighters were not so successful and were replaced by the Navy's F4 and A7. Navies have generally taken a more scientific approach than Armies. I find it fascinating that the first tanks to see combat was developed by the Royal Navy not the army.

 

[Reluctant Poster]

So to put this thread back on topic. I'm going to reiterate that the US made the best of the best engines during the war. The best 2 where the R-1830 and the R-2800, and the reason that makes them the best is they are still going and even many years after the war where in aircraft working making dollars.
You can not say that for the recip engines that had beginnings or manufacture during or close after the war from any other country. Especially now there is just a very small handful of non Pratt & Whitney engines running in flying aircraft. Allison's and Merlin's sure they work, but TBO is horrible, and I don't know of many that were flying passengers in the late 60's and 70's. R-3350's can be factored in as well, gosh even the R-4360 has a great 1950's into the early 70's I think it was service record. So US aircraft recips from WW2 to about 30 years past where in service. How many Napier's, Centaurus's, Allison's, Merlin's, Griffons, and all the other countries engines lived that long. Oh and I'm sure there are still R-1830's and R-2800's flying some place for hire in Canada, Alaska, and other countries as we write this. So the best are still in use.

Rolls Royce saw the future more clearly than Pratt and Whitney and Wright. They cancelled their big commercial recips (the Pennine and the Snowden) to concentrate on turboprops and jets. Why bother developing Merlins and Griffons any further when you have the Dart and the Avon already running in 1946. Pratt and Whitney's first Turbojets were old Rolls Royce centrifugal designs which RR had moved on from in favor of the axial Avon. P&W was 4 years behind in jet technology and Wright was already a basket case by the end of WWII.

 

[Reluctant Poster]

Germany:

Germany conducted the most in depth research on almost every single engine system.
I can state that I believe their supercharging work is stunningly good (see attached pic SC), and were the only ones
towards the end who started developing engines which were on the truly modern path philosophically,
of radically increasing crankshaft speeds, and having flexible valve timing controls; which with the
possibilities of direct injection are really knocking on the door of all modern engines, in terms
of control possibilities.

However they utterly failed in the task of taking all this research and putting it into one, or two
engines which would actually be able to be mass manufactured in time to have any useful
war impact.

The Jumo 213J and DB603N, were in several respects light years ahead of their time, due to
design features like hydraulic VVT, swirl throttling and mean piston speeds over 66fps well over 4000rpm, bu due to pitiful organization and planning - were militarily, non-events. If you see the list of engines DB developed you will never believe it, its like an engines menagerie.

Germany gets a gold-star too in my book for having carried out all this research and work
under horrific conditions, which really makes it a wonder they did anything useful at all.

Their greatest failure was not getting a two-stage supercharged engine with charge-cooling
into service. Which was really criminal, as their drawing offices and test stands were littered
with them.


Britain:

Generally made very "simple" engines (ignoring Napier...) and the only country I think which
understood not only what it needed to do, but understood its own strengths and weaknesses.

Unlike the Germans, Rolls-Royce brutally culled engine projects before they dragged on draining resources
from the critical work (eg Vulture being cancelled, dramatically increased the resources available for Merlin development according to Geoffrey Wilde).

Understanding the limited time and people they had, Britain more or less conducted its entire war
effort on one engine series, and would have (sorry to Bristol and Napier fans) been entirely able to
have finished in the same circumstances with only Merlins. Which I dont think you can really
say about any other nation. The "stick with what you`ve got and develop it" pragmatic approach
probably won the war for Britain in the air.

I think the Merlin 60 series, two-stage with charge-cooling was really the ubiquitous liquid
cooled V12 of the war (in terms of mass produced operationally significant engines, that
were fitted across several aircraft platforms). The significance of the introduction of the Merlin 61
is very apparent from reading German technical intelligence reports, and internal DBenz reports,
no other Allied engine is really mentioned much, but the 61 and V1650 had them quite panicked;
although they did meticulously take apart and test every other engine the Allies made too, as did we.

I think Britain's great failure was an embarrassing reliance on carburetors, which in view
of the problems it caused, and the open possibilities to change it early on - was really very very bad,
and I`m sure cost many pilots their lives until the pressure carburettors were put on by Packard.


USA:

The Americans clearly got their act together with Turbocharging and fuels research in a way
that nobody else did (although plenty of behind the scenes stuff credit on fuels has to go to
Brits like F.R.Banks). However turbo setups in the 1940`s were horribly heavy and gigantic in
size, which did mean that without a really good two-stage mechanically blown engine, their
smaller fighters were a bit limited, which is really why the P51 was a little hamstrung for a while.

I think the big Wasp radials with turbo`s were amazing engines. I think their greatest failure was
not developing a really good supercharger for the V1710, which was in many respects a
better basic engine than the Merlin. The combustion chamber shape of the Allison is much
better than that of the Merlin, and is very similar to a modern engine, inclined 4 valve narrow-valve angle
pent roof, and splitting the crankcase down the crank centre-line, then using the whole sump as a
main bearing ladder-frame is very modern in concept, it makes for an extremely strong and stuff
crankcase structure and bearing alignment.


Russia:

I am not knowledgeable on Russian engines yet, but I do know that we can credit them for the very clever
introduction of the supercharger swirl-throttleon the AM35 engine. Which was quickly copied by Werner Von Der Null at the DVL
and eventually pressed into service on the Jumo 213 and DB603L & N.


Overall

Its very open to interpretation, but your question was "which country DESIGNED the best engines", I`m going to
vote Germany. The fact they never really managed to actually put many of them into a plane is a second thread !

The best DESIGNS, were I think the DB603N (which went to wet-liners, and conventional bolted head joints) and
the Jumo213J, which was really the only engine of the war to move seriously towards very high speed crank speeds.

According to internal german comparisons, which compared all the major engines, Sabre, Cyclone, AM35, AM38, Merlin, Griffon, DB`s, Jumo`s, BMW`s - the Jumo 213 scores first place in just about all categories, only loosing
out to engines like the P240 which was never used (developed by the Mercedes Silver Arrows automotive
racing dept !).

Kg/PS Kilograms engine weight per PS (basically a horsepower) (see pics 1,2,3,4 - sorry they are so blurry!)
PS/m^2 Engine frontal area
PS/m^3 Engine package volume
MEP Mean Effective Pressure
MPS Mean piston speed

Of course you can invent other categories in which it scores very little, such as was it introduced
early enough and in sufficient numbers to actually matter.....probably not really. I`ve attached a couple of snippets on the Jumo213EB, which even ended up in a real aircraft, amazingly...haha, the amazingly
flat power vs altitude curves can easily be mistaken for a turbocharged engine, but are in fact due to
the Swirl Throttle (copied from the Russian AM35). Which dramatically lowers pumping losses below rated heights.

I`d also say that the DB624 turbo-twin-supercharged engine would have been superb, and Benz had completed
their 100hour tests on turbocharged DB`s in 1941. So while USA deserves tremendous credit for getting not only
the science right, but ALSO the scheduling, and production - German turbo research has laid it all on the plate
for their country too. They just never got their act together to make proper use of much of it (we can all thank
Ernst Udet & Göring for that).

In terms of things that were actually made in enough volume to be war-influential, then I think I can only pick the Merlin, because if you waved a magic wand and said "ok its 1939 and you only get to have ONE engine for the
rest of the war for ALL your planes" I think its the only one that really could have done that well, and for
Britain more or less actually did...but I dont think its necessarily a particularly advanced engine, it was just
developed very well to do one thing, using a simple proven layout. Therefore it really stops being an aircraft engine
and starts being just, a useful mass produced, reliable war-machine - and I think Germany spent rather too much
time trying to build clever engines, and forgot about the fact they needed war-machines.

But all this was very strongly tied in with fuels, and strategies, Germany never really managed to figure out what it was
supposed to be doing with their engines, and the fuels situation was also catastrophically poorly planned, and run. So
I think its really very very difficult to compare like for like, every country had their own constraints and targets, although it was the same war, very few in Germany were really trying to do what the Allied designers were trying to do, and visa-versa, its not as if each side had to just make an engine that could reach 30,000 feet first, or use least fuel
and so on. Its really hard to say what "best" is without knowing the background to each.

I am also "cheating" with this post, because its the topic for a book I`m writing which should be finished in the next few months. So I get unfair advantage of having piles of stuff right at my desk. I would post alot more info, but its all copyrighted and I cant upset the people and places who gave me this stuff, by just posting it all verbatim.

("Umfangsgeschwindigkeit" means "supercharger impeller tip speed" in the pic SC and the last pic means "German Aeronautical Research Institude - Berlin Aldershof, Institute for Turbomachinery report by Dietrich, Report on the Analysis of the two-stage, two speed supercharger system from the high altitude engine Merlin 61 with after-cooling & housing cooling").

The combustion chamber shape of the Allison is much
better than that of the Merlin, and is very similar to a modern engine, inclined 4 valve narrow-valve angle
pent roof

The Allison combustion chamber design may vaguely resemble a modern shape but it does not function in the same way as a modern four valve. In fact with its incredibly convoluted intake manifold it cannot. In the 1960s Westlake and Duckworth developed independently developed the concept of what Duckworth called barrel turbulence and others called tumble swirl for their F1 engines. The secret is not in the shape of the combustion chamber so much as getting the air into the cylinder with a swirling motion parallel to the longitudinal axis of the engine. Look at the cross section of the Cosworth DFV and note that the intake has a straight shot into the cylinder, impinging on the exhaust valve side creating the tumbling motion.This was a revolution in engine that launched the popularity of 4 valve engines, up to that point high performance engines were usually 2 valve, sometimes with swirl induced about the axis of the piston (eg Jaguar racing engines). See the following illustrations.
https://www.andreadd.it/appunti/pol.../appunti/9_moto_della_carica_nel_cilindro.pdf
The Allison intake manifold has airflow entering each cylinder in a group of three in a different way. It is unlike any other intake manifold. It is more like an exhaust system where where header are if equal in length a opposed to more typical plenum designs. Also note that contrary to popular opinion it a not a ramming manifold. Ramming manifold have individual runners to each cylinder whereas the Allison's are in groups of three. Ramming manifolds also retain energy by designing the runners to minimize abrupt changes in direction. The Allison intake is the worst from a fluid dynamics perspective i have ever seen with very sharp elbow directly joining each other.

 

[wuzak]

The Merlin's manifold was simpler, with a central tube feeding 3 outlets on each side that fed 2 cylinders each.

https://www.enginehistory.org/members/articles/ACEnginePerfAnalysisR-R.shtml
Chart 5 shows the Merlin intake and Chart 6 shows the Allison intake.

The Allison's seems to have some degree of intake ram, while the Merlin doesn't even attempt it.

The Allison may lose some of the advantage of the ram through the convoluted piping to get to the final bit of the manifold.

The Merlin merely relies on boost.

When the V-1710 was hooked up to a 2 stage Merlin supercharger, its performance was nearly identical to the Merlin.

Which leads me to conclude that the supercharger performance dominated other factors in determining overall engine performance, at least in comparing the Merlin and V-1710.

 

[Shortround6]

Rolls Royce saw the future more clearly than Pratt and Whitney and Wright. They cancelled their big commercial recips (the Pennine and the Snowden) to concentrate on turboprops and jets. Why bother developing Merlins and Griffons any further when you have the Dart and the Avon already running in 1946. Pratt and Whitney's first Turbojets were old Rolls Royce centrifugal designs which RR had moved on from in favor of the axial Avon. P&W was 4 years behind in jet technology and Wright was already a basket case by the end of WWII.

A bit harsh aren't you?

Merlin and Griffon development was coming to an end because without improved fuel (over 150 PN ) more boost wasn't going to work (and didn't work that well for cruising in any case) which leaves higher rpm as the only avenue.
Saying the Avon was running in 1946 is a bit of stretch, running in what form? and how well, it took until Aug 1948 to get two Avons into the air in the outer nacelles of a Lancaster.

P & W knew they were behind in jet engines due, in part, to US government policy during the war. An example of that was that the General Electric team working on centrifugal engines in one plant were not allowed to talk to/communicate with the General Electric team working on axial engines in another plant even about things like burners/combustion chambers. It was government policy that the big engine makers were NOT given contracts to develop jet engines during the war, not choices made by engine company management.
P & W, once free of that restriction at the end of the war went to RR to licence their designs, however P & W did have the foresight to insist that RR design for P & W a bigger centrifugal engine that RR themselves were interested in as part of the deal for the Nene, this became the Tay.
Wright engine division wasn't quite as bad as you make out, kept out of jets during the war by the government they too went to England for a jump start and hooked up with Bristol, however one the major things that saved Bristol was the falling out at RR between Hooker and Hives which lead to Hooker joining Bristol in 1948. Wright as a piston engine maker after WW II was 2nd only to P&W in the west and was still building a trickle of large piston engines in early 1960s.

 

[swampyankee]

One other issue is that Pratt & Whitney Aircraft spent more money on jets than Curtiss.

 

[Shortround6]

We may be getting confused here.
Curtiss was the airframe part of "Curtiss-Wright" (and propeller) while Wright had evolved into the Engine maker. "Curtiss" had stopped making engines back in the early 30s with the end of the V-12 water cooled engine line.

"Pratt & Whitney Aircraft" was a division of United AIrcraft which included Sikorsky, Vought and Hamilton Standard. The corporations may not have been structured the the same but nobody talks about SIkorsky or Vought spending money on jets.

Wright was late getting into the jet game and could not take the Bristol Sapphire (J-65) either much further or use that experience to design a replacement/enlargement of it.

 

[wuzak]

You mean Armstrong Siddeley Sapphire, which was produced before the merger with Bristol in 1960.

The Sapphire can trace its roots back to the Metropolitan Vickers F2.