A V12 engine for combatants in 1939-45

[tomo pauk]

Favored mostly in Europe for fighters, it was also useful in bombers of all sizes. US Army fighters were also mostly designed & produced around V12s in this time.
Similar to the another thread about the engine choice this time about the another established type. Engine should be in service use by 1939, in good numbers, with good reliability, while making power required. You can make a spin-off from an existing type, or suggest some hybrid; different types for different engine-making countries. The engine itself should be 'designed' with an eye towards the country-specific requirements and technology in use, so the start of service can be as smooth as possible. Metallurgy, fuel and superchargers of the day can be used; granted, not everything was available for just any country. Engine with or without a motor-cannon feature. What company should design it in a selected country?
'Design job' starts in 1935. You can kill other engine projects so this one gets support from respective air forces.

 

[swampyankee]

Looking around, in 1935, a supercharged V-12 could have HP/in^2 of piston area of about 3.25 - 3.5.
Picking a bore of 5.5 in would give 83 hp/cyl, so 998 hp. Size and weight is worsened by long strokes, but fuel efficiency is improved (at least slightly). With a piston speed of 2500 fpm, a 5 in stroke would give rpm of 3,000.

So, the Swampyankee 12V55-01 would be:
60 degree V-12
4-valve head, double overhead cams
Bore: 5.5 in
Stroke: 5 in
Disp: 1425 in^2 (118.8/cyl)
Weight (est): 1200 lb
Power: 998 hp @ 3000 rpm
Piston speed: 2500 fpm @ 3000 rpm

Length: 58 in
Width: 31 in
Height: 32 in

Details: fork-and-blade connecting rods. Counterweighted crankshaft. If left- and right-handed engines are desired, an idler would be added to the gearbox. Obviously, dual ignition.

Comments: Growth potential is hard to measure. If this could be developed equally to the Merlin, 1,500 hp would be available in 1943 and about 2,100 in 1945.
-----

Realistically, V-12s for aircraft are somewhat constrained: the maximum bore for a high-speed spark ignition engine is around 6 to 6.5 inches, which (at 3.5 hp/in^2) limit a V-12 to 116 hp/cyl or about 1400 hp (power densities went way up with time). A "square" engine with a bore of 6.5 in would have a displacement of about 2590 cid and a weight of about 2000 lb.

 

[tomo pauk]

Me, I like the bigger V12s better
It would've been easiest for the Rolls Royce to came out with such and engine in a required time frame. Take the 'R' engine and work from there. For the 1st iteration, use supercharger designed around an 11-12 in impeller (the Griffon have had a 10 in impeller, smaller than what most of 'normal' Merlins had). Hopefully it could be run at 2700 rpm? It should be good for ~1400 HP at altitude on 87 oct fuel; ~1700 HP on early 100 oct down low (more if a 2-speed S/C is used), later a 2-stage supercharger + intercooler + a bit better fuel for 2000+ HP.
With water injection or 150 grade fuel going well past 2300 HP.

 

[tomo pauk]

For the Soviets - the base is M-35 line from Mikulin. The historical M-35 was making 1200 HP at 4500m, followed quickly by -35A with 1200 HP but at 6000m. Both engines had the Polikovsky's swirl throttle for better low-altitude performance (that was already used on the M-34FRN).
1st change that I'd do for the M-35A will be cutting down the compression ratio ASAP, from 7:1 to perhaps 6.5:1, if not to 6:1 already. Sacrifices a bit the hi-alt performance, while allowing for greater boost at lower altitudes and thus more power down low.
Next, introduce the strengthened internals as per AM-38, so the rpm and boost can go up. Don't change the S/C drive ratio that much as it was the case with AM-38, if at all.
Introduce the 2-speed S/C drive for early 1942.
By 1943, we should have the AM-39 equivalent in service. Fuel injection by 1944.

 

[Shortround6]

AS we have noted in other threads in the past, fuel injection is a double edge sword, at least direct fuel injection. Throttle body fuel injection solves some problems at a much cheaper price but doesn't have some of the benefits of direct injection. Direct injection calls for a lot of precisely machined parts which may be beyond the capabilities of some countries in the 1930s and early war years. Or it can be made but what else doesn't get made?

we also seem to be using the time machine a bit here. In 1935 when design starts 100 octane fuel is pretty rare stuff and 150 octane is in the realm of science fiction and faster than light drive

The Hispano V-12 was a bit dated in 1935 (heck it was dated in 1933) and shows some of the problem. It had a good power to weight ratio in 1933-37 as it only weighed about 1085lbs?
However it's light whippy crankshaft without counter weights wouldn't go much more than 2400rpm, the fact that it was a 36 liter engine made up a bit for the low RPM. With counter weights later versions got 2500rpm. Russians got it up to 2700rpm but added about 200lbs to it and reduced the bore by 2mm to strengthen the cylinder walls.
A single stage two speed Griffon of 36.7 liters went 1790lbs.

Nobody was going to buy a 1600-1800lb V-12 in 1935-37 that only made 1000-1100hp running on 87 octane fuel.

To use 100 octane and higher you need a stronger crankshaft and reciprocating parts and a stronger crankcase.

The Swiss Saurer YS-4 was a post war pretty much last generation Hispano derivative. It weighed 1555lbs and gave 1600hp for take-off and 1580hp at 15,300ft using 100/130 fuel Both at 2800rpm, piston speed was 3122fpm.
It used a variable speed supercharger and direct fuel injection, injection pressure was 2850 lb/sq/in. It also had 4 valve heads instead of the two valve heads of the original Hispano.

You can start design work in 1935 but the engine should NOT be ready until 1940-41 if you want it to last until 1945 without major rework.

Merlin may be the only exception to this (Allison included, it wasn't really ready until 1940-41 despite being started in 1930-31) but how much a Merlin II had in common with a Merlin 85 is certainly subject to question.
for very late war the Merlin 100 differs from a Merlin 85 in having,
Strengthened universal crankcase for end oil feed
Strengthened cylinders with rocker cover breathers
stiffened valve springs
new coolant pump
improved short intake elbow for mechanical accelerator pump
overhung first stage supercharger rotor
auxiliary gear box drive
others?

 

[tomo pauk]

AS we have noted in other threads in the past, fuel injection is a double edge sword, at least direct fuel injection. Throttle body fuel injection solves some problems at a much cheaper price but doesn't have some of the benefits of direct injection. Direct injection calls for a lot of precisely machined parts which may be beyond the capabilities of some countries in the 1930s and early war years. Or it can be made but what else doesn't get made?

Soviets have had a fuel-injected engine in production and use in 1944. I've suggested that my stipulated engine gets those in 1944, not in the 1930s. What does not get made are thousands of carburetors - Mikulin's V12s used 4 carbs each.

However it's light whippy crankshaft without counter weights wouldn't go much more than 2400rpm, the fact that it was a 36 liter engine made up a bit for the low RPM. With counter weights later versions got 2500rpm. Russians got it up to 2700rpm but added about 200lbs to it and reduced the bore by 2mm to strengthen the cylinder walls.
A single stage two speed Griffon of 36.7 liters went 1790lbs.

With Rolls Royce around, I'm not sure why would anyone pick HS 12Y as a V12 engine that British should be looking as example.

Nobody was going to buy a 1600-1800lb V-12 in 1935-37 that only made 1000-1100hp running on 87 octane fuel.

Indeed. Though, people will be buying a 1600-1700 lb engine that does 1250-1300 HP on 87 oct fuel.

You can start design work in 1935 but the engine should NOT be ready until 1940-41 if you want it to last until 1945 without major rework.

Yes, the rework will be needed for the engine to remain competitive even in 1945. Like it was the case for all of ww2 engines.

 

[tomo pauk]

Italian V12 for the specified era. Their best chance is that government does not start favoring the air-cooled engines in the 1930s, so both Fiat and Isota-Fraschini are still making new liquid cooled engines. Granted, the new engines will need to feature en-bloc cylinders, supercharging etc; Fiat can also try to apply the know-how from their racing engines where applicable.
For Fiat themselves, this might mean they make a 'new-tech' take on the 32.3L engine, sharing the bore and stroke from their A.24 engine. In return, this probably means 1000+ HP on 87 oct fuel at altitude even before 1939 - nothing earth-shaking, just an useful engine that is much better choice than radials the Italians were installing on their aircraft.
For I-F, they can also still remain in the 32.65L 'category' as it was the case with the Asso IX, but will need to make a whole new engine - the construction methods moved on fast in 1930s. Cylinders in a block, mixture coming from S/C through tubing via the Vee rather than from outer side of the engine, a new take on S/C, a new crankshaft, bearings and whatnot so the engine that can do 2400+ rpm (in a more regular fashion) rather than 2250 etc. Again hopefully we can have 1000+ HP on alt and on 87 oct fuel in a timely manner.

 

[Shortround6]

Soviets have had a fuel-injected engine in production and use in 1944. I've suggested that my stipulated engine gets those in 1944, not in the 1930s. What does not get made are thousands of carburetors - Mikulin's V12s used 4 carbs each.

6 carbs, but the carbs are relatively simple and most parts don't require precise machining. I don't know about the Russian fuel injection but the German systems needed over 500 parts and many of them were made to very close tolerances.

With Rolls Royce around, I'm not sure why would anyone pick HS 12Y as a V12 engine that British should be looking as example.

Just using it as an example of an engine that existed (in production) in 1935 and the weight it gained and changes needed to get to be a 1500-1600hp engine in 1945-47.
Some engines needed an awful lot of changes. Some never made it. US Hyper engines?

Yes, the rework will be needed for the engine to remain competitive even in 1945. Like it was the case for all of ww2 engines.

For most nations that meant pretty much new engines.

For V-12s only the Allison and Merlin went through the war and stayed competitive (mostly) in 'tweaked" form. And both of them got 100/130 fuel if not better and new parts.

The DB605 was a problem and was being replaced by the DB 603 at the end of the war.

I will take some flak from the black cross boys for that but the DB 605 gained very little in the way of 1/2 hour or 1 hour ratings even though the peak ratings went up with the later versions. You can't fly heavy bombers with sprint rated engines. Same for the Merlin and Allison, they were getting too small in long duration ratings. However both engines were improving their service life considerably, something that cannot be said for some other engines.

Lets not forget that the Merlin was 'supposed' to have been replaced by the Sabre, Vulture and Centaurus. All of which were in development by the late 30s. Other projects were also in the works. The idea that you could eventually get a Merlin to give 1190hp for 30 minutes while climbing or a max rich cruise of 1090hp at 13,250 ft would have been meet with stares of disbelieve in 1936-37. (Merlin 502 commercial engine post war)

How much of the allied advantage was in materials I don't know. We know the Allison went through 4 different crankshafts between 1940 and 1944/45. Only one was visually different.

 

[Deleted member 68059]

For V-12s only the Allison and Merlin went through the war and stayed competitive (mostly) in 'tweaked" form. And both of them got 100/130 fuel if not better and new parts.

The DB605 was a problem and was being replaced by the DB 603 at the end of the war.

I will take some flak from the black cross boys for that but the DB 605 gained very little in the way of 1/2 hour or 1 hour ratings even though the peak ratings went up with the later versions. You can't fly heavy bombers with sprint rated engines. Same for the Merlin and Allison, they were getting too small in long duration ratings. However both engines were improving their service life considerably, something that cannot be said for some other engines.

How much of the allied advantage was in materials I don't know. We know the Allison went through 4 different crankshafts between 1940 and 1944/45. Only one was visually different.

Its a fruitless exercise attempting to make any direct like-for-like comparisons between German and Allied WW2 aero engines, the DB605 wasnt any more of a problem than any other DB engine in WW2. If you want to know about materials advantages, I`ve written a book on it which will arm you rather well for this thread.

 

[tomo pauk]

6 carbs, but the carbs are relatively simple and most parts don't require precise machining. I don't know about the Russian fuel injection but the German systems needed over 500 parts and many of them were made to very close tolerances.

Mikulin engines used 4 carbs.
Russians used direct fuel injection on the ASh-82FN.

Just using it as an example of an engine that existed (in production) in 1935 and the weight it gained and changes needed to get to be a 1500-1600hp engine in 1945-47.
Some engines needed an awful lot of changes. Some never made it. US Hyper engines?

A quick peek at the engine displacements I've suggested - roughly 32-37L - here will point out that Hyper engines (engines where "hp per cu in" was the most important metric) are not wanted.

For most nations that meant pretty much new engines.
For V-12s only the Allison and Merlin went through the war and stayed competitive (mostly) in 'tweaked" form. And both of them got 100/130 fuel if not better and new parts.

V-1710 received new reduction gear, the crankshaft got the new tech/material several times, it's counterbalance was improved twice, pistons & piston rings were improved, bearing lubrication was introduced, strengthened connection rods, larger oil pump, stronger supercharger drive (since the old will not support the 9.6:1 drive ratio), 3 times the piping connecting S/C and cylinders were changed.
Merlin - 2-piece block introduced, piston design chaged twice, strengthened con rods and crankcase, strenthened drive for S/C for 2-stage engines past Mk.61. (just skimming the book 'Merlin in perspective')
All this is before counting the 2-stage superchargers these engines received, changes in fuel distribution (ie. carb types) and before the Merlin 100 series and V-1710 G series that introduced each it's own set of improvements.

The DB605 was a problem and was being replaced by the DB 603 at the end of the war.

It was not being replaced by DB 603.
DB 605 with a big 1-stage supercharger was about as good as Merlin 61 or 2-stage supercharged V-1710.

I will take some flak from the black cross boys for that but the DB 605 gained very little in the way of 1/2 hour or 1 hour ratings even though the peak ratings went up with the later versions. You can't fly heavy bombers with sprint rated engines. Same for the Merlin and Allison, they were getting too small in long duration ratings. However both engines were improving their service life considerably, something that cannot be said for some other engines.

DB 605 was not powering heavy bombers. The 1 hour ratings on V-1710 or Merlin were not something to brag about, either.

Lets not forget that the Merlin was 'supposed' to have been replaced by the Sabre, Vulture and Centaurus. All of which were in development by the late 30s. Other projects were also in the works. The idea that you could eventually get a Merlin to give 1190hp for 30 minutes while climbing or a max rich cruise of 1090hp at 13,250 ft would have been meet with stares of disbelieve in 1936-37. (Merlin 502 commercial engine post war)

A 10 year development that is lavishly funded by government tends to give results like that.
We can note that DB 605A was good for up to 1400 HP on 30 min rating, and did 1080 HP at 18500 ft on max continuous. During the war.

How much of the allied advantage was in materials I don't know. We know the Allison went through 4 different crankshafts between 1940 and 1944/45. Only one was visually different.

Allies have had ample quantities of nickel and other rare materials. Meaning that they never had the corroding exhaust valves problem, that led to the severe engine problems whether on ground or worse. Not having copper, cobalt, phosphor etc in quantity was never a cause of problems in the West.
I can only recommend Calum's book, goes in details describing these and a lot of other developmental issues. Ditto for his 'webinar' at the Youtube.

Granted, RLM and engine companies have their own share of the blame for the 'engine woes'.

 

[tomo pauk]

For Germany - probably something of capacity and the S/C size of what the DB 605 had, but with oil system from the Jumo 211. Compression ratio down to perhaps 6.5:1, if not lower. We will not get to 2800 rpm by 1939 with the long stroke it had, under 2500 rpm is far more likely. Fuel injection, variable speed S/C drive, and if possible the swirl throttle for even more power under the rated height.
An odd man off might be a big V12 from BMW. They were making the BMW 117 - a bit bigger displacement than the DB, but it seems ... fragile at barely beyond 500 kg (at least when looking Wikipedia data). Another suggestion might be a 40+L from them, using the large bore of 160mm from their liquid-cooled engine. It obviously need to feature modern tech (cylinders in a block, supercharger - doh, fuel injection, counter-balanced crankshaft etc.). I'd prefer also shortening the stroke, so the engine can be smaller and higher-revving.
The competitor from DB - the DB 603 - is again a contender here, even if in 1939 it will not be making the power it was making in 1943 and on.
Germany might want to introduce the 'over-pressure' cooling system for their engines, too, ASAP.

 

[pbehn]

I have never really understood why Rolls Royce chose the bore and stroke they did for the Merlin when they had already made engines with the bore and stroke of the Griffon. They already had the basis of their desired 2000BHP engine right there.

 

[Deleted member 68059]

I have never really understood why Rolls Royce chose the bore and stroke they did for the Merlin when they had already made engines with the bore and stroke of the Griffon. They already had the basis of their desired 2000BHP engine right there.

Tests were done on the R-Engine to try to "realise" the race power in service conditions. By the time they changed the fuel, lowered the crankshaft speed (to make it live longer) and reduced the boost pressure to match the anti-knock of service fuels, there was barely an advantage over the existing types. Therefore, the R-Engine was not simply slightly detuned and turned into a great fighter engine without bothering with Merlins. The question of exactly why the Merlin bore and stroke were made smaller than the R-Engines is discussed a little bit here:

Ramp Head Merlin

 

[pbehn]

Tests were done on the R-Engine to try to "realise" the race power in service conditions. By the time they changed the fuel, lowered the crankshaft speed (to make it live longer) and reduced the boost pressure to match the anti-knock of service fuels, there was barely an advantage over the existing types. Therefore, the R-Engine was not simply slightly detuned and turned into a great fighter engine without bothering with Merlins. The question of exactly why the Merlin bore and stroke were made smaller than the R-Engines is discussed a little bit here:

Ramp Head Merlin

As it says in the article it was an extraordinary decision, the optimal bore and stroke seems to be that used by the Griffon, and many other radial engines. Nice to see the late L J K Setright getting his big daft face into a serious discussion, I am old enough to remember his attention seeking nonsense on motorcycles, I didn't realised it stretched to pontificating on serious matters like the build up to a war.

 

[wuzak]

The size may have been determined by a power target, likely around the 1,000hp mark.

 

[tomo pauk]

Tests were done on the R-Engine to try to "realise" the race power in service conditions. By the time they changed the fuel, lowered the crankshaft speed (to make it live longer) and reduced the boost pressure to match the anti-knock of service fuels, there was barely an advantage over the existing types. Therefore, the R-Engine was not simply slightly detuned and turned into a great fighter engine without bothering with Merlins. The question of exactly why the Merlin bore and stroke were made smaller than the R-Engines is discussed a little bit here:

Ramp Head Merlin

Care to share some details about that experiment? Like what fuel was used, S/C used, rpm and power achieved?

 

[Deleted member 68059]

Care to share some details about that experiment? Like what fuel was used, S/C used, rpm and power achieved?

Basically they were trying to type-test it at 1500hp, and despite the de-rating it kept breaking. Looking through the rest of the file, it never passed the
basic air ministry type test at 1500hp, and on 26th June 1935, they decided to scrap the remaining R-engines and all the parts. (yes really!)