Advanced French Fighters vs 1942/1943 contemporaries

[Bretoal2]

Thank you.

The 1938 Janes (reprint) gives 536kg for a 14Kfs but that version is direct drive, no reduction gear. Possible source of confusion?
The 1938 Janes (reprint) also has a typo (?) as it gets the letters out of order (?) or leaves one out.

Trying to figure out the 14K letter code. I think the letter r in the 3rd position (K_r_ means reduction gear and s in last means supercharged?
Letter code maybe a hold over from the 7 and 9 cylinder engines?

In the 1946 edition of Wilkinson the 14N had gone on a diet and the -58 was now a svelte 620kg. Of course it had also lost 220hp at take-off from the 1941 edition as a -50

Yes. The 14K engine has continued to be improved and, above all, reinforced. It therefore gained weight throughout his life.

The very first versions (direct drive, no supercharging) weighed just over 500 kg.

Furthermore, we do not know if the weights given in commercial documents are the "standard" ones - engine equipped, but without exhausts and baffles. As for export electric generators, magnetos and fuel pumps could be changed, it is possible that the weights are given without these accessories.

For the name of French engines, it is correct: r for "réducteur" = reduction gear and s for "suralimenté" = supercharged. The preceding letter is the version, in pairs (a b, c d, ...., i j, ...) designating identical motors but rotating in opposite directions. After 1937, these designations (irs/jrs, for example) are remplaced by numbers, always in pairs as previously.

For the 1946 Wilkinson, it is true that post-war 14 N were slightly derated owing to some reliabiliy problems. But slightly only.... And attention ! The 14 N-50 does not exist, it is a 14R (much more powerful...). The 14R was presented at the 1938 Paris Aero salon under the name 14 N-50, undoubtedly for reasons of defense secrecy....

 

[Bretoal2]

Obviously not a 14 N... but a 14 R !

 

[TM06]

Was France sitting stacks of Iron and Coal just waiting for the Germans order something or were the Germans trying to get the French to ship steel from French iron ore works/steel mills to German factories (or French ones) even to make cooking pots or truck fenders. The French were trying to slow down production to the minimum that would just keep the Germans from stealing the machinery and transporting the workers to Germany. Suddenly producing hundreds of tons of war material under subcontract to France?
For high quality steel and parts you often need exotic elements to make the alloys. Like the manganese, nickel and chromium that Germany could not get for their own engine and armor production. Maybe there was some sitting in a few French warehouses, but the French using that to build high quality stuff for the Italians after not giving it to the Germans? Not going to go well.

If anything, France being contracted to mass produce Italian equipment would give them more justification for giving Germany the bare minimum. The Germans sure wouldn't like it (which would greatly please the French), but there's not much that they could do about it because it's still helping them overall. Some of the Italian things they'd be producing would be superior to their German equivalents such as the G.55 and Beretta modello 38, and forcing France away from the deal with Italy to produce for Germany would have serious repercussions on Germany and Italy's relationship.

And by the way, the Alfa 135 was pretty much a disaster. Let's also look at the basic specifications. It was two Bristol Mercury engines stuck together. It might have been hot stuff in 1935. French would have been better off trying to make a G-R 18N in 1939-41. At least the French engines didn't have the valve springs flapping around in the breeze and using 4-5 grease fittings on each cylinder head.

I've heard a different story.
What I've read is that the 135 was a very good engine once they fixed its teething issues, and that the entire Alfa radial line was based around the Bristol Jupiter / Pegasus. I lack information that would allow me to reach a definitive conclusion, but I believe that should the 135 and particularly the 136 be mass produced, they'd be very capable engines.

France has no ability to to supply 100 octane fuel, either to themselves or to the Italians. They may have been able to import it up until June of 1940 but without a domestic source of supply and domestic refining French 100 octane in the war years is not happening, UNLESS, the Germans give them a synthetic fuel plant to run? In which case why not give the fuel plant to their allies, the Italians, to begin with?

Oh so France wasn't making 100 Octane, they were importing it? I was under the impression that they were producing it and that they just didn't have enough time to make enough of it. Dang, I had no idea.

 

[Shortround6]

If anything, France being contracted to mass produce Italian equipment would give them more justification for giving Germany the bare minimum. The Germans sure wouldn't like it (which would greatly please the French), but there's not much that they could do about it because it's still helping them overall. Some of the Italian things they'd be producing would be superior to their German equivalents such as the G.55 and Beretta modello 38, and forcing France away from the deal with Italy to produce for Germany would have serious repercussions on Germany and Italy's relationship.

You are counting on a lot more autonomy than Vichy had historically. The French would have to have done a lot better in the spring/summer of 1940 to force such a conclusion.

There were a number of things that could have supplied Italy but the G.55 was not one of them, it showed up too late and it needs to have an engine swap (H-S 12Z?) instead of the DB 605. That or get the French to build DB 605s but with the degree if autonomy you want the French to have that may not happen. The more autonomy your version of Vichy has, the less likely the Germans are going to give any production information for new weapons/engines to them.
The timing for the Beretta 38 is also off. Good as the Beretta was a submachine gun, submachine guns are not what is wanted for desert fighting. They are much better in hills, woods and in cities/towns.
French could have built FM 24/29s LMGs for the Italians. The Italians never had enough Breda M 30s and since the Breda M 30 was one of the worst LMGs ever built by anybody. It is a double win.
French could have built mortars for the Italians. Not sexy but the Standard Brandt 60mm mortar would have been a useful addition to the Italian forces. Pretty much the same as the US 60mm (Americans had licensed it). Brandt was a bit ahead of his time and was working on mortars that were adopted around the world although not so much in France. Brandt 120mm mortars were used in Russian-Japanese border incidents and accelerated Russian interest in the 120mm mortar. For the artillery poor Italians this seems like another double win. Brandt was cataloging 3 different 120mm mortars before WW II shut him down.

I've heard a different story.
What I've read is that the 135 was a very good engine once they fixed its teething issues, and that the entire Alfa radial line was based around the Bristol Jupiter / Pegasus. I lack information that would allow me to reach a definitive conclusion, but I believe that should the 135 and particularly the 136 be mass produced, they'd be very capable engines.

A Mercury was a short stoke Jupiter, and the Pegasus was a Mercury that had the stroke restored to the original length. Some accounts claim the 136 never made it off of paper.
The US had several engines (at least 3) that looked good on paper and were a total waste of money, manpower and raw materials when they built them.

One of the most common phrases/sentences you find in books discussing aircraft engines is " It was a very good engine once they had fixed it's teething issues, right before they canceled it".

Oh so France wasn't making 100 Octane, they were importing it? I was under the impression that they were producing it and that they just didn't have enough time to make enough of it. Dang, I had no idea.

I may have been in error.
There may well have been a refinery making 100 octane on French soil, or capable of making 100 octane. There were two major refineries on French soil. Both were relatively new.
French had a few problems though, The French had been trying to refine just about all of the products for domestic French consumption at these refineries and importing very little refined product. Not sure how well they could shift production over from one product to another.
There was a very, very small domestic crude production in France, just about all crude was imported. France was very late to the "game" of oil production/exploration and most of their consumption was was from a consortium/partnership of 4 major companies, France being one of the four. But without overseas oil France was lucky they could keep the street lights on.

The next problem is "what is 100 octane?"
There are literally 100s of recipes for 100 octane fuel. Everybody knew that 100% isooctane would give you 100% octane rated fuel, except 100% isooctane fuel was very, very expensive per gallon/liter. And there are other qualities you need for aviation fuel. Like vapor pressure and few other things. You can use a few other types of compounds and soup them up with lead and/or other additives. Which is what the British and Americans did but in 1939-40 they were NOT making the same fuel. 100 octane only refers to the lean rating.
US 100 octane fuel of 1939/40 would, in a liquid cooled engine limit you to 15-20% less manifold pressure than British 100 octane fuel. For air cooled engines the difference was much less.
So..................What were the French planning on making? and when? and after the French surrender, how? Getting tankers into French ports is not going to go well. Basically it is coming from the Mideast.

 

[Shortround6]

It's good to rewrite history, I suppose, but you still need to know some facts and figures.

Given my lack of ability with other languages, am I correct in interpreting that document as an order or proposed order/schedule for HS 14R engines?
Dated June 11th 1943 (after several earlier messages/communications?) with an expected delivery schedule as shown, 10 in March of 1944, 100 in Aug 1944 and 200 in November 1944?

If nothing else it speaks to readiness of production and the time needed to get up to several hundred of engines per month.

 

[TM06]

There were a number of things that could have supplied Italy but the G.55 was not one of them, it showed up too late and it needs to have an engine swap (H-S 12Z?) instead of the DB 605. That or get the French to build DB 605s but with the degree if autonomy you want the French to have that may not happen. The more autonomy your version of Vichy has, the less likely the Germans are going to give any production information for new weapons/engines to them.

The G.55 and Beretta 38 were more throwaway examples of good things France could produce in numbers higher than Italy could, but your points are valid.
The DB engines are an odd case, because there is a precedent of Germany allowing them to be produced under license by its allies. In Italy the 605 was license-produced as the Fiat RA.1050 Tifone and in Japan the DB 601 was license-produced as the Kawasaki Ha40, so France making them under license (Perhaps under Renault or HS?) wouldn't be unthinkable.

However I do like the sound of a 12Z-engined G.55. If we go with the theoretical limit of the 12Z without major redesigns of ~1,550 hp, that's still ~100 hp more than the 1,450 hp Tifone was making at a lesser weight. The possibility of an earlier 12B being fitted is also there, which would be roughly comparable to the DB 603 - an engine that was successfully mated to the G.55 airframe with few modifications.

The timing for the Beretta 38 is also off. Good as the Beretta was a submachine gun, submachine guns are not what is wanted for desert fighting. They are much better in hills, woods and in cities/towns.
French could have built FM 24/29s LMGs for the Italians. The Italians never had enough Breda M 30s and since the Breda M 30 was one of the worst LMGs ever built by anybody. It is a double win.

Better in hills, woods and urban areas, right? Like the geography found over most of France perhaps?
The Beretta would perfectly suit France, and would be a welcome replacement over the MAS 38. The MAS wasn't a bad gun per say, but it had plentiful flaws - something that can't be said for the Beretta 38.
The FM 24/29 completely slipped my mind as an option, and it absolutely should replace the Breda 30. Literally anything was better than the Breda, but the FM would be a significant improvement.
Maybe they could do a technology swap, where France gets the blueprints to the Beretta 38 and Italy gets the blueprints to the FM 24/29? Seems like an excellent agreement for both parties involved.

French could have built mortars for the Italians. Not sexy but the Standard Brandt 60mm mortar would have been a useful addition to the Italian forces. Pretty much the same as the US 60mm (Americans had licensed it). Brandt was a bit ahead of his time and was working on mortars that were adopted around the world although not so much in France. Brandt 120mm mortars were used in Russian-Japanese border incidents and accelerated Russian interest in the 120mm mortar. For the artillery poor Italians this seems like another double win. Brandt was cataloging 3 different 120mm mortars before WW II shut him down.

Mortars are not my specialty, but the Brandt 60 mm would be a very good replacement for the mediocre Brixia 35, and mortars larger than the 81/14 mod 35 would certainly be appreciated.

A Mercury was a short stoke Jupiter, and the Pegasus was a Mercury that had the stroke restored to the original length. Some accounts claim the 136 never made it off of paper.
The US had several engines (at least 3) that looked good on paper and were a total waste of money, manpower and raw materials when they built them.

One of the most common phrases/sentences you find in books discussing aircraft engines is " It was a very good engine once they had fixed it's teething issues, right before they canceled it".

The 136 may or may not have been built, most sources seem to say "probably not".
However the 135 was still built in small numbers and never got canned, so it obviously wasn't a hopeless engine. From what I could find, the weakest point of the engine was its mediocre supercharger. If Gnome Rhone is producing it - just as an example - they might be able to retrofit or redesign the supercharger they used on the 14R to fit the 135/136. If the engine is capable of ~1,600 hp with room to grow then that immediately puts it on the radar as an option to replace the 14R in certain installations (according to the specs, it was wider than the BMW 801 but shorter and lighter). And if the 136 is capable of 2,000~2,400 hp, that's an extremely compelling option for France.
That's all conjecture though, but it does warrant consideration due to its potential. It was mentioned earlier that post-war they couldn't get the 14R and 18R to work, so maybe the 135 and 136 are on the cards.

 

[tomo pauk]

The 136 may or may not have been built, most sources seem to say "probably not".
However the 135 was still built in small numbers and never got canned, so it obviously wasn't a hopeless engine. From what I could find, the weakest point of the engine was its mediocre supercharger. If Gnome Rhone is producing it - just as an example - they might be able to retrofit or redesign the supercharger they used on the 14R to fit the 135/136. If the engine is capable of ~1,600 hp with room to grow then that immediately puts it on the radar as an option to replace the 14R in certain installations (according to the specs, it was wider than the BMW 801 but shorter and lighter). And if the 136 is capable of 2,000~2,400 hp, that's an extremely compelling option for France.
That's all conjecture though, but it does warrant consideration due to its potential. It was mentioned earlier that post-war they couldn't get the 14R and 18R to work, so maybe the 135 and 136 are on the cards.

Perhaps the rose tint is applied in a too thick fashion on them glasses?
Italians have had 5+- years to perfect the 135, but still they didn't managed, and the engine never powered an in-service aircraft but filled the warehouse(s). Expecting them to whip up the sibling of that engine that can leisurely make above 2000 HP is an example of a misplaced trust IMO.

 

[TM06]

Perhaps the rose tint is applied in a too thick fashion on them glasses?
Italians have had 5+- years to perfect the 135, but still they didn't managed, and the engine never powered an in-service aircraft but filled the warehouse(s). Expecting them to whip up the sibling of that engine that can leisurely make above 2000 HP is an example of a misplaced trust IMO.

Rather than misplaced trust or rose-tinted glasses, it's an statement based on lacking information and conjecture. A 2,000 hp 18-cylinder radial doesn't seem very unreasonable for this period, there's a few examples from other nations that are around that ballpark like the M-71, Homare, Ha-43, Centaurus I, Twin Wasp and Duplex Cyclone.
But if there's more information to be shared that proves my statement wrong, I'd love to know so I can correct that.

 

[Shortround6]

Rather than misplaced trust or rose-tinted glasses, it's an statement based on lacking information and conjecture. A 2,000 hp 18-cylinder radial doesn't seem very unreasonable for this period, there's a few examples from other nations that are around that ballpark like the M-71, Homare, Ha-43, Centaurus I, Twin Wasp and Duplex Cyclone.
But if there's more information to be shared that proves my statement wrong, I'd love to know so I can correct that.

The rose tinted glasses come from the generous time period and the fact that some of those engines didn't work well until the war was over.

A number of engines passed state (government) tests and turned into utter disasters in actual use. Some Soviet accounts do not go into detail about failures.
The M-71 was sort of derived from the M-70. Things get a little convoluted. The M-70 was sort of a twin M-25 (Wright R-1820 F) while the M-71 was sort of a twin M-63 and since the M-63 was a developed M-62 (Wright R-1820 G100?) but while the M-71 passed a state test, it was not put into production (trial batches only) and it was superseded by the M-72 with planned production in late 1945 but was replaced by the ASh-73 with a shorter engine stoke (coincidently the same as the Wright R-3350 used in the B-29s, 3 of which landed in Russian during the war). testing of the ASh-73 started in 1946 and it passed it's test in 1948 although production started in 1947 for the Tu-4 (B-29 copy). Roughly 9-10 years from start of the 18 cylinder project.
Japanese Ha-43? 1945 prototypes are not the same as 1942 production engines. Which brings us to the Centaurus I or the IV? or the V? The Centaurus I only flew in the Folland test bed aircraft. The Typhoon was flying in Oct 1941 (Centaurus IV) but was very soon rebuilt but didn't fly again until Dec 1942? Vickers Warwick was the only before 1944 user and that was in 1943? with most Warwick's using 1850hp P&W engines, Granted Bristol was a little busy making Hercules engines, which sort of camouflages the Centaurus development cycle. They had around 6 years to sort it out before sticking it in the Tempest II.
And we all know the saga of the Duplex Cyclone and the B-29 (it was not trouble free in the Lockheed C-69).

A lot of people had the goal of a 2000hp 18 cylinder radial, achieving that goal, especially by 1943, is a totally different story.
And I am sorry, relying on 4-6 grease fittings per cylinder head for lubrication to the valve train instead of pressure fed oil in 1942-43 is not even close to state of the art.

 

[bf109xxl]

I have already mentioned many times that the major problem with the M-71 engine was not the long piston stroke at all, but the fact that no one was involved in its fine-tuning. There are evidences of Lev Berne, who was one of the leading engineers at Shvetsov's plant 19 at that time. The M-71 had less thermal stress than the M-82, and could be perfected in about the same times as the latter. But there were not enough personnel at the Design Bureau to finalize both engines simultaneously. At the beginning of 1941, both engines had approximately the same degree of completion. I do not know who exactly made the decision to focus all the efforts on the M-82. It is possible that Shvetsov himself did not believe in his own capabilities. Or the party leadership decided, not quite reasonably, that it would be easier to finish a less powerful and lighter engine. The stroke of the piston was not decisive. It is likely that the piston stroke was changed after getting acquainted with the R-3350 on the principle "American engineers are not stupid, so we should do the same".

 

[Bretoal2]

Granted Bristol was a little busy making Hercules engines, which sort of camouflages the Centaurus development cycle. They had around 6 years to sort it out before sticking it in the Tempest II.

Yes. Do not forget that when conflict starts, development of the Centaurus was seriously slowed down by the obligation to make the Hercules - and, to a lesser extent, the Pegasus - more reliable and mass produced.

Another element to consider is the increasingly difficult relationship between Roy Fedden and the Bristol board, culminating in his departure in 1942.

Furthermore, it is true that many 18-cylinder projects have not seen the light of day, or have given birth to engines that were approved but caused serious problems once mounted on aircraft. To return to the subject - French industry - the G&R 18L, although approved, never flew and its successors 18P and 18R were never developed. The 18R was the first engine abandoned by SNECMA in 1945.

And the Italian "clone" of the 18L, the Piaggio PXII, was manufactured in small series but remained very troublesome. despite its reduced stroke (while G&R had increased it compared to the 14K/N). It was an engine problem that led to the death of Bruno Mussolini, son of the dictator, with one of the P-108 prototypes (August 7, 1941).

 

[Shortround6]

Yes. Do not forget that when conflict starts, development of the Centaurus was seriously slowed down by the obligation to make the Hercules - and, to a lesser extent, the Pegasus - more reliable and mass produced.

Fedden and Bristol had bitten off more than they could chew. It was unforeseen. They could make sleeve valve engines in small quantities with a skilled work force. This may or may not apply to suppliers. Was Bristol making their own forgings for the sleeves or were they buying the sleeves and and doing all the finish work? Finish meaning boring and turning from rough forging. Bristol wound up in a real bind and so did the RAF, some Hercules engines had to be pulled from service in as little 20 hours due to high oil consumption. This was 1939 and/or early 1940, Bristol and Fedden improved things and here is where the Centaurus benefited. Bristol was able to take all of the "stuff" they had learned from the Hercules and transfer it over to the Centaurus during 1940-41-42-43.
Some of the Pegasus and Hercules engines were pretty terrible and followed somewhat different but not unknown curve. Early, low production engines were pretty reliable or well within expectations. early volume production engines were terrible but improvements came quickly and even by mid war engine life and reliability were very good and got even better
as the war went on.
Bristol may have gotten the basics of the Centaurus right ( no serious vibration problems or other engine specific problems) and the flow of knowledge from the Hercules (better sleeves, better fins, better cylinder heads, etc) may have been easy to integrate. Trying to mass produce (hundreds per month) 2000hp Centaurus engines in 1941/1942 might not have gone very well. At the very least you have to introduce the needed changes to more production lines at the same time. Better heads for both Hercules production Centaurus production?
Bristol was also helping set up shadow plants for Hercules production at the time. They were already farming out Mercury and Pegasus production to shadow factories.
Like many (all?) radials increased power meant better/more fins on the cylinders and heads. Whatever they were doing in the Hercules could be transferred over to the Centaurus without much trouble.

18 cylinder engines turned out to harder than most designers thought. P&W had built 3 different 14 cylinder engines (and redid one of them) before they got the R-2800 into production and they had a crap load of trouble with the R-2800 in testing, hundreds of hours in testing to short out vibration problems. Which they pretty much solved on the test stands and not in aircraft. Now as some of the articles on other sites show, some of the vibration problems get a lot worse, very fast with higher rpm. But using an 18cylinder engine and restricting it's rpm due to vibration problems may not give you the advantage over the 14 cylinder engine that you want.

 

[tomo pauk]

Rather than misplaced trust or rose-tinted glasses, it's an statement based on lacking information and conjecture. A 2,000 hp 18-cylinder radial doesn't seem very unreasonable for this period, there's a few examples from other nations that are around that ballpark like the M-71, Homare, Ha-43, Centaurus I, Twin Wasp and Duplex Cyclone.
But if there's more information to be shared that proves my statement wrong, I'd love to know so I can correct that.

Alfa Romeo's track record wrt. the high-power service-worthy engines was non-existing.
Just believing their 'roadmap' is a very, very long shot to take.

 

[Shortround6]

Just for fun I looked through the 1938 Jane's (Aug/Sept?) and found 6 different 18 cylinder radials.
These were the ones announced to the public, not what was behind closed doors.

British............Alvis "Alicides"............G-R 18L under a new name, may never have been built?
French..........G-R 18L.................
...".."...............Lorraine Sirius............
...".."...............Salmson 18 ............a water cooled 2 stroke with direct injection with 9 banks of 2 cylinders each
Italy................Alfa 135..................
...".."...............Fiat A.80...................

What was not shown is some of the behind the closed door stuff.
The P&W R-2800
The Wright R-3350
The Bristol Centaurus
The Soviet M-70
All of which were being worked on even if not flown or even run at the time.
I haven't checked the Japanese for plans/prototypes in 1938.
I don't think the Germans had anything in the works but perhaps something on paper.

For whatever reason none of the "announced" 18 cylinder engines made it into large production (more than 150-200?)

Design teams too small? (not enough manpower)
Lack of materials (exotic metals?)
Out of date? (requirements had passed them by and needed a change in basic structure?)

I will note that there were two different Wight R-3350s. The ones used in the Douglas XB-19 pretty much shared the bore and stroke with the later engines.
Wrights design team had taken a break from the R-3350 while they worked on the R-2160 Tornado and when they came back (and with some stuff from the R-2600) they pretty much threw everything out and started over. They even added several inched between the two cylinder banks. Supposedly when one engineer asked why the empty space one of the leaders said "don't worry, we will fill it with something" and they did. Larger counter weights and dynamic balancers. The XB-29 engines were rated at 2800rpm compared to the 2400rpm pf the XB-19s engines.
Wright was very successful at making large aircraft engines. They were also ruthless when it came to throwing out everything except the Bore & Stroke and and the name of the engine and starting over to get the results they wanted. They didn't spend a lot of time 'tweaking'. They told the engineers "what would you different and why". And then they did it.
But without Wright's (or P&W or Bristol's) money and manpower the chances of equaling their success is very, very slim.

 

[tomo pauk]

Italy................Alfa 135..................
...".."...............Fiat A.80...................

Ah, the A.80, what an amazing success.
When you need 18 cylinders to equal other people's 9 cly radials of the late 1930s, let alone the 14 cyl types.

 

[Shortround6]

Ah, the A.80, what an amazing success.
When you need 18 cylinders to equal other people's 9 cly radials of the late 1930s, let alone the 14 cyl types.

well, you have to give it some slack.
At 1600-1625lbs it was only around 300lbs heavier than a Wright R-1820 but about 300lbs lighter than a Wright R-2600 and ran great on regular gas, not that fancy hi test stuff

Or to look it at another way for only an extra 125lbs it gave you the same power you could get from an R-1830 Twin Wasp running on 87 octane fuel but 2000ft higher.
Maybe if they stuck a two speed supercharger on it they could have gotten 1200hp out of it at sea level?

The problem with a lot of the European radials is that they were designed for low octane fuels and were built light to get good performance.
The Early R-1830 Twin Wasp on 80-87 octane fuel was good for around 800hp and weighed around 1200lbs (a lot of early models had few or no sales) and this was with some sort of supercharger and reduction gear. By the time we get to the 1100-1200hp versions and 91-100 octane fuel the engine has gone into the mid 1400lb range. A 20% gain in weight had to go somewhere (or a number of somewhere's) had to have been done for good reasons.
But light weight on the European engines means you can't just stick in the higher octane fuel and twiddle the governor to allow 3-500rpm extra without the engine coming apart.
You have to go back a redesign the whole (or most of) engine. Which also means new tooling (and casting molds and forging dies) which means a lot of money.

 

[Bretoal2]

...".."...............Salmson 18 ............a water cooled 2 stroke with direct injection with 9 banks of 2 cylinders each

This engine was drawn from the Salmson 18CM, with its famous siamesed cylinders. Same two-stroke arrangement as Jumo 205.

It never worked.... (crankshaft had a bad habit, to break easily at mid or full power.) but to get the necessary manifold pressure, its two designers conceived a fabulous supercharger ! They were André Planiol and Joseph Szydlowski.

 

[TM06]

So what I'm gleaning from all this is "ditch the Alfa 135". Shame, would've been neat to have it as a strong 18-cylinder radial but I guess it wasn't meant to be. That leaves us with very few options for high-output radials - only really the 14R and 801, with the potential of the 18R and maybe the P.XII.

 

[Shortround6]

So what I'm gleaning from all this is "ditch the Alfa 135". Shame, would've been neat to have it as a strong 18-cylinder radial but I guess it wasn't meant to be. That leaves us with very few options for high-output radials - only really the 14R and 801, with the potential of the 18R and maybe the P.XII.

For 1942-43 you may not have any.
The P.XII was about 78% as heavy as the early (and crappy) Wright R-3350. As used in the XB-19 it had no turbos but did have a two speed supercharger.
There were reasons the French and Italian engines were so much lighter, they were not built to handle the power. You want more power you have to beef up (redesign) most or all of the engine.
Now for the French and Italians we hit problem #2. If you don't have good gas you are limited as to the boost you can use and that means in order to get high power (more fuel burned per minute) you have two/three choices. More displacement = Larger cylinders (or more cylinders, 21-22 cylinder engines anyone?) or higher rpm. Both mean more weight and with higher rpm you do not have the benefit of more cylinder wall to help with the cooling. Same size cylinders at higher rpm need more finning to keep cool and you start running into fabrication problems. Can you make the fins deeper, thinner and closer together with your current manufacturing technology. Both P & W and Wright gave up on machining fins into steel barrels. P & W went to an aluminum fit set (called a muff) that was shrunk/pressed in place on the steel barrel. Got to make sure that your aluminum and Steel alloy have the same coefficient of expansion at the temperatures involved. Wright went to the already mentioned sheet metal fins. Bristol went to the aluminum fins at some point (late war/peacetime?)
Now since the heads actually got rid of more heat than the cylinder barrels did and since the heads were already aluminum the needed casting/forging/machining needed was getting to epic levels.
Using a better supercharger allows you to make the power. It is all the rest of the 'stuff' that allows the engine to survive for more than a handful of seconds.
Japanese did use a lot of water injection but that only solves part of the heat problem. It does nothing for the mechanical strength problem.

 

[TM06]

For 1942-43 you may not have any.

I should note that I'm totally fine with the timeframe being shifted to beyond 1943. The original purpose of this theoretical was asking how the listed aircraft would square up versus the aircraft from 1942~1943 in a vacuum, but given that this discussion has moved well passed that, stretching the timeframe to 1944 or 1945 is entirely OK to me.

The P.XII was about 78% as heavy as the early (and crappy) Wright R-3350. As used in the XB-19 it had no turbos but did have a two speed supercharger.

Piaggio radials are interesting in this context due to their close relation with the Gnome et Rhône radials. A majority of Piaggio radials were either licensed produced versions and/or derivative versions of either the 9K or the 14K - with the P.XII functionally being two 9K's put together.
Parts commonality between the two manufacturers doesn't seem possible - the 14N was an almost total overahul of the 14K, and the 14R even moreso - but a shared development process might be plausible.

There were reasons the French and Italian engines were so much lighter, they were not built to handle the power. You want more power you have to beef up (redesign) most or all of the engine.
Now for the French and Italians we hit problem #2. If you don't have good gas you are limited as to the boost you can use and that means in order to get high power (more fuel burned per minute) you have two/three choices. More displacement = Larger cylinders (or more cylinders, 21-22 cylinder engines anyone?) or higher rpm. Both mean more weight and with higher rpm you do not have the benefit of more cylinder wall to help with the cooling.

I'm not entirely sure how the power-weight ratio works for aircraft, but would it be fine to use lower powered engines if they're significantly lighter? Certain Japanese fighters were made with this in mind, the Ki-44 in particular was an excellent aircraft utilizing the same design principal. If so, then they likely wouldn't need to push past around 1,750 on the 14R while maintaining its light weight.