Japanese logistics, purchase programs and war booty, reality and alternatives 1936-44

[Reluctant Poster]

:Sigh: Again, you're simply memory projecting, assuming that "just becoz we did it, they should'a too". Firstly you are assuming that is what the Japanese wanted when the Lockheed was sold to them, which it wasn't. The Lockheeds were bought as TRANSPORTS and were needed as such by the Army. Secondly, you are believing falsely that the army would carry out what was essentially a navy job, and by doing so you a demonstrating a complete lack of understanding of how bitterly the navy and army behaved toward one another, and the nature of their military set up - Tachikawa and Kawasaki supplied the type to a contract for the Army, not the Navy. Thirdly, and this concerns the Hudson, it wasn't just simply a modified Lockheed 14, it was based on it but a lot of work was done to the airframe to meet the needs of the British. Johnson, Hibbard and other Lockheed engineers spent several months in Britain working with the Air Ministry to finalise the design. You are also assuming that the Japanese would naturally contemplate doing so just becoz you have an article that says it could be done? How do you know whether or not the Japanese even saw the article???

You're the one projecting. Your diatribe does has very little to do with what I actually wrote. Also its apparent that you didn't actually read my posts before launching your rant.

I never said they should do it I quite specifically said they COULD do. This was deliberate word choice. I never offered an option on what they should have done.
I did not state that the Japanese wanted a bomber. I merely stated that Lockheed 14 was the basis for the Hudson which was very successful in the ASW role. Obviously they bought a transport and that what they used it for. I never said otherwise.

Your next statement makes it crystal clear that you never actually read my posts, I quote:
"Secondly, you are believing falsely that the army would carry out what was essentially a navy job, and by doing so you a demonstrating a complete lack of understanding of how bitterly the navy and army behaved toward one another, and the nature of their military set up."
Here you are demonstrating a complete lack of understanding of what I wrote. I am well aware of the Japanese underservice rivalry and clearly stated that in my posts. In Post 52 I wrote "The problem of course is that the Tachikawa Type LO Transport Aircraft was an Army program and giving them to the navy would be unthinkable'' In post 74 I reiterated that " ..inter service rivalry would likely prevent that from happening."

Nowhere did I state that it was developing a bomber from the Lockheed 14 was trivial exercise.

A question for you. Do you actually believe that the Japanese were unaware of the Hudson? It was not some secret project. It entered frontline service in mid 1938, three years before the Japanese entry into the war and was widely reported on. It was not a closely guarded secret hidden from view.
There was plenty of prewar reporting on it.
Aircrafttotal Encyclopedia
Lockheed Hudson Mk.I | This Day in Aviation
In fact the Hudson was the star of a pre war movie "Captain of the Clouds"

View: https://www.youtube.com/watch?v=cj38Y6oIaws#ddg-play

 

[GrauGeist]

In Post 52 I wrote "The problem of course is that the Tachikawa Type LO Transport Aircraft was an Army program and giving them to the navy would be unthinkable'' In post 74 I reiterated that " ..inter service rivalry would likely prevent that from happening."

However, it did happen on several occasions.

The Army transferred some of it's KI-35s to the Navy, which was then designated L1N1 Type AT-2.

The Army adapted their KI-56 from the Navy's Type LO, which itself was license built from the Lockheed Model 14.
And what may be of interest, is that Tachikawa, which was owned by the Army (1936-1945), manufactured the Type LO for the IJN.

 

[TM06]

Nakajima invested a lot in the Mamori/Mamoru engine type, that certainly taxed the engine division improving and debugging other engines.
The Ha 219 seems to me as a more conventional engine than the Homare - perhaps that might've been a boon wrt. to the Japanese situation back in ww2? It was also heavier than the Homare by 300+ kg, and wider/taller (1280 mm vs. 1180) - it will require a more substantial aircraft than the Homare. Ha 219 was supposed to make about 20-25% better power than the Homare - that is a hefty difference in power indeed.

Oh god the Mamoru, I completely forgot about that gutter trash of an engine... If any meaningful progress is to be made towards the Ha 219 or even the Homare, the Mamoru absolutely cannot make it any further than the ink of the pen it was drawn up with.
But yes, the Ha 219 is a relatively conventional engine as far as I can tell, as it was quite easily able to be dropped into the Ki-84 creating the Ki-84N / Ki-117 - I've seen scattered sources around the Ki-84N claim that it could reach 725 kph / 450 mph at its critical altitude, which is a pretty noticeable improvement over the base Ki-84's 687 kph / 427 mph even despite the weight hike.
Generally speaking, the 219 seems to be similar in dimensions to the Kasei, a boon for us in this theoretical as it means the early Kasei-N1K would be able to be fitted with the 219 relatively easily. Hell, it might even fit decently into the J2M.

As for the Homare's problems - two questions are still to be answered, 80 years later:
- how much the headache was the Homare really?
- how much of the problems Homare had were actually due to the engine itself, and how much these problems were due to the general Japanese situation in the last 12 months of the war wrt. the lack of nickel and the like, fuel octane rating, factories and repair centres being bombed etc?

As far as I know, the major problems plaguing the Homare were due to its size and high RPM - compounded by the deteriorating situation of the war.
The Homare was tiny for an 18-cylinder radial, and while that was a boon for the IJA and their relatively small carriers, the level of precision and skilled craftsmanship required to make such an engine meant it couldn't be mass produced in the numbers needed under war stress without major quality and reliability flaws. I believe some of the early production engines were struggling to make ~1,400 hp?
The high RPM was also a fault here, trying to run an engine that fast (~2,900-3,000 RPM I believe?) in that poor of quality is always a recipe for disaster.
The war stress can take the lion's share of blame for the engine's problems, but I'd argue that it was a fundamentally flawed engine due to its small size which caused and/or compounded most of the issues. A larger, simpler and more robustly built engine would suffer much less in the same situation.

Reverting back to the Ha 219, the Mitsubishi's counterpart (Ha 42) seems to be a reliable engine under the same conditions, while the all-new tech Ha 43 never flew a combat sortie. So indeed the Ha 219 might've been a better choice, despite it's bulk & weight.

Now that I've scratched the Ha 42 - that seems like an engine worthy of an 1-engine fighter wrapped around it. Kill the Ki 67 for all I care.

I'd argue against the Ha 42 for single-engined aircraft. It was even heavier and a fair bit bigger than the Ha 219. While a majority of the bigger fighters such as the Ki-84 or N1K (A7M is a coinflip but I'm leaning towards 'no') could be reasonably fitted with the 219, I have significant doubts the same could be said for the Ha 42.

Instead, it might be a solid choice for larger bombers specifically. Weight and size isn't as much of an issue on bombers - especially of the strategic variant that the Japanese were sorely lacking in. Perhaps the G5N wouldn't have been as much of a failure if it was fitted with Ha 42's instead of the Mamoru? The Ki-91 is also a highly appealing bomber that was already going to use the Ha 42, so that's worth considering.

 

[tomo pauk]

But yes, the Ha 219 is a relatively conventional engine as far as I can tell, as it was quite easily able to be dropped into the Ki-84 creating the Ki-84N / Ki-117 - I've seen scattered sources around the Ki-84N claim that it could reach 725 kph / 450 mph at its critical altitude, which is a pretty noticeable improvement over the base Ki-84's 687 kph / 427 mph even despite the weight hike.
Generally speaking, the 219 seems to be similar in dimensions to the Kasei, a boon for us in this theoretical as it means the early Kasei-N1K would be able to be fitted with the 219 relatively easily. Hell, it might even fit decently into the J2M.

Let's not get carried away with the Ha 219, and with the performance figures of the aircraft that never flew.
Engine was supposed to use +550 mm Hg boost, vs. Homare +450 and later +500 (the two engines shared the CR of 7.2:1) - that is a really tall order when Japanese fuel situation is considered.
Weight hike is rarely a reason to the aircraft not making the desired speed (heavier aircraft were usually faster), but drag hike is always a reason for the speed drop. Ha 219 will make the drag go up, so will the increase of wing area, that Ki-84N had.
Ha 219 was 50% heavier than the Kasei.

As far as I know, the major problems plaguing the Homare were due to its size and high RPM - compounded by the deteriorating situation of the war.
The Homare was tiny for an 18-cylinder radial, and while that was a boon for the IJA and their relatively small carriers, the level of precision and skilled craftsmanship required to make such an engine meant it couldn't be mass produced in the numbers needed under war stress without major quality and reliability flaws. I believe some of the early production engines were struggling to make ~1,400 hp?

I'm not sure that size determines engine's reliability.
High RPM was a product of short stroke (150 mm, shared with Sakae family), strong crankcase made of steel, and balanced crankshaft. Short stroke keeps piston speeds manageable.

Thus far, I'm not aware of anyone really making a good account on real problems of the Homare, so my opinion is that most of these problems - if they really were such - was a product of fuel not being of the required octane rating (at least 91 oct required), dubious supply of nickel and the like past Autumn of 1944, as well as indeed of general problems that Japanese industry and military endured in that time.
A possible cure to the fuel and valve material quality issue for the Homare might've been the reduction of compression ratio (something that Mikulin's team did several times in ww2).

If the Ha 219 boost must be reduced due to the lower octane fuel and the valve materials not being as specified, expecting it to make the 'book' numbers is not something I'd do.
Will the Nakajima company made the same amount of the 1150 kg engines, as they made of the 835 kg engines?

The high RPM was also a fault here, trying to run an engine that fast (~2,900-3,000 RPM I believe?) in that poor of quality is always a recipe for disaster.
The war stress can take the lion's share of blame for the engine's problems, but I'd argue that it was a fundamentally flawed engine due to its small size which caused and/or compounded most of the issues.

Apart from the war stress part, I disagree.

I'd argue against the Ha 42 for single-engined aircraft. It was even heavier and a fair bit bigger than the Ha 219. While a majority of the bigger fighters such as the Ki-84 or N1K (A7M is a coinflip but I'm leaning towards 'no') could be reasonably fitted with the 219, I have significant doubts the same could be said for the Ha 42.

1150 kg for the Ha 219, 950 kg for the Ha 42.
Ha 42 was of the slightly bigger diameter, 1370 mm vs. 1280. With CR of 6.5:1, it was still able to run well on 87 oct fuel, although 91/92 oct was needed for it to go 2000 HP (US intel says on 40.5 in Hg/+270 mm Hg). Add water-alc injection for more power.

Instead, it might be a solid choice for larger bombers specifically. Weight and size isn't as much of an issue on bombers - especially of the strategic variant that the Japanese were sorely lacking in. Perhaps the G5N wouldn't have been as much of a failure if it was fitted with Ha 42's instead of the Mamoru? The Ki-91 is also a highly appealing bomber that was already going to use the Ha 42, so that's worth considering.

Mamoru indeed needs to go, ASAP.
A fighter powered by an 1-ton big radial might've gotten the Japanese an equivalent of the Tempest II?
Repeating this for the n-th time - both Mitsubishi and Nakajima need to be led to focus on the big engines, and to out-source the small engines (Zuisei and Sakae families, respectively) ASAP.

 

[Shortround6]

As far as engine size goes.

Ha-109 146 x 160 mm cylinders, 37.5 liters.
Homare 130 X 150 mm cylinders, 35.8 liters.
R-2800 146 X 152 mm cylinders. 46 liters.

If you only have 78% of the displacement you need a lot of tricks to make up for it. And running at 3000rpm instead of 2700rpm is not it. 11% more rpm only gets you 1/2 way there, assuming that everything else is equal.

Granted 130 mm pistons are lighter in weight than 146mm pistons but the stress loads go up with the square of the speed.
P & W used a compression ratio of around 6.7:1. give or take 0.05.
R-2800 at sea level was using 52in (560mm) for the non-two stage engines and bit more for the F4U and F6F.
Where was the Homare power coming from? Better supercharger? An increase in compression of 0.3:1 (7.0:1 in the Homare 11-22) doesn't cover it. Maybe the 8.0 compression in the Homare 22 and up helps but that really means you need better fuel.

And lets look back at the Sakae engine. 14 130 X 150 mm cylinders, 27.9 liters. So they added 4 more cylinders for 28.6% more displacement and expect to get 50% more power (Homare 11) ?
The Ha 219 used 18 of the Ha-109 size cylinders for 48.2 liters displacement. This should have been a lower risk option, if they had not tried for 2400hp. 1860hp using the same rpm and boost as the engine in the Ki-44. Or 1568hp at 5,200 meters altitude. With an extra 100rpm and using 300mm of boost????

 

[Shortround6]

out-source the small engines (Zuisei and Sakae families, respectively) ASAP.

To who?
Hitachi was making a 9 cylinder radial with 130 x 150 cylinders but of 640hp max?
They were also the 3rd largest manufacturer of aero engines.
Hitachi was already building Ha-26 and Ha-112 for the Japanese army. In typical Japanese fashion it appears they build no engines for the Navy.

Hiro had been building Lorraine 12 and 18 cylinder W engines in the 1920s and early 30s but the facilities were transferred over to the Yokosuka Naval Arsenal but despite some R & D work not much of anything usable in service showed up.

There were a few even smaller companies but Japan did not have the resources the US did. And even the US was not unlimited. The engine companies that made trainer engines pretty much stayed making trainer engines. New factories were built/equipped to make the big engines. Japans ability to provide the needed machine tools to equip new factories was limited.

 

[tomo pauk]

If you only have 78% of the displacement you need a lot of tricks to make up for it. And running at 3000rpm instead of 2700rpm is not it. 11% more rpm only gets you 1/2 way there, assuming that everything else is equal.

Where was the Homare power coming from?

R-2800B did 2000 HP without the water-alcohol injection, Homare 20 series was making 2000 HP using w-a injection and 3000 rpm operation.

An increase in compression of 0.3:1 (7.0:1 in the Homare 11-22) doesn't cover it. Maybe the 8.0 compression in the Homare 22 and up helps but that really means you need better fuel.

Nakajima table provided by Shinpachi says CR of 7.2:1 for all of the Homare that saw use, includes the 20 series for the Navy. Americans were initially of opinion that 20 series used 8:1, however (note the red encircled passage):

And lets look back at the Sakae engine. 14 130 X 150 mm cylinders, 27.9 liters. So they added 4 more cylinders for 28.6% more displacement and expect to get 50% more power (Homare 11) ?

Where is the greater RPM and water-alcohol injection accounted there?

The Ha 219 used 18 of the Ha-109 size cylinders for 48.2 liters displacement. This should have been a lower risk option, if they had not tried for 2400hp. 1860hp using the same rpm and boost as the engine in the Ki-44. Or 1568hp at 5,200 meters altitude. With an extra 100rpm and using 300mm of boost????

With 2700 rpm and +350 mm Hg boost (Ha 109 used 2600 and +250), the Ha 219 was expected to make 2050 HP at 6400m. Homare 20 series was making 1620 HP at 6100m, at 3000 rpm and +350mm boost.
(all per the Nakajima table as above)
Will the Ha 219 still be a paragon of reliability under the same circumstances that befell the Homare come late summer/early Autumn of 1944? Size and weight of a fighter powered by the Ha 219?

To who?
Hitachi was making a 9 cylinder radial with 130 x 150 cylinders but of 640hp max?
They were also the 3rd largest manufacturer of aero engines.

Kawasaki was the 3rd largest manufacturer of the aero engines in Japan, granted by just a small margin vs. Hitachi. Hitachi was also making the Sakae and Kinsei types of engines; Kawasaki was making the Sakae engine family, too. Aichi was also making radials under licence before the V12 switch
Ideally, neither Kawasaki nor Aichi should've gotten in the DB 601 production, they should've been making the radials in the good numbers instead. Ideally, the smaller types, so that Nakajima and Mitsubishi can focus on the bigger engines.
Army not embarking on the Ki-45 means that a lot less of Zuiseis is required.

 

[tomo pauk]

There were a few even smaller companies but Japan did not have the resources the US did. And even the US was not unlimited. The engine companies that made trainer engines pretty much stayed making trainer engines. New factories were built/equipped to make the big engines. Japans ability to provide the needed machine tools to equip new factories was limited.

Even the greater reason to move away from the small engines, that required two to be installed per aircraft so that aircraft is worthwhile. A fighter with two 1100-1200 HP engines is not an equivalent of a fighter with one 1800-2000 HP engine, and possibly not even to a fighter with one 1500 HP engine. However, two 1100-1200 HP engines and propellers will cost perhaps 80% more than one 1500 HP engine and one prop.
A thing that RR figured out (Peregrine vs. Merlin), ditto for the most of the countries & companies. Granted, some of them fell into the trap of small engines that we now need two per aircraft.
Aircraft with two small engines will also use more fuel, a thing that Japanese might find interesting.

One 18 cyl 2000 HP engine will still cost less than two 1100-1200 HP engines + props required, while the resulting aircraft will be far more capable.

 

[Shortround6]

Where is the greater RPM and water-alcohol injection accounted there?

I rounded the Sakae up to 1200hp and I used 1800hp for the Homare 11.
Going from the 2700rpm of the late Sakae to the 2900rpm of the early Homare is 7.4%.
I will ignore the higher internal friction ( a few fractions of a percent ).
so we are now up to 36% leaving 14% to come from higher boost pressure/water injection.
Late model Sakae engines used water injection. For some reason/s it didn't work as well as they hoped. Perhaps it would be better sorted out on the Homare.

When comparing Japanese engines to American there are several large differences. In power the US had better fuel, a lot better. Water injection helps but how much?
An R-2800 running on 100 octane (American 100/100) was limited to 47in of boost and not the 52-54 in that 100/125, and 100/130 allowed. This might have resulted in nearly a 200hp loss?
There were two early R-2800 that were not manufactured that were listed (experimental or just a study?) that were listed as using 90 octane fuel. They were rated at 1625hp for take off (pressure not given) and 1625hp at 6500ft. One was single speed and one was two speed. They also ran 100rpm slower, but this was not unheard of for US engines that ran on different grades of fuel.
Early water injection in the P-47 was good for about 4in of boost (100mm?) on the 100/130 fuel.
F4Us used about 5.5-6.5in of boost depending on supercharger (neutral, low or high).

There is an interesting report here on the R-2800 used in the F4U and water injection.

http://www.wwiiaircraftperformance.org/f4u/f4u-1-50030-final.pdf

Granted they were trying to break the engines (somewhat) to find the problems quicker and they succeeded. They broke all six engines used in the test. But they did try to keep them operating within or close to the max temperature limits. This required adjustments to climb procedures and shortening some flight times.


One of the things with water injection is once you are making the power how do you keep the engine together? The water helps with cooling (but doesn't solve everything) so we won't worry about that but when do the cylinder bolts start to stretch or pistons break or con rods start to bend or bearings start to fail?
Water injection has to balanced against the engine life and it also has to have the supercharger configured to take-advantage of it. It does not give any greater altitude on it's own, at least at max power, it may help with max cruise?

IN the F4U test outside air temperatures impacted both cooling and carb inlet temperatures. Perhaps different cowl, cooling flaps, ducts could have helped on the cooling and perhaps different ducting and/or increased intercooling size could have helped with the carb inlet temperatures?
Navy was interest in this test was in max performance out of existing aircraft without breaking engines, not developing new engine installation.

Getting back to the Japanese. Water injection is a very useful solution to the 90-92 octane fuel problem, but it was never going to get them to even 100/100 fuel equivalent.

Abbreviated octane to PN chart.
Octane............................PN
87.....................................68.29
89.....................................71.80
91.....................................75.68
93.....................................80.00
95.....................................84.85
97.....................................90.32
99.....................................96.55
100...................................100

The octane scale in not linear.
Granted the DEI oil/gas was not 92/92. it was somewhat higher (more aromatics) but nobody really knows how much better?
Maybe they had 92/98?
End of war/post war US 91 octane fuel was rated at 91/96 which would show a nice improvement at full rich mixture.

Trouble for the Japanese is that the US was using
Better fuel
intercooling (once they got passed the P-39 and P-40)
and water injection
Larger air cooled engines (once past the F4F)

Most Homare powered planes are using just one of those, even large amounts of water injection cannot make up for more than one other factor?

 

[tomo pauk]

Late model Sakae engines used water injection. For some reason/s it didn't work as well as they hoped. Perhaps it would be better sorted out on the Homare.

Americans note the same boost on 92 oct as they note on 92 oct + ADI, ie. 41.7 in Hg.
For a 'proper' small-ish radial with ADI, we can take a look at Kinsei 60 series. Soviets pushed it to 1260 mm Hg (49.6 in Hg, or +500 mm Hg) on 92 oct fuel, for 1620 CV max; Americans say 1620 HP, on same boost and fuel. That is 260+- HP more than the 50 series (no ADI, same RPM), or 20%.
Not bad for a light, 1970 cu in engine turning a moderate RPM (Homare was at 2185 cu in, but also ~25% heavier and turning 3000 rpm vs. 2600 for the 50 and 60 series Kinsei).
Kasei gained about 250 HP by ADI, or about 20%.

The real data showing Sakae having ADI or/and the gains from having the ADI seems to be badly lacking.

so we are now up to 36% leaving 14% to come from higher boost pressure/water injection.

The two Mitsubishi engines gained 20% due to the higher boost allowed by ADI.

When comparing Japanese engines to American there are several large differences. In power the US had better fuel, a lot better. Water injection helps but how much?

On radials, water-alcohol injection seems to gave a lot. On the P-47D, it gave 15% more initially, and 30% (600 HP) more quickly after that. Similar gain was on the P-47N and M (700 HP gain).
On V12s, the V-1710 gained about 400 HP on the P-63, or some 25%.

One of the things with water injection is once you are making the power how do you keep the engine together? The water helps with cooling (but doesn't solve everything) so we won't worry about that but when do the cylinder bolts start to stretch or pistons break or con rods start to bend or bearings start to fail?
Water injection has to balanced against the engine life and it also has to have the supercharger configured to take-advantage of it. It does not give any greater altitude on it's own, at least at max power, it may help with max cruise?

Let's not make a mountain out of a mole hill.
Nobody said that ADI is a replacement for a (much) improved supercharger.

Water injection is a very useful solution to the 90-92 octane fuel problem, but it was never going to get them to even 100/100 fuel equivalent.

ADI was providing a 20% power gain over what the non-ADI was good for. No amount of wishing and thinkering was able to provide them with the high octane fuel, but ADI was available and was working.

Trouble for the Japanese is that the US was using
Better fuel
intercooling (once they got passed the P-39 and P-40)
and water injection
Larger air cooled engines (once past the F4F)

Most Homare powered planes are using just one of those, even large amounts of water injection cannot make up for more than one other factor?

Will the Sakae or Zuisei be a better choice than the Homare for the Japanese?

 

[TM06]

I'm not sure that size determines engine's reliability.
High RPM was a product of short stroke (150 mm, shared with Sakae family), strong crankcase made of steel, and balanced crankshaft. Short stroke keeps piston speeds manageable.

Thus far, I'm not aware of anyone really making a good account on real problems of the Homare, so my opinion is that most of these problems - if they really were such - was a product of fuel not being of the required octane rating (at least 91 oct required), dubious supply of nickel and the like past Autumn of 1944, as well as indeed of general problems that Japanese industry and military endured in that time.
A possible cure to the fuel and valve material quality issue for the Homare might've been the reduction of compression ratio (something that Mikulin's team did several times in ww2).

If the Ha 219 boost must be reduced due to the lower octane fuel and the valve materials not being as specified, expecting it to make the 'book' numbers is not something I'd do.
Will the Nakajima company made the same amount of the 1150 kg engines, as they made of the 835 kg engines?

Apart from the war stress part, I disagree.

I'm not an expert on aircraft engines so my statements were more conjecture based on my knowledge of racing engines than anything truly concrete.
That being said, I still do believe that the Ha 219 would have an easier time under war stress than the Homare; it doesn't require as high of a degree of precision and craftsmanship owing to it being more conventionally built - amongst other things. It probably wouldn't be making that 2,400 hp figure consistently, but it likely would be making more power than the Homare provided consistently, an exceptional boon for late-war Japan.

 

[tomo pauk]

I'm not an expert on aircraft engines so my statements were more conjecture based on my knowledge of racing engines than anything truly concrete.
That being said, I still do believe that the Ha 219 would have an easier time under war stress than the Homare; it doesn't require as high of a degree of precision and craftsmanship owing to it being more conventionally built - amongst other things. It probably wouldn't be making that 2,400 hp figure consistently, but it likely would be making more power than the Homare provided consistently, an exceptional boon for late-war Japan.

I don't doubt that the Ha 219 would've indeed been a boon to the late-war Japanese aircraft to be powered with. With some shortcomings, however, that stemmed from it's greater weight and drag (meaning that aircraft powered by it would've need to be bigger = draggier & heavier, less quick to make, and that engine itself would not be as available as the smaller and lighter Homare*).

Judging by the numbers produced and factories either making it or were in process of re-tooling, Homare became a staple among their late-war engines. The Musashi complex (Mushasino + Tama production lines that merged mid-war, one making engines for the Navy, other for Army; lines being separated earlier by just a fence) was the main source, and Japanese tooled up the Omiya Engine Works (~1400 Homare engines made) and Hamamatsu Engine Works (under 400 Homare engines made). Kawasaki was tasked to re-tool for production of Homare come Spring 1945.

*Army called the Homare as Ha 45, but I'm going by the more known designation

We also have the situation at Hitachi, where their plant at Tachikawa was making Sakae (in 1943-45), Kinsei (1944-45) and Ha 42 (late 1943)** engines, along with the small engines for the trainers. Good knows how much of the time and resources was wasted in tooling up of one factory to make 4 different engine families in 5 years, and how much that cost was in actual engines not produced.

** or whatever the Army called them

tl;dr - Homare was not a perfect engine, however Japanese seem to prefer it come 1944/45, and were willing to put their money where their mouth was; further - Japanese axing several other engine types (like all of the V12 production - at Kawasaki and Aichi - plus the Sakae and Zuisei by mid-war) and consolidating the engine production might've been a better idea than to axe Homare

 

[Shortround6]

Will the Sakae or Zuisei be a better choice than the Homare for the Japanese?

Never said that the Japanese would be better off using small engines.

Problem was that the Homare was too small, just like the Sakae was too small.
The Sakae was 92% as large as the Twin Wasp and while you can make up some (all) of that with WI, or a better supercharger or ? when you try to go to a higher level you are really depending on being cleverer than your opponents.
Just going to 18 cylinders instead of 14 is an easy path and uses a lot of the same tooling. Going for higher RPM makes up some of the difference. But it doesn't get the Japanese to where they needed to be.

In the US Doolittle was experimenting with WI in 1932-33 for the Shell Company, other people were experimenting with it later in the 1930s.

P&W had not gone to an 18 cylinder version of the R-1830 (an R-2350?) but to the 14 cylinder R-2180. But the jump wasn't big enough. They sketched out an 18 cylinder R-2600, but when they heard about the Wright 14 cylinder R-2600 they stretched the design out to the 18 cylinder R-2800 using the R-2180 size cylinders.

The 2187(?) cu/in (35.8 liter) size of the Homare was too small and required more sophistication vs brute force.
The small diameter cylinders help with the cooling (surface area vs volume) but they are not enough, if you make big power you need lots of fins, very deep and closely spaced. Higher RPM helps with a amount of air flow but more rpms means more heat in the cylinders. Water injection helps, but you are counting on the enemy not to develop WI. High RPM means solving vibration problems and lubrication/bearing problems.

Just using a big 14 cylinder engine does have problems of it's own. But they were different problems and were better known. It turned out that for some reason going from 14 cylinders to 18 was a bigger problem than going from 7 cylinders to 9 cylinders on a single row engine. Going to higher rpm was not as easy as they (everybody) thought. Every time you raise the max rpm you increase the number of possible harmonic vibrations. Bearings/lubrication was often a problem.
Using the cylinders from the Sakae gave a good starting point but it was also a sever limit.

Would effort on a different 18 cylinder have paid off better or would more effort on one or more large 14 cylinder engines have paid off, even accepting the larger diameter/s ?

 

[tomo pauk]

Never said that the Japanese would be better off using small engines.

I was trying to point out that Japanese military engine procurement have had many, many issues to deal with, before we start saying 'Homare bad'.

The Sakae was 92% as large as the Twin Wasp and while you can make up some (all) of that with WI, or a better supercharger or ? when you try to go to a higher level you are really depending on being cleverer than your opponents.
Just going to 18 cylinders instead of 14 is an easy path and uses a lot of the same tooling. Going for higher RPM makes up some of the difference. But it doesn't get the Japanese to where they needed to be.

IMO, the main problem the Japanse had come late 1943/early 1944 was the lack of modern supercharging. Insisting on the Sakae and Zuisei even in 1944 (Sakae also in 1945) was a far greater problem than making the Homares.
Homare getting 70-80% more power than the Sakae was no small feat, it was a comparable gain that R-2800 had over the R-1830/-2000, or the R-3350 vs. late-war R-1820s.

Just using a big 14 cylinder engine does have problems of it's own. But they were different problems and were better known. It turned out that for some reason going from 14 cylinders to 18 was a bigger problem than going from 7 cylinders to 9 cylinders on a single row engine. Going to higher rpm was not as easy as they (everybody) thought. Every time you raise the max rpm you increase the number of possible harmonic vibrations. Bearings/lubrication was often a problem.
Using the cylinders from the Sakae gave a good starting point but it was also a sever limit.

Perhaps the Japanese engineers and technicians were just good in their job, despite the ever worse conditions they worked?

Would effort on a different 18 cylinder have paid off better or would more effort on one or more large 14 cylinder engines have paid off, even accepting the larger diameter/s ?

Kasei was pretty much at it's limits with the 20 series. A 2-stage S/C would've improved it a lot, though, even if the absolute power. Ha 109 was a missed opportunity to develop further (2-stage S/C, water-alc injection, better exhausts).
At Nakajima, the Mamori was an attempt on a big 14 cyl engine, however it seems that Navy did not judged it as good enough, and at any rate it was quickly phased-out, Navy concentrating on the Homare.

 

[TM06]

tl;dr - Homare was not a perfect engine, however Japanese seem to prefer it come 1944/45, and were willing to put their money where their mouth was; further - Japanese axing several other engine types (like all of the V12 production - at Kawasaki and Aichi - plus the Sakae and Zuisei by mid-war) and consolidating the engine production might've been a better idea than to axe Homare

The Homare likely should stay, yes. I wasn't suggesting that it be cut from production, my stance was more that it might've been a better choice to use the 219 as the primary high-powered fighter radial for the big hitters like the Ki-84 or N1K.
My line of thought is that in an ideal scenario with a highly developed Ha 109 along with the Sakae and Mamoru out of the picture, the Ha 219 might be the easiest 18-cylinder radial for Nakajima to mass-produce given that it's directly related to the Ha 5 series.

 

[Shortround6]

Homare getting 70-80% more power than the Sakae was no small feat, it was a comparable gain that R-2800 had over the R-1830/-2000, or the R-3350 vs. late-war R-1820s.

Problem is that the Homare was only 28.3% larger than the Sakae, and as I have tried to point out before, the R-2800 was 53% larger than the R-1830.

Getting 70-80% more power out of the Homare was indeed a great feat. It was also a degree of difficulty that was unneeded. Pick/design a bigger engine to begin with and they could have had the required power without the huge increase in specific power called for by scaling up/revving up/ boosting the Sakae.

Now to be somewhat fair, a number of other countries also made smaller or larger mistakes trying to design small diameter, high revving engines of great power.
Wright went way past Nakajima when they designed the R-2160 cu/in (35.4 liter) Tornado and flushed 6.5 million dollars and tens of thousands of manhours down the Toilet.
As a back up Wright had simply either taken the R-1820 and shortened the cylinders by 15mm and then stacked two engines together or taken a 14 cylinder R-2600 and just added two more cylinders to each row. Of course it is never really that simple but the Early R-3350s were not turning higher RPM than the contemporary R-1820s or R-2600s. They also were not dealing with WI (at least to start) and they had better fuel to begin with.
Late model R-3350s did get up to 2800rpms but by that time both the R-1820s and the R-2600s were running at 2700rpm. The late R-3350s had new crankcases that were longer and had room for the counterweights/vibration dampers that the few handfuls of early engines did not. And as we all know, the 1943-44 R-3350s had a lot troubles despite having better fuel, better materials, better access to high tech manufacturing. A 2200hp R-3350 was only trying to make 40.1hp per liter and a BMEP of 187lb/sq in.

A Homare that was trying to make 2000hp was trying to make 55.8hp per liter. An 1800hp Homare was trying to make 50.28hp/liter. A 2000hp Homare was trying to make the same power per liter as a 1500hp Merlin.
A BMW 801 making the same power per liter as a 2000hp Homare would have been making 2330hp.
Basically 2000hp Homare was trying to make the same power per liter as a turbo-charged R-2800 using 100/130 fuel and water injection (2nd version) and the R-2800 needed a lot help from the turbo even at low altitude to get the the needed manifold pressure. The Navy engines with the mechanical blowers at low altitude were a few hundred HP lower in power even with water injection.

A bigger 14 cylinder or 18 cylinder engine would have been bigger in diameter, perhaps heavier, had more drag but it might have suffered few problems and/or made advertised power in the field.

 

[tomo pauk]

Problem is that the Homare was only 28.3% larger than the Sakae, and as I have tried to point out before, the R-2800 was 53% larger than the R-1830.

No problem as I see it.

A Homare that was trying to make 2000hp was trying to make 55.8hp per liter. An 1800hp Homare was trying to make 50.28hp/liter. A 2000hp Homare was trying to make the same power per liter as a 1500hp Merlin.
A BMW 801 making the same power per liter as a 2000hp Homare would have been making 2330hp.
Basically 2000hp Homare was trying to make the same power per liter as a turbo-charged R-2800 using 100/130 fuel and water injection (2nd version) and the R-2800 needed a lot help from the turbo even at low altitude to get the the needed manifold pressure. The Navy engines with the mechanical blowers at low altitude were a few hundred HP lower in power even with water injection.

The way I read it, it is a veiled praise to the Nakajima people.

A bigger 14 cylinder or 18 cylinder engine would have been bigger in diameter, perhaps heavier, had more drag but it might have suffered few problems and/or made advertised power in the field.

Nakajima tried with the Mamoru. A 55L engine, a bit heavier than the Homare, 200mm greater diameter. Here is from the Japanese Wikipedia, my edit:

Despite the fact that it was under development, Nakajima strongly requested that it be installed in the Tenzan and Fukayama mountains [aircraft], but production was discontinued after only 200 units due to the lack of the specified output, high vibration, lack of reliability, and a series of failures.

Use the Kasei on a fighter, and hope for 380 mph as-is?

A 'classic' 18 cyl engine, like the Ha 42, was 110-120 kg heavier than the Homare, of a greater diameter, and was supposed to be as good on just 92 oct as the Homare was on 92 oct + ADI. OTOH, Nakajima made far more Homares than what the production of the Ha 42 was - Mitsubishi getting rid of the Zuisei might've increased the tempo of the Ha 42 production.
The 'no free lunch' rule applies as ever.

 

[ThomasP]

I wonder what would have happened if the Japanese had attempted to adopt the sleeve valve for their engines? Assuming they had done so early enough. I remember reading that there was at least one Japanese automotive company that built a few sleeve valve engines in the late-20s or early-30s for a small number of cars (& trucks?), but they were small 2- and 4-cylinder engines of relatively low power (30-50 HP IIRC). They were more of a curiosity for the wealthy than anything else.

Given what the Japanese accomplished in some of the other areas involving aircraft engines, I have to wonder if they could have made a go of sleeve valves as well or better than the UK.

Production and materials would have been a problem in anything near the real timeline, but this is a what if.

 

[tomo pauk]

Given what the Japanese accomplished in some of the other areas involving aircraft engines, I have to wonder if they could have made a go of sleeve valves as well or better than the UK.

What problem should've the sleeve valves solve for the Japanese?

 

[z42]

What problem should've the sleeve valves solve for the Japanese?

Lose the war quickly and decisively enough that nukes aren't necessary? /s