Japanese Design Philosophy

[Shortround6]

I'd say that the Merlin X in 1938, as well as the 1940-vintage M-105 and M-88 with 2-speed S/C were very, very rare engine types.

They were rare.
But the Merlin X was listed, with some details, in the 1938 Jane's and in the British aviation magazines.
I have no idea who knew what about the Soviet engines

Now the information in Jane's is certainly not enough to design anything but it shows the potential benefits and it shows them using 87 octane fuel.
Maybe the Japanese were too busy just getting the 14 cylinder radials to work with single speed superchargers?
But taking 3-4 years just to get a 2 speed drive on a supercharger is slow progress.

The Japanese had entered negotiations for the DB 601 in 1937 and signed the deal in 1938, but the engines and drawings and such don't show up until 1940.
The entire DB601 may have been a step too far in manufacturing capability or possible not enough effort, I don't know. But a 2 speed supercharger on a radial seems like not a whole lot of R&D needed. Picking up either 2000 meters of FTH or increasing T-O power substantially seems a worth while goal for not a lot of investment.

 

[tomo pauk]

Now the information in Jane's is certainly not enough to design anything but it shows the potential benefits and it shows them using 87 octane fuel.
Maybe the Japanese were too busy just getting the 14 cylinder radials to work with single speed superchargers?
But taking 3-4 years just to get a 2 speed drive on a supercharger is slow progress.

Well, it took almost a decade and a half for the V-1710 to became a debugged engine

On a serious note, Japanese were indeed just getting their indigenous engine business in order by the late 1930s. Kasei was with a 2-speed S/C from the get-go, and eg. the 1-speed Ha-41 was certainly a better bet than the best 2-speed R-1830, while not forcing the user to pay an increased weight penalty vs. the best R-1830s.
Ha 109 was no worse than the BMW 801C, while being far lighter and not bigger.
The 2-speed Zuisei was in service in second half of 1941, and was a no worse engine than a 2-speed R-1830 (actually, power vs. altitude was ~95% of the 2-stage R-1830, with Zuisei being much lighter).

Merlin certainly needed a 2-speed S/C - being a small engine has/had it's drawbacks. Showing an engine in a sales brochure does not equal having the engine in service.

IMO - Japanese figured out how to make very good, if not excellent radials; their problems were allocation of the engines (leaving most of the fighters with weak engines), inability to make them as much as they needed, and insisting too much with low-powered types until too late; yes, the superchargers used were not up the task from 1944 on.

 

[bf109xxl]

By 1940 the Soviets were building two speed superchargers on the M-105s and on the M-88 radials and planning them on the newer engines.

The first Soviet two-speed SC was introduced by Mikulin on the M-34 in 1932. Two-speed SCs were installed on the M-62 (1937), M-63 (1938), M-64 (1939), M-65 (1939), M-81 (1939), M-82 (1940), M-88 (1938), M-104 (1939), and M-105 (1940).
But I have a suspicion that what is really meant is two-stage superchargers...

 

[Shortround6]

But I have a suspicion that what is really meant is two-stage superchargers...

No, two speed. One impeller driven by a two gear ratio drive system.

Two-speed SCs were installed on the M-62 (1937), M-63 (1938), M-64 (1939), M-65 (1939)

Not that a great an achievement although it does show that keeping up the rest of the world was important to the Soviets.
The M-62 used a two speed drive based on the Wright G-1820G-103 engine. The next 3 engines (modifications to the M-62) were developments that sometimes kept the original two speed set and sometimes modified it.
But yes, the Wright R-1820 being sold with the two speed supercharger in 1937.

The supercharger used in the M-34 didn't work. Problem with the drive or problem with the supercharger itself????

 

[bf109xxl]

Not that a great an achievement although it does show that keeping up the rest of the world was important to the Soviets.

I never told about a great achievement. Just mentioned that _even_ the Soviets had six engines with 2-speed SC in mass production (or close to the adoption to mass production or already cancelled mass production) to 1940.

The supercharger used in the M-34 didn't work. Problem with the drive or problem with the supercharger itself????

The 2-speed SC was not succeed, whereas the single-speed one worked properly.

 

[Shortround6]

IMO - Japanese figured out how to make very good, if not excellent radials; their problems were allocation of the engines (leaving most of the fighters with weak engines), inability to make them as much as they needed, and insisting too much with low-powered types until too late; yes, the superchargers used were not up the task from 1944 on.

The thing is that using a 2 speed supercharger is an easy "fix",

Using figures for the Wright R-1820 engine.

Engine/octane....................gear ratio.................take off power/rpm.....................altitude power/height/rpm.
G1820-G2/91..........................7.0..............................1000hp/2200...................................850hp/5,800ft/2100
G1820-G3/91..........................8.31............................875hp/2200.....................................850hp/8,700ft/2100
G1820-G3B/91.......................8.31.............................900hp/2200.....................................820hp/8800ft/2100
G1820-G5/91...................7.14/10.0.........................1000hp/2200....................850hp/6000ft/2100--750hp/15,200ft/2100rpm.

I will note that the altitude power for these engines is not military power but is the max continuous power.
Most French, Italian and British single speed engines used an altitude rating of around 11-14,000ft and their take-off power suffered accordingly. The Merlin III being among the most notable.
Maybe Wright did not use the best choice of gears for combat with the 2 speed with a large gap in the FTHs.

 

[AerialTorpedoDude69]

Japanese engines were getting pretty good power/weight ratios as a rule, Homare is nothing out the ordinary for them. The feather-weight Kinsei 60s were making 1600-ish HP with water injection, for example; the Ha 109 was also very light for a 1500 HP engine on 91-92 oct fuel and no ADI.
Later in the war, effect of direct and indirect Allied 'brake' to the supply of the raw materials (nickel, chromium, tungsten etc.) + bombing + suspicious octane rating of the fuel (91-92 oct was the 'book' value, the actual oct value was ??) + dubious supply of spare parts = it will be a miracle if the book values were obtained in everyday service.
Homare was noted as 'new tech' engine, perhaps the 'old-tech' 18 cyl Ha 104 was less susceptible to the glitches, while weighting 25% more - sometimes going conservative has it's appeal.

Western engines, like the R-2800 or BMW 801, might've been over-built? Nothing wrong with that, but it might result in the over-weight an/or over-sized fighters. The 2-stage B-series R-2800s were with small impellers, that were also not refined (the straight vanes, instead of the curved ones), so it might be argued that a more refined and big impeller on the Homare was as good as it gets.

As always, good comment. I would also like to add that the frontal areas of Japanese engines were oftentimes very small, compared to similar output engines from other nations. As pointed out by Greg (from YouTube, not these forums), some of the better Japanese engines used RPMs to achieve higher output and lower displacement/frontal area. In general, Japanese aero engines were very well engineered and of technical sophistication similar to countries in the West.

What Greg didn't mention is that Japanese engines have higher oil consumption. The big reason is that Japanese engines have loose tolerances. Meaning, they aren't as tightly sealed and fitted as US and British engines. The loose fit is because of economic reasons. Rather than relying on expensive imported industrial equipment, Japan's war machine relied on a large number of less expensive skilled machinists. Because of hand finishing, their engines had looser tolerances and leaked oil constantly.

As such all blue prints had to take into account that they would be mass manufactured using lots of skilled labor. Furthermore, Japanese strategic planners demanded low-weight and low-cost designs in order to avoid overreliance on, again, imported raw goods. These two factors had significant impact on the design of many Japanese tanks and aircraft. Although this rule does not apply to its naval ships, which were overbuilt and overpowered.

SOURCES: I apologize for loosely mentioning sources, but for the most part, you can find this information in the following texts (if my memory is correct):

Eagles of Mitsubishi: Information on tolerances and economic considerations in manufacturing. The military kept pushing for using smaller, weaker engines.
Secret Weapons and World War II: Japan in the Shadow of Big Science: This book mentioned the economic situation in Japan, although it's primarily about Japan's failure to centralize its cutting-edge scientific research programs.

 

[JoblinTheGoblin]

It seems that the thread is approaching a general consensus on Japanese engines, that they were complex and powerful enough, and were held back by primarily external factors, largely Japanese shortage in key resources like avgas and the latest industrial equipment. I'll agree that the Japanese were catching up to Western engine technology quite quickly, but I have my doubts that Japanese engines were ever on-par with, or exceeded, novel or prototype Western engines further down the production pipeline. I can't say much now, but, at a glance, Japanese aircraft, especially carrier-borne aircraft—however relevant they were at this stage in the war, were barely keeping up with the latest Allied designs in terms of level speed and climb rates / times, and were likely inferior in other aspects of manoeuvrability at higher speeds. Armament for fighters of all types—as some have pointed out here—including bomb loads, doesn't seem to be have been all that improved or that competitive with Allied or German counterparts, though I can't say for certain now. This is all in light of Japanese engines, late-war examples in particular, supposedly being similarly powerful to Western counterparts.

 

[NevadaK]

Not that the Japanese were incapable of designing aircraft that were equal to those coming from the US. The material shortages and production challenges certainly impacted what could be brought in to active service. This aircraft for example would have been quite effective.

Mitsubishi Ki-83 - Wikipedia

en.m.wikipedia.org

 

[JoblinTheGoblin]

Actually, looking over some data over at wwiiaircraftperformance.org, it looks like figures for some Western aircraft, RAF aircraft like the Hornet in particular, can vary considerably. Still, manoeuvrable and speedy aircraft like the P-51H (>760kph, 6500m / 472mph (410kt), 21200ft) and the Hornet (~764kph, ~6400m / 475mph (412kt), 21000ft) would be a threat for any Japanese aircraft, even Japanese jet aircraft perhaps.

 

[MIflyer]

Well, the Japanese figured out that they needed more power and much better altitude performance.

 

[tomo pauk]

As always, good comment. I would also like to add that the frontal areas of Japanese engines were oftentimes very small, compared to similar output engines from other nations. As pointed out by Greg (from YouTube, not these forums), some of the better Japanese engines used RPMs to achieve higher output and lower displacement/frontal area. In general, Japanese aero engines were very well engineered and of technical sophistication similar to countries in the West.

You will hopefully forgive my eyebrows raising when Greg of Youtube is mentioned
The only high-rpm Japanese engine I'm aware was, probably, the Homare. Other radials and V12s were operating under 2800 rpm.

Nakajima with Homare was not cheating - they knew just too well that small stroke is a good thing for high RPM (for more RPM = more HP), and that engines with more cylinders usually make better power than the engines with less cylinders but with same displacement. High rpm required that crankshaft is very well balanced, so they engineered the balancers in. Steel casing for extra strength. No hi-oct fuel = we much supply the ADI system by default.

What Greg didn't mention is that Japanese engines have higher oil consumption. The big reason is that Japanese engines have loose tolerances. Meaning, they aren't as tightly sealed and fitted as US and British engines. The loose fit is because of economic reasons. Rather than relying on expensive imported industrial equipment, Japan's war machine relied on a large number of less expensive skilled machinists. Because of hand finishing, their engines had looser tolerances and leaked oil constantly.

Thanks for that detail.

 

[AerialTorpedoDude69]

tomo pauk I know the Ha-43 was also high RPM but I think there may have been other prototype late-war models that had over 2,800 RPMs.

JoblinTheGoblin That seems like a reasonable line of conjecture. The most important point to make is that Japan was far outspending most other nations in terms of their gross domestic production on importing technologies. Germany, France, and many other nations used a similar industrialization strategy, although Japan modernized far more rapidly than any European economy. It's the reason why all the Western nations had export versions of their military hardware. The export versions typically removed key technologies relating to superchargers and other cutting-edge developments. In many cases, Japanese engineers developed work arounds (such as high RPMs and special alloys and lubricants). But given that they had fewer engineers that weren't centralized, the longer the war went on, the more their technologies fell behind the Allied standard. But as far as I'm aware, they were mostly on par with the Allies in 1945. Deficient in many aspects of engineering but ahead in others.

As far as I'm aware, the major shortcoming of Japanese engines weren't the design though. If you are interested in design, supposedly, the major shortcoming was propeller design according to Australian technical intelligence. This is strange though because most of their props were licensed VDMs or Hamiltons, manufactured by Sumitomo (IIRC). The electric Pe-32 used on the Ki-84 had voltage problems however. So it might be that their voltage regulators weren't up to Allied standards. Australian technical intelligence only mentioned that Japanese prop design was years behind the Allies. But unfortunately we don't have much more documentation than a second-hand anecdote.

We do know though that the DH Hornet was a contemporary of the Ki-83. As they were roughly comparable in technical sophistication, and time frame of production, this speaks volumes about Japanese engineering standards.

 

[bf109xxl]

Bill Gunston's opinion from his book, "The development of Piston Aero Engines" (pp.171-172):

Turning briefly to other wartime countries, I was fortunate to be able to look at almost all the Japanese engines, and formed the view, 'When you've seen one, you've seen them all.' Almost all were conventional radials, two showing signs of Bristol ancestry and the rest having a strong American flavour. The chief exception was a licensed copy of the Daimler-Benz 601, which in the Ki-64 prototype was used in a unique twin-engined installation, one engine in the nose and the other behind the cockpit, with steam cooling and wing/flap skin condensers. A small air radiator under the right wing cooled the oil. The Navy version of the same German engine was made by Aichi as the Atsuta, and the unfinished Yokosuka R2Y1 was to have been powered by two of these coupled side by side in exactly the same manner as the DB 606. This bulky engine was to be mounted amidships, with a long shaft passing between the two crew to the tractor six-blade propeller. The only other remarkable Japanese engine was the Nakajima Ha-505, very like a Wasp Major but even bigger, with four rows of nine cylinders and a target power of 5,000 hp. At least one Ha-505 was built, but I do not believe it flew.

Seems a bit oversimplified.

 

[tomo pauk]

Seems a bit oversimplified.

And that's an understatement.
The intellectual damage done by many American and British authors in the 20th century when describing non-American and non-British ww2 stuff cannot be overstated. Also, a lot of them haven't limited the damage done by themselves just to the non-Anglo-American stuff.

 

[tomo pauk]

I know the Ha-43 was also high RPM but I think there may have been other prototype late-war models that had over 2,800 RPMs.

Ha-43 never flew in combat. Experimental BMW 801F was making 2900 rpm, the 'normal' Bristol Hercules was sometimes pushed to 2900 rpm for test purposes (probably also for combat?).
Japanese didn't have in-service engines pushing 3250 like the Jumo 213, or 3200 like V+-1710 was supposed to do by late 1944/early 1945, let alone the 3800+- rpm of the Sabre.

tl;dr - I'd say again that Greg is wrong on the RPM thing. Not that it surprises me, if I can be cocky

 

[NevadaK]

And that's an understatement.
The intellectual damage done by many American and British authors in the 20th century when describing non-American and non-British ww2 stuff cannot be overstated. Also, a lot of them haven't limited the damage done by themselves just to the non-Anglo-American stuff.

Steve Twomey's excellent Countdown to Pearl Harbor focuses on how that attitude help make the Pearl Harbor attack possible.

 

[fannum]

If we talk about the speed only, including such an experimental model like A7M, here is J8M with 890km/h.
Combat result with a P-51 would have been like this


View: https://www.youtube.com/watch?v=c1Pi6cxiLbU&t=23s

It's amazing how invulnerable the J8M is, and how instantly effective it and the Zeros are against the usually sturdy B-29s and P-51s.
Also, those A6Ms seem to have gained magic superchargers to operate so effectively at those B-29 altitudes.
Wow!

 

[Shortround6]

Two things were the general limit on RPM.
One was piston speed. Most engines used just about 3000fpm as a limit.
However a few engines traded BMEP for piston speed (like the Pegasus) but some of that was because of the history of the engine. Trying to upgrade old designs sometimes lead to not using the best modern practice.
Radials generally used less rpm than V-12s. Putting 7/9 cylinders on one crankpin tended to discourage high rpm. Some engines came close. But also look back at piston speed.
The little G-R 14M engine (19 liters) could run at 3000/3030rpm but it's short stoke also meant a piston speed of 2258fpm.

The other big trade-offs were weight and engine life.
And most radials had cooling problems/limits.

The P&W R-1830 was actually rather unremarkable engine if you just look at the common stats.
1200hp for T-O and 1000hp at 12,500ft in high gear using US 100 octane fuel for just under 1500lbs.
But the late 30's/1940 R-1830s were getting over 300 hours in air line use. But that service life had to paid for somehow.
R-1830s also had a cooling problem. But it is masked by just not pushing the engine very hard. Any improvements past 1200hp T-O of 1940 were pretty much in durability/engine life despite changing from 100/100 to 100/130 fuel.
The R-1830s also didn't gain that much from changing from 91 octane to 100/100 fuel.
T-O power stayed the same.
FTH heights on the supercharger (with the same supercharger and gear ratios) went down with the 100 octane fuel while power went up slightly, like some other engines but the change was much less marked than the liquid cooled engines. Low gear the change was from 1050hp at 7500ft to 1100hp at 6200ft for max continuous. For military power 100 octane got you 1200hp at 4900ft instead of 1200hp at 3700ft. Same military power 1200ft higher.
High gear the change was from 900hp at 15,400ft to 1000hp at 12,500ft for max continuous. For military power 100 octane got you 1050hp at 13,100ft instead of 900hp at 17.400ft.
I don't think there was any official change for using 100/130 fuel. 100/100 (it was never labeled as such) disappeared as original supplies ran out. This was the orgianla under 2% aromatic 100 octane fuel used by the Americans but never the British.
The limits seem to be the the fact that the radials were running closer to the detonation limits to begin with.
The R-1830 only went to 1350hp with new cylinders with better cooling fins near the end of the war (and about another 100lbs of weight) but I don't know what the engine life was at thot point.

I will note that cylinder size, valve size and rpm may interrelate in radial engines in ways we may not be taking into account.
The Homare engine used 130 X 150 cylinders compared to the R-2800s 146 X 152 cylinders.
2mm difference in stroke doesn't amount to much in piston speed.
The smaller pistons do mean less reciprocating mass.
The smaller bore means better cooling in general (assuming equal fin pitch/depth/thickness) but the smaller bore also means smaller valves, or perhaps it is better to say less available room for the valves, without actually know the size it is just guesswork. But the Homare cylinder/head is smaller than the bore of an R-1830 cylinder.

we haven't gotten into (and with out very good data/drawings/actual inspection we are not going to) valve port size and shape or inlet pipe size/shape or supercharger efficiency.

 

[AerialTorpedoDude69]

JoblinTheGoblin I forgot to mention is that there are two issues regarding Japanese aircraft top speeds:

1. There is a recording discrepancy possibly. Going off the raw data available (such as horsepower and wing area), Japanese aircraft are consistently showing slower speeds than what calculations would indicate when zero-lift drag coefficients are known as recorded in Francillon. Propeller design could explain this but it doesn't explain all of this.

2. Japanese aircraft had large wing surface areas, relative to their horsepower and weight, which negatively impacted top speed. It's a separate discussion as to why Japanese strategic planners demanded handling over performance.

At the end of the day, Japan's aero engine program suffered from reliability issues that mostly related to its immature industrial production capabilities. According to a Nakajima engineer, Mizutani, the biggest problem in developing a high performance engine was in dropping from 100 octane fuel to 92 or less and in finding suitable lubrication systems. They also struggled with alloys. As a result, while they succeeded in developing a compact, high performance engine, it was never fully reliable due to issues with skilled labor, maintenance issues, and material shortages.

This is all in light of Japanese engines, late-war examples in particular, supposedly being similarly powerful to Western counterparts.

The Ha-43 had the smallest frontal area relative to output out of all 2,200-HP radials at the time of its production, even compared to prototype radials from other nations. But it wasn't reliable nor was it fully developed due to a lack of official support from the Japanese military IIRC (their brass had picked the Homare over the Ha-43 for most applications). It's important to note that a key US advantage was in being able to cost effectively build high performance, high reliability hardware in massive numbers.

The Japanese could build high performance aircraft, in low numbers, with low reliability.

tomo pauk I think the Kinsei 50 was capable of 3,000 RPMs, according to this post.