Japanese aircraft were behind in timing to Allied aircraft.

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Shortround6

Major General
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Jun 29, 2009
Central Florida Highlands
The maneuver vs speed argument has gone in a number of directions including this one.

My thought is that the 1942 A6M2 and Ki-43 had basically 1940 performance and armament. It did not get a lot better as the war went on. Perhaps they closed the gap to one year?
Criteria are in squadron service aircraft, not prototypes or service test.
The early fighters had great range, they sacrificed things to get it (firepower and protection).
Many other Japanese fighters did not have a range outside the range that is "normal" for the fuel capacity/speed for other fighters.
The Japanese were always behind in armament, and let's not go by barrel count but actual fire power.

The Japanese did face several handicaps. One was fuel quality, but you can't just pour in Allied fuel and get allied power levels. You often need better materials (another short coming ) and better cooling, which also may require changes in tooling and/or basic structure.
Another handicap, faced by many of the smaller nations, was the size of the engineering force. Not "Idea men" but the engineering grunts that did the stress calculations and other calculations and the draftsmen to do the drawings. Some fighters had tens of thousands of parts and each part needed at least one drawing and sometimes several. A larger company or company in a larger country can complete a project in less time due to the greater resources that can be used to bring the project to completion. Has nothing to do with talent or skill of the designer (or design team).

For Japanese army fighters
The Ki-43 II entered service in Dec 1942/Jan 1943
The Ki-44 entered "service" in late 1941 but they only built 50 of them until the service Ki-44 II showed up in Dec 1942?
Ki-61 entered service in Dec 1942/Jan 1943?
Ki-84 showed up in actual service (not trial unit) in the summer of 1944.
 
I do pretty much agree with this as an outsider looking in. For instance, the Zero and Ki-43 were indeed designed in the late 1930s using the best tech the Japanese had at the time. I also feel that the IJA and IJN were either fighting mostly obsolescent aircraft in China or were facing the western allies who didn't field the "latest and greatest" like they did in the ETO. That pattern remained for quite a while until almost the point where Germany was on it's last legs as far as land based fighters (the P-38 excepted).

Granted, the Hellcat and Corsair were probably the best naval fighters to see widespread service during the War in the Pacific.

And yes, I know that the Spitfire evolved heavily and was was a mid 1930's design, and the P-51 Mustang was designed in 1940. But both were fairly forward thinking designs and had development potential, and were actually sort of exceptions that prove the rule. The Spitfire 24 only shared its basic fuselage structure with the Spitfire I and the XP-51F/G and P-51H diverged into becoming almost totally new designs to take advantage of know-how gained since 1940. Ironically, the P-51B/D were originally known as the XP-78 due to the switch from the Allison to the Packard Merlin, though most of the tooling to make the P-51/P-51A were used to make the P-51B/D. XP-78 might have been better used for the Lightweight Mustangs, as they had relatively little in common with the B/D models.

And as also pointed out, Germany ran into similar stagnation in aircraft design at about the same time. One somewhat ironic point is that though Japanese fuel was nothing special compared to US/British fuel, it was still somewhat better than Germany's and Italy's. 91-92 octane was usually what the IJA and IJN used, while Germany and Italy were stuck with 87 octane.
 
Hey Shortround6,

I would say that your premise is true for the most part. The only change I would make is relative to the effects that high grade 100/130 fuel could have had if available to the Japanese at the beginning of the war.

Using the Sakae 12 as an example. There is no reason that the Japanese could not have had ~1100 BHP at about the same 13,000 ft altitude where it had 950 BHP in real life. As it was with 87/92 grade the Sakae was limited to +3/+4.8 lbs, which was basically pre-war MAP for US and UK radials.

Obviously this is not a war winner, but the A6M2 would have gained about 15 mph at ~15,000 ft.

If 100/130 grade had been available to the Japanese engine designers at the start of the war, they would have been designing their follow-on engines to that standard which could have made significant differences in engine progress.

Again obviously not a war winner, but this would have allowed increases in useful loads for the various aircraft - possibly including armour, SSFT. and improved/heavier armament.
 
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Interesting discussion regarding fuels and japanese engines. What kind of power would the Sakae-21 do on 100 octane, and potential speed increase for A6M3/5? And same question for all variants of Kasei, Kinsei, Ha-41/109 etc., pretty much all major japanese engines. I know it's a lot, but i'm very curious about this subject. Is it a percentage increase? And how about the methanol/water injected late-war japanese engines running on 100 octane fuel, like Homare, Kasei-20 or Kinsei-60 series etc.?

I have read that one of the reasons they resorted to water/methanol injection (which brought all kinds of complications) for instance in the design of the Homare as early as 1941 i believe was the very lack of 100 octane fuel.
 
The only change I would make is relative to the effects that high grade 100/130 fuel could have had if available at the beginning of the war.

Using the Sakae 12 as an example. There is no reason that the Japanese could not have had ~1100 BHP at about the same 13,000 ft altitude where it had 950 BHP in real life. As it was with 87/92 grade the Sakae was limited to +3/+4.8 lbs, which was basically pre-war MAP for US and UK radials.

Obviously this is not a war winner, but the A6M2 would have gained about 15 mph at ~15,000 ft.

You have made some good points but the knock-on effect comes into play.
You are not going to get 1100hp at 13,000 from the Sakae 12 because the supercharger won't supply enough air. You could get 1100hp at lower altitude though this assumes the engine will take the power and will cool at the higher power levels.
You can change the supercharger (bigger) to make 1100hp at 13,000ft on the Sakae (with the above limitations) but then you will not get quite the cruising range from the Sakae 12 because it will take more power to turn the supercharger, You can take off with more fuel with more power though.
The Sakae 12 weighed 530kg (1168lbs) and was over 200lbs lighter than the R-1830 used in the P-36.
I would also note that Sakae 12 was rated at 2500rpm and the Sakae 21 was rated at 2700rpm (and weighed 60kg more.)
Also of note is that the R-1830-9 used in the P-35 and making 950hp for take off at 2450rpm on 87 octane fuel only weighed 1292lbs compared to the later versions of the R-1830.
There is no free lunch.
 
I know there are many engine experts here, but if the above would be true, how do we explain the Merlin-III going from 1030HP on 87 octane to a whooping 1310 HP with 100 octane, almost 30% increase (there might be time and altitude limitations though)? I don't recall reading about any major modifications made on the engine.

If we go by a similar radio the Sakae-12 would do something like 1200HP on 100 octane fuel! And applying a roughly similar ratio we get something like 1400 HP for the Sakae-21?! But maybe i miss something.

PS: i realize we talk about 91/92 octane japanese fuel vs UK 87 octane, which on the surface suggest the japanese fuel is better, on the other hand i'm sure i've read over here that octane number is not necessarily everything, f.e. the german 87 would be roughly 91 or 92 octane by US or UK measurements? So is the japanese 91/92 indeed better than the UK 87?
 
Interesting discussion regarding fuels and japanese engines. What kind of power would the Sakae-21 do on 100 octane, and potential speed increase for A6M3/5? And same question for all variants of Kasei, Kinsei, Ha-41/109 etc., pretty much all major japanese engines. I know it's a lot, but i'm very curious about this subject. Is it a percentage increase? And how about the methanol/water injected late-war japanese engines running on 100 octane fuel, like Homare, Kasei-20 or Kinsei-60 series etc.?

I have read that one of the reasons they resorted to water/methanol injection (which brought all kinds of complications) for instance in the design of the Homare as early as 1941 i believe was the very lack of 100 octane fuel.
Somewhat address in previous post.
If you want to use the potential of 100/130 fuel you have make the engine strong enough to handle the strain and you have to design the cooling fins to handle the heat load.

I am certainly not saying you can't increase the power output of the Japanese engines by using 100/130 fuel but you are not going to get a big increase without major changes in engine structure.

The Bristol Mercury and Pegasus serve as illustrations. Both got minor bumps in power, a bit more on the Mercury.
Also see end of war R-1830 engines rated at 1350hp on 100/130 fuel. Weight had climbed to 1565lbs for single speed engine comparable to the Engine used in the P-35. Almost 300lbs.
 
Hey Shortround6,

re "You are not going to get 1100hp at 13,000 from the Sakae 12 because the supercharger won't supply enough air. You could get 1100hp at lower altitude though this assumes the engine will take the power and will cool at the higher power levels.
You can change the supercharger (bigger) to make 1100hp at 13,000ft on the Sakae . . ."

Or you can change the SC impeller ratio (Merlin 45 at 9.089:1 vs Merlin III at 8.588:1) and/or the impeller Ø (Merlin 46 at Ø10.85" vs Merlin III/45 at Ø10.25") - or both if the fuel allows the charge temperature increase - which I am pretty sure it would. A combination of the above would allow the relatively minor increase in MAP and power I am talking about for the Sakae 12. I have no way of knowing if the Japanese SC designs were of comparable efficiency to the 'Hookerized' types used on the Merlin, but the SC on the Sakei 12 and 21 were more efficient than the standard engine mounted SC designs used by the US radials and the V-1710 at the start of the war.

Again, you are I believe mostly correct in that changes would have to be made. Again however, I have to add that if 100/130 grade fuel had been available at the start of the war there is no reason I can think of that we would not have seen improvements in the Japanese engines similar to what occurred with the US and UK engines - particularly incremental improvements in strength and cooling. But I have no way of predicting what the Japanese Air Ministry would have prioritized, or if there were enough industry resources available.
 
I know there are many engined experts here, but if the above would be true, how do we explain the Merlin-III going from 1030HP on 87 octane to a whooping 1310 HP with 100 octane, almost 30% increase (there might be time and altitude limitations though)? I don't recall reading about any major modifications made on the engine.

If we go by a similar radio the Sakae-12 would do something like 1200HP on 100 octane fuel! And applying a roughly similar ratio we get something like 1400 HP for the Sakae-21?! But maybe i miss something.
You did, basically altitude and cooling.

The Merlin III made 1310hp using 12lbs of boost at 9,000ft, the 1030hp was at 16,250ft.
Liquid cooled engines usually had more head room for power increases. The air cooled engines were operating closer to the detonation limits.

I would note that for major US radials, NO engine was OK'ed for WEP without water injection. Also NO engine was rated at increased power levels (subject to supercharger limitations) without a major changes in engine structure, except the R-2800 when it went from 1850hp to 2000hp. The 2100hp engine in the P-47M was an entirely new engine.
 
PS re range

Again, if 100/130 grade fuel was available at the beginning of the war we have to presume that the Japanese aircraft and engine designers, as well as operation planners, would take any effects on range into account.

The higher power would allow greater useful loads to be carried, as I mentioned above - I am now including more fuel if that is the over-riding factor.
 
Hey Shortround6,

re "You are not going to get 1100hp at 13,000 from the Sakae 12 because the supercharger won't supply enough air. You could get 1100hp at lower altitude though this assumes the engine will take the power and will cool at the higher power levels.
You can change the supercharger (bigger) to make 1100hp at 13,000ft on the Sakae . . ."

Or you can change the SC impeller ratio (Merlin 45 at 9.089:1 vs Merlin III at 8.588:1) and/or the impeller Ø (Merlin 46 at Ø10.85" vs Merlin III/45 at Ø10.25") - or both if the fuel allows the charge temperature increase - which I am pretty sure it would. A combination of the above would allow the relatively minor increase in MAP and power I am talking about for the Sakae 12. I have no way of knowing if the Japanese SC designs were of comparable efficiency to the 'Hookerized' types used on the Merlin, but the SC on the Sakei 12 and 21 were more efficient than the standard engine mounted SC designs used by the US radials and the V-1710 at the start of the war.

Again, you are I believe mostly correct in that changes would have to be made. Again however, I have to add that if 100/130 grade fuel had been available at the start of the war there is no reason I can think of that we would not have seen improvements in the Japanese engines similar to what occurred with the US and UK engines - particularly incremental improvements in strength and cooling. But I have no way of predicting what the Japanese Air Ministry would have prioritized, or if there were enough industry resources available.


You do make some points. Especially the the point about the Sakae 21 supercharger, I am not sure about the Sakae 12 supercharger. The Sakae 21 seems to be about equal to the two-stage supercharger used in the F4F which may be more a reflection on the state of the art of supercharger design in the US?

For the US engines the higher powered late war engines (1943 and later) required major changes in engine construction. Wright for instance in order to go from 1700hp on the R-2600 to 1900hp change the crankcase and crankshaft, (after changing both to go from 1600hp to 1700hp) developed the "W" fin which was sheet metal that was rolled/calked into groves machined into the cylinder barrels instead of either machining the fins out of steel or using an aluminum "muff" of fins over the steel barrel. They also used this on the 1300-1350hp R-1820s and the later R-3350s. P & W went to the aluminum muff system. Both companies had to go to forged instead of cast heads and develop new machinery to cut deeper but thinner fins in the cylinder heads that were more closely spaced.

As far as the change from the Merlin 45 to the Merlin 46 goes, yes it boosted the altitude, it also limited the power by about 100hp at most altitudes below 20,000ft.

Also we need to look at the power that is NOT 5 min combat power or what ever that is called by any particular country. Once the Merlin went much past the IV or X just about ALL Merlin's were rated at 2850rpm/9lbs boost for 30 minutes regardless of the boost allowed for combat.
 
I am being an AR type here, but at some point in the mid-war, the single-stage Merlins after the Merlin V and X were all rated at 2850 rpm and +9 lbs for 1 hr. I have never been able to find out exactly when this occurred.

Merlin XX (from 1944 I think)
Merlin XX ratings late-war.jpg


Merlin 45 (also from 1944 I think)
Merlin 45 ratings late-war.jpg
 
My thought is that the 1942 A6M2 and Ki-43 had basically 1940 performance and armament. It did not get a lot better as the war went on. Perhaps they closed the gap to one year?
Criteria are in squadron service aircraft, not prototypes or service test.
The early fighters had great range, they sacrificed things to get it (firepower and protection).

It might be argued that Ki 43 have had, in 1942, lower performance and firepower than what the better European fighters had in 1938.

Agreed, Japanese fighters were very rangy and maneuverable, although not that much better than what the Bf 109F or Spitfire V had, presuming all of the fighters compared carry drop tank(s) and fly at same speed and altitude.

The Japanese did face several handicaps. One was fuel quality, but you can't just pour in Allied fuel and get allied power levels. You often need better materials (another short coming ) and better cooling, which also may require changes in tooling and/or basic structure.

Small engines (like Merlin, V-1710, Sakae, Zuisei, probably also Kinsei) were very dependant on high octane fuel. Big engines - DB 601/605, Jumo 211, Kasei - not so much. Another workaround is having ADI systems available, helps a lot if the supply of hi-oct fuel is not guaranteed. A simple solution (not taken by Japanese, but very much in favor with Mikulin and RR, for example) is reducing the compression ratio, or keeping it modest.
We know that availability of hi-oct fuel was not a substitute for a good supercharger - another area where Japanese were behind, and even the engines fueled by 87-92 oct fuel were very much depending on it.

Interesting discussion regarding fuels and japanese engines. What kind of power would the Sakae-21 do on 100 octane, and potential speed increase for A6M3/5? And same question for all variants of Kasei, Kinsei, Ha-41/109 etc., pretty much all major japanese engines. I know it's a lot, but i'm very curious about this subject. Is it a percentage increase? And how about the methanol/water injected late-war japanese engines running on 100 octane fuel, like Homare, Kasei-20 or Kinsei-60 series etc.?

Engine weights and construction tell a lot.
Heavier engine of the same generation and of the same construction (advantage for liquid cooled types here) should be able to withstand greater boost, that is available via use of higher octane fuel. Light radial engines, like Sakae for example, will not be able to mimic what Merlin was doing (not even the Hispano 12Y - being light - will mimic it, despite being a liquid cooled type).
Unlike ADI, high oct fuel does not provide internal cooling, even with engines running overly rich.
Mercury XV went for some 20% increase in output, 100 oct vs. 87 oct. Pegasus was more modest, Perseus even more modest. American engines (R-1830, 1820) were making usually about 100-150 HP more with better fuel - talk 10-15% increase. Americans were also modifying basic designs constantly, still power increase was small, and it took ADI for real jump in power levels - same as with Japanese engines.

Soviets went from ~500 kg M-103 to 620 kg VK-105F, so the engine can make better power while requiring high octane fuel - the 'no free lunch' applies as ever.
 
Unlike ADI, high oct fuel does not provide internal cooling, even with engines running overly rich.
Kind of/sort of? we are crossing over. Most radials used a considerable amount of fuel for internal cooling at high power. The higher octane fuel, as you say, does not provide any additional cooling over a lower octane fuel. P & W R-2800 cut back the fuel by at least 1 gallon per minute when the water injection kicked in even though the engine was making more power.
Mercury XV went for some 20% increase in output, 100 oct vs. 87 oct. Pegasus was more modest, Perseus even more modest.
The 3 British engines had the most minimal amount of work possible to get them to run on higher octane fuel, again you just can't grab the can/drum of high octane fuel and dump it in the fuel tanks and take-off. In some cases it was more to allow a plane to refuel if only high octane was available.
Sometimes you needed different sparkplugs to handle the increased lead, sometimes you just needed more frequent spark plug changes or cleaning. Sometimes a change in exhaust valves or valve/valve seat coating/treatment was needed (sometimes higher octane fuel came with an additive to reduce the lead deposits on the exhaust valves/seats).

Thing was that each engine was a bit different due to combustion chamber and locations of hot spots in the cylinder/head. The upper part of the Mercury and Pegasus was practically identical but I am not sure if the longer stroke did anything. There were reasons why engine makers were very against changing the cylinder dimensions. They often spent hours examining the combustion process in test cylinders that sometimes included quartz viewing ports for cameras. Build up of deposits could often take dozens if not hundreds of hours or happed very quickly (100/130 with 2.6 cc of lead or 100/130 with 4.6 cc of lead). please remember that the fuel specifications list the MAX amount of lead that can be used, there was no minimum.
 
The Japanese were not stupid. Howard Hughes used 100 octane fuel to set the world speed record in 1935. There were plenty of discussions in trade papers or seminars about 100 octane fuel. For the Japanese the problems were several.
Getting 100 octane fuel in general.
What was needed to turn lower grades of fuel into 100 octane fuel.

The soviets never made anything over 96 octane in quantity during WW II. They sometimes needed help with additives.
The Soviets just used larger engines of similar weights to some of the western engines.
The Mig 3 used that large, heavy AM-35A engine BUT it made 1150hp at 7000 meters according to one source and did it on 96 octane fuel instead of the 100/130 that the Merlin 46 needed to get into the same area.
your other choice is to make a two stage supercharger (with intercooler) and run try to run combination of under 100 octane fuel.

fuel problems and altitude were known in WW I.
Some German planes used engines without superchargers that could not be operated at full throttle at low altitudes without wrecking the engines due to the compression ratio used.
They used two (or three) gates on the throttle and and moved the throttle lever into the appropriate gate/slot for the altitude. The higher compression engine gave more power at the higher altitudes.
 
Hey tomo pauk and RCAFson,

Thank you. Can either of you provide me with the appropriate DTIC document link? This appears to be one I have not run across before.
 
Hmmm . . . interesting.

The Nakajima Engine History book lists the cylinder compression ratio as 7.2 for both the Sakae 12 & 21.
The DTIC charts tomo pauk posted list give the cylinder compression ratio as 6.7 and 7.0 for the Sakae 12 and 21 respectively.

I wonder which is correct, or if both are correct. Maybe the Sakae 12 is one that had its compression reduced due to poorer quality fuel availability. Or possibly the engines were in poor shape? I would think the personnel measuring the values would know what they are doing, but . . . Maybe rounding error on the Sakae 21?
 
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