Why are the Japanese planes so slow?

[F4UDOA]

JoeB.

I didn't realize your were a Philly guy.

I am in Cherry Hill now, Grew up around George Washington High.

Or maybe we talked about this already and I forgot.

Anyway
Go Birds!

[joeblogs]

Yes, we are pretty darn close.

-Blogs

Originally posted by F4UDOA
JoeB.

I didn't realize your were a Philly guy.

I am in Cherry Hill now, Grew up around George Washington High.

Or maybe we talked about this already and I forgot.

Anyway
Go Birds!

[flakbait]

It may have been fuel, differing documentation and engine ratings, Karnak. We know they had 87 octane fuel, but fuel with higher octane ratings is rarely if ever mentioned. High octane fuel is needed if you want to hit high speeds with any piston engine. The higher the octane rating, and the greater refinement done, the harder you can push the engine.

As for engine rating and actual power, Baugher has a tid-bit about this on his page regarding the A7M Reppu.

The A7M1 prototype flew for the first time on May 6, 1944, test pilot Eisaku Shibamaya being at the controls. Test pilots reported that the A7M1 handled extremely well, and that the use of the combat flaps made the A7M1 just as maneuverable as the Zero. However, they also reported that the aircraft was significantly underpowered for its weight. The Homare 22 delivered only 1300 hp at 19,685 against a calculated rating of 1700 hp, and at this altitude maximum speed was only about 350 mph. In retrospect, Horikoshi was right. Because of its disappointing high-altitude performance, on July 30, 1944 the Navy ordered that further work on the A7M1 be suspended after the second prototype had been built.

I got that info from over here. If one engine wasn't producing its rated power at a given altitude, others could've had the same problem to a lesser degree. We know the Ha40 and Ha140 engines (copies of the DB601) were notorious for rarely putting out their rated power. But I doubt all of them had this problem. The Sake 12 and Sake 21 engines (copies of the P&W R-1830) worked flawlessly and delivered their rated power on demand. The most plausable explination is Japanese aircraft were faster than documentation gives them credit for. An easy way to check the speed differential between fuels would be to take a look at test reports of a given aircraft using different octane rated fuels. If the F4U was tested with 87, 110 and 120 octane fuels a quick comparison between top speeds would let anyone see how much speed is gained from using a given type of fuel.



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Flakbait [Delta6]

[Karnak]

I cannot see how going from 87 octane to 100 octane on an engine designed for 94 octane would yield a 39mph speed gain.

Some gain certainly, maybe even 20 or 25mph.  Not 39mph.

Maybe if the Japanese fuel was more in the 80 octane range.

[Angus]

Karnak:
I think you are right there.
However, the climb numbers would show this better, that's usually the case by boosting up.
Are there any around?

[HoHun]

Hi Flakbait,

>AC of WW2 gives the 109E4 using a DB601Aa engine at 1,175hp while Baugher, AC of WW2 and J-Aircraft have the A6M2 pushing out 940-950hp at takeoff.

Roger. That DB601Aa is somewhat of a mystery to me, some good experts claimed it wasn't ever used in the Emil, but a recently recovered Me 109E from Russia clearly has one.

The Battle-of-Britain Me 109E-4 had the DB601A-1 in the 4.5 km full throttle height variant, though, and it didn't get more than 1050 HP. Though often higher take-off ratings are listed for the DB601A-1, they actually are for a 60 s rating (enforced by a mechanical clockwork) that apparently didn't make it into service at all.

>The A6M3 data from J-Aircraft and Baugher gives 1,130hp from the Sake 21. Hence the reason I chose to compare the 1,175hp DB601Aa with the 1,130hp Sake 21.

I see. Going from 940 HP at sea level to 1130 HP would have boosted the A6M2 from 434 km/h to 461 km/h. That's still some way below the Me 109E-4's 480 km/h, and now it's the Emil that has less power. (Speed only increases by the cubic root of power, so you have to add a lot of power to get a worthwhile speed increase.)

>Still, no matter which way you cut it, the difference in speed between a radial engine and a hot-water 12 of similar power isn't much. Not nearly enough to account for the huge speed discrepancy of Japanese fighters after 1942, anyway.

Well, looking at the A6M2 alone, the difference was bad enough in a 1940 comparison. I think we both agree that there's not much need to discuss the Zero in the context of the original question, though, as it pretty much stagnated at a low power level.

The mid-war to late-war engines were better, and I'd agree that at least at a first glance, the Japanese aircraft weren't all power-handicapped.

Looking at the different Japanese designs, the sequence Ki-27 - Ki-43 - Ki-44 - Ki-84 seems to be especially interesting.

The Ki-27 was a very manoeuvrable aircraft, but the Ki-43 was built for performance already and almost failing the acceptance tests as a result. Still, by western standards, it was under-powered and extremely manoeuvrable. If you look closely at the Ki-84, you'll notice that it is very similar in size and shape to the Ki-43, and to me it looks like Nakajima designed the same aircraft once more, but with a much more powerful engine.

The Ki-44, on the other hand, stands out from the others in that set. It has a much smaller wing - smaller than an Emil's, actually, is very light - hardly heavier than the Emil - and yet features a 1500+ HP engine. That's a pretty unique combination - you could consider it a pocket Lavochkin ;-)

Still, even the Ki-44-II tops at 616 km/h @ 5030 m. The low altitude makes this absolute top speed seem relatively low, but at sea level, the Ki-44-II does 542 km/h which is better than the Me 109G-2 and not that far from the Fw 190A-5. In terms of climb rate, the Ki-44-II was spectacular.

It was the lack of a decent high-altitude supercharger that deprived the Ki-44 of a good top speed. I'm not sure about the reason - it may be that they were lacking two-stage superchargers, but on the other hand, the German aircraft didn't use these either and didn't fall behind that badly anyway. Maybe it was a question of a badly chosen design point - but on the other hand, why choose a design point for an interceptor that doesn't result in optimum performance at the level where the bombers are to be expected?

I'm a bit at a loss here.

Regards,

Henning (HoHun)

[Karnak]

I'd like to have a Ki-44-II-Otsu is AH.


I do like the Ki-84, I was just expecting a bit more speed and a bit better high speed handling.

[Angus]

Ki44...what nickname again?

Anyway, from HoHun
"It was the lack of a decent high-altitude supercharger that deprived the Ki-44 of a good top speed. I'm not sure about the reason - it may be that they were lacking two-stage superchargers, but on the other hand, the German aircraft didn't use these either and didn't fall behind that badly anyway."

I tend to disagree with this point.
From the Merlin 61 onwards for almost 2 years, the Germans were indeed completely inferior in the very high altitude department.

[Karnak]

Ki-44 is Tojo

[flakbait]

HoHun, look closely:

A6M2    950hp    331mph
A6M3    1,130hp 338mph

The A6M2 tops out at 331mph, the A6M3 tops out at 338mph and has clipped tips. I'm not comparing aircraft based on the year they were made, I'm comparing them based on engine power and top speed. Though even with clipped tips the A6M3 wasn't faster than the Emil. Hell, it was 9mph slower at altitude. Still, after mid 1942 the A6M design was completely outclassed by other aircraft both from an engine output standpoint and an aerodynamic standpoint. From there on it was no different than the Bf-109 or the Ki-43; too much weight, not enough engine, and terrible controls at high speed.

The Ki-44 is a rather promising aircraft and an absolute rocket in a climb. When production started in 1942 it could hold its own at 376mph, and was definitely an excellent design. What makes me think, though, is the fact that Baugher says "It was made obsolete by the Ki-84." If the Ki-44-III was made obsolete by the Ki-84, how come the Ki-84 in AH has lead elevators and is only 14mph faster? That's not obsolete, that's a close call and a narrower gap than many other fighters. Either someone in Japan made a bad call or the Hayate was a lot better than the paperwork gives it credit for. If the Tojo had a turbo, or even a double deuce (two speed two stage super) that would've brought up the top speed at altitude and maybe increased the critical alt. Who knows why it was never fitted with one of these. The Japanese did have two-speed supers and used them fairly regularly. But it doesn't look like they used a double deuce except on a few experimental types. The same goes for their turbos.

The Ki-43 was a joke by 1942 since nearly anything in the Pacific could outrun it at will. Only at very low speeds, where the Oscar was a dragster in acceleration, could it beat an opponent. Otherwise it was too flimsy, underpowered and undergunned.

The Ki-61 was, at best, an interesting experiment and a learning experience. The Ki-100 was better, roughly on par with the Tojo in terms of maneuvering, speed and firepower though nowhere near as fast a climber.

The Ki-84 looks like the big brother of the Oscar, and both look like they share the same wing. If it really did have excellent maneuverability and could hit 427mph, most aircraft would be hard pressed to match it. The high speed would also make the Ki-84 the best Japanese fighter of the war.


Regarding Japanese fuel, does anyone know the octane ratings of fuel produced by the Japanese? As best I can figure it, 87 looks like the most common stuff they made. Could it be that Japan was in a similar boat as Germany in making high-test AV gas?


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Flakbait [Delta6]

[joeblogs]

Problem is that we don't know the Japanese engines can go up in octane. Once you get into the high lead ranges, valves & bearings have to made of different materials.

In the (limited) data I have on Japanese engines, none are rated at an octane number above 92. What's more, none generate more than 700HP at 19,000 feet.

Correction: The Sakae 21 develops 1,150 HP at sea level and 950 HP at 19,700 feet at military power.

-Blogs

Originally posted by flakbait
.... An easy way to check the speed differential between fuels would be to take a look at test reports of a given aircraft using different octane rated fuels. If the F4U was tested with 87, 110 and 120 octane fuels a quick comparison between top speeds would let anyone see how much speed is gained from using a given type of fuel.



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Flakbait [Delta6]

[Oldman731]

Originally posted by joeblogs
Yes, we are pretty darn close.

-Blogs

Yah.  Me, too.

- oldman

[flakbait]

Actually the reason I asked was so we could try to reverse-calculate the Ki-84 speed. If the TAIC test used 120 octane fuel, and the Hayate normally used 92, maybe another aircraft has a set of numbers from two different fuels. Granted it wouldn't be perfect, or exact, but it would be a rough guess as far as the actual top speed. Hence my example of the F4U; if it had numbers from two different fuels, the speed difference could be used to roughly SWAG the Ki-84 speed difference between the TAIC test and the actual top speed.



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Flakbait [Delta6]

[HoHun]

Hi Flakbait,

>Still, after mid 1942 the A6M design was completely outclassed by other aircraft both from an engine output standpoint and an aerodynamic standpoint.

I absolutely agree.

>What makes me think, though, is the fact that Baugher says "It was made obsolete by the Ki-84." If the Ki-44-III was made obsolete by the Ki-84, how come the Ki-84 in AH has lead elevators and is only 14mph faster?

Well, the Ki-84 seems to have been plagued by engine trouble at least initially, and I've read that some Japanese pilots didn't consider it a progress over the Ki-44.

The Ki-84, however, seems to have been a leap forward in terms of ease of fabrication, requiring only 56% of the resources per airframe the Ki-43 did (and I'd think that the relation to the Ki-44 was similar).

The lead elevators seem to be based on a complaint about the first series production Ki-84 - no idea whether that was corrected later.

>But it doesn't look like they used a double deuce except on a few experimental types. The same goes for their turbos.

Roger. That was hi tech at that time, and in fact, the Germans didn't have many of these either.

>The Ki-43 was a joke by 1942 since nearly anything in the Pacific could outrun it at will.

As I understand it, it had to be kept in production for lack of high-performance engines. Tough, but even the US kept producing the outdated FM-2 and P-40 without even being as desperate as the Japanese.

>The Ki-61 was, at best, an interesting experiment and a learning experience. The Ki-100 was better, roughly on par with the Tojo in terms of maneuvering, speed and firepower though nowhere near as fast a climber.

The Ki-61 actually was a development based on the Heinkel He 100. The ancestry is a bit of a mystery still since Heinkel sold the plans and a production  licence to the Imperial Navy, not the Army, but the contemporary Kawasaki designs show a distinct Heinkel influence on some other points - like surface condensation cooling - as well. The earlier Ki-60 seems to have closer to the Heinkel than the Ki-61, which underwent an extensive redesign, primarily to improve range.

I'm not sure what to think about the Ki-61 performance. It was pretty good for a DB601A-1-engined aircraft, but I'm not sure it was ever improved on since the more poweful versions of that engine appear to have been prohibitively troublesome.

With regard to the Ki-100, I'm not sure about the exact performance.

>Regarding Japanese fuel, does anyone know the octane ratings of fuel produced by the Japanese? As best I can figure it, 87 looks like the most common stuff they made. Could it be that Japan was in a similar boat as Germany in making high-test AV gas?

The German C3 actually was pretty much comparable to 100/130 grade US fuel. I believe Robert Mikesh mentions that the Japanese were limited to 92 octane maximum, but that came from one oil field only and apparently was in limited supply towards the end of the war, or maybe the oil field was actually lost. I've read the Navy got hold of most of that fuel, probably because they ran the tankers, and only little of it reached the Army units. Water injection might have made up for some loss of octane, though.

Regards,

Henning (HoHun)

[flakbait]

From what Baugher said the lead elevators were corrected when the airframe underwent changes between the pre-production and the full production model. Its also where the jet-thrust exhaust stacks came in, along with a host of other changes and improvements. All told the Ki-84, both to the eye and on paper, looks like the mother of all Japanese fighters. Definitely something to be reckoned with!

The Ki-61 was supposed to get a redesigned engine (Ha-140) for the Ki-61-II model, but it was a nightmare to keep running. Between crank failures, main bearing failures, and cooling system hiccups it was enough to give anyone a fit. On the rare occasion when it did run properly, it had 14mph more speed than the KAIc and a much faster climb rate. Though I remember a Smithsonian tech saying, while he was rebuilding a DB605, that the Germans managed to get it just right. Three degrees more inclination of piston angle would've broken the crank, two degrees less inclination and it would've siezed up. If the Japanese changed the crank angles up it would explain some of the crankshaft failures they had. The rest could be traced to badly skilled workers in the engine factory... before it was bombed (bad omen maybe? )

As best I can tell, the Ki-100 was a bit quicker to accelerate than the Ki-61 KAIc and a better climber thanks to an extra 400+ horses. Otherwise the two were pretty close from a performance point of view. The Ki-100 and Ki-61-II with an Ha-140 motor are almost twins performance-wise; the Ki-100 being 20mph slower is the only real diff. Baugher's joint (bottom link posted earlier) has the spec for it and quite a few other Japanese fighters.

What really makes me rack my brain is Japanese engines semed almost hit or miss. The Sake 21 worked very well, the Ha-22 was 500hp below spec, the Ha40 and Ha140 both had trouble staying in one piece and rarely delivered full rated power, the Ha45 had teething troubles but eventually worked just fine. The Ha33 on the Ki-100 was a proven and very reliable 1,500hp motor, even the Mk9A radial at 2,200hp was a proven design. Why not use one of the more proven engines instead of tinkering with an inverted V or keeping failed engine designs around?



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Flakbait [Delta6]