Japanese fighters' performance: what is the verdict?

[tomo pauk]

We were, and still are, witnesses to many debates whether this Bf-109 or that Spitfire was making 390, 400, or maybe 410 mph. Yet the data for the Japanese fighters is at even greater discrepancy, we can read the speeds of under 380 mph for fighters with powerfull engines, of modest size weight. The low numbers (found eg. on Wikipedia) seem to stem from Francillion's book, more than 40 years old now. The high numbers (400-420 mph for Hayate, Raiden Sinden-KAI) are from TAIC tables, and seem to me as a more credible.
So what is the verdict? How fast they really were? Is there a redoubtable source for the performance of the IJA/IJN fighters' performance?

 

[CORSNING]

Great question tomo. I wish I had an answer. I will be watching this thread closely just in case a real good answer comes along.
Jeff

 

[pinsog]

Could quality of fuel be the difference? How much difference would fuel quality make?

 

[Denniss]

With low quality fuel you have to reduce boost, sometimes even rpm, to prevent early detonation of the mixture.

 

[tomo pauk]

The lack of suitable fuel was mostly felt at altitudes under the full throttle heights, where the engines were able to use the better fuel to make greater manifold pressure. Japanese fuel was mostly of 92 octane, the water injection use to achieve greater manifold pressure (negating the effects of low oct/PN fuel) was widely used at last two war years. Later engines for Mitsuishi Raiden were making more than 1500 HP above 18000 ft, and 1700-1800 HP between 16-17000 ft. And then we read on Wikipedia that Fw-190-sized plane was as fast as Spitfire V, or Bf-109F1/F2???
The engine details can be read in our forum, some of the TAIC reports about engines planes are available at Mike Williams' site.

 

[davebender]

Nothing wrong with IJA Ki-61 and Ki-84. Building them in adequate numbers with adequate quality control were the fatal problems.

 

[GregP]

One man responsibe for saving many Japanese aircraft is Ed Maloney of the Planes of Fame. Our A6M5 Model 52 is really Ed's aircraft, and he has saved the last J2M Raiden, one of two Yokosuka D4Y Judys in existence, a real Mitsubishi J8M Shusui complete with real engine and landing gear assembly (it was his first airplane!), a real MXY-7 Model 11 Ohka, and a G4M Betty bomber displayed in "as crashed" condition.

According to Ed, the higher numbers were as flown after the war on high-grade US fuels and the lower numbers were for operational Japanese fuels. The Japanese fighters of late WWII had good performance in combat and were 370 - 400 mph aircraft when in combat as required. They were maneuverable and well made. Their propellers were a bit shorter than western practice at the time and of slightly more narrow chord, and that accounts for some small performance losses, particularly in climb. The Japanese aircraft that I worked on (the Judy) and witnessed (the rest) are of good workmanship, but of a different philosophy than US and British fighters.

While the Zero remained a maneuvering beast, the Ki44, Ki-84, J2M, and the Kawanishi Geroge were all very good air defense fighters that much more closely matched the later US fighters in performance than the Zero ever did. The Ki-84 was one of their best, but the rest of these four were all very good.

The issue with the Ki-61 was the engine. Japanese aircraft mechanics and technicians were all trained on radials and could not seem to keep the license-built DB-601 copies in a good tune for operations. The solution, in the middle of a war, could either be to train more mechanics or go to the raidals that they were all trained on and already knew. In the event, they chose the latter option and the liquid-cooled Ki-61 became the radial Ki-100 (and performed better, too, and was probably one of their two best fighters ... the other being the Ki-84). The liquid-cooled early Judy became the radial Judy. There are others, too. All the radial versions flew well and were good performers, though even better with better fuels in post-war testing.

Our museum used to have a flyable Ki-84 but, in the 1970's ... there simply was no interest from the US airshow public. Could not get an airshow booking for it and eventually sold it to a Japanese Museum where it still is ... though no longer flyable. We still have all the manuals and a few odd parts. We also have one of the last flight-restorable Aichi D3A Vals in existence and plan to restore it to flying status when some of the other ongoing projects are completed and space is created for it. The original Japanese workmanship is good, but the repairs done by the former owners are amateurish at best and positively dangerous in reality. It will all have to be redone to make the Val flyable. Meanwhile we have our movie Val that was built from a BT-13 for "Tora, Tora, Tora," and it flies in our annual airshow.

While the Raiden is technically restorable to flying condition, the corrosion means that it will need a new wing spar, new tail spar, new longerons, a lot of new skin ... and the engine would HAVE to be restored since it was set well back and used an extended prop shaft that no American radial can duplicate. It is possible but daunting. The cockpit is enormous!

Sorry for no exact numbers ... but they depend on who was flying it and on what fuel that was used at the time. All US pilots who flew them liked them. I believe Eric Brown even said the Zero was one of his favorites of all times.

In the 1944 Fighter Conference proceedings, it is interesting to note that virtually all of the US and British fighters tested had engine problems or problems of SOME kind that limited the boost or rpm ... and even resulted in aborted test flights, at least some of the time, but the Zero never had ANY engine issues during the conference testing! Ran great each and every time. That should say SOMETHING to the members if nothing else does. Maybe, if nothing else, i says that the Japanese 1,150 - 1,250 HP radials were very reliable compared with 1,500 - 2,000 HP western engines of the day. I daresay the ubiquitous DC-3 / C-47 didn't have too many engine problems either with its pair of 1,200 HP Wrights (1820's) or Pratts (1830's).

And, at the end of the war, the late-model Zeros could climb 4,500 fpm ... still on realtively low HP compared with western rivals. They were simplty never all that fast. Then again, neither was the FFVS J-22 in Sweden but it, too, performed quite well on a 1,200 HP radial and could easily be called a "Swedish Zero," though I doubt the Swedes would take that as a complement ... even though it was intended that way. They are possibly the best two performers of the radial 1,200 HP engine equipped fighters ever produced.

 

[raumatibeach]

Cheers Greg, that was great.

 

[cherry blossom]

There was a discussion at Type 4 Fighter (Ki 84) maximum speed which made the point that the 388 mph was for an early Ki-84 and that we should expect some increased speed as the engine power increased.

 

[parsifal]

I always believed engine build quality was a bit patchy. Sakai somewhere compares the zero engine to post war US engines that he saw. He described the US engine compartments as cleean and neat, and no evidence of leaky oil. Not so the Japanese engines which were untidy and leaked oil everywhere....Dont know how true that is.

Conversely Ive got several books that clearly state that may published figures for US types under tropical combat conditions were unattainable. Generally because of poor maintenance or excessive wear . This seemed to be the case with a lot of carrier borne Hellcats. Rated to fly at 370mph, some were so clapped out in early 1944 that they could barely exceed 350mph.

So it may be just a case of relativity

 

[Aozora]

Great summing up. Considering the potential of some of the prototypes the Japanese were flying or about to fly there were some world class designs:
Nakajima Ki-87 - with a decent turbocharger a rival to the P-47
Mitsubishi Ki-83 - Grumman F7F territory
Mitsubishi A7M2 - a big fighter but reputedly almost as manoeuvreable as the Zero and had the performance of the F6F-5.

 

[GregP]

Let's keep in mind that none of the WWII aircraft used an air cleaner except the "tropical" units. Added to this is the fact that tropical weather will kill anything man-made everntually Usually quite quickly if left unattended and in the open..

So ... if they flew off a coral atoll ... the engines would wear quite fast. If they flew off sandy terrain, they would wear quite fast. if they flew off grass, not nearly as much wear and tear.

Ditto the propellers, when flying with a lot of FOD (coral, dust, gravel, etc., the props would wear much faster than if flying off grass ... and performance would suffer. Today's planes, flying off pavement, have less propeller and engine wear than even planes flying off grass in many cases. Wear out is a fact of life, even in the absence of abrasives into the induction, just slower. If guns were hard-mounted, the impulse from firing could also damage the structure over time. Most WWII fighter guns were hard-mounted with no provision for recoil.

The untimate test for this were the first B-25's fitted in the field with a 75 mm cannon by Pappy Gunn in the PTO. After 15 - 20 shots, the rivet holes in the wings were egg-shaped and the plane was scrapped when the wings flopped around after landing. Factory planes with the 75 had later provision for absorption of recoil, and were not damaged much by firing. Field units just bolted the cannons to the flooring or the structure and ALL the recoil was tramsmitted to the airframe. I'm told they lost 7 - 10 mph of airspeed with each discharge of the cannon, but cannot confirm it other than by hearsay and "war stories." So, while I have a suspicion it is correct, I can't really say. Heard it from 3 guys who were there, but who were not in contact with one another until I introduced them at a gathering to discuss WWII at lunch. They had a joyous reunion and they took off the rest of the day to discuss it all. I went back to work after an hour.

The modern A-10 has the same issue with added complication. They can't fire more than about 10 rounds all at once without flaming out the engines due to flying through their own gun gas (no more oxygen for combustion of fuel). So they fire repeated short bursts and lose a lot of airspeed with each burst. This was from a student A-10 pilot in the 1980's when I lived in Arizona. He lived above me and we partied on the weekends. I can't say it was 100% correct, but he and his buddies (A-10 pilot trainees) all said it was true, so I have my suspicions that it was correct. ALL had the same story, and several ahd flamed out the engines at low altitudes and destroyed the APU by emergency start of same from stopped to running in less then 4 seconds. It usually melted but worked well enough to get at least ONE fan going at 50 feet and decaying airspeed .. and get the crate back to base.

 

[tyrodtom]

I don't see why anyone would have to fire the A10's cannon for 5 seconds, let alone 10. Ten seconds would be 700 rounds of 30mm, over half what they carry.
And if the engine was going to flame out from gunsmoke inhalation, why would it take ten seconds? The gunsmoke is going to be inhaled by the engine a fraction of a second after the gun fires.
The Mig 9 had that problem, but it had it's cannons stuck out right in front of the intake.
The shop foreman of one of the places I used to work was a x A-10 pilot, from when the USAF first had them in the mid-late 70's.

 

[GregP]

Doesn't take 10 seconds; takes 10 ROUNDS. So ... SHORT bursts.

 

[Shortround6]

10 rounds isn't enough to get the gun up to speed.

Even at the old low rate of 2100rpm that is 35 rounds per second.

The smaller 20mm gun that fires at 6000rpm ( 100 rounds per second) actually only fires about 70 rounds in the first second because of the time needed to accelerate the barrels up to speed.

You could fire a 10 round burst but I don't now what the cycle rate would be. 1 1/2 turns of the barrels starting from a dead stop?

 

[tyrodtom]

Somehow I misread that Greg, I saw 10 seconds in my mind. Getting old.
But it would be hard to just fire less than 10 rounds. The Gau-8 fires around 50 rounds a second, the first second, and 70 rps thereafter, so someone is firing it in long burst. And the A-10 is the only thing that mounts the Gau-8. The Gau-8 now only fires at one rate, 3900 rpm, instead of the 2100 and 4200rpm rates of the earlier models.

I was a crewchief/doorgunner, I could fire 3 round burst from a M60, with no problems. But I don't know if I could have done that while flying a aircraft at the same time.

But, the A-10 might have a burst fire capability built into the armament system settings.

 

[varsity078740]

Let's keep in mind that none of the WWII aircraft used an air cleaner except the "tropical" units. Added to this is the fact that tropical weather will kill anything man-made everntually Usually quite quickly if left unattended and in the open..

So ... if they flew off a coral atoll ... the engines would wear quite fast. If they flew off sandy terrain, they would wear quite fast. if they flew off grass, not nearly as much wear and tear.

Ditto the propellers, when flying with a lot of FOD (coral, dust, gravel, etc., the props would wear much faster than if flying off grass ... and performance would suffer. Today's planes, flying off pavement, have less propeller and engine wear than even planes flying off grass in many cases. Wear out is a fact of life, even in the absence of abrasives into the induction, just slower. If guns were hard-mounted, the impulse from firing could also damage the structure over time. Most WWII fighter guns were hard-mounted with no provision for recoil.

The untimate test for this were the first B-25's fitted in the field with a 75 mm cannon by Pappy Gunn in the PTO. After 15 - 20 shots, the rivet holes in the wings were egg-shaped and the plane was scrapped when the wings flopped around after landing. Factory planes with the 75 had later provision for absorption of recoil, and were not damaged much by firing. Field units just bolted the cannons to the flooring or the structure and ALL the recoil was tramsmitted to the airframe. I'm told they lost 7 - 10 mph of airspeed with each discharge of the cannon, but cannot confirm it other than by hearsay and "war stories." So, while I have a suspicion it is correct, I can't really say. Heard it from 3 guys who were there, but who were not in contact with one another until I introduced them at a gathering to discuss WWII at lunch. They had a joyous reunion and they took off the rest of the day to discuss it all. I went back to work after an hour.

The modern A-10 has the same issue with added complication. They can't fire more than about 10 rounds all at once without flaming out the engines due to flying through their own gun gas (no more oxygen for combustion of fuel). So they fire repeated short bursts and lose a lot of airspeed with each burst. This was from a student A-10 pilot in the 1980's when I lived in Arizona. He lived above me and we partied on the weekends. I can't say it was 100% correct, but he and his buddies (A-10 pilot trainees) all said it was true, so I have my suspicions that it was correct. ALL had the same story, and several ahd flamed out the engines at low altitudes and destroyed the APU by emergency start of same from stopped to running in less then 4 seconds. It usually melted but worked well enough to get at least ONE fan going at 50 feet and decaying airspeed .. and get the crate back to base.

Paapy Gunn didn't install 75 mm guns in B-25s.

Duane

 

[Njaco]

Then who did?

B25s with the 75mm cannon

The modification of the B-25 into a low level straffer was done by the Third Bomb. Gp., 5th Air Force. The preliminary expeirimenting was done at their base at Charters Towers, Q'land., Aust. The work was spearheaded by Col. P.I. "Pappy" Gunn and N. Am. Tech Rep Jack Fox. The actual modifications were done in Brisbane, and later came out of the factory. Several configurations were tried, but the most successful, and most used one was with the 4 50Cal. guns in the nose - and, yes, they did eliminate the bombardier. I don't recall that we ever got any out the factory with the 75mm gun, but we did have two expeirimental models "Pappy's Flying Tank" and the "Lil Fox".

 

[Shortround6]

It seems to be a question of when and where. I would not "read" into that statement more than is there. Pappy Gun was certainly instrumental in getting the first straffers built and into action. However there seems to be little proof that the first straffers ( or even the first few score of straffers) had ANY 75mm guns. As mentioned they used four .50s in the nose although other configurations were tried.

View attachment 224149

And see: B-25C/D Strafers

The Factory was working on the 75mm gun installation in the late summer/early fall of 1942

See: North American B-25G Mitchell

Once again Pappy Gunn was not happy with the factory product and modified the "AIRPLANE" and "ARMAMENT" but not necessarily the 75mm gun itself. The factory planes coming with only two .50 cal guns in the nose with the 75mm originally.

Pappy Gunn's "experimental" plane with the 75mm could very well have come with the 75mm and HE was responsible for fitting extra .50 cal guns including more guns in the back of the plane to help balance the weight.

It would also take something of an idiot to try to mount a 75mm gun without the recoil mechanism in an aircraft.

View attachment 224150

The recoil mechanism has the atachment points to the rest of the carriage.

The 75mm field gun also recoils 44" IN the mount and still needs the trail and spade to keep from moving.

 

[Shortround6]

Duplicate post.