Details of the later ZERO Fighters A6M5 follow-on versions

[kettbo]

Firstly, noted many of the tests on captured planes did not include WEP settings
Discussed lots here have been the later Bf 109s, more recently the Raiden J2M series
Now to the later Zeros, any skeletons in the closet here> new top speeds?

Second, looked at my small Wm Green books from the 1960s/1970s, and a few others here and a look at Wiki
Pretty much the info after the A6M5 series, coverage gets sparse
A6M6, looking for more info, numbers made and starting when, entering service date, etc
Also, A6M7, can find little info. Believe it was strengthened as a dive bomber but know little else

The A6M8 (2 prototypes) so no addl info needed

Liking the idea of more power (nose MGs deleted to get engine room and the 1x20 and 1x 51 cal per wing armament
Underwing rockets a plus

 

[vanir]

Some Japanese forumites at various aviation forums I've noted have repeatedly mentioned or claimed, the published specifications of all Zero types are maximum continuous outputs for the engine and military outputs (ie. maximum climb setting in eurospeak/military rating in NACA terminology), and that actual war emergency power at sea level is approx 150hp higher. This isn't hard to believe, because we can all document this is the case with the entire P-40 series, none of them have their maximum, say for the 40E 1470hp factory rated war emergency rating, they all have the "military rating" of 1150hp printed. If you gave that in Europe they'd say, why do we want to know the maximum climb rating for? Tell us the maximum short term output at 6500 feet like everyone else. Compare this engine with the RR or Daimler properly and it's actually about the same, just does everything at lower alt. Schoolkids are running around thinking Spits have 400hp over a Warhawk in balls out pole racing. It doesn't.

Same story basically is what these Japenese guys were saying about the Zeros and I really could see where they were coming from. I even downloaded one of the references by one of them, some wartime Japanese documents printed up in their version of Squadron Signal or something like that, but it's all in heiroglyphics.

The USN mentioned that due to ignorance about Japanese tuning (they use different fuels than the west, from the dutch east indies), they restricted the power settings when evaluating their captured Zeros. They didn't risk breaking the engines. It may have cost around 150hp worth of energy, the speed/climb characteristics of all Zeros maybe understated. By the same token, US reconditioned captured Ki-84 and other late war types actually returned better performance in American hands using American fluids than they did in wartime Japan.

And this fuel issue has me curious. Japanese got the same fuel Burma got. RR engines started pinging at +6lbs on that fuel. I suspect all Japanese motors maintained small diameter blowers because of that fuel, though I'm sure their processing improved quality somewhat. Still, I've heard oil people talking about fuel oils before, and south pacific oils isn't as good as middle eastern oils for fuels.

 

[tomo pauk]

To the Zero's engines: if I'm reading your post right, vanir, Japanese were able to extract WER from an air-cooled engine without water injection, while other belligerents were not capable to do so? Even the glorified R-2800 needed help of ADI.

 

[vanir]

Tomo it depends entirely on the overboost you're using. Under 5000 feet you can still just richen it up and overboost about 3PSI from normal take off/emergency without water injection, fuel dependent. This SOP for bombers loaded heavy on frontal fields, which mostly use radials like Wrights and such.

It's about controllable settings more than installed equipment, so long as the pilot isn't trying to do anything too dramatic you can get away with it. Richening the mixture alone can actually throw your altitude tuning out very easily, reason auto pressure units were installed (soviet planes use manual for the whole war), but it does allow you to raise boost just a couple of PSI extra without pinging, that's where the extra power comes from when they say pilots sometimes use rull rich at take offs. It's because they're overboosting. Look up wartime bomber flight manuals, one of them will talk about it.

Obviously it doesn't control pinging as well as water injection or improved intercooling, but it's a bit like ram air in terms of extra pilot input on what the plane does in gentle slopes. Just something extra pilots use to help control pinging a bit, so you can get away with a little overboost, or some crappy fuel, or the weather is making the motors go all screwy, etc.
I mean not all that different to what it does for a turbo/blown car. Old street racers trick is up the jets, richen it right up and overboost but there's a sweet spot if you go past it reduces torque then pings anyway. This method of short term power increase (2mins) is fairly marginal, but P40 pilots used it to routinely overboost well beyond factory specifications. There's documentation for it.

 

[tomo pauk]

Thanks for the insight - so the extra fuel acts as ADI? I reckon it the extra fuel will not burn in cylinders, but simply exit through valve openings.
Think Shortround6 was talking some time ago along this lines.

 

[Jenisch]

This isn't hard to believe, because we can all document this is the case with the entire P-40 series, none of them have their maximum, say for the 40E 1470hp factory rated war emergency rating, they all have the "military rating" of 1150hp printed.

Interesting. I already heard of the Soviets overboosting their P-40's, and consequentely having a lesser life of their engines.

But that would not turn the supossed advantage of the P-40 against Japanese planes with energy tactics even greater?

 

[Shortround6]

I think we have several things going on here.

1. What is WEP for different countries and times?
Foe instance before WWII the American P&W R-1830 was rated at 1200hp for take off but only 1050hp at max continous (or climb) there was NO military rating let alone WEP rating. Some earlier pilots manuals show a military "EMERGENCY" rating equal to the take-off rating for some engines. This is equal to the 'later' military rating but not WEP.
The R-1830 was allowed to use the take-off rpm and boost levels for "military" power but never received a WEP rating which would require even higher boost. Engines were rarely allowed to over rev to reach a WEP rating.

Given the problems in translating documents and the changing definitions of some terms (many engines had an 'international' rating before WWII, this rating disappeared postwar) I can fully believe that some Japanese planes were rated at max continous power and not at take-off or " military" power while having no WEP rating.
Please note that ALL British climb specifications are for max climb power and not max 5 min power.

I could be wrong on the Japanese engines but since different countries did measure performance in different ways or under different conditions trying to compare them gets tricky.

I have one book that gives the top speeds of many US Navy fighters at max continous power,quite a change from max power

 

[tomo pauk]

The absence of internationla 'rules' about WER or MIL or what ever really skews any comparison.
Maybe the best way couls be the allowable setting per allocated time, but there we have 1 minute, 3 min, 5 min, 15 min, 30 min etc, and not all the time limits were used by all the countries/manufacturers/users.

 

[Arossihman]

I would imagine the fuel quality the japanese and germans used when they ran short started to decrease as their end came closer and closer....this i imagine would have really hampered performance. I know later models of the thunderbolt used water injection to achieve WEP, did other U.S. aircraft use water injection also?

 

[vanir]

I think we have several things going on here.

1. What is WEP for different countries and times?
Foe instance before WWII the American P&W R-1830 was rated at 1200hp for take off but only 1050hp at max continous (or climb) there was NO military rating let alone WEP rating. Some earlier pilots manuals show a military "EMERGENCY" rating equal to the take-off rating for some engines. This is equal to the 'later' military rating but not WEP.
The R-1830 was allowed to use the take-off rpm and boost levels for "military" power but never received a WEP rating which would require even higher boost. Engines were rarely allowed to over rev to reach a WEP rating.

Given the problems in translating documents and the changing definitions of some terms (many engines had an 'international' rating before WWII, this rating disappeared postwar) I can fully believe that some Japanese planes were rated at max continous power and not at take-off or " military" power while having no WEP rating.
Please note that ALL British climb specifications are for max climb power and not max 5 min power.

I could be wrong on the Japanese engines but since different countries did measure performance in different ways or under different conditions trying to compare them gets tricky.

I have one book that gives the top speeds of many US Navy fighters at max continous power,quite a change from max power

Indeed and well said. I always seem to find it hard getting across the default premise that international conventions vary dramatically between nations. I remember that "international rating" as it was used in all the tech magazines writing up the German engines during the war, like Aviation Monthly, who did a full spread on the BMW 801 and DB601, it was really cool, stripped down to the bearings. Those roller bearings on the Daimler by the way are seriously trick, that's like a modern 25-grand race engine, no kidding. They knew their stuff. It was specified however that the "international rating" was synonymous with the "maximum continuous power" setting, and that engineering nomenclature would generally present these in comparative testing. The ca.950hp of the Sakae 12 is, according to some Japanese forum enthusiasts this rating.

Now that creates a lot of problems. Firstly, the US Doc AFAMC-5 Oct23 1942 provides the standard on performance rating of the Zero-21 from thereafter, ie. 335mph/16000ft max level speed, etc. And they gave an estimated 840bhp "normal power" and 900bhp for maximum take off power at 35"Hg/2600rpm.
Yet USN documentation I've laying around somewhere, and I believe Michael Bougher's blogs specifies that for that particular Zero US engineers guessed the engine tuning and specifications. It had to be rebuilt as it was crashed and not in flying condition. A caburettor from an Allison was used. The fuel is a different type and grade. They were unsure about exceeding safe limits and had no information to go by, so no overboost/rich or settings beyond the throttle gate or normal operating auto-boost regulation used on their own. Much of the flight testing was concerned with preserving the aircraft as it was a rare find at that time (in 44 wrecks and spares were all over the place).

Now if anyone can read Japanese I do actually have documentation from Nakajima factory listing complete specs on all their wartime engines. I can't read it, it's like a 30pg scanned book one of the Japanese enthusiasts I've been talking about emailed to me.
The one I think is the Sakae-12 says maximum normal power is 1100hp/2700rpm at +200mm (38"Hg) boost in low blower at 2550 metres altitude and 980hp/2700rpm at +200mm boost in high blower at 6000 metres altitude. It says the maximum war emergency power is +300mm (42"Hg) boost in low blower only (ie. at take off and under 5000ft or thereabouts only, presumably for carrier take off) is 1130hp/2750rpm/full rich.


Hey none of you can read Japanese can you?

The one I think is the Sakae-21 says 1220hp high blower and 1440-1500hp possible in low blower, same settings as the Sakae-12. I mean their only other 14-cyl radial has 1650hp so that can't be it.

I keep finding more stuff. Note that also Wright engineering dept. did an full tear down of a Kinsei 14-cyl radial (lower powered than Sakae-12, fitted to A6M1 original prototypes), they rate that engine for 850hp max climb and 1050hp for max take off. Surely the Sakae 12 is higher than that, by any convention, the Sakae made production versions for that reason (and two blower gears), but the USAAF initially rates the Zero-21 as worse than this engine stock specifications. That's in error, it definitely is.

 

[tomo pauk]

Now if anyone can read Japanese I do actually have documentation from Nakajima factory listing complete specs on all their wartime engines. I can't read it, it's like a 30pg scanned book one of the Japanese enthusiasts I've been talking about emailed to me.
The one I think is the Sakae-12 says maximum normal power is 1100hp/2700rpm at +200mm (38"Hg) boost in low blower at 2550 metres altitude and 980hp/2700rpm at +200mm boost in high blower at 6000 metres altitude. It says the maximum war emergency power is +300mm (42"Hg) boost in low blower only (ie. at take off and under 5000ft or thereabouts only, presumably for carrier take off) is 1130hp/2750rpm/full rich.


Hey none of you can read Japanese can you?

The one I think is the Sakae-21 says 1220hp high blower and 1440-1500hp possible in low blower, same settings as the Sakae-12. I mean their only other 14-cyl radial has 1650hp so that can't be it.

I keep finding more stuff. Note that also Wright engineering dept. did an full tear down of a Kinsei 14-cyl radial (lower powered than Sakae-12, fitted to A6M1 original prototypes), they rate that engine for 850hp max climb and 1050hp for max take off. Surely the Sakae 12 is higher than that, by any convention, the Sakae made production versions for that reason (and two blower gears), but the USAAF initially rates the Zero-21 as worse than this engine stock specifications. That's in error, it definitely is.

Perhaps you could attach the scan here, so Shinpachi can take a look at it, when he founds time, of course?

 

[gorizont]

I keep finding more stuff. Note that also Wright engineering dept. did an full tear down of a Kinsei 14-cyl radial (lower powered than Sakae-12, fitted to A6M1 original prototypes), they rate that engine for 850hp max climb and 1050hp for max take off. Surely the Sakae 12 is higher than that, by any convention, the Sakae made production versions for that reason (and two blower gears), but the USAAF initially rates the Zero-21 as worse than this engine stock specifications. That's in error, it definitely is.

But A6M1 had Mitsubishi Zuisei 13 not Kinsei. It had a smaller capacity compared to Sakae (contrary to Kinsei).

 

[Gixxerman]

Aviation Monthly, who did a full spread on the BMW 801 and DB601, it was really cool, stripped down to the bearings. Those roller bearings on the Daimler by the way are seriously trick, that's like a modern 25-grand race engine, no kidding.

That's not so surprising (for the DB engine at least) as IIRC it was born from the 'national prestige' project Germany's cars in international racing had become.

The story of fuels is (as Arossihman has mentioned) very relevant too - oils too.
These must have placed ever increasing limitations on German Japanese designs.

To return to the initial topic......the last Zeros have always intrigued me (the A6M8s?), they look to have a reasonably high spec along with Ki100's look like they would have posed serious problems (assuming Japan was able to maintain a pool of experienced pilots).

 

[kettbo]

Yup, interesting comments so far but nothing on A6M6 or A6M7
Really enjoying this less-talked-about business on how stuff was rated, 'testing' proceedures

When the Army sent me to Guam, Rota, Tinian, and Saipan in 2002, some wreckage still present...cool stuff

 

[vanir]

here it is, a translation would be good, I can only guess that I was looking at the right figures.

 

[kettbo]

WOW! Wealth of info there IF I could read this! Let me ask a few people

 

[vanir]

Yeah it traces engine development by Nakajima through the 20s-40s all neatly in tables, comments and specifications, but I can't read it

Need translation, because the way I'm reading it is the A6M6/ie. water injected high boost Sakae, should be the only 14-cyl with a WER of +400mm boost. That says 1850hp. Kind of gonna need confirmation on that.

 

[tomo pauk]

Our own Shinpachi, IIRC, had already translated these tables to English some time ago. The 3 tables:

 

[vanir]

I can't download any hosted zips/rar from here for some reason, only from remote file hosts like mediafire.
But I did find proper details on the Sakae 21 at least,

HP:
Nominal:
1,080 @1st stage of supercharger(on the ground)
1,100 @1st stage of supercharger(alt. 2,850meters)
980 @2nd stage of supercharger(alt. 6,000meters)
Lift-off:
1,130


RPM:
Nominal: 2,700
Lift-off: 2,750

Manifold air pressure(Mercurial column in milimeter):
Nominal: +200*
Lift-off: +300

Nominal altitude(meter):
2,850 @1st stage of supercharger
6,000 @2nd stage of supercharger

Reduction Gear Ratio:
7/12 (0.5833)

Fuel:
Specific gravity: 0.72
Type: Aviation type92 volatile oil


Sakae model 21, TAIC 1944 p. 852
Take-off 1115 hp/2750 rpm/41.7" SL
WEP 1115 hp/2750 rpm/41.7" SL
WEP 1180 hp/2750 rpm/41.7" 7500*
WEP 1040 hp/2750 rpm/41.7" 18000*
MIL 995 hp/2700 rpm/37.8" SL
MIL 1085 hp/2700 rpm/37.8" 9350 ft
MIL 965 hp/2700 rpm/37.8" 19700 ft

"Manifold air pressure(Mercurial column milimeter)
Nominal 225* * normal max (1st stage)
+200 @ nominal 1st stage, 2nd stage
Lift-off +300 "

 

[tomo pauk]

Okay, try this download (same zip as above):
nakajima.zip