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Mitsubishi A7M « Reppu » ("Sam")

lastdingo

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I assume the A7M Reppu is well-known among the readers of this forum. I've got a question about it and found no dedicated A7M thread, so here's one!

For starters: It was a prototype for a new Japanese carrier-borne fighter; didn't make it into production till the end of WW2. It was designed as a true successor to the A6M.



I'm aware that this fighter (would have) combined adequate protection, good armament, very good range and excellent (turn) agility.
Yet, there's one thing that irritates me.
It's the same as with the Ki-100 and several other Japanese fighters (and even the F6F Hellcat).

The top speed (sources generally agree on about 630 km/h) looks way too slow, and it's usually given for medium altitude (like about 6,000 m). Aircraft are slow at low altitude because of the higher drag (more dense atmosphere), but 630 km/h is ridiculously slow for 1945. New European propeller fighters of 1944/45 ranged at speeds between 700 and 780 km/h, and new versions of old models made between about 650 and 750 km/h.

A rule of thumb says that fighters weren't able compensate for a 80 km/h speed disadvantage. Agility still helped for defensive maneuvers, but such a speed disadvantage was simply unbearable for fighter pilots in WW2. They were prey for hit&run tactics in slow fighters.

630 km/h is like the Fw190's speed in 1942. It's unacceptably slower than a P-51D/H, P-47D/N, late Seafire, Bearcat and late Corsair.


Therefore my question (about A7M top speed and about similar cases, like Ki-100):
Does anybody have hints that could explain or falsify this top speed?


I know that somewhere deep in this forum someone already showed test flight reports (of WW2) that mentioned a higher Hellcat top speed than is usually given in sources. I hope someone could uncover something like this.


For those who expected some eye candy:
http://www.ijnafphotos.com/jbwa7m1.htm
or info:
http://www.aviastar.org/air/japan/mitsubishi_a7m.php
 

gral_rj

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Japanese AvGas was of quite low quality; IIRC, 87-octane fuel was high quality for them, and the Japanese never produced 91-octane fuel in anything bigger than laboratory test quantities.
 

blackkite

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According to this book, Naval Arsenal Aeronautical Technology forced Mitsubishi to apply 130kg/m2 wing loading instead of 150kg/m2 wing loading for A7M. Mr.Horikoshi wanted to apply 150kg/m2 wing loading.
This resulted about 19km/h speed down.
A7M2 marked 624km/h in 1944/10/13 with MK9A engine.
Priority for design specifications are as follows.
1.Air combat(dog fight).
2.range.
3.Landing to carrier.
4.speed.
5.Climb.
6.Take off from carrier.
Mr.Horikoshi also wanted to apply RAIDEN type propeller shaft extension and forced cooling, but rejected by the Navy.
I also inform you that Ki-84 HAYATE marked 687km/h with high octane gasoline after war in Australia by American pilot while it's official top speed was 624km/h.
 

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blackkite

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Additional information.
A7M2;Wing span:14m,Wing area:30.86m2,MTOW;5290kg,Wing loading:152.1kg/m2(weight increased),
Engine power:2200HP,Max speed:627km/h(5660m)

Sea Fury FB11; Wing span:11.71m,Wing area:26.04m2,MTOW;6650kg,Wing loading:217.9kg/m2:Max Engine power:2480HP,Max speed:740km/h(5490m)

F8F-1,Wing span:10.82m,Wing area:22.67m2,MTOW:5877kg,Wing loading:187.9kg/m2,
Engine power:2100HP,Max speed:678km/h(5660m)

P-51D;Wing span:11.28m,Wing area:21.9m2,MTOW:5493kg,Wing loading:209.4kg/m2,
Engine power:1490HP,Max speed:685km/h(6100m)/703km/h(7620m)
 

Apophenia

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The A7M's size verges on that of the Centaurus-powered Blackburn Firebrands.

Firebrand TF Mk. IV; Wing span: 15.62m, Wing area: 35.44 m2, MTOW: 7,360 kg, Wing loading: 203.6 kg/m2, Max Engine power: 2,500 hp, Max speed: 560 km/h
 

T-50

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nice rare photos of the Reppu windtunnel models!
T-50
 

gral_rj

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lastdingo said:
German aviation gas was poor as well, and I doubt that Japanese aircraft specs were from test flights with substandard fuel.
Japanese AvGas was worse than the German one; the 87-octane fuel that was premium-grade for the Japanese entered widespread use in the Luftwaffe by 1938-39, IIRC. It wasn't the single factor pushing down performance, but if memory doesn't fail me, it cost them at least 10% of what would be the available engine power.
 

blackkite

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Sharp eyed already recognized from posted book cover of “烈風と烈風改(Reppu & Reppu-kai)”,
there was a plan of Reppu modification version.
Reppu-Kai was planned to install turbocharged MK9A and shoulder mounted 30mm cannon for B-29 interception. It was high altitude interceptor.
I will post some information of Reppu-Kai soon.
“改” means modification. 紫電改(Shiden-kai) means modified 紫電(shiden).
 

blackkite

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Wing span:14.0m, Over all length:11.964m, MTOW:5,675kg, Max speed:638km/h(345knot)@11,000m,
Wing loading:181.4kg/m2, Engine power:2,130hp(6,800m)/1,920hp(10,300m)
Armament:30mm cannon x 2(wing),30mm cannon x 2(fuselage,slanting cannon)
 

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T-50

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The A7M Reppu is one of my favorite Japanese fighers its sad that the Reppu dind made it into service it had punished the F4U Corsair a lot that's for sure! especially the Kaizo version.
Its into my eyes the Japanese counterpart to the Hawker Tempest and P-47 Thunderbold.
Are there more drawings about the Reppu kai? its a very promising version of the Reppu
I hope some one has some pics or drawings of this pimped version of the Reppu and i must say this is a very interesting topic!
cheers T-50
 

Deadtroopers

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To extrapolate an estimate for speed from an uprated engine, all other things being equal - i.e. no gross aerodynamic refinement or degradation, I cube a known variant's speed and divide it by it's known horsepower. The result I use as the divisor for any other cubed speed to generate the horsepower. This gives a reasonable forecast of performance from a particular horse power. If I do the same for Japanese Pacific War aircraft, in the majority of cases there is a substantial shortfall between actual performance and my estimates. I am aware that quality control became almost impossible for a variety reasons but I don't know of any authority who is explicit of how bad this was and the reasons/combination of reasons this was so.

A number of you have referred to the octane figures for Japanese fuel, please see Bill Gunston, Plane Speaking, Patrick Stephens Ltd., 1991 ISBN 1-85260-166-3, the chapter on the Zero, it was determined in test flying that the A6M used 100 octane fuel.
 

Skyraider3D

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For some authentic A7M windtunnel test reports, go to http://www.jacar.go.jp/english/index.html and do a search for A7M. You'll get three search results. To view, click Browse Image on each. You may need to install the DjVu plugin for it from http://www.celartem.com/en/download/.
 

blackkite

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Recently I find following data.
IJN Saiun(彩雲)carrier reconnaissance plane(C6N1) marked 694.5km/h(375kt) at post war test in the United States with 130 octane gasoline and high quality spark plugs while IJN's test record was 634.9km/h(6,000m) with 92 octane gasoline.(Source:FAMOUS AIRPLANE OF THE WORLD No108)
Wing span:12.5m
Overall length:11.12m
MTOW:5,274Kg
Wing area:25.5m2
Wing loading:176.5kg/m2
Engine:NK9H(2,000HP/take off,1,620hp/6,100m)
 

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robunos

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lets stick to the Reppu please
Blackkite's post _is_ relevant here.
It's been discussed above how the poor quality of Japanese aviation fuel prevented many of their combat aircraft from reaching their full performance.
Blackkite's post has produced some evidence of this.


cheers,
Robin.
 

blackkite

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Thanks Robin. I will post another item of Reppu near future. ;)
 

T-50

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robunos said:
lets stick to the Reppu please
Blackkite's post _is_ relevant here.
It's been discussed above how the poor quality of Japanese aviation fuel prevented many of their combat aircraft from reaching their full performance.
Blackkite's post has produced some evidence of this.


cheers,
Robin.
its offcourse true that fuel made an important part of a aircraft performance,butthe reason that i replay on Blackkites post is that he was talking about a very different aircraft type.
If he was talking about the common problem of Japanese fuel why does he not say it and starts a new topic.
If he mentioning the fuel problems of the Reppu than was there no need for my replay on his post
I wanted to say only Reppu related post on this topic
 

T-50

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blackkite said:
Thanks Robin. I will post another item of Reppu near future. ;)
Hello Blackkite I reacted on your topic because it was in my eyes not relevant to this topic,although offcourse the fuel was a common problem in the last stadium of the war for the Sayun and the Reppu.
But I read more forum topics for example the PAK-fA and there are people who posting things that are totally not relevant to the topic. and that's sad.
My intention wasn't to disrespect you,but the only thing i wanted to say to stay by the supject of this topic thats all
cheers T-50
 

blackkite

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Hi T-50! I always enjoy your post very much.
I agree your opinion.
I should have added some explanation before Saiun's data,for example Robin's post.
I believe my post is good data for this topic. Don't you think so?
 

T-50

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Thank you blackkite for the compliment,good to hear that some one enjoying my post!
If the data concerns the Reppu Illagree that the fuel topic is on the right topic.
cheers T-50
 

robunos

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Found some more info on this topic, in 'Japanese Aircraft of the Pacific War', pp.400-401, by Francillon.

"Disregarding Jiro Horikoshi's [the designer] statement that the requred performance could only be
attained by use of the Mitsubishi MK9A or MK9B engine....
in September 1942 the Navy instructed Mitsubishi to install...the lower powered NK9K Homare.
Unfortuneately Jiro Horikoshi's warnings that...the aircraft would be underpowered were well
founded.
At 6000m (19,685 ft) the engine developed only 1,300hp against a calculated rating of 1,700hp
and at this altitude maximum speed was only 300-310kts (345-357 mph)...
Soon after this Jiro Horikoshi suceeded in obtaining the Navy's authorisation to install the
Mitsubishi MK9A on the sixth airframe, which became thi first prototype of the A7M2 series...
It soon became apparent that the Navy had at last found a sucessor to the A6M Reisen."

And this, from the new 'Japanese Secret Projects', paraphrased to conform to forum rules,

"high grade aviation fuel was to be reserved for the Homare series of engines only..."


cheers,
Robin.
 

Hardrada55

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Have the original 16-Shi Japanese Navy specifications for the successor to Mitsubishi's A6M "Zero" fighter ever surfaced?

There was a delay in starting design work on the design in 1940 and 1941 because of problems with development of the 14-Shi Mitsubishi J2M land based interceptor "Raiden" and the illness of chief designer Jiro Horikoshi. By the time Mitsubishi was able to work on the successor to the Zero, it was April of 1942 and the specifications had been updated to the 17-Shi version. These 17-Shi specifications resulted in the Mitsubishi A7M "Sam" carrier fighter.
 

blackkite

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Hi! I can't find any specifications about 16-shi carrier fighter.
I find only 17-shi carried fighter specifications.
Source:My No.2 Bible
 

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blackkite

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Hi! Reppu No.4 picture.
Source:Reppu & Reppu-kai(烈風と烈風改),Gakushu Kenkyusha(学習研究社)Tokyo,2003,ISBN4-05-602990-3 C9421.
 

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T-50

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Hi Blackkite very nice pics of one of the most beautiful radial fighter of the second world war!
But I must say I believed that what the artist called the Reppu A7M1 infact is the production model of the Reppu A7M2 and the other pic is the A7M1.
Because the production version has a simplified cool arrangement like Fw-190,and the prototype A7M1 has cooling lips above and beneath the engine.
And the A7M3 has cooling lips aside the engine,depicted in most drawings of the A7M3 version.
The Schragermusik style gun arrangement is therefore right
Its a very interesting fighter with a lot of potency and had a great punch,with i believe four 20mm cannons
 

JFC Fuller

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Can someone confirm what the A7M3 variant actually was (not the J variant pictured above), sources seem unclear and confused as to what engine it had and whether it was meant to be carrier or land based??
 

Apophenia

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Combined Fleet says carrier fighter but, oddly, other sources say that the A7M3 (Model 23) was based on the airframe of the A7M2 (Model 22) but without the wing-folding mechanism.

Either way, the A7M3 was powered by a Mitsubishi MK9C (Ha-43-31 with three-stage two-speed compressor - 2,250 hp T/O, 2,000 hp at 1,800 m, 1,800 hp at 5,000 m, and 1,660 hp at 8,700 m). Armament was increased to six 20 x 101 mm Type 99 Model 2, all wing-mounted.

By contrast, the land-based A7M3-J was to be longer (presumably ahead of the firewall), have greater wing area, and would be powered by a turbocharged engine (Mitsubishi Ha-43-11 Ru). Armament was to be six 30 x 122 mm Type 5 cannons (2 x oblique fuselage-mounted, 4 x wing-mounted).

Other sources say that the A7M3 and A7M3-J were both powered by Mitsubishi MK9Cs, differing only in the armament fitted.

http://www.combinedfleet.com/ijna/a7m.htm
 

T-50

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T-50 said:
Hi Blackkite very nice pics of one of the most beautiful radial fighter of the second world war!
But I must say I believed that what the artist called the Reppu A7M1 infact is the production model of the Reppu A7M2 and the other pic is the A7M1.
Because the production version has a simplified cool arrangement like Fw-190,and the prototype A7M1 has cooling lips above and beneath the engine.
And the A7M3 has cooling lips aside the engine,depicted in most drawings of the A7M3 version.
The Schragermusik style gun arrangement is therefore right
Its a very interesting fighter with a lot of potency and had a great punch,with i believe four 20mm cannons
Ive seen the pics I'm must admit I'm wrong
 

Apteryx

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blackkite said:
Hi! Enjoy.
Blackkite, are you able to tell what the reason is for the "fastback" shape of the A7M1 prototype in orange on your last image? I've seen these renderings, and wondered whether they have any documented source, or whether they are just speculative--a land-based interceptor a la the Raiden, for instance.
Thanks--Ian
 

blackkite

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Sorry I have no source. I will try to find it.
 

blackkite

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Hi MIKI PRESS.
MIKI PRESS already published KOKEN LONG RANGE PLANE, KITSUKA(橘花) jet fighter, SHUSUI(秋水) Rocket fighter, KI-94 high altitude fighter and Reppu(烈風) carrier fighter. You can find various blue prints in those books!! ;D
http://www.mikipress.com/archives/airplane/index.html
 

Apteryx

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blackkite said:
Hi MIKI PRESS.
MIKI PRESS already published KOKEN LONG RANGE PLANE, KITSUKA(橘花) jet fighter, SHUSUI(秋水) Rocket fighter, KI-94 high altitude fighter and Reppu(烈風) carrier fighter. You can find various blue prints in those books!! ;D
http://www.mikipress.com/archives/airplane/index.html
Thanks--this publisher's Reppu book was unknown to me, and I'm going to try and acquire a copy. My problem, of course, with all the Japanese-language books is the language!
I actually have a copy of Gakken no. 40, the Reppu book wherein are renderings of the "fastback" version of the A7M1. If there is evidence cited for this variant, it's in the Japanese text. :-[

Again, thanks, Blackkite!
 
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