J2M Raiden Performance

The reason for rather low top speed values listed for the J2M's is because the propeller efficiency was not good which had bad effect to its max speed. Furthermore the speed is stated at Military Power, without the use of Water-Methanol boost

US TAIC are calculations and based on the aircraft profile and wing area they calculated what the top speed of the Raisen would be. However they didn't know about the lackluster propeller

Laurelix said:

The reason for rather low top speed values listed for the J2M's is because the propeller efficiency was not good

Click to expand...

Is this due to a high tip velocity, or the geometry of the blades? I remember the F4U-1's 13'4" propeller causing problems at high altitude as well.

Furthermore the speed is stated at Military Power, without the use of Water-Methanol boost

Click to expand...

Do you know what power settings were produced with water-methanol boost?

J2M3 is powered by Kasei 23a

1550hp at Sea Level with Military Power
1575hp at 1800m with Military Power
1410hp at 4800m with Military Power
-
1820hp at Sea Level with Water-Methanol

J2M3 Speed should look like this:
Max Speed: (100% / WEP)
Sea Level: 520kph / 549kph
1000m: 537kph / 567kph
2000m: 555kph / 576kph
3000m: 562kph / 582kph
4000m: 570kph / 601kph
5450m: 596kph / 614kph
6000m: 595kph / 613kph

J2M3 is slightly slower than F6F-5 at low altitudes but more slower at 4000-6000m but it's not like huge difference. On the other hand the raiden has much better rate of climb and acceleration and turn rate over the hellcat.

Although US TAIC uses calculation without realising propeller issues of the Raiden and that the power curve is somewhat different to the official Japanese that they calculated it from we can see how the WEP behaves for this engine.

If it has 1550hp at SL achieving 520km/h and with 1820hp it would do 549km/h

WEP multiplier of 1.1742
However at 2000-3000m due to probably gear shift the WEP at these altitudes doesn't offer the full 1.1742x power over military but it does at 3500-5450m. After 5450m WEP stops to work slowly.

I agree with Laurelix on most of his points except possibly acceleration and turn rate and would like to add that by the time the J2M was encountered in combat practically all Japanese aircraft suffered enormously from poor build quality, suspect fuels, and shoddy maintenance practices. It has been said that the maximum speed of late war German fighters were hampered by as much as 25 mph (40 km/h) for the same reasons and I am quite certain that their Japanese counterparts were no different in this regard. Granted, the standard Hellcat in fleet service would normally not hit factory numbers too but the difference in performance was not nearly as great.

The climb rate of the 'Jack' was it's most potent characteristic. In pristine condition it could reach 20,000 feet nearly two minutes before the F6F, and this is why it was primarily employed as an interceptor. But the Japanese Navy knew of it's many limitations and it was quickly decided to make the far superior N1K their primary fighter from late 1944 onward.

Noted aviation historian Henry Sakaida said that many Japanese pilots openly despised the Raiden because of it's lack of maneuverability, stating that it could not survive against a Hellcat or a Mustang in a dogfight. That's a pretty powerful statement to the overall inferiority of the J2M to other late war Japanese designs and allied types alike.

DarrenW said:

I agree with Laurelix and would like to add that by the time the J2M was encountered in combat practically all Japanese aircraft suffered enormously from poor build quality, suspect fuels, and shoddy maintenance practices. It has been said that the maximum speed of late war German fighters were hampered by as much as 25 mph (40 km/h) for the same reasons and I am quite certain that their Japanese counterparts were no different in this regard. Granted, the standard Hellcat in fleet service would normally not hit factory numbers too but the difference in performance was not nearly as great.

The climb rate of the 'Jack' was it's most potent characteristic. In pristine condition it could reach 20,000 feet nearly two minutes before the F6F, and this is why it was primarily employed as an interceptor. But the Japanese Navy knew of it's many limitations and it was quickly decided to make the far superior N1K their primary fighter from late 1944 onward.

Click to expand...

That performance is official good quality. Issue lies with the propeller design

Besides the level speed advantage, the F6F could also out dive the J2M and take far more punishment. It should also be remembered that although it was designed for naval use the Raiden couldn't operate at sea and because of this the navy would have served itself better by adapting the army's Ki-84 instead and abandon the J2M altogether. But then again the Japanese navy and army hated each other almost as much they did the enemy so that idea would've been completely impossible at the time.

Prop efficiency was a problem on the J2M's which caused their lack of top speed. US Calculations were based on information they knew and didnt know about the propeller efficiency issue, so they calculated the performance of how fast a Raiden might be without prop issue.

Laurelix said:

J2M2:
Empty Weight: 2348kg
Loaded Weight: 3210kg
Wing Area: 20.05m2
Engine: MK4R-A Kasei 23a
Take Off: 1820hp / 1575hp at 1800m / 1410hp at 4800m
-
Max Speed: (Military Power)
596km/h at 5450m
-
Rate of Climb: (Military Power)
Time to 6000m: 5:38
-
Turn Time:
17 seconds
-
Stall Speed: (At Sea Level, No Flaps)
157km/h IAS
-
Armament:
2x 7.7mm Type 97 (550 rounds per gun)
2x 20mm Type 99 Mk 2 (100 rounds per gun)

———————————————-

J2M3:
Empty Weight: 2490kg
Loaded Weight: 3440kg
Wing Area: 20.05m2
Engine: MK4R-A Kasei 23a
Take Off: 1820hp / 1575hp at 1800m / 1410hp at 4800m
-
Max Speed: (Military Power)
596km/h at 5450m
-
Rate of Climb: (Military Power)
Time to 6000m: 5:40
-
Turn Time:
18 Seconds
-
Stall Speed: (At Sea Level, No Flaps)
163km/h IAS
-
Armament:
2x 20mm Type 99 Mk 1 (190 rounds per gun)
2x 20mm Type 99 Mk 2 (210 rounds per gun)

———————————————-

Click to expand...

Just a comment on the J2M2 and J2M3 speed. Wouldn't the heavier J2M3 be slower than the J2M2 with the same engine? It is heavier by 140kg empty and 230kg full than the J2M2. I know Francillon might be outtaded but he lists the 596kph for J2M2 but 583kph for the heavier J2M3, it makes much more sense to me.

Based on the WEP numbers mentioned earlier the J2M3 would do about 600kph at 6000? Or maybe the numbers in the japanese table on the previous page showing 596kph for M2 and 611kph for M3 should be reversed or something (how can the heavier M3 be faster)? And IF that was at Mil Power, then with WEP should be about 630kph for M2 and 610kph for M3?

mack8 said:

Just a comment on the J2M2 and J2M3 speed. Wouldn't the heavier J2M3 be slower than the J2M2 with the same engine? It is heavier by 140kg empty and 230kg full than the J2M2. I know Francillon might be outtaded but he lists the 596kph for J2M2 but 583kph for the heavier J2M3, it makes much more sense to me.

Based on the WEP numbers mentioned earlier the J2M3 would do about 600kph at 6000? Or maybe the numbers in the japanese table on the previous page showing 596kph for M2 and 611kph for M3 should be reversed or something (how can the heavier M3 be faster)? And IF that was at Mil Power, then with WEP should be about 630kph for M2 and 610kph for M3?

Click to expand...

Laurelix said:

J2M3 is powered by Kasei 23a

1550hp at Sea Level with Military Power
1575hp at 1800m with Military Power
1410hp at 4800m with Military Power
-
1820hp at Sea Level with Water-Methanol

J2M3 Speed should look like this:
Max Speed: (100% / WEP)
Sea Level: 520kph / 549kph
1000m: 537kph / 567kph
2000m: 555kph / 576kph
3000m: 562kph / 582kph
4000m: 570kph / 601kph
5450m: 596kph / 614kph
6000m: 595kph / 613kph

J2M3 is slightly slower than F6F-5 at low altitudes but more slower at 4000-6000m but it's not like huge difference. On the other hand the raiden has much better rate of climb and acceleration and turn rate over the hellcat.

Although US TAIC uses calculation without realising propeller issues of the Raiden and that the power curve is somewhat different to the official Japanese that they calculated it from we can see how the WEP behaves for this engine.
View attachment 584345
If it has 1550hp at SL achieving 520km/h and with 1820hp it would do 549km/h

WEP multiplier of 1.1742
However at 2000-3000m due to probably gear shift the WEP at these altitudes doesn't offer the full 1.1742x power over military but it does at 3500-5450m. After 5450m WEP stops to work slowly.

Click to expand...

I agree on all the J2M3 performance assumptions Laurelix stated. There seems to be a lot of contradictions about J2M2, M3 M4 and M5 performance, so I seeing a J2M3 faster than J2M2 isn't such a surprise. I think it's an error. Also weight doesn't affect top speed that much. I'd guess J2M3 should be 2-4kph slower due to weight increase (but idk really).

I hope a small topic change won't be a bad thing:
I'm trying to learn about J2M5 performance now. It's because I'm making a bug report for War Thunder about J2M5 engine performance and its climb and speed. At the bottom, I'll put all the sources I have gathered so far, together with duplicates from this thread for organisation purposes. I can delete them if you want ofc.

What I'm wondering about J2M5's Kasei 26 engine:
Most sources state 1510 hp at 2800m, 1410 hp 6800m and 1310hp at 7200m
In [13] "The Technical History of Mitsubishi Aero-Engines", they say that Kasei 26 supercharger diameter was enlarged compared to Kasei 23, which would explain raised critical altitudes (2800m and 6800m). However I guess those crit. alts are stated with top speed ram effect, becasue they state J2M5 top speed being at 6585m or 6800m. If crit alts were given without ram effect, then top speeds would have to be higher, above 7km. This is in contrast to J2M2 and J2M3 data, that seems to have critical altitudes with no ram effect, because they are lower than top speed altitudes. What do you all think?

When it comes to 1310hp at 7200m, it seems ridiculous that they would make a 3rd speed with only 400m difference, and so big power drop (90hp), that it might as well not exist. It's becasue a natural power drop above a crittical altitude of this engine at this altitude is similar to 90hp. It seems obvious that there is no 3rd stage but I can't find a definite proof. Only statements about increasing supercharger diameter [2] and [13] or stating a 2nd supercharger speed, not 3rd in a table [5] and [6].

The source references:
[1] Eagles of Mitsubishi: The Story of the Zero Fighter (1981), Jiro Horikoshi, ISBN: 9780295958262
J2M Raiden Performance
[2] The History of Mitsubishi Aero-Engines (2005), page 96 and 110, chosha Matsuoka Hisamitsu ; kanshū Nakanishi Masayoshi, Hisamitsu Matsuoka, Masayoshi Nakanishi Miki Shobō, Tōkyō, ISBN:9784895224611, 4895224619
[3] Japanese Aero-Engines 1910-45 (2017), Mike Goodwin, Peter Starkings ISBN:9788365281326
[4] I.J.N Interceptor Raiden (J2M series) PICTORIAL BOOK, MODEL ART, (1996)
[5] 局地戦闘機「雷電」 : 異貌の海鷲 (文春文庫) ICBN: 9784167249137
国立国会図書館オンライン | National Diet Library Online
(Not 100% sure it's from this book. I got this from this link below)
J2M Raiden Performance
[6] Famous Airplanes of the World Navy Interceptor "Raiden" | 1996| No. 61 ISBN 10: 489319058X
[7] Specifications_and_Performance_of_Service_AirPlanes_of_the_I.J.N (1945) https://ww2aircraft.net/forum/attachments/japanese-aircraft-performance-pdf.363376/
[8] JAPANESE AIRCRAFT PERFORMANCE & CHARACTERISTICS T A I C MANUAL "°l (1945-06-01) ASIN ‏ : ‎ B00442OU92
Japanese aircraft: performance & characteristics, TAIC manual no.1. - World War II Operational Documents - Ike Skelton Combined Arms Research Library (CARL) Digital Library (oclc.org)
[9] 海軍局地戦闘機―本土上空を死守せよ! (2004) ISBN-10 ‏ : ‎ 476981206X
J2M Raiden Performance
[10] 日本の航空機 海軍機篇, 岡村純・巌谷英一, (昭35)
22/4/18 J2M4 Kai incorrect armanent and missing turbocharger
[11] 戰史叢書
22/4/18 J2M4 Kai incorrect armanent and missing turbocharger
[13] The Technical History of Mitsubishi Aero-Engines

Hi Alpakinator, for J2M5 you have the secondary research by WW2航空機の性能:WarbirdPerformanceBlog Look for his <Discussion 13> Raiden 33 and Mars 26. He is not super familiar with technical terms but combining with "History of Mitsubishi Engines" you get better sense. He describes the differences in performance of Kasei 26a been theoretical calculations vs what actually went into service. Maybe J-wiki is worth looking also on Kasei engines.

This is what I surmised a few months ago-
The Raiden Model 33 (J2M5) was a 2 speed NOT 3 speed supercharger, the error of 3 speeds came as (some) specifications of the Kasei 26a gave 3 values, English technical interpreters took it as 3 speeds. The Kasei 26a had two supercharger ratios like all Kasei 2x series has, but the Kasei 26a two gear ratios are 7.7 & 10.1 , against earlier Kasei 2x ratios 7.0 & 9.12 ,and J2M5 also had improved air ram passages in the cowl and a 10mm smaller supercharger housing (for a "tighter fit" supercharger fan inside it). These three changes were the reason for its very improved high altitude performance.

Thanks taly01! I got a nice resource from WW2航空機の性能:WarbirdPerformanceBlog, showing higher gear ratios of Kasei 26. However in the reposnse to my other post Question about "three speed and three-stage superchargers"
you mentioned (2-3)The_History_of_Mitsubishi_Aero-Engines.pdf and i couldn't find Kasei 26 gear ratios there, only the 7.0 and 9.12 of Kasei 23. They also mention that Kasei 26 supercharger diameter was increased compared to Kasei 23. Here's a google translate of that section:


Could they both increase diameter of blades and shrink the housing that you mentioned? It seems unlikely.

I can't from memory find where I saw it but I thought it was a table of supercharger fan and housing sizes, its possible I created it in trying to make sense of the conflicting information, J-wiki says its a smaller fan (but one researcher says no one really knows the size for sure) and Mitsubishi history says its a larger fan? Given the great praise of the J2M5 it must be more than just a gear ratio change? It is a technical question but its performance remains.

Ask the man who owns one.
GregP

Laurelix said:

I still think TAIC is way too overoptimistic. To get 671 out of J2M3 would be unrealistically low drag for such a bulky plane.
Ki-43-II according to TAIC has 558km/h at 6000m whereas japanese recorded 515km/h at 6000m at military power (530km/h with WEP, calculated)
theres nothing in taic regarding overload max speed for J2M.

Click to expand...

The J2M is a lot of things, but bulky isn't one of them. It looks big in pictures when it is the only airplane in the pic but, next to another fighter of western origin, it isn't large.

Let's compare it to the P-51 Mustang, which is not exactly a large airplane.

The Mustang is 726 pounds heavier when empty and 2721 pounds heavier when at gross weight.
The Mustang has 9% more wing area, but the weight means the Mustang, at gross weight, has a wing loading of 41.7 pounds per square foot while the J2M has a wing loading of 32.8 pounds per square foot. So, the J2M should turn quite a bit better at any altitude.
At takeoff and gross weight, the Mustang is 6.58 pounds per HP. At WER, the P-51 is 5.70 pounds per HP. The J2M is 3.93 pounds per HP at gross and should easily outclimb and out-accelerate the P-51.
They are almost exactly the same length (32.25 ft for P-51 and 32.66 ft for J2M).
The J2M has 1.6 ft less wingspan than the P-51.

"Ask the man who owns one."