J2M Raiden Performance

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Laurelix said:
its the best ive got. I dont know kanji myself and i can make out the performance.
Click to expand...

My Wife can read kanji and tries to translate to the extent she is capable of understanding the technical terms.
What book by Horikoshi are you using?
I believe a lot of the problem with bad data comes from early "researchers" who could not read Japanese.
If you can't read the notes, then notes like "max continuous", "climb power", "low blower' and other such details might be missed.

- Ivan.
 
Looking at the Raiden's wing area, weight and engine power, it looks very similar to the French Bloch MB-157. Hope this is helpfull
 
Ivan1GFP said:
Hello DarrenW,
How are you doing? Hope the holidays went well.
I hope I didn't mis-characterize your baby.

- Ivan.
Click to expand...

I've been good, thanks for asking. I hope you're doing well too and that your holidays were as enjoyable as mine were.

And you've always been objective concerning the Hellcat so I can't fault you regarding your take on it's relative merits. At least you haven't called it a piece of garbage like I've read elsewhere on this forum...
 
Hello Laurelix,

Thanks for getting a better scan from the Horikoshi J2M book.
Yes, you are reading the table correctly. It DOES say maximum speed. My Wife just did a quick translation a couple minutes ago.
So, what it is presumably saying is 322 Knots @ 5450 Meters Altitude == 370 MPH.
I would like you to make another observation of the same list of specifications.
Look three rows above the speed specification for the engine power ratings in 1st speed and 2nd speed Supercharger.
Note that the power levels specified there are well below even the Military ratings that TAIC claims for the Kasei 23.
Perhaps these were early versions of the engine before the problems had been worked out.

- Ivan.
 
Laurelix

Just to be clear, the stuff you wrote in the first post is the same as in the scans of the book with the Japanese text?
 
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The Japanese table from Jiro states the take off power (WEP) and then the 2 other powers are actually military power. J2M TAIC states WEP at high altitudes also. But I don't trust TAIC since 2 planes with same engines have different top speed magically and somehow... clearly it's all calculated and guess work using different drag coefficients
 
Furthermore Japanese sources state this for Ha-45-21
Take off: 1990hp (WEP) / 1625hp at 6100m at military power.

US TAIC states
Take off: 1970hp (WEP) / 1675hp at 6100m

the Japanese military power stated for Ki-84 from Japanese sources is below that of US military power at that altitude.
 

Hello Laurelix,

Which row are you reading?
The fourth row down shows engine power. The column for J2M3 says "Same as Left" in kanji. That would be the data for J2M2.
The J2M2 data says 1st speed 1575 HP @ 1800 Meters, 2nd speed 1410 HP @ 4800 Meters.
Where do you see WEP or Take-Off power anywhere in this table?

Regarding the TAIC Data:
One can note that they are not very consistent.
Their engine table actually shows data which is consistent with their data sheet for the Jack 21 even though the aircraft at the bottom says "Jack 11".
I presume this is a case of better information being used in the summary table.


Regarding different top speeds for Jack 11 and Jack 21:
Note that Jack 11 has a maximum speed of 407 MPH at 17,400 feet
Military Power is listed as 1560 HP @ 17,900 feet. -- There is no high altitude WEP rating listed at all.
So why is maximum speed reached at a lower altitude than even the military rating.
This does not make sense. With ram effect, it should be slightly higher......






Now look at maximum speed(S) for Jack 21.
417 MPH @ 16,600 feet. Note that Jack 21 DOES have a WEP rating of 1785 HP @ 16,600 feet.
For Jack 21, Military Power is listed as 1560 HP @ 18,100 feet.




Now if you look at page 2 of the data sheet for Jack 21 for the Speed versus Altitude graph, you will see that for MILITARY power, the Jack 21 achieves around 406 MPH @ around 18,000 feet or almost exactly what the Jack 11 getting for maximum speed at almost exactly the same altitude.
I suspect that TAIC simply had much less information when they published the sheet for Jack 11 and never ran it at emergency power at altitude.
This is why I do not believe there is any actual discrepancy between these two TAIC test as you believe there is.

 

Hello Laurelix,

THIS discussion properly belongs in a thread about the Ki 84 instead of one about J2M.
First of all, WHICH Japanese sources state this this and for which aircraft?
Please note that even though the N1K2-J and Ki-84 both use the Homare 21 / Ha 45-21, there are slight power differences as noted by TAIC. I attribute this to differences in their induction systems and ram efficiency.
Another problem when dealing with Japanese aircraft is remember when the numbers are being quoted in metric HP and noting that this is slightly less than US HP. I tend to gloss over this a lot in discussions, but I do know that it is there.

Regarding military power differences between Japanese and US sources, they may not be for the same versions of engines as Hiromachi pointed out in a very interesting thread. Also, one has to note the date of the information and determine whether it is representative of the aircraft you are interested in.
I believe the Middletown test report gives pretty good confidence that the Homare 21 / Ha 45-21 was actually capable of achieving the power levels attributed to it WITH the fuel that was available to the Japanese.
Even with this level of power, there are many that believe (for quite legitimate reasons) that the Ki 84 never could achieve the speeds claimed for it.

- Ivan.
 
Gentlemen,

Attached is the other TAIC data sheet (A1) for the Jack 11 that I believe supports my argument that the tests of Jack 11 were conducted without proper knowledge of the aircraft's engine. Please look at the speed versus Altitude graph for Military and "War Emergency" Power and contrast those against the same graphs from sheet B1 from Jack 21.



Please note that the War Emergency and Military curves match above 20,000 feet.
Note that in the same graph for Jack 21, AT NO ALTITUDE do the War Emergency and Military graphs match.
Why would there be a difference????
The answer is actually pretty simple.
The War Emergency setting for Kasei 23 isn't just a boost pressure increase but also a RPM increase and it does not appear that TAIC knew that or took that into account when they were testing Jack 11. This RPM increase can be seen in the TAIC Kasei engine data posted earlier.

- Ivan.
 
May I ask on what do you base your assumption that the above graph is based on actual Jack 11 test ?

In the very Introduction of the TAIC No. 1 (page 3 of the original document) it is stated that: "Except where otherwise stated, performance figures represent estimates of the Technical Air Intelligence Center and have been calculated after a careful analysis of information derived from intelligence, captured equipment, drawings, and photographs using power ratings derived from the same sources. When authoritative evidence is not available, it is the policy of TAIC to give the Japanese Aircraft performance every benefit of the doubt within reasonable limits".
The above comes from original TAIC No. 1 document from December 1944 and nowhere is it stated that performance figures are anything more than calculations. Jack 21 data were first mentioned in TAIC No. 1 supplement 2 and neither there is it stated that information are based on actual real life tests. Final Jack estimates were posted in August 1945 TAIC No. 1 Supplement 5, which provided also "preliminary estimate of performance" of J2M4 (i.e. variant with turbocharger). But again and for the last time, there is no statement coming with the figures, that data are based on a live test.

Note that certain data are either based on live test or captured documentation usually is provided in General Data section. For example in regard to Oscar 2 TAIC 152A-2 from May 1945 it is stated that: "A captured handbook states that the maximum radius is 560 miles after allowances for take-off and 20 minutes of combat. It further states that diving speed is to be limited to 370-400 mph". The speed data in that chart are in line with Japanese documentation (top speed for Oscar 2 is 333 mph at 19,100 ft), while previous report for Oscar 2 from December 1944 gave it a more optimistic performance with top speed of 347 mph at 20,000 ft.
So information from TAIC should be taken with a decent pinch of salt and treated as estimates, not live tests unless proven otherwise. That is the rule of thumb that was applied by default, which is surprising why in this and other threads the opposite is taken.
Of course another story is the fact that Laurelix quotes some performance calculations for various aircraft, produced by himself or somebody else, which look awfully close to the data sheets produced for a particular game, an arcade flight simulation to be specific.
 
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Also, forgot to mention the engine performance data. There are a lot of mixed information about Kasei 23 ko, however one of the Japanese publications (of Gakken Pictorial Series, also known as Gakken Rekishi Gunzo) some time ago published bits from J2M technical manual. Kasei 23 Ko is stated to have following performance:
Take-off: 1820 HP / +450 mmHg MAP / 2600 RPM
1600 HP / + 300 mmHg MAP / 2500 RPM / 1st stage
1520 / + 300 mmHg MAP / 2500 RPM / 2nd stage
The above is confirmed in another publication I have and in Jiro Horikoshi's publication.

Since drag and propeller were also brought into the discussion, Jiro Horikoshi provided specification for 14-Shi fighter (later to become J2M1) among which was calculated drag of 0.0249. In regard to J2M2 - 3 it's 0.0265 and prop efficiency is 0.74 (source: 堀越・奥宮の「零戦). English version of Jiro Horikoshi's publication is less detailed, but still contains a 14-Shi publication.
 
Hello Hiromachi,

Glad to see you here.

Hiromachi said:
May I ask on what do you base your assumption that the above graph is based on actual Jack 11 test ?
Click to expand...

There were multiple flyable examples of the Jack 21 and a pretty extensive evaluation. As you point out, things are much less certain about Jack 11. I have already pointed out that TAIC didn't seem to know what they were doing in the "test" of Jack 11. It would make pretty good sense if that test were actually a performance estimate with not so good information.


Discussion about Oscar 2 is a bit off subject but also somewhat indicative of at least how *I* am interpreting this information.
The initial evaluation shows War Emergency Power to achieve 347 MPH.
Since the Japanese really didn't list a WEP rating, the Take Off rating was used up to the altitudes to which the supercharger was able to maintain it.
The speed data in the Japanese manual certainly does not use "Emergency Power" and may be even less than "Military" Power.
If this is the same as the translated copy of the captured manual I got from J-Aircraft a few years ago, this is also discussing the long wing Oscar 2 while the TAIC description is of the short wing version.
There are also notes in the translation that the IAS and TAS do not make sense and there are some other issues in this translation that I brought up earlier in a discussion about turn performance.

A note by the analyst at the end of the manual translation is also interesting:

This document shows OSCAR to be a ship of fair performance, good climb, and excellent maneuverability. There is no evidence that OSCAR pilots take the restrictions seriously and they seem to get away with it. The engine limitations appear to be too stringent and the performance in ATAD #T1 is based on power ratings slightly higher than those presented here. There have been reports of OSCAR showing high "flash" performance and it is possible that some sort of power-boost may now be incorporated. There is reason to believe that Jap pilots prefer OSCAR to the higher performing TOJO and TONY.

An actual account of a pretty similar engine being "abused" under combat conditions can be found in one of the books by Saburo Sakai that describes his engagement against multiple Hellcats.


Note that there is no attempt to use Take Off Boost and RPM at altitude. TAIC was working on the assumption that since this was possible, the Japanese pilot might do it as Sakai did.


It is not surprising that J2M1 is lower drag considering the canopy differences. As for the propeller efficiency, WHICH propeller is being described here? Is it the 3 blade version from J2M1 or the one of the 4 blade versions in the later aircraft? Note also that eventually they figured that propeller blade stiffness or lack contributed to the engine vibrations and there were attempts to modify the propeller to solve this problem.

- Ivan.
 
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Yes, there was extensive evaluation just like with the N1K1-J, Ki-61, Ki-44 and Ki-84. But scope of this evaluation was not the maximum performance (speed or rate of climb) but flying characteristics. The latter ones were of primary interest because allowed US pilots to exploit whatever flaw were found.

The discussion about Oscar 2 was brought as an example of situation where TAIC indicates different set of data used to produce the information. And yes, initial evaluation indicated 347 mph top speed with War Emergency Power. But top speed curve in graph on opening page also listed what I think is 342 mph at 21,000 ft Military Power. The speed in Japanese documentation indeed is based on rated power, however you are mistaken as to the assumption that specific manual was indicative of performance of a long wing version (11.437 m wingspan). I have this long wing version piloting handbook too and it gives a top speed of 515 km/h (aprox. 320 mph), whereas the short wing is rated for 536 km/h (aprox. 333 mph) which is exactly what is listed in TAIC 152A-2.
Again, the focus is not the Oscar performance but the fact that whoever compiled the report indicated specifically that performance data are based on captured Japanese handbook. If no such note would be there, it should be assumed that data are based on estimates.

4 bladed propeller, thought its pretty obvious from the text. J2M1 propeller was supposedly rated at 0.70, but J2M2 - 3 four bladed unit at 0.74

Modifications to increase propeller rigidity are a one thing, but other is poor efficiency of Japanese propellers. This was discussed on j-aircraft some time ago. I also have somewhere on my hard drive (cant find it right now) a report indicating that Sumitomo in general had issues with producing high quality and optimal blades for the propellers. Furthermore it was stated that Sumitomo and Mitsubishi / Nakajima did not cooperate and there was no supervising institution that would make two companies work together since engine and propeller construction where directly related to each other. One peculiar note was that Japanese were unable to produce a thin blades for their newer propeller designs such as N1K2-J and this cost them performance. Thin blade designs had a tendency to crack. However report indicated that eventually such prototype of thinner blade was produced for N1K2-J and it increased top speed of George by aprox. 10 knots (if I find the report, I will quote it in greater depth, right now Im mentioning what I remember).
 
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