22/4/18 J2M4 Kai incorrect armanent and missing turbocharger

[Goldkoron 109]

Vehicles affected: J2M4 Kai

 

Issue: Historically the J2M4 Kai featured two wing mounted type 99 model 1 20mm cannons and two wing mounted type 99 model 2 20mm cannons. These cannons are already present ingame, however there were two more type 99 model 1 cannons oblique mounted in the fuselage in a Schrage Musik style setup for attacking bombers.

 

Issue #2: The J2M4 Kai should feature a turbosupercharged engine allowing its rated power without WEP to be 1420HP up to 9200m. Before the recent J2M changes, the J2M4 Kai did have rated engine power up to this altitude and had a controllable turbocharger, but now it has no turbocharger control with a new supercharger gear which does not reach this rated power at altitude.

 

 

 

 

 

 

Solution #1: Two Type 99 model 1 cannons could be added behind the cockpit of the J2M4 which can be activated using the existing Schrage Musik bind ingame that other aircraft already use. Although it is proving difficult to find images beside the one drawing I found that shows where exactly the cannons were fitted. I have seen mentioned at multiple websites that the fuselage cannons were mounted at at 70° angle but no book source for this. The addition of these two upward facing cannons could increase the interest in this premium aircraft and increase sales due to the unique setup.

 

Solution #2: Remove the second supercharger gear and restore the turbocharger system that was in the game before but retain the new aerodynamics changes.

 

 

 

 

 

Sources: 

“Japanese Aircraft of the Pacific War.” Japanese Aircraft of the Pacific War, by Rene J. Francillon, Naval Institute Press, 2000, pp. 392–395.

 

Izawa, Yasuho, et al. J2M Raiden and N1K1/2 Shiden/Shiden-Kai Aces. Osprey Publishing, 2016. (Page number not exactly known because I have the book on a kindle app)

 

 

[Rapitor 10,702]

Thank you for your report, I will investigate.

 

Regards

[s9723 508]

According to this source, oblique guns are two type99 mark2 mod4 cannons.

 

 

Another source mentions angle of the guns. “around 30 degrees”

[Rapitor 10,702]

Your second abstract says that on the 2 made J2M4, only the second one used a Kasei D engine.

We might as well asusme that the current IG model is the other one without the turbo.

 

It doesn't solve the gun issue though, which seems to be missing

[Goldkoron 109]

The J2M4 we have in-game is definitely that second variant because of the longer nose. But the Dai-Nijuichi variant still has the turbocharger on the right side of it, so I am not certain the turbo was removed on the second variant. 

 

EDIT: It shows it on the last drawing that says it is for the Dai-Nijuichi version. It is also mentioned that both J2M4 models had turbocharger problems.

 

EDIT #2: Interestingly, I noticed J2M4 is getting exactly 1420HP at 7000m flat, 1420HP is the stated engine power for 9000m in multiple sources so maybe there was a mix-up.

 

Translating those armanent specifications from s9237 suggests that the oblique type 99 cannons have 150 rounds per gun.

Edited April 13, 2018 by Goldkoron

[PainGod85 8,050]

52 minutes ago, Rapitor said:

Your second abstract says that on the 2 made J2M4, only the second one used a Kasei D engine.

We might as well asusme that the current IG model is the other one without the turbo.

 

It doesn't solve the gun issue though, which seems to be missing

 

The ingame J2M4 model has a modeled turbocharger on the right side of the fuselage.

 

Note the cursor position.

E: It's also missing the exposed exhaust stacks, which would otherwise be visible as on the J2M3 to provide exhaust thrust.

Edited April 12, 2018 by PainGod85

[s9723 508]

21 hours ago, Rapitor said:

Your second abstract says that on the 2 made J2M4, only the second one used a Kasei D engine.

We might as well asusme that the current IG model is the other one without the turbo.

 

It doesn't solve the gun issue though, which seems to be missing

 

There are two types of J2M4. One was made by Mitsubishi and has extended cowling and modified oil cooler. WT J2M4 is Mitsubishi type.

 

Another was made by Naval Air Technical Arsenal.

Both of them have turbo supercharged engine.

 

 

There is a contradict source about oblique gun.

http://gen.lib.rus.ec/book/index.php?md5=7C889D0967CBAB3C7A9BF0FC75152BD7

“According to the plan, Mitsubishi J2M4 should have 2*20mm oblique gun to attack B29 from below. However, it is very likely that the prototype doesn’t have it.”

 

 

 

 

[Rapitor 10,702]

Lot of different information depending on the source.

 

Very interesting though. The truth lies somewhere in all this, we just have to keep digging in

[Goldkoron 109]

I have a feeling they had every intention to add the oblique guns, but they never made it to the prototype before the design was abandoned due to the engine complications. However it is hard to know because I have not been able to find any photos of the prototype that show the fuselage behind the cockpit.

 

EDIT: It depends if the J2M4 ingame is intended to be a production model or the prototype, but it seems in either case the Mitsubishi J2M4 was supposed to have the oblique guns.

Edited April 14, 2018 by Goldkoron

[tester188@psn 1,413]

This is the explanation of J2M4 in the Japanese Navy aircraft name list ordered on November 20, 1944.

• Experimental aircraft, Tentative name, Raiden Model 32 (J2M4)
  • Raiden Model 31 (J2M6) equipped with an exhaust turbine supercharger and two 20 mm Type 99 Mark 2 Fixed Model 4 cannon at front upper.

Source

Spoiler

Historical documents:

 

Quote

實驗機　假稱　雷電三二型

Experimental aircraft, Tentative name, Raiden Model 32 (J2M4)

 

雷電三一型ニ排氣タービン過給器並ニ前上方ニ九九式二十粍二號固定機銃四型二挺ヲ装備セルモノ

Raiden Model 31 (J2M6) equipped with an exhaust turbine supercharger and two 20 mm Type 99 Mark 2 Fixed Model 4 cannon at front upper.

Summary of military secret order: category-5 aviation (軍極秘内令提要：第５類　航空). by Ministry of the Navy (Japan) (海軍省). November 1944 (昭和十九年十一月). Page 7.

JACAR(Japan Center for Asian Historical Records)Ref.C13072067300, (National Institute for Defense Studies)

https://www.jacar.archives.go.jp/aj/contents/pdf/C13/C13072067300.c1160c00005.naireiteiyou_017.0827_01.pdf

https://www.jacar.archives.go.jp/das/meta-en/C13072067300

 

[Rapitor 10,702]

OK.

 

So J2M4 should have a turborcharger, not the current supercharger, and a Schragge muzik in the body.

?

[Goldkoron 109]

11 minutes ago, Rapitor said:

OK.

 

So J2M4 should have a turborcharger, not the current supercharger, and a Schragge muzik in the body.

?

Yes. I believe the devs did a good job before with modeling the turbocharger so I am not sure why the critical altitude was lowered from 9000m to 7000m and changed to 2 supercharger gears.

 

The Schrage Musik would be 2 cannons in the body, there were actually multiple J2M3s that got field modifications for Schrage Musik guns toward the end of the war and I did read that a pilot shot down a B-29 with one on his J2M3.

[s9723 508]

1 hour ago, Rapitor said:

OK.

 

So J2M4 should have a turborcharger, not the current supercharger, and a Schragge muzik in the body.

?

 

Precisely speaking, J2M4 has both turbocharger and supercharger. Engine of J2M4 is similar to Kasei 23a of J2M3, but it has an extra turbocharger stage. Such engine is called Kasei 23b.

 

[Goldkoron 109]

Found another source for the cannons.

 

 

 

[Rapitor 10,702]

One last stretch (mostly aimed at people with japanese skill

 

can anyone get data / power curve for the MK4R-C [Ha-32] 23c  ?

 

That's our engine, and I'd like to submit this as reference to have the new engine set properly, not only changed to turbo randomly.

 

EDIT: maybe something in here: WARNING; PDF IS HEAVY, 650 pages

http://dlisv03.media.osaka-cu.ac.jp/contents/osakacu/kiyo/111C0000001-79.pdf

 

[s9723 508]

16 hours ago, Rapitor said:

EDIT: maybe something in here: WARNING; PDF IS HEAVY, 650 pages

http://dlisv03.media.osaka-cu.ac.jp/contents/osakacu/kiyo/111C0000001-79.pdf

 

 

I just checked the article. It doesn’t mention turbocharged version of Ha-32.

Edited April 21, 2018 by s9723

[Rapitor 10,702]

Damn...

 

I really would like to provide some documentation about the Ha-32 turbocharged to give the devs a solid basis to model the power accurately.

 

1420hp at 9000m is not enough to do some proper work

 

 

[Goldkoron 109]

4 hours ago, Rapitor said:

Damn...

 

I really would like to provide some documentation about the Ha-32 turbocharged to give the devs a solid basis to model the power accurately.

 

1420hp at 9000m is not enough to do some proper work

 

 

Turbochargers at least from what I have seen from other planes who have them in this game tend to maintain an engine's rated power at all altitudes up to a critical altitude. For example, P-47s pretty much run on the same exact engine HP up until an altitude like 8000 or 9000m. Ki-87 maintains same engine HP up until an altitude of about 6000m. Turbochargers only work until the air gets too thin that the turbocharger would start damaging itself trying to bring enough air in to maintain an engine's rated power.

 

J2M4 Kai before the recent update had about 1420HP at all altitudes on 100% until 9000m, and about 1820HP at all altitudes until 9000m with WEP. That might seem like a lot of power, but before the recent flight model update the J2M4 felt like it was twice as heavy as it does now so its climbrate was abysmal even with that extra power. 

 

I do not think any other planes historically used the turbocharged version of this Ha-32 Model 23 engine, so if guesswork has to be applied, I would have the engine start losing power on the same curve the normal J2M2 and J2M3 does from 1420HP but starting at 9000m.

 

I will still be on the lookout for a power curve for this engine, but I am uncertain if it exists.

[Rapitor 10,702]

I don't agree with your interpretation of how WEP should work.

 

If the engine can do 1420HP at 9200m with ram, there is no way on earth that it could do also 1800hp at the same altitude.

 

However, your mention of J2M4 being correct in previous update allowed me to find a power curve from in game. Not perfect, but that'll do it for now.

 

Your Bug Report is submitted. (twice, as per the 1 issue per thread policy)

 

This thread will remain unlocked for 7 days in order to allow anyone with information / evidence / examples to post them.

It will also serve as a place where the developers may post questions for you to answer, so please keep up to date here.

 

Thank you for helping us improving the game.

 

Sincerely,

Rapitor, for the ™ team

[PainGod85 8,050]

Quite honestly, from what I've been reading here, the SL engine power of 18XX hp can only be realized if one of two things apply:

 

1. The engine retained the two-speed supercharger from its previous versions and the turbo was essentially just added to the system later on without any real changes being made to it, or

 

2. the turbo allowed for military power at 9XXX m, and the critical altitude for WEP was subsequently ~1-2 km lower. After all, the Japanese usually didn't test performance at emergency power rating, just military power.

[Rapitor 10,702]

That is what I reported.

 

The japanese datasheet from Burindo mentions 1820HP, which I assume is S.L, and 1420hp at 9200m, which I assume is at top speed with ram air.

 

But then, 1820HP at 9200 is indeed impossible. I extrapolated it to about 7000m, but that was using the same degression as the Kasei 23a, which I am not entirely sure to be 100% legit, although I don't have anything better

[PainGod85 8,050]

On 22.4.2018 at 6:51 PM, Rapitor said:

That is what I reported.

 

The japanese datasheet from Burindo mentions 1820HP, which I assume is S.L, and 1420hp at 9200m, which I assume is at top speed with ram air.

 

But then, 1820HP at 9200 is indeed impossible. I extrapolated it to about 7000m, but that was using the same degression as the Kasei 23a, which I am not entirely sure to be 100% legit, although I don't have anything better

 

Yeah...if the P-47s and P-38s are anything to go by, turbo MAP takes a nosedive worse than on SC engines, probably because the decrease is self reinforcing - lower MAP results in less exhaust to drive the turbine which results in even lower MAP.

Edited April 23, 2018 by PainGod85

[s9723 508]

4 hours ago, PainGod85 said:

Quite honestly, from what I've been reading here, the SL engine power of 18XX hp can only be realized if one of two things apply:

 

1. The engine retained the two-speed supercharger from its previous versions and the turbo was essentially just added to the system later on without any real changes being made to it.

 

I think 1. is very likely to be true. This design can be seen at several Japanese late-war engine.

Green line is Ha-42-21, and blue line is Ha-42-21 ru with adding turbocharger. They have identical performance and sea level. FTH without turbo are 2000m ( 2300 hp ) & 6500m ( 2030 hp), while FTH with turbo are 7200m (2100 hp) & 10400m ( 1770 hp). Adding turbocharger increases FTH of both 1st ans 2nd speed. Lacking of intercooler results in reduced hp at FTH.

 

Then let’s back to Kasei 23. FTH of No turbo Kasei 23a are around 1300m (1600hp) & 4100m (1520hp).  We only know FTH of Kasei 23c 2nd speed is around 9200m (1420hp) with ram(?), but no data of 1st speed is available.

 

In this table from 戰史叢書 , there are two max speed data of J2M4, 318 kt at 5450m & 311 kt at 9200m. Thus FTH of 1st speed with ram might be ~5450m. Hp of 1st speed at FTH should be less than 1600, maybe around 1520+hp?

Edited April 22, 2018 by s9723

[s9723 508]

Power curve of Kasei 23 may look like the drawing.

Edited April 22, 2018 by s9723

[Rapitor 10,702]

Interesting. I will add this to the report.

 

I think that is a fair point, and might explain some stuff