J2M Raiden combat history

[Mister Fork]

LOL.....many of you still don't understand that simply putting higher octane gas in a plane designed for low octane gas will do nothing to improve the performance.

That only works on cars that have knock sensors in their digital fuel injection systems.

Didn't any of you read the recent thread about this?

I know right! They (the plane mechanics) tuned the engines injection systems to work with the gas they had, not gas they WISHED they had. Performance is performance. I can bet that any performance figures from the country of origin is based on gas they HAD.  Not post-war stuff. 

[oboe]

The difference in octane rating was always the explanation I'd heard for the higher TAIC numbers.  I'm not sure what numbers the TAIC numbers are in disagreement with, since it seems unlikely that Japan would publish performance data for an aircraft developed during wartime...

[Krusty]

Oboe, there's more to it. If an engine is designed for 87 octane and you put 100 octane in, you need to tune and adjust it so you can get more compression out of it.

If the engine is designed and built to run on 130-octane because you were far too optimistic, then you down-rated all the power settings in all your pilot training and all your documentation, you could much more easily put 100 octane in it and get more from it.


The latter is closer to the situation the Japanese were finding themselves in. That other octane thread wasn't very useful IMO and there wasn't much "discussion" -- just one point of view trying to promote a preconceived notion, not trying to find the real answers.

The truth is that the TAIC numbers on numerous tests with captured Japanese aircraft achieved better performance out of their retuned or repaired engines than the Japanese who flew them in combat enjoyed. Any and all TAIC numbers should be discounted across the entire field of aviation testing. At the time it was all they had, but it was flawed testing methodology and flawed results.

[oboe]

Oboe, there's more to it. If an engine is designed for 87 octane and you put 100 octane in, you need to tune and adjust it so you can get more compression out of it.

If the engine is designed and built to run on 130-octane because you were far too optimistic, then you down-rated all the power settings in all your pilot training and all your documentation, you could much more easily put 100 octane in it and get more from it.


The latter is closer to the situation the Japanese were finding themselves in. That other octane thread wasn't very useful IMO and there wasn't much "discussion" -- just one point of view trying to promote a preconceived notion, not trying to find the real answers.

The truth is that the TAIC numbers on numerous tests with captured Japanese aircraft achieved better performance out of their retuned or repaired engines than the Japanese who flew them in combat enjoyed. Any and all TAIC numbers should be discounted across the entire field of aviation testing. At the time it was all they had, but it was flawed testing methodology and flawed results.

Thanks Krusty-

But how do we know what kind of performance the pilots who flew them experienced?  After-the-War personal interviews?  Captured documentation from Japanese aircraft manufacturers or military?

I've also heard the Japanese fuels suffered from "quality" problems but not sure if that just referred to lower octane ratings or actual contamination from either production or transportation difficulties.

[Krusty]

This is a bit of the problem. Japanese testing wasn't as methodical or logical as some Western counterparts. It also either wasn't documented very well or a lot of the records were lost.

For example, some noted Japanese aces didn't even know what throttle settings they used or the horsepower they were running. They knew what they needed and in my own words was much more of an analog "fly by feel" type of thing at times. Some didn't even recall which type of plane sub-model they flew. However there are some documents and some tests. They are spare but they can be found. They also reflect the down-rating of most late-war engines because of battlefield conditions, bad fuel, lack of quality control when either the engines or even things like pushrods, crankshafts, etc are made. They reflect these problems and also the math seems to add up better.

Remember that towards the end of 1944 into 1945 they were creating turpentine from tree sap (one of the few resources they could make it with) and then thinning down their gas stocks with it because the refining process for the gas was so crude. If they got 87 octane it was a good day. There is even a number of records that the A6M3 was supposedly designed and built for 130 octane but this simply was never available outside of a test.*

It's a murky area, so some people like to cite the abberant TAIC records as gospel because it's easy, even if inaccurate.


* = citation needed, I recall reading about it on this forum, but not if it was m2, m3, or if it was 100 octane or 130 octane. You get the gist of it, though.

[morfiend]

Krusty,

  How exactly does one "tune" and engine to get more compression out of it?  You could get higher manifold pressures and maybe change the ignition timing but you cant get more compression other than changing the piston and/or cylinder head.

  All the higher octane means is it slows detonation issues and allows higher MAP settings.

  I'm sure the Japanese had to reduce MAP because of poor fuel and detonation issues and thus would have less than rated HP.


  You could design an engine with a certain compression ratio and a higher ratio may need higher octane fuel to reach it's maximum manifold pressure,but that engine will still run at lower setting as long and you dont get pre-ignition detonation using a lower rated fuel. It may be necessary to change the plugs and adjust ignition timing but thats all they did when the US went to 150 octane!


   

[icepac]

Sorry Krusty.........they did not deviate from the factory manuals.

They did not "retune" the engines.

Do you even know how much work goes into tuning an engine?.........something I am paid sometimes $500 for a single dyno session?

The engines were not "retuned" to take advantage of the higher octane.

All that happened is that they had a higher safety margin which made it safer to fly them.

Remember how many planes tested after the war had incomplete testing?

There is a reason for that.

Unlike the planes captured during the war which were picked apart and tested endlessly, most planes tested after the war were run until they failed and little time was spent fixing them.

They were often scrapped for minor problems and not fully tested.

Why?......because the war was over.

[Krusty]

Ice, don't confuse what YOU do on engines with what was done in WW2. It was very much a wild west of engine maintenance and repair. They did a lot of things (documented, too) which you wouldn't ever do.

Especially the Japanese, who designed an engine for x horsepower on y gasoline and only ended up producing 2/3 x with z gasoline, so they derated the engines.

Even the Germans derated the engines on Fw190s that were more war weary from the fighting in the west and moved them to the Russian Front. Same engine, same everything, just worn and can't make as much power output, so they derated them and only allowed certain RPM/ATA as the max power settings.

It happened, and it was NOT abnormal.

[icepac]

You are incorrect and arguing way out of your skill level.

[DaveBB]

What did the Pratt & Whitney reps do to R-2800s in the ETO on P-47s to get more HP out of them? 

[icepac]

First they got a prop that could make use of the extra horsepower, then they raised boost and implemented water injection to combat detonation.

Later, they raised the usable rpms but I don't remember if they changed the gearcase ratios.

I visited my friends at udvar hazy this week in the restoration department and we discussed testing of enemy warbirds after the war.

[nrshida]

  How exactly does one "tune" and engine to get more compression out of it?

[icepac]

Back in the 90s during the era of Email Newsgroups, we used to chat with a B-17/B-29 bombardier.  He said the J2M was the only high altitude Japanese aircraft that they encountered on any frequency.  So at least we know it had the speed and high altitude performance to intercept B-29s.

Alt.games.warbirds and alt.games.air-warrior.........also was in alt.games.duke3dediting.

I posted at those two as well as rec.martial-arts and a ton of car and airplane related newsgroups.

J2M was fun in warbirds but that CoFl change in 2005 or so really made it more uber than it should have been.

Stopped flying it after that.

[Gaston]

I think you'll find that non-TAIC numbers show it was slower than the Ki-84 we already have and had a much lower FTH as well. It would be around 370mph at 16K.

That would put it about par with our Ki-61, which was woefully obsolete in 1944 when the J2M was starting to show up:

(Image removed from quote.)

Remember that they had been trying to produce it since 1942 after the Battle of Midway. Setbacks, technical issues with the engine/cowling, bombing factories causing delays etc etc meant that the design didn't roll off the line and into the hands of units until (mostly) Feb 1944. By that time, the N1K2 and the Ki-84, the A6M5b, and other designs were already around. It was too little, too late.

So, it wouldn't be any kind of super plane. It would still be quite the underdog. It would be very cool, though.

   I can't believe that decades after the 389 mph top speed of the Ki-84 has been thoroughly debunked, this ridiculous chart is still using that grotesque figure as a reference... Read captured pilot interrogation accounts for Pete's sake... Or Iwo Jima Radar operator opinions...

  The Ki-84 was a 700 + kph fighter (420 mph), as it should very well be with anywhere near the low weight and high power that it had. To believe otherwise is just to ignore common sense...

  The Ki-44 was 650 kph, so around 405 mph, as quoted in official Japanese documents about the defense of Tokyo.

  Only the Ki-61-1 appears anywhere near the usual quoted figures, being around 595 kph.

  And so was the Ki-100, which, despite that and an extra 200 lbs over the 61, did not keep it from whipping single handed 3 X Ki-84s, switching pilots, and repeating the same feat. (A superiority achieved by using turn-climbing, then firing while turning or diving from the gained altitude, it seems)

  With 1800 hp of course the lightweight J2M was a 400 mph fighter... The Navy had better fuels, and yet the the Ki-84 was 420 mph...

  That the Zero have WEP only in the later 52C models (as claimed elsewhere here) is also highly suspect, since its pilots are quoted that it had only "a little more boost" in the later 52bs. 52s were likely 590 kph and earlier models around 560. 52cs were slower than 52bs due to increased weight...

  Japanese boost was ten minutes, and no official figures recorded its performance values, since the Japanese kept only lower setting data. That the J2M was 650 kph capable is perfectly obvious to anyone who reads any encounter with P-51s. How can these absurd low speed values rise from the grave where they have been buried nearly 20 years is really beyond me.


  Gaston
 

 

 

   

   

[Vraciu]

Necrobump..........what's wrong with this picture?

(Image removed from quote.)

Didn't think a single picture was worthy of a new thread so I added it to the collective here.

For those who wondered...