J2M Raiden

[CORSNING]

Vanir is correct. Top speed is only used to get to or away from a fight in combat. TAIC reported the War Emergency top speed of the J2M3 as 359 mph./S.L. As I stated before pilots who flew the Jack praised its ease of handling up to 325 mph. I have never read anything that said the controls on the J2M3 get so stiff that it could not be manuevered at higher speeds. The Spitfires 14's top speed at +18 lbs. is 359 mph./S.L. also.

 

[Vincenzo]

. I used power figures from the Griffin 65 at +18 boost sinse that was the boost used from January 8, 1944 to March 21, 1945.

i can ask what boost was used before and after of this ?

 

[CORSNING]

January 8, 1944 the Mk.14 entered combat. In 1945 a few were prepared to handled +21. It is not known if +25 was ever used in combat.

 

[Vincenzo]

thank you

 

[CORSNING]

The figures that follow relate to any given Spitfire. She was a beautiful bird and one of the absolute best to ever sail the skies. Within her realm she was supreme. The Jack was an after thought that was close to being abandoned at one time. It was resurrected because of its exceptional climb. In the latter stages of the Pacific war a lot of Japanese fighters suffered from lack of quality and maintenance. So while the following figures relate to the standard Mk.14 Spitfire, the figures for the Raiden apply to those in excellent condition only: The figures are for War Emergency Speed (mph) / Maximum Climb Rate (fpm).

Height.........Spitfire Mk.XIV...J2M3

Sea Level......359/4,700.......359/4,835
.1,000m........376/4,675.......374/4,940
.2,000m........390/4,625.......380/4,650
.3,000m........405/4,510.......382/4,270
.4,000m........416/3,850.......403/4,320
.5,000m........415/3,690.......415/4,350
.6,000m........422/3,670.......410/3,760
.7,000m........434/3,510.......404/3,160
.8,000m........448/2,960.......394/2,440
.9,000m........444/2,400.......383/1,850
10,000m........437/1,875.......368/1,150

Power and wing loading were on the Jack 21's side as long as the engine held out. Above 20,000 ft. (6,000m+) the mighty Griffin 61 or 65 took over.

 

[GregP]

Kreighund, I am astounded. You say the only way to get a real performance analysis is by SOFTWARE?

Software implies a thorough analysis of the aircraft, which results in performance equations and accurate performance graphs. Exactly where do you think the performance analysis will come from?

If we had the performance results, we wouldn't be having this discussion, we'd know.

There seems to be whole generations that think a flight sim is accurate, but it really isn't accurate unless the model is correct. The only aircraft with accurate models are well documented. WWII prototypes or short-run production types cannot possibly be accurately modeled unless we restore one and test it rather thoroughly. VERY unlikely. If anyone restores one, they fly it very carefully. They don't thrash it to see what it can do!

Software is only as good as the programmer, and always will be only that good, I think ... at least until the software starts self-learning. When it does, we are done as a species.

 

[krieghund]

Kreighund, I am astounded. You say the only way to get a real performance analysis is by SOFTWARE?

Greg, I wasn't talking about software that costs $19.95. I talking about the stuff we use here to calculate mods to aircraft and fitting stores. It must be thoroughly investigated and substantiated before we go to flight trials. By inputting all the physical attributes a reliable drag value can be obtained.

If we had the performance results, we wouldn't be having this discussion, we'd know.

This is the problem, you have one set of data that says the J2M3 goes 369 mph and another that goes 400+. That is a wide variance to calculate the drag.

Of course the other options are to fly the surviving aircraft, have one duplicated or put it into a full scale wind tunnel. Without knowing the drag value we will be discussing this until the cows come home.

 

[CORSNING]

Sagittario64,
Are you still out there buddy? I have been working on graphs and figures for the J2m3 vs. La-7 of 1945. The La-7 was one of the top four VVS fighters at the end of the war. The side by side comparison was actually suprising to me. The Raiden compares very well to the Lavochkin. The following figures are for the La-7 No.452132-76 production test trials of April 1945: Height (meters) / Speed (mph) / Climb Rate (fpm):

S.L........383 / 4762
.1,000...397 / 4762
.2,000...411 / 3936
.3,000...408 / 3660
.4,000...401 / 2952
.5,000...405 / 2952
.6,000...418 / 2499
.7,000...414 / 2007
.8,000...405 / 1495

The Raiden could outclimb the La-7 at any altitude. Maximum speed was fairly close. The La-7 had a 24 mph advantage at sea level, speed was even around 3,000m and the J2m3 had a 10 mph advantage around 6,050m. The la-7 regained the advantage above 5,500m. Both planes had excellent turning ability. The La-7 had an advantage in roll rate from what I can tell. It was comparable to the Fw-190. Just an opinion: the Raiden probably ruled the vertical and the La-7 probably had a slight advantage in the horizontal.

 

[GregP]

My entire contention is that the J2M Raiden was never documented with accuracy, with the power settings, propeller settings, any boost settings, or any OTHER settings. What we have is factory basic data.

And it is self contradictory. Logically, it looks very much like a P-47 (we have the only J2M in existence at the Planes of Fame) and it is very slick. If would be fast and would climb well. The J2M pilots we have had speak at the museum say they could disappear vertically from any American figher they encountered, but were not quite as fast ... but could catch a B-29 ... barely.

I'd really like to restore the J2M to flight status, but intergrannular corrosion on the wing spar (or spar caps) is the issue. Someone has to fund the resto ... and nobody has stepped up to do so.

 

[spicmart]

I wonder how the Raiden would have fared if it had gotten the same enignes as the Hellcat and Corsair?
Or any of the other top japanese fighters.

 

[tomo pauk]

In case they can fit it, we'd probably see a 700 km/h fighter.

 

[spicmart]

With a much better power to weight ratio. Would be the question if it can take the enormous horse power structurally to use full potential. It certainly could challenge a Bearcat then.

 

[GregP]

Part of the disparity in J2M performance might perhaps be due to the fact that when we tested it over here, we used our own fuel. The Japanese may well have achieved only 369 mph if they were running on 87-Octane type fuels, I have no way to verify at this late date, but the reports are that the fuel wasn't the best for most of the last half of the war.

Perhaps we are hashing over things that are easily accounted for, perhaps not.

Stranger things have happened.

 

[Shortround6]

I wonder how the Raiden would have fared if it had gotten the same enignes as the Hellcat and Corsair?
Or any of the other top japanese fighters.

In case they can fit it, we'd probably see a 700 km/h fighter.

As Tomo has noted In case they can fit it.

The engine in a Raiden went a bit over 1700lbs. The engines in the Hellcat and Corsair went 2480lbs. Then to make use of the power you need a propeller like the Hellcat and Corsair used. About 480lbs for the big 3 blade units.
Engine used in the F8F-1 Bearcat weighed a mere 2359lbs despite loosing the auxiliary supercharger.

A Raiden loaded but clean weighs around 500lbs more than an F8F-1 does empty.

Interesting photo:

The Raiden was actually a pretty small airplane compared to the American aircraft.

 

[tomo pauk]

As Tomo has noted In case they can fit it.

The engine in a Raiden went a bit over 1700lbs. The engines in the Hellcat and Corsair went 2480lbs. Then to make use of the power you need a propeller like the Hellcat and Corsair used. About 480lbs for the big 3 blade units.
Engine used in the F8F-1 Bearcat weighed a mere 2359lbs despite loosing the auxiliary supercharger.

A Raiden loaded but clean weighs around 500lbs more than an F8F-1 does empty.

Interesting photo:
...
The Raiden was actually a pretty small airplane compared to the American aircraft.

Yes, it was a small aircraft when compared with US mid-war stuff, even the Wildcat was bigger.
The Raiden's engine went to almost 1900 lbs due to the extension shaft, fan, gearing for fan and neccessary strengthening. The single-stage R-2800 'B', as used on B-26 or A-26, was as wide and as heavy, so it should've been an easier fit than the two-stage version. Ditto for the 12.2 ft four bladed unit vs. bigger 3-bladed ones.
The Kasei was making better altitude power than 1-stage R-2800, however.

 

[GregP]

I can tell you this. In person, the cockpit is enormous!

American fighters had big cockpits relative to British fighters. Most Japanese fighters had small cockpits, too. But the cockpit on the J2M has more room in it than any other cockpit I have seen on any other WW2 or post-WW2 fighter. You might be able to get two people in there, side by side!

Look at the pic above and compare the cockpits of the Hellcat and Spitfire with the J2M with them.

Below is the Planes of Fame J2M-3 sitting outside Fighter Rebuilders at Chino last time we had it out for an event.

The Yokosuka D4Y is in the background. The J2M is static and the D4Y is a bit better than static. You can start it up and taxi it, but the structure is not airworthy at this time. It would need new longerons and a new wing spar. Who knows, it could happen someday.

 

[BiffF15]

Greg,
Do you guys have any history on yours? Also, do you have any cockpit shots?
Cheers,
Biff

 

[GregP]

Hi Biff,

We know when and where it was captured, and we know the manufacturer's serial numbers bacause the data plate is still attached. We also know the unit it was assigned to and the markings because they were still on the plane when it was captured. From that, we can dig out other items of interest, but we have no specific combat history on the airframe as far as I know. To be complete, I'll check again this coming weekend.

I sent you a PM about cockpit shots.

All the best, - Greg

 

[Laurelix97]

From Jiro Horikoshi's book (The designer of A5M, A6M, J2M, A7M)

All performance is with Japanese 92 octane fuel. The engine wasn't built to run on higher fuel.

J2M2:
Wing Area: 20.05m2
Loaded Weight: 3210kg
Engine: Kasei-13
(1820hp at sea level at WEP / 1420hp at 2,600m at military power / 1300hp at 6,000m at military power)
Max Speed: 596km/h at 5,450m at military power
Time to 6,000m: 5:38 at military power
-
J2M3:
Wing Area: 20.05m2
Loaded Weight: 3440kg
Engine: Kasei-23A
(1820hp take off power / 1600hp at 1,300m at military / 1510hp at 4,150m at military)
Max speed: 596km/h at 5,450m at military power
Time to 6,000m: 5:40 at military power
-
J2M4:
Wing Area: 20.05m2
Loaded Weight: 3947kg
Engine: Kasei-23c
(1820hp take off power / 1420hp at 9,200m at military power)
Max speed: 590km/h at 9,200m at military power
Time to 10,000m: 19:30 at military power
-
J2M5:
Wing Area: 20.05m2
Loaded Weight: 3507kg
Engine: Kasei-26
(1820hp take off power / 1400hp at 7,200m at military power)
Max speed: 615km/h at 6,585m at military power
Time to 6,000m: 6:20 at military power
-
J2M6:
Wing Area: 20.05m2
Loaded Weight: 3435kg
Engine: Kasei-23A
(1820hp take off power / 1600hp at 1,300m at military / 1510hp at 4,150m at military)
Max Speed: 589km/h at 5450m at military power
Time to 6000m: 5:38 at military power

Note: Performance figures are at military power, thus you should compare it to US fighters at military power.
Based on weight, wing area, wing lift coefficient, stall speed and air density, I calculated their sustained turn time at WEP, 1000m alt no flaps used

J2M2 - 18 seconds
J2M3 - 19 seconds
J2M4 - 22 seconds
J2M5 - 19 seconds
J2M6 - 19 seconds
-
F4U-1a - 21 seconds
BF-109G-10 - 19 seconds
La-7 - 19 seconds
Yak-3 - 18 seconds
Ki-44-II - 18 seconds
Ki-84 (Ha-45-21) - 17 seconds
N1K2-J - 17 seconds
F6F-5 - 21.5 seconds
F4U-4 - 20 seconds

 

[Ivan1GFP]

Hello Gentlemen,
The original question was how would the J2M Raiden have done if it had fought in Europe instead of the Pacific.
I take this to mean how did its performance compare to contemporary fighters in Europe.

My own opinion is that it would have done quite well and would not have been out of place but it would also depend on what altitude it had to fight at. At low altitudes, it was pretty hot, but typical combat against bomber escorts was much higher in Europe and although its altitude performance was good by Japanese standards, it wasn't good by European standards.
(1560 HP @ 17,900 feet Military Rating)
Then again, if it was operated in Europe, it probably would have had better than the Japanese Navy 92 octane fuel and would not have needed water-methanol injection most of the time.

The J2M seems to have had a lot of problems with its engine installation but the basic engine was a proven design that powered many other aircraft such as the G4M Bomber, B6N Torpedo Plane and H8K Flying Boat. This might have had something to do with the time it was produced more than the design itself.

As for swapping engines, the whole concept of this aeroplane was to fit a very large diameter high powered bomber engine into a fighter.
The engine was very wide but not very deep, so I am guessing that to convert to a P&W R-2800 would require quite a bit of structural modification.
As for using the additional power, I do not believe this would have been a bit deal.
Note that there were two different propeller blade designs used on Raiden. They are noticeably different at the root of the blade.
The propeller is 3.30 meters (10 feet 10 inch) diameter but apparently was sufficient to handle 1870 HP in its current state... and that was for the "lower activity factor" version that was installed in the aeroplane tested by TAIC.
The biggest issue that it was having for performance was that Kasei 23 did not make that much power at altitude and that is where the P&W R-2800 (two stage) would have helped.
The change would most likely have cascaded into a bunch of other quite feasible changes such as
A Higher Activity Factor propeller as mentioned
A change in the reduction gear to address the higher RPM of the R-2800. (The Kasei only ran at 2500-2600 RPM max.)
and probably a serious adjustment in propeller pitch range to account for differences in power coefficients between the two installations.
There might be some differences in fuel consumption to address.
The J2M3 carried 390 liters in the main tank ahead of the cockpit along with a 90 liter tank in each wing root....
...but it also carried a 120 liter water-methanol tank ahead of the fuel tank.
With better fuel, perhaps the volume taken by this 120 liter tank could be used for additional fuel.

Comments and Thoughts?

- Ivan.