Jack vs. Tojo - Which was better? Why?

Ivan1GFP said:

The J2M3 sometimes had broad blade propellers installed, but the one that was tested did not have those.
They can be recognized by corners at the root of each propeller blade. I don't know if that difference would have improved speed, but I would expect that a bigger propeller would not have been installed if it didn't help anything.

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Just some photographs for a comparison.

- Ivan.

CORSNING said:

J2M3 m21 vs. P-47N.
The following quote is from page 53 of Erik Pilawskii's 'Fighter Aircraft
Performance of WW2'.
" The J2M3 was remarkable for its tremendous flying horsepower, possessing
what was likely the most formidable power loading of any aircraft in the Pacific
war. Meanwhile, the P-47N model was a longer ranged development of the
P-47D, complete with larger wings and increased tankage. Against the 'Jack',
the Thunderbolt would have to rely on its modest speed advantage*, being
inferior to the J2M in every other performance characteristic. With equal pilots
at the controls this would not have been enough, and it is hard to see past a
victory for the J2M3 under normal circumstances."

The normal power loading for the Model 21 was about 3.65 lb./hp. which was
very good compared to the '47N's 5.64 lb./hp.

P-47N (J2M3 with 92 octane and smooth running engine.)
432 (402) mph/6,000 m.
444 (397) mph/7,000 m.
456 (388) mph/8,000 m.
463 (377) mph/9,000 m.
467 (363) mph/10,000 m.

*Modest speed advantage?

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Mr. Pilawskii's view is very simplistic and doesn't take into effect the strategic situation in which the two aircraft were forced to operating within. From late 1944 onward, the J2M was almost exclusively employed within the Japanese home Islands as a point defense interceptor, making the J2M's primary opponents the high flying B-29s and their escorts. The overall performance of the J2M wasn't stellar at these heights, and when pitted against aircraft such as the P-47N it suffered accordingly. His statement concerning the overall inferiority of the P-47N is a difficult pill to swallow, given the fact that it exceeded the performance of the Japanese aircraft in practically every metric at these altitudes, with the possible exception of climb rate.

I am also under the impression that the performance numbers given in the TAIC reports for the 'Jack' were mere calculations. They apparently used an incorrect propeller efficiency which gave overly optimistic results. Flight testing was only performed in order to discovery basic flight characteristics and the airplane was never pushed to any real limit.

Hello DarrenW,

Regarding the altitudes at which the P-47N and the J2M3 might have met, I would pretty much disregard anything past about 8000 Meters.
The B-29s did initially bomb from higher altitudes but found that bombing from the Jetstream wasn't doing good things for accuracy and later bombing missions were from much lower altitude.

Another thing to keep in mind is that the P-47M/N didn't have very good initial acceleration. Being able to get to 460 MPH might be cool, but being able to recover energy after maneuvers is also a great tactical advantage and the J2M wins in that regard. Climb rate and acceleration are both an indication of surplus power.
Regarding my claim about initial acceleration, look for the stories about "Wonderful Winnie", a P-47M in the ETO, whose pilot raced P-51Ds and won.
Initially they would leave him behind, but EVENTUALLY he would catch up and overtake them.

With regard to propeller efficiency, one has to wonder about how poor Japanese aeronautical engineering really was if they could not build a good propeller for an engine that was in production for quite some time before the J2M came along. The Kasei had been in service in bombers for a long time and inefficient propellers would have cost them range which would not have been acceptable.
It also matters at what speeds a propeller is efficient or inefficient.

- Ivan.

One thing about the radien most people don't remark on until they see it up close and in person is the size of the cockpit. It is huge. A Japanese pilot could probably take evasive action by jumping around inside the cockpit!


Here is a side view of the Planes of Fame Raiden. The lower wheel covers had not yet been fitted after a paint job. The fellow walking in front is John Maloney of the Planes of Fame. He painted the Radien and did a lot of touch-up sheet metal repairs.

Here are the lower wheel covers after they were fitted:


Here is the tailwheel:


All for now.

You can make a very good bomber propeller, that doesn't mean it will be a good fighter propeller and vice versa.

For instance Lancasters used 3 blade 13 ft propellers. Try sticking that on a Spitfire or Hurricane

It would have been interesting if they made a "short-nose" J2M, without the 3ft extension shaft and cooling fans, the extension shaft/fans may have caused some of the vibration problems, and the cooling fans robbed some 80hp+ from engine, probably close to that lost by air drag from a blunter nose. The failed service introduction of the J2M was a disaster almost up with the Helldiver SB2C, and Me210, that should have had a more radical response.

The small diameter nose does seem to have let them use quite a small diameter propeller? A larger cowl would have meant a larger propeller.

taly01 said:

It would have been interesting if they made a "short-nose" J2M, without the 3ft extension shaft and cooling fans, the extension shaft/fans may have caused some of the vibration problems, and the cooling fans robbed some 80hp+ from engine, probably close to that lost by air drag from a blunter nose. The failed service introduction of the J2M was a disaster almost up with the Helldiver SB2C, and Me210, that should have had a more radical response.

The small diameter nose does seem to have let them use quite a small diameter propeller? A larger cowl would have meant a larger propeller.

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Taly,

I don't follow your comments regards prop size compared to cowl size. Why would a larger cowl allow for a larger prop? I thought the limitation was usually for prop clearance to prevent ground strikes?

Cheers,
Biff

Shortround6 said:

You can make a very good bomber propeller, that doesn't mean it will be a good fighter propeller and vice versa.

For instance Lancasters used 3 blade 13 ft propellers. Try sticking that on a Spitfire or Hurricane

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Hello Shortround6,

Agreed, but keep in mind that Kasei was used in not just big multi engine bombers. There were relatively small twins and single engine aircraft using the same engine.....

- Ivan.

BiffF15 said:

Taly,

I don't follow your comments regards prop size compared to cowl size. Why would a larger cowl allow for a larger prop? I thought the limitation was usually for prop clearance to prevent ground strikes?

Cheers,
Biff

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I think he meant would require a larger prop. A larger cowl would direct more of the prop's wash into engine cooling, reducing the disc area devoted to propulsive thrust. The only way to regain that area would be to increase blade length, unless you want to totally redesign the prop, which it appears they did. Upthread there was mention of a "paddle blade" prop with "notches" in the blade roots. This is the classic silver bullet approach to gain more thrust and more cooling flow from the same horsepower without increasing diameter, but faces some major challenges in material strength and harmonic vibration. Comparable to the US P47 prop upgrade.

Ivan1GFP said:

Another thing to keep in mind is that the P-47M/N didn't have very good initial acceleration. Being able to get to 460 MPH might be cool, but being able to recover energy after maneuvers is also a great tactical advantage and the J2M wins in that regard. Climb rate and acceleration are both an indication of surplus power.

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Hi Ivan,

Actually, I am only assuming the J2M could out-climb the P-47N at these heights (due to it's excellent reputation for climb). However, having only TAIC calculations to turn to above 20,000 feet, I wouldn't be able to say with any degree of confidence that it actually could.

I'm also not sure that above critical altitude the J2M could out-accelerate the P-47, as the turbocharged American fighter maintained sea-level horsepower close to 30,000 feet, in return probably giving it a better power-to-weight ratio at these higher altitudes.

Ivan1GFP said:

With regard to propeller efficiency, one has to wonder about how poor Japanese aeronautical engineering really was if they could not build a good propeller for an engine that was in production for quite some time before the J2M came along.

Click to expand...

I never said the propeller was of poor quality, just that the Americans were assuming a higher efficiency when calculating performance figures for the type. According to Jiro Horikoshi the J2M3 had a propeller of 0.74 efficiency, which is lower than the generally accepted 0.80 figure of the day.

And then there was the issue of propeller shaft vibration, which seems to have never really been fully understood or overcome. This must have had a negative effect on the actual engine thrust available at certain RPMs.

The Planes of Fame could consider restoring their J2M3 to flying status. The problems included corrosion and the engine. Corrosion is fixable, but there is no other suitable engine that has an extended propeller shaft. So, only the original engine setup could be used. The main issue is the population of spare parts, which amounts to zero.

As far as I know, there is no other extension shaft available for use in overhaul of the Kasei. It would be possible to make one, but that would require some serious funding that would only be reasonable if the airframe were to be overhauled, too. That means the entire project would have to be considered and likely funded or at least turned into a project before any work would begin, and the J2M is likely not that high on the priority list at this time. I'm guessing there, but we also aren't working on it, so the guess wouldn't seem to be all that far off.

XBe02Drvr said:

This is the classic silver bullet approach to gain more thrust and more cooling flow from the same horsepower without increasing diameter, but faces some major challenges in material strength and harmonic vibration.

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Imagine your "classic" slender variable pitch propeller blade before paddle blades came along. It tapers smoothly from a round cross section at the root to an airfoil of about the same cross sectional area at approximately the radius of the cowling, then assumes a progressive twist to keep the angle of attack constant across the radius at any rotational rate. Now with each power pulse this "tuning fork" flexes slightly, with the deflection distributed smoothly along its length like a fly rod in a cast, but increasing toward the tip as the cross section thins out. This is relatively easy to do with homogeneous materials and relatively simple harmonic tuning.
Now enter the designer who wants a prop to generate more cooling flow near its hub and dissipate more horsepower outside the cowl diameter without increasing blade count or overall diameter. Now we're looking at a robust (and stiff) wide chord twisted airfoil with likely squared, or nearly squared tips, and airfoil cross section extended nearly to the hub. No long smooth tapers here, and a sharp transition to a
round cross section at the hub (the "notches").
Now, what's happened to our tuning fork? It's become a stiff board with a hinge at one end, concentrating the bending action at the root and creating a huge metal fatigue issue. Some of this can be tuned out with mathematics that are beyond me, but it will almost certainly require exotic alloys and sophisticated manufacturing techniques.
You don't want to lose a blade in flight, as the resulting imbalance will likely rip the engine from its mounts or the mounts from the firewall, causing aircraft disintegration. It has happened. Not a fun day.

The J2M was an innovative design which IMHO should have never been built. The R&D required took much needed time and resources away from the development of the A7M (which by all appearances looked to be an outstanding concept) and after a protracted delivery the JNAF ended up with a sub-par fighter at best. Luckily Kawanishi was hard at work with the N1K during this time, which at least gave them some measure of hope in maintaining control of their own skies, albeit with devastating consequences in the end.

I do find the approach used to the reduce frontal area with an engine equal in diameter to the R-2800 a very novel one, and like taly01 wonder what kind of performance and reliability would have been possible if Mitsubishi chose to stick with a more traditional engine layout.

I disagree (see X above), but not in a bad way. I just like the Raiden but not enough to argue about it. Altogether a very nice airplane that COULD have been a high water mark had the engine and landing gear quality been better.

It's kind of like the Ta 152. The Ta 152 was not very effective since they basically only delivered 47 of them. But, one on one, they were amazing airplanes with impressive specs.

The Raiden was very good when it was running right. Some did, but not enough to matter all that much. Still, it is an impressive airplane in person and in the specs.

Raiden had better armament. Four 20mm cannons. Especially against the B-29. Better high altitude ceiling, too.

DarrenW said:

The J2M was an innovative design which IMHO should have never been built. The R&D required took much needed time and resources away from the development of the A7M (which by all appearances looked to be an outstanding concept) and after a protracted delivery the JNAF ended up with a sub-par fighter at best. Luckily Kawanishi was hard at work with the N1K during this time, which at least gave them some measure of hope in maintaining control of their own skies, albeit with devastating consequences in the end.

I do find the approach used to the reduce frontal area with an engine equal in diameter to the R-2800 a very novel one, and like taly01 wonder what kind of performance and reliability would have been possible if Mitsubishi chose to stick with a more traditional engine layout.

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Hello DarrenW,

I am not entirely convinced that the A7M would have been a world beater had it actually been built. I believe the designers were counting on engines with the level of output that were never actually available and without them, that very large airframe would not have had any better performance than the typical late 1943 fighter. That wasn't going to be enough when there was such inferiority in numbers and pilot training.
As long as the aircraft remained a prototype and never entered production or service, it can remain "perfect".

Regarding propeller efficiency: As I stated before, it matters quite a lot at what speeds that efficiency is achieved. I have never actually done any significant calculations on the J2M to really understand how its engine and propeller under ideal conditions compare against comparable aircraft.
From flight evaluations, there WERE problems with vibrations at certain speeds, but in the test aircraft those speeds could easily be avoided.
Whether or not those aircraft were flown in tests for maximum speed, they were flown fast enough to test control response at quite high indicated airspeeds.
Sometimes one can find some pretty extraordinary and unexpected things when looking at the actual numbers such as when I did some poking around with specs of the Lockheed P-3 Orion.

XBe02Drvr said:

Imagine your "classic" slender variable pitch propeller blade before paddle blades came along. It tapers smoothly from a round cross section at the root to an airfoil of about the same cross sectional area at approximately the radius of the cowling, then assumes a progressive twist to keep the angle of attack constant across the radius at any rotational rate.
.......
Now, what's happened to our tuning fork? It's become a stiff board with a hinge at one end, concentrating the bending action at the root and creating a huge metal fatigue issue. Some of this can be tuned out with mathematics that are beyond me, but it will almost certainly require exotic alloys and sophisticated manufacturing techniques.
You don't want to lose a blade in flight, as the resulting imbalance will likely rip the engine from its mounts or the mounts from the firewall, causing aircraft disintegration. It has happened. Not a fun day.

Click to expand...

Hello XBe02Drvr,

I believe if the propeller blade were uniform thickness and construction, that would make sense, but many propeller blades are hollow which would affect some of those uniform vibrations. Another possibility is to increase the thickness of the "paddle blade" as it gets closer to the hub. The relative airflow will be much slower, so there doesn't need to be quite the same thin section as needed at the tip.
One of the very interesting things about the propellers on the P-47 from what I have seen in some performance comparisons is that although the "Paddle Blades" were more efficient at low airspeeds, they were not quite as efficient as the original "Toothpick" propellers at high speed and there was a significant difference between the fairly common Curtiss-Electric Asymmetrical Paddle Blade and the Hamilton Standard Paddle Blade with the H-S being a bit better at high speed. There were at least two different kinds of paddle blade propellers made by each manufacturer.

- Ivan.

I've seen NTSB reports on hollow blades that had corrosion failures in flight an lost blades in cruise or climb. None of them were pretty and none were survivable. All the report I saw were from twin turboprop small airliners, and none survived. When I say "hollow," I don't mean absolutely hollow, but a hollow aluminum blade with rubber-like filling in the hollow.

All the blades that failed had some sort of impact around the hub that was never dressed or looked at very hard. All experienced some vibrations never before felt before failure.

GregP said:

I disagree (see X above), but not in a bad way. I just like the Raiden but not enough to argue about it. Altogether a very nice airplane that COULD have been a high water mark had the engine and landing gear quality been better.

It's kind of like the Ta 152. The Ta 152 was not very effective since they basically only delivered 47 of them. But, one on one, they were amazing airplanes with impressive specs.

The Raiden was very good when it was running right. Some did, but not enough to matter all that much. Still, it is an impressive airplane in person and in the specs.

Click to expand...

Besides a better than average climb rate at medium altitudes, what was so "impressive" about it's performance? The J2M was the least favored of the late-war Japanese fighters, with many pilots commenting that it lacked the handling and maneuverability to successfully dogfight with a Mustang or Hellcat. They also disliked the very high landing speed (138 mph) and poor forward visibility. Pilots had to be proficient at dead sticking the plane as engines seized so often. When given the choice some even reverted back to the older but trusty Zero. Only a seasoned pilot like the eccentric Sadaaki Akamatsu had any words of praise for it.

TAIC pilots rated the performance of a captured example as "good", which to me is a far cry from being "impressive".

TAIC pilots rated the performance of a captured example as "good", which to me is a far cry from being "impressive".[/QUOTE]

Darren, sometimes "good" is a good thing.

Technical Air Intelligence Command
The captured fighter (J2M3) was tested by the senior pilot attached to TAIC who had flown virtually every
Allied fighter, as well as the Messerschmitt Bf 109, the Focke-Wulf Fw 190, and such Japanese types as the
Nakajima Ki-43 Hayabusa and Ki-84 Hayate, the Kawasaki Ki-45 Toru and the Mitsubishi A6M Zero-Sen.
After logging three hours and twenty minutes in the Raiden he stated unequivocally that it was the best Japanese fighter that he had flown, offering a good performance, good stability, good stalling charateristics, and good take-off and landing qualities.
Good Features:
1. Good stability.
2. Good stalling characteristics.
3. Comfortable cockpit.
4, Good take-off and landing qualities.
5. Good overall performance.
6. Maneuver flaps.
Bad Features:
1. Brakes and rudder brake action poor.
2. Heavy ailerons and lack of maneuverability at high speeds.
3. Low mechanical reliability.
4. Short range.

Note about the maneuver flaps from Air Enthusiast July 1971 Vol.1, No.2.
Page 103: Rolls, Immelmans and turns are executed with ease at normal speeds, although ailerons are
heavy at all operating speeds. and the aircraft cannot be rolled as rapidly as a P-51 (Merlin).
Maneuver flaps of Fowler type are fitted, and are controlled by a safety switch and trigger on the stick.
These are extended only when the trigger is depressed and retracted immediately when the trigger is
released, and their operation is superior to any used on our (US) aircraft.

Funny you should say the landing speed was 138 mph since the design specification was that landing speed be no higher than 81 mph and it met the specs.

The J2M-3 (most-produced: 435 built) hit 370 mph and had a 360° turn time of 18 seconds (speed not specified), which is right in there with a Yak-3, widely regarded as the best turner in modern WWII fighters. The J2M-1 (8 built) turned in 16 sec and the J2M-2 (141 built) turned in 17 seconds. A Hellcat could not match 18 seconds and neither could a Mustang. Really. A Messerschmitt Bf 109G was 22.6 - 22.8 sec. A Mustang I was 23 sec.

It had two 20 mm cannons and two 30-cal MG, which is effective enough considering the number of Allied aircraft shot down by that exact combination, which is ... like ... almost all of them in the Pacific Theater.

I have been in the cockpit and the forward visibility is not bad at all compared with a Mustang or a Hellcat. I have a great pic of the visibility but have been asked not to post cockpit pics, so I won't. But the visibility is quite good.

Not sure where you are getting all your objections, but the only ones that seen true to me are engine and landing gear problems.