J2M Raiden vs. F8F Bearcat

Discussion in 'Aviation' started by spicmart, Sep 19, 2016.

  1. spicmart

    spicmart Member

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    I wonder how the Raiden would have fared against the Bearcat if given the right fuel and a competitve engine as it seemed to have similar mission profile and similar dimensions.
     
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  2. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The best speed figure I was able to find for the Raiden is ~380 mph, with engine using water injection. Early Bearcat was good for 420+ mph, and will have more engine power in any regime. Raiden was smaller, with thinner wing - not enough to overcome lack of engine power?
    It would've been interesting situation with Raiden using 100/130 PN fuel, though we don't know how well would've engine withstand greater mainfold pressure and hence greater power.
    Raiden has better armament, the early Bearcat is with 4 .50s, but then again Raiden was not provided with self-sealing fuel tanks?
    Maneuverability - raiden has Fowler ('butterfly' flaps), so it should've turned better.
     
  3. Shortround6

    Shortround6 Well-Known Member

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    a competitive engine vs the F8F means a while new engine for the Raiden at which point comparison becomes very difficult.
     
  4. spicmart

    spicmart Member

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    I guess it's also hard to estimate the potential that layed in the Raiden design. It was very light for its size so that it might not be structurally strong enough for certain manoeuvres at high speeds where aileron reversal can occur.
     
  5. GregP

    GregP Well-Known Member

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    #5 GregP, Sep 20, 2016
    Last edited: Sep 20, 2016
    I've never read a report on the Raiden that cited any structural difficulties. In fact, about the only serious negative I have read is the occasional unreliability of the engine. It could have used a better propeller, too. By better, I mean a bit bigger.

    Attached a pdf below.
     

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  6. spicmart

    spicmart Member

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    Thanks. I will read it as soon as I can.
     
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  7. alejandro_

    alejandro_ Member

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    J2M Raiden had so many development and teething problems (*) that in June 1944 it was ordered to stop production and focus on Kawanishi N1K1-J Shiden. The Raiden was to be produced in small numbers until A7M became operational. The first B-29 raids reversed the decision, as the Raiden was one of the few Japanese aircraft capable of reaching and fighting at that altitude.

    It was the first Japanese aircraft to be designed taking into account armor protection and self-sealing fuel tanks. Even if these were not up to American standards, it was better than previous Japanese models.

    US evaluation noted heavy aileron and lack of manoeuvrability at high speeds. In any case, the F8F have some clear advantages (speed, climb rate [also range?]).

    Any comparison with US aircraft is hard because by 1944 Japanese fighters were underperforming. Teenagers were involved in the manufacturing, and the fuel was of poor quality. When the Ki-84 was tested in the US the maintenance crews/pilots were able to obtain much better performance.

    (*) Including oscillation issues that were never found/corrected.
     
  8. GregP

    GregP Well-Known Member

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    #8 GregP, Sep 20, 2016
    Last edited: Sep 20, 2016
    For some period of time, about a decade or so, our museum had a Ki-84 Hayate in flyable condition. It vibrated, too, and they traced this to slightly bent propeller. Since there were no replacements anywhere in the world to be had, they just flew it at reduced power levels until interest in it dried up completely and they sold it to a museum in Japan, where it still lives today.

    I wonder if the J2M had the same issues? Probably not, because the J2M has a unique engine setup, with a VERY long driveshaft. We have a J2M ready to restore, but there is no engine that will fit other than the original due to the long extension prop shaft. If I were betting, I'd be that was the main source of vibration. It's right at the length where Northrop engineers installed a torque converter to avoid a long shaft in our N9M-B flying wing since the long shaft created vibrations.
     
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  9. Shinpachi

    Shinpachi Well-Known Member

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    #9 Shinpachi, Sep 20, 2016
    Last edited: Sep 20, 2016
    Though this is a trivia -

    IJN ace fighter pilot Sadaaki Akamatsu (1910-1980) taught his students how to fight the P-51s and the F6Fs with their low-powered J2Ms, or A6Ms.

    1. Make sure to take advantage of altitude in advance.
    2. Dive aiming at the opponent's cockpit only.
    3. Don't approach to it from 6 o'clock but 4, 5, 7 or 8 as it's equipped with the armor in the back.
    4. After shots, success or failure, escape immediately snaking on the dark green mountains if possible.
    Half-rolling to turn is also effective to avoid the opponent's high-speed chasing (as footage shows).
    5. Repeat above 1 to 4 as long as your situation and fuel allows.

    He commented about the J2M like "My sole frustration for the J2M was its small fuel tanks. When I wanted to fight more, my time was often over with no gas".
    Sadaaki Akamatsu.JPG
     
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  10. spicmart

    spicmart Member

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    What's the thing with the A7M Reppu? It is a very large fighter with dimensions slightly surpassing that of the Hellcat.
    At the end of the war fighter designs tend to become lighter to achive peak performances as engine power allows. So such a big plane is quite an anachronism. I can hardly imagine how it can fight a bearcat on anything other than a slow turning dogfights.
     
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  11. spicmart

    spicmart Member

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    And what is it with the japanese engines? They are often rated with high horse power, rivalling those of allied and german descent. Yet the planes never seemed to live up to that. Is that just the potential power of those engines. With the proper fuel they should have been real monsters.
     
  12. GregP

    GregP Well-Known Member

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    #12 GregP, Sep 21, 2016
    Last edited: Sep 21, 2016
    Probably available fuel, poor quality due to war, and few wind tunnel tests.

    Not sure their airfoil research was up to snuff during the late-war bombing attacks, once the B-39s got started dropping stuff. I doub tif they ever discovered partial liminar flow beofre the war ended and were no doubt baffled by the extra speed of late-war Allied planes. Take a P-51 and use a normal 1941 airfoil with no Merrideth effect radiator, and you'd have a very average fighter. Possibly an average Japanese fighter that jusy didn't turn very well with respect to other Japanese figthters.

    The Ki-84 am close, but the Ki-61/100, J2M, N1K2, etc. didn't seem to be bad, just mostly not aerodynamically advanced.

    The again, had WE been bombed day in and day out, I doubt if wind tunnels and research would have been the highest priority for us. More likely it would have been AAA and interceptors. The J2M and Ki-44/84 were very GOOD interceptors with useful climb rates and good armament. Just not enough, soon enough to make much of a difference\ ... sort of like the aviation development in Italy. Good, but not game-changing. Their planes flew remarkably well, but didn't do anything particularly better than the competition and there were a LOT more Allied planes around, late-war. Safety in numbers and death in being the only target around worth noting for a large group of enemies. Somewhere in there are some bullies (fighter pilots of all nationalities) and they always pounce on any perceived weakness, even if it is just numeric. Sometimes they pounce even when there IS no weakness, like in the Battle of Britain or a Kamakaze attack. People still love them for it almost 80 years later.
     
  13. Shortround6

    Shortround6 Well-Known Member

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    It is a bit more complicated than that.
    For instance the engine in the J2M was a 14 cylinder 2560 cu in engine, only a bit smaller than a Wright R-2600 (2603 ci) the same size as a BMW 801 (different bore and stroke) and bit larger than an ASh-82 (2503ci).

    All ran at close to the same rpm (it varied from model to model of the same engine) 2400-2700rpm pretty well covers it.
    That leaves boost as the other main variable to making power.

    Standing up the power is the next question, and it is the hidden or hard to figure out part as it relates to the durability of an engine, most engines are quite capable of making enough power to either wear the engine out quite quickly (a matter of hours) or destroy the engine in a matter of minutes. Higher power ratings could be achieved by trading overhaul life.
    Another major factor for short term power limits was cooling. Over heating meant cooking the oil and loosing lubrication which would result in engine failure real quick.
    A one minute take-off rating could be higher than a 5 minute combat rating at altitude due to cooling. the 5 minute rating is higher than a 15 minute or 30 minute rating due to cooling limits. Just about all pilot or engine manuals will also state that the time limit is subject to temperature limits. If the engine (or oil) temp goes past a certain limit than the engine should be throttled back regardless of the time limit.
    Some countries had different limits or standards on what they were willing to accept for short term power.
    ALL fuel had pretty much the same BTUs per gallon, there was no "magic" fuel. The higher octane fuel used by the Allies allowed higher boost to be used without getting detonation. Higher boost means more fuel burned per minute (or second) and that is where the power comes from. It does nothing for power above the rated altitude of the engine. Below the rated altitude of the engine it can allow for more power. Rated altitude is where the supercharger cannot flow anymore air.
    Of course burning more fuel in the same amount of time means you have to get rid of more heat in the same amount of time so not only is the engine limited by it's strength (pressure in the cylinders) but we are back to cooling.
    The R-2600 went from a 1700hp engine to a 1900hp in later models in part due to using sheet metal fins pressed into place rather than cast/machined fins. The R-2800 engine in the Bearcat was a "C" series engine which had much increased finning over the "B" series engines used in the F4U and F6F which allowed for either higher power or less cooling air to go through the engine cowl at the same power levels.
    What this boils down to is that the Engine/s in the J2M was rated at over 1800hp for take-off (for how long) and that was running 100rpm faster than the combat ratings at altitude) but only a bit over 1500hp at altitude. The American R-2600 was good for 1350hp at altitude ( 15,000) while running about 100 rpm less than the J2M engine.
    Fuel for the 2 engines is questionable. the R-2600 was never given higher ratings simply by changing fuel even though it was available. the 1700hp rating was done with early American 100 octane not 100/130 and the 1900hp versions used 100/130 but were almost entirely new engines. Japanese fuel is rated at 92 octane but that is the lean rating, I have not seen a rich rating. The Dutch east indies fuel was high in aromatics and should have a higher rich rating although how much richer is speculation. 122 would certainly be too high but 98-100 might be reasonable. (British early 100 octane was actually about 115-120) and some post war 91 octane was actually 91-98.
    Pouring 100/130 fuel in the fuel tanks of a Japanese fighter and cranking up the boost is a good way to have engine pieces depart the airplane at high speed.
     
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  14. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The engines never got 2-stage superchargers, that will cost speed even if the basic/take off power is high.
    As for speed itself, it depends what one reads. Francillion (as a best known Western source) often states lower speed figures than ot was/is the case with TAIC data, for exmple. Eg. early model of the raiden was stated as good for 407 mph (pdf), late model of Raiden, in good shape, was supposed to make 417 mph; basically very comparable vs. La-7 in a good shape, or an early Fw-190. Compare with Francilion stating 370 mph, give or take.
    Or, Ki 84 - Francilion states 380-390 mph, Allied docs say up to 427 mph.

    Japanese were quick to introduce a (partial, okay) laminar flow wing, that is with double-slotted Fowler flaps, on the Nakajima Saiun. Apart from A-26 and B-29, I doubt that any other aircraft had those in ww2.
    The wing on the Raiden looks like a very thin item, the aircraft looks roughly like a radial-engined Spitfire when looked from the front.
    We can't expect that Ki-100 outperforms a late war Allied aircraft - low powered (for 1945) radial engine, wing profile was not that modern in 1945 (2R16).
    Those attacks from B-39 were indeed dangerous ;)
     
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  15. alejandro_

    alejandro_ Member

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    Very interesting Shinpachi, thanks for the translation. Akamatsu was quite a character, a heavy drinker and a womaniser. He was also one of the most experienced pilots in Japan, with 8.000 flight hours. He ended the war with 27 kills and was one of the most succesful exponent of J2M.

    It was a improvement over the A6M, which the Japanese desperately needed.

    According to Eric Brown the Ki-61 was like a 1939 figther (it was deployed much later). The Ki-100 was popular because it was more reliable -the liquid cooled engine of the Ki-61 was a nightmare- due to the air cooled engine.

    The N1K2 was a derivative from a hydroplane, designed by private initiative. The wing had to be changed. It was quite a decent design considering the circumstances, but as other advanced Japanese fighter it was hamstrung by the poor reliability of the engine.

    IMO the Japanese engine industry was not as mature as that of US/UK, and struggled to field an engine with +1.800HP The Ki-61 engine was a DB 601 produced under license, but the design had to be simplified to take into account Japanese industry standards, which were not as advanced.

    Greg, perhaps you could share you impressions in another topic. I have always been very interested in P-51 aerodynamics.

    Regarding the J2M, there is a very good article about it in the magazine Aeroplane (Feb 2016). The development has been covered before, but all the Kokutais that operated the type are reviewed.
     
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  16. Shortround6

    Shortround6 Well-Known Member

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    The A7M Reppu was running late, it is more of a contemporary of the Hellcat design wise but the Japanese didn't have enough engineers to handle all the projects they tried to run at once and the A7M took a back seat to more urgent needs.
    I would also note that while the Bearcat was smaller that wasn't all due to how advanced it was. In part it was due to holding about 2/3rd the fuel of the F6F and in the first versions, using 2/3rds the armament. Bearcat also gave up the two stage supercharger and inter-coolers sacrificing high altitude performance.
    Since the A7M was supposed to be an A6M replacement range and endurance could not be sacrificed too much.
     
  17. alejandro_

    alejandro_ Member

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    The propeller was also modified in the J2M to avoid the oscillations issue. The prototype used a 10ft 6in-diameter three-bladed propeller, together with the shaft extension that allowed a tapered cowling with less drag.

    In production versions the propeller was replaced with a four-bladed type. The extension shaft was reduced by 1 foot (~30cms). The cooling system was modified. The vibration issue was partially fixed by increasing the rigidity of the propeller blades and the resilience of engine-mount shock absorbers.

    The wing was of laminar type, having a single main spar at 35 per cent chord and smooth flush-riveted stressed skinning. Apparently it was the source of delays, but no reason on why.
     
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  18. Randall Rydjeski

    Randall Rydjeski New Member

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    #18 Randall Rydjeski, Sep 24, 2016
    Last edited: Sep 24, 2016
    From what I remember the Bearcats held the climb to height record for a prop driven aircraft for many years. Add to that the lack of ace pilots in Japan and the high quality of US naval aces like David McCampbell just to name one of many, we'll that about says it all. I remember reading about a naval aviator who flew Bearcats out of Pensacola, they used to mix it up with the local AF boys who were flying Mustangs. The Navy had no problem defeating the AF in every acm envelope, sort of like the Hornet against the F-35. For my own amusement, Molders in a 109E vs Nishizawa in an A6M3. Now that would be interesting! my money would be on Nishizawa, hands down.
     
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  19. BiffF15

    BiffF15 Well-Known Member

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    Excellent read Greg!

    Cheers,
    Biff
     
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  20. drgondog

    drgondog Well-Known Member

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    One of the deceptive aspects of the comparison between F8F and 'Mustang", and making sweeping statements, is always "which version', "which pilots", "what load outs" and "what, if any restrictions were they operating with".

    The P-51H, with the same amount of internal fuel, with no restrictions on boost up to 90" w/WI and 150 octane fuel should trounce an F8F above 20,000 feet given good pilot skills - and should be a handful below that.

    With the same amount of fuel (150 gallons) the P-51H will weigh less than 9000 pounds, have a lower wing loading, a lot less drag and better climb performance from any given speed in level flight. It was never timed from standing start to 10K but the XP-51G did 20,000 in 3.85 minutes with equivalent Power Available to Power Required curves.

    The reason that neither the P-51F or G went into production is that both were designed without an internal fuselage fuel tank and by the time it was ready to fly the P-51B had the 85 gallon tank internally and Berlin was a necessity that could not await that mod for the G/F. The P-51H was ultimately the resulting modification.
     
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