MiTasol
1st Lieutenant
Another of Japans problems, according to the Germans was discussed on pages 16/17 of the same file.
Japanese Zero vs Spitfire vs FW 190
- Thread starter Chiron
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Shortround6
Major General
Well, giving them the construction rights for the Jumo 222 engine was one way to ensure they would not dominate Germany after the axis won WW II 
Hello MiTasol,
Historically, that was the development path for the J2M Raiden and it seemed to work pretty well. The firewall does not appear to be particularly far aft. This design resulted in one of the fastest Japanese fighters of the war.
Here is a diagram to show what the layout actually was.
- Ivan.
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Hello Tomo Pauk,
I do not believe these objectives are all achievable with the amount of power of the Mitsubishi Kasei engine. Of course we may have different ideas on what "useful fuel tankage" means, and what constitutes proper protection for the pilot and fuel, but just keep in mind that the Raiden carried a relatively large amount of fuel for a Japanese fighter and still didn't have great range with the Kasei engine. Its speed was excellent for a J-fighter but only adequate when compared to its adversaries.
The "mission" was no longer required by the time the program was completed. THAT was the point I was trying to make.
Regardless of whether it was ideal, this is what actually happened. There were no long range successors to A6M and Ki 43.
I believe that was what the choice of swapping the Sakae engine for the Kinsei on the A6M fighter really meant and this was why the choice was made so late. Without the Sakae engine in the A6M, the Japanese Navy no longer had a long range fighter.
- Ivan.
MiTasol
1st Lieutenant
Another page from the same document (p209) shows the German understanding of what the A6M5 was and could do. Note the automatic fire extinguisher for the fuel. A lighter option to self seal tanks and of unknown (to me) capabilities. I would like to know more how it was supposed to work and how effective it was
Amout of fuel was not that large once we account for engine power that was 50+-% greater than Zero, Ki-43 or -61. 390+180 internal is in the ballpark with what Japanese fighters with 1000-1100 HP carried, while fuel in drop tank was less than Ki 43 or Ki 61 carried. 'Useful range' should be about 90% of what Zero was doing.
Kasei was making better power than any Japanse engine before Homare emerged. 1500-1800+ HP is a lot more than Ha 40 was capable for. That engine powered rangy Ki-61 that nobody considered as a pushover in air combat.
Having a fighter whose performance is adequate is a big an advantage vs. having a fighter whose performance is inadequate.
No problems. We will waste no time to convert the production line from a floatplane fighter design into a 'classic' fighter (since the production line already makes those), unlike what happended with the Kawainshi fighters' saga.
Of course they don't have a long range fighter once Zero gets a proper engine - a direct result of IJN wasting time and resources into niche aircraft instead of crucial thing: the timely replacement for the Zero.
Ki-84 was almost as rangy as Ki-43.
Hello Tomo Pauk,
Internal fuel capacity was nearly identical for J2M and A6M3-22 and A6M5-52 at around 570 liters. The J2M COULD carry up to a 400 liter drop tank which was larger than any carried by the A6M series. The fuel capacity of the Ki 61-I is not a great comparison because depending on the exact model, it could vary from 500 liters up to 750 liters.
The Ki 61-I may not have been a "pushover", but it also was not particularly competitive in any aspect of its performance either. At best, it was adequate against competition such as a P-40 and totally outclassed by later aircraft. It would have been great had it been available in 1941.
I still don't see how you can expect decent performance from the same engine as on J2M while adding all of the additional features needed to make it into a good carrier fighter with excellent range.
The Kawanishi line of development created possibly the best all around fighter operated by the Japanese Navy. The alternative you are describing SHOULD HAVE HAPPENED is very hard to compare when there can be no details or specifics.
The Ki 84 used the same engine and carried the same fuel load as the N1K2-J. The N1K2-J had substantially less range than the A6M fighters as has been described in interviews with surviving Japanese pilots.
- Ivan.
michael rauls
Tech Sergeant
- 1,679
- Jul 15, 2016
Not sure I'd agree that the ki61 was not competitive with later designs unless by later designs you mean verry late in the Pacific war stuff, p51, late model f4u etc.
Even then although for sure it was not as good I don't think I'd say it wasn't competitive at all.
As near as I can tell it had verry similar performance to a late F/ early G series 109.
I don't think anyone would argue those were not competitive with mid war designs and even later ones to a degree.
Huh? Different arena, different combat conditions, demands and expectations, sounds like a non sequitur comparison to me. It would seem to make more sense to gauge competitiveness in light of the time and place and opposition in question rather than some arbitrary universal scale. Or maybe I'm just out in left field. Wouldn't be the first time.
Cheers,
Wes
Ki-61 carried circa 750 liters internally, unless people opted not to fill all internal tanks, or removed an internal tank. It also carried two drop tanks, so it was easily better in that regard than J2M. Once we facture in the greater power (and thus consumption) of the Kasei vs. Ha-40, no woder the range was short vs. what Ki-61 offered.
What Ki 61 needed by late 1943/early 1944 was a substantial increase of engine power, that didn't happened until 1945.
I can expect decent performance of 'my' fighter since it will have 50+% more engine power than the current carrier-borne fighter.
We can arrive at some specifics. Like the wing profile and area, expected weight, engine power, and then go from there.
The biggest fuel load for the N1K2-J that I was able to find is 1064 liters (281 US gal), that includes 400L drop tank. Biggest fuel load for the Ki-84 is 359 US gals, that includes 175 gals in two drop tanks.
michael rauls
Tech Sergeant
- 1,679
- Jul 15, 2016
I should have made more clear I was referring to performance stats, climb, dive , top speed etc. Which is what the poster I was answering seemed to be referring to.
cherry blossom
Senior Airman
- 513
- Apr 23, 2007
I think that I agree in practice. However, I have been playing at designing the perfect fighter with a Kasei and it is not very hard because the Kasei length, diameter and weight are all less than those of the R-2800. Thus I simply imagine mounting a Kasei in a Grumman Bearcat, which assumes that information on the design of the Fw 190 v5 had been sent to Japan on the Raider Komet and arrived by November 1940.
The initial Ha-32-13 Kasei for the Raiden prototype gave 1460 ps at 2450 rpm for take off and 1420 ps at 2000 metres and 2200 rpm or 1300 ps at 6000 metres at 2200 rpm. The R-2800-22W used by the Grumman Bearcat prototype was rated at 2,100 hp for take off and 1,600 hp at 16,000 ft. The Bearcat prototype attained 393 mph at sea level and 424 mph at 17,300 ft. If we take the ratio of 1600 to 1300 as 1.2308 (neglecting the effect of ps vs. hp and the different altitudes), we might expect to only lose about 9% of maximum speed using the v cubed approximation. Thus we might expect a Bearcat with a Kasei-13 equivalent engine (without the extension shaft) to have a maximum speed of at least 389 mph at around 6,000 metres.
The prototype Bearcat had 160 US gallons of internal fuel (606 litres) although that was increased to 183 gallons (693 litres) in the production aircraft. As the Raiden had around 570 litres, a Bearcat derivative should go further.
We will have to move something to maintain the CoG as the Kasei is significantly lighter than the R-2800. I doubt if a Japanese oil cooler design from 1941 will be as efficient as that of the Bearcat. Fortunately, we don't need to design a new airfoil as the Bearcat's NACA 23018 was used in the Brewster F2A.
Hello Michael Rauls,
The Ki 61-I was faster than a Me 109E but not nearly as fast as a Me 109F or G and only had the engine power of the 109E.
Its climb rate was quite low and power to weight ratio was relatively low.
Firepower was mediocre at best with 4 MG except for two versions. One was the 400 aircraft that mounted the MG 151/20 that were imported by submarine from Germany. Unfortunately after those guns were used up, there were no more coming.
The other version with good firepower was the Ki 61-Id which mounted a pair of Ho-5 20 mm cannon in the cowl. There was not enough space to mount these guns in earlier aircraft but unfortunately the Ki-61-Id also gained extra armor and was the heaviest of all and had no more engine power than any of the other versions.
So, basically with the Ki 61, you have an aircraft that handles well and can dive but can't climb well, isn't particularly fast, can't accelerate, and is not nearly as maneuverable as other J-fighters.
- Ivan.
Hello Tomo Pauk,
Regarding the internal fuel load of the Ki 61-I, you are simply incorrect. Early aircraft seemed to carry the larger fuel loads, but the wing tanks varied in size and the fuselage tank was not always installed especially in later aircraft.
EDIT for more detail
The Ki 61-Ia had the following
2 x 190 liter Wing Tanks
1 x 170 liter Wing Center Tank
1 x 200 liter Fuselage Tank
-----------------------------
Total 750 liters
Ki 61-Ib had three variations
early production was same as -Ia (s/n 501-513)
mid production deleted the fuselage 200 liter tank for a new total of 550 liters (s/n 514-649)
late production (s/n 650-1092) had the following
2 x 170 liter Wing Tanks
1 x 160 liter Wing Center Tank
No Fuselage Tank
----------------------------
Total 500 liters
Ki 61-Ic had the following
2 x 170 liter Wing Tanks
1 x 160 liter Wing Center Tank
No Fuselage Tank
----------------------------
Total 500 liters
Ki 61-Id had the following
2 x 170 liter Wing Tanks
1 x 160 liter Wing Center Tank
1 x 95 liter Fuselage Tank
----------------------------
Total 595 liters
The two drop tanks carried by the Ki 61 were only 200 liter capacity each, so it carries no more fuel in drop tanks than the J2M did.
When you say "needed by late 1943", I take this to mean "needed at its introduction" which was 1943. It was always somewhat underpowered.
The problem with expecting decent performance out of 'your' fighter is that it is hard to see your requirements adding LESS than 50% more weight than the current carrier-borne fighter.
- Ivan.
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Hello Cherry Blossom,
Thanks for putting a bit more substance into this discussion.
The problem is that this Bearcat with a Kasei engine would not really meet the requirements that Tomo Pauk had specified.
389 MPH isn't really quite fast enough for a new fighter to make it competitive. It is no faster than the F6F and much slower than the F4U.
The internal fuel load of the Bearcat was fairly small (also about 700 liters IIRC), so something more needs to be added to make it into something with a bit more range if we want something comparable to the A6M series.
Now considering that we are running a Kasei engine with Japanese 92 octane fuel, do we account for the Water Methanol tank that is needed to run rated and maximum engine power?
On the Raiden, the Fuel load was 570 liters but there was also 120 liters of Water-Methanol that was carried.
For weight, this is easily the equivalent of the fuel load of the Bearcat.
The Raiden had an excellent climb rate, but it was also a relatively light aircraft. The same Kasei engine in a larger and certainly heavier aircraft isn't likely to result in an aircraft that climbs as well. If we are comparing the basic Raiden airframe to the Bearcat, the Raiden weighs 7080 pounds, the F8F-1 Bearcat weighs 9334 pounds.
- Ivan.
cherry blossom
Senior Airman
- 513
- Apr 23, 2007
My point was that the Bearcat designers made a brilliant job of building the smallest and lowest drag fighter possible with a R-2800 engine and seem to have produced a lower drag design than Mitsubishi, whose J2M1 could only manage 357 mph at 6,000 m with the Kasei-13 (which did not use water injection). To get speeds around 380 mph, Mitsubishi needed to fit the Kasei-23 which gave 1900 ps at 2600 rpm for take off and ratings at 2500 rpm of 1720 ps at 2100 metres or 1580 ps at 5500 metres with water injection. The Kasei-26 of the J2M5 was optimised for higher altitude and gave 1400ps at 6800 metres, which allows an easy comparison with the R-2800-30W of the F8F-2.
WWII Aircraft Performance has Standard Aircraft Characteristics F8F-2 "Bearcat" which notes that the maximum speed at normal rating is 363 knots (418 mph). Now normal rating is 1,450 hp at 22,000 ft (far below the wet combat rating of 1,800 hp). Thus a Kasei-26 with water injection is about 60 hp less powerful but 250 kg lighter. Thus I am guessing that a Bearcat with a Kasei-26 would have a max speed of around 360 knots (414 mph). By contrast, Mitsubishi J2M Raiden (Thunderbolt) says that the J2M5 had a maximum speed of 332 knots. Of course, the actual performance of the J2M5 is uncertain with figures between 382 mph and 421 mph being quoted but the higher numbers are speculative.
I don't know how Grumman did such a good job with the F8F but I suspect that the fuselage is as narrow as it can be, never much wider than the R-2800, and that the exhaust helps to accelerate the cooling air and to fill in as the fuselage narrows. I suspect but have not measured that the Raiden is slightly fatter and certainly longer.
The Bearcat is heavier because it has a heavier engine, armour and an arrestor hook as well as generally thicker skinning and the strength to land repeatedly on a carrier. The empty weights are 7,650 lbs for the F8F-2 and perhaps 5534 lbs for the J2M5. Naturally, the extra weight is necessary for a carrier fighter.
Lastly, Mitsubishi did do a better job in one respect as the Raiden had good spin recovery whilst the Bearcat was rather more dangerous near the stall.
WWII Aircraft Performance has Standard Aircraft Characteristics F8F-2 "Bearcat" which notes that the maximum speed at normal rating is 363 knots (418 mph). Now normal rating is 1,450 hp at 22,000 ft (far below the wet combat rating of 1,800 hp). Thus a Kasei-26 with water injection is about 60 hp less powerful but 250 kg lighter. Thus I am guessing that a Bearcat with a Kasei-26 would have a max speed of around 360 knots (414 mph). By contrast, Mitsubishi J2M Raiden (Thunderbolt) says that the J2M5 had a maximum speed of 332 knots. Of course, the actual performance of the J2M5 is uncertain with figures between 382 mph and 421 mph being quoted but the higher numbers are speculative.
I don't know how Grumman did such a good job with the F8F but I suspect that the fuselage is as narrow as it can be, never much wider than the R-2800, and that the exhaust helps to accelerate the cooling air and to fill in as the fuselage narrows. I suspect but have not measured that the Raiden is slightly fatter and certainly longer.
The Bearcat is heavier because it has a heavier engine, armour and an arrestor hook as well as generally thicker skinning and the strength to land repeatedly on a carrier. The empty weights are 7,650 lbs for the F8F-2 and perhaps 5534 lbs for the J2M5. Naturally, the extra weight is necessary for a carrier fighter.
Lastly, Mitsubishi did do a better job in one respect as the Raiden had good spin recovery whilst the Bearcat was rather more dangerous near the stall.
Shortround6
Major General
we also have to remember that the Bearcat was designed around the "C" series R-2800 which used about one part (legend says the starter dog) in common with the B series engines that powered the vast majority of R-2800 powered planes in WW II. Direct comparisons to other engines are difficult due the increased fins and different baffles that allowed the C series to make 2000 hp with 10% less cooling airflow and thus nearly 10% less cooling drag. (or the C series made more power with same drag).
Hello Cherry Blossom,
I believe the biggest difference of opinion here is what you believe the maximum speed of the J2M series really was.
I am inclined to believe the TAIC data sheet which gives about 407 MPH under Military Power and 417 MPH under "War Emergency Power" for the J2M3. It seems like you are more inclined to believe the more typically quoted 370 MPH figure.
IF the 370 MPH figure is correct for maximum power (WEP) and not just for "Normal Power", then the engineers at Mitsubishi did an extraordinarily BAD job of design for an airplane of this size with a fairly high level of installed power to achieve speeds barely 20 MPH faster than the A6M series. This is also about the same level of engine power as the F6F and it would be a rather poor showing to be slower than a much larger and heavier aircraft that has a wing over 50% larger.
The Bearcat also had some load factor limitations because of the design for break-away outer wing panels. Eventually this was addressed but it took a very long time.
- Ivan.
cherry blossom
Senior Airman
- 513
- Apr 23, 2007
I am profoundly agnostic on the performance of the Raiden. Fortunately, we have a survivor so it should be possible to measure everything exactly and use software developed to predict the performance of modern aircraft. The two obvious problems are cost and that there may not be good programs to predict cooling drag.
One interesting difference between the Bearcat and the J2M was that according to J2M Raiden for the Raiden "The propeller is 3.30 meters (10 feet 10 inch) diameter" (thank you for the information) whilst the Bearcat had a 12-foot-4-inch propeller (3.774 metres). Thus the volume of air accelerated by the Bearcat's propeller is 30% greater and thus for any given thrust the increase in the velocity of the air is 30% less. Does this mean that the air flowing over the Bearcat's fuselage is moving slower than the air flowing over a Raiden's fuselage? Does that reduce the Bearcat's drag or make its propeller more efficient?
Of course the cost is a longer undercarriage, weighing more, and an increased risk of propeller strikes but the short length of the Bearcat also helped.
The weakness in the wings was linked to the wing folding. A Japanese Bearcat would not need folding wings if it were a land based fighter or might even be accepted on an IJN carrier without folding as it would still be smaller than their dive bombers. Either way, it would save weight and have stronger wings.
Ever hear of the term disc loading; the horsepower applied to a prop divided by the area of the thrust- producing portion of the prop? The heavier the disc loading, the more power is "wasted" in tip vortices, noise, and heat. Ever hear a small, high powered floatplane (Maule M4, Cessna 185, 206, 207) trying to climb out of a small lake in a narrow mountain valley? BBLLLAAAAATTAAOOWWW! That's wasted power from a high disc loading. The obvious solution is a larger propeller, but the floats get in the way. More blades help raise the total thrust output somewhat, but at the cost of weight, expense, and less efficiency of each individual blade.
So, in answer to the efficiency question, yes; done right, the larger prop should be more efficient. Notice that due to blade shape and a minimalist hub, the Bearcat has a larger portion of its disc diameter actually developing thrust, an advantage conferred by the superior metallurgy available to the US. The stresses and harmonics in that kind of blade design would be too great for the alloys traditionally used in propeller blades.
Cheers,
Wes
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