Ehh, it would be nice if someone actually based on a decent source in regard to Ki-61.
First, the fuel capacity. Early Hiens had four fuel tanks : two 190 l wing fuel tanks, one 170 l center-wing fuel tank and one 200 l rear fuselage fuel tank. The last one was only used in very long flights and even during escort missions it was preferred to carry two drop tanks rather than load the rear fuel tank. Why ? Because it created stability issues moving the Center of Gravity of the machine to the rear (reminds P-51D, doesnt it ? ). Most of the time this fuel tank was left empty or even removed.
Soon after production of Ki-61-I Otsu started (after producing 90 or so airframes) it was removed completely. Thus total capacity was reduced from 750 to 550 liters.
This was further decreased after producing about 150 Ki-61-I Otsu, when additional protection to the fuel tanks was provided, reducing capacity of wing fuel tanks to 170 l and center-wing fuel tank to 160 l - overall capacity decreased from 550 to 500 liters.
And then we have this report:
http://www.wwiiaircraftperformance.org/japan/Tony-I.pdf
No under seat tank and total fuel capacity of
about 550 liters, arguing over 2-3 liters is foolish. Especially considering manufacturing tolerances and conversion charts/formulas.
Apparently there was quite a variation in tanks fitted and perhaps even their capacities.
Also of interest is the performance of the captured plane against US fighters, most of the comparisons are pretty much forgone conclusions but comparing it to the FM-2 is interesting, especially considering the test weight of the Tony was 6150lbs and not the 6982lbs shown in some of the other charts with the 199-200 gal fuel load.
Perhaps the captured plane's engine wasn't running right or the plane was mis-rigged (out of alignment?) but it was a dog when climbing compared to the FM-2 (which is over 1000lbs heavier) and adding 300lbs of fuel and then extra protected tank weight certainly wasn't going to help.
This was one of the two Ki-61s tested in US. I believe in one of them engine stopped working during the testing leading to plane crash. Either this was the mentioned in report model or the other one. But makes no difference, since aircraft had multiple issues. None of the Hiens was captured even in decent conditions and it took engineers weeks to bring them back to flyable condition. Hardly it represents the actual machine performance.
Fortunately I have Ki-61 Piloting Procedure (sort of a pilots handbook) captured in 1944 in Hollandia. I once made a comparison of it to Bf 109 F-1 / F-2 powered by Db 601 N so a bit better performing engine if compared to Ki-61 powered Ha-40 (license built Db 601Aa).
Results at rated power were :
Ki-61 (Ha-40) vs Bf 109 F-1 / F-2 (Db 601 N)
Level speed
Alt
1 km 496 km/h 514 km/h
2 ....... 520 ......... 534
3 ....... 545 ......... 553
4 ....... 569 ......... 573
5 ....... 589 ......... 592
6 ....... 591 ......... 594
7 ....... 589 ......... 590
8 ....... 580 ......... 580
9 ....... 561 ......... 565
10 ....... 523 ......... 523
Time to altitde in min (rate of climb in m/s)
Alt
1 km 1-20 min (14.3 m/s) / 1 min (16 m/s)
3 ............... 3-34 (16.8) / 3-12 (16)
6 ............... 6-50 (11.1) / 6-30 (11.2)
8 ............... 10-48 (6.9) / 10-30(6.4)
10 ............... 17-14 (3.3) / 18-42(2.5)
Data for Bf 109 F-1 / F-2 based on Specification sheet for the Bf 109 aircraft type, models F-1 and F-2 with DB 601N engine from Kurfurst.org website -
http://kurfurst.org/Performance_tests/109F1F2_Kennblatt/Kennblatt_fur_Bf109F1F2_DB601N.PDF .
Ki-61 certainly wasn't the best performing aircraft around, but it wasnt nearly as bad as the US report made it look like. As often it is captured aircraft fail to present full level of performance simply due to state they were captured in, lack of knowledge about operation of the aircraft by the intelligence and crews and finally lack of desire to push the aircraft to the limits and loose the precious object.