Ki-84 - uber aircraft?

[Sgt. Pappy]

Hey,

I've been looking all over the web and I've been coming across sites many a time stating that the Ki-84 was actually a much superior plane to what the official figures state.

The Ki-84 we all know has a top speed of ~ 380 - 390 mph. This is on the lower-grade octane used by the Japanese during WWII. When tested in the U.S., many sites claim that the Ki-84 had reached ~ 430 mph in level flight when stripped of paint, ammunition (not sure if the weapons were in there or the fuel % being carried) and with the use high-grade U.S. fuel. What grade was this? 100/130 or 115/145? Big difference.

Trying to get to the bottom of the Ki-84's true performance.

Thanks!

 

[merlin]

In Japanese Aircraft of the Pacific War by RRene J Francillon, in the last paragraph on this aircraft he states:

Although production Hayates were plagued by inferior workmanship, they were the most successful Japanes aircraft operating during the Okinawa campaign and in the defence of the homeland, and Nakajima and Mansyu delivered 3,382 production Ki-84s in seventeen months, no mean feat considering the chaos brought about by the B-29 raids. As demonstrated by a captured aircraft restored at the Middletown Air Depot, Pennsylvannia, in the spring of 1946, the Ki-84's performance was truly spectacular: at a weight of 7,490 lb, considered representative of combat operations, the aircraft reached a speed of 427 mph at 20,000 ft using War Emergency Power.

 

[delcyros]

This particular performance is not representative for normal Ki-84´s. Not only have they lightened the plane and used higher grade fuels but also parts of the fuel system and the engine had to be remanufactured. It is not known in how far performance gains may be attributed to these improvements.

 

[Vincenzo]

also the common figure speed 380/390 mph is not representative, japanese not use WEP in official speed test. the japanese figure can't comparate with allied or german

 

[HoHun]

Hi Vincenzo,

>also the common figure speed 380/390 mph is not representative, japanese not use WEP in official speed test. the japanese figure can't comparate with allied or german

Thanks for the information, that's quite interesting! Do you have a source where this is defined (or explained)? It would be most interesting - information of this type is usually hard to find!

Regards,

Henning (HoHun)

 

[Vincenzo]

i read in a forum, in this forum Oleg Maddox's Ready Room - Forum Powered by eve community

 

[Sgt. Pappy]

Thanks!

Though, Vincenzo, that's not really a source since it's just some other person saying the same thing. We mean like official documentation.

Delcyros,
So they tuned the engine differently in order to handle the octane?

 

[Soren]

The Ki-84 did feature excellent low alt performance though, being faster than most US fighters there.

However the main advantage enjoyed by the Ki-84 was its superior maneuverability to all US British fighters.

 

[Vincenzo]

true a forum is not a source, but it's very strange that the japanese fighters is so slow comparate to alllied or european axis fighters. some can try ask a source in that forum.

 

[Vincenzo]

i see may be the our forum document the source see Performance of Late War Japanese Fighters - Topic Powered by eve community
the link a THESE

 

[delcyros]

Delcyros,
So they tuned the engine differently in order to handle the octane?

Yes, I belive so. RG_Lunatic wrote something on this here on an old thread.

 

[Tony Williams]

Using better fuel would not of itself make much difference to performance. The whole point of higher-octane fuel is that it enabled higher cylinder pressures to be developed (through using higher compression ratios or higher supercharging pressures) without the fuel reaching detonation point, thereby producing more power.

So you would have to modify the engine to get significant benefit from better fuel.

 

[JoeB]

Though, Vincenzo, that's not really a source since it's just some other person saying the same thing. We mean like official documentation.

AFAIK there is no definitive published source about the 'real' speed of the Type 4 Fighter (Ki-84, 'Frank'). Anotehr forum with high quality discussion about Japanese a/c is j-aircraft.com, see their FAQ's page for archived Ki-84 threads which cover this topic. No definitive answer but two likely facts are that Japanese official numbers did indeed tend to be conservative, and 388 is for an early not definitive version. I agree web forums always have the question of 'who are these guys?' and usually several people saying opposing or not exactly the same things; OTOH serious researchers and authors do post on web forums.
Return to Faq

Another piece of info, though not an answer either, is this US intel manual (below) from March '45 listing the top speed of the Type 4 as 427mph at 20k ft. Note this is before the end of the war and therefore the postwar trials which according to Francillon achieved the exact same number, suggesting the possiblility that 427 was a calculated estimate, and no trial ever produced it. AFAIK nobody has found the original trial results Francillon refers to.

As to actual Type 4 combat results, we had a good thread here recently comparing claims and losses from Japanese, US and Chinese published sources for Type 4 v P-40 ops in China in 1944. US/Chinese P-40 units held their own.
http://www.ww2aircraft.net/forum/aviation/p-40-vs-late-war-japanese-fighters-10144.html

Some other two side documented (losses are given, claims not mentioned) combats including Type 4's are:

Jan 7 '45: 4 P-38's of 475th Grp fought a single Type 1 later assisted by a single Type 4, Leyte area. 2 P-38's were lost (including the ace Tommy McGuire) plus the Type 1 lost/KIA; the Type 4 crashlanded.

Jan 8, 45: FM-2 Wildcats from VC-20 and VC-21 downed apparently 3 and 5 respectively from a mixed force of 73rd Sentai Type 4's and 19th Sentai Type 3's ('Tony'), without loss.

July 28, 45: 47th Sentai lost 8 a/c when bounced near their airfield by VF-16 F6F's.

Aug 13, '45: 22nd and 85th Sentais lost 11 fighters (probably all Type 4's) v 1 507th FG P-47N lost in the Seoul, Korea area.

August 14 '45: 47th Sentai lost 2 Type 4's v 1 35th FS P-38L.

"Naval Aviation Combat Statistics" quotes USN claims and losses by type for Sept '44 thru end of war, as 114 Franks downed v 12 F6F's 28:4 for F4U's. Problem is, besides the usual of not knowing exactly how those US victory credits correlate with actual Japanese losses, there were a lot of mis-ID's among a pretty large number of basically similar looking Japanese radial fighter types late in the war. For example, no FM claims v Franks are listed because in the case above the FM's believed the radial opponents were 'Tojo's'; and several of the F6F losses were in a combat Henry Sakaida shows in "Genda's Blade" to have been v. JNAF 343rd Air Group Shiden (N1K1J 'George'; that book estimates btw the 343rd was on short end of a 1:3 actual kill ratio v US fighters; it's not the same type, but at least it's data of two sided research of a bunch of late war combats for a comparable type, AFAIK there's no systematic data for any Type 4 unit in the home defence theater).

That's a pretty small sample of all combats including Type 4's (others, please ) but the point is there aren't many two side documented cases of Type 4's defeating US fighters, AFAIK. The 'other' factors tended to be stacked against the Type 4's; and in the Type 4's case there's more uncertainty than usual about the 'plane' factors, even besides the usual question of how to convert a technical measure like speed into a quantitative measures of combat effectiveness.

Joe

 

[Sgt. Pappy]

Thanks again all! Very interesting info. Especially that writeup, JoeB. Is that all from the link?

True, Williams. But this cannot be said for all engines. The Merlin 66 at one point ran on 100 grade UK Octane (100/125 US grade I think?). With almost no modification to the engine took on 150 UK grade (115/145 US grade) and look at the huge performance boost it got at low-med alts just from that octane grade.

It seems that some octane grades differ enough to boost performance.

Kind of like an exam. Say you need 75% to get some kind of award or degree. If you get 60% you don't fail the test but you don't get your degree. If you get 74% that's great but you still need 1%. So a fuel grade of say, 140 UK grade (just an example) would probably not increase performance, but it is substantially higher graded than 100. Then just 10 more grades up and voila, performance boost.

 

[JoeB]

Thanks again all! Very interesting info. Especially that writeup, JoeB. Is that all from the link?

No, the relevant stuff on the j-aircraft FAQ's (especially Ki-84 part 2), is mainly about the speed question, so most of what I posted isn't there, and OTOH I recommend that link for lots of stuff I didn't post

Joe

 

[Tony Williams]

True, Williams. But this cannot be said for all engines. The Merlin 66 at one point ran on 100 grade UK Octane (100/125 US grade I think?). With almost no modification to the engine took on 150 UK grade (115/145 US grade) and look at the huge performance boost it got at low-med alts just from that octane grade.

It seems that some octane grades differ enough to boost performance.

The "almost no modification" consisted of changes to the supercharging in order to increase the boost pressure quite considerably, and that's what increased the performance - which is the point I made.

I have in front of me "The Merlin in Perspective", an official publication of the Rolls-Royce Heritage Trust. This includes the following information:

The Merlin was first developed on 87 octane fuel, at which the maximum permissible boost pressure was +6 psi. Changing to 100 octane immediately enabled the pressure to be increased to +12 psi, which increased the power from just over 1,000 to 1,300 hp.

Further development (particularly a two-stage supercharger, together with modifying the constituents of the fuel to better suit the engine) enabled the boost pressure to be increased to +18 psi, increasing the power to 1,600 hp.

The final development came with 150 octane fuel in 1944, which enabled the boost pressure to be raised to +25 psi and the power to over 2,000 hp.

Through all of the above, the Merlin stayed basically the same (apart from durability/longevity improvements); the increasing performance was entirely down to increasing supercharger boost pressures, which was only made possible by using improved fuels.

 

[Sgt. Pappy]

Ah yes. I have borrowed that book and I really want to get myself a copy.

That's interesting. The 150 grade, though, doesn't seem to need modification to the supercharger. I'm still bad with my terminologies but I'm reading off of Spitfire IX Trials at +25 boost
I could be wrong, but I just haven't found any modification pertaining to the supercharger or other parts to allow the use of 150 grade.

The other grades, yes but not 150.

 

[merlin]

Fellow 'posters' may be interested in the introductions to the Nakajima Ki-84 Hayate.

First from Francillon:

The Nakajima Ki-84 Hayate, undoubtedly the best Japanese fighter aircraft to see large-scale operation during the last year of the war, was as feared by Allied crews as it was praised by Japanese pilots. Well protected, well armed, fast and manoeuvrable, this fighter gave a good account of itself in the desperate battles over the Phillipines, the Ryukyu Islands and the Japanese Home islands, and Japan's faith in it is emphasized by the fact that at the end of the war they were building inderground factories with a planned rate of 200 Hayates per month.

Second from Wllm Green:

During the summer of 1944 the J.A.A.F. introduced a new warplane, the Ki-84-1a or Type 4 Fighter, Model 1a, which was destined to become for the Allies the most troublesome Army fighter encountered in combat from that time until the end of the war. Employed in all operational theatres, and used for high-, medium-, and low-altitude interception, close-support and dive-bombing, the Hayate differed radically from earlier J.A.A.F. fighters, in that relatively light construction gave place to an extremely sturdy structure. It compared favourably with the best of its antagonists; it was slightly slower than the P-51H Mustang and the P-47N Thunderbolt, but it could out-climb and out-manoeovre both American fighters.

For such good write-ups, the designers must have done something right. It was not the aircraft's fault if, at times poor workmanship or maintenance gave it problems at crucial times.

 

[JoeB]

Fellow 'posters' may be interested in the introductions to the Nakajima Ki-84 Hayate.

First from Francillon:

The Nakajima Ki-84 Hayate, undoubtedly the best Japanese fighter aircraft to see large-scale operation during the last year of the war, was as feared by Allied crews as it was praised by Japanese pilots.
Second from Wllm Green:

During the summer of 1944 the J.A.A.F. introduced a new warplane, the Ki-84-1a or Type 4 Fighter, Model 1a, which was destined to become for the Allies the most troublesome Army fighter encountered in combat from that time until the end of the war.
For such good write-ups, the designers must have done something right. .

This is apropo to the recent off topic tangent on another thread about aviation authors. It particularly mentioned criticism of Green, who I defended as a good basic source but outdated. Francillon wasn't mentioned but has also written a lot of accurate, and some pretty inaccurate, things over his long career.

See my post on the first page (and the link to excellent earlier thread on this forum about Type 4 ops in China). I don't know of any two side documented combats where Type 4's were so successful as to be 'feared' or even very 'troublesome'. A potentially good plane yes, but actually successful or 'feared' in the circumstances pertaining, much more doubtful, at least as far as fighter v fighter combat.

As a kid I read Green's series when it was pretty new, and I still refer to Francillon's 'Japanese A/c...' all the time (though with due caution, not just about those kind of generalizations, but which units operated planes, how many produced, etc. there are apparently a fair number of errors in that info). Once upon a time I would assume the kind of general characterizations in those books were backed up with a lot of well documented examples of particular combats, but now I realize that's a doubtful assumption.

Joe

 

[renrich]

Merlin, I would be extremely surprised if the KI 84 could out climb a P51 H although I don't know if they ever encountered one another. A fighter the KI 84 probably did encounter which it would not have had many if any advantages over would have been the F4U4.