Thoughts on the Nakajima Ki-84 and Kawasaki Ki-100

[taly01]

Was your Ki-100 model included in some Il2 1946 mods or mod packs?

No, I had started playing with the il2 air files last year and I ended up changing so many planes it took me ages to test them, I have a sorted set now thats all tested. I will probably release the "buttons" pack of them at mission4today some time, and also put the raw files up for any other people who make il2 mods.

I think most flight sim gamers just pull and pull because, otherwise, they cannot keep their opponents in sight / in-screen.

I used to play Warbirds online back in the 2000's, playing vs real people is different to AI, I barely had a 1:1 kill:death ratio. Most people just were really good at pulling max. G turns to get the kills but a few times I came up against "experts" who would avoid combat and not go for the quick kill, then they would totally get me out of position and energy and shoot me down, a lot more embarrassing than just been out turned

TrackIR (or similar) head tracking software definately transforms the flight sim experience, been able to lean and look a bit around the cowl when landing is very cool.

 

[MiTasol]

Has anyone seen the US report on their testing?

Nakajima Ki-84 Hayate (Gale) 'Frank' from the right

Here we see a Nakajima Ki-84 Hayate (Gale) 'Frank' that had been captured by the Americans and used as a test aircraft. The K-84 was the best Japanese fighter to see significant service during the Second World War, and Nakajima's last radial powered fighter.

www.historyofwar.org

There are two reports here on the site somewhere but I cannot find them so am reposting below

 

[Darthtabby]

Can anyone verify that the 427mph figure for the Ki-84 was actually achieved in testing rather then being an estimate? The Interim Report No 3 that MiTasol posted includes speed and climb figures on the "Factual Data" page, but section 3. d. Climbs says that "It is apparent that the rate of climb of the Frank-1 is very good although no performance climbs were attempted due to flying time restrictions." while section 5. Performance simply says "None obtained."

Francillon's Japanese Aircraft of the Pacific War credits the 427mph figure to testing at Middletown Air Depot in 1946 but I wasn't able to find anything about speed in the Middletown Test document that MiTasol also posted (though under Operational Limits on Page 133 there was a comment that "Rate of climb with maximum power up to 20,000 feet is approximately 3000 feet per minute.").

 

[spicmart]

I sometimes read that the Ki-100 was a very good diver which is hard to believe as it is not very aerodynamic nor does it weigh much nor does its engine has too much power.
It were able to keep up in a dive with a P-51 which frankly is ridiculous.

 

[eagledad]

Darthtabby

Perhaps this will help?


Eagledad

 

[spicmart]

How do you think would a Ki-84 powered with Allied high-quality-fuel have fared against a late-war Spitfire XIV?

 

[Shortround6]

Not well.

Supercharged aircraft engines were rather complex.

Water Methanol injection does a number of things at the same time.

It cools the intake charge, this does several things. The lower intake temperature carries right through the engine, lower peak temperature in the cylinders and lower exhaust temperature. it acts like an internal coolant. The lower intake temp means the intake charge is denser (more fuel/air per cubic ft) meaning a bit more power. The cooler intake charge has bit more head room before detonation sets in. If this allows a bit higher boost to be used then you get even more fuel/air into the engine for more power (although now the temperature starts to go up again).

The water/methanol acts like an internal coolant. It absorbs some of the heat from the engine (and/or the heat of combustion in the cylinder) and carries it out the exhaust.
It also provides reaction mass for the exhaust thrust. exhaust thrust is the total mass of exhaust gasses/products time the exit veleocity.

Now will substituting allied high quality aviation fuel satisfy all those requirements?
Perhaps if you run it really rich so unburned fuel is leaving the exhaust pipes you can get some or most of those benefits.

How close to the edge was the Homare running to begin with in regards to engine strength and cooling?

If the engine over heats you cook the oil and the carbon deposits are going to score cylinder walls/piston rings pretty quick and lead to bearing failure.

The problem with most of these engines was not making power to begin with, it was keeping the engine running at high power levels without something breaking.

Please remember that the F4U-4 and F6F-5 used C series R-2800 engines which required about 10% less cooling air flow to cool the engine if it was making the same power as the older B series engines. They also used intercoolers to cool the intake charge. They also used water/methanol injection to further cool the intake charge and the engine at high power levels.

The Homare didn't have increased cylinder barrel and cylinder head fin area, it didn't use an inter cooler (or after cooler), it was using a fair amount of water injection to reach the power levels it did have. It was also not known for either reliability or longevity at the existing power levels.

Filling the tank/s with 100/130 or higher and cranking the boost up was not likely to end well.

 

[MiTasol]

Cooling using fuel is normal on air cooled engines at takeoff power and can be scheduled for other settings if required by the designer. This also allows higher engine power through higher boost but the offset is that there is a partial power loss due to the mixture being outside the most efficient range plus a lot of the oil on the cylinder walls is washed away leading to lower engine life.

And structurally if the cylinder head to barrel joint is designed for maximum cylinder pressure of X whenever you are operating above that pressure there is a significant chance of the head splitting in two and/or jumping threads. Both then often lead to other failures and consequences. For the airframe driver a windshield covered in oil is probably the most attention grabbing. If it is a lower cylinder the rapid loss of oil can result in other attention grabbing failures.

One place I worked we had one self proclaimed genius destroy 3 R-1340s over three weeks before we learnt he was using 40" for takeoff when the engine is only rated for 36". He never did that while another pilot was flying with him but when on his own or with non flying/non maintenance staff on board he always did it.

Fortunately a cleaner dobbed him in before he killed an aircraft or passengers.

 

[Shortround6]

On some of the R-2800s when water injection was being used a de-enrichment circuit in the carb/ throttle body cut the amount of fuel being introduced into the intake airstream.

For the older F4U

Note that at WEP the engine used 45 gallons an hour less than at take off or low altitude (engine supercharger only) settings while making more power. The extra 30-45 gallons per hour (0.5-0.75 gallons per minute) was being used as coolant when water injection was not being used.

 

[Ivan1GFP]

I sometimes read that the Ki-100 was a very good diver which is hard to believe as it is not very aerodynamic nor does it weigh much nor does its engine has too much power.
It were able to keep up in a dive with a P-51 which frankly is ridiculous.

Hello Spicmart,
The issue with diving speed limitations often isn't one of power or weight but one of structural strength, especially when discussing Japanese aircraft. One place this can be seen is in the evaluation of Koga's A6M2. The US pilots thought the diving speed was actually pretty good when compared to the Wildcat and others during the test. What they didn't have was an operating manual for the aircraft which might have told them that they were exceeding the allowable speeds for the type.... The A6M2 didn't weigh all that much either.
The Ki 61 / Ki 100 had a particularly strong airframe in comparison to other Japanese types.
Another issue might be when it encountered Compressibility. That was the main advantage the P-51 had over other US fighters in Europe.

How do you think would a Ki-84 powered with Allied high-quality-fuel have fared against a late-war Spitfire XIV?

I believe that at low altitudes, the Ki 84 would have been fairly competitive with a Spitfire XIV. Each has its advantages but I would give a slight edge to the Spitfire even assuming the Ki 84 was running up to specifications which most were not. Of course I have never flown either one....
At higher altitudes, the Spitfire had all the advantages. The Ki 84 had a relatively low displacement engine for a radial, it didn't run all that much boost even at maximum settings, didn't have an intercooler and didn't have enough supercharger to really compete. Its maximum boost pressure was only about 50 inches Hg. It is rather interesting that the engine could make as much power as it did though one has to wonder about long term durability.

As for a change in fuel, I don't think it would make any difference at all unless you reconfigure the engine management but at that point, you are not really dealing with a Ki 84 any more. The aircraft was designed to run on 91 / 92 octane fuel with automatic use of Water Injection when certain boost settings were reached. Those settings were quite low. Basically almost anything over maximum cruise power would cause Water Injection to kick in. That is why it carried so much of it in proportion to the internal fuel load.
This is all detailed pretty well in the Middletown Test Report.
I uploaded it here a few years back but no one seems to ever find it and read it.
Japanese Aircraft Performance

- Ivan.

 

[DarrenW]

Please remember that the F4U-4 and F6F-5 used C series R-2800 engines

Hey Shortround great post with lots of interesting information but I need to make a small correction. The F6F-5 only used the B series R-2800, while the two prototype XF6F-6 were equipped with the C series engine. Small detail I know but I thought it was worth mentioning.

 

[DarrenW]

I don't believe the F6F-5 made 410 mph.

I think it was the F6F-6 (population 2).

Either way, the F6F was enough to win in the Pacific.

Cheers.

Hi Greg,
I think Dawncaster was referring to a modified F6F-3 which had many features of the later F6F-5. We had a discussion about the 410 mph top speed in another thread and we believe the reason was due in part to less operational restrictions which would eventually reduce engine power in later aircraft (possibly to provide greater safety margins and longer engine life). The speed was obtained at 21,000 feet during January 1944 testing. These restrictions caused a drop in speed for the F4U-1A as well (431 vs 417 mph).

 

[GregP]

The Ki-100 has always been a bit of mystery to me. Most literature generally sings its praises, as one of the greatest high performance late war fighters to enter service, however that is juxtaposed with its actual performance numbers. The airplane probably would have been excellent in 1942-43, but its contemporaries in 1945 were the P-47N, Spitfire Mk.XIV, Ta-152, etc. Some of which had an almost 100mph speed advantage

Have to disagree with this post. The Ta 152 and Spitfire XIV were never true contemporaries of the Ki-48/100. These airplanes (Ta 152 and Spitfire XIV) fought in the ETO and never made an appearance in the PTO during the war. Contemporary in time, sure. Contemporary in combat, no.

The P-47N was, as was the P-51D, F6F-5 and P-38. When compared with these the Ki-84 and Ki-100 come out pretty well. They weren't as fast as the fastest Allied planes that fought there but, they were fighting over their home and didn't need to run anywhere. The Ki-84 was fast enough to be ignored by the U.S. forces on radar unless the Ki84(s) were approaching for an attack. Both could mix it up with the aircraft being flown by the Allies and, if well-flown, could hold their own and give back pretty well.

They were definitely the cream of the crop of Japanese WWII fighters when compared with other choices except for the N1K and J2M families.

They produced 3,423 Ki-84s, 395 Ki-100s, and 2,803 Ki-61s. That is 6,321 fighters. Add another 2,000 or so for the N1K and J2M and you have about 8.200 fighter aircraft of the first rank. Everything else that was modern added up to maybe 18,000 wartime fighters (10,500 A6M, 5,920 Ki-43, 1,1225 Ki-44). That is just over 31% of the fighters that were really 1st-tier. That is not counting the A6M, which I would tend to add to the good side of the airplanes, if not to the best-performing side.

So, the Ki-84 and Ki-100 likely were highly sought-after as assignments for top fighter pilots that never saw a Ta 152 or Spitfire XIV and likely never heard of either.

Hi Dawncaster. At top speed, yes, the F4U is slightly faster using ram air. At normal flying speed, it isn't. If they are flying at 330 mph of less, there is nothing to choose between them, speedwise, and they fly side by side at equal power settings. At absolute top speed, the Corsair is faster, especially once you get to the F4U-4 variant and above. An F4U-1? Not really much faster, if any, except on paper. The guys that fly them today say that, not the William Green, et al books, and certainly not me as personal claim. But I DO believe the pilots today who fly the warbirds.

 

[Just Schmidt]

Have to disagree with this post. The Ta 152 and Spitfire XIV were never true contemporaries of the Ki-48/100. These airplanes (Ta 152 and Spitfire XIV) fought in the ETO and never made an appearance in the PTO during the war. Contemporary in time, sure. Contemporary in combat, no.

The P-47N was, as was the P-51D, F6F-5 and P-38. When compared with these the Ki-84 and Ki-100 come out pretty well. They weren't as fast as the fastest Allied planes that fought there but, they were fighting over their home and didn't need to run anywhere. The Ki-84 was fast enough to be ignored by the U.S. forces on radar unless the Ki84(s) were approaching for an attack. Both could mix it up with the aircraft being flown by the Allies and, if well-flown, could hold their own and give back pretty well.

They were definitely the cream of the crop of Japanese WWII fighters when compared with other choices except for the N1K and J2M families.

I agree that comparing with fighters in other theaters at least from a practical standpoint is not neccessary, even though it has its place in a discussion of their theoretical merits as designs.

However I do not agree that the Ki 100 belongs in the same legue as the Ki 84, and apart from nice handling it is not head and shoulders over everything but the N1K and J2M.

The Ki 43 III managed about the same speed and got cannons, the Ki 44 already in 43 beat its performance, and the A6M8 also reached about the same speed. The Ki 43 and A6M8 were not produced in large numbers, but there were no technical reasons why they could not have been. The Ki 61 that arriwed more than two years before had about equal performance, amongst other thing exellent diving characteristics, and even if not handling as well as the Ki 100 it did not handle badly. Its achilles heel was the temperemental engine, but as performasnce was considered in ferior to new allied types, the more powerful Ki 61 II was put into production with less than stellar results. The first 270 or so Ki 100 were engineless Ki 61 II airframes. The decision to continue production from there on probably was partly to avoid disruption of production by switching to another type, partly because the Ki 100 was no worse than the newest army types, exepting the Ki 84 that in my opinion easily bested all the others. The Ki 1000 did have a more reliable engine, though.

Not all green pilots did well with the Ki 100. The 111th sentai formed on july 10th 1945 was quickly decimated ( Green and Swanborough, Japanese army fighters part 1 Macdonald and Janes 1976: 45. That they are in no way dismissive of the aircraft and indeed notes its popularity with its pilots. But maybe the pilots of the Ki 43 III had praised that too, had production priority not switched to the (far superior) Ki 84?

I do consider the Ki 100 a good fighter, but it was, in my opinion, two years too late.

 

[DarrenW]

The Ki-100 generally had a better build quality than the Ki-84 and the engine was more reliable so I suspect it performed closer to factory specifications. It's well accepted that the true performance of the Ki-84 was never fully realized by front line units. Lastly, the JAAF thoroughly tested the two aircraft side by side and judged the KI-100 to be the superior fighter.

 

[MiTasol]

Would love to see that comparison

 

[DarrenW]

Now when the engine was upgraded in the F4U-4 and XF6F-6, the Corsair gained significantly more speed while the Hellcat did not.

Actually both aircraft gained about 25 mph in maximum level speed with the C series R-2800 engine, a difference similar to earlier variants (446 and 425 mph respectively).

 

[DarrenW]

I do have one Japanese book with 367 mph top speed and pretty god climb ... about on par with the F6F-5, which was its main adversary

The F6F-5 in clean condition using WEP could honestly touch 400 mph and with wing pylons, belly shackles, and rocket launchers was still good for about 385 mph (per US Navy wartime documents). By comparison the Ki-100 stated speed of 367 mph (Francillon says 360 mph) was most likely attained at the factory in pristine condition and with quality fuels, which by 1945 was a very rare thing to find with Japanese aircraft in general.

 

[GregP]

I sometimes read that the Ki-100 was a very good diver which is hard to believe as it is not very aerodynamic nor does it weigh much nor does its engine has too much power.
It were able to keep up in a dive with a P-51 which frankly is ridiculous.

Not very aerodynamic? It is easily more streamlined than the P-47, and a P-47 has a great reputation as a good diver. Why not the Ki-84? Facts would indicate it was limited by wing flutter, not by aerodynamic drag. Anything diving with 2,000 hp isn't exactly going to be slow unless it has big dive brakes.

Engine does not produce much power? The P-47 had 2,000 hp for most of its service life. The Ki-84 did, too.

Doesn't weigh much? Overload for long range is over 11,000 pounds! About the same weight as a P-51D at long-range weight, give or take a bit.

Just saying ...

 

[DarrenW]

Hi Dawncaster. At top speed, yes, the F4U is slightly faster using ram air. At normal flying speed, it isn't. If they are flying at 330 mph of less, there is nothing to choose between them, speedwise, and they fly side by side at equal power settings. At absolute top speed, the Corsair is faster, especially once you get to the F4U-4 variant and above. An F4U-1? Not really much faster, if any, except on paper. The guys that fly them today say that, not the William Green, et al books, and certainly not me as personal claim. But I DO believe the pilots today who fly the warbirds.

Official US Navy testing utilized specialized test equipment and in general found comparable models of the F4U faster than the F6F in most cases by about 20 mph up high and 30 mph down low under all power settings. This had nothing to do with airspeed indicator errors as all of this was taken into account during testing.

One thing to remember is that the Hellcat in a clean condition could often fly about as fast as a Corsair having wing pylons, belly shackles, and rocket launchers (this configuration reduced top speed of F4U by up to 25 mph). This is a reason why under certain circumstances they could fly side by side at similar throttle settings. During the war Hellcats often flew top cover for Corsair squadrons performing dive bombing missions.