Ki-84, "Macho blue yonder" and P-51-'38-'47 killer or just another stop gap fighter?

[Karnak]

Wotan,

I actually do think it has been pretty much proven that the service Ki-84 did well over 400mph at it's best altitude.  What has not been proven is exactly how fast it actually was.

Red Tail 444,

Must be you.  The great majority of my fights in the MA do not end in an HO by either participant.

[gwshaw]

Originally posted by Wotan
There's no need to do a 388mph top speed version. It adds nothing to the game at all.

A Homare - 21 @ 1970hp should have np reaching 427mph. The problem lies in finding accurate source info.

Whatever you do dont believe the hype that just because 100 octane was used that it added some 40mph to the Ki84's top speed.

Read that document Nashwan posted in the 150 avgas thread.

"Depending on the plane it gave an average increase of 5 - 15 mph."

That is going from 100/130 to 104/150. Not quite the same as going from going from 87 octane, be generous and call it a PN of 68/98, to 100/130 PN fuel.

Keep things easy, say the Homare was limited to 40 in Hg on a PN of 98. At a PN of 130 that should give a MAP limit of 50.75 in Hg. That is roughly a 25% increase in power. Sqrt of 25 is 5, so about 5% increase in speed, or roughly 19-20 mph.

The P-51D only went from 67 in Hg to 72 in Hg on 104/150, about 7.5% good for about 2.7% higher speed. About 12 mph, right in line with Nashwan's posting.

Those are real rough SWAG figures, I haven't taken lower FTH (or ram) at the higher MAP into account. But going to 100/130 should easily be enough to put it in the 405-410 mph range. I doubt the Japanese fuel was even that good, 68/80 - 68/90 was more likely. That would give another 5-10 mph.

If anyone has some decent Homare/Ki-84 performance figures I plug them and see what engine and plane figures come out.

Greg Shaw

[HoHun]

Hi guys,

If you could sum up the data on the prototype and on its condition and the power settings used, and give me information on which power settings (or levels) were used on the service Ki-84, I could make a fairly reliable estimate how fast the prototype would have gun in service condition.

Do you think you've got enough data for that? I didn't follow all of the posts here.

Regards,

Henning (HoHun)

[Karnak]

HoHun,

Send an email to Mitsu.  He is most likely to have that data.  brady might as well.

[Red Tail 444]

Hey Slash!!!!

Karnak,

Respectfully, IMO the MA is the HO capital of the online flight sim universe, which is why I fly in the CT mostly.

[Wotan]

(AIREVIEW's General View of Japanese Military Aircraft In ThePacific War, Vol.1,pg.320):

Ha-45/11 NK9-B(IJN-nomenclature)
HP(T.O.): 1,800 @ 400mmHg & 2,900rpm
HP(2,000m/6,562-ft): 1,650 @ 250mmHg & same-rpm
HP(5,700m/18,701-ft): 1,460 @ 250mmHg & same-rpm

Ha-45/21 NK9-H(IJN-nomenclature)
HP(T.O.): 2,000 @ 500mmHg & 3,000rpm
HP(1,800m/5,901-ft): 1,860 @ 350mmHg & same-rpm
HP(6,400m/20,997-ft): 1,620 @ 350mmHg & same-rpm

Notes:

1- The Ha-45/21's more-oft quoted T.O.HP is: 1,990, in most other literature - and the less-oft quoted(fully):2,000Hp was more reserved for the "finally-arrived & matured" Ha-45/22, as the very next step, i.e., that the Model 21 was "almost" the Model 22.

[Karnak]

gwshaw,

Note that the use of 100 octane fuel in the US tests were to try to duplicate the effects of methonal-water injecting to attain higher boost settings.  The prototypes did not, as I recall, have methonal-water injection whereas the service Ki-84 did.

Red Tail 444,

I do agree HOs happen more often by far than is desirable, but 90% is a rather huge exageration.

[Red Tail 444]

karnak

For one fight to end in an HO, by an uninvited guest, it's one too many for me.

I've been grounded for several months, so I hope it's gotten better.

[Kaz]

Any progress gwshaw/HoHun?

[gwshaw]

Using starting figures of:

Weight - 7955 lbs
Wing Span - 36.87 ft
Wing Area - 226 ft^2
1460 hp @ 18,700 ft
392 mph @ 20,080 ft
P% - 80% (generally a good ballpark figure)
e - .85 (tapered, rounded wingtips, another good ballpark figure)
Pre-production used an exhaust collector ring, so no significant exhaust thrust recovery

Rammed hp @ 20,080 ft works out to:

(392/100)^2 = 15.37
1460 * sqrt (251.3 / (15.37 + 248.76))
1460 * sqrt (251.3 / 264.13)
1460 * sqrt (.9514)
1460 * .975 = 1424 hp

Gives a Cd0 of .0212

349 mph @ SL on 1800 hp

Min drag at 153 mph IAS, and SL climb of almost exactly 5000 fpm @ 1800 hp, just barely under 4000 fpm @ 2 km on 1650 hp, about 2650 fpm @ 5700 m on 1460 hp.

Everything matches the charts Butch2k posted on the other thread pretty closely.

(edit: looks like butch2k's chart is for the /21 engined version, I missed seeing the power figures in the second chart)

I'll use this as a starting point and see what I can work up for the /21 engined versions a little later.

Greg Shaw

[Wotan]

Crossing posting Butch's chart from the other thread



We can see that your max speed  figures match up with a Ha-45/11 (388/392mph).

[Mitsu]

Let's count down for Ki-84...

[Karnak]

Wotan,

That is just the TAIC estimated performance, correct?

Here is the other document posted by Butch.  Given the Japanese characters it may be more meaningful.

[gwshaw]

Similar starting assumptions

Weight - 7955 lbs
Wing Span - 36.87 ft
Wing Area - 226 ft^2
1620 hp @ 21,000 ft  
P% - 80% (generally a good ballpark figure)
e - .85 (tapered, rounded wingtips, another good ballpark figure)
Slightly cleaned up airframe, so I'll calculate at Cd0 figure of .0210
Call it 150 lbs of exhaust thrust recovery (7.5% of peak TO power, that is the SWAG I typically use)

Give it 2000 ft of ram, matches the 23,000 ft figure in Butch2k's TAIC figures. A bit better than the 1300 ft the prototypes managed.

Use 420 mph as the target speed to calculate charge temp increase for rammed power.

Rammed hp @ 23,000 ft works out to:

(420/100)^2 = 17.64
1620 * sqrt (246.76 / (17.64 + 242.76))
1620 * sqrt (246.76 / 260.4)
1620 * sqrt (.948)
1620 * .973 = 1577 hp

At a Cd0 of .0210 I'm getting a vMax of 441 mph @ 23,000 ft. But, that is a mach number of about .63, which is well into the drag rise area. But the TAIC numbers of 427 sound easily plausible. 427 is doable at a Cd0 of about .0234, about a 10.5% increase in drag. (1140 lbs to 1260 lbs from a Cd0 of .0210 to .0234 @ 427 mph)

I'll work out some other speed/altitude and climb figures later.

Greg Shaw

[HoHun]

Hi Greg,

>At a Cd0 of .0210 I'm getting a vMax of 441 mph @ 23,000 ft. But, that is a mach number of about .63, which is well into the drag rise area. But the TAIC numbers of 427 sound easily plausible. 427 is doable at a Cd0 of about .0234, about a 10.5% increase in drag. (1140 lbs to 1260 lbs from a Cd0 of .0210 to .0234 @ 427 mph)

Using the power figures you provided, I get a 423 mph figure.

There's some uncertainty margin about it, but I think the unknown factors of the source data currently are greater than the inaccuracies of my calculation :-)

It's worth noting that Karnak's data doesn't give a 7 km full throttle height at full speed but just 6.5 km. That difference alone might shave 6 mph off the top speed.

Regards,

Henning (HoHun)