1,990 hp N1K2-J... Naw, not a chance.

[Widewing]

I have not been able to locate specific drag numbers for the N1K2. However, we can make some well founded judgements based upon aircraft of similar size and configuration, for which, I do have data.

To begin, once you know the drag coefficient of the aircraft, you can calculate the flat plate area.

Cdo = Drag Coefficient
Sw = Wing area in square feet.

Cdo x Sw = flat plate area.

Now, take the known horsepower and divide it by the flat plate area. This gives us the available HP per square foot of flat plate area, or HP/f.

Let's look at the F4F/FM-1. It has a zero-lift drag coefficient of .0253 and a flat plate area of 6.58 sq/ft. With 1,200 hp available, the HP/f is 182. This allowed for a max speed of about 320 mph.

How about the P-47B? Its Cdo was .0213 (its wing was especially clean and thin) and a flat plate area of 6.39 sq/ft. With 2,000 hp on tap, the HP/f is 313. This aircraft was capable of speeds just over 420 mph.

Now, let's look at the lowly P-39D. Its Cdo was an excellent .0217 and a flat plate area of 4.63 sq/ft. Having 1,150 hp, this provides for a HP/f of 248. Max speed was 368 mph.

Finally, we can look at the N1K2. Based upon camparible radial engine fighters, I will give it a generous Cdo of .0240. We find that the wing area is 253 sq/ft.

So, 253 x .0240 = 6.07 sq/ft.

Let's assume for a minute that the Homare radial actually generates 1,990 hp.

1,990/6.07 = 328 HP/f

That's considerably higher than the P-47B, yet the Thunderbolt is more than 50 mph faster! How can this be? Simple, the Homare was not making anything close to 1,990 hp.

Let's plug in 1,500 hp into the equation.
1,500/6.07 = 247 HP/f.

At this point, let's go back to the P-39D with its HP/f of 248. The P-39D could manage 368 mph. The N1K2 could reach only 369 mph.
Do you see the correlation? Based upon this method, the Homare was making no more than 1,525 hp, which is fully 465 hp less than rated.

This may be a backdoor method of calculating approximate horsepower, but I'll wager large that it stands up well to any other methodology used for the N1K2-J.

Now, as to climb. This is largely determined by weight and power. However, drag is also a critical factor. Let's compare the Bell P-63A and the N1K2.

Normal combat weight for the P-63A is 8,800 lbs. The N1K2 weighs in at 8,818 lbs loaded for combat (no external stores, full fuel and ammunition for both). It takes the N1K2 7.36 minutes to get to 19,685 ft (6,000 meters). The P-63A gets to 20,000 ft in 5.72 minutes. The Bell has only 1,325 hp available. So why does the P-63A climb so much faster than the N1K2 if the N1K2 has more power and equal weight? The answer is that the N1K2 had much less power than rated. Moreover, the P-63A has much lower drag numbers.

Cdo = .0182
Sw = 248 sq/ft
Flat Plate area = 4.51 sq/ft
HP = 1,325
HP/f = 293

If the N1K2 was making 1,990 or even 1,800 hp, it would climb as well as the P-63A. The fact is that it does not even come close. So,
this tends to support the 1,525 hp estimate.

For JimDandy:
Power is determined by HP and propeller efficiency. Typically the WWII fighters had prop efficiencies in the 80% range, give or take 2%. Based upon this, Francis (Diz) Dean provides a simple formula to determine drag as equalized by thrust.

Thrust (in pounds) = 375 x prop efficiency x horsepower/TAS (true airspeed).

His example is that of a P-40 maintaining a constant 280 mph with 900 hp.

T = 375 x .80 x 900/280 = 964 lbs of drag, which must be equalled by 964 lbs of thrust to maintain a constant speed.

No WWII fighter ever produced thrust equal to its weight. Even the F8F would require over 10,000 lbs of thrust to accelerate straight up. Let's assume he is climbing at
125 mph, and not accelerating.
T = 375 x .80 x 4,500 hp/125 = 10,800 lbs, which is pretty close to weight + drag.
This would allow for a climb rate of about 11,000 ft/min., straight up. This is not out of line for the hotrod F8F that set the time to 10,000 ft record of just under one minute. However, this was a stripped down fighter making nearly 4,000 hp. We know that the production F8F could manage 4,570 ft/min. with 2,100 hp. Surely, it had nowhere near a 1:1 thrust to weight ratio. 1:2 at the very best. So, yes, you were probably looking at the numbers associated with the record breaking hotrod F8F.

Other interesting HP/f ratios:

P-51D: 366 (437 mph)
P-38J: 355 (421 mph)
P-47M: 422 (475 mph)
F6F-5: 253 (380 mph)
F8F-1: 368 (440 mph)
F7F-1: 372 (445 mph)

The correlation is interesting but certainly not linear.

Data sources:

America's One Hundred Thousand by Francis Dean

The American Fighter by Angelluci and Bowers

The Complete Book of Fighters by Green and Swanborough.

My regards,

Widewing

[Karnak]

Widewing,
I think your calculation is not taking into consideration that the Japanese fuel, at 87 octane, will cause the engine's power to diminish far more rapidly than the high octane fuel that the US used.  Thus the N1K2, like all Japanese fighters, will be much more competetive at low altitude where there is more oxogen for the engine to breathe.  Any climb to 19,000 feet is going to introduce this weakness of the Japanese fighters, and thus increase the amount of time it takes to reach altitude.

That said, it is an aknowledged fact (I have heard) that the N1K2 performs too well at altitude in AH.  It also bleeds energy a little too slowly in turns.

------------------
We few, we happy few, we band of brothers;
For he to-day that sheds his blood with me
Shall be my brother

Sisu
-Karnak

[fscott]

You know, I try to look at all these numbers and equations - people think up some amazing things to try and force an aircraft's handling the way they think it oughta be, and I just shake my head.

I go back to a statement I see over and over in US pilot journals and aircraft books, which states plainly that the Niki's maneuverability was *almost unbelievable*.


fscott

[Widewing]

 

Originally posted by Karnak:
Widewing,
I think your calculation is not taking into consideration that the Japanese fuel, at 87 octane, will cause the engine's power to diminish far more rapidly than the high octane fuel that the US used.  Thus the N1K2, like all Japanese fighters, will be much more competetive at low altitude where there is more oxogen for the engine to breathe.  Any climb to 19,000 feet is going to introduce this weakness of the Japanese fighters, and thus increase the amount of time it takes to reach altitude.

That said, it is an aknowledged fact (I have heard) that the N1K2 performs too well at altitude in AH.  It also bleeds energy a little too slowly in turns.

I have mentioned this elsewhere and this is exactly my point. What prevented the Homare from developing its rated power was the 87 octane fuel limitations. This results in lower manifold pressure. Usually, the propeller is re-indexed to provide greater efficiency at lower MAP. Indeed, it was the lower octane fuel that kept power down to the 1,500 hp range. However, this was a supercharged engine and it shifts from low to high blower based upon altitude and throttle setting. The intention is to maintain something close to sea level density in the intake air charge. The lower octane limits MAP, and has no significant relationship to altitude. The anti-knock compounds have no idea what height you are flying at.   The fact remains that you are limited to, let's say 44 in/Hg, regardless of your altitude. Exceed this with the Homare and you will experience detonation and rapid engine failure (not unlike the Allison V-1710-F17). Without higher octane, or at least ADI (water injection), the Homare could not produce anywhere near its rated power.

Just for the hell of it, I graphed some HP/f vs TAS examples. Lo and behold, they are far more linear than I had originally thought.

Here's the graph:

 

My regards,

Widewing

[Sorrow[S=A]]

Just want to add 1 thing to this before it goes too far:

Unlike the US fighters you are mentioning the Homare (like the Russian Ash-82FN) was only a Single stage supercharger. This meant the figures for the homare of 1,980 hp at Sl were probably correct for it's max throttle and supercharger settings at SL. However there was no second setting for the supercharger when the engine was operating higher- based on the detailed Ash-82FN figures I have my guess was it's performance was similar and began to lose it's max manifold pressure by 8,000 ft or so.
This BTW is correlated by all the information I have seen on this plane listing it's power as an optomistic 1600hp at 19,800 ft.
 Thus widewing your figures should have some sort of descending scale to represent the loss of power over critical altitude where any of the single stage supercharged planes will have a variation in their hp/sqft ratio.

Or something like that  

------------------
If your in range, so is the enemy.

 

[This message has been edited by Sorrow[S=A] (edited 02-13-2001).]

[Karnak]

I understood that the Homare had Water Injection to prevent detonation.  This would affect both the N1K2 and Ki84.

I will see if I can locate the post that stated this.

------------------
We few, we happy few, we band of brothers;
For he to-day that sheds his blood with me
Shall be my brother

Sisu
-Karnak

[This message has been edited by Karnak (edited 02-14-2001).]

[BBGunn]

I think Widewing makes a good point and there are also quite a few general references to problems with Homare engines.  The N1K2 appears to have a thicker wing section than US fighters like the P47-wouldn't that keep its speed down also.  Does anyone know what the real 20mm ammo loadout was for the N1K2?

[Karnak]

Here we go:

 

Originally posted by brady in the "N1K2-J"George" SHIDEN-KAI and MW-50" thread:
I was wondering if anybody new if the wep on the N1K2 in the game is Methanol(MW50), my book on the George, Aero Detail 26 Shiden kai, shows that on the surviving examples in the US (3 out of the 4 taken from Japan and shipped hear for evaluation) were equipped with this,their is photographic evidence on multiple Aircraft.
Also the book states that 4 60kg or 2 250kg bombs could be caried.The four smaller ones would be kind of nice to carry on JABO missions sometimes.
The book also shows that the inboard gun had 200 rounds and the outboard 250 rounds,for a total for all 4 guns as 900rds.
This book is filled with very detailed photos of these planes taken in the various museums where these planes are on display, I highly recommend it,they have a whole series of these books on all sorts of planes.

Originally posted by Pyro in the "N1K2-J"George" SHIDEN-KAI and MW-50" thread:
The Ki-84(using the same Homare engine) had water injection as well. Ammo load on the George has been discussed in another thread and that's something I'll be changing in the next version. However, the Aero Detail is not exactly a good source for this information as they cite about 3 different ammunition capacities throughout the book.

 

Originally posted by Nath-BDP in the "N1K2-J"George" SHIDEN-KAI and MW-50" thread:
Hrmm... the Ki.84s didn't use Homare powerplants unless the Ha-45(Army Type 4) 23 is the IJAAF name for the NK9H Homare 21?
Looking at the HP output it doesn't seem so.
And:
p.s. The A6M6c with the Sakae 31 had methanol/water injection.

 

Originally posted by brady in the "N1K2-J"George" SHIDEN-KAI and MW-50" thread:
Nath.. They are the same engine,The Japanese army and navy had the mother of all service rivalries going on, they used totally different designation systems.
And as Pyro was kind enough to point out both had Methanol injection systems.
It would be cool if we get the 4 60kg bombs for the George it would make it nice for flak diving  

------------------
We few, we happy few, we band of brothers;
For he to-day that sheds his blood with me
Shall be my brother

Sisu
-Karnak

[This message has been edited by Karnak (edited 02-14-2001).]

[funked]

Widewing:

You can't use high-altitude speed readings together with sea level power ratings.  At sea level, P-47D top speed is about the same as the N1K2-J.

Likewise you can't use sea level power ratings with 0-20,000 feet climb times.  At sea level the N1K2-J outclimbs the P-39 (any variant) by up to 1000 fpm.

Hint:  Repeat analysis using sea level speeds and climb rates.  Good equations, bad data.

[This message has been edited by funked (edited 02-14-2001).]

[funked]

PS I just realized that the sea level info for the N1K2-J I am talking about comes from HTC's charts.  I'm assuming those are from a historical reference.  If that assumption is wrong then my argument is circular, and the analysis I suggested will only tell us what sea level hp value HTC used in their N1K2-J model.

[brady]

Karnak, I could not of said it better myself  

Brady

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[This message has been edited by brady (edited 02-14-2001).]

[niklas]

When i look at the climbrate of the N1k in AH, then it seems to be modeled with ~1700Hp.

[Jimdandy]

I think Sorrows has a good point. That would explain the drop in performance at higher alt. while maintaining excellent lower and medium alt performance.

There has been some mention of fuel in here. I have a question. Wouldn't the fuel blend play a big role in the over all performance. I understand the aircraft fuel has more oxygen in it for better performance at high altitude. I have heard that it also contains nitro methane. I would think that any of these were lacking in the Japanese fuel and the US had it there would be an advantage at higher alt. I would also think that the MW injection would not only work for controlling the hot spots in the cylinder head but as a mild oxidizer too. Wouldn't you also increase your charge density thus increasing volumetric efficiency? Can anyone help me out on this. It's been to many years since chemistry.  

One more question. I've read that at altitudes above approximately 32k if the ignition system isn't designed for those altitudes it will fail. Could it be that the Japanese hadn't figured that out and it limited the high altitude performance of their aircraft? Am I wrong about the ignition thing? It's something I seem to have read in an article about the P-47 and the F6F.

If anyone can slap me into shape on both of these I would appreciate the info.   Thx

[This message has been edited by Jimdandy (edited 02-14-2001).]

[F4UDOA]

Widewing,

Re-map your charts for sea level where the air density is a constant. If you do a couple of birds will be out of wack with the others. The P-47 and F4U namely.

I'm really not disagreeing with you. But in order to get flat plate drag area you need accurate Cdo numbers. Some of those numbers from AHT are a little suspect considering the speeds they were measured at vary greatly. From about 200 to 250mph in some cases. I have been searching for the NACA report with drag info for American fighters for a long time. If you have any of this please share.

Thanks
F4UDOA

[F4UDOA]

Jimdandy,

The problem was with the F4U and F6F cutting out at about 32K. The problem was that the ignition area(Don't know exactly??) was not pressurized properly due to manufacturing irregularities. Causing the A/C to cut out at high alt. This was resolved after the first few hundred A/C built.