Interesting discrepency in N1K2 data

[wells]

In Francillon's book, 'Japanese Aircraft of the Pacific War', the specs for the N1K2 are given:

Engine:  1625 hp @ 6100m
Speed:  321 kt @ 5600m

Doesn't that look a little strange?  Usually, a plane will top out some 1000m above the critical altitude of the engine due to ram air effect.  At least that's the case with the 109, 190, F4u and others.  So let's say that with ram air, the manifold pressure could be maintained to 7100m.  Power would be about 1670 hp owing to the temperature difference between those heights and speed would most likely be in the area of 396 mph!

At the altitude of 5600m, the engine is probably only putting out 1600 hp.  Even with no ram air effect, speed should still peak at 6100m, giving 378 mph.  I notice that in the TAIC manual, they calculate 1675 hp @ 6000m.  If that data were to be used, we'd get 380 mph (TAIC manual calculates 407 mph but Francillon's speed figure is probably more accurate coming from Japanese sources).

Off to do some test flying!  

[Seeker]

Coddam enineer types, USE SHORTER WERDS!

Is it too fast or too slow?

(Hopes it's too slow and looks forward to the whine fest when it's made faster!)

[wells]

I would think it to be anywhere from 9-27 mph too slow, but it's fine below 18k.

[Vermillion]

Speaking from memory here, but isn't the 1625hp number from the very early models of the Homare engine?

Primarily in the N1K1-J and the very early N1K2-J?? I was under the impression that most of the N1K2's had the upgraded 1800-1900hp models.

I could be very wrong however, since I'm going entirely from memory.  

I still only think its fair however that both the N1K2-J and the Ki-84 get to use 100 octane fuel like all the Allied birds   *dreams of a 427mph Ki84*  Be afraid, be very afraid !  

[niklas]

Originally posted by Vermillion:
Speaking from memory here, but isn't the 1625hp number from the very early models of the Homare engine?

1625hp@6100m ! Donīt forget, it is running in the second gear of the supercharger in this altitude. For takeoff it must have more power, just look at the performance charts.

niklas

[kreighund]

I read quite a bit of argument about the Nakajima Ha-45-21 Homare of the N1K2-J and Ki-84. This should pour a bit more lighter fluid on the discussion. If you compare the output of the Pratt-Whitney R-2180 E series engines to the Homare you can get a reasonable comparison. First the data;
The P&W R-2180E is exactly 2181 cu in. Bore and stroke of 146 by 152.5mm. The same cylinders as the R-2800 but in 14 cylinders. Max RPM is 2800 and MAP is 54”.

The BHP performance figures are:

Take off
1650 SL
1800 ADI

WEP (ADI)
1800 to 2700'
1550 to 13Kft

MIL
1650 to 3000’
1300 to 16Kft

Normal
1400 to 6000’
1250 to 15.5Kft

Max Cruise
1300 to 8000’
1150 to 17.5K

The Nakajima Ha-45-21 (NK9H) Homare 21 is exactly 2186 cu in. Bore and stroke are 130 by 150mm. The same cylinder as the Nakajima SAKAE 21 but in 18 cylinders. The max RPM is 3000 and the MAP is unconfirmed.

The BHP performance figures are;

Take off
1670 SL
1830 to
1970 ADI

WEP (ADI)
1830 to 5700'
1610 to 16Kft

MIL
1655 to 9300’
1360 to 20Kft

Normal
1400 to 12Kft
1250 to 18.5Kft


Max Cruise
1200 to 15Kft
1100 to 21Kft

Remember the RPM are faster and probably the fuel is 115/130 octane. Also the supercharger is made for a fighter application whereas the R-2180 is made for the SAAB 90A airliner.

As a comparison of an engine which normally runs on “Hi-Test” is the R-2800-B series is rated at 2100-54in (2400-56in ADI) takeoff and 1800-45in SL max continuous. With 91 grade fuel the take off is reduced to 1650-42in (no ADI) and 1380-38.5in SL max continuous.

So there is my two cents into the ring….so cry havoc and loose the dogs of war!!!

[wells]

Right Verm and Niklas,

1990 hp for takeoff

Checking out the Ki-84 speed data (same engine?), shows it peaks at 6120m.

kreighund,

What's your source of data for the Homare 21?

[kreighund]

Pardon me, I should have stated extrapolation. I have a mountain of books on aircraft engines; the best one are by Wilkinson. I have them from the first edition in 1941 thru 1962. If one assumes that the T.O. BHP for the Homare 21 is 1970 to 1990 with ADI then its T.O. power without ADI would fall between 1680 and 1750. By using its critical altitude speed you can get a rough idea of the ram recovery and then graph the power as well as the military, normal, and max cruise ratings. Looking at other aircraft with similar Homares (A7M1) gives some idea of it application in other airframes, then when different engines are used with known power ratings you can get an idea of the performance of the engine. Crude, but in absence of really good data best guess would be the only alternative. I think that the testing by TAIC would be a slightly erroneous to real world operations due to the fact that you had a team of experts tweak your machine and that 100 octane or better may have been used for testing.

[Hobodog]