Ki-84 - The Real Maximum Speed?

[Laurelix]

So many of you probably went searching through the internet for the max speed of Ki-84 and you kept coming across various sources stating as low as 624km/h , 634km/h and even as high as 687km/h.

Which of these is correct?
Tbh all are correct, but 687 is half right.

How come?

Ki-84's were powered by Ha-45 engine and it had many variations of it. Ha-45-11, Ha-45-12, Ha-45-21, Ha-45-23, Ha-45-25
Early Productions Ki-84's were powered by Ha-45-11 engine. These were by far the most common ones.

US TAIC for Ki-84 is for a Ha-45-21 powered KI-84 but its purely calculated using a bit over generous drag coeffcient and a slightly incorrect power curve. US Ha-45-21 power curve has 50 horsepower more at 6000m than it did in reality.

If you look for sources regards to Ki-84, these are the most common engines youll find.

Ha-45-11 had (From engine history of nakajima fighters)
1800hp at Sea Level (WEP)
1650hp at 2000m (100%)
1460hp at 5700m (100%)
-
Ha-45-21 full power had (from engine history of nakajima fighters)
2000hp at Sea Level (WEP)
1860hp at 1750m (100%)
1620hp at 6100m (100%)
-
Ha-45-21 Derated power had (No idea where i got this from 5 years ago, can someone help me with that pls?) - Shinpachi might know.
1800hp at Sea Level (WEP)
1680hp at 2300m (100%)
1500hp at 6500m (100%)

---------

Initially Ki-84 powered with Ha-45-11 engine achieved 624km/h at 6000m at military power. This is correct.
Source: Bunrindo: Famous Airplanes of the World

Later the japanese wanted to upgrade the fighter to use Ha-45-21 engine, however in its early stages the engine was extremely unreliable and prone to overheating. Until the engine issues were resolved the japanese chose to de-rate the engine power. This is where the 634km/h at 6550m comes from.
(Source: The translated record is a collection of Paul E. Garber facility. The aircraft was tested at 3400kg with 3000rpm +350mm rating.)

Then finally there is the Ki-84 US TAIC which is full power Ha-45-21, thing is the source is purely calculated.
Here US claims 687km/h at 6000m
http://www.wwiiaircraftperformance.org/japan/Ki-84-156A.pdf

--------------------

Now when it comes to my opinion of how really fast a Ki-84 with Ha-45-21 was, i simply take the fact that the Ki-84 can do;
624km/h at 6000m with roughly 1440 horsepower using the Ha-45-11.

With Ha-45-21 it would have 1625hp at 6000m at military power. This means Ki-84 top speed would be about 650km/h at 6000m at military power and 672-674km/h with Water/Methanol Boost.

 

[Shinpachi]

According to data in my hands,
The Ki-84 was designed for the maximum speed of 680km/h at the altitude 5,000 meters with 100 octane fuel.
Actual tested maximum speed with 91 octane fuel was various like 614km/h (alt. 5,000 meters), 640km/h (6,000 meters), 631km/h (6,120 meters) and 660km/h (6,000 meters) as it depended on the testing condition as well as the pilot's skill. Field pilots testified the average maximum speed was around 650 to 655km/h and some times more. No time to check the engine type but most of the data are based on the Ha-45-21.

 

[Ivan1GFP]

Hello Shinpachi,

Do you happen to know what power output and altitude the 680 Kph was achieved with?
The reason I ask is because from the testing of the overhauled engine of the Ki-84-I at Middletown in 1946, I believe that even with 91/92 octane fuel and automatic ADI, the Ha-45 engine was capable of making all the power claimed for it.

Hello Laurelix,

I believe you do not understand the way that Japanese engines used ADI. Water Methanol was used at just about anything above cruise power.
Even Military Power required ADI and it was automatic. That is why they carried so much of it in proportion to the amount of fuel onboard.

- Ivan.

 

[taly01]

Like shown in comments above the Ki-84 has logical explanations for its speeds and their is enough pilot reports and test data from the time to back it up. (pity the N1K-J doesn't have that level of data!).

 

[Shinpachi]

Do you happen to know what power output and altitude the 680 Kph was achieved with?

The army planned the engine Ha-45 of 2,000hp for the maximum speed of 680km/h at the altitude 5,000 meters with 100 octane fuel.

 

[Laurelix]

According to data in my hands,
The Ki-84 was designed for the maximum speed of 680km/h at the altitude 5,000 meters with 100 octane fuel.
Actual tested maximum speed with 91 octane fuel was various like 614km/h (alt. 5,000 meters), 640km/h (6,000 meters), 631km/h (6,120 meters) and 660km/h (6,000 meters) as it depended on the testing condition as well as the pilot's skill. Field pilots testified the average maximum speed was around 650 to 655km/h and some times more. No time to check the engine type but most of the data are based on the Ha-45-21.

Ah i see, 673-674 would represent high quality version such as the prototype but the average quality Ki-84 with unqualified labour at the end of ww2 would do around 650-660.

 

[windhund116]

According to data in my hands,
The Ki-84 was designed for the maximum speed of 680km/h at the altitude 5,000 meters with 100 octane fuel.
Actual tested maximum speed with 91 octane fuel was various like 614km/h (alt. 5,000 meters), 640km/h (6,000 meters), 631km/h (6,120 meters) and 660km/h (6,000 meters) as it depended on the testing condition as well as the pilot's skill. Field pilots testified the average maximum speed was around 650 to 655km/h and some times more. No time to check the engine type but most of the data are based on the Ha-45-21.

Did the Japanese even have 100 octane fuel available, in 1944-45? Or was much of the max speed tests done by the Allies, using captured Hayates and US fuels?

Thanks!

 

[Shinpachi]

Although the 100 octane fuel was available to the end of war, stock was not enough. It was mainly used for the reconnaissance planes like the C6N Saiun. The Ha-45-21 engine was redesigned so that it could generate 2,000hp with 91 octane fuel by adopting the water-methanol injection system.
All maximum speed tests were taken place in Japan during the wartime.

 

[Ivan1GFP]

The army planned the engine Ha-45 of 2,000hp for the maximum speed of 680km/h at the altitude 5,000 meters with 100 octane fuel.

Hello Shinpachi,

Was this Ha-45 on 100 octane fuel achieving 2000 HP at Sea Level or at 5000 meters?
If this was at Sea Level, then the wartime Ha-45-21 was able to achieve this level of power at Take-Off (Emergency) Boost with 91/92 octane and Water Methanol injection and there was probably enough supercharger to maintain this level of boost up to 5000 meters.
If this was 2000 HP at 5000 meters, then one must consider that 5000 meters would be High Blower and the power achieved at Sea Level in Low Blower would be much higher with the same boost. This boost pressure would need to be substantially higher than that achieved by operational versions of the Ha-45-21 because a simple change in fuel would not do it.
This also suggests that the supercharger would be a bit more capable and that critical altitude in High Blower would be significantly greater.

- Ivan.

 

[Shinpachi]

No data about maximum speed at sea level or diving condition for the designer.
No indication of fuel octane by the army except the engine Ha-45 of 2,000hp either.

 

[windhund116]

From what I could find the Nakajima BA series, Ha-45 II (Homare 23). Navy Code NK9H-S. Army Code Type 4. Installed in ? number of late model Ki-84.

Rated HP at 1,800 meters (~6000 feet) = 1890HP. 6,400 meters (~21,000 feet) = 1625HP. Both with 350mm Hg boost. Indirect fuel injection.

From, Japanese Aero Engines. Goodwin and Strarkings. MMP Books, 2017. ISBN: 978-83-65281-32-6. Page 181.

 

[mad_max]

If the super-charger doesn't use a fluid drive, then HP figures would slowly decrease after FTH was reach in the 1st gear, until the 2nd gear was engaged. The HP curve would show after FTH in 1st gear a decrease in HP; just like any other 2 speed gear driven supercharger in use by other countries, for a couple thousand feet or so before the 2nd gear would be engaged.

Only the DB [ 601/605 ] engine; after the second fluid drive pump provided the lock up [ minus the loss of efficiency ] of the drive, would power be almost the same until FTH was reached. The P-63 also had a fluid drive unit driving a second stage, so expect a flatter hp curve and of course the turbo driven second stage of the P-47 or P-38 would have a flat power curve until FTH which I believe was around 30k (for the P-47) or so if I remember right.

 

[Ivan1GFP]

If the super-charger doesn't use a fluid drive, then HP figures would slowly decrease after FTH was reach in the 1st gear, until the 2nd gear was engaged. The HP curve would show after FTH in 1st gear a decrease in HP; just like any other 2 speed gear driven supercharger in use by other countries, for a couple thousand feet or so before the 2nd gear would be engaged.

Hello mad_max,

There is no disagreement between what you posted and what is being stated about the Ha-45-21 engine.
The critical altitude in Low Blower +350 mm (equivalent of Military Power is 1860 HP @ 1750 Meters altitude.
The critical altitude in High Blower +350 mm (equivalent of Military Power is 1620 HP @ 6100 Meters altitude.
These are most likely metric HP values though.

The interesting thing is that the testing from Middletown of an engine removed from a Ki 84, overhauled and bench tested gave significantly better results.

- Ivan.

 

[turret]

The Ha-45-21 engine was redesigned so that it could generate 2,000hp with 91 octane fuel by adopting the water-methanol injection system.

did this engine get into use for the likes of the Ki-84? ive always read that these engines needed 100 oct to not have knocking so this is interesting to read.

 

[Shinpachi]

did this engine get into use for the likes of the Ki-84? ive always read that these engines needed 100 oct to not have knocking so this is interesting to read.

The Ha-45-21 was the most popular model of Ha-45 series.
These planes like C6N (Myrt), Ki-84 (Frank), N1K1&2 (George) etc adopted it.