Speed of Japanese Fighters

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#1

In aircraft books, the top speed of Japanese fighters are very different from what the allies tested them to be capable of post war. Does anybody how the book figures came about, are they “original Japanese”, and in that case, why did a Zeke do 595km/h, a George 630km/h etc. in allied post war tests? Did they race them beyond normal military limits (if that´s possible), provide them with better fuel or measure the speed low on fuel. (US and German practice for speed testing was max. normal fuel load)

In some place, in Polish I saw the figure 762km/h stated for the Ki-83, I found a wordbook in the library and found that this figure was followed by what translated into “achieved”. I´ve been looking everywhere for any confirmation of this without luck. Normally it´s quoted with 705km/h. At least one Ki-83 was tested by the US, and they probably wanted to know how fast it could go. That migth explain the 762-achieced, but not why nobody outside Poland bothers about it;)

#2

More than 700 km/h looks very optimistical to me.

#3

I think the “achieved” is very relative concept.
The meny kinds of aircraft could achieve the 700-800 km/h in dive from a hight altitude.
But i strongly doubt the Ki-83 was able to reach 762 km/h speed on horisontal fly.

#4

The Mitsubishi Ki 83 attained 438MPH-over 700KPH at 32,810 feet. I have to wonder why you question this when the 430MPH at 30,000 feet of the Northrup P-61C is widely acknowledged. The P-61C weighed in at 30,600 lbs. and used a pair of R-2800s of 2,100 HP each-2,800 on water injection. The Ki 83 weighed 19,687 lbs. with 2 Ha.211ru of 2,200HP each. This HP is listed for this engine everywhere but doesn’t specify if it is with war emergency power or not. Even so this works out to 4.4 lbs per/HP while the P-61C is 5.4 lbs. per/HP.

The Ki 83 was a fantastic plane beyond sheer speed at altitude. I was maneuverable in the extreme. In October 1944 the 1st prototype executed a loop at 403MPH at 9,500 feet. The loop took 30 seconds and was but 2,200 feet in diameter!

This aircraft hit and exceeded the mark in its concept for performance.

#5

I´m feeling quite foolish while wrting this, but it´s almost sad that the Ki-83and the deHavilland Hornet is no longer among us, along with someone capable testing- and writing about them, tripple test with the the P-82 (Twin Mustang), as with cars in the better car mags. And with big glossy colour fotos…

#6

We have factory performance tests for most when they were new. No one would consider putting these 3 antiques through maximum performance tests if all 3 were together today. Far too risky!

We can simply appreciate the statistics for what they were and not attempt to compare them in unrealistic scenarios. I’ve heard far too many times something like, “which would win…given equal pilots?” There are far too many factors to deciding an actually combat opposed to a friendly fly-off. Even if pilots are “equal” in experience there is nothing to control what offensive or defensive maneuver both may know but one decides to use 1st.

As computers go through their programmed moves in chess deciding which to use our pilots do the same but may use less logic in their decisions making the outcome quite surprising.

I do agree it would be cool if one experienced pilot had flown all 3 back then and could give a subjective idea which one he liked best and why.

#7

I don’t think the speed of a fighter is relivant,It is it’s ability to climb,turn and dive.
And then of course at what altitude.
Not many fighters could out turn a Zero.
The only fighter that could out climb or out dive a Ki-61 in it’s time in the pacific was the P-38.
Only a fool would try to out dive a Tony.As many of our piulots found even the latest Corsair could not match it.

#8

The planners and designers at the time found the maximum speed extremely relevant (for whatever reasons).

Only a fool would try to out dive a Tony.As many of our piulots found even the latest Corsair could not match it.

Isn´t that a question of speed?

Generally he correaltion between max speed in straight line and dive velocity is quite close.

What I´m trying to find an answer to here is why there is such a big difference between “book speed” and post war test speed.

#9

I get your meaning the Allied tests of most of the captured aircraft were talked down.
I had the Pilots notes on the Tony and they didn’t rate it that well.
But our pilots certinly thought it was a verry good fighter.

#10

I get your meaning the Allied tests of most of the captured aircraft were talked down.

I´m trying to figure out why they performed better in speed and climb in post war tests, than they are credited for in books.

The Kawanishi N1K2-J did 669km/h at 5800m in British post war test (normally credited with 599); big difference!
The Ki-84 did 686km/h in a US test (vs 631).

(The 190D-9 was tested to climb at 31,7m/s (MW50 boosted) by the British (normally stated 16,7m/s (the 7,1min to 10000m you saw if you read the small print in the datasheet posted in the 190 thread is probably a misprint of 17,1min, as it took c2min to 2000m, and 7min 6s to 6000m…)))

Do you have Pilots Notes on other captured types?

#11

I think one reason they did better in later war tests is that the japanese planes were being tested with hi grade fuel. the Ki 84 with Japanese fuel could reach 390 mph but with high grade fuel it reached 430 mph. I would like to know how fast the other jap planes went with hi grade fuel

#12

I would guess the other reasons would be the condition of the aircraft. Those used by the Japanese for their aceptance or proof tests would be factory fresh and brought to near perfect condition by the best mechanics the manufactor had. Those tested by the US pilots either had a fair number of flight hours, and or were ordinary production models with all the tiny flaws that cut precentage points off the theoretical performance. The mechanics preparing them for the tst flights may not have accomplished all the maintiance correctly. Small errors add up to another few percent off the performance.

#13

When evaluated by the Japanese, were the planes fitted with the same armor,fuel load, and equipment used in field service, or just the planes themselves?

#14

km/h book quote post war test
Ki-84 631 at 6100m 687 at 6100m at 3400kg (US)
Kawanishi N1K2-J 599 669 at 5800m (UK)
A6M5 565 595 (UK)

The US Ki-84 was tested at 3400kg, “considered representative of combat operations” (probably 3/4 fuel (normal US practice), no external stores (max TO was 3890kg, empty weight 2660kg) reaching 687km/h at 6100m using War Emergency Power, at Middletown Air Depot, Pennsylvania spring 1946. “This speed exceeded that of the P-51D-25 and P-47D-35 at the same altitude by 3mph and 22mph respectively”.
The Ki-84 is stated to have “outclimbed and outmanouvred” the P-51H and P-47N in US post war tests.

Don´t know about the British test conditions.

The B6N, P1Y, B7A, J2M, G8N and D3Y, A6M2 (the last wartime) and probably other types were also tested by the US. I haven´t been able to find any test figures for these.

Almost all Japanese aircraft were slow compared to foreign aircraft of similar power-weight ratios. The post war test speeds fall closer to the “normal”.
Wonder how the normally published figures in aircraft books was arrived at. If they´re from japanese sources, they might have had another defintion of max speed, perhaps perhaps without water injection? (But the MW boosted A6M6c (the A6M5 didn´t have it) is qouted with only 557km/h (often slower due to detoriating workmanship on engine and airframe), so that didn´t help much…).