The real combat history of the Ki-43

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So Ki-43-III was powered with Ha-115? For some reason I always thought it was either Ha-112 or Ha-45. I guess that makes more sense.
 
In 1944 Nakajima's engineers were mostly working on the Ha-45 or Homare and had managed to get around 2000 hp at 3000 rpm. It seemed attractive to use that work to raise the power of the Ha-115, Ha-35 or Sakae by dropping in 14 of the Homare cylinders and possibly increase the rpm. It wasn't quite as simple as that as the valve timing was different and it would have been good to have a new supercharger. However, an engine was created called Ha-315, Sakae 31 or Ha-35 31. It may have given 1360 hp when it worked but that seems to have rarely occurred (Goodwin and Starkings, page 177). Photographs of the Ki-43 IIIb prototype show a Ha-115 diameter engine, so the Ha-315 is a good guess for its powerplant.
 
andrewgeorge said:
So Ki-43-III was powered with Ha-115? For some reason I always thought it was either Ha-112 or Ha-45. I guess that makes more sense.
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It should be the Ha-115-II, an advanced variant of the Ha-115. Its horsepower was around 1150 BHP. Ki-43-III carried a 70L water-methanol tank, enabling it to utilise maximum power for approximately 40 minutes.
 
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UnderPressure said:
It should be the Ha-115-II, an advanced variant of the Ha-115. Its horsepower was around 1150 BHP. Ki-43-III carried a 70L water-methanol tank, enabling it to utilise maximum power for approximately 40 minutes.
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According to TAIC's briefing on the Ki-43-III, there was no MW50 tank. Their briefing had a fuel tank that was aft of the pilot's seat in the rear cockpit. However, I believe this to be a mistranslation of captured documents or a misunderstanding of an interrogation document.
Thanks for the info. I don't have access to Goodwin and Starkings, but taly01 was good enough to share their knowledge of the engine. According to him, it was the Sakae 32 which was used in the Ki-43-III and the Sakae 31 with MW50 injection was never a viable engine due to development issues.

According to Bunrin-do, the engine in the Ki-43-III only produced 1,230 HP (I don't have the numbers in front of me so something close to that), but I'm not clear whether that included water injection. Japanese wikipedia suggests the Army's variant of the Sakae had MW50 to improve fuel reliability and not for performance.

Would you know if Goodwin and Starkings had any information on the Ha-115-II's MW50 injection system? And do they mention a Sakae 32 in it?
 
Goodwin and Starkings seem to suggest that the story was one of a slow retreat from the planned Sakae 31 back towards the performance of the Sakae 21:

"In November 1944 one was installed in the A6M6c Model 53c" ...snip... "By then this engine model had been de-rated, although it still offered improved altitude performance." ...snip… "when its Sakae 31 engine performed correctly the aircraft was over-powered and suffered from tail vibrations"…. snip …. "Apart from its water-methanol injection system, the Sakae 31 differed from earlier production models in having a higher geared supercharger and a modified valve timing system adapted from that of the Homare. As injection system problems could not be resolved it was deleted from later production units resulting in the Sakae 31a with a correspondingly reduced performance. Furthermore, as the new supercharger proved ineffective, the type used for the Sakae 21 was substituted, resulting in the Sakae 31b."

Unfortunately, the Army models are less documented and it is possible that the Army solved some of the problems plaguing the Navy without telling them the solution.
 
Wow, that's really interesting! Never knew that engine even existed. But was it ever mounted on a plane?
AerialTorpedoDude69 said:
According to him, it was the Sakae 32 which was used in the Ki-43-III and the Sakae 31 with MW50 injection was never a viable engine due to development issues.
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It couldn't have been the Sakae 32 since that was a Navy engine. It would at least have a new (Army) designation, if they used it at all. The 'base' Ha-115 differed significantly from the Sakae 21, namely with a higher RPM limit.
The version I've read is that the MW50 system in the Ha-115-II wasn't to increase power, but to allow maximum power settings to be used for much longer than usual, making overboost truly useful in combat. This is also around the time where the Ki-43's top speed is registered for this power setting and not military power, making it seem that the -III is much faster than the -II.
 
The irony is that the less technically minded IJA fielded aircraft that tended to have better performance compared to their naval counterparts. For example, the Ki-44 vs the J2M did more with less. The Ki-84 vs the N1K2-J. The Ki-45 vs the Gekko/Irving J1N. The Ki-43 ended up having the same performance as the A6M5 but with armor plate and protected tanks. And apparently MW50 injection.

I don't believe that Nakajima had better designers. If anything, Mitsubishi's design team was superior. So why wasn't it Mitsubishi's engineers who were working to develop water injection? They got it working on the Kasei engine. Nakajima's team got water injection working on the Homare. Anyone have any ideas?

Unless the IJA had an MW50 upgrade kit, it's highly likely that they simply had a separate assembly line at the Nakajima factory (or any of the other corporations which assembled those engines).

beers said:
It couldn't have been the Sakae 32 since that was a Navy engine. It would at least have a new (Army) designation, if they used it at all. The 'base' Ha-115 differed significantly from the Sakae 21, namely with a higher RPM limit.
Click to expand...
The author who the Sakae 32 claim is attributed to is a very well respected Japanese aviation historian. Unless Taly01 got the quote wrong (and I can't track the quote down but have no reason to doubt him) it's likely that he had to create a name for the Ha-115-II with water-methanol injection as the IJA had burned their records.
As I understand it, that is also correct. Water injection should improve both overboost length and fuel reliability due to cylinder head temperature reductions, which reduce the risk of predetonation. However, in the source material, the Army used 87 octane, instead of the 92 used by the Navy, which should be more reliable though.

Here's a better AI-assisted translation of Japanese Wikipedia's entry on the Ki-43:
However, if we go to the source for Wikipedia, we get this:


In other words, the purpose of the army's MW50 injection was to improve fuel reliability. It looks like improved WEP was a byproduct of that.
 
GrauGeist said:
Are you thinking or the NK1E, perhaps?
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I don't recall which engine the NK1E was. I know NK1-series were the Sakae and friends, but what did the E change?
AerialTorpedoDude69 said:
For example, the Ki-44 vs the J2M did more with less. The Ki-84 vs the N1K2-J. The Ki-45 vs the Gekko/Irving J1N. The Ki-43 ended up having the same performance as the A6M5 but with armor plate and protected tanks. And apparently MW50 injection.
Click to expand...
Agreed... with some caveats. The Ki-44 had far lighter armament and lower top speed, and the J2M probably had more development potential especially with the hotter engines that later powered the Ki-83 and 87. It also looked amazing and for that alone I'm glad they made it.
The N1K2-J was suboptimal due to being derived from a seaplane, even if it ended up being a surprisingly good performer; A7M Reppu could/would have been available earlier but Mitsubishi spent too long redesigning the Zero several times (maybe the Model 50s were a waste of time). Ki-84 was a clean-sheet design with all the benefits that came from making the similar Ki-43 and Ki-44 earlier.
J1N... don't know much, but it was a serviceable night fighter, superficially similar enough to Bf 110.

For the Ki-43 it's a personal favorite so I'm a little biased. Along with the pilot armor I'd argue it actually had better firepower (thanks to gun placement and ammo available) and visibility. 20mm cannons are great but when you only have 60rds per gun, they're way out in the wings, and their velocity is low... I think I'd rather have the .50s. Zero's reflector sight is also quite small and sits low. I'm not counting the Ki-43-I, between its low production numbers, and obvious cost-cutting measures; the -II was definitely THE Ki-43.
I can't help but nitpick that because the Army would never use a Navy engine if they could help it. They only started cooperating in equipment very late war and not in much.
AerialTorpedoDude69 said:
However, if we go to the source for Wikipedia, we get this:
Click to expand...
That's a VERY cool page, good information on things you never get to see. Definitely saving it for future reference.
AerialTorpedoDude69 said:
In other words, the purpose of the army's MW50 injection was to improve fuel reliability. It looks like improved WEP was a byproduct of that.
Click to expand...
If I had to guess, worsening fuel situation made WEP impossible to use without this system. Germany also had a lot of issues with early DB 605As, and they outright prohibited use of WEP - limiting 109 Gs to little over 1300hp. This is definitely a better alternative over losing a good chunk of power.
 
beers said:
I don't recall which engine the NK1E was. I know NK1-series were the Sakae and friends, but what did the E change?
Click to expand...
The NK1 was the Japanese Navy designation for the Sakae engine, the NK1E Sakae 31 was the 1,130hp engine equipped with methanol/water injection that boosted it to 1,210hp.
 

Japanese Navy and Army independently developed the engine Mitsubishi supplied to their own planes and needs. The Navy did not get the Sakae 32 with water injection (MW) working as they had a crisis when the new type propeller reduction gears on the A6M5b/c began having failures, so the Navy design team was diverted to solve propellers failures on the A6M5b/c..... (LOL) rather than getting the MW of A6M6c working. This was before the battles in the Philippines 1944.

Sakai 31 engine

I heard that A6M5c used this engine and that Sakai 21 and Sakai 31 had same military performance except the Sakai 31 differed in the WEP power category. anyone have data about this?
ww2aircraft.net

The use of the names Sakae 31 or 32 is a bit of a simplification, as all the engines did come from Mitsubishi anyhow,..... the new universal engine naming system was only just coming in use late 1944 ....Sakae 32 is basically same as Ha115-II. The Army started development of the MW injected Ki43-III much earlier than the Navy A6M6c, in fact in Q2 1944 so had many months to get to grips with it.

The Ki-43-III could still be effective at lower altitudes (~<3000m) as thats where its MW power boost was most effective, and diving speed was less an issue at that height. But at higher altitudes than that it was definately obsolete in 1945.
 
Regarding the Ki-43's armament, it was certainly light, but it had special explosive shells: the Ma-Dan shell, which was a fuzeless round.

Sources vary on the name, but according to Japanese Wikipedia, the IJA developed a special "adiabatic" contact fuse, which used a friction-based detonation scheme. The fuzeless shell was far more reliable than mechanical detonators. Laurelix wrote about the Ma-Dan shell here, but I thought to add it to this thread to cast more light on the Ki-43's late-war performance against Allied aircraft.

By the war's end, the IJA had completed development work on a 12.7mm adaptation of the thin-walled Minengeschoss rounds, although these never reached production. But I'm curious as to how much RDX could have been crammed into a thin-walled, fuzeless Ma-102 or ma-103 round (which was dubbed the Ma-106).


There's also some additional information on the round here:
 
Unfortunately some of the these estimates of Ho-103 performance and ammo performance tended to use rose colored goggles.

The fuse-less design was innovative. However the sentence "Production efficiency also rose—eightfold compared to the older mechanical fuse." needs a little closer look.
Fuses are expensive and a fuse-less design was going to be much cheaper, eight times seems a bit much but who knows. You still have the same cost of the cartridge case/primer and just about the same cost of the propellent so even IF the cost of the projectile (including HE/chemical filler) is 1/8th the cost of the complete round is not 1/8th.

And................."Compared to the AN/M2's 12.7×99mm rounds, the 12.7×81mmSR was 20–30% lighter and smaller, offering higher rate of fire but lower muzzle velocity, effective range, and ballistic flatness."
Quite true except it leaves out the fact that the 12.7X99 bullets were also about 20% heavier. Which means they hit a lot harder. Like rated AP penetration at 500 meters was 19mm instead of the 12mm at 300 meters of the Japanese AP ammo. Long range ballistic performance was based on two things. Weight per unit of frontal area (sq cm/grams) and the shape/streamlining of the bullet. Heavier 12.7mm starts off with an advantage over lighter ones. . The US .50 cal use a lot of it's weight for a more pointy nose and a tapered boat tail, it was one of the most streamline bullets of WW II. This is air to air combat and shooting from moving plane to another moving plane means that actually hitting at much more than 400-500yds is very difficult but at long ranges .50 cal ammo hits with a lot of punch.
US was also not standing still in regards to ammo either. The quoted dated for the Japanese introducing the Ma-103 ammo is not that far off from the US introducing the .50cal M8 API round which introduced about 0.97 grams of incendiary material ahead of the AP core. Not as much as the Japanese were using but as supplies increased the US changed to using it as the standard round. Not 1/3 of this and 1/3 that and 1/3 something else but over 90% M8 API. Total amount of incendiary material delivered by a 2 second burst was not that bad.
The KE of the .50 cal API was about 60% greater than the KE of the Japanese 12.7mm type 1 AP round at close range. The difference was even greater at long range. The Japanese desperately needed the HE & HE/incendiary rounds to try to make up the difference. And here the Ki-43 really trips and falls into a trench. The Ho-103 gun is faster firing than the US M2 gun. Assuming the Japanese gun fires at 900rpm compared to the 750-800rpm of the US gun. (some sources say 750-850 with an 800rpm average but I will go for a bit lower average for the US) and a max rate for the Japanese at in actual use the Japanese often did not use the Ho-103 gun in unsynchronized mountings in the wings. Ki-43 use two guns in the cowl, rate fo fore could be as low as 400rpm. To be generous I will say 600rpm ? Ki-44 often used four guns, two in the cowl and one in each wing. Ki-61s came with two Ho-103 guns in the cowl and a single 7.7 in each wing to start (very rare) and then 4 guns. Later planes had two 12.7mm guns in the cowl and German MG 151s in/under the wings they ended with two 20mm guns in cowl and a 12.7mm in each wing. Ki-84s used two 12.7mm cowl guns and one 20mm Ho-5 in each wing.
US stopped putting .50 cal guns in the Fuselage of just about everything except P-39s (some A-36s?) by the end of 1941. Actual average rate of fire of the Ho-103 may not show much difference over the US .50 cal armed fighters with their mostly wing mounted guns.

And then we have

"
• Ma-103 Fuzed HE-I
- Projectile Mass: ~ 36.59 g
- Muzzle Velocity: 780 m/s
- Explosive type: RDX + Incendiary
- Explosive mass: ~ 0.6 g + 1.45 g
(Barium Nitrate dominated incendiary)


• Ma-102 Fuzeless HE-I
- Projectile Mass: ~ 36.30 g
- Muzzle Velocity: 780 m/s
- Explosive type: RDX + PETN + Incendiary
- Explosive mass: ~ 0.96 g + 0.96 g + 1.46 g
(Barium Nitrate dominated incendiary)

More Info:
RDX = 1.6x effectiveness factor vs TNT
PETN = 1.66x effectiveness factor vs TNT

Ma-102 TNT equivalent explosive power
= (0.96 x 1.6) + (0.96 x 1.66)
= 1.54g + 1.59g
= 3.13g TNT equivalent explosive power

This is one deadly bullet considering it has 50% the explosive power of 20mm Hispano at higher rate of fire + 1.46g of incidiary that is mostly Barium Nitrate.
By removing the fuze it allowed the Japanese to create a round that holds far more explosive and incendiary power."

Trouble with this is that the British and US were not using TNT in their 20mm ammo. They were using Pentolite or Tetryl as filler. Pentolite is 50/50 PETN/TNT and is about 1.22% more powerful than TNT. Next problem is that the 20mm Hispano shells held 10.5 grams of Pentolite................or 12.8grams TNT equivalent. Japanese shell is about 25% as powerful, not 50% as powerful. The Allies uses other loads/fillings like 10.2 grams of Tetryl. They also loaded an HEI shell with 7grams of Tetryl (8.12g TNT equivalent) and 4.3g of incendiary.
This shell has 2.59 times as much HE power and 2.94 the amount of incendiary. Granted it is a 130gram HE shell and the Hispano has a lower rate of fire. But the Hispano has better Velocity. British also had a cheap and cheerful API 20mm round. They just filled a standard HE shell body with about 10 grams of incendiary and screwed a hardened nose cap in the end instead of fuse. Shell body and nose doesn't get much cheaper for a 20mm. If it hit anything substantial the force of the impact split the shell body open and scattered the HE compound around the vicinity of the impact.
 
First, thank you for sharing, your analysis is dope af. Second, I apologize for not doing a better job of presenting the data.

The article described the "fuzeless" fuze (silly for me to describe it as fuzeless) as being very simple. It used didn't have a mechanical trigger, but rather used heat generated by the compression of air to detonate a tiny explosive. I believe that they were referring to the fuze and not the entirety of the shell.

(EDIT: I removed something stupid that I wrote)

Here's the missing context:


According to the original Wikipedia page, which Copilot AI butchered in the translation, there is still a "fuze" inside of the Ha-102 and Ha-103 (other sources claim that only the Ha-102 shell was fuzeless, but I believe that to be in error).

Also, the velocity might not be correct. If the fuzed shell had a velocity of 780 m/s than the lighter, fuzeless shell with more propellant should be slightly faster. But the velocity is listed as the same.
Shortround6 said:
Trouble with this is that the British and US were not using TNT in their 20mm ammo.
Click to expand...
The IJA used a fuzeless version of the shell used in the Ho-5 in combat. INTERESTINGLY ENOUGH, they also managed to put into production a minengeschoss version of the Ma-Dan Ho-5 shell. It's unknown whether it was used in combat. My guess is that it was. Interestingly, the minengeschoss, Ho-5, Ma-Dan shell (such a long word) had a significantly higher velocity than the regular Ho-5 shell, almost certainly because of the lighter weight and possibly increased propellant.

Here's a HORRIBLY translated clipping from Japanese Wikipedia's entry on the Ho-5:

 
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AerialTorpedoDude69 said:
Also, the velocity might not be correct. If the fuzed shell had a velocity of 780 m/s than the lighter, fuzeless shell with more propellant should be slightly faster. But the velocity is listed as the same.
Click to expand...

At one stage I had several of the Japanese Ho-40 cannon shells and I would say that the fuseless shell would actually be slower because on the ones I had the propellent exited the back of the shell through a ring of holes instead of over the full charge diameter. I would expect that this reduced the push the propellent was able to exert and therefore the shell velocity.
 
Do you mean the Ho-301 which fired 40mm caseless, not fuseless? Those were designed to be like rockets in order to move a larger payload. The propellent ejection holes were designed quite differently from the Ma-Dan shells.

But I am amazed that you managed to get your hands on some of those. I'm looking for the post now, if you shared it.
 
You are correct 40mm caseless not fuseless.
I found them in the very few remains of a Ki-44 at Alexishafen PNG. It appeared to be a victim of an incendiary bomb - no crater but very little left of the aircraft and what was left was very burnt. Far more burnt than a standard aircraft fire.
 
Although the Allies reported shooting down Ki-44 over New Guinea, the IJA units which were deployed there weren't equipped with the Ki-44 on account of its longer takeoff run, short range, and the poorer-quality air strips operated by the Japanese. However, it's possible that simply no records exist of such a deployment.

The weapon which you found may not have been a Ho-301 but rather something else entirely.
 
Given there was an engine and two main gears and two cannons and assorted other distorted steel and burnt alloy components laid out about where one would expect them I would say it was definitely an aircraft and I do not know of any other aircraft with such guns which is why I thought it was a Ki-44.
 
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