The real combat history of the Ki-43 (6 Viewers)

[andrewgeorge]

The Ha-112 (Kinsei in IJN naming) wasn't ever fitted to the Ki-43, this was a typo in Fracillion's book that never got corrected. It was much more powerful, late models of both engines would have been around ~1500hp and ~1200hp respectively.

There was also a short-lived proposal to fit the Ha-45 Homare (now unified designation) to the Ki-43. For maybe obvious reasons it never went anywhere.

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.

 

[cherry blossom]

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.

 

[UnderPressure]

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.

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.

 

[AerialTorpedoDude69]

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.

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.

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.

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?

 

[cherry blossom]

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.

 

[WARSPITER]

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.

That wouldn't be a surprise either.

 

[beers]

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.

Wow, that's really interesting! Never knew that engine even existed. But was it ever mounted on a plane?

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.

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.

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.

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.

 

[GrauGeist]

The version I've read is that the MW50 system in the Ha-115-II

Are you thinking or the NK1E, perhaps?

 

[AerialTorpedoDude69]

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).

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 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.

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.

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:

The Model III (Ki-43-III), fitted with the Ha-115-II engine equipped with a water–methanol injection system to extract more power from low-octane fuel, achieved 560 km/h at 5,850 m. The water–methanol tank capacity was 70 L, and the maximum speed was effective only while the supply lasted. Chief designer Ōshima, in charge of the Model III, evaluated the system positively: "Its speed surpasses all Zero variants, and it exceeds them in climb, range, and handling; the only inferior aspect is armament." Pilots testified to its effectiveness, with one saying, "I survived because I flew the Type 1 Model III—had I been in another aircraft, I probably wouldn't have." Even so, its speed was only on par with contemporary aircraft without injection, meaning it compensated for a shortfall rather than providing a decisive advantage.

However, if we go to the source for Wikipedia, we get this:

This water methanol injection does not obtain explosive cal (calories) by directly burning water ethanol, but suppresses the abnormal explosion (detonation) caused by high heat generation when the engine is compressed and rotated higher than before, by cooling it with water methanol, and improves the explosiveness of gasoline. This device is designed to protect pistons and valves from melting and breaking.

Originally, it is enough to spray water alone, but when it rises to a high altitude other than hot areas, it becomes below 0 degrees Celsius and the water freezes, so methanol (methyl alcohol) is added to lower the freezing point and make it antifreeze. As a device, a certain amount of water ethanol is injected with an auxiliary injection control device using bellows at a boost pressure of +200mmHg or more against gasoline, and it is introduced into the cylinder with a mixture to suppress the detonation, but at low boost such as cruising, water ethanol is not injected at all, so it was effective at the best time of combat action.

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.

 

[beers]

Are you thinking or the NK1E, perhaps?

I don't recall which engine the NK1E was. I know NK1-series were the Sakae and friends, but what did the E change?

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.

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.

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.

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.

However, if we go to the source for Wikipedia, we get this:

That's a VERY cool page, good information on things you never get to see. Definitely saving it for future reference.

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.

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.

 

[GrauGeist]

I don't recall which engine the NK1E was. I know NK1-series were the Sakae and friends, but what did the E change?

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.

 

[taly01]

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?

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.

 

[AerialTorpedoDude69]

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.

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).

Performance and Evolution of the Ho-103 Machine Cannon

The Ho-103 had a favorable rate of fire and offered advantages over its model—the American AN/M2 12.7mm—by being smaller, lighter, and capable of firing explosive shells (Ma-103), which the AN/M2 lacked. However, its lightweight, low-powered ammunition resulted in inferior destructive power and effective range.

In its early stages, the mechanical fuse of the Ma-103 was prone to malfunction, causing shells to explode inside the barrel (a phenomenon known as chamber burst), which damaged the aircraft. To mitigate this, early production models had steel plating wrapped around the barrel to reduce damage from such incidents.

As mass production of the Ho-103 and Ma-103 progressed, these issues were gradually resolved. By late 1943, a new version of the Ma-103 shell was developed and quickly deployed to frontline units. This improved shell used an air-pressure fuse newly developed by the Army, which drastically reduced premature explosions. Additionally, the simplified fuse mechanism allowed for more internal space, enabling an increase in explosive payload, thereby enhancing firepower. Production efficiency also rose—eightfold compared to the older mechanical fuse.

Naturally, even this improved 12.7mm round had limitations compared to full-fledged 20mm explosive shells, which were larger, heavier, and packed with more explosive and propellant. To meet demands for greater firepower, the Army later developed and adopted the Ho-5 20mm fixed machine cannon, based on the Ho-103.

Despite its smaller caliber, the new Ma-103 was so effective in combat that U.S. pilots frequently misidentified hits as 20mm shell impacts. This was confirmed in reports from American aircrew who engaged with Ki-43 fighters equipped with the new Ma-103.

✈ Combat Example: Rangoon, December 1, 1943

On December 1, 1943, a formation of 82 American aircraft arrived over Rangoon and was intercepted by Japanese Army fighter units led by the 64th Sentai. During the battle, six B-24 bombers were confirmed shot down, including aircraft piloted by Lt. Col. Plummer of the 493rd Bomb Squadron and Maj. O'Brien of the 308th Bomb Group. One P-51A from the 530th Fighter-Bomber Squadron was also confirmed destroyed.

Japanese losses were relatively light: two aircraft shot down (with one pilot killed) and five damaged or forced to land. This engagement marked the combat debut of Corporal Jūshi Ikesawa, who later became an ace and testified that he began using the new Ma-103 shells around this time.

Ammunition Loadout of the Ki-43

Each Ho-103 cannon mounted on the Ki-43 carried 270 rounds. The ammunition was typically divided evenly among three types:

• Type 1 Tracer Armor-Piercing rounds
• Ma-103 explosive shells
• Ma-102 incendiary shells (same shell type as Ma-103, but designed to ignite targets)

There's also some additional information on the round here:

Overview of the Ho-103 Machine Gun

• Each round weighs approximately 86 grams.
• Ammunition types include:
  • Type 1 Armor-Piercing Tracer
  • Type 1 Ball
  • Type 1 Tracer
  • Ma-102 (Incendiary-Explosive)
  • Ma-103 (High-Explosive)
  • Plus training rounds used as substitutes.

In combat, the main rounds used were Type 1 Armor-Piercing Tracer, Ma-102, and Ma-103, typically in equal proportions.

Performance and Ammunition Details

• Type 1 Armor-Piercing Tracer: Penetrated 12mm of armor plate at 300 meters.
• Type 1 Ball: Training use; muzzle velocity of 803.5 m/s.
• Type 1 Tracer: Training use; tracer composition includes 0.7g of tracer and 0.3g of igniter.
• Ma-102: Incendiary-explosive round without a fuse; detonates from frictional heat upon impact with aircraft fuel tanks.
• Ma-103: High-explosive round with an impact fuse; unique to the Ho-103 and not found in the American AN/M2 .50 caliber rounds.

Technical Origins

• The Ho-103 was based on the American Browning AN/M2 aircraft machine gun (MG.53-2), specifically the compact MG.53-A version.
• It used 12.7×81mmSR ammunition, derived from the Italian Breda SAFAT 12.7mm machine gun, which was imported along with Italian heavy bombers and later domestically produced.
• 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.

Fuse Development and Reliability

• Early Ma rounds had mechanical fuses that were overly sensitive, causing premature explosions or chamber detonations.
• In late 1943, a new air-pressure fuse was developed:
  • Simple design with a hollow cavity sealed by a thin metal plate.
  • Upon impact, the plate deforms, compressing air and igniting the explosive via adiabatic compression.
  • Adopted by both Army and Navy, referred to as "fuse without striker".

This new fuse:

• Greatly improved reliability.
• Increased production efficiency by 8×.
• Allowed more space for explosives, enhancing destructive power.

American pilots often mistook hits from the new Ma-103 for 20mm shells due to their explosive effect.

Combat Deployment

• The new Ma rounds were widely deployed by late 1943, notably in the 64th Sentai on the Burma front.
• On December 1, six B-24 bombers were reportedly shot down using these rounds.

 

[Shortround6]

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.

 

[AerialTorpedoDude69]

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.

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:

• Design:
  • The fuse contained an internal cavity at the tip of the projectile, sealed only by a thin metal plate.
  • When the round struck a target, the thin plate deformed, compressing the air inside the cavity.
  • The adiabatic compression of this air ignited a small internal charge, triggering the main explosive.
• Advantages:
  • Extremely simple and reliable design
  • No firing pin required (hence the Navy named it the "No-Firing-Pin Fuse")
  • Adopted by both the Army and Navy for various 12.7 mm and 20 mm ammunition types.

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.

Trouble with this is that the British and US were not using TNT in their 20mm ammo.

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:

• Ma 202 Type 2 Special Incendiary Bomb. Warhead weight 78.2g (US military data). 3.2g PETN on the head, 8.7g incendiary agent on the inside[10]​. It explodes due to frictional heat when it penetrates the outer plate of an enemy aircraft.
• Ma-206 Type 4 thin-walled grenade and Type 4 grenade. Warhead weight 72.4g (substitute ammunition), muzzle velocity 831.9m/s[11]​. Install a Type 4 rigid transmitting pipe (air fuse).

Air fuses

In Showa 18, by the invention of Colonel Kuwata, an authority on land artillery fuses, Japan's own "pneumatic fuse" was developed. It has a structure in which an air hole is provided at the head of the bullet and a thin plate covering is attached to the tip of the bullet, and when the bullet collides with an enemy aircraft, it ignites due to adiabatic compression of the air hole. The initial cause of the Ho-5's cavity was a complex fuse assembly error, so the Army's aviation personnel jumped on the success of the development of this fuse.[13]​

This fuse was used for the Ho-5 high-explosive from the middle of Showa 19, immediately after its development, and then for the Ho-103 ammunition. The elimination of complex mechanical fuses has dramatically improved the productivity of ammunition, making it a win-win situation[Annotation 4]​. A similar fuse was also used in the Navy.[14]​

 

[MiTasol]

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.

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.

 

[AerialTorpedoDude69]

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.

 

[MiTasol]

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.

 

[AerialTorpedoDude69]

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.

 

[MiTasol]

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.