Nakajima Ki-84 Hayate Frank Pt. 2 

This channel has the right amount of in-depth detail I want on my aviation content. Usally you get a simple "this plane, big engine, very fast" video and that's it. But Greg goes to discussing the possible origins of the nuts that hold the horizontal stabilizer actuator.

My Fav Japanese fighter of the war. I’ve got a beautiful 1/32 model set in a revetment on Clark field. Thank you for the excellent work on this aircraft.

Great video, thanks for sharing this information

As a young boy I started collecting William Green's War planes of the second world war. In vol. 3 he says this about the Ki.84: "It compared favorably with the best of its antagonists; it was slightly slower than the P-51H Mustang and the P-47N Thunderbolt, but it could out-climb and out-manoeuvre both American fighters." The top speed for the Ki.84 is listed at 388 mph @ 19,680 ft. In volume 4 , the P-51H top speed is listed as 487 mph @ 25,000 ft. and the P-47N top speed as 460 mph @ 30,000. I could never figure out how it could "compare favorably" with my favorite US fighters. Fifty-some years later you are helping me understand. Great video! Now how about addressing Mr. Green's comment about the Kawanishi N1K2-J Shiden-Kai (George 21) when he says "the Shinden-Kai, was undoubtedly the finest J.N.A.F. production fighter of the war." How does it compare with the J.A.A.F. Ki 84?

Hope for ki-100 or type5 in the comparison

13:58 I'd think the 加速ポンプ(acceleration pump) in the upper right corner is the hand operated fuel boost pump. It seems crazy to try pumping fuel with that handle whilst trying to fly with a center stick control and a throttle on the left side...

Greg bringing the highest quality aero and engine content to the world, as always! As to the metallurgy, a trusted friend, welder, machinist, and metallurgist said when viewing that report - "Wow, thats a triple alloy steel, same as Early Tiger Is very impressive even for today standards, very close to todays 4340 and if it had less phosphorus and sulfur contaminates it would pass MIL-DTL-12560 for armor plating for today's US Main Battle Tanks. Im surprised the Japanese was able to make them considering their situation in 1944-45."

In addition to Greg's unmatched, deep, detailed examinations of these aircraft, I just want to thank knowledgeable commenters from around the world who provide even more detail and context to WW2 Japanese aviation. I always read the comments in Greg's channel and I can't think of anything more praiseworthy.

First time commenter, I've really enjoyed all of your videos sir. As a former Naval Aviator, I greatly appreciate the level of detail provided in all your videos. I'm very biased towards anything Navy/USMC aviation of course, so topics covering the Pacific Theater are always of great interest to me. I enjoyed the first video on the Ki-84 so much, it inspired me to order a couple of books on the subject and I even ordered Arma Hobby's 1/72 scale Ki-84 model. Ironically, it arrived this morning just prior to me watching this video. While watching the video, at around time stamp 19:30 there is a picture of an abandoned Ki-84 with no description about the date/time/location but I immediately recognized that aircraft from the artwork on the Arma Hobby box I received this morning so I paused the video and went and grabbed the box to look at the artwork again. Sure enough, on the back panel of the box, there are 6 examples of Ki-84s with different markings/color schemes. Per the info provided on the box, that exact aircraft is one of the six represented on the box and is aircraft serial number 1446 of the 2 Chutai 11 Sentai squadron/unit based in the Philippines in the 1944-45 period.

Been a fan of Japanese aircraft since I was a kid, probably because little is generally known about them. I've had the Aero publishers book on the Ki 84 since the '70s. So these are a rare treat. One often overlooked favorite of mine was the Mitsubishi Ki-46 Dinah Recon Plane.

One thing about having a high quality channel - is the quality and contributions of viewers who would provide things like rare technical manuals and - translations of them. Kudos here to all involved. .

Any chance of a review of the Ki-44? IIRC, it was the 1st Japanese fighter to buck the entrenched Japanese Military doctrine of a fighter being highly maneuverable.

Excellent as always Greg! WWII japanese airplanes have typically been “in the shadows” save for the Zero, exploring them this way is most interesting! Are you planning on studying the J2M Raiden or tej C6N Saiun? That would be awesome!

Greg, Your videos are the best and you have one of my favorite channels on RU-vid! These KI-84 videos have been really fascinating. Watching the last video raised a question regarding the engine design that I wondered if you might address moving forward. The reason given for the engines lower displacement, higher RPM levels, and higher compression ratio, were primarily smaller frontal area. I'm positive this was a big factor, but I can't help but see some commonality with the trends presently occurring in the automotive space; could one of the reasons for this change in design philosophy be an effort to reduce specific fuel consumption? I would be curious to see a comparison of fuel consumption with larger allied engines at given power settings. I imagine conserving fuel must have been on the radar of the Japanese in the latter stages of the war. I wonder if the increase in RPM and associated frictional losses were offset by the reduced throttling losses and higher efficiency of the increased compression ratio. Any insight you could offer would be greatly appreciated. Thank you for all that you do for us aircraft buffs!

Well done, Greg - as usual, and my thanks as a viewer to both of your new sources of information. Since my Dad flew a water-injected F6F-5 with VF-19 in the fall of 1944, and shot down three Japanese fighters during the Leyte campaign (an A6M and a pair of Ki-44 Tojos), but - to my knowledge - never encountered a Ki-84, I'm really looking forward to the performance comparison. He had squadron mates who DID encounter at least one Ki-84, which they dispatched in a low-level fight, but that might easily have been a case of a single Frank vs. multiple Hellcats.

Greg, as a professional involved with research and data reporting I would like to commend you for setting straight people's misconceptions regarding survivorship bias. Wonderful video, as always!

Another well researched and effectively presented aviation history lesson. We thank you Sir.

A generic comment about the alloy for the armor: Many alloys that has nickel as the base belongs to the so called "super alloys" group. From a machining point of view these stand out enough to give them their own class due to how difficult they are to machine, quickly wearing out the tools even when everything is done correctly. Crome and molybdenum in high amounts give steel very strong characteristics so I wouldn't be surprised if they also worked similar in a nickel base. (And a bit of rant about metal properties, many people confuse hardness, tensile strength and impact resistance, the relation between these can vary quite a bit and the difference between elastic and plastic deformation must be considered as well. Material technology is a fascinating subject that I wish I had more then scratched the surface of.)

If possible maybe a video about the other "best" Japanese fighters, the IJN's candidate the N1K-J Shinden Kai or George. And maybe, as I read so often about its performance the K-100 as another candidate for best Japanese fighter. Frankly, I think it IS the Frank ( pun intended) and it seems like its a no brainer but there is of course some writing that other planes take this title.

This is so good, when I am among such WW2 aeroplane fanatics I feel at home, and not like the nutter my Mrs tells me I am - I just wish some of you were round my house for a beer!

Hi Greg, thanks for the update. The armour steel looks pretty good stuff, particularly the charpy value which is a measure of toughness which is good energy absorbtion. The rubber mounting of the plate would undoubtably aid in impact resistance. I would be surprised if the tests included the rubber but obviously I don't know. If the testing didnot include it then the resistance to penetration is an under estimate. Water used for head cooling is indirectly an anti-knock since hot spots cause knock too. Basically another great video and thanks to your contributors who provided the info.

The "wobble pump" you're looking may be the farther of the huge handles to the right. 加速ポンプ = accelerator pump, the only pump that I see on the diagram. That translation doesn't sound like the right thing, but JP Wiki talks about it as basically an auxiliary pump to keep the carb from leaning out, and the illustration on that page is similarish to the English diagrams I'm seeing for wobble pump. Let me know if you need a bit of translation as you go through the Japanese aircraft--I don't know much about planes (other than what I've learned from you) but have been engineering and talking Japanese for 35 years.... ja.wikipedia.org/wiki/%E5%8A%A0%E9%80%9F%E3%83%9D%E3%83%B3%E3%83%97

I sure glad i ran onto this channel, its got a lot of interesting information. Thanks for all you do

I feel like this video really highlights that Greg has built more than a RU-vid channel here. He’s built a community with the breadth of knowledge and the real passion needed to give these machines the definitive accounts they deserve.

The graph at ~ 14:00 top right corner 8th from the top, 油圧ポンプレバー, which translates to oil pump lever, which points to a big lever just next to the right leg paddle, that *should* be the hand oil pump Edit: i got it wrong, it should be translated to hydraulic oil pump lever which has nothing to do with fuel

Sound was fine for me. Early Festivus gifts for Greg. Looking forward to part 2!

​Greg, will you compare the Ki-84 vs the Mustang?

Wow. Running a wobble pump in a fight would be a pain. I'd like to know more about that. I feel like there may be more to that. Perhaps somthing done just prior to pulling more than 3Gs? Somthing done just prior to entering combat?

13:53 8th line on the right says "oil pressure pump lever" (油圧ポンプレバー). It points to the second stick on the right.

Have you done one about the Ki-100, the evolution of the Ki-61, I think. And I'll give one special credit to the Ki-84 - it has the most beautiful fuselage lines of almost any aircraft in WWII. Oh! You've already done it, and i just saw it! GREAT as usual, thanks!!!!

Thanks for the superior quality content!! Yeah, if we want to compare apples to apples it's just right that we compare the very best of them, despite quality differences, just the best scenario...the reality I guess, is history😁

In regards to the exhaust on the KI-84 only the first few prototypes had the single exhaust on each side of the fuselage. The multiple exhaust were implemented used as it was proven to give a slight speed increase due to thrust augmentation. This is also well documented in regards to the A6M5 Koi/Otsu/and Hei models as the A6M1,2 and A6M3 Model22 Zero had single exhaust exiting at the bottom of the cowling. With the A6M5 the speed was increased to 352 mph due to the slightly more powerful engine combined with said thrust augmentation exhaust stacks. This can also be seen in the late models of the KI-43 III Ko Oscar as well as other such aircraft 1943 to late war such as the N1K1-J Shiden, N1K2-J Shiden Kai, J2m3 Raiden, and many other fighter and bomber types used by Japan in WW II.

Regarding the individual exhaust pipes, the publications that I saw (also Japanese) suggested that it was the individual exhaust type that was destined for mass production, instead of the collective. This was due to the superior volume of the "jet" exhaust, that thos individual exhaust stacks created instead lower volume by collective system. This makes sense if you look at it in the context of other airframes being modified to that exhaust stack arrangement or by all newly procured airframes (N1K1-J) which sported such solution. Both Japanese Army and Navy started using individual exhaust systems on all their aircraft since 1943. You can see that even with a Zero. A 1941 A6M2 or 1942 A6M3 had collective exhaust system, with gasses directed below the fuselage. In 1943 the A6M5 model 52 Zeros started appearing with individual exahust stacks, which blew the gasses directly behind the aircraft, and they indicated a small, but nevertheless worth mentioning, performance improvement with top speed jumping from 292-294 knots to 302 knots. Similarly in 1943 you would start seeing G4M1 Betty, Ki-43-II Oscar or Ki-44-II Tojo with such individual exhaust arrangements. I have a Japanese 1943 G4M1 Betty 11 report, which studied that "jet exhaust" effect and results for a bomber were similar, increasing top speed by 5 to 10 knots and climb rate.

You should give a really obvious analogy for survivorship bias for the people still complaining. Something to the effect of: "The planes that came home were not hit in the cockpit, engines, or fuel tanks; so it must be hard to aim for those. We should armor wingtips snd empty fuselage." - Survivorship Bias Conclusion "The planes that came home were not hit in the cockpit, engine, or fuel tanks; so we should armor those areas instead of empty fuselage or wingtip areas" -Normal Conclusion

Regarding the manual fuel pump, it seems to be the rightmost of the two long handled rods with balls on the end on the right side of the cockpit. The word 'pump' （ポンプ）is very legible but the kanji for fuel (燃料）is not. In 'The Miraculous Torpedo Squadron' the autobiography of Juzo Mori, he describes one of his early sorties in China when his engine began to lose power. Having been trained to crash his airplane (a Kate) into an enemy position if unable to make it back to friendly territory, he asked his backseaters if they were okay with that (they were) and began looking for an enemy position to crash into. However, he did start using the manual fuel pump and that kept the engine going long enough for them to make back to their lines.

Hi Greg! (and your supporters :) I'm just wondering: the armor analysis document wears a mark of the Office of Scientific Research and Development and as such it should be in the Public Domain... So... Where is it?

Apart from the excellent work and videos you do, I really want to say I like listening to you. People who speak like that usually know what they are doing or saying. It is maybe not the compliment you are expecting doing technical videos, but hey !

Armor plate might save the pilot but the aircraft is still destroyed. I'd prefer a rear observer telling me to "BANK ! NOW ! .."

Greg, the K-84 looks a lot like Kawanishi N1K2-J Shiden Kai "GEORGE". Is there a link between the planes ?

Goodwin and Starking's book on Japanese Aero-Engines indicates that the Ki-84 prototype used the Army equivalent of a Homare 11 which was switched to the Ha-45 (army equivalent to the Homare 12--revised cylinder heads for improved cooling) with the single exhausts in early trials aircraft. Fairly early on, exhaust was switched to ejector style. The engine still didn't perform at altitude as hoped but even that engine in the Ki-84 resulted in it being too powerful for the airframe and propeller at lower levels with resulting better airplane performance available at higher altitude for pilots. Engine was then updated to [Ha-45]12 which improved fuel pressure (which had been an issue) among other changes. At the end of 1943, deliveries of next revision [Ha-45]21 with a more powerful supercharger and higher compression ratio began and when enough engines were available, update was introduced for Ki-84 production. Later in the production run, some aircraft received [Ha-45]23 engines (Homare 23 equivalent) which definitely had newer indirect fuel injection.

Greg, Google translate seems to do a pretty good job of translating the cockpit diagram for the Ki-84 in your video. Check it out.

I checked several Japanese books about Ki-84 and there was no cockpit heating system. One of the books mentions that IJA did not require heating system inside cockpit in their specs. So, Nakajima did not go beyond IJA’s specs and left Ki-84 pilot’s life in the cockpit cold and miserable. However, IJA provided Ki-84 pilots electric heated flight suit. There was a switch for that in electrical switch panel installed to the pilot’s right-hand side. Ki-84 came back and flew over Japan’s sky in 1973. I was in the university which was a part of former Nakajima factory. Our university was next to Chofu Airport (former IJA air base). One day, I was lying on the lawn skipping the class as usual, there suddenly came thundering airplane engine sound. That was not the engine sound from familiar Cessna or Piper. When I looked up the sky, green aircraft with Hinomaru on its fuselage and wings climbing over our university’s main building. That was Ki-84! Later, I learned that our university’s main building was the place where Ki-84 was designed. I do not know whether the pilot of that time, Mr. Lykins, knew he was flying over Ki-84’s birthplace or not. I can still remember the engine sound and the view of climbing Hayate over its birthplace as if it happened a minute ago.

Has to be my favourite Japanese plane of the war. Kinda looks like their version of a P-47 Thunderbolt.

Wasn't there one of those in front of Clark Field in Philippines ? Until base commander had it scrapped in the 70's ? What a waste.

Sound quality is much improved. Thanx Greg.

The audio is much better, thank you.

what's amazing is that Japanese industry was in relatively bad shape in WW2 and everyone knew it. Everyone knew they couldn't compete with the Allied nations for resources, manufacturing, etc. Yet, they were in better shape overall than Russia is today in Ukraine to manufacture equipment and replace losses. Rather interesting comparison. Granted, modern aircraft and weapons are much more complex and Russia can't resort to making planes out of wood this time.

We need more in-depth analysis of imperial Japanese aircraft. Keep up the good work

It looks like a P-47 Thunderbolt and a A6M Zero had a love child.

Love Greg / no interest in Japanese warbirds. My brain can only be interested in so much. I am sure its great !

Can you do some Italian planes?

Great stuff! Just a note on the armor thickness: I suspect the variation in thickness between the armor of the two planes tested could well be just down the the manufacturing tolerance of the sheet metal used. This variance is within the current manufacturing tolerance of normal hot-rolled sheet. I am not sure if armor plate is held to a tighter tolerance.

Hi Greg, I hope my email about a better way to translate japanese manuals than Google Translate (using an OCR website in between) reached you - by now, several helpful folks with actual knowledge of japanese have basically confirmed what my guesstimated results were, but perhaps the same problem comes up in the future as well, and I suppose it's a good tool to have for simpler questions (i.e., that method does work for the instrument panel components quite completely). Also, I can add that using a different translation engine such as "deepl" gave me a lot better results when I tried to translate the scanned Kanji symbols compared to Google. Cheers and I hope all is well with your recovery!

Solid Shoutout to Chris from @MilitaryHistoryVisulized

A Civil War (US) historian stated that whenever he hit a dead-end on research he would post what he had and invariably someone would come back with something like a copy of a letter from their great-great-grandfather detailing how the commander of the XX Alabama was killed at Antietam/Shiloh/Gettysburg. This internet thingie can be useful.

I'm officially renaming this episode the "Ki-84 Addendum and Corrections." episode. Thanks for the follow-up. Edit: Survivor bias exists because those who did not, refuse to comment.

wobble pump ! yea ! for years i've wondered what is a wobble pump.

Greg, is a treasure of the interwebbies...........that Al Gore invented!

The sound quality is good.

You dindt make one guy gets field marshald for this info ?

HI Greg I just emailed you translated image from 14 minute 29 second mark of this video, hope it helps.

Definitely love the Japanese aircraft, they’re so unique and have interesting stories

Can you add Spitfire Mk VIIIs and P-51Ds to the comparison?

hardening metal, such as armor, makes it more brittle

Is it just me or does anyone else see a slight resemblance to the P-47 in this aircraft. It's almost like a near copy with what they had to work with. Or it is just chance resemblances.

Subaru.

Congrats on great success with these videos. Just being honest, video games like War Thunder have sparked curiosity in many people's hearts. It's as if there are more WW2 and conceptual technologically aware people than ever, thanks to content like this.

Greg i wanna ask,does British have dive bomber?and if so can you explain why its not mass build and use on it aircraft carrier?

As to the metallurgy of the armor, another older and more commonly used term for "carburizing," is case-hardening. It is done by heating the plate in an oven, surrounded by a source of carbon (generally wood charcoal), in the absence of oxygen, and then allowing it to cool slowly. This allows carbon from the charcoal to migrate into the outer surface of the metal, making it very hard, compared to rest of the mass of the metal in the interior of the part, whatever it may be. I'm not sure how long the process has been around, but I'm familiar with it from experience with antique firearms, where it was used in revolver frames and rifle receivers prior to the availability of stronger alloys starting in the late 19th century.

So. Japanese, wwII, aviation enthusiasts... I've never considered that for some reason. But of !Course! they're out there! Thank you for your contribution!

Thank You Greg 😀😊😀 Great Part 1.5 and Thank you Too The Kind Person Who Provided The Missing Links By Providing The Original Manuals 😊😀👍🏼

>>> Never EVER enough truth about ALL Japan WW2 aircraft !!!

Frank Part 7, Post proposed titles below

Very impressive sources! Thank you to those that brought them forward.

if look at frank prop has it differant from time other franks

Eleventh from the top on the right seems to end with "pump" at least. And i don't think it's a matter of the designers being ahead, but rather the Japanese manufacturing ability being badly behind. And for comparison, use the best and the average or the best and the worst "normal". Ie. see what it was commonly capable of and what it was supposed to be capable of rather than how it fared when it was held back by poor manufacturing.

Only tangentially related, but I was looking at pictures of the N1K Kyoufuu/Rex (original seaplane version of the N1K1-J Shiden/George) and I cannot figure out where the intakes for the charge air or the oil cooler are. They are plainly visible on the Shiden, but not on the Kyoufuu, even though it uses the wider Mitsubishi Kasei engine while the Shiden uses a Nakajima Homare. I though that it might use an engine fan similar to the J2M Raiden/Jack, which uses the same engine, but Japanese wikipedia claims this is not the case. Even if it was, it still wouldn't make sense, since only the charge air intake is internal on the Raiden, and I'm pretty sure the Kyoufuu's fuselage is narrower than the chunky Raiden. Anyone have some insight into this?

8:30 Just about every picture I've seen of Ki-84-Ia,b, and c at Sentai level has the thrust augmented exhaust. The first preproduction series of a hundred or so had the single per side collector exhaust. I don't recall a single picture of these early collector exhaust Hayates with Sentai markings.

"Sometimes new information raises as many questions as it answers." I think that's the nature of almost all scientific and historical research. I've never come away from a project satisfied that I found all the answers - and when I thought I did, I was wrong.

Almost forgot, there was a submarine carrier, Japanese, i think it carried a zero with floats

How about one on the Jack? We all have favorites and mine is the Jack.

I am so glad that I have discovered this channel. As someone interested in military engineering I love the deep dives into the aircraft of WW2 etc. And it is great to see some info of the Japanese aircraft, they are much better than I had imagined. Keep up the good work!

22:14 Don't. From all I've read on the Hayate it was a production and especially maintenence nightmare. As production continued until the end of the war successive batches of Hayates suffered from decreasing levels of quality due to material and assembly shortfalls. The 388 mph Hayate should be your guide for comparisons to Allied fighters in 1944-45 as this was IMO a best case scenario. I'm sure the Hayate suffered from increasingly inferior avgas into 1945 which no doubt further decreased performance and shortened engine life. Hayates in tip top shape tuned to run on American AvGas are in no way representative of their performance in combat for the simple reason that the Japanese didn't have access to it.

Thank you for the dedication to the depth of detail. Your work has not gone unnoticed.

Might I suggest if you have a Android phone, using Google Lens to translate it. I did so off the screen video and it was able to handle, or at least do a decent job of translating. Using it, it labels one thing an "Accelleration Pump". I'm familiar with what that does on the carberator on an automotive gas engine, basically it squirts extra fuel into the mix when you accelerate. Could this be the pump you are looking for, but are missing through translation?

Great presentation, Greg. Your videos give an outstanding degree of technical information.

Ref mechanical fuel pump: that’s the standard T-6 set-up, you gotta use the wobble pump if you notice the loss of fuel pressure. Fuel pressure going up under Gs, May happen by gravity if the fuel tank is higher than the mechanical fuel pump, just by increased weight of fuel under Gs.

00:26 "I've got information man, new shot has come to light!"

Trust. That is what we have when we listen to, and believe, this stuff. I am electronics technical, not mechanical technical - perhaps that is what makes this so interesting for me. Also, a reliance on proper sources without getting bogged.

Greg Great video in an excellent series. I’d love a comparison of the Ki-84 with the P-51D & FW190 Dora at some later stage

Let's retune and retest every Axis fighter to run on the far superior American AvGas. It's fun to see what a Ta-152H-1 would REALLY do with the inferior German fuels replaced by American AvGas. I'll bet that 472 mph maximum speed figure would really jump. ...but not realistic.

Exceptional aviation research. Thank you Greg

Wait, November is best possible model of Thunderbolt? Didn't it had made some sacrifices to have bigger wings to hold more fuel?

Carborizing is for wear and is only on the surface 0.010 - to 0.0 40 thick. Rockwell 65 to 70 hardness . The harder the material, the more brittle it becomes, and can shatter on high impact.

Wait why would the person with the data want to hide it?

From the engineering point of view, Nakajima (like their German comrades) had to design a high performance engine based on the tyranny of low grade fuel, bad lubrication oil and bad material (substitutes) for the main bearing. All their technological effort went into addressing this. All later problems in production and maintenance were due to these three factors. Was it an success? Well, operation "Strangulation" - the mining of the Japanese Sea by B-29 - went on mostly unopposed. And this very operation was the most decisive factor in forcing the Empire of Japan to surrender in 1945 without the need of invasion.

This need to be 1.5

Regarding the fracturing of the armor plate, the heat treat used (according to the specifications you'd supplied) showed the outer "casing" was done to a depth of a tenth of an inch as was also listed on the Rockwell "C" scale, a hardness of 64. That is VERY HARD. Almost 40 years ago, I hand engraved (on a Deckel GK21 pantograph milling machine) quite a few Poco 3 (graphite) electrodes for use in an Electro-Static Discharge Machine (E.D.M.) This was in order to burn in very fine detail for plastic injection molding inserts of S-7 tool steel, heat treat hardened to that same Rockwell 64 on the "C" scale. The applicatrion was for Hewlet Packard's yet to be released consumer line of ink-jet printers, specifically, these were the nozzle design's test molds. I had to hold to .0002" accuracy (I managed) using CNC generated aluminum templates supplied by Hewlet Packard, and for over forty versions of these nozzle designs, each requiring some 6-8 electrodes. One bad Friday, as Tom Magee removed form the oil tank of the E.D.M., a fully finished, identical hardness to the Frank's armor plate, Rockwell 64 "C" scale, S-7 tool steel insert , the surface oil remaining caused him to lose grip on the approximately one cubic inch insert. From a height of little more than three feet up, it hit the shop's concrete floor shattering as though it was made of cheap glass. That "64" is rather hard, but also rather brittle. We both laughed as that represented a better part of a week's work for each of us. What else could we do?

Isn't there data from the Planes of Fame ki-84 from the late 70's?

30-'06 M2 ammo is "only" 150 grain, Boat Tail FMJ, not AP.... Also, most US Naval (& British Fleet Air Arm) tail gunners had .30s, and .303s for their machineguns.