Nerf Japanese planes

Machinery of War Discussion Aircraft
194

Years ago I read that some Japanese aircraft were manufactured with wider safety margin. Minor structural bending was sustained past the safety speed, but the destruction speed was far away from that.

I know the IJN had 1.8 as safety factor regulated, and some static test showed failure happens over 2.0. Considering the light weight and the use of super duraluminium, I would see A6M is structurally strong in static, but with the airload, things get different.

Ki-61’s 850km/h is from a test flight. The main designer stated there was no fluttering and no visible damage. After that they even wanted to make a lighter wing as they saw no need for that exessive structural strength.

There’s little information on whether the airspeed was correctly calibrated. Ki-61 with 7.2 AR and utilizes high camber convexity airfoil (NACA24000) should meet compressibility well before 800kph. Even the P-51 Mustang, utilizing an laminar flow airfoil, meets compressibility starting at 813kph IAS below 5000ft.

Later 1000km/h was claimed in combat with Ki-100s, which had the same old wing and new speedometer.

Seems like the pitot static system failed in compressibility, which is common at that time. There were pilots of bf109 made similar claims, and Me262 pilot claims on breaking the sound barrier, which wasn’t possible.

Also Ki-61 pilot had to keep the engine within certain RPM and boost settings during high speed dives, which apparently wasn’t done automatically.

This is quite common, diving RPM limit widely exist at that time.

One peculiar thing about Ki-61s is the lack of fancy combat flaps, which became practically a standard thing in other Japanese single engine fighters.

Neither did combat flap saw in Ki-84 manual, nor in the American/British test of Ki-84. The operation seems to only provides 15deg and 30deg. However, pilots with experience could use flap switch, or hydraulic valve to make flap stop at any intermediate position, thus providing a combat flap setting, but less convenient. It looks like IJA tends to remove the use of combat flap in late war, due to unknown reason. Perhaps to make pilots more used to energy fight? I heard that the Ki-84’s high stick force was also made in purpose.

In game “rip speed” is supposed to be IRL dive speed limit +5%. I have no idea where Ki-44 and Ki-84 get their numbers from. J2M and A7M limits I haven’t seen either, so I suppose they are vaguely modelled to fit 400knot requirement.

If 400knots was incorporated, we should expect a rip speed around 790kph.

1 Like
195

learn to play

2 Likes
196

Nakajima’s butterfly flaps are said to have been slow and difficult to use and I don’t think navy’s automatic system ever found it’s way into army aircraft. It might have been impressive in tests, yet in practice it wasn’t used that much either. Unknown how reliable the hydraulic parts were.

2 Likes
197

It’s not optimistic, they went beyond that. I have also found zero mentions of Ki-61s breaking up in flight due to high G forces, or even issues relating to this.

These effects were already very well known by the time the Ki-61 was made.

And an inherently more fragile wing spar design, on top of easily removable wings that introduced an obvious point of failure. Still, the 109 was quite a tough little plane.

If it was reading accurately at 750kph IAS (the manual limit) then anywhere above that would be faster, proving that the 109 could dive well beyond 750kph.

Higher mach limit, which is what really counts here if we’re talking about compressibility. And one of the P-38’s minor weaknesses.

Sounds like I was right.

1 Like
198

I found this quote:

なお開発時に、土井技師の不適切な対応もあり、急降下時に補助翼がフラッター(異常振動)で千切れ飛ぶと言う事故が発生しているが、無事着陸に成功し事なきを得ている。

There were flutters happen on the Ki-61 during the development phase, and caused its aileron been blown off. This coincides what I have said, that over-spanned aileron causes flutter issue on almost all japanese fighter design, and it seems ki-61 was not an exception.

If it was reading accurately at 750kph IAS (the manual limit) then anywhere above that would be faster , proving that the 109 could dive well beyond 750kph.

In fact different nations did have different standards on dive limits. The German and Japanese manual tends to give ONE specific IAS limit, just like the in-game mechanics, instead of a piece wise limit corrected to Reynolds effect as British and Americans did.

For example, Spitfire was known to have extremely good dive limit and high critical mach number of 0.89, but in-game figure used its manual IAS limit at 20000ft (450mph @ 6000m) + 5% margin, causing them to rip at airspeed significantly slower(only 774kph) compared to Ki-61’s 850. Clearly the Spitfire could dive to a much faster IAS at 10000ft (presumably 970kph IAS could be allowed), and even more near the ground.

This had backed to the main conclusion: Japanese aircrafts in-game do not follow the same policy that applied to every other nation.

As for your claim about 850kph, that was really doubtful, was that a calibrated reading? Did they used the correct the pitot static reading? Were they giving IAS,CAS or TAS? Almost every other aircraft had dirty claims on achieving much faster dive than on the manual, said once P47-C achieved 725mph in a dive, yet the game still complied with its manual number of 522mph IAS at 5000ft + 5%margin as the rip speed.

The manual gives 700kph, which may be somewhat conservative, but so for almost every other aircraft. There were no other first-hand source that can support Ki-61 to do a higher speed dive. If following the same policy, Ki-61 should be given 735kph as its IAS limit, instead of 850kph.

199

“During development, due to inappropriate handling by Engineer Doi, an accident occurred in which an aileron fluttered (abnormal vibration) during a steep dive and was torn off, but the aircraft was able to land safely without incident.”

Pilot error, according to your own quote.

It is not impossible, but extremely unlikely that several aircraft, with completely different design philosophies, manufacturers, and powerplants have the same exact rip speed.
The manual numbers are more likely than not a placeholder, using those makes no sense when we do have primary sources of the Ki-61’s flight testing.

200

As it was said earlier Ki-61 airspeed indicator even couldn’t show speed over 700km/h so I really think that limit was done according to this fact

1 Like
201

Dr.Doi is the chief designer of the ki-61, not the test pilot.

202

Test flight aircraft often uses different airspeed tube and indicator to acquire correct value. At least in other nations they did.

203

Limits at manuals is written for army pilots with their simple indicators, not for the special one from testing

1 Like
204

2016 called, they want their whine back.

3 Likes
205

NO, the reason why good players stick to the bottom is because the upper BRs of Japan is a barren wasteland! The only fix is more Japanese aircraft…

1 Like
206

Reading through Bunrindo no.16 on the Ki-44 and the dive limit is confirmed as 850kph:

Untitled
Untitled1007×869 108 KB

(page 55)

Translation is never perfect but it is unequivocally claimed to be 850kph

image

Page 11 has more:
Untitled

207

Everything count as in first hand source, such as the flight manual.
image
The official diving speed limit for Ki-44 II was 650kph IAS, limited by tail buffeting.
One thing you have to understand is that static structural experiment/calculation does not stand for actual in-flight performance, as there will be aeroelastic effects and compressibility effects.

208

They did not get to 850kph through static testing. In fact, page 11 makes no mention of its G limits, the goal being to make a wing with a very high dive limit.

After all, why go through the trouble of making a fighter with a strong emphasis on speed and climb rate, and not enable it to dive any faster than the Ki-43 that was also developed at the same time?

It was considered a dangerous plane to fly, the 650kph manual limit was very likely there to keep pilots from pushing too far.

image
TAIC manual no.1 corroborates this by claiming “and a high diving speed”. Despite the manual limit of “650kph”, you will not find “high diving speed” on the Oscar 2’s entry, for which it is claimed as 400mph (~643kph), in-line with known information on the Ki-43.

1 Like
209

When a secondary source you mentioned claimed that Ki-44 could dive at 850kph, there was no mention of whether it was “IAS” or “TAS”, and it seems to me that they completely ignored the wing mach effects and compressibility effects, and the “850” may just be the TAS limit design goal, set up for structural design group to construct the main spar. Since an “850kph” IAS is highly unlikely to be achieved in a dive unless at a very low altitude, something that even a Mustang couldn’t pull out of.

Ki-44 II’s flight manual records:
image
The ki-44 ii dove for 2000 meters, and reached a maximum speed 650kph IAS, and then it requires 1500 meters of altitude to pull out the dive. The real dive limit considers more about whether the aircraft could pull out without getting into an uncontrolled compressibility dive. The structure of Ki-44’s wing spar may support it to perform an 850kph dive without being ripped apart, but it has no guarantee on its tail/ailerons, nor its compressibility dive characteristics.

And again I would say that the diving limits in War Thunder are based on the flight manuals for every other nation, except for Japan. The diving speed, say for the Spitfire, was set up based on its flight manual figure at 20000ft. By comparing this, setting Ki-44 's dive limit to 850kph according to a secondary source memoir is heavily biased.

210

Which isn’t really a factor in WT thanks to our incredibly strong pilots. Our concern is whether or not the plane will break up in flight.

The spitfire was very lightly built, it benefits from a high mach limit mostly thanks to very thin wings, but in terms of IAS limitations it’s not fantastic. The P-51H saved a lot of weight over the D models by using ‘british standards’ for structural strength. It was inevitably more fragile but it’s hard to say no to the performance it allowed.

Spitfires also have pretty big ailerons and had their own share of accidents caused by exceeded IAS limits. In that entire book, which spends quite a few pages detailing the many issues with the Ki-44, dive limits were never mentioned. This was not the case for the Bunrindo book on the Ki-43.

Page 11 wasn’t covering the interview with a veteran pilot and was not a “memoir”.

211

That is what I thought the limit in manual was for. It’s indeed not a disintegration limit, but when pilot should start recovery. The dive angle must be somewhat steep to require 1500m. With that much altitude drop, the speed would keep increasing further 100-200km/h, until plane is level again.

1 Like
212

More “Japan OP!” Tries to turnfight without learning how the game works

1 Like
213

It’s not about strong pilot, when a plane was thrown into compressibility dive, the control surfaces just become useless.

The spitfire was very lightly built, it benefits from a high mach limit mostly thanks to very thin wings, but in terms of IAS limitations it’s not fantastic. The P-51H saved a lot of weight over the D models by using ‘british standards’ for structural strength. It was inevitably more fragile but it’s hard to say no to the performance it allowed.

No it’s not. The spitfire was allowed for 450mph IAS @ 20000ft, while P-51D was limited by 400mph at the same altitude. We see the IAS limit for spitfire was actually HIGHER than the Mustang. Which wasn’t surprising, the IAS limit for allied aircraft was usually set differently for different altitude, which perfectly reflects the mach/reynolds effect. Something that Imperial Japan lacked the research at. With altitude becomes lower, the IAS limit will release further.
image
image

Clearly Ki-44 couldn’t reach 850kph in a dive, nor it could achieve 12.6G load factor. Everything you’ve mentioned was just structural design goal for the main wing spar, and has nothing to do with the aircraft level performance.

We see the design goal for ki-44’s wing spar been to withstand 850kph dive and 12.6G load. That is the goal for single discipline. But in reality, only 5G load and 650kph IAS was allowed in actual service, which reflects the actual performance in aircraft level, which was a multi-disciplinary result. So I see no reason you use those quote to prove ki-44 could dive 850kph, without even a single first-hand source show its ability to make a steep, controlled dive in compressibility region.

The contemporary IJA fighter manuals give Ki-43 a load factor limit of 6G, and Ki-61 with 7G. But for Ki-44 II, only 5G was allowed. At that time(late 1943), IJA already had a lot of experiences with ki-44, which reflected that the Ki-44 was structurally weak. In fact, due to this, Ki-84 was set to have a heavy elevator control to prevent the pilot from pulling too hard to damage the structure.

So I would suggest that “850kph” figure claimed in later memoirs in Ki-44 and Ki-61 may just been converted from IAS. We don’t know the altitude been set for that 650kph/700kph IAS limit, but if that happened around 15000ft, then the TAS would be 800-850kph. Which solves the myth for both Ki-44 and Ki-61’s mysterious claim on performing 850kph dive.

2 Likes