Stiffening of Controls for the A6M/A7M series

[Laurelix]

Maximum safe dive limits: (as far as I know)

A6M2 Mod 11-21: 630km/h IAS
A6M3 Mod 22: 630km/h IAS
A6M3 Mod 32 (Hamp): 670km/h IAS
A6M5 Mod 52: 670km/h IAS
A6M5 Mod 52 Ko/Otsu/Hei: 740km/h IAS
A6M7 Mod 63: 740km/h IAS
A7M1 / A7M2: ???km/h IAS


The A6M3 Hamp had smaller clipper wing
The A6M5 had re-designed smaller wing giving it better roll rate at higher speeds (but worse at low speeds) due to smaller wing span reducing the loading slightly but due to smaller wing and less lift it was worse in rolling at low speeds compared to the big wing Zeroes.

The later versions of A6M5, starting with the Ko had re-inforced wings which increased their maximum dive limit from 670km/h to 740km/h from baseline A6M5… or… 630km/h —> 740km/h compared to the full wing Zeros.

Grok 3 estimates that late A6M5 with 740km/h maximum dive limit delays the control stiffening forces by 130-190km/h compared to the full wing Zeroes. Considering its AI… I wonder if how true this is and wether there are sources to back it up.

Then there's the A7M Reppu series…

 

[Casor]

In the book the Cactus Airforce the pilots indicated the Guadalcanal version era Zero's ailerons (whatever version that was) would lock up at 225mph which accounts for the F4F tactic of diving through a Zero formation since the Zero could not reliably follow.

 

[taly01]

Grok 3 estimates that late A6M5 with 740km/h maximum dive limit delays the control stiffening forces by 130-190km/h compared to the full wing Zeroes. Considering its AI… I wonder if how true this is and wether there are sources to back it up.

I would give no credit to GrokAI (or other consumer AI) for that matter. If you know a subject well start asking any AI some questions and you will see how dumb it is. I expect to see an increase in stupid decisions and actual disasters from Humans with low knowledge on a subject (ie. Politicians) relying on AI for guidance.

P.S. The heavier wing skin on later Zero 52 ( and Zero 53 more internal bracing), would give little change to aileron effectiveness (in 250-300mph range). I have never seen any document saying it was so.

 

[Ivan1GFP]

Regarding "Control lockup" and degraded roll rate, I believe this is way overstated. If you watch a few videos of the only surviving A6M5 performing a roll and time it with a stopwatch, you will be amazed at the roll rate and I doubt it is being pushed very hard. I was getting about 120 degrees per second. If you listen to interviews by the current pilots, they state that the roll rate of the A6M5 is "very good" and "about half again as fast as a Hellcat".
I do believe the controls stiffen with higher airspeeds, but even then, the actual roll rate doesn't degrade that low. I believe that part of the problem was that the trigger for the guns on the A6M series was on the throttle which meant that only one hand could be on the stick if the pilot intended to shoot something.

If you are just interested in roll rates, check out this video about 20 minutes in.

View: https://www.youtube.com/watch?v=Cs5m5ZbtRQg

- Ivan.

 

[Engineman]

Regarding "Control lockup" and degraded roll rate, I believe this is way overstated. If you watch a few videos of the only surviving A6M5 performing a roll and time it with a stopwatch, you will be amazed at the roll rate and I doubt it is being pushed very hard. I was getting about 120 degrees per second. If you listen to interviews by the current pilots, they state that the roll rate of the A6M5 is "very good" and "about half again as fast as a Hellcat".
I do believe the controls stiffen with higher airspeeds, but even then, the actual roll rate doesn't degrade that low. I believe that part of the problem was that the trigger for the guns on the A6M series was on the throttle which meant that only one hand could be on the stick if the pilot intended to shoot something.

If you are just interested in roll rates, check out this video about 20 minutes in.

View: https://www.youtube.com/watch?v=Cs5m5ZbtRQg

- Ivan.

A very good video, expertly presented by Steve Hinton.
The old recording lacks some clarity but, this footage is still worth watching. I particularly enjoyed the cockpit start, taxy and warm-up with commentary.
Where else could you see a a close-up formation take-off of that aircraft? Steve Hinton has some serious skill, the lead photo plane looked to be a GA twin, so that T/O sequence
shows just how well handling the Zero is.
Rate of Roll is good and the cockpit shots of the loop show how easily the aircraft handles in the vertical.
The performance details given here are general, but Steve points out the positive advantages.

Eng

 

[Ivan1GFP]

What is amusing is that during the tests of the Aleutian A6M2, the dive performance of the Type 0 was quite favorably compared to that of American fighters such as the Wildcat. At the time, no one had provided the USN with a proper manual, so they had no idea that the "Maximum Dive Speed" was as low as it was and the aircraft was no worse for wear.
The controls stiffened with increasing airspeed, but from hints from various sources, I do not believe the roll rate ever fell below about 60 degrees per second. That isn't great but compare that to a Hawker Hurricane.

Keep in mind that there were a lot of things that the restorations of captured A6M never got quite right and Allied tests should be taken in that context.

- Ivan.

 

[Casor]

The proof is in the first-hand account combat pudding, not tests of captured Zero's. The F4F's dived and Zero's rarely followed. It's well documented.

 

[Ivan1GFP]

The proof is in the first-hand account combat pudding, not tests of captured Zero's. The F4F's dived and Zero's rarely followed. It's well documented.

A combat report is what the pilot CHOSE to do with the aircraft, not necessarily what the aircraft was capable of.

 

[Casor]

Yes, exactly. And the Japanese pilots CHOSE not to dive after F4F's for that very reason.

 

[MIflyer]

Note that the test reports of captured Zeros also said that the elevator forces became excessive as well.

 

[Ivan1GFP]

Yes, exactly. And the Japanese pilots CHOSE not to dive after F4F's for that very reason.

I can think of a couple other reasons the typical Japanese pilot might choose not to pursue a target in a prolonged dive.
We are used to the idea of radio communications. The typical Type 0 didn't have that, so separation was bad.

 

[taly01]

Note that the test reports of captured Zeros also said that the elevator forces became excessive as well.

The Elevator on the Zero is famous for having purposely designed stretchy cable! to prevent high forces over-stressing the plane.

I remember someone (Sakai?) said the Zero would almost fly itself in level flight, this self stability may have worked against it in 300mph+ maneouvers. Possibly move than any aileron/elevator problem that a pilot would "feel".

 

[PStickney]

I would give no credit to GrokAI (or other consumer AI) for that matter. If you know a subject well start asking any AI some questions and you will see how dumb it is. I expect to see an increase in stupid decisions and actual disasters from Humans with low knowledge on a subject (ie. Politicians) relying on AI for guidance.

P.S. The heavier wing skin on later Zero 52 ( and Zero 53 more internal bracing), would give little change to aileron effectiveness (in 250-300mph range). I have never seen any document saying it was so.

I agree, and dread what's going to happen as the use of Generative AIs spread. The answers you get are determined by, basically, the AI logic sifting though whatever databases it searches, or was trained on, and delivers a Statistically Averaged answer. Fine for fun and games, OK for creating a mediocre code sample - but anything involving history, or analysis of technical historical data, is flooded by hard facts being plowed under by whatever the popular view happens to be. Add in that the programming of these things is to always return a positive answer to who (or what) is forming the query, and you've got Wikipedia run by Golden Retrievers.

 

[Holtzauge]

While the stick forces on the Zero certainly would have restricted the roll rate, even reducing these would probably not have achieved much given that the so-called aileron reversal speed on the Zero was probably quite low given its light construction. In fact, AFAIK the Japanese did try aileron servo tabs on the Zero to address the aileron force problem and one prototype even crashed in testing. However, if you just lower the control forces but don't stiffen up the wing, all you will be doing is twisting the wing at higher speeds and not getting much higher roll rate. As an example, the original Spitfire wing only retained about 35% of its theoretical stiff wing rolling capacity at 400 mph due to this effect, and which is why they had to stiffen it up in later models. So the Zero being restricted to rather modest maximum speeds in dives is not necessarily connected to control forces, but could (and probably was) instead be due to aeroelastic effects like aileron reversal.

 

[Casor]

While the stick forces on the Zero certainly would have restricted the roll rate, even reducing these would probably not have achieved much given that the so-called aileron reversal speed on the Zero was probably quite low given its light construction. In fact, AFAIK the Japanese did try aileron servo tabs on the Zero to address the aileron force problem and one prototype even crashed in testing. However, if you just lower the control forces but don't stiffen up the wing, all you will be doing is twisting the wing at higher speeds and not getting much higher roll rate. As an example, the original Spitfire wing only retained about 35% of its theoretical stiff wing rolling capacity at 400 mph due to this effect, and which is why they had to stiffen it up in later models. So the Zero being restricted to rather modest maximum speeds in dives is not necessarily connected to control forces, but could (and probably was) instead be due to aeroelastic effects like aileron reversal.

Excellent point