The Zero's Maneuverability

[ThomasP]

I suspect that the problem of pulling Gs and handling the throttle trigger at the same time, and/or that the requirement to do both at the same time, is being overstated.

When in a maneuvering fight the pilot will have to be able to handle both the throttle and stick, to one degree or another at the same time, whether the trigger is on the throttle or stick. Otherwise, when turning at significant Gs, the pilot will not be able to push the throttle forward to gain/maintain energy, or chop the throttle in order to prevent overshooting the target aircraft. Yes, I am sure there would be some instance where this might not be possible, but that would (I think) be the exception.

The A6M had problems with the controls stiffening up at high speeds (over 300 mph per the US evaluations) but not at normal maneuver speeds (which were usually in the 150-250 mph range). The aircraft was considered by the Japanese pilots to be very responsive at these speeds, with acceptable control forces, and this was backed up by the Allied evaluations.

And (though I may be thinking about this wrong) when turning at any rate over around 3 Gs the pilot in a typical WWII fighter will not be able to see the target aircraft (at effective firing range) anyway, as it will be hidden below the nose of the firing aircraft. Pulling around 3 Gs would not require particularly high stick forces in the fighters of the time (including the A6M), and even 4-5 Gs normally did not require particularly high stick forces. When we add that (from what I have read) most effective shooting occurred when the attacking pilot was able to relax on the Gs after gaining the necessary lead angle for the shot. Or the shot could be taken without having to pull high Gs in the first place (ie 80% or more of the shoot downs occurred without the victim being aware that the attacking aircraft was in a position to take the shot). I have only seen a relatively small number (easily less than 100) of shoot downs caught on camera, but in most of them neither the attacker or the attacked appeared to be pulling high Gs at the time of the kill shots.

Make sense?

 

[Clayton Magnet]

I have always been of the same opinion that you are describing here. There are some people however who take some of the pilot reports literally rather than figuratively. I have heard arguments that when the pilot described the stick as feeling like it was "set in concrete", that is literally what he meant. Concrete, immovable.... When these kinds of comments start getting posted, it is time to find something else to do.

One man's "set in concrete" is another mans "started getting a little heavy".
This is from Skip Holms, flying a Bf 109G6 (Although it may also have been a HA-1109);

"And the speed it loves to roll around is 250 mph and below. The roll rate is very good and very positive at 250 mph. Above 250 mph the ailerons get heavy and at 300 they are very similar to a P-51. Any speed after that results in the ailerons getting fairly solid and you need two hands on the stick for any meaningful roll rates. Most of my flights have been in formation with P-51s and the Me-109 is more maneuverable than the P-51 in most conditions."

 

[Ivan1GFP]

I suspect that the problem of pulling Gs and handling the throttle trigger at the same time, and/or that the requirement to do both at the same time, is being overstated.

When in a maneuvering fight the pilot will have to be able to handle both the throttle and stick, to one degree or another at the same time, whether the trigger is on the throttle or stick. Otherwise, when turning at significant Gs, the pilot will not be able to push the throttle forward to gain/maintain energy, or chop the throttle in order to prevent overshooting the target aircraft. Yes, I am sure there would be some instance where this might not be possible, but that would (I think) be the exception.

The A6M had problems with the controls stiffening up at high speeds (over 300 mph per the US evaluations) but not at normal maneuver speeds (which were usually in the 150-250 mph range). The aircraft was considered by the Japanese pilots to be very responsive at these speeds, with acceptable control forces, and this was backed up by the Allied evaluations.

And (though I may be thinking about this wrong) when turning at any rate over around 3 Gs the pilot in a typical WWII fighter will not be able to see the target aircraft (at effective firing range) anyway, as it will be hidden below the nose of the firing aircraft. Pulling around 3 Gs would not require particularly high stick forces in the fighters of the time (including the A6M), and even 4-5 Gs normally did not require particularly high stick forces. When we add that (from what I have read) most effective shooting occurred when the attacking pilot was able to relax on the Gs after gaining the necessary lead angle for the shot. Or the shot could be taken without having to pull high Gs in the first place (ie 80% or more of the shoot downs occurred without the victim being aware that the attacking aircraft was in a position to take the shot). I have only seen a relatively small number (easily less than 100) of shoot downs caught on camera, but in most of them neither the attacker or the attacked appeared to be pulling high Gs at the time of the kill shots.

Make sense?

When you have an aircraft whose controls stiffened up at fairly moderate airspeeds, even a small change in direction for a simple tracking shot may require high effort on the controls.

 

[GregP]

agree on rudder but I have never been in let alone flown a sailplane so cannot comment on that.

DO IT. Trust me. Go fly a sailplane. You'll like it, a lot.

 

[GregP]

To be honest, I find that circle-jerk to be BS.

Years ago, we were over the Mojave with our Cherokee Warrior and started a series of tight turns to port.
We started at about 10K AGL and after about five consecutive turns, realized we had dropped about 4K and bled off enough airspeed that we were about to enter a serious stall.
We levelled out at about 5K AGL or so and decided that was enough shenanigans for one day.

Found out later that the Air Density for that area was up and we had actually ended up been much lower than we thought.

Had we tried 75 or 100, we'd have been digging holes with our chins...

I'm pretty sure you would have noticed the ground approaching and would have adjusted your trajectory to prevent such catastrophe from happening. Hopefully, there was no Zero on your tail ...

Years ago, I was over Saguaro Lake just outside Phoenix, AZ and was in a Cessna 172 RG. I was at 6,500 feet. I started a circle to watch the boats and had my head outside the airplane for about a turn and a quarter. When I looked back inside, my airspeed was a few knots below redline and climbing. I terminated the turn and very gently leveled out and started a shallow climb until the airspeed was back to normal. Luckily, I was alone and nobody ever knew until now. At the time, I had maybe 100 hours PIC time.

As a result, even now, if I want to make a steep turn, I'll focus my attention on flying and not on scenery outside. Shallow turn (30°), no problem. Steep turn (45°+), pay attention!

 

[GregP]

I figure this is the natural tendency to use two hands as stick forces get higher.
This brings up one of the features of the A6M series that I have always found curious and non-optimal:
The trigger for the armament is on the throttle.
If you need both hands on the stick in order to pull enough angle to get a shot, how do you take a shot when the trigger is on the throttle?

I'm not sure you are right above. There is a trigger on the stick. The throttle has an armament selector switch that allows the pilot to select cannons, MG, or both to shoot when the trigger is pulled. It might be depending on model, too.

 

[ThomasP]

re the A6M's trigger on stick vs throttle

A picture of the A6M2 throttle quadrant:

The A6M throttle quadrant arrangement remained the same through the early A6M5. I do not know about the late A6M5 or A6M7.

 

[ThomasP]

re

When you have an aircraft whose controls stiffened up at fairly moderate airspeeds, even a small change in direction for a simple tracking shot may require high effort on the controls.

It is of course possible that an aircraft - whose specification required it to be maneuverable enough to mix it up with biplanes and the early monoplanes - could be so poorly designed that "even a small change in direction for a simple tracking shot may require high effort on the controls." - aerodynamics in general says this is not likely at normal maneuver speeds.

Also, the designer would have to be a poor one, the pilots who do the flight testing would have to be ignorant or corrupt (and not mention the problem in their flight tests), the people supervising the program would have to be ignorant or corrupt (and hide/cover-up/not mention the problem in their reports), and the Japanese combat pilots would have to repeatedly fail to mention the problem in after-acton reports (even with war-time secrecy and the language barrier this would have come to light in the post-war intel debriefs).

 

[Ivan1GFP]

The image of the throttle quadrant along with a description of the mechanism for weapon selection is in one of the reports posted in this thread. It has also been mentioned that some pilots did not like this and had the trigger moved to the control stick though I have never seen a photograph or drawing of such an arrangement.
As for "aerodynamics in general", keep in mind the aircraft we are discussing here and how little speed it takes to reduce roll response.
Clipped wings on Model 32 was an attempt to address the issue. I believe that aileron span was also reduced at one point.

 

[GregP]

Yeah. I've heard of the trigger it both ways. In fact, the Museum's Zero has that trigger and I was thinking of another one I saw some 40 years ago.

I think the trigger on the throttle was much more widespread and simultaneously more disliked. It WOULD make it harder to be offensive at higher speeds when two hands were needed on the stick.

 

[ThomasP]

re

I think the trigger on the throttle was much more widespread and simultaneously more disliked. It WOULD make it harder to be offensive at higher speeds when two hands were needed on the stick.

and

It has also been mentioned that some pilots did not like this and had the trigger moved to the control stick . . .

It would be nice if there were any mention, in any reports written by Japanese pilots, to the effect that the position of the trigger was a problem. There are a limited number of such (test or combat) reports that have been translated into english, and I am sure that I have read only a relative few of them, but none of the ones I have read mention any such problem. I have only read a couple of books either written by former Japanese A6M pilots or as biographies written with the help of others, and there was no mention of such a problem.

Does anyone have any such references available?

 

[Holtzauge]

I was not planning to post anything more here because we had reached a deadlock when it comes to if US trial data was representative or not.

But having thought some more about this I realized that there is another approach to the problem:

There is actually one data point which all seem to agree on: That the Zero did 316 mph at the so-called normal power setting with +50 mm boost and 2350 rpms.

So I added this power setting to my A6M2 Zero model in C++, and was happy to see that it was almost spot on as it was. I actually had to increase the value of the Cdo a few percent but it was really close.

And with the model now tuned to the 316 mph with the +50 mm at 2350 rpm, I again tried the power setting in the US trial, i.e. US 35" at 2575-2600 rpms, and the result was 334.5 mph. So basically spot on with the US trials.

Thus satisfied with the model, I now tried with the Sakae 12's "WEP" +250 mm boost 2550 rpm setting, and the speed was increased to 337.8 mph.

So why does the speed not go up higher with so much more added boost? Like to the vaunted 345 mph figure?

Well because at the same time as the power goes up, this extra power is generated at a lower altitude. And what this means in practice, is that while going from +50 to +250 mm and increasing the rpms certainly gives a much higher power, it at the same lowers the FTH to a lower altitude. And at lower altitudes, the air is denser, and the aircraft therefore experiences much more drag thus "eating" up the gain in power.

And this is why I have been posting the Spitfire MkI speed chart: The Spitfire's Merlin produces circa 1050 hp at +6.25 boost at around 5 km, and with +12 boost about 1310 hp, but this is at an altitude which is a bit below 3 km. And pushing the aircraft through the dense air down below 3 km eats up most of the added power. And that is what the chart shows: While the speed for the Spitfire at lower altitudes is greatly increased, the absolute top speed number at the FTH is not. And the effect is just the same for the Zero and the Sakae 12. And this is incidentally why you need simulations: Because if you assume that the added power is available at the "old" FTH, then 345 mph is most certainly possible. But this is simply wrong. This is not how physics works.

So in summary: With a C++ model replicating both the Japanese 316 mph with +50 mm, and the US test data at 35", the top speed of the A6M2 Zero at the +250 mm 2550 rpm setting can be expected to be in the order of 337-338 mph.

 

[GregP]

re

and


It would be nice if there were any mention, in any reports written by Japanese pilots, to the effect that the position of the trigger was a problem. There are a limited number of such (test or combat) reports that have been translated into english, and I am sure that I have read only a relative few of them, but none of the ones I have read mention any such problem. I have only read a couple of books either written by former Japanese A6M pilots or as biographies written with the help of others, and there was no mention of such a problem.

Does anyone have any such references available?

I'm not too sure it was a "problem" as much as possibly annoying at higher speeds when you might need both hands to make a hard roll or pull. If you were using both hands, then it was hard to shoot. I'm not too sure when it happened, but many just-post-war American fighters had a turning handle on the throttle. It was sort of like a motorcycle throttle.

You get on the tail of the enemy and start closing. As you do, you twist the throttle handle one way or the other (toward you or away from you) and adjust the gunsight reticle (which was a circle of about 12 - 16 light spots on the windscreen) until it matched the wingspan of the target. When it did, you were in range and could shoot with some degree of certainty of a hit if your aiming point (a light circle in the middle of the reticle) was in the right place. If you were leading him with a deflection shot, it would be in front of the target along his line of travel. If you were in trail, it would be when the aiming point was on him.

Sounds complicated, but was and IS actually simple in actual use. I'm pretty sure most of the members in here have seen or tried this technique, at least on a simulator.

I have tried it in inside a hangar sitting in the front seat of a MiG-15 UTI 2-seat trainer. The gunsight is EASY to operate and we had fun using it to set the reticle so it just matched the wingspan of a Corsair picture taped to the wall in front of the MiG right in front of the gunsight. This was at Deer Valley airport, Arizona. I had a friend who had a MiG-15 UTI and we got it running about 1994 or so. We managed to start it an taxi it, but he passed away before he flew it. Last I heard, it was donated to a Museum in Boise, Idaho, though I'm not too sure if it ever got there. This particular guy also had an AT-6G and a mint-condition Cessna 180 with the rear seats removed so the dog (big, friendly German Sheppard) could ride. It was a kick to fly from short gravel patches around the Phoenix area. We landed once on a friend's driveway (gravel) and taxied up to the farm house. I'd have sworn we could not get in there but my friend, Curt Earl, landed there frequently and was very familiar with the approach. Interesting, to say the least.

Anyway, throttle-mounted stuff for gunsights and other functions have been a staple. Why not a trigger?

 

[SaparotRob]

I'm not too sure it was a "problem" as much as possibly annoying at higher speeds when you might need both hands to make a hard roll or pull. If you were using both hands, then it was hard to shoot. I'm not too sure when it happened, but many just-post-war American fighters had a turning handle on the throttle. It was sort of like a motorcycle throttle.

You get on the tail of the enemy and start closing. As you do, you twist the throttle handle one way or the other (toward you or away from you) and adjust the gunsight reticle (which was a circle of about 12 - 16 light spots on the windscreen) until it matched the wingspan of the target. When it did, you were in range and could shoot with some degree of certainty of a hit if your aiming point (a light circle in the middle of the reticle) was in the right place. If you were leading him with a deflection shot, it would be in front of the target along his line of travel. If you were in trail, it would be when the aiming point was on him.

Sounds complicated, but was and IS actually simple in actual use. I'm pretty sure most of the members in here have seen or tried this technique, at least on a simulator.

I have tried it in inside a hangar sitting in the front seat of a MiG-15 UTI 2-seat trainer. The gunsight is EASY to operate and we had fun using it to set the reticle so it just matched the wingspan of a Corsair picture taped to the wall in front of the MiG right in front of the gunsight. This was at Deer Valley airport, Arizona. I had a friend who had a MiG-15 UTI and we got it running about 1994 or so. We managed to start it an taxi it, but he passed away before he flew it. Last I heard, it was donated to a Museum in Boise, Idaho, though I'm not too sure if it ever got there. This particular guy also had an AT-6G and a mint-condition Cessna 180 with the rear seats removed so the dog (big, friendly German Sheppard) could ride. It was a kick to fly from short gravel patches around the Phoenix area. We landed once on a friend's driveway (gravel) and taxied up to the farm house. I'd have sworn we could not get in there but my friend, Curt Earl, landed there frequently and was very familiar with the approach. Interesting, to say the least.

Anyway, throttle-mounted stuff for gunsights and other functions have been a staple. Why not a trigger?

Great post!

 

[GregP]

Great post!

Thanks, SparotRob.

It is a good trip down memory lane to think back to those days and the friendship and flying we did. I wound up with a smattering of very interesting time in the logbook, courtesy of just being at the right place and the right time, with the right group of people who just happened to be quite friendly. Deer Valley was a hotbed of warbirds and interesting people. Scottsdale had it's share but, due to the layout, was not nearly so easy to meet other people as at Deer Valley. After the start of fencing off airports, it got even harder.

Today, a kid would be lucky to accidentally meet someone who was both friendly and semi-available to meet unless his parents had an airplane at that airport. Makes we wish for the friendly old days before fences were deemed necessary. I wouldn't do it today (threat of litigation), but in the past I have given rides to maybe 25 kids who were delighted to fly for the first time. About half of them had mom or dad along.

Fun times. First time I flew a turbine was a Cessna Grand Caravan with 3 kids along for the ride. That makes a great recreational airplane as long as you can pay for the fuel! Decently fast, too.

 

[Ivan1GFP]

I was not planning to post anything more here because we had reached a deadlock when it comes to if US trial data was representative or not.

This is part of what I wonder about. Just about every report has notes and explanations as to why the performance obtained with the Akutan A6M2 may not be representative of an operational aircraft and yet you ignore those notes that are in the actual report.
25-45 degrees happens to be the correct pitch range for A6M2.
29-49 degrees happens to be the pitch range for early A6M5. Later aircraft seemed to have a wider pitch range.
If accounts of aerial battles are to be believed, there is at least one Airacobra pilot who is probably convinced he could not outrun a A6M2 at low altitude.
Mr. Sakai tells of chasing one down and Airacobra are not particularly slow at low altitude.

But having thought some more about this I realized that there is another approach to the problem:

There is actually one data point which all seem to agree on: That the Zero did 316 mph at the so-called normal power setting with +50 mm boost and 2350 rpms.

So I added this power setting to my A6M2 Zero model in C++, and was happy to see that it was almost spot on as it was. I actually had to increase the value of the Cdo a few percent but it was really close.

And with the model now tuned to the 316 mph with the +50 mm at 2350 rpm, I again tried the power setting in the US trial, i.e. US 35" at 2575-2600 rpms, and the result was 334.5 mph. So basically spot on with the US trials.

Thus satisfied with the model, I now tried with the Sakae 12's "WEP" +250 mm boost 2550 rpm setting, and the speed was increased to 337.8 mph.

I am curious as to what horsepower reading you got from your simulation at "Normal" power and at what altitude.
What altitude did you use for the US speed run trial and which test case did you see which showed an RPM over 2550?
What altitude did you use for the Japanese speed run trial? What speed did the simulator hit before use of Overboost?
I am fairly convinced that the supercharger on Sakae 12 had more capacity at its rated altitude.
If engine starts putting out black smoke, it is a pretty good indication that they are running a super rich mixture and a noticeable burst of speed is probably non-trivial.
So far we have been working on the assumption that Overboost was the same as Takeoff power but do we really know this was the case?

So why does the speed not go up higher with so much more added boost? Like to the vaunted 345 mph figure?

Well because at the same time as the power goes up, this extra power is generated at a lower altitude. And what this means in practice, is that while going from +50 to +250 mm and increasing the rpms certainly gives a much higher power, it at the same lowers the FTH to a lower altitude. And at lower altitudes, the air is denser, and the aircraft therefore experiences much more drag thus "eating" up the gain in power.

And this is why I have been posting the Spitfire MkI speed chart: The Spitfire's Merlin produces circa 1050 hp at +6.25 boost at around 5 km, and with +12 boost about 1310 hp, but this is at an altitude which is a bit below 3 km. And pushing the aircraft through the dense air down below 3 km eats up most of the added power. And that is what the chart shows: While the speed for the Spitfire at lower altitudes is greatly increased, the absolute top speed number at the FTH is not. And the effect is just the same for the Zero and the Sakae 12. And this is incidentally why you need simulations: Because if you assume that the added power is available at the "old" FTH, then 345 mph is most certainly possible. But this is simply wrong. This is not how physics works.

So in summary: With a C++ model replicating both the Japanese 316 mph with +50 mm, and the US test data at 35", the top speed of the A6M2 Zero at the +250 mm 2550 rpm setting can be expected to be in the order of 337-338 mph.

I do not believe the Spitfire is a good analog to the A6M2 with a Sakae 12 engine.
The Sakae 12 made more horsepower at rated power at its critical altitude of 4200 Meters than it did with Takeoff power at Sealevel.
Its supercharger was tuned specifically for "higher altitudes". The Sakae 11 apparently made about 30 more HP but down at 3000 Meters.
To be honest, I am not entirely convinced 345 MPH is entirely correct either which is why I have never gone back to revise my own simulator model.

 

[Holtzauge]

I Ivan1GFP : I only posted again because I was hoping you would take this new information about the replication of the 316 mph with the normal power setting to heart. But I've come to the conclusion that nothing I post here will convince you that the A6M2 Zero with its magical black-smoke producing over-boosted Sakae 12 of yours will not do 345 mph so I'm giving up now. Cheers, and good luck with your own simulation modeling.

 

[tyrodtom]

This is part of what I wonder about. Just about every report has notes and explanations as to why the performance obtained with the Akutan A6M2 may not be representative of an operational aircraft and yet you ignore those notes that are in the actual report.
25-45 degrees happens to be the correct pitch range for A6M2.
29-49 degrees happens to be the pitch range for early A6M5. Later aircraft seemed to have a wider pitch range.
If accounts of aerial battles are to be believed, there is at least one Airacobra pilot who is probably convinced he could not outrun a A6M2 at low altitude.
Mr. Sakai tells of chasing one down and Airacobra are not particularly slow at low altitude.



I am curious as to what horsepower reading you got from your simulation at "Normal" power and at what altitude.
What altitude did you use for the US speed run trial and which test case did you see which showed an RPM over 2550?
What altitude did you use for the Japanese speed run trial? What speed did the simulator hit before use of Overboost?
I am fairly convinced that the supercharger on Sakae 12 had more capacity at its rated altitude.
If engine starts putting out black smoke, it is a pretty good indication that they are running a super rich mixture and a noticeable burst of speed is probably non-trivial.
So far we have been working on the assumption that Overboost was the same as Takeoff power but do we really know this was the case?



I do not believe the Spitfire is a good analog to the A6M2 with a Sakae 12 engine.
The Sakae 12 made more horsepower at rated power at its critical altitude of 4200 Meters than it did with Takeoff power at Sealevel.
Its supercharger was tuned specifically for "higher altitudes". The Sakae 11 apparently made about 30 more HP but down at 3000 Meters.
To be honest, I am not entirely convinced 345 MPH is entirely correct either which is why I have never gone back to revise my own simulator model.

I think the account of Sakai running down the Cobra was in Samurai , I've read it more than once, but the last time about 20 years ago.
But I remember Sakai recalling that he would have never caught the Cobra if it had just flew straight. The Cobra kept zig zagging , maybe trying to see better behind him, or thinking he could shake the Zero off, but Sakai went to the inside of every turn, or just basically flew straight and caught him.

 

[Greg Boeser]

Buzz Wagner reported that the Zero accelerated faster than the Airacobra, but the 'Cobra would eventually pull away.

 

[R Leonard]

My father's log records six flights in the recovered Akutan Type 00 #4593 while he was Director of VF training at ComFAirWest. He was to first to fly it after arrival at ComFAirWest. His flights were on 14 Sep 44 (0.6 hrs - comment: "test flight"); 18 Sep 44 (1.0 hrs - comment: "altitude test"); 19 Sep 44 (1.0 hrs - comment: "test against F6F"); 14 Oct 44 (0.7 hrs - comment: "test after repairs"); 21 Oct 44 (0.8 hrs - comment: "fight with Capt Crommelin in FM-2 - pretty even"); and 25 Oct 44 (0.5 hrs - comment: "test"). By 4 Nov 44 my father was detached from ComFAirWest and on the way to TF-38 as Jimmie Thach's assistant.

In early February 1945 that particular airplane was the victim of a taxiway run-over by an SB2C and ended up a pile of scrap in a hangar at NAS San Diego. Shortly thereafter, when the TF-38 staff was rotated out and was briefly stateside, he had three or four opportunities to fly an A6M5, #5357. During that period, February-March 1945, he collected from the #4593 debris pile the port wing tip, the original manifold pressure gauge, longitudinal and lateral trim wheels, and the airspeed indicator. We carried those parts around with us from station to station for the remainder of his naval career; he retired in 1971. In 1986 he donated, much to my disappointment, the pieces to the Navy Museum at Anacostia where, I presume, they still reside. I've got some color photos around here somewhere of these pieces-parts. The transmittal letter for the recovered items can be found below.

He wrote out his comments on the A6M2 #4593 in a letter to Admiral James Russell in the 1981, this before the article went to Anacostia. I don't have a finished product of that letter, but I do have the rough draft, which I once transcribed, as below. His write up touches on some of the issues raised about #4593 in various places in this forum thread:

START

Dear Jim,

Hope all these pages will not be discouraging and that they will satisfy some of your interest in the Japanese Zero Model 21 about which you wrote me in your letter of 14 Feb. It's a subject near and dear to me, for there was a time when I considered that Zero "my airplane" with only John Crommelin (on occasion) to say nay. So, if this reply is prolix, you can blame it on unbridled sentiment.

After the Zero's demise I was able to corral a few surviving pieces, such as:
- Left wing tip, the folding part complete with locking device, wiring, port running light
- Pedestal mounting longitudinal and lateral trim wheels
- Manifold pressure gauge - units in centimeters, at sea level pressure, low reading -40, hi reading +25
- Airspeed gauge - units in knots. Non-linear scale is stretched in the low speed range - excellent for landing approach
- Few pictures of the beauty in Hangar 40, North Island.

All the above remain with me except the pedestal, which remains, unlocated since moving out of quarters. Search continues. All will probably go to a worthy museum in due course; I'm not finished with them yet.

There was a 2-day delay in getting started on this reply waiting while the Naval Safety Center searched for data on the Zero mishap. It was a futile wait. I am informed with impressive finality that the mishap was not reported or recorded in any surviving format the Safety Center possesses. That means we shall have to do with my recollections - or those of J.G. Crommelin if you care to pursue it farther.

I, too, saw this Zero as a pile of salvage at NAS San Diego - in the balloon barn. The A & R did a beautiful job of restoration. At that time I was freshly back form Midway as a CV-5 survivor. I left for Pearl & SW Pac in Oct '42 so couldn't follow developments as it was being rebuilt. By the time I returned from SW Pac in July 1943, the Zero had been long gone to the east coast. It went to Tactical Air Intelligence Center (TAIC) and base at Anacostia. After F.M. Trapnell and a number of other worthies such as "Boogie" H. tested, compared, & evaluated it, the Army put it through similar paces.

From Aug 1943 to 4 Nov 1944 I was VF training officer staff ComFltAir West Coast and assistant to Jim Flatley through most of that time until he went to work for Marc Mitscher in TF-58. He was relieved by John Crommelin. While working for Flatley I learned that the Zero still at Anacostia was flyable but in a state of disuse. We got some pressure up (you remember J. H. Flatley, Jr.!) and got the machine ferried out to Hangar 40 North Island, our office and general hangout. The Zero was in dire need of attention and care and got it.

All this took time and I'm not sure the plane could be flown before Jim went out to the Fast Carriers. My log shows what must have been one of the earliest flights in our custody - 14 Sep 1944. Several hops later my log show 21 Oct - "Flight with J.G. Crommelin - he in FM-2 - pretty even." My last hop in this Zero was 25 Oct 44. On 4 Nov., as a result of the long reach of J. Thach, I was flying to Ulithi to go to work for him on J.S. McCain's TF-38 staff. Sometime during my absence the Zero received strike damage because when I returned to Coronado for a few weeks in Feb 1945 the wreckage of the Koga Zero was piled up in Hangar 40. My guess is that the mishap occurred in Jan or Feb 1945. Grief over this was short lived - we got a beautiful low-time Zero, model 52, captured on Guam and I got some mightily interesting flights in this bird, but that's another story.

As to the Zero 21, I believe most of my information comes from John Crommelin concerning its loss. Since his brother, Richard, was involved he had more than casual interest in the mishap. Dick, a friend, classmate from USNA, classmate Pensacola, roommate almost a year while we were in VF-42, Yorktown, was headed West with his squadron, VF-88, and they were in San Diego for transportation. As C.O., but also with John seeing to Dick's education, it was logical he should get a Zero hop. On taxiing out for this hop, Dick was overtaken by an airplane, SB2C-4, which has miserable vision ahead when in the 3 point attitude. The "Beast" just sawed its way through the Zero from tail to cockpit stopping just short of Dick. Truly, it as a tragedy for the machine, but a miracle for Dick. Pity we later lost him over Hokkaido on one of our last TF-38 strikes of the war.

As to the Zero 21, it was a mighty sweet machine even in its superannuated state. As you noted, the refined aerodynamic design was not compromised by mass production. Fit and finish of all plates, rivets, the close and accurate fit of fairings, engine cowl, access plates, canopy and wheel doors was most faithfully executed. The propeller spinner faired into a cowling that smoothed the contours of the reduction gear housing of the engine. The interior and dynamics of the engine cowling permitted the adequate cooling of the 2-row 14-cylinder engine with a remarkably small intake area. Contrast that with the intake area in an F4F-3/4, which originally came with a spinner but had to sacrifice it to cure engine over-heat problems. The Sakai engine looked and sounded like our 1830. It ran smoothly and cool. Displacement was somewhat less than the P&W 1830, but its 1130 HP was smooth and adequate. It was not supercharged as extremely as the R-1830-86/86 and at very high altitude (>30,000) compared very poorly with the P&W, but we hardly ever encountered Zeroes above 10,000 feet with our F4F-3/4 so we were carrying supercharger hardware as extra baggage. The F4F-5, which became the FM-2, was re-engined with the Wright 1820 with about the same power as the R-1830, but much less supercharger. This was a better machine to fight Zeroes, but we didn't get it in squadrons until 1944 and by that time the Zero was not the problem it had been in the beginning.

By the time I was flying the Zero 21 it may have had some automatic systems disabled. An example is the automatic altitude compensation of carburetor mixture. First time I went for altitude it began to cut up disgracefully above 5000 feet. Pretty much worried the engine was giving up, I tried one or two things. Mixture came to mind. On this machine full rich was a rearward position of the mixture control, manual lean comes by easing this control forward. On gingerly doing this the engine smoothed up beautifully and the machine jumped ahead with about 500 more horses.

Prop was auto hydraulic cum Hamilton - no mysteries. We ran the engine as though it as an 1830, but did not let RPM go above 2600.

The case of the manifold pressure gauge has been cracked in the crash on Akutan and leaked. It was left in the instrument panel but we used a standard AN type attached to a bracket nearby. I later repaired the original gauge and used it for automotive tuning; I now keep it sheltered with other keepsakes but it's a good gauge once you are accustomed to its readings.

The Throttle sat in the quadrant outboard of the mixture control. It was shaped like the handle of a knife - complete with wood side plates for contour. It was about 5 inches long and on the top had a switch to be operated by the left thumb. This switch was for cutting in or out your 20 mm cannon. Zero carried many rounds of 7.7 mm for the two fixed fuselage guns and only 80-100 for each of the 20 mm wing guns. Ergo, sight in with 7.7 then cut in the 2 20's for telling shots. I dimly remember there was a trigger lever you could bull back up and squeeze on the front edge of the throttle. If you were not in combat, this lever would drop down where inadvertent firing was precluded (remember we had sad events because our trigger in the stick was easily squeezed in excitement).

Cockpit was not so tidy as the F4F but easily as tidy as the early F4U and earlier Vought birds. Instruments were much like ours but metric for pressure, temperatures, altitude. As I mentioned, airspeed was in knots. It had an inner and outer scale as the needle needed to go around about 11/2 circles to get to the high end of the scale. In the Zero-52 there was an exhaust temperature gauge as well as the usual cylinder head temp. My guess is that it was a refinement to fine tune the mixture to get the remarkable endurance and range the Zero was famous for. Gyro horizon had a sky blue upper half like some German WWII instruments I have seen. To the envy of every F4F pilot, the landing gear was hydraulic actuated! Tail wheel fully retracted behind tight doors. Tail hook faired into a recess along the keel. The hook was hinged on the end of its strut; catched in the snatch position to catch the wire then dumped so the Zero could taxi forward over other wires unimpeded. Understand we toyed with this idea, but gave it up because of worries it might misbehave and cause unarrested landings. Brakes were hydraulic - weak. The wide tread and relatively low landing speed favored weak brakes so you might say they were adequate. Rudder bar was center pivoted with stirrups for each foot. Brakes were actuated by a hand lever; rudder angle determined which wheel received the braking action.

The canopy gave a beautiful view of the outside world, noticeably good to the rear in contrast to our VF. The enclosure was made up of many panes of plexi, some contoured. Wind noise was moderate. Some of the enclosure had been destroyed and was remade by A & R. The windscreen section was original, for it bore deep craters from the corrosion that took place during its dip into the marsh of Akutan. These cavities would have a way of coming into focus when air speeds built up. I often wondered why they had not been replaced by A & R. In VF-42 we had had some nasty experiences with the original F4F windscreens blowing in on us when Vi > 300 kt. Grumman corrected it with a beef up that robbed us of valuable forward vision, but it ended the problem. Zero had no such heavy structure in the first place so it was a source of uneasiness.

We encountered a serious problem just before our first flights from North Island, in Sep. 1944. Someone had blabbed and J. H. Flatley and I found ourselves invited to an audience with CFWC, RAdm W. K. Harrill. Seems he was dealing with an Army type who claimed that flying a Zero around San Diego would wreck the integrity of the West Coast Air Defense. His solution: ban flights now and forever. As a fall back: permit flights, but only on prior notice as to times and location and always in formation with other VF. For this contretemps W. K. Harrill was superb (so was the counsel of J. H. Flatley, Jr.!). He directed Zero flights only in the immediate vicinity of North Is., and if not reported after a few flights, then loosen the tether. Upshot was that there were no reports and we ended flying this machine when - where - and as we wished.

Zero 21 had no primer for engine starting. The carburetor had a large capacity acceleration pump you could feel when you moved the throttle. To start, you had the mech wind up the inertial starter as you wobbled up fuel pressure and worked the throttle 2-3 times to spray in the discharge of the acceleration pump. On contact the engine rolled over readily, caught, and picked up to run without complaint. The carburetor barrel had an oil hacker through which circulated lube oil to combat any tendency to form ice. I'm not sure whether it was always in action or selectable from the cockpit. We never touched it, as I remember, seems to be a tidy way to handle ice and cool oil.

Well Jim, I hope all these words have not dampened your interest. The account applies mostly to Koga's Zero Model 21. In Feb-March 1945 I had a dandy low time, fresh caught (Guam) Zero 52 to fly. It was much like the 21, but heavier because of 2 more 20 mm guns. It had a hundred or so more horses, ejection type exhaust stacks, but flew essentially like the model 21, very sweet. On 5 Apr 45 I had to return to the wars in W.Pac with J. Thach, McCain & Co and so ended my Zero flying.

These machines had ersatz Bureau Numbers, arbitrary, I believe:
Zero 21 = 4593 Jap designation A6M2 or Zero Model 21
Zero 52 = 5357 " " A6M5 " " " 52

There is the usual story that I believe: John Crommelin on first take-off in Z 21 slow rolled climbing out wheels coming up - just to make sure it realized the old master was in charge.

. . . (personal stuff sliced out)

As ever, and best wishes!

Bill
END

Along with pictures of my retained photos of the wingtip, airspeed indicator, and manifold pressure gauge, I also have the set of photos taken in the hanger in the fall of 1944, all suitably stamped as official USN on their backs.

Oh, and that manifold pressure gauge? The housing, as he mentioned, was cracked, which precluded its operation. Sometime in the early 1960's it was the subject of a work bench project and my father determined that it could be repaired and made functional. And so he did, a mystery to me, but in the early 1970's I drove a 1966 GTO which often had mounted in it the fully functional gauge . . . gently removed before state inspections and when the time came to trade in for a new car. Very cool.

Of some possible interest might be the list of items the A&R folks at San Diego decided HAD to be repaired before the anyone tried to test fly. A 15 August 1942 memo from the Commanding Officer of the U.S. Naval Air Station, San Diego, to the Chief of the Bureau of Aeronautics, listed repairs that #4593 needed to make it airworthy. The following is a transcription of the text of that memo:

1. Subject airplane can be put into flying condition in six weeks, provided no unexpected trouble is encountered. It will be necessary to manufacture numerous replacement parts, particularly bolts, machine screws, etc., as they appear to be metric. Work has commenced and will be expedited by day and night shifts, seven days a week.

2. The engine appears to be in good general condition. The bottom front cylinder was dented, apparently by the bullet, which severed the forward sump oil line. The Station will straighten and re-hone this cylinder, and it is believed that it will be in satisfactory condition. The carburetor and possibly other engine accessories are in bad shape internally from corrosion, and will need considerable reconditioning. No undue difficulty in accomplishing this is anticipated.

Structural Repairs Necessary to Fuselage and Wings:
1. Rebuild fin.
2. Repair both elevators.
3. Repair rudder.
4. Rear section of fuselage out of line and bulkheads buckled necessitating considerable repair.
5. Repair fuselage belt frame at stations 9 and 11.
6. Replace top fuselage skin and stringers
7. Rebuild sliding cockpit enclosure
8. Repair seat
9. Straighten fuselage adjacent to cockpit both sides at stations 2-5.
10. Repair fuselage skin at station 4.
11. Repair fuselage at top forward of pilot at station 1.
12. Rebuilt entire engine cowling
13. Repair cowl flaps
14. Rebuild both sides of landing gear (both main attaching fittings sheared off)
15. Rebuild left landing flap
16. Replace all ribs on right landing flap
17. Cut and splice main left wing beam at landing gear attachment
18. Rebuild one wing tip
19. Repair left bottom wing skin at station 2
20. Repair bullet holes in left wing at station 0
21. Repair leading edge skin on right wing at stations 1.4 and 2.
22. Remake gun cover in right wing between stations 2 and 2.25
23. Patch right wing leading edge skin at station 3
24. Patch skin and splice main wing bulkhead at station 3.7
25. Manufacture two aileron fittings which have been sawed off
26. Replace pilot tube located on left wing
27. Manufacture various nuts, bolts, etc. which are missing and patch various small holes in skin.
28. Check all wiring. It may be necessary to replace fifty percent of wiring in ship
29. Test oil and gas tanks. Overhaul is probably necessary.
30. Re-rig all surfaces and other controls.

Necessary Engine Repairs:
1. Straighten and repair nine push rods.
2. Repair one cylinder.
3. Rewire and overhaul harness.
4. Replace two missing spark plugs with LS321 plugs.
5. Completely overhaul carburetor (badly corroded - all springs and some other parts to be replaced)
6. Recondition magnetos (badly corroded).

Instruments:
1. Overhaul all instruments, hydraulic units
2. If necessary, replace instruments and other small units with Navy standard articles

The transmittal letter to the Navy Museum at Anacostia follows:

29 Sept. 1986

From: Rear Admiral William N. Leonard, USN (Ret)
To: Director, The Navy Museum, Washington Navy Yard
Washington, DC 20374

Subj: Japanese Zero Fighter Serial No. 4593, donation of parts and their significance
Ref: (a) Mikesh, Robert C. "The Zero Fighter" ISBN 0-517-54260-9
(b) Polmar, Norman "Aircraft Carriers" Library of Congress Cat. Card 69-12186
Encl: (1) Copy, pages 22, 25,26,27, ref (a)
(2) Copy, pages 233, 234, ref (b)

1. This donor is a carrier fighter pilot who in the Coral Sea and Midway air battles and later in the Solomon Islands campaigns received an early and extended exposure to the wily Zero fighter. In mid-1944, through some contriving and more luck, donor was successful in expanding the duties of his assignment to include flying captured Zeros. The first of these fighters he flew was the one captured on Akutan Island, in the Aleutians of Alaska. Those of us privileged to fly this Zero found it to be a sparky yet sweet flying, well behaved mount. We mourned the crash that ended its valuable service.

2. References (a) and (b) and enclosures (1) and (2) are sources describing how this Zero came to be captured, how it was impressed into the US Navy and on being returned to flight status entered the Navy inventory for operations. Here it was assigned its original Japanese serial number 4593 and appears in pilots' flight logs and various records with that identity.

3. Personal records and a flight log of the donor permit extending the history of Zero 4593 beyond the accounts of the references above. In the summer of 1944 the Zero was transferred from NAS Anacostia DC, to NAS North Island, San Diego, CA. Here it was to base and be operated by the Fleet Air Commander's training section. It was scheduled in flight operations with and against our squadrons that were being readied for combat. The idea was to give our folks a glimpse of the real thing – a preview of coming attractions, so to speak. Donor was in charge of this scheduling and one of the few pilots authorized to fly the Zero in this employment. He continued in this work until called back to combat duty late October 1944. On a temporary return from WestPac in February 1945, he found that Zero 4593 had received strike damage and was no more. The pilot, in a narrow escape was LCDR Richard G. Crommelin, USN, Commanding VF-88 later killed in action over Hokkaido, Japan. The Zero had been overrun in a taxi accident outbound for a flight. The propeller of the offending airplane chewed the Zero to pieces beginning at the tail and ending just short of the cockpit. The Zero's wreckage had been gathered and placed in Hangar 40 at the NAS. Donor was permitted to take over items described below for safekeeping and as reminders of a uniquely useful airplane. The fate of the remaining wreckage is unknown.

4. Description of donated parts of Japanese Zero A6M2 (Type 21) no. 4593 follow:

Engine Manifold Pressure Instrument: Provides absolute pressure readings in centimeters of mercury, positive pressures in red sector (British style). Logo of T.O.M. Sopwith Aircraft Ltd. shows this to have been a licensed product. Instrument was cracked in Akutan mishap, but donor repaired it (post war) with epoxy cement. Japanese characters embossed on dial state: "1st​ type issue intake pressure instrument 2nd​ version". In other words: "Pressure gauge Mk 1, Mod 2", USN Style.

Airspeed Meter: Appears to be native Japanese. This instrument gives readings in knots as one should expect in a sea going fighter. The needle travels past one complete turn to reach high readings. Scale at medium and low speed end is "Stretched" to favor ease of reading for cruise navigation and carrier landing approaches.

Port Wing Tip (folding panel): wing tips on A6M2 (Type 21) were foldable to permit its fitting on the smallish elevators of certain Japanese aircraft carriers. Hinges and locking bar were manually articulated, and a small metal flag popped into view to warn when the panel was unlocked and unsafe for flight. This wing tip had been damaged during the Akutan Is mishap. It was beautifully restored by the technicians at NAS North Island. The skin of the upper surface is original Japanese alloy. The bottom skin and some of the ribs inside are US material. The Japanese material still has some of the bluish transparent protective lacquer that served this purpose so well. The US material is anodized duraluminum and bears the usual zinc-chromate treatment. Aging has warped the red plastic running light cover; there was a time when the contours were true. This Zero as restored was replete with examples of the skillful blending of US materials and repair techniques with original Japanese structure to reconstitute an authentic and impressively flyable Zero fighter.

5. As discussed in paragraph 3 above, the parts being donated came into the donor's possession in February 1945. At that time the chief concern was to provide for safe keeping of a memento or so of a uniquely historic and useful airplane, mementoes that otherwise might have been lost, victims of wartime distractions. The time has come to place these items where they will be safely kept and also available for display. Accordingly, these parts of Japanese Zero fighter A6M2 (Type 21) serial 4593, our first and useful example of air intelligence exploitation of a flyable enemy fighter are donated to The Navy Museum.

/s/

And lastly, the Navy was aware of the A6M2 - #3372 - recovered near Luichow - see the Bruce Holloway 23d Fighter Group evaluation report http://www.wwiiaircraftperformance.org/japan/p5016.pdf from February 1943, which seems to basically track along with the earlier Sanders' report presented earlier in this thread. This the Type00 that eventually ended up at Wright-Patterson and has left generations of model model builders and researchers confused by its louvred side panels. The USN requested parts from the plane (see attached) but was apparently politely declined.