The Zero's Maneuverability

[GregP]

From operational experience with a A6M5 Model 52, the engine and propeller match up just fine.

The engine basically runs like a P&W R-1830.

The propeller is a licensed copy of a Hamilton-Standard unit built by Sumitomo for Mitsubishi and everything operates well.

Our Zero has no trouble climbing quite nicely on the original engine and propeller. I think the one in the test was definitely underperforming.

 

[SaparotRob]

From operational experience with a A6M5 Model 52, the engine and propeller match up just fine.

The engine basically runs like a P&W R-1830.

The propeller is a licensed copy of a Hamilton-Standard unit built by Sumitomo for Mitsubishi and everything operates well.

Our Zero has no trouble climbing quite nicely on the original engine and propeller. I think the one in the test was definitely underperforming.

How close is the P&W Zero to the Sakae powered one? I believe I read that most flying Zeros have the 1830. Are the modifications to the airframe drastic? How badly(?) does the engine swap affect the handling of the plane?
I'm talking about what's in the sky today. No weapons unless dummy ones installed for CoG purposes. How much difference is there between the Planes of Fame Museum's A6M5 and a P&W powered one?

 

[Engineman]

Post #10 in this thread is by GregP.
I tried a search on AGM evaluation and found pretty much nothing.
Can you confirm the source?
The comment about pitch stop was in the report.
No idea how testers were trying to run the engine.
Manual says +250 mm and 2550 RPM for Takeoff.

Yes, that should have been #38, "A6M Evaluationpdf. Not sure how I messed that up!

My question about the Japanese manuals is, what rpm/manifold pressure should be achieved on stationary ground test?
If the test that only achieved 2000 rpm for a prop set to 25 degrees low pitch and should have made something like 2550 rpm, then the engine was low on power or the prop controller was miss-set/faulty.


Eng

 

[Ivan1GFP]

Yes, that should have been #38, "A6M Evaluationpdf. Not sure how I messed that up!

My question about the Japanese manuals is, what rpm/manifold pressure should be achieved on stationary ground test?
If the test that only achieved 2000 rpm for a prop set to 25 degrees low pitch and should have made something like 2550 rpm, then the engine was low on power or the prop controller was miss-set/faulty.


Eng

There is no mention about ground running that I can recall seeing in the translated copy that I have. Not to say the original may not have had something but I believe that was unlikely.
This was a set of specifications as a reference for pilots, not for maintenance personnel.

As for the A6M Evaluation.....
Hmmm.... How should I say this.....
In a word, most performance specifications from this report are TOTAL GARBAGE. (Emphasis intended.)
As I mentioned in another thread, the Japanese did not change their Manifold Pressure Gauge from that of the Mk.I fighter when they started building the Mk.II.
Without a manual or any kind of guide to work by, the folks at Eagle Farm just made the assumption that the boost settings were the same as they were for the Sakae 12 which they had seen before. At least they figured out (sort of) that the RPM range was a bit higher, but the document lists the RPM for Sakae 21 as 2600 RPM as opposed to 2750 RPM as it should be.
This report makes for entertaining reading but should not be used as any kind of reference for performance for Type 32 "Hap" aircraft. Typically the lack of performance was attributed to "tired engines" but it was basically operator error.

Who in their right minds would put a gauge reading only up to +250 mm boost on an aircraft with an engine that could make +300 mm boost???
Now you know the answer. In case you believe this is incorrect, look at the gauge installed in the Smithsonian's A6M5.

 

[GregP]

I spoke with Steve Hinton about our A6M5 Model 52 Zero today and it's flying characteristics in general. His information is quite different from the stuff we read in here.

What he said, almost word for word, is that the controls on the Zero are always heavy. They get heavier above 200 knots, but even at 350 knots (yes, he has gone that fast in it) the controls, while heavier than at lower speeds, remain effective. If you can pull hard enough it will reach its flight limits.

He said that is true for a LOT of WWII fighters. There are write-ups that say the controls get heavy and they do, in fact, "heavy up" with speed increases, but they generally remain effective if you can make it happen.

His F8F-2 Bearcat, according to Steve, doesn't exactly have "light" controls, and they heavy up with speed, too, but remain very effective if you can pull or push hard enough to make your maneuver. He and the pilots who fly it can make it maneuver up through high speeds.

So, my take on Steve's comments is that rumors of controls that "lock up" at high speeds is hogwash from 60 – 70 years ago. It might seem that way to a five-foot four-inch pilot (162.5 cm) who is 120 pounds (54.5 kg) and NOT seem that way to someone who is six-feet one-inch (185.4 cm) and 190 pounds (86.2 kg). Take these reports with a grain of salt. What Eric Brown, who was not large, and a pilot today at over 200 pounds might describe as "heavy controls" are two different things entirely. People today are generally bigger and stronger than in WWII as an average. Also, a WWII pilot who was fresh from the USA out of flight training might have been in considerably better shape than someone else who had been in combat in the South Pacific for 8 months and who might also have some tropical maladies to deal with while flying.

My own experience with P-51D controls at 225 knots IAS was very nice. It wasn't heavy and responded very nicely. I have maybe 20 - 25 hours in the back seat of an AT-6 and it flies quite well until you stall it in uncoordinated flight. Think: uncoordinated turn at 100 mph. Then it spins very nicely, but also recovers nicely. I wouldn't call it "twitchy," but also don't want to stall it in the landing pattern. After 2 - 3 flights in it, I'd never let that happen.

 

[tyrodtom]

A pilot in combat is going to have a great deal more strength that a test pilot just doing a job.
Adrenalin.

The WW2 generation may not have worked out in gyms very much, but a lot of them were used to hard manual labor, from childhood.
My dad started working in a coal mine at 12 years old. He was only 5'6", but when he took his shirt off he looked like a lean Hercules.

When you look at WW2 era pictures of troops in very hot areas with their shirts off you'll notice trim ,fit, men usually, no cream puffs.

 

[MiTasol]

Absolutely correct.

 

[Ivan1GFP]

I spoke with Steve Hinton about our A6M5 Model 52 Zero today and it's flying characteristics in general. His information is quite different from the stuff we read in here.

What he said, almost word for word, is that the controls on the Zero are always heavy. They get heavier above 200 knots, but even at 350 knots (yes, he has gone that fast in it) the controls, while heavier than at lower speeds, remain effective. If you can pull hard enough it will reach its flight limits.

Just for context: In many flight tests, the specification is a maximum of 60 pounds of force on the stick. A real pilot may be able to apply more but that was how the aeroplane was tested.
Also worth noting is that in one of the reports, there is a comment that at 200 Knots, A6M2 would complete a 360 degree roll in 5.4 seconds. That may not be great performance for the time, but it is still over 60 degrees per second.

 

[GregP]

Wasn't suggesting anyone was a cream puff.

Was suggesting that someone who was 140 pounds might consider flight controls "heavy" while someone 50 pounds heavier might not. I'm 73 years old and I can pull harder than 60 pounds on a control stick easily.

Was also suggesting that write-ups describing "heavy controls" are subjective at best. if you want a GOOD writeup, it will have something like "pounds per g-force" at some predetermined speed. If that speed is under 250 knots, it doesn't really mean much since combat basically starts at around 250 knots or more. We ALL have seen the writeup saying the Zero was pretty decent at under 200 knots and pretty "heavy" over that speed.

I just heard Steve Hinton, the guy with likely the most warbird time in the world, tell me that while the controls in the Zero are "heavy," they are also very effective when used, even at 350 knots. He is one of two guys with the most Zero time in the world. The other one would likely be John Maloney.

To say I believe Steve Hinton over inexact ramblings in an old flight test report would be the understatement of the year.

Your mileage may vary, but Steve's word on an airplane's flying characteristics is Gold to me. I've personally seen him fly more than 10 different warbirds in the same afternoon, and do an aerobatic show in half of them. He has no axe to grind about the effectiveness of the controls and doesn't maintain it is difficult in any way to fly. What is IS, is rare, nothing more. ALL the pilots who fly our A6M5 like it, a lot, even Charles Lindbergh, whose name is in the log book. Can't recall the duration of his flight, but I saw the entry in the logbook.

 

[Ivan1GFP]

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.

 

[GrauGeist]

There is also the situation where a pilot, who is used to one type and it's characteristics, climbs into an aircraft they are not used to, and then forms an opinion based on that.

So what if a Japanese pilot, who flew a KI-43 for two years, climbed into the cockpit of a P-40 for a test flight? How would his evaluation be?

How would a veteran Fw190A pilot evaluate a P-47D after a test flight?

Sorry, but these "test evaluations" are bullshit as far as I'm concerned.

They were important at the time (during the war) to see a way to counter the enemy, but post war, it made no difference.

It's the test data from the manufacturer during development and the worda of the pilots who flew them at the time, that counts.

Also basing the performance of an aircraft on a gauge of a captured aircraft, which changed hands dozens of time before ending up in a museum is sketchy as hell.
The Smithsonian's A6M5 has no clear chain of custody, so the cockpit gauges cannot be confirmed as authentic. During restoration, they even found a USN flashlight entombed in the port wing - unless there is a clear confirmation that the cockpit and all of it's contents are confirmed by providence, it's eye candy and has zero gravity in performance confirmation.

 

[GregP]

Planes of Fame has a startlingly clear pedigree for EVERYTHING in our Zero including engine, propeller, instruments (except for the very few that were replaced with US instruments to fly in US airspace) and they know exactly what was changed in it. Net is not much.

There are a few US instruments, F8F Bearcat rudder pedal assemblies, and the seat was moved back a few inches to fit our pilots. Aside from that, we did a major overhaul before the pandemic and replaced fight control cables and pulleys, and added ADSB. Even the paint is original colors.

 

[Ivan1GFP]

Also basing the performance of an aircraft on a gauge of a captured aircraft, which changed hands dozens of time before ending up in a museum is sketchy as hell.
The Smithsonian's A6M5 has no clear chain of custody, so the cockpit gauges cannot be confirmed as authentic. During restoration, they even found a USN flashlight entombed in the port wing - unless there is a clear confirmation that the cockpit and all of it's contents are confirmed by providence, it's eye candy and has zero gravity in performance confirmation.

I don't believe you are following the discussion. The question of performance of captured aircraft was about Koga's A6M2 and the Eagle Farm A6M3 Model 32.
For various reasons which have now run 10+ pages, neither really seems to have performed as well as a typical operational aircraft (at least in my opinion and I got into this discussion pretty late).
The idea of using the Smithsonian's A6M5 as a reference isn't because I believe that every part of the aircraft is original. As you pointed out, it is a RESTORATION as are all the aircraft in the museum. I am trusting their research and knowledge on the subject. As an example, the paint on the aircraft is certainly not original, but it is appropriate to the model being displayed. I have seen the workshop at Udvar-Hazy where some of these projects are being restored. It really is an amazing sight. I was interested in the B-26 Marauder they are putting back together. A few decades ago, I visited Silver Hill where other restorations were done in the past. As for the pieces in these museum planes, are they original or even genuine? Maybe and maybe not, but they will look as close to the original as current knowledge allows.

 

[Holtzauge]

While Saburo Sakai has been credited in this thread as saying that the Zero did 345 mph with WEP, this is actually IMHO a bit misleading, since 345 mph is a very precise number and can therefore be interpreted as being quite accurate just by being so precise. However, what he actually is quoted as having said, is that the Zero could do "about 300 knots". Now when you hear it like that, that sound more like a nice round number and a ballpark value doesn't it?

In addition, what does 300 knots actually mean in this context? Probably that he while flying saw the needle hovering there during combat, nothing more. So firstly, how accurate is this reading at all? Did he actually read off an IAS corresponding to 290 or 295 knots and rounded this off to 300? And what was the instrument error on his IAS dial? In addition, an RAAF report on the Hap has a POC chart which shows that the IAS was off in the order of 12-13 mph at those speeds. So the true TAS may well have been more in the order of 330-335 mph when corrected for these effects. We just don't know. So with the above in mind, I would say that the often quoted 345 mph figure needs to be taken with a large grain of salt.

And if I reverse engineer the US results at 35" boost with 2550-2600 rpm to the Japanese at the +150 mm 2500 rpm Mil rating, by my calculations the lower boost and the higher rpms in the US test nearly evens out compared to the Japanese settings, resulting in a top speed with the Japanese Mil settings at circa 330 mph which seems to be in the right ballpark (albeit leaning towards the optimistic) given that the numbers usually quoted by Dunn from various sources are in the 316-336 mph range.

Then when adding the +250 mm 2550 rpm WEP to the simulations, it turns out that this mostly improves the low altitude performance (much like this example for the Spitfire when going to +12 and +16 boost) and does little to improve the top speed at the FTH, which only goes up to circa 339 mph. But certainly, this is getting closer to the 345 mph Sakai mentions, but remember that this is possible only assuming the very optimistic 330 mph at the standard +150 mm setting, which seems optimistic considering that Sakai's number is only 275 knots (316.5 mph) at this setting, which incidentally also aligns well with the 316 mph found in a captured Japanese flight manual. So adjusting my optimistic 330 mph down to 316 mph as in the Japanese flight manual, it may well be so that the true top speed with WEP should also actually be about 15 mph lower than the often quoted 345 mph.

In addition, about the US tests being "TOTAL GARBAGE" as some have stated based on the fact that they did not get the rpms they expected (about 2600 rpms) but only around 2000 rpms, and needed to shift the pitch range to do so: True, one reason for this could be that the engine was in poor shape. On the other hand, since there seems to be at least two instances of this happening, it seems like quite a coincidence that both these particular aircraft with sub-performing engines happened to be captured.

On the other hand, another and more plausible explanation, could be that the Japanese had actually moved the pitch operating range towards coarser on purpose in order to improve the range: Sakai himself mentions this in his memoirs: Flying at low speeds with high boost and very low revs to get drastically more range out of the Zero. And at low speeds, the standard pitch range was probably enough to attain sufficiently low revs. But in combat areas, you don't want to be flying at the low speeds Sakai mentions in his memoirs, and in this case the only way to get the revs down also when cruising at higher speeds, is to be able to set even coarser settings than the standard performance optimized range allows. Personally, I find this explanation much more likely than the one that the US just happen to capture two plane whose engines were so bad that they only allowed them to rev up to around 2000 rpm compared to their rated 2500-2550 rpms. Especially given that with the pitch adjustment range set back towards more performance optimized, one of the captured Zeros managed a very respectable 336 mph.

 

[GregP]

How close is the P&W Zero to the Sakae powered one? I believe I read that most flying Zeros have the 1830. Are the modifications to the airframe drastic? How badly(?) does the engine swap affect the handling of the plane?
I'm talking about what's in the sky today. No weapons unless dummy ones installed for CoG purposes. How much difference is there between the Planes of Fame Museum's A6M5 and a P&W powered one?

We have flown our Zero with the P&W-powered Zero, but they didn't exactly compete with one another. What they did was fly in formation for airshows. They do that very well. There is not much of a change in flying characteristics, but the cowling lines are slightly different.

The Sakae is 1,300 pounds and the R-1830 is about 1250 pounds. That isn't much different and a few accessories more or less makes then about equal in weight. The Sakae 31 is 1,130 hp at altitude and the R-1830 is about 1,200 hp for takeoff. If you are flying at an airshow, they are just about equal.

Not too sure if you are at combat power and 12,000 feet, but they won't be too far apart.

The cowling differences are more about carburetor location and air routing than anything else.

I'd call them more or less even. Both are reliable and both are 14-cylinder, 2-row radials with very similar power output. Sakae 31 bore and stroke are 5.1 and 5.9 inches. R-1830 bore and stroke are 5.5 and 5.5 inches. Not a lot to choose between them. Both generally used a 3-blade propeller.

 

[Ivan1GFP]

While Saburo Sakai has been credited in this thread as saying that the Zero did 345 mph with WEP, this is actually IMHO a bit misleading, since 345 mph is a very precise number and can therefore be interpreted as being quite accurate just by being so precise. However, what he actually is quoted as having said, is that the Zero could do "about 300 knots". Now when you hear it like that, that sound more like a nice round number and a ballpark value doesn't it?

In addition, what does 300 knots actually mean in this context? Probably that he while flying saw the needle hovering there during combat, nothing more. So firstly, how accurate is this reading at all? Did he actually read off an IAS corresponding to 290 or 295 knots and rounded this off to 300? And what was the instrument error on his IAS dial? In addition, an RAAF report on the Hap has a POC chart which shows that the IAS was off in the order of 12-13 mph at those speeds. So the true TAS may well have been more in the order of 330-335 mph when corrected for these effects. We just don't know. So with the above in mind, I would say that the often quoted 345 mph figure needs to be taken with a large grain of salt.

And if I reverse engineer the US results at 35" boost with 2550-2600 rpm to the Japanese at the +150 mm 2500 rpm Mil rating, by my calculations the lower boost and the higher rpms in the US test nearly evens out compared to the Japanese settings, resulting in a top speed with the Japanese Mil settings at circa 330 mph which seems to be in the right ballpark (albeit leaning towards the optimistic) given that the numbers usually quoted by Dunn from various sources are in the 316-336 mph range.

First of all, Sakai would not have seen 300 Knots on his ASI. He got some number for IAS and corrected it to TAS of 300 Knots. So the idea that he got some nice round number on the gauge is probably incorrect.
As for the US tests, I still have yet to find one that shows a stated RPM of 2600 at a particular altitude with a Manifold Pressure for A6M2. Your assumption that the US settings which tended to be around 2550 RPM and +129 mm is as good as the standard Japanese settings implies a knowledge of the torque curves of this engine that we simply do not have.
Keep in mind also that Koga's A6M2 was a bent bird with issues in the fit of the Canopy and Main Gear covers as noted in the report by Cdr. Sanders.
316 MPH / 275 Knots is a number that is straight out of the aircraft's manual for A6M2.
It is basically puttering along with +50 mm or just under 1 pound of boost and 2350 RPM.

Then when adding the +250 mm 2550 rpm WEP to the simulations, it turns out enthat this mostly improves the low altitude performance (much like this example for the Spitfire when going to +12 and +16 boost) and does little to improve the top speed at the FTH, which only goes up to circa 339 mph. But certainly, this is getting closer to the 345 mph Sakai mentions, but remember that this is possible only assuming the very optimistic 330 mph at the standard +150 mm setting, which seems optimistic considering that Sakai's number is only 275 knots (316.5 mph) at this setting, which incidentally also aligns well with the 316 mph found in a captured Japanese flight manual. So adjusting my optimistic 330 mph down to 316 mph as in the Japanese flight manual, it may well be so that the true top speed with WEP should also actually be about 15 mph lower than the often quoted 345 mph.

In addition, about the US tests being "TOTAL GARBAGE" as some have stated based on the fact that they did not get the rpms they expected (about 2600 rpms) but only around 2000 rpms, and needed to shift the pitch range to do so: True, one reason for this could be that the engine was in poor shape. On the other hand, since there seems to be at least two instances of this happening, it seems like quite a coincidence that both these particular aircraft with sub-performing engines happened to be captured.

As stated above, 275 Knots / 316 MPH is fast cruise setting. It isn't even close to a maximum speed.
Regarding the statement of "TOTAL GARBAGE", I don't think you actually were reading the context of that statement. It was about the performance testing of A6M3 Model 32 HAP rebuilt from wrecks out at Eagle Farm in Australia. If you disagree with my conclusion, I suggest you actually read the report.
Basically they operated the engine, a Sakae 21 as if it were a Sakae 12 and got correspondingly poor performance.
Their critical altitude was about 4,000 Feet too low and engine output was about 100 HP too low. This meant that it was giving less output than a good running Sakae 12 but interestingly enough, its speed wasn't very different from Koga's A6M2.

On the other hand, another and more plausible explanation, could be that the Japanese had actually moved the pitch operating range towards coarser on purpose in order to improve the range: Sakai himself mentions this in his memoirs: Flying at low speeds with high boost and very low revs to get drastically more range out of the Zero. And at low speeds, the standard pitch range was probably enough to attain sufficiently low revs. But in combat areas, you don't want to be flying at the low speeds Sakai mentions in his memoirs, and in this case the only way to get the revs down also when cruising at higher speeds, is to be able to set even coarser settings than the standard performance optimized range allows. Personally, I find this explanation much more likely than the one that the US just happen to capture two plane whose engines were so bad that they only allowed them to rev up to around 2000 rpm compared to their rated 2500-2550 rpms. Especially given that with the pitch adjustment range set back towards more performance optimized, one of the captured Zeros managed a very respectable 336 mph.

You need to read the rest of the paragraph where they were twiddling with the pitch range settings on Koga's A6M2. Its original setting was confirmed by comparison with other recovered wrecks. As for the "two planes", you are really comparing two fairly different aircraft between Koga's A6M2 and the Eagle Farm A6M3. The A6M2 wasn't in the best of shape. The A6M3 was in unknown condition because the testing was never to the limits the engine should have been run at.

 

[Holtzauge]

First of all, Sakai would not have seen 300 Knots on his ASI. He got some number for IAS and corrected it to TAS of 300 Knots. So the idea that he got some nice round number on the gauge is probably incorrect.

That is really a strawman argument: I never said he read off 300 knots on his ASI: What I wrote was : "Did he actually read off an IAS corresponding to 290 or 295 knots and rounded this off to 300?"

And Sakai saying "about 300 knots" still sounds very much of a ballpark number and not something one would tune a simulation model based on. At least not in my book.

As for the US tests, I still have yet to find one that shows a stated RPM of 2600 at a particular altitude with a Manifold Pressure for A6M2. Your assumption that the US settings which tended to be around 2550 RPM and +129 mm is as good as the standard Japanese settings implies a knowledge of the torque curves of this engine that we simply do not have.
Keep in mind also that Koga's A6M2 was a bent bird with issues in the fit of the Canopy and Main Gear covers as noted in the report by Cdr. Sanders.
316 MPH / 275 Knots is a number that is straight out of the aircraft's manual for A6M2.
It is basically puttering along with +50 mm or just under 1 pound of boost and 2350 RPM.

No torque curves needed: I have an original Japanese chart for the Sakae 12 where I can read off power for different boosts from -350 to +250 mm in the 1700-2550 rpm range, and the Japanese +150 mm 2500 rpm setting generates a little less power than the US test at +35" 2550-2600 rpm, hence the slightly lower speed (330 mph) with that setting in my estimate.

As stated above, 275 Knots / 316 MPH is fast cruise setting. It isn't even close to a maximum speed.
Regarding the statement of "TOTAL GARBAGE", I don't think you actually were reading the context of that statement. It was about the performance testing of A6M3 Model 32 HAP rebuilt from wrecks out at Eagle Farm in Australia. If you disagree with my conclusion, I suggest you actually read the report.
Basically they operated the engine, a Sakae 21 as if it were a Sakae 12 and got correspondingly poor performance.
Their critical altitude was about 4,000 Feet too low and engine output was about 100 HP too low. This meant that it was giving less output than a good running Sakae 12 but interestingly enough, its speed wasn't very different from Koga's A6M2.

OK, my bad if I made a wrong assumption and assumed you were talking about the US BuAer Wright Field test in which they got 336mph. But that is the test I have been referring to all the time, and you still seem to think the problem that they initially only reached 2000 rpm was due to the engine underperforming, and that this was why they had to move the pitch range. Here we simply have to disagree: I think it was due to the Japanese range optimization effort as outlined below, and not a poorly performing engine in the US test.

You need to read the rest of the paragraph where they were twiddling with the pitch range settings on Koga's A6M2. Its original setting was confirmed by comparison with other recovered wrecks. As for the "two planes", you are really comparing two fairly different aircraft between Koga's A6M2 and the Eagle Farm A6M3. The A6M2 wasn't in the best of shape. The A6M3 was in unknown condition because the testing was never to the limits the engine should have been run at.

You seem to miss my point: I'm saying that the Japanese changed the pitch range to improve the Zero's range at the cost of performance (trading high speed and high climb rate for long range). So the fact that this seems to be the case with many of the wrecks found actually bolsters my point that the low revs mentioned in US evaluations before they changed the pitch range was due to the Japanese employing this setting on a wider scale to get range, and not due to the engine in the US Wright Field test of the A6M2 being worn out.

 

[PAT303]

It was about the performance testing of A6M3 Model 32 HAP rebuilt from wrecks out at Eagle Farm in Australia. If you disagree with my conclusion, I suggest you actually read the report.

I have to disagree with the assumption that planes built out of wrecks are somehow inferior in performance, many hundreds if not thousands of aircraft were rebuilt during the war and that A6M would not have flown if it wasn't airworthy, no pilot would test fly a lashed together aircraft and having gone to such effort to acquire one for testing no air force would then risk loosing it, yes the engine might not have been run at full power but the Merlin 46's in the RAAF Spitfires wasn't either.

 

[GrauGeist]

And those "hundreds if not thousands" of rebuilt aircraft were most likely rebuilt with either new parts or cannibalized parts from a pool of war-weary or battle damaged/written-off donors.

Not cobbled together from three different wrecks.

 

[Ivan1GFP]

I have to disagree with the assumption that planes built out of wrecks are somehow inferior in performance, many hundreds if not thousands of aircraft were rebuilt during the war and that A6M would not have flown if it wasn't airworthy, no pilot would test fly a lashed together aircraft and having gone to such effort to acquire one for testing no air force would then risk loosing it, yes the engine might not have been run at full power but the Merlin 46's in the RAAF Spitfires wasn't either.

The Eagle Farm A6M3 was probably in better shape than any of the three A6M rebuilt in the United States.
As GrauGeist pointed out, they had other wrecks to cannibalize pieces from.
The three A6M in the US that were performance flight tested that I know of were a A6M2 captured by the AVG and rebuilt by Curtiss.
It never really ran right with a maximum speed under 300 MPH. It can be recognized by a custom louvered panel replacing a lost panel in the engine accessory area.
The Akutan A6M2 has already been discussed ad nauseum.
The A6M5 that was tested later in the war was a seriously broken bird. The report itself stated that it was not to be used as a reference for performance figures.
This aircraft would vibrate in flight at speeds over 250 Knots.
In each of these cases, there was basically ONE airframe and the people working on it had to use what they had. Does a pilot fly a lashed together aircraft? Apparently they did because that is all they had to test with.

Regarding running the Merlin 46 of the RAAF Spitfire at full power, there is a difference. The maintenance personnel knew how to work on it and it was a choice. In the case of the A6M3, the people working on it had no idea what the proper engine limits were and basically went by what they saw on the gauge faces. This meant that their Type 0 Mk.II was making significantly less power than the older Mk.I would have.