Aerodynamic Drag Properties of the A6M

[Ivan1GFP]

Hello all,
I have a question that is slightly off-topic. I seem to recall the earliest A6M external tanks were fixed while the later ones were jettsionable. Regrettably my library is currently hors de combat.
Please advise.

Thanks,
JC1

Hello Jetcal1,
Actually all the A6M external tanks were droppable even though the fairings might have been a bit different.
The problem was that when flying the longer missions, the A6M pilots did not have the option of dropping the tanks because they carried a substantial portion of the total fuel of the aircraft.
Basically, if they dropped their tanks, they could not complete their missions.
As it was, during the Guadalcanal campaign, many A6M pilots found that they did not actually have enough fuel to make it home because the missions left so little margin for combat or other incidents.

This also meant that any fuel tank damage was as good as a kill because the aeroplane was not getting home.
These fellows had it rough and a lot of them didn't make it.

Just for numbers:
A6M2-21 - 145 Fuselage, 2 x 195 Wings - Total 535 Liters
A6M3-32 - 60 Fuselage, 2 x 210 Wings - Total 480 Liters
A6M3-22 - 60 Fuselage, 2 x 264 Wings - Total 588 Liters
A6M5-52 - 60 Fuselage, 2 x 264 Wings - Total 588 Liters

The typical external tank held 330 Liters.

- Ivan.

 

[DarrenW]

The maximum speed listed in the manual for A6M2 is 316 MPH and for A6M5 it is 338 MPH but these are obviously not at maximum power. That is why I do not believe the 335 MPH maximum for a captured A6M5 is representative.

Actually Ivan I never said that there weren't some A6Ms in service that could manage the airspeeds noted in published works, I'm just skeptical that the majority in the field could do likewise. And we all hear stories of that one "special" aircraft which performed better than the rest, that everyone in the unit wanted to fly. Why wouldn't an ace and celebrated war hero such as Sakai be given that honor from time to time? So even if the claim of 345 mph was true for the particular machine he was flying that day, it still doesn't lend credence to the argument that it could normally be acheived by the other A6M2s in service at the time.

And then of course there are the countless action reports from Hellcat pilots themselves stating that they had absolutely no issues chasing down or eluding a Zero within visual range. This is why I tend to think that an ordinary in-service A6M5 of the time could maybe muster around 330-340 mph, as opposed to the average F6F-5 Hellcat which could comfortably reach 380-390 mph in level flight. I've read however that one Japanese aircraft Hellcat pilots tended to have difficulty catching was the Nakajima C6N Myrt, which reportedly had a maximum level speed very similar to that of the Hellcat.

But again the discussion here is whether or not the A6M5 was aerodynamically cleaner (or more correctly put, refined) machine than the A6M2. I feel that the reduced wing area was the biggest factor that accounted for the nominally improved speeds from the earlier model, although the increased horsepower rating of the Sakae 21 engine most likely aided a bit as well. I just can't imagine that the modified cowling and exhaust system had much to do with it, the improved exhaust thrust notwithstanding.

 

[Ivan1GFP]

Hello DarrenW,
Does it lend credence that the majority of a type if not all could achieve a level of performance if it is listed in the aircraft's flight manual? The numbers Sakai gave either matched the manuals or were plausible when compared to test reports. You can choose to accept those numbers or not.
I have my own beliefs as to how these numbers actually fit together, but it there are places I extrapolated on data and discarded numbers that did not seem to fit.

You commented earlier on the Water-Methanol system of Sakae 31.
To me it was strange that the Navy seemed to have problems getting the system to work properly while the Army did not.

According to listings I have seen in books, the C6N was capable of a maximum speed from about 370 - 395 MPH, but is there any reason to believe that late in the war, a Recon aircraft would be better maintained than a Fighter? Why do you doubt the 351 MPH maximum speed of A6M5 but don't seem to have a problem with the C6N?
As I see it, there is a much greater likelihood that the typical C6N would have mechanical issues than the typical A6M5. The Sakae 21 was a reliable engine by reputation while the Homare installed in C6N tended not to perform up to specifications. This was the same engine as in the N1K2-J and the Ki-84.
What is also interesting is that the Ki-43 was noted as capable of very high "Flash Performance" but there is no mention of the same for the A6M series even though the two aircraft had equivalent engines.

At this point, I don't believe I have any more useful information to contribute to the discussion beyond speculation.

- Ivan.

 

[jetcal1]

Hello Jetcal1,
Actually all the A6M external tanks were droppable even though the fairings might have been a bit different.
The problem was that when flying the longer missions, the A6M pilots did not have the option of dropping the tanks because they carried a substantial portion of the total fuel of the aircraft.
Basically, if they dropped their tanks, they could not complete their missions.
As it was, during the Guadalcanal campaign, many A6M pilots found that they did not actually have enough fuel to make it home because the missions left so little margin for combat or other incidents.

- Ivan.

Thank you sir.

 

[Ivan1GFP]

Thank you sir.

You're Welcome Jetcal1,
The numbers I posted were straight from the manual for the A6M, but a couple comments might be appropriate.
Note that the A6M3 and A6M5 have much smaller Fuselage Fuel Tanks.
This is because that tank was located between the firewall and the cockpit and the new Sakae 21 engine took a lot more space there.
Unfortunately, the Sakae 21 also consumed more fuel, so range was a lot shorter.

The A6M3-32 came out after the A6M2-21 and this coincided with the beginning of long range missions (to Guadalcanal?) and they found that the new hot fighter didn't have the range to fly those missions. They had to go back to the A6M2-21.
The A6M3-22 was an attempt to address that issue and had two additional fuel tanks mounted in the outer wing panels
See attached image for locations of Fuel Fillers. Only the Model 22 has the tanks in the outer wing panels..
This image is of a Tamiya model kit from Amazon but is sufficient for noting fuel tank locations.
Although the A6M5 shows the same fuel volumes as Model 22, the tank arrangement is different and there is only a single tank in each wing.

- Ivan.

 

[tyrodtom]

Hello Tyrotom,
The Airspeed Indicator on the A6M actually was calibrated in Knots and the listings in the manuals were also in Knots.
This was typical of Japanese Navy aircraft. The Japanese Army used Kilometers per Hour.
The ASI on the A6M rotated twice to indicate the full speed range and had an inner scale and outer scale for numbers.
You can easily confirm this with an image search on the Internet.

Of course Manual is in TAS and the gauge reads in IAS, but if Sakai was an experienced aviator as he certainly was, this would be pretty obvious. Also, considering he was dead-on with his note on the maximum speed under normal power, then he clearly knew enough to make conversions.

- Ivan.

I came on this forum to learn, and I'm still doing that.
The Japanese Army and Navy agreed on just about nothing, didn't they ?

 

[Ivan1GFP]

I came on this forum to learn, and I'm still doing that.
The Japanese Army and Navy agreed on just about nothing, didn't they ?

Hello Tyrotom,
That is a pretty accurate statement in general.
They used many of the same engines but there were enough differences that the power ratings didn't always match up completely.
Each service had different names for basically the same series of engines.
Just from memory:
The Sakae 12 used by the Navy was called the Ha-25 by the Army.
The Sakae 21 used by the Navy was called the Ha-115 by the Army
The Homare was also called the Ha-45....

Life only got worse from there.
Each service used a 7.7 mm Vickers type machinegun.
The Navy used a copy of the .303 British cartridge.
The Army used a semi-rimmed bottle necked round that looked more like a typical Mauser cartridge.

The Army and Navy both had 12.7 mm machineguns but they were different of course.

The Navy used 20 mm Type 99-1 and Type99-2 blowback cannon that were based on the Oerlikon guns.
The Army used the 20 mm Ho-5 cannon based on the Browning HMG.
Of course the cartridges were different.

One has to wonder how the Navy was able to keep things straight. They, of course, had their own infantry but the ammunition used by their weapons and the weapons themselves were the same as the Army guns. This meant that their infantry weapons didn't use the same ammunition as their aircraft weapons. The issue is that some of those aircraft guns such as a Lewis MG were also suitable for infantry use....

Their aviation fuel was also different. The Navy used a 91 octane standard and the Army used 92 octane.
Even for the same roles such as land based fighters and bombers, none of their aircraft were the same until the very end of the war.
There is a lot more than what I just touched upon here.
There have been comments that they hated each other worse than they hated the actual enemy.

- Ivan.

 

[DarrenW]

Does it lend credence that the majority of a type if not all could achieve a level of performance if it is listed in the aircraft's flight manual?

Yes, and as you pointed out earlier the flight manual for the A6M5 gives a maximum level speed of 338 mph. If a higher speed could be expected then the manual would have most likely stated it. The given speed is in all probability the safe operating limit for the design (without incurring damage to the engine), and even then it was taking into account that the aircraft would be in good repair and using fuel of a sufficient octane rating. Granted, there may have been some A6M5s that exceeded the published speeds, but it obviously wasn't expected and we don't really know what condition these aircraft may have been in after doing so. That said, it's my current belief that it became more and more difficult as time went on to hit the factory numbers in the field.

You commented earlier on the Water-Methanol system of Sakae 31.
To me it was strange that the Navy seemed to have problems getting the system to work properly while the Army did not.

From the verbiage used in the Navy report it doesn't seem that the water injection system was even installed in the test aircraft, though the reason behind this is unclear. Could it have been removed by the Japanese before its capture on Saipan? Did all Sakae 31 engines happen to have water injection or was it sporadic in nature? Your guess is as good as mine.

According to the US Navy report, a completely different A6M5 was to be tested by the US Army Air Force and I believe the results of these tests are presented in TAIC Report #38. It too had the Sakae 31 engine but there is no reference made to the use of water injection, but they do happen to list boost pressures. You seem to know a lot about the Nakajima Sakae engine, would 42" Hg be indicative of this engine under WEP?

TAIC bulletin 102D states that only 340 mph was obtained during actual test flights of a A6M5, although they "calculated" a possible level speed of 358mph using WEP. I really don't know how they determined this, or whether or not this was the same aircraft involved in comparative testing with American warplanes.

Why do you doubt the 351 MPH maximum speed of A6M5 but don't seem to have a problem with the C6N?

On occasion Hellcat pilots would comment on the difficulty of intercepting the speedy C6N. And while poor quality control, engineering difficulties, and substandard maintenance practices obviously affected its overall performance, the Myrt was still somewhat of a challenge to engage and destroy. The same could not be said of the A6M however.

 

[DarrenW]

I decided just for fun to plug the performance numbers at sea level for each type into the formulas that I have for the coefficients of total drag, zero-lift drag, and the equivalent flat plate area. Here are the results that I came up with:

A6M2:
CD=0.0202
CD0=0.0192
Eq. Flat Plate Area=4.64ft^2

A6M5:
CD=0.0221
CD0=0.0210
Eq. Flat Plate Area=4.83ft^2

Sources: TAIC bulletin 102D; The World's Great Fighter Aircraft (Green/Swanborough); Quest for Performance: the Evolution of Modern Aircraft (Loftin)

It's interesting that, even with the improved speed of the A6M5, all drag calculations happen to point to it being a somewhat 'dirtier" airplane than the A6M2 (but not overly so). This was true even with the coefficient of induced drag (CDi) being basically equal between the two. If we are to believe that these calculations are representative of the results that would be found in actual wind tunnel testing, the shortened wingspan and increased engine power obviously allowed the latter model to overcome its slightly less-refined aerodynamics and as a result increased maximum level speed accordingly.

From what I can gather, the desire to improve the Zero's speed was at least part of the reason behind the reduction in wing span, starting with the A6M3 (improved roll rate may have been the other reason or just a byproduct of it). If the Japanese felt the performance of the machine was acceptable then why would they not leave the wing as it is?

 

[Ivan1GFP]

Yes, and as you pointed out earlier the flight manual for the A6M5 gives a maximum level speed of 338 mph. If a higher speed could be expected then the manual would have most likely stated it. The given speed is in all probability the safe operating limit for the design (without incurring damage to the engine), and even then it was taking into account that the aircraft would be in good repair and using fuel of a sufficient octane rating. Granted, there may have been some A6M5s that exceeded the published speeds, but it obviously wasn't expected and we don't really know what condition these aircraft may have been in after doing so. That said, it's my current belief that it became more and more difficult as time went on to hit the factory numbers in the field.

Hello DarrenW,
I don't think you understood what I was telling you. These speeds in the manual were listed for "Normal Rated Power". This isn't even what we would call "Military Power" and certainly well below "Overboost" or "Emergency Power". It is probably pretty close to what we would call Maximum Continuous Power.
The Japanese as a rule did not test their aircraft for speed at maximum power settings.
Just to put some numbers to give a comparison (For Sakae 21)
Normal Rated Power was 32.9 inches Hg @ 2500 RPM (+75 mm)
Military ? Power was 37.8 inches Hg @ 2700 RPM (+200 mm)
Take Off Power was 41.7 inches Hg @ 2750 RPM (+300 mm)

If this aeroplane is making 338 MPH at Normal Rated, do you REALLY think it won't go quite a bit faster running 5 inches more boost and an additional 200-250 RPM? How about with 9 inches more boost? (assuming that the supercharger is capable.)

For the sake of completeness, for the Sakae 12 we have:
Normal Rated Power was 31.9 inches Hg @ 2350 RPM (+50 mm)
Military ? Power was 35.8 inches Hg @ 2500 RPM (+150 mm)
Take Off Power was 29.8 inches Hg @ 2550 RPM (+250 mm)

At Normal Power, the manual lists 316 MPH for the A6M2, but we know from tests that it was capable of AT LEAST 335 MPH (19 MPH faster) without Emergency Power.

From the verbiage used in the Navy report it doesn't seem that the water injection system was even installed in the test aircraft, though the reason behind this is unclear. Could it have been removed by the Japanese before its capture on Saipan? Did all Sakae 31 engines happen to have water injection or was it sporadic in nature? Your guess is as good as mine.

According to the US Navy report, a completely different A6M5 was to be tested by the US Army Air Force and I believe the results of these tests are presented in TAIC Report #38. It too had the Sakae 31 engine but there is no reference made to the use of water injection, but they do happen to list boost pressures. You seem to know a lot about the Nakajima Sakae engine, would 42" Hg be indicative of this engine under WEP?

TAIC bulletin 102D states that only 340 mph was obtained during actual test flights of a A6M5, although they "calculated" a possible level speed of 358mph using WEP. I really don't know how they determined this, or whether or not this was the same aircraft involved in comparative testing with American warplanes.

You don't actually need to guess. I am sure that someone with more interest in Japanese aircraft has done the research.

41.7 inches Hg would be Take Off power.
I would be interested in knowing at what altitude TAIC calculated for 358 MPH.
It would give some insight into how good the supercharger actually was on the Sakae 21.
I was also coming up with numbers a bit over the typically listed 351 MPH but there were a lot of presumptions about the shape of drag and power curves.

On occasion Hellcat pilots would comment on the difficulty of intercepting the speedy C6N. And while poor quality control, engineering difficulties, and substandard maintenance practices obviously affected its overall performance, the Myrt was still somewhat of a challenge to engage and destroy. The same could not be said of the A6M however.

There were models of the C6N that did not exceed 370 MPH. I believe you are making the assumption that every Hellcat was in good enough condition to reach the higher speed ranges claimed for the type. I suspect that many of them would not even make 370 MPH.
Just keep in mind how these aircraft were stored.

- Ivan.

 

[DarrenW]

If this aeroplane is making 338 MPH at Normal Rated, do you REALLY think it won't go quite a bit faster running 5 inches more boost and an additional 200-250 RPM? How about with 9 inches more boost? (assuming that the supercharger is capable.)

As far as I can tell, switching the R-2800-10 from a Normal Rated to Military Power setting increased boost by about 4" Hg and yielded a 4-5 mph increase in the Hellcat's maximum speed at critical altitude. If we assume that the Zero would benefit in the same fashion from this increase, that would mathematically place the A6M5's maximum attainable speed to around 343 mph in Military Power (37.8 " Hg), but this would still be below the 350+ mph that we see published in many reference books. I think it's also very optimistic to believe that another 4" Hg could make up that much of a difference.

I would be interested in knowing at what altitude TAIC calculated for 358 MPH.

The bulletin has the altitude at 22,000 feet while in WEP. That's quite a bit higher than the 18,000 and 19,500 feet quoted in both the Navy and Army reports while in Military Power. But then again, the bulletin gives a critical altitude of 23,000 feet while in Military Power as well. What does the A6M5 manual say the critical altitude is while in a "Normal Rated" setting?

I suspect that many of them would not even make 370 MPH.

This is interesting. So you are completely fine with the notion that "many" F6Fs couldn't reach their published maximum speed, but on the other hand are quite confident that most A6Ms could??? The Hellcat pilots manual gives a maximum level speed of 388 mph for an F6F-3 in an "overload" condition. If we are penalizing an in-service Hellcat by roughly 5 percent, then why can't we do the same for the Zero? If we did we'd be seeing about a 17 mph decrease in speed, which would whittle the often quoted 351 mph figure down to around 335 mph, which was the maximum speed of the aircraft tested by the Navy and also happens to fall within the range that I predicted in an earlier post.

And for what it's worth, maintenance on US warships was impeccable to say the least, which as most agree was a far cry from their poorly maintained and serviced Japanese counterparts.

 

[Ivan1GFP]

As far as I can tell, switching the R-2800-10 from a Normal Rated to Military Power setting increased boost by about 4" Hg and yielded a 4-5 mph increase in the Hellcat's maximum speed at critical altitude. If we assume that the Zero would benefit in the same fashion from this increase, that would mathematically place the A6M5's maximum attainable speed to around 343 mph in Military Power (37.8 " Hg), but this would still be below the 350+ mph that we see published in many reference books. I think it's also very optimistic to believe that another 4" Hg could make up that much of a difference.

Hello DarrenW,
Post some numbers. I don't happen to have a copy of the R-2800-10 SEFC handy at the moment but I still doubt that the Hellcat was able to achieve decent speeds with the engine turning at 2450 RPM.

What I am wondering about is why you are choosing a radically different aircraft to make a comparison and ignoring two very comparable aircraft. We have at least some data on A6M2 which is a whole lot closer to A6M5. For that, we have 316-335 MPH as a minimum.

We have quite a lot of data on the very comparable Ki 43 with very similar engines.
The throttle setting for "Normal Power" for the Sakae engine is incredibly low as compared to its maximum. It is only 2-3 inches above ambient pressure at sea level. I honestly am not sure what it is equivalent to when compared to US engines or even if there was an equivalent.
As I have stated elsewhere, you are welcome to come to any conclusion you like.

The bulletin has the altitude at 22,000 feet while in WEP. That's quite a bit higher than the 18,000 and 19,500 feet quoted in both the Navy and Army reports while in Military Power. But then again, the bulletin gives a critical altitude of 23,000 feet while in Military Power as well. What does the A6M5 manual say the critical altitude is while in a "Normal Rated" setting?

I believe the speed numbers for Sakae 21 were pretty close to 6000 meters which was the engine's critical altitude.
I am not sure if ram effect would account for a bit more altitude, but I am knowledgeable enough to make this calculation.
One thing to note is that as the manifold pressure drops, the altitude to which it can be maintained is higher.

This is interesting. So you are completely fine with the notion that "many" F6Fs couldn't reach their published maximum speed, but on the other hand are quite confident that most A6Ms could??? The Hellcat pilots manual gives a maximum level speed of 388 mph for an F6F-3 in an "overload" condition. If we are penalizing an in-service Hellcat by roughly 5 percent, then why can't we do the same for the Zero? If we did we'd be seeing about a 17 mph decrease in speed, which would whittle the often quoted 351 mph figure down to around 335 mph, which was the maximum speed of the aircraft tested by the Navy and also happens to fall within the range that I predicted in an earlier post.

And for what it's worth, maintenance on US warships was impeccable to say the least, which as most agree was a far cry from their poorly maintained and serviced Japanese counterparts.

That is a very amusing interpretation of what I have been arguing.
I have been commenting on what the capabilities of the A6M5 and A6M types were, not what an aircraft pieced together from wrecks or running on pine root oil was likely to do. That gets into a whole different discussion and there are folks who know a lot more than I do on that subject.
What I AM stating is that a typical carrier aircraft stored on the flight deck and only brought down to the hangar decks for maintenance and operating in the rather harsh carrier deck landing environment after a few months is not likely to perform quite as well as a cherry picked example presented to the Navy for performance testing.
This was in reference to your comment that the Hellcat had trouble in catching the C6N recon aircraft and why that was the case.

As for maintenance, I don't believe the Japanese were any worse at keeping their aircraft operational that US personnel were until the later stages of the war when supply lines were destroyed and qualified technician were conscripted.

- Ivan.

 

[DarrenW]

Post some numbers....

There are numerous Hellcat test documents on the Williams/Stirling website that support the notion of a nominal increase in speed between the two settings at critical altitude. I can post the links if you would like, but I'm confident that you know your way around the site as well as anyone else here.

What I am wondering about is why you are choosing a radically different aircraft to make a comparison and ignoring two very comparable aircraft. We have at least some data on A6M2 which is a whole lot closer to A6M5....

But I have been comparing these two machines all along. For the drag calculations I actually used data for the A6M2 that is a bit on the high side from what was discovered during actual flight testing. Same can be said for the A6M5.

As an obvious proponent of the Zero's virtues, what performance figures do you feel are the most credible and representative and why?

What I AM stating is that a typical carrier aircraft stored on the flight deck and only brought down to the hangar decks for maintenance and operating in the rather harsh carrier deck landing environment after a few months is not likely to perform quite as well as a cherry picked example presented to the Navy for performance testing.

While I agree with some of what you say here, from what I read only a small number of the total aircraft aboard could be kept above deck, as there wasn't nearly enough room top-side for a large portion of aircraft stationed on a typical carrier. When they were not in use, most of the aircraft were secured below deck in the hangar bay, where maintenance would normally be performed. But even so we must also acknowledge that US Naval aircraft were still extensively maintained wherever they may have been kept or stored.

And I'm sure you are well aware that, until the resounding defeat of the IJN at the Battle of the Philippine Sea, the Zero was regularly deployed aboard carriers so it too would have been subjected to a similar "harsh carrier deck landing environment". But of the two, which one do you think would hold up best under these adverse conditions? My money is on the Hellcat all the way.

So to sum things up, your theory that the average Hellcat was only about 10 mph faster than the average Zero just doesn't hold water. I guess we will have to continue to agree to disagree on this for the time being….

This was in reference to your comment that the Hellcat had trouble in catching the C6N recon aircraft and why that was the case.

The Myrt was difficult but not impossible to intercept and many were shot down by Hellcat pilots during the course of the war. I was only comparing it to the much slower A6M, which by all accounts was far easier to engage and destroy than the C6N. This is very compelling to say the least.

As for maintenance, I don't believe the Japanese were any worse at keeping their aircraft operational that US personnel were until the later stages of the war when supply lines were destroyed and qualified technician were conscripted.

I didn't realize that we were in disagreement here. Besides the reasons you mentioned, there were other factors (such low quality replacement parts) that added to the maintenance dilemma. Aircraft plants often used unskilled labor during manufacturing and cut corners in other areas as well. So yes I agree that, by the middle of 1944, IJN and IJAAF aircraft were in a much worse state of repair than any of their opposition.

 

[Ivan1GFP]

There are numerous Hellcat test documents on the Williams/Stirling website that support the notion of a nominal increase in speed between the two settings at critical altitude. I can post the links if you would like, but I'm confident that you know your way around the site as well as anyone else here.

Hello DarrenW,
I was wondering how long it would take to get this thread to a "Hellcat is Great" discussion.
That is why I asked in the beginning what you were really interested in.
Since you won't post the data, I will post an engine chart from the Hellcat Pilot's Manual for reference.
If you look at the closest engine settings to the "Normal Maximum" for Sakae engines and meet the criteria of Boost Pressure barely above Sea Level ambient and RPM about 250 below maximum, what you get for an equivalent for the Hellcat is "Maximum Cruise" at
34 inches Hg and 2400 RPM.
I am Guessing that this would only be about 1200-1300 HP at best.

Now if you believe that kind of engine setting gives anywhere near representative performance, I can't agree.

But I have been comparing these two machines all along. For the drag calculations I actually used data for the A6M2 that is a bit on the high side from what was discovered during actual flight testing. Same can be said for the A6M5.

As an obvious proponent of the Zero's virtues, what performance figures do you feel are the most credible and representative and why?

Basically you have been selecting what data you like and ignoring the most relevant data that does not agree with the point you are trying to make. The A6M2 gained about 19 MPH from one power setting to the other and you are trying to "reason" that very similar A6M5 should only gain about 5 MPH based on data from.... HELLCAT Engine settings???? Really!?!?

You may believe that I am "an obvious proponent of the Zero's virtues", but that is far from the truth.
It had its virtues but it also had a lot of faults which I have commented about in other threads.
This thread was about the "Aerodynamic Drag Properties", so I believe it makes sense to discuss what an aircraft in good condition could do rather than argue about how poor the condition of the average Japanese aircraft was.

While I agree with some of what you say here, from what I read only a small number of the total aircraft aboard could be kept above deck, as there wasn't nearly enough room top-side for a large portion of aircraft stationed on a typical carrier. When they were not in use, most of the aircraft were secured below deck in the hangar bay, where maintenance would normally be performed. But even so we must also acknowledge that US Naval aircraft were still extensively maintained wherever they may have been kept or stored.

I believe the practice with USN carriers was to store aircraft on the flight deck. British and Japanese carriers tended to store aircraft below in the hangar spaces. On USN carriers, the aircraft get spotted forward when others are landing and then are spotted aft when launching for a strike.

And I'm sure you are well aware that, until the resounding defeat of the IJN at the Battle of the Philippine Sea, the Zero was regularly deployed aboard carriers so it too would have been subjected to a similar "harsh carrier deck landing environment". But of the two, which one do you think would hold up best under these adverse conditions? My money is on the Hellcat all the way.

So to sum things up, your theory that the average Hellcat was only about 10 mph faster than the average Zero just doesn't hold water. I guess we will have to continue to agree to disagree on this for the time being….

See note above for aircraft storage.
Regarding Hellcat being only 10 MPH faster than the average A6M5, I never made such a statement.
Heck, I wasn't trying to compare anything with the Hellcat at all. That is a rather boring game and I am tired of it.

The Myrt was difficult but not impossible to intercept and many were shot down by Hellcat pilots during the course of the war. I was only comparing it to the much slower A6M, which by all accounts was far easier to engage and destroy than the C6N. This is very compelling to say the least.

I didn't realize that we were in disagreement here. Besides the reasons you mentioned, there were other factors (such low quality replacement parts) that added to the maintenance dilemma. Aircraft plants often used unskilled labor during manufacturing and cut corners in other areas as well. So yes I agree that, by the middle of 1944, IJN and IJAAF aircraft were in a much worse state of repair than any of their opposition.

Regarding intercepting C6N: One of the things I learned from Flight Simulators is that if someone doesn't want to engage, then you need a fair amount of speed advantage to execute a pursuit..... either that or a lot of time and fuel. Fighters are expected to engage in combat. Folks are not hard to catch when they are trying to bring guns to bear on you. Recon planes have better things to do, like get home and report what they found.

The engines installed in C6N and A6M have radically different reputations for reliability and maintenance issues. The Sakae / Ha-115 was pretty reliable and according to TAIC's evaluation of Oscar 2 was pretty tolerant of being pushed to its limits or even of pilots disregarding those limits for "flash performance".
The Homare / Ha-45 had a tendency for accessory failures and often did not make the power claimed for the engine.

As for what I believe about the A6M series:
I believe that when they are new, they probably were able to achieve the performance levels claimed for them.
I also believe that they tended to degrade fairly quickly in harsh environments because of how fragile their structures were.
Their light weight had a cost in durability. Early in the war, and even on bases that were not cut off from the supply chain, this delicate lady was well cared for and performed well. On bases that were not well supplied or cut off and overrun such as when broken aircraft are left by departing troops, conditions and performance would suffer even when the aircraft was repaired after capture.

- Ivan.

 

[DarrenW]

Hi Ivan,
I was hoping that it wouldn't come to this, as the trading of insults isn't my style, especially after the trauma that I have endured recently in my personal life. I have always respected your opinion and really enjoy bouncing ideas off of you in order to help me clearly see both sides of the argument and get to the heart of the truth.

But if you are bored by all this then by all means stop responding to my requests for information. I'm sure that there are others who can further assist me with my question, but I do thank you for your involvement thus far. Without someone challenging my beliefs I wouldn't continue to expand my knowledge of WW2 aviation, which would kinda be a bummer in you know what I mean.

Peace to you going forward good Sir. I hope we can still discuss other topics on the forum with a renewed sense of cooperation and good will towards one another.

P.S.,
After all the confusion thus far I think it's a good time to provide the link to those still curious about the level speed differences of the F6F while in Normal Rated and Military Power. There are many examples to be seen here. Enjoy!

F6F Performance Trials


Now back to the threads original topic at hand, the aerodynamics of the A6M....

 

[DarrenW]

Any altitudes to go with those values? I presume this is TAS.

Here is what I got:


A6M2
Published works:
316mph/16,570ft
332mph/14,930ft
346mph/14,930ft
Wartime flight testing:
289/15,000ft
326/16,000ft
335/16,000ft

A6M3
Published works:
338mph/19,685ft
Wartime flight testing:
310mph/9,300ft
328mph/16,000ft
346mph/21,000ft (calculated???)


A6M5
Published works:
346mph/19,685ft
351mph/19,685ft
Wartime flight testing:
327mph/19,500ft
335mph/18,000ft
358mph/23,100ft (calculated)

 

[Shortround6]

Perhaps I missed it but there was a major change in the A6M5 from the A6M2 & 3. The early aircraft used an exhaust system that pretty much just dumped the exhaust out the bottom through two outlets, much like the P-36, F4F and F2A.
the later planes used ejector exhaust with two cylinders per pipe.

This exhaust system might be worth around 100hp in high speed flight at around 20,000ft.
Depending on amount of water injection it might be worth more (mass times velocity?)
This change in the amount of real power being generated vs power to the propeller only might have some bearing on the issue?

Figuring power from exhaust is rather tricky since while the concept is simple the execution is not. DB601s in a 109 may have generated a fair amount of exhaust thrust.DB 601s in a Bf 110 may have done little as the pipes point down on the inside of cowls instead of rearwards (to route exhaust under wing and away from cockpit?) and upwards on the outside of the cowl (keeps exhaust gases going over the wing and not back into the radiator).

Just a thought.

 

[DarrenW]

This exhaust system might be worth around 100hp in high speed flight at around 20,000ft.

After learning from you in an earlier thread about the value of exhaust thrust this certainly seems plausible. In your best estimation would the exposed exhaust pipes in any way disturb the air flow over the fuselage and possibly nullify a portion of the added thrust provide by the different exhaust arrangement?

 

[Ivan1GFP]

Hi Ivan,
I was hoping that it wouldn't come to this, as the trading of insults isn't my style, especially after the trauma that I have endured recently in my personal life. I have always respected your opinion and really enjoy bouncing ideas off of you in order to help me clearly see both sides of the argument and get to the heart of the truth.

But if you are bored by all this then by all means stop responding to my requests for information. I'm sure that there are others who can further assist me with my question, but I do thank you for your involvement thus far. Without someone challenging my beliefs I wouldn't continue to expand my knowledge of WW2 aviation, which would kinda be a bummer in you know what I mean.

Peace to you going forward good Sir. I hope we can still discuss other topics on the forum with a renewed sense of cooperation and good will towards one another.

P.S.,
After all the confusion thus far I think it's a good time to provide the link to those still curious about the level speed differences of the F6F while in Normal Rated and Military Power. There are many examples to be seen here. Enjoy!

F6F Performance Trials


Now back to the threads original topic at hand, the aerodynamics of the A6M....

Hello DarrenW,
My sympathies for your loss. I saw your announcement but don't know you well enough to have anything more meaningful to say.

My apologies if you interpreted any of my comments as insulting.
I was just expressing my annoyance at yet another discussion going in a predictable fashion.
You accused me of being a "proponent of the Zero's virtues" which I found somewhat ironic because I believe I had just been posting information with some commentary for perspective but without any assertion of relative merit except against other Marks of the A6M.

Regarding the information in your link, I still wish that you had posted the numbers instead of a link.
The "Normal Rated" Power for Hellcat isn't really the same thing as what was called "Normal Maximum" for the A6M series.
Here is why:
Military would be 53.0 inches Hg @ 2700 RPM for 1650 HP
Normal would be 49.5 inches Hg @ 2550 RPM for 1550 HP
4 MPH difference for 100 HP doesn't sound unreasonable.

This isn't nearly the same thing as the Sakae bopping along with manifold pressure barely above what would be seen in an unsupercharged engine at Sea Level.

Regarding conditions of A6M types on board what carriers were left in the Japanese Navy:
I suspect they were all in pretty good condition because on the average, they were very new aircraft.
....They were new aircraft flown by new pilots because the loss rates were so high by that stage of the war.....

Good Night.
- Ivan.

 

[Shortround6]

After learning from you in an earlier thread about the value of exhaust thrust this certainly seems plausible. In your best estimation would the exposed exhaust pipes in any way disturb the air flow over the fuselage and possibly nullify a portion of the added thrust provide by the different exhaust arrangement?

It may have been possible.
Trying to figure exhaust thrust with any accuracy is just about impossible without a lot more data than we have for most planes. The only really good figures I have seen are for a Merlin XX in a Hurricane under test by RR.
You need the mass of the engine airflow (weight of the air + weight of the fuel being used at a given altitude +the weight of any water/alcohol if used) and then you need to know the exhaust gas velocity. Which changes with altitude due to the back pressure on the nozzle (air pressure at that altitude) and the force with which the gases leave the cylinder and the route the pipe/s take. SHort 90 degree (or almost) stacks will give the most velocity while pipes that wind their way through an engine compartment with 3 or more major bends are going to have a lower velocity. More than 3 cylinders per pipe doesn't work very well.
Then you have the angle of the pipe/nozzle outlet. exactly in line with aircraft or angled 5-10 degrees from the line of flight so you have to figure vectors? is a slightly larger nozzle that sticks further out into the airstream causing more drag better with exact alignment than a shorter smaller nozzle that is point 15 degrees out to the side and wasting some power?

Unfortunately the RR tests were at max throttle at each height recorded so trying to interpret difference due to internal pressure in the engine is just guessing. As in does an engine running 12lbs boost have a much higher exit velocity than one running at 6lbs boost? Since each height has a different back pressure and even 12lbs boost at 15,000ft has a different mass flow than 12lbs boost at 20,000ft there are too many variables for me to deal with

I am sure there was some sort of net gain for the Zero. Some people claim the stacks on the B-25s were worth 10-11mph?