The Zero's Maneuverability

[Ivan1GFP]

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.

I can't comment as to the accuracy of that quote. At one point I believed it to be overly optimistic but as I read more, I am finding that his claim is quite plausible in the context of other evidence.

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.

b
US test reports seem to always quote RPM figures in the 2500 - 2550 RPM range. You are stating that the Japanese chart gives a power reading for +129 mm at 2600 RPM for a Sakae 12 engine? That would be interesting.
If the +150 mm boost setting at 2500 RPM is giving 330 MPH in a bent bird then what do you suppose +250 mm and 2550 RPM would be giving on a non-bent bird?

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.

I believe this is a poor argument for the following reasons:
1. At the "Normal" engine setting of 2350 RPM, A6M2 cruised at 316 MPH.
2. The long range missions to Guadalcanal were flown at very slow airspeeds on lean mixtures.
Assuming the same advance ratio, half the airspeed and half the RPM is awfully low, my guess is that it is too low to be practical.
3. One other point that is worth noting is that Koga's A6M2 had no need to be configured for any super long ranges if such a configuration was even possible. He was flying off a carrier where low speed acceleration off the carrier deck was certainly more important.

 

[Holtzauge]

I can't comment as to the accuracy of that quote. At one point I believed it to be overly optimistic but as I read more, I am finding that his claim is quite plausible in the context of other evidence.

Well here we just have to agree to disagree: For me "about 300 knots" remains just that: An about number just as in a ballpark number.

b
US test reports seem to always quote RPM figures in the 2500 - 2550 RPM range. You are stating that the Japanese chart gives a power reading for +129 mm at 2600 RPM for a Sakae 12 engine? That would be interesting.
If the +150 mm boost setting at 2500 RPM is giving 330 MPH in a bent bird then what do you suppose +250 mm and 2550 RPM would be giving on a non-bent bird?

Yes. The chart goes up to 2550 and and this line drawn above the 2500 line in the chart is quite close, meaning that the engine was close to peak rpm's and would not be producing much more power at 2600.

Then about what the +250 mm and 2550 RPM would add: I already explained that with the Spitfire MkI chart I linked to in post #334: The extra 50 rpm's from 2500 move the FTH speed a little towards higher speeds, but this is only marginal adding just a few mph at the FTH. The main gain is at lower latitudes, not at the FTH. Just as the effects on the Spitfire MkI when going from 6.25 to 12 and ultimately +16 boost.

And I don't understand why you are so fixated with "bent birds"? Unless a rebuilt aircraft is put together in a very bad way the effects on performance would be minimal. But since you seem to think there are many mph to be had here, just what was "bent" and how many mph would "un-bending" these defects do? 1,2, 3 or 5 or 10 mph? Because if this was missed by the BuAer engineers in charge of the testing, they were not very good at their jobs were they?

I believe this is a poor argument for the following reasons:
1. At the "Normal" engine setting of 2350 RPM, A6M2 cruised at 316 MPH.
2. The long range missions to Guadalcanal were flown at very slow airspeeds on lean mixtures.
Assuming the same advance ratio, half the airspeed and half the RPM is awfully low, my guess is that it is too low to be practical.
3. One other point that is worth noting is that Koga's A6M2 had no need to be configured for any super long ranges if such a configuration was even possible. He was flying off a carrier where low speed acceleration off the carrier deck was certainly more important.

We have been so fixated with speeds so far in this thread, that we have forgotten to consider that the climb rates in the US tests tell a story as well: And if you look at the climb rates in those tests you can see that the engines were delivering according to specs since they measured a bit over 2700 fpm SL climb rate for the A6M2's in both those tests, which is just as expected looking at the power loading W/P. So this proves without a shadow of a doubt that there was nothing wrong with the engines and that that reason for the low revs they measured when testing initially was due to the propeller pitch setting being adjusted for range, and not performance.

 

[Reluctant Poster]

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.

We've been through stick forces before

The P-38J and L in the European theater.

Control forces were studied in NACA Report No 755 Requirements For Satisfactory Flying Qualities of Airplanes. See attached file. The target for maximum aileron control force at below 80% of maximum speed was: a. Wheel-type controls: +/- 80 pounds applied at the rim of the wheel. b. Stick-type...

ww2aircraft.net

 

[Reluctant Poster]

If he didn't or couldn't keep count of how many turns he made, it's just a guess.

What I find amazing is that the guy behind him would do 75-100 turns behind him before he finally decided it wasn't going to work.
It wouldn't be fatal for the German to reverse his turn, and that's probably how he broke off the combat.

Staying on one opponent so long, in the same airspace, while the Mustang pilot is on the radio trying get all his buddies to come help him, just doesn't seem smart, or likely.

You seem to have your own misunderstanding of basic facts.

I am curious as to how long it would take to do 100 circles. Does anyone have any idea?
I believe it would take about 20 seconds to complete a circle. If so that's over 30 minutes at full power. Fuel becomes an issue. Also 30 minutes at high Gs must be very tiring.
Edits in bold

 

[tyrodtom]

If it takes 20 seconds to complete a circle, then it would take 33 minutes to complete 100.
Somebody check my math.
That's a long time at full power, and in one area.

Depends on what escort mission he was on , but just how much extra time did a Mustang have to go after the Luftwaffe ( as Doolittle told them to do) after escorting the bombers to the target, and was then released to search and destroy.

 

[Reluctant Poster]

If it takes 20 seconds to complete a circle, then it would take 33 minutes to complete 100.
Somebody check my math.
That's a long time at full power, and in one area.

Depends on what escort mission he was on , but just how much extra time did a Mustang have to go after the Luftwaffe ( as Doolittle told them to do) after escorting the bombers to the target, and was then released to search and destroy.

Yes I missed a zero. Since 5 minutes at full power is the budget the P51 pilot isn't getting home

 

[GregP]

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.

"Set in concrete" might mean he can't bend it around with one hand relatively easily. But, if you are a bigger, stronger guy and use both hands on the stick, it might be way different.

 

[Ivan1GFP]

Yes. The chart goes up to 2550 and and this line drawn above the 2500 line in the chart is quite close, meaning that the engine was close to peak rpm's and would not be producing much more power at 2600.

Then about what the +250 mm and 2550 RPM would add: I already explained that with the Spitfire MkI chart I linked to in post #334: The extra 50 rpm's from 2500 move the FTH speed a little towards higher speeds, but this is only marginal adding just a few mph at the FTH. The main gain is at lower latitudes, not at the FTH. Just as the effects on the Spitfire MkI when going from 6.25 to 12 and ultimately +16 boost.

I can't agree that the Spitfire's behavior is relevant to the behavior of A6M2. The A6M2 has substantially MORE power at its critical altitude than it does at sea level.
Its rated power is higher than its takeoff power. When you add in a bit more RPM and Manifold Pressure as Overboost at altitude, the result isn't going to be lower than it was at low altitude.

And I don't understand why you are so fixated with "bent birds"? Unless a rebuilt aircraft is put together in a very bad way the effects on performance would be minimal. But since you seem to think there are many mph to be had here, just what was "bent" and how many mph would "un-bending" these defects do? 1,2, 3 or 5 or 10 mph? Because if this was missed by the BuAer engineers in charge of the testing, they were not very good at their jobs were they?

The defects were noted in the "Sanders Rpt" which has been posted. Please look at the "Notes" section on "Page 3" of the report.
It also states that that they believed they compensated for this by running higher than rated power but the reality was that they were not.
35 inches MP is only +129 mm which is well below rated power.
Note also on this page the comments that they were having some problems with getting the carburetor to work correctly. In reality, they never really got things to work completely right.
Note on the first page of this report (unnumbered), that there is a statement that there is a comment on the propeller pitch and the "damaged condition" of the aircraft.
The people at San Diego did their jobs as best they could but without spare parts, they had to make do with what they had. There certainly were remaining defects which affected performance.

We have been so fixated with speeds so far in this thread, that we have forgotten to consider that the climb rates in the US tests tell a story as well: And if you look at the climb rates in those tests you can see that the engines were delivering according to specs since they measured a bit over 2700 fpm SL climb rate for the A6M2's in both those tests, which is just as expected looking at the power loading W/P. So this proves without a shadow of a doubt that there was nothing wrong with the engines and that that reason for the low revs they measured when testing initially was due to the propeller pitch setting being adjusted for range, and not performance.

As stated before, I don't think it is reasonable to configure a carrier borne fighter in such a manner and I do not believe this was actually done.
If you REALLY want to work with Power to Weight ratios, take a look at the A6M3 from Eagle Farm.
The actual output of the engine is listed in the report and it compares quite interestingly to the A6M2, especially the Akutan A6M2.
The SL output is 960 HP which is about 20 HP higher than the rating for the typical A6M2, but the aircraft also weighs about 100 pounds more than the weight of the Akutan A6M2 as tested. Is that a pretty even match? I think so.
Note that their climb rate is over 3400 FPM rather than 2700 FPM. What does that say about your argument about power to weight being as expected???

Note also that coarsening the pitch of a propeller to bring the revs down should not affect the maximum speed. In fact, the commentary is that messing with the propeller to reduce pitch most likely cost them speed (first page of the Sanders Rpt).

 

[Ivan1GFP]

We've been through stick forces before

The P-38J and L in the European theater.

Control forces were studied in NACA Report No 755 Requirements For Satisfactory Flying Qualities of Airplanes. See attached file. The target for maximum aileron control force at below 80% of maximum speed was: a. Wheel-type controls: +/- 80 pounds applied at the rim of the wheel. b. Stick-type...

ww2aircraft.net

We have been through just about ALL of these arguments before. I know because I was involved in a couple and posted an awful lot of data about 5 years ago.
The report on the Eagle Farm A6M3 was posted back in 2010 by Micdrow. I was in that conversation as well.
This conversation is getting to the pointless deja vu stage pretty quickly and that is why for a couple years I didn't bother visiting this place.

 

[Holtzauge]

I Ivan1GFP : I read your last reply to me and I think we just have to agree to disagree: Right now I can't really see that anything more has been brought to the table in terms of actual numbers or solid data, and we are just going around in circles exchanging opinions now.

Over the years, I have found that the most reliable data is usually that which has been compiled by the nations who operated the aircraft themselves in combat. For example, for German aircraft I have found that the so-called Kennblatt data is usually quite accurate. Unfortunately, I have seen no similar data for Japanese aircraft which is a shame, since I believe this would have given us a much better picture. But nothing tangible like that has unfortunately surfaced in this thread. Granted, evaluations by the opposition don't always reveal an aircraft's true potential, but we have now been debating this back and forth for a long time, and I have yet to see anything solid which would sway me away from the opinion that the 335 mph top speed figure for the A6M2 is optimistic.

So this is why I think it's time to call it a day for me. But I do appreciate your input and the civil discussion, so thanks for that.

 

[GregP]

I am curious as to how long it would take to do 100 circles. Does anyone have any idea?
I believe it would take about 20 seconds to complete a circle. If so that's over 3 minutes at full power. Fuel becomes an issue. Also 3 minutes at high Gs must be very tiring.

I don't believe any WWII fighter will complete more than ONE circle in about 20 seconds. There is just not enough power. After the first one, slowing down all the way, it will start to slow down from best cornering speed and will wind up in the 25 - 35 second range unless the pilot also loses height to maintain energy. If he does that, the ground is the limiting factor. After he reaches ground level, he will be going around slower than best-cornering speed, which is usually called "maneuvering speed" on the flight envelope diagram, and it is located where full aft control stick/wheel movement aft will just produced the g-limit.

To stay there, a LOT of power is required and WWII fighters generally just don't have the power to sustain that point of the flight envelope curve. I'd figure 21 seconds for the first circle and 30 - 35 seconds for the rest, putting 100 circles right at about 50 minutes.

Like I said, nobody does that, ever.

 

[MiTasol]

"Set in concrete" might mean he can't bend it around with one hand relatively easily. But, if you are a bigger, stronger guy and use both hands on the stick, it might be way different.

or even move it with one hand easily. There are so many variables - the pilots size, upper body strength, how tired he is, what he mentally considers stiff (in comparison with what he last flew, how well fed he is, etc, etc, etc.

For example for a Piper J-3 or PA-11 pilot the T-6 and P-40 is heavy on the controls and the C-47 aileron response is slower than grass growing or paint drying.

 

[GrauGeist]

While this conversation has been going in circles, just how much altitude have we lost so far?

 

[GregP]

or even move it with one hand easily. There are so many variables - the pilots size, upper body strength, how tired he is, what he mentally considers stiff (in comparison with what he last flew, how well fed he is, etc, etc, etc.

For example for a Piper J-3 or PA-11 pilot the T-6 and P-40 is heavy on the controls and the C-47 aileron response is slower than grass growing or paint drying.

A C-47 needs a lot of rudder to turn quickly. By quickly, I mean as opposed to turning with insufficient rudder. In that regard, it is kind of like flying a sailplane.

 

[GregP]

While this conversation has been going in circles, just how much altitude have we lost so far?

1 tall tale ...

 

[MiTasol]

A C-47 needs a lot of rudder to turn quickly. By quickly, I mean as opposed to turning with insufficient rudder. In that regard, it is kind of like flying a sailplane.

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

 

[Ivan1GFP]

I Ivan1GFP : I read your last reply to me and I think we just have to agree to disagree: Right now I can't really see that anything more has been brought to the table in terms of actual numbers or solid data, and we are just going around in circles exchanging opinions now.

Over the years, I have found that the most reliable data is usually that which has been compiled by the nations who operated the aircraft themselves in combat. For example, for German aircraft I have found that the so-called Kennblatt data is usually quite accurate. Unfortunately, I have seen no similar data for Japanese aircraft which is a shame, since I believe this would have given us a much better picture. But nothing tangible like that has unfortunately surfaced in this thread. Granted, evaluations by the opposition don't always reveal an aircraft's true potential, but we have now been debating this back and forth for a long time, and I have yet to see anything solid which would sway me away from the opinion that the 335 mph top speed figure for the A6M2 is optimistic.

So this is why I think it's time to call it a day for me. But I do appreciate your input and the civil discussion, so thanks for that.

As I see it, we have been discussing a crashed and recovered aircraft that was flipped and had parts of its engine under water for a month which can not have helped future performance potential. The propeller was bent, the carburetor was repaired by people who didn't know how it was supposed to work.
It was flight tested with known and some documented aerodynamic flaws limiting performance and a propeller, engine and carburetor in questionable state as mentioned in reports.
Its engine parameters were set much lower than typical for the type and although an overboost setting was present and observed to have been used in the type operationally, it was not used for testing.
Even with these limitations, the testing revealed an aircraft that could achieve 328 - 335 MPH in actual test flights.
One has to wonder what an operational example of this aircraft without the aerodynamic and mechanical flaws might have been capable of.
Even 345 MPH on Overboost is not blazing fast for the time, but it fits in with more of the reports from the field.

What I have noticed is that you have a tendency to ignore the contents of the reports which were written by people who examined and flew this single example of a captured A6M2.

I have done simulator models of the A6M starting over 20 years ago. The information I had back then was pretty poor. By the time I did my model of the A6M2 about 5 years ago, I had found out quite a bit more though I was still unwilling to accept that the older aircraft was aerodynamically superior. Evidence is pointing in that direction though.
At some point, you need to decide whether your simulator model is accurate and representative of the type and what you want to do about it. I have no investment in your model.

 

[GrauGeist]

1 tall tale ...

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...

 

[Ivan1GFP]

"Set in concrete" might mean he can't bend it around with one hand relatively easily. But, if you are a bigger, stronger guy and use both hands on the stick, it might be way different.

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?

 

[MiTasol]

Good point.