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.