Spitfire vs different models of zeros

[HoHun]

Hi Ivan,

>This may be a silly question, but what are the the standards for atmospheric pressure for the various manifold pressure ratings?

For conversion:

1 ata = 98.0665 kPa (1 ata = 1 kp/m^2).

1 lb/sqin = 6.89476 kPa.

1 mm Hg = 0.133322 kPa

1 inch Hg = 33.86788 kPa

US and German measurements are absolute, so there is no reference pressure to be considered.

I'm pretty confident that during WW2, all nations were using the same reference pressure if they didn't use absolute pressure indicators, and the standard atmospheric pressure was then as now 101.325 kPa.

However, I cannot be entirely certain of the Japanese.

I think I pulled the above numbers from Kuchling, "Handbuch der Physik" when I put them into a spreadsheet. For convenience, I've simply pulled them from my spreadsheet today.

Regards,

Henning (HoHun)

 

[HoHun]

Hi Ivan,

>The point I was trying to make was that if the speed of the A6M3-32 was 335 mph without even using full throttle, I would imagine that it would be significantly faster at the full throttle setting, yet most sources quote a figure around 335 mph for this plane.

Absolutely. I've compared all of the Zero tests that I could find, often in the original thanks to the diligent work of people like Mike Williams, Micdrow or Shinpachi, and I don't think there is one for the A6M3 or A6M5 that ever gave a result representative for the type in good condition with perfectly working supercharger high gear.

In my opinion, as a result of these tests, A6M performance with the two-speed supercharged engine is generally underestimated as a result. Unless the engine somehow consistently failed to reach the published figures, the A6M3 and A6M5 must have been top speeds quite a bit faster than the numbers we're familiar with.

Ever since Shinpachi provided the translation I referred to, I meant to run an analysis of the A6M3 to highlight this point. Somehow, I can't find the time for it ... maybe I should try harder!

Regards,

Henning (HoHun)

 

[Ivan1GFP]

Hello HoHun,

Glad we are all back online. I was (and still am) wondering what exactly happened.

Regarding your previous post, I don't believe the German manifold pressure setting is an "absolute" because it is a multiplier of the reference pressure which is 1 ata. The only numbers that are not a plus something or times something are the American ones.

I take it from your message that 1 ata. == 1kg / cm^2. Let me know if I am reading this wrong.

The Japanese pressure standard was pretty easy to figure out with the various throttle settings (+ NNN mm) and their corresponding American settings in inches of Mercury. It looks like the base number is 760 mm which makes sense because it is the STP.

Thanks for the help!
- Ivan.

 

[HoHun]

Hi Ivan,

>Glad we are all back online.

I absolute agree!

>Regarding your previous post, I don't believe the German manifold pressure setting is an "absolute" because it is a multiplier of the reference pressure which is 1 ata. The only numbers that are not a plus something or times something are the American ones.

It's definetely absolute as "ata" means "atmosphere, technical, absolute"

There is also "atü" ("atmosphere, technical, 'Überdruck'" = overpressure) which is used in other aviation applications such as for the tyre pressures, compressed air, oxygen and the like.

The choice of the unit signals whether it's an absolute or a relative pressure.

>I take it from your message that 1 ata. == 1kg / cm^2. Let me know if I am reading this wrong.

Strictly speaking, it's "kp/cm^2" as kg is a unit of mass, not force, but of course you're right that it's per square centimeter, not per square meter - I screwed up that bit because my brain works in SI

>The Japanese pressure standard was pretty easy to figure out with the various throttle settings (+ NNN mm) and their corresponding American settings in inches of Mercury. It looks like the base number is 760 mm which makes sense because it is the STP.

Note that all the Russian boost figures I've seen are in absolute mm Hg, too. It's not just the Americans who used absolute pressures.

Regards,

Henning (HoHun)

 

[slaterat]

Terrence Kelly's encounters against zeros, probably A6M2 's, left him with the impression that there was very little difference in performance between the Zero and the Tropical Hurri IIB. Which would seem to indicate that the 335 mph figure is pretty close to correct,at least for the A6M2.

Slaterat

 

[peril]

There is an ANA Boomerang document of roll vs speed comparison tests that show this quite nicely as well. The Hamp = A6M3-32 (clipped wing) is a direct comparison to the data originally discussed in this thread. Also note control forces are listed here as 30lbs.

Looks like about 90 deg/sec @ 125 mph BUT tapers off quickly as speed rises.

Was report 868 wrong?? Who knows but given the Grey areas of test state it's not very definitive.


This document below certainly has the forces and the type of Zero listed so it removes most of the doubt in those areas.

 

[kool kitty89]

Wow, the Tomahawk had a dramaticly better roll rate than the P-40F (and that was at 30 lb stick force rather than 50 lbs!).

The only reason I can think for this would be the increased wing armament. (there were some minor changes in deflection angle used, but I don't think that's part of it)
I wonder how it would have done with metal skinned ailerons.

 

[peril]

I think those tests exist for P40 ailerons?