F4F Wildcat versus P-40E Tomahawk

Hi Renrich,

>Actually, in looking at the chronology of the two Ac, a comparison of the F4F3 and P40E makes more sense.

OK, here it is. Do you think the A6M2 is the most representative Zero variant to compare these two against?

Regards,

Henning (HoHun)

I think the A6M2 is contemporaneous with the two. I do not believe the A6M2 ever had WEP. Are your graphs based on your calculations or are they taken from some other source?

Hi Renrich,

>I think the A6M2 is contemporaneous with the two. I do not believe the A6M2 ever had WEP. Are your graphs based on your calculations or are they taken from some other source?

My graphs always rely on other sources, often a collection of sources that have been compared and assessed by running the calculations for each of them and noting the inconsistencies and contradictions, and deciding on the most realistic parameters to use for the 'final' calculation.

In the case of the A6M2, you're right that it is usually portrayed as not having any WEP capability. However, the Navy's own tactical intelligence sheets list the engine of the A6M2 with MIL and WEP boost levels:

TAIC 1944 p. 851
Sakae model 12
Take-off: 925 hp/2550 rpm/39.8" SL
WEP: 925 hp/2550 rpm/39.8" SL
WEP: 1010 hp/2550 rpm/39.8" 11000*
MIL: 820 hp/2500 rpm/35.8" SL
MIL: 935 hp/2500 rpm/35.8" 13800 ft

Additionally, Richard Dunn has also mentioned "overboost" in his article on A6M performance: Zero Model 21 Performance: Unraveling Conflicting Data (Not that I agree with his conclusion, but the article is interesting nevertheless.)

However, the TAIC engine data seems a bit suspect to me at least for the Sakae 21 and 31A data, and I'm not sure it's entirely realistic especially for the latter engine. If you're aware of any other sources, please let me know

Regards,

Henning (HoHun)

I have a source which published the test results in abbreviated form for the Attu A6M2 versus US fighters and a later model 52 Zero but there are no exact technical data. The comparison for the Wildcat V Zero is pretty complete but the flyoff for the P40F is not because almost all of the AAF fighters broke down during the tests and could not achieve max performance. I have a fairly lengthy technical article on the Zero and I can find no mention of WEP on A6M2.

It may just refer to it as "take-off" power instead of WEP. (as the rating is the same)

Hi Renrich,

>I have a source which published the test results in abbreviated form for the Attu A6M2 versus US fighters and a later model 52 Zero but there are no exact technical data.

Sounds interesting! Is it available online somewhere?

>The comparison for the Wildcat V Zero is pretty complete but the flyoff for the P40F is not because almost all of the AAF fighters broke down during the tests and could not achieve max performance.

I think this must be Informal Intelligence Summary No. 85, which is available at Richard Dunn's site, I believe. Unfortunately, it has no information on the engine settings used for the A6M2, except that power is estimated at 900 HP @ 16000 ft, which as the speed graph shows is the high-speed figure (rated altitude increased by ram effect). If the TAIC engine data is correct, this is consistent with a lower boost level than what TAIC lists for MIL, meaning we should expect the A6M2 at the WEP settings to be faster than the No. 85 figures.

Richard Dunn notes in his abovementioned article that Intelligence Brief #3 (which I have not seen) gave the boost pressures as follows 35" Hg and 38" Hg: "U.S. notations 35 and 38 in. Hg actually reflect Japanese ratings of +150mm/35.4 in. Hg and +250mm/37.8 in. Hg)". On checking his conversion, that does not seem to be correct as +250 mm Hg amounts to 39.8" Hg according to my calculation, which is the figure also given in the TAIC report.

Jim Rearden's "Koga's Zero" shows a photograph of the boost gauge of the A6M2 recovered on the Aleutians, and it has a marked arch from 0 to +25, which would be consistent with Dunn's "250 mm Hg" figure (presumably from intelligence brief #3) and the 1944 TAIC data sheet.

So the question remains whether the data given in Intelligence Summary No. 85 was for +150 mm Hg or for +250 mm Hg. With the later TAIC data being consistent with No. 85, the high full throttle height of 16000 ft mentioned in No. 85 suggests that the speed figures were really achieved at just +150 mm Hg. Whatever one would call the +250 mm Hg setting, an A6M2 using it would be faster than the No. 85 figures

Regards,

Henning (HoHun)

The test summaries for the Attu and model 52 Zeros are in "The Great Book of WW2 Airplanes" in the section about the Zero. I have not seen them online. I was surprised at how well the FM2 compared with the Model 52. The earlier test with the A6M2 was against an F4F4 and was not nearly as even. The test with the P40F was not completed because the engine in the P40F could not get full power.The A6M2 had a Sakae 12 engine. The model 52 had a Sakae 21 with takeoff power of 1130 HP.

Hi Renrich,

>The test summaries for the Attu and model 52 Zeros are in "The Great Book of WW2 Airplanes" in the section about the Zero. I have not seen them online.

I guess the A6M5 material is from the reports uploaded here: http://home.att.net/~historyworld/TAICzero.pdf

>The model 52 had a Sakae 21 with takeoff power of 1130 HP.

According to the linked file above, both the examples tested by the US Navy and the USAAF had a Sakae 31A with 1120 HP take-off power. Not much of a difference, I'll admit - the Sakae 31A only differed noticably in its high supercharger gear.

The Navy A6M5, which was the heavier example, had the higher top speed - 335 mph @ 18000 ft. The Air Force noted poor aerodynamic condition, smoke and rough running for their example. Their 326 mph were achieved at 19400 ft though, and they give the engine conditions as 42" Hg, 2750 rpm.

All considered, this looks more like the Sakae 21 ata than the Sakae 31A data since the latter ran at 2800 rpm in WEP, 2700 rpm in MIL, and had a full throttle height of 20400 ft (static) in WEP, 21700 ft in MIL. You book might be right regarding the engine

Regards,

Henning (HoHun)

The book says the Sakae 21 is rated at 1130 hp takeoff, 1100 HP at 2850 M, and 980 HP at 6000 M. The model 52a has Vmax at 6000M of 302 knots, 343mph. Time to climb to 6000 M is 7 min 1 sec.

Hi Renrich,

>The book says the Sakae 21 is rated at 1130 hp takeoff, 1100 HP at 2850 M, and 980 HP at 6000 M. The model 52a has Vmax at 6000M of 302 knots, 343mph. Time to climb to 6000 M is 7 min 1 sec.

The quoted ratings seem to be close to the ratings the TAIC quotes for MIL power (see below). However, either the full throttle height at full speed would be higher than 6000 m, or the engine data is for power with dynamic pressure (in high-speed flight), meaning it would be decidedly different from the TAIC data.

Here is an interesting article on the A6M3 Model 32:

http://skyraider.allaboutwarfare.com/files/japan/Hamp_Design_Analysis.pdf

One interesting thing is the manifold pressure gauge which shows a marked arch ending at +250 mm boost. This is the same as on the A6M2, and less than the TAIC engine data ascribes to the A6M3. The TAIC data for the Sakae 21 is:

Sakae model 21, TAIC 1944 p. 852
Take-off 1115 hp/2750 rpm/41.7" SL
WEP 1115 hp/2750 rpm/41.7" SL
WEP 1180 hp/2750 rpm/41.7" 7500*
WEP 1040 hp/2750 rpm/41.7" 18000*
MIL 995 hp/2700 rpm/37.8" SL
MIL 1085 hp/2700 rpm/37.8" 9350 ft
MIL 965 hp/2700 rpm/37.8" 19700 ft

41.7" Hg converts to +300 mm Hg, so if we assume that the marked arch indicates the boost range up to the war emergency rating, the A6M3 at least would have to be considered to have a lower maximum power than this TAIC data.

The article I linked above shows that there is a supercharger control on the throttle quadrant, and while the scan is not very good, I think I can make it out in the cockpit shot too, which would verify that the picture is not from an A6M2 cockpit (which would be misleading).

Interestingly, the article also identifies one button in the cockpit as "emergency power booster", which might answer one of our open questions.

>The model 52a has Vmax at 6000M of 302 knots, 343mph. Time to climb to 6000 M is 7 min 1 sec.

Is the weight for the specific aircraft given? I get about 6 min for 6 km if I use MIL power from the TAIC data with the weight of the heavier of the two tested A6M5 examples, 6096 lbs.

Regards,

Henning (HoHun)

The weight given for the model 52a is full load-6035 lbs. It actually shows a layout of the cockpit.

Hi Renrich,

>The weight given for the model 52a is full load-6035 lbs.

Thanks, that seems to fit the Navy test aircraft.

>It actually shows a layout of the cockpit.

Is the boot pressure indicator visible? It would be interesting to see if it has the coloured sector from 0 to +250 mm Hg, or if it actually goes to +300 mm Hg. (If the layout is schematic only, I'm afraid we're out of luck.)

Regards,

Henning (HoHun)

Statistics on Japanese zero's from the book zero by Robert C Mikesh published by Warbird History

Interesting Micdrow. For Mikesh's sources see:

Source 1: Informational Intelligence Summary No 85.
Source 2: Performance Flight Test on a Japanese Hamp, AAF No. EB-201.

ponsford said:

Interesting Micdrow. For Mikesh's sources see:

Source 1: Informational Intelligence Summary No 85.
Source 2: Performance Flight Test on a Japanese Hamp, AAF No. EB-201.

Click to expand...

Very interesting ponsford, I noticed that the documents that he listed as sources dont match the actual documents for max speeds but they do match rate of climb.

Very interesting and many thanks.

Hi Ponsford,

>Source 2: Performance Flight Test on a Japanese Hamp, AAF No. EB-201.

Highly interesting!

The settings used for this test were +150 mm Hg, 2400 rpm ... TAIC data credits the engine with +200 mm Hg, 2700 rpm for mil and +300 rpm, 2750 rpm for WEP.

Comparing sea level powers:

WEP 1115 hp/2750 rpm/41.7" SL
MIL 995 hp/2700 rpm/37.8" SL

If we assume that power is linear to rpm and boost pressure, this means that the A6M3 in the test got only about 837 HP at sea level under the test conditions.

If the engine actually made these +300 mm Hg, 2750 rpm at WEP, that would yield a sea level top speed of roughly 308 mph or 496 km/h (assuming that top speed increases to the third power of power) instead of the 280 mph achieved in the test. That seems to be quite a bit faster than most Zero data I have seen ...

In fact, if I simply use the A6M2 drag and wing data in combination with the weight data for the heavier A6M3 in combination with the TAIC engine data for WEP, that gives me a top speed of 486 km/h @ sea level, which is faster than most A6M data I've seen, too - but still a conservative guess as the A6M3 has a smaller wing and thus less drag in high-speed flight.

Accordingly, the test performance of the A6M3 and my calculations seem to have at least a semi-decent fit - I guess that for assessing A6M performance, it comes down to the question: "Which ratings did the Sakae engines really use"?

I think we have a good idea of the boost pressures used (big thanks to Micdrow for the excerpt from Mikesh's instruments book - very useful! , but the maximum rpm are still open ... maybe there are some markings on the rev counters, too?

Regards,

Henning (HoHun)

Hi again,

>I think we have a good idea of the boost pressures used (big thanks to Micdrow for the excerpt from Mikesh's instruments book - very useful! , but the maximum rpm are still open ... maybe there are some markings on the rev counters, too?

Reading the rest of the reports on Mike's site WWII Aircraft Performance I notice that the A6M2 Material Command memorandum assigns the following values to the A6M2:

Speed at sea level: 277 mph @ 2600 rpm, +120 mm Hg

This is less than the +150 mm Hg ascribed to the engine by the TAIC report for the MIL setting - but it turns 100 rpm faster than the TAIC MIL setting, too. I'm beginning to get confused!

On the other hand, the above speed at sea level is not compressiblity-corrected.

Regards,

Henning (HoHun)

Your welcome Henning, though like you I am confused on a few things also. 5years ago I researched this aircraft for 2 years and I never did find complete answers and ended up giving up though in the last few years more info has surfaced.

I get the impression the P40 was a great help to USA's allies especially Britain in the DAF 1941/1942 against the best German pilots even if Britain's tactics brought more losses. USA had better planes they were building up later when they went all in in Europe but not enough to share so the P40 became a workhorse in the smaller theatres. Not many 200 plane battles against 200 enemy. The Navy plane got in some large battles with many planes and got more credit. I'm just starting to read about PTO and should probably read "Bloody Shambles" as suggested. P40 was there for the whole war but eventually got reduced air to air missions so reduced air to air kills. The MTO history has recently been said to be more successful than I thought for the USAAF and the P40. I enjoy all the reading here I get.