F4F-4 vs Zero 21

[FDutchmn]

Originally posted by HoHun
Hi Mitsu,

>Nope, actually ZEKEs didn't have that problem.

Do you have any source for that? The A6M2 (serial number 4593) flown by Tadayoshi Koga, recovered and test-flown by the Americans after its crash on Akutan, seems to have displayed negative G cut-outs, and though some minor changes were necessary to make the A6M airworthy again, it looks like the carburettor still was original.

Regards,

Henning (HoHun)

Hiya everyone,

There seems to be this notion that the A6M suffered from engine cut off in negative G conditions.  However, this is not the case.

Here is the first page of an article written by Mr. Haruo Niiyama, the designer/engineer of the carburetor used on the Sakae21 engine.

The title says: CARBURETOR Mounted on "Sakae21": Zero's Air Combat Capabilities Supported by its Carburetor.  The article is about 5 pages long, but I will not post all of it because I do not want to infringe copyrights, nor will I translate this directly.  (I know that Mitsu or somebody sent me this article but I forget where this came from... I will search for that when I can get hold of Mitsu or when the public library opens... it's holiday season now.)

Anyway, in the article, it says that Mr. Niiyama specifically worked on the problem of effects of negative G, zero G, and excessive G conditions on the performance of the carburetor, since the 6th year of the Showa era (that's 1931).  A number of innovations were tried from introducing a ball valve to a slide valve to modifying the needle valve.  In the end, he was successful in having a carburetor capable of withstanding different G conditions.  The changes to the carburetor was completed to the production planes by the 12th year (1937).

Since this is some four years before the outbreak of the war, I find it unlikely that Airman Koga's Zero was equipped with a carburetor that was in use some four to five years before.

The carburetor design was the float-type which was not in use for airplanes in the US.  This may contribute to mistakes when an engineer who is not familiar with the parts when he re-assembles them after inspection.

[FDutchmn]

oh geez... I just noticed that this something... this thread is almost 2 years old!  What's it doing being revived anyway!

[Sikboy]

Nice to see this thread again.

If nothing else, I think it reminds me how important the A6M3 is, with the 99II cannons. They may not be great, but they are a hell of a lot better than the 99I that we have on the A6M2.

I have high hopes that we'll see the 3 when (or not long after) the P-38G shows up.

-Sik

[HoHun]

Hi Dutchman,

>oh geez... I just noticed that this something... this thread is almost 2 years old!  What's it doing being revived anyway!

My fault - I liked this thread so well I thought I'd just append my question to it so all the context would be in easy reach :-)

I'm quite happy that you gave such a detailed answer to the old question regarding negative G carburetting as my interest in that one was still alive :-)

As that level of detail is what I'm looking for: Do you have anything on the maximum lift coefficient for the A6M (any model)? I've archived a low-resolution copy of a Japanese diagram someone posted here that shows spanwise lift distribution, but I'm interested in a single factor which I can't derive from that diagram.

(Information on stall speed and airspeed indicator calibration would be welcome, too.)

Thanks again! :-)

Henning (HoHun)

[HoHun]

Hi again,

>The 16:9 ratio would appear to make more sense than the 3:2 ratio, but the FM-2 manual has a comment on not using more than 2500 rpm in the climb above 20500 ft due to propeller efficiency losses that suggests the 3:2 ratio might have been used.

OK, I've found out now that the R-1820 of the F4F-4 had the 3:2 ratio, which might explain some of the BuAer performance charts pecularities that confused me so far. Maybe propeller tip speeds are also significant for the F6F top speed topic also discussed 2 years ago :-)

Still, if someone could help me with data on the R-1820-56, it would be very much appreciated!

(One preliminary result for the latter engine is that with water injection, it was cleared for a much higher boost than the supercharger would normally deliver :-)

Regards,

Henning (HoHun)

[joeblogs]

Everything I can find on this engine cites the two reduction gear ratios, which are used in versions of the Cyclone since the rated RPM was increased to 2600 RPM (later 2700 RPM) in the H series engines.

A Wright manual of that era shows two types of reduction gearing corresponding to the 3:2 and 16:9 ratios in a G200 series engine with two speed supercharger (I suspect for the Buffalo). I'll bet the choice of gearing depended on the propeller and constant speed unit selected. This might be done, for example, to avoid harmonic vibration between the propeller reduction gearing and the crankshaft.

Can you post the exact propeller and constant speed unit from the FM-2 manual? Also, can you post max RPM, HP, and manifold pressure at some stated altitudes. With that I might be able to match to some commercial or airforce tables.

-Blogs

Originally posted by HoHun
Hi everyone,

I'm currently trying to figure out the Grumman fighters' performance. One information I can't seem to find is the gear ratio for the R-1820-56 used in the FM-2. It seems there were variants of the R-1820 with a 16:9 ratio as well as others with a 3:2 ratio.

The 16:9 ratio would appear to make more sense than the 3:2 ratio, but the FM-2 manual has a comment on not using more than 2500 rpm in the climb above 20500 ft due to propeller efficiency losses that suggests the 3:2 ratio might have been used.

Could anyone please help me with this information? :-) Thanks in advance!

Regards,

Henning (HoHun)

[joeblogs]

If we have the max RPM of the engine, the length of the propller and the reduction gearing, we can calculate the maximum tip speed and see if we are getting anywhere close to transonic.

I doubt tip speed explains the speed question for the F6f. An easy way to check this is to verify that the reduction gearing on the Double Wasp used in the F4u is the same as for the model used in the F6f and then compare the propeller length on the two planes. I believe the F4u propeller was at least as large and the Max RPM of its engine (especially in later models) was higher. In that case, it should be the F4u with the propeller tip speed problem...

-blogs

Originally posted by HoHun
Hi again,

...

OK, I've found out now that the R-1820 of the F4F-4 had the 3:2 ratio, which might explain some of the BuAer performance charts pecularities that confused me so far. Maybe propeller tip speeds are also significant for the F6F top speed topic also discussed 2 years ago :-)

Still, if someone could help me with data on the R-1820-56, it would be very much appreciated!

(One preliminary result for the latter engine is that with water injection, it was cleared for a much higher boost than the supercharger would normally deliver :-)

Regards,

Henning (HoHun)

[HoHun]

Hi Joe,

>I'll bet the choice of gearing depended on the propeller and constant speed unit selected. This might be done, for example, to avoid harmonic vibration between the propeller reduction gearing and the crankshaft.

Interesting aspect, I hadn't thought of that!

>Can you post the exact propeller and constant speed unit from the FM-2 manual?

It's a Curtiss Electric hub 05325D-A20 with blades 109354-12. The diameter (not found in the manual) seems to be 10 ft.

>Also, can you post max RPM, HP, and manifold pressure at some stated altitudes. With that I might be able to match to some commercial or airforce tables.

Four different versions of the R-1820-56 were used in the FM-2, two of them limited to 2600 rpm and two of them to 2700 rpm.

The Military Power engine curve common to all of them (at 2600 rpm):

Alt      HP     Boost
00000 1250 46.5" Hg
03400 1290 46.5" Hg
13000 0970 34.0" Hg/43.0" Hg
17800 1000 43.0" Hg
30000 0620 26.5" Hg

The R-1820-56 and R-1820-56W (with water injection) are limited to 2600 rpm throughout, the R-1820-56A is cleared for a 2700 rpm takeoff setting, and the R-1820-56WA (with water injection) is cleared for 2700 rpm in low blower, 2600 rpm in high blower.

Combat power with water injection is 50" Hg in low blower, 52" Hg in high blower with water injection, 46" Hg in high blower without water injection.

Enough water for 10 min operation is carried, 5 min continous operation at combat power is permitted.

The manual seems a bit confusing in claiming the non-"W"-engines do not have a combat power setting while it seems it should be possible to get 46" Hg in high blower without water injection.

The R-1820-56 apparently was used in the Dakota as well. For the R-1820-56AM2, an FAA document gives a 16:9 gearing and 1350 HP @ 2700 rpm, 48.0" Hg take-off power. This seems to be a good result as I'd linearly extrapolate 1340 HP for that combination, and usually expect less than linearly increased effect from higher boost/higher rpm.

Use of the R-1820-56 in the Dakota required a modified rudder balance tab as so much power would otherwise create dangerous single-engine characteristics 8-O

Regards,

Henning (HoHun)

[joeblogs]

Hohun:

Thanks, there should be enough detail here for me to match up to an engine with a different (i.e. commerical) designation number. I have a good crosswalk between military and civilian numbering for Pratt &Whitney engines, but I don't for the Wright engines used by the Navy.

-blogs

One issue that makes the late Cylcones a bit dfficult to match is that Wright adopted a new fin technique late in the war that significantly improved cooling of the heads. This, combined with a stiffer crankshaft, allowed for higher RPM and some additional manifold pressure. Unforthunately, I don't think these changes resulted in a new model number so it's not always clear whether a given engine used on a plane had these improvements or not.

-Blogs

Originally posted by HoHun
Hi Joe,

>I'll bet the choice of gearing depended on the propeller and constant speed unit selected. This might be done, for example, to avoid harmonic vibration between the propeller reduction gearing and the crankshaft.

Interesting aspect, I hadn't thought of that!

>Can you post the exact propeller and constant speed unit from the FM-2 manual?

It's a Curtiss Electric hub 05325D-A20 with blades 109354-12. The diameter (not found in the manual) seems to be 10 ft.

>Also, can you post max RPM, HP, and manifold pressure at some stated altitudes. With that I might be able to match to some commercial or airforce tables.

Four different versions of the R-1820-56 were used in the FM-2, two of them limited to 2600 rpm and two of them to 2700 rpm.

The Military Power engine curve common to all of them (at 2600 rpm):

Alt      HP     Boost
00000 1250 46.5" Hg
03400 1290 46.5" Hg
13000 0970 34.0" Hg/43.0" Hg
17800 1000 43.0" Hg
30000 0620 26.5" Hg

The R-1820-56 and R-1820-56W (with water injection) are limited to 2600 rpm throughout, the R-1820-56A is cleared for a 2700 rpm takeoff setting, and the R-1820-56WA (with water injection) is cleared for 2700 rpm in low blower, 2600 rpm in high blower.

Combat power with water injection is 50" Hg in low blower, 52" Hg in high blower with water injection, 46" Hg in high blower without water injection.

Enough water for 10 min operation is carried, 5 min continous operation at combat power is permitted.

The manual seems a bit confusing in claiming the non-"W"-engines do not have a combat power setting while it seems it should be possible to get 46" Hg in high blower without water injection.

The R-1820-56 apparently was used in the Dakota as well. For the R-1820-56AM2, an FAA document gives a 16:9 gearing and 1350 HP @ 2700 rpm, 48.0" Hg take-off power. This seems to be a good result as I'd linearly extrapolate 1340 HP for that combination, and usually expect less than linearly increased effect from higher boost/higher rpm.

Use of the R-1820-56 in the Dakota required a modified rudder balance tab as so much power would otherwise create dangerous single-engine characteristics 8-O

Regards,

Henning (HoHun) [/B]