XP-39 II - The Groundhog Day Thread

GregP said:

They didn't need quantitative test because all the active PTO combat pilots knew what they could do.

When we did the full airframe overhaul, about a 30-cal bullet in the canopy frame was found, just inside about a 30-cal hole. The bullet was removed and the hole was repaired.

I doubt the flight test got to "best power" and :max speed" as they didn't seem all that sure what that might be at the time. They out about 190 hours on the airframe during the 1944 Fighter Conference. In that time, Zero 61-120 was the only fighter aircraft being flown that didn't break down even once ... it was dead reliable.

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Hello GregP,

From what I remember, the Sakae 31 aircraft have a slight difference that is externally visible at the aft end of the cowl.
The gap between the cooling flaps and the fuselage appears to be slightly longer than for the Sakae 21.
Perhaps this was to allow room for the Water Methanol tank?
This might also explain the 348 MPH speed you were quoting as compared to the more common 351 MPH speed listing, or perhaps it was the later additional wing guns or larger cutouts for the 13.2 mm MG in the cowl?

In any case, in this particular TAIC Report No. 17 there is no listing for details on engine power or throttle settings or any real performance detail regarding speed other than 335 MPH. Best climb speed seems a bit low to me at 105 Knots indicated which suggests engine power was a bit low (Note that best climbing speed in testing for A6M5 No. EB-2 was 135 MPH which seems a bit more reasonable) and another odd characteristic was the note on vibrations in dives at airspeeds over 250 Knots IAS which should not be happening. This wasn't even noted for the A6M2 and the A6M5 had much higher diving speeds according to the manual. In any case, I do not believe these results are indicative of what a A6M5 in perfect condition could actually do.

In the other comparable TAIC Report No. 38, from what I can tell from the graph, maximum speed achieved was about 326 MPH but there WERE many discrepancies noted and they DID attempt to run the engine at full Emergency Power when they figured out what was wrong with it. The majority of the tests were not run at full manifold pressure but the performance tests were and there is a note that there were some problems with the airframe that limited performance results.

I am pretty sure that by the time these aircraft were being tested, a couple manuals had been captured. Whether they were widely distribute and to the people doing the testing is uncertain though. The thing to note in TAIC Report No. 38 is that from what I can tell, they were running a maximum of 42 inches Hg for manifold pressure in their testing which translates to +306.8 mm Hg which isn't too far from the official limit in the manual of +300 mm Hg. The difference may be due to my reading of the graph, but it does not seem that they were running the engine too low.

- Ivan.

P-39 Expert said:

Clearly the additional 836lbs had nothing to do with the P-39D being 11mph slower or climbing 1000fpm slower.

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The extra weight would make a difference, as would a variation in engine performance.

I would have expected the heavier aircraft to have its peak numbers at lower altitudes than the lighter aircraft. Not sure if that is a fair assumption.

P-39 Expert said:

How about this, what if the P-39D weight was reduced to that of the P-39C? Would it not have the same performance as the P-39C?

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That I cannot say, and nor can you.

There were detail differences in the two aircraft - the D was longer and had a fillet in the tail fin. The D had a different propeller and had the extra guns in the wings, which would have had some aerodynamic effect (I guess you would say to remove these).

And we don't know the actual power the engines produced on the tests. The power numbers come from (two different) standard charts.

A few pages back, I observed that the climb numbers for the P-39C make sense while the climb numbers for the P-39D do not. The predicted rate of climb follows the P-39C decently but not perfectly, and the climb numbers for the P-39D do NOT look logical.

Don't know why since I wasn't there, but they got the power numbers from a two charts instead of from rpm and manifold pressure. They MIGHT have used MAP and rpm but, if so, they didn't note the readings for the report, so it's hard to see what might be wrong when you don't know any particulars.

It is almost like they made the P-39D chart all at 2,600 rpm but recorded it differently. I can't say, really.

Gents,

I know some of our planes were captured and tested by the Axis. Is there any reports of what performance they obtained with our equipment? I'm curious if they got the same results out of our equipment without manuals or instruction.

Cheers,
Biff

I've got several captured aircraft books, Biff (3 F's) and will look through them when I get home

Hi Biff.

I don't read German, so I'm sort of left out in the dark there. The reports are usually scanned pictures instead of pdf's so you can't copy and paste into a translator. But, I'll se what I can find on the P-39 in German and maybe Russian. The numbers are usually selfevident.

GregP said:

Hi Biff.

I don't read German, so I'm sort of left out in the dark there. The reports are usually scanned pictures instead of pdf's so you can't copy and paste into a translator. But, I'll se what I can find on the P-39 in German and maybe Russian. The numbers are usually selfevident.

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I speak German, so I can translate if necessary. It is just a matter of if I have time or not.

BiffF15 said:

Gents,

I know some of our planes were captured and tested by the Axis. Is there any reports of what performance they obtained with our equipment? I'm curious if they got the same results out of our equipment without manuals or instruction.

Cheers,
Biff

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Hello BiffF15,

The Germans tested a captured Soviet Lavochkin La 5FN at Rechlin. This is obviously not an American aeroplane but it is interesting to note that the performance that they got was much lower than that typically attributed to the same aircraft by the Soviets.
This report has been translated into English and is not that hard to find. I have attached a copy.
As a simple comparison, the maximum speed of the La 5FN in Soviet service tended to vary a bit in Soviet Service but a fair estimate is something in the 390-403 MPH range.

Maximum speed of tested aircraft was 560 KPH. 403 MPH would be around 648 KPH.
Other performance figures are correspondingly low.
The Germans seemed to have good information on how to operate the engine of this aircraft.
The fuel quality (C3) available to Germans was at least as good quality as that typically available to the Soviets.
Perhaps this was a worn out aircraft?

In the report "8" is the category for single engine fighter, so "8-109" is the Me 109 and "9-190" is the FW 190.

Incidentally, the book by Hans Werner Lerche that came up in discussion a while back is full of his evaluations of captured aircraft.

- Ivan.

Ivan1GFP said:

Hello BiffF15,

The Germans tested a captured Soviet Lavochkin La 5FN at Rechlin. This is obviously not an American aeroplane but it is interesting to note that the performance that they got was much lower than that typically attributed to the same aircraft by the Soviets.
This report has been translated into English and is not that hard to find. I have attached a copy.
As a simple comparison, the maximum speed of the La 5FN in Soviet service tended to vary a bit in Soviet Service but a fair estimate is something in the 390-403 MPH range.

Maximum speed of tested aircraft was 560 KPH. 403 MPH would be around 648 KPH.
Other performance figures are correspondingly low.
The Germans seemed to have good information on how to operate the engine of this aircraft.
The fuel quality (C3) available to Germans was at least as good quality as that typically available to the Soviets.
Perhaps this was a worn out aircraft?

In the report "8" is the category for single engine fighter, so "8-109" is the Me 109 and "9-190" is the FW 190.

Incidentally, the book by Hans Werner Lerche that came up in discussion a while back is full of his evaluations of captured aircraft.

- Ivan.

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Ivan,

That's an excellent report. I find it interesting that the German view of Russian aircraft at that time was so poor. Especially in the handling department. This is considering particularly the landing phase as compared to the Me-109 with it's known vices. Also, given the short legs of the Me-109 and the FW-190 that they thought the La-5 was short legged.

Also, as per the Zero in US hands, the top speed tested was not the same as claimed by the country of manufacture. I'm curious to see if this is a trend among other nations (not just the US).

Cheers,
Biff

BiffF15 said:

Gents,

I know some of our planes were captured and tested by the Axis. Is there any reports of what performance they obtained with our equipment? I'm curious if they got the same results out of our equipment without manuals or instruction.

Cheers,
Biff

Click to expand...

Book - "Luftwaffe Test Pilot" by Hans Werner-Lerche
Here are some of the Allied planes he tested, I believe some are estimates on his part such as range, but everything else seems to be from his data. Not sure why he has the Mustang's climb performance only to 5k when the Thunderbolt's got to 20 and 25k, or the Airacobra only to 5k.

FWIW here's his rather simplistic chart, not a lot of "in depth" data, he just has the basics listed:

Type | Max Speed | Climb | Ceiling | Range

American

B-17F | 325MPH @ 25,000ft | 20,000 - 25min 42sec | 37,500ft | 4,420 miles

B-17G | 302MPH @ 25,000ft | 20,000ft - 37min 0sec | 35,000ft | 1,800 miles

B-24D | 303mph @ 25,000ft | 20,000ft - 22min 0sec | 32,000ft | 1,800 miles

B-24J | 300mph @ 30,000ft | 20,000ft - 25min 0sec | 35,000ft | 1,700 miles

B-26B | 317mph @ 14,500ft | 15,000ft - 12min 0sec | 23,000ft | 1,150 miles

P-39D | 335mph @ 5000ft | 5,000ft - 1min 54sec | 29,000ft | 600 miles

P-47D-2 | 420mph @ 30,000ft | 20,000ft - 11min 0sec | 42,000ft | 835 miles

P-47D-10 | 433mph @ 30,000 | 25,000 - 15min 0sec | 42,000ft | 835 miles

P-51B | 446mph @ 30,000ft | 10,000ft - 1min 48sec | 42,000ft | 2250 miles

British

Lancaster Mk 1 | 281mph @ 11,000ft | 20,000ft - 41min 36sec | 24,500 | 1,730 miles

Wellington Mk IV | 247mph @ 14,500ft | 10,000ft - 18min 0sec | 17,700ft | 2,250 miles

Tempest Mk V | 426mph @ 18,500 | 15,000 - 5min 0sec | 36,500ft | 1,530 miles

Typhoon Mk IB | 405mph @ 18,000ft | 15,000 - 6min 12sec | 34,000ft | 1,000 miles

Spitfire Mk IIA | 357mph @ 17,000ft | 20,000ft - 7min 0sec | 37,230ft | 406 miles

BiffF15 said:

Ivan,

That's an excellent report. I find it interesting that the German view of Russian aircraft at that time was so poor. Especially in the handling department. This is considering particularly the landing phase as compared to the Me-109 with it's known vices. Also, given the short legs of the Me-109 and the FW-190 that they thought the La-5 was short legged.

Also, as per the Zero in US hands, the top speed tested was not the same as claimed by the country of manufacture. I'm curious to see if this is a trend among other nations (not just the US).

Cheers,
Biff

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Hello BiffF15,

The FW 190 was a particularly nice handling aircraft. The British acknowledged in their testing of a captured example.
In another, there was the possibility of the aircraft not having the ailerons set up properly which caused a few issues.
In comparison, even some of the other users of the Lavochkin fighters were not so impressed with their handling.
They just had the engine power and performance that prior Soviet fighters lacked.

If flown by the manual, the 1180 mm Hg @ 2500 RPM setting was only good for about 5 minutes and only useable in Low Blower.
This would give 1850 HP and in theory was a Take-Off setting and not useful much past 1650 Meters critical altitude for low blower.
The equivalent of military power was 1700 HP with 1000 mm Hg @ 2400 RPM in Low Blower.

From what I have been able to find, climb rate at "military power" was somewhere under 3500 fpm which is good but not that special, but at its take-off setting, climb rate is about 4000 fpm which was very competitive for the time.

I have a lot more detail in the Soviet manuals for the aircraft if you wish to calculate the actual fuel consumption of the aircraft for range purposes. One odd thing to note is that the fuel in the Rechlin report seems to weigh more than the typical 6 pounds per US Gallon that one might expect.

I believe that in this particular test at Rechlin, the Germans may have captured the La 5FN AFTER it had been beaten to heck by the prior Soviet users. Soviets didn't tend to stick by the manuals with the Airacobra and probably didn't with anything else either. It generally didn't matter when the lifespan of an aircraft measured in weeks.

Regarding the Zero and Japanese claims for speed. From what I can tell, there actually are no official claims for what we would consider "Maximum Speed".
In their manual for the A6M2, they only list a maximum speed for "Normal Power" +50 mm @ 2350 RPM which is what we might consider max continuous or something close and that was for 275 Knots or 316 MPH.
The 345 MPH claim was by an experienced pilot, Saburo Sakai. For a long time, I was certain this number was inaccurate but not because Sakai was dishonest, but after reviewing the reports recently and other sources in the context of these discussions, I am now more certain he was correct.

- Ivan.

Just as an FYI, the App Google Translate will use your phone camera and translate live time so you don't need to cut and paste, just point and read.

Peter Gunn said:

Book - "Luftwaffe Test Pilot" by Hans Werner-Lerche
Here are some of the Allied planes he tested, I believe some are estimates on his part such as range, but everything else seems to be from his data. Not sure why he has the Mustang's climb performance only to 5k when the Thunderbolt's got to 20 and 25k, or the Airacobra only to 5k.

FWIW here's his rather simplistic chart, not a lot of "in depth" data, he just has the basics listed:

Type | Max Speed | Climb | Ceiling | Range

American

B-17F | 325MPH @ 25,000ft | 20,000 - 25min 42sec | 37,500ft | 4,420 miles

B-17G | 302MPH @ 25,000ft | 20,000ft - 37min 0sec | 35,000ft | 1,800 miles

Click to expand...

Robert Mikesh has a nice book (found this link), on captured B-17s by the Japanese in WW2.

Captured B-17s

Peter Gunn said:

Book - "Luftwaffe Test Pilot" by Hans Werner-Lerche
Here are some of the Allied planes he tested, I believe some are estimates on his part such as range, but everything else seems to be from his data. Not sure why he has the Mustang's climb performance only to 5k when the Thunderbolt's got to 20 and 25k, or the Airacobra only to 5k.

FWIW here's his rather simplistic chart, not a lot of "in depth" data, he just has the basics listed:

Type | Max Speed | Climb | Ceiling | Range

American

B-17F | 325MPH @ 25,000ft | 20,000 - 25min 42sec | 37,500ft | 4,420 miles

B-17G | 302MPH @ 25,000ft | 20,000ft - 37min 0sec | 35,000ft | 1,800 miles

B-24D | 303mph @ 25,000ft | 20,000ft - 22min 0sec | 32,000ft | 1,800 miles

B-24J | 300mph @ 30,000ft | 20,000ft - 25min 0sec | 35,000ft | 1,700 miles

B-26B | 317mph @ 14,500ft | 15,000ft - 12min 0sec | 23,000ft | 1,150 miles

P-39D | 335mph @ 5000ft | 5,000ft - 1min 54sec | 29,000ft | 600 miles

P-47D-2 | 420mph @ 30,000ft | 20,000ft - 11min 0sec | 42,000ft | 835 miles

P-47D-10 | 433mph @ 30,000 | 25,000 - 15min 0sec | 42,000ft | 835 miles

P-51B | 446mph @ 30,000ft | 10,000ft - 1min 48sec | 42,000ft | 2250 miles

British

Lancaster Mk 1 | 281mph @ 11,000ft | 20,000ft - 41min 36sec | 24,500 | 1,730 miles

Wellington Mk IV | 247mph @ 14,500ft | 10,000ft - 18min 0sec | 17,700ft | 2,250 miles

Tempest Mk V | 426mph @ 18,500 | 15,000 - 5min 0sec | 36,500ft | 1,530 miles

Typhoon Mk IB | 405mph @ 18,000ft | 15,000 - 6min 12sec | 34,000ft | 1,000 miles

Spitfire Mk IIA | 357mph @ 17,000ft | 20,000ft - 7min 0sec | 37,230ft | 406 miles

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I'm looking at the Time-to-height value for the P-51B. The average rate of climb is about 5,500 fpm, which strikes me as very high. Is there a typo in there?

swampyankee said:

I'm looking at the Time-to-height value for the P-51B. The average rate of climb is about 5,500 fpm, which strikes me as very high. Is there a typo in there?

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Agreed, I was a bit suspicious of that myself, that's the way it is in the book so it may very well have gotten a bit mixed up when the publisher set the type.

Ivan1GFP said:

Hello BiffF15,

The FW 190 was a particularly nice handling aircraft. The British acknowledged in their testing of a captured example...

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I would not call 190 a particularly nice handling a/c because its nasty/violent stall behaviour and it stalled practically without warning. That with clean a/c, at landing configuration there was plenty of warning and the stall itself was much milder. A Geschwaderkommodore of JG 51 killed one of his Gruppenkommandeure when soon after take-off and still a steep, climbing turn he lost control of his 190 which whipped over onto its opposite wing and smashed into Kommandeur's 190. Hauptmann Busch (40 victories) was flying as wingman to Geschwaderkommodore Oberstleutnant Nordmann (78 victories), who survived with injures but it was also the end of his combat career even if he recovered from his injuries he was unable to get over the accident. Otherwise 190 had fairly nice handling with exceptionally high rate of roll and very good harmony of control.

Ivan1GFP said:

In comparison, even some of the other users of the Lavochkin fighters were not so impressed with their handling.

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I agree. When one of his top aces, Klubov (33 + 3 shared victories) crashed on 1 Nov 1944 during his first La-7 flight was killed Pokryshkin decided to forget La-7 and his fighter division kept its P-39s to the end of the war.

Ivan1GFP said:

I believe that in this particular test at Rechlin, the Germans may have captured the La 5FN AFTER it had been beaten to heck by the prior Soviet users. Soviets didn't tend to stick by the manuals with the Airacobra and probably didn't with anything else either. It generally didn't matter when the lifespan of an aircraft measured in weeks.

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IIRC The La-5FN tested at Rechlin was old and worn-out a/c. On La-5FN max speed, the new production a/c usually were capable to 625 to 635 km/h and the 648 km/h was the speed of a prototype. Soviet prototypes in early 40s tended to be faster than the production a/c.

Ivan1GFP said:

Regarding the Zero and Japanese claims for speed. From what I can tell, there actually are no official claims for what we would consider "Maximum Speed".
In their manual for the A6M2, they only list a maximum speed for "Normal Power" +50 mm @ 2350 RPM which is what we might consider max continuous or something close and that was for 275 Knots or 316 MPH.
The 345 MPH claim was by an experienced pilot, Saburo Sakai. For a long time, I was certain this number was inaccurate but not because Sakai was dishonest, but after reviewing the reports recently and other sources in the context of these discussions, I am now more certain he was correct.

- Ivan.

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I agree with that, too.

wuzak said:

The extra weight would make a difference, as would a variation in engine performance.

I would have expected the heavier aircraft to have its peak numbers at lower altitudes than the lighter aircraft. Not sure if that is a fair assumption.




That I cannot say, and nor can you.

There were detail differences in the two aircraft - the D was longer and had a fillet in the tail fin. The D had a different propeller and had the extra guns in the wings, which would have had some aerodynamic effect (I guess you would say to remove these).

And we don't know the actual power the engines produced on the tests. The power numbers come from (two different) standard charts.

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Just to be clear, the loss of 1000fpm of climb was due to a few inches of extra length, the fin fillet, the different propeller (of the same diameter and manufacturer) and the aerodynamic effect of the wing .30s (not the weight)? And the same model engine maybe producing different power? Any other differences in the two planes?

I'm still going with the 836lbs less weight.

P-39 Expert said:

Just to be clear, the loss of 1000fpm of climb was due to a few inches of extra length, the fin fillet, the different propeller (of the same diameter and manufacturer) and the aerodynamic effect of the wing .30s (not the weight)? And the same model engine maybe producing different power? Any other differences in the two planes?

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All possible issues yes, as has been pointed out by various posters many times already. Setting aside of course, any CoG issues.

P-39 Expert said:

I'm still going with the 836lbs less weight.

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Certainly a logical and possible reason, but again, others more versed in actual aviation experience have pointed out the whys and why nots.

Peter Gunn said:

All possible issues yes, as has been pointed out by various posters many times already. Setting aside of course, any CoG issues.



Certainly a logical and possible reason, but again, others more versed in actual aviation experience have pointed out the whys and why nots.

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Oh, I forgot about the CG issues. Should have added that to the list. Were there actually any CG issues in either plane? None were mentioned in either test. And the C model didn't have any nose armor. Should have made it unflyable, right?

Hmmm...methinks I smell troll.