XP-39 II - The Groundhog Day Thread (2 Viewers)

[windhund116]

66 Pages of still trying to turn a sow's ear into a silk purse.

Lots of coulda' shoulda' woulda' mumbo jumbo about trying to turn a mediocre low altitude fighter into a world beater.

Isn't all of this more of a mental exercise than a reflection of history?

 

[fubar57]

Could go in the "What If" section

 

[P-39 Expert]

Actually the P-39N was very competitive with anything in 1943, except possibly the Spitfire IX and the Merlin P-51 in the last month.

The early P-39s (D/F/K/L) would have been competitive with anything in 1942 had they not been 800+lbs overweight, as the AAF finally figured out. Except the two stage Spitfires.

If the P-39 had received the two stage V-1710-93 in early 1943, it would have been competitive with pretty much everything. Not nearly as heavy as the P-63 and much earlier.

 

[XBe02Drvr]

Hey guys, I'm back from my vacation from this thread, and notice it's grown a few pages. Just curious; when you all were discussing the weight differences between the P39C and D, did anybody bring up the added structural weight and moment of the elongated aft fuselage and enlarged tailfeathers of the D? The added moment would certainly require added weight forward (gearbox armor?) to keep the CG out of lomcevak land.

 

[P-39 Expert]

Hey guys, I'm back from my vacation from this thread, and notice it's grown a few pages. Just curious; when you all were discussing the weight differences between the P39C and D, did anybody bring up the added structural weight and moment of the elongated aft fuselage and enlarged tailfeathers of the D? The added moment would certainly require added weight forward (gearbox armor?) to keep the CG out of lomcevak land.

So, just exactly how much longer was the D model than the C model?

 

[P-39 Expert]

66 Pages of still trying to turn a sow's ear into a silk purse.

Lots of coulda' shoulda' woulda' mumbo jumbo about trying to turn a mediocre low altitude fighter into a world beater.

Actually 66 pages of me telling you that the 1942 P-39s (D/F/K/L) were way too heavy (836lbs) and could have climbed much better (1000fpm) if redundant/unneeded items were deleted, and showing you the official performance tests.

And you all telling me that the 1000fpm difference in climb between the two planes was from a slightly different propeller of the same diameter, an inch or two more length, a fin fillet, phantom CG issues that weren't there in the test planes, and other irrelevant mumbo jumbo.

And a few pages of your personal firearms.

 

[Stig1207]

Gen. Harmon was unhappy with the performance of the P-400 over Guadalcanal; 67th Sqd had been roughly handled in it's first engagement, and in consequent engagements, the inability to get up to the altitude of the incoming bombers. The main reason being that the P-400, originally intended for the British, were equipped with a high pressure oxygen system; 'no supply of high pressure oxygen bottles were available om Guadalcanal' so they were forced to operate at low altitude (p. 85 of the report). There were other issues as well, even if the oxygen supply problem was solved, Harmon (and Vandegrift) did not consider the plane suitable as an interceptor and out-classed by the Zero.

In the attachment I have highlighted the suggestion given Harmon that the P-39's enroute to New Caledonia could be stripped of some 1500 pounds (20% of it's operational weight, in the field ?!?) and pointed to Australia where ...'considerable success with P-39's against Zeros is being achieved'.

By Australia I guess was meant New Guinea, which I believe was the only scene of combat between P-39's and Zero's at this time. The P-39 units there were credited with 95 victories against Zero's (15 actual losses), so the percieved success was not all that 'considerable'.

 

[Stig1207]

only the Soviet Union loved it, and they did great with it.

This is, imo, the main reason this thread is still going; the Soviets did better but maybe not great. I have earlier posted a link to actions over Roumania in 1944, where Soviet flown P-39's overclaimed massively. Here is a quote from another, this time from the Kuban in 1943:

So, the total losses of the Messerschmitts amounted to exactly 103 ******* aircraft, including 42 destroyed and 61 damaged. Of these, only 27 "Messers" were destroyed in air battles and 23 more received various damage. In other words, Soviet fighter pilots, who during the battles in the Kuban were credited with more than 700 (!!!) "shot down" Me-109s (calculations are made on the basis of data from the book by M. Yu. Bykov), in reality, can celebrate victory over them only, exactly, in fifty cases. And, if the Germans exaggerated their successes, on average, 2.5 times, then ours increased this indicator, on average, up to 14 times, although there were exaggerations and much more.

Luftwaffe fighters in the sky of the Kuban

These not just P-39's, but they were involved and among the claimants are some of the big names, Rechkalov and Pokryshkin .

Also, the P-39's in New Guinea did great too against Zero's, if you go by the credited victories, per my post above.

 

[Ivan1GFP]

Could go in the "What If" section

Hello Fubar57,

I believe a much better place for this thread would have been the Religion section.
These discussions are looking a lot like religious arguments.
Creationism versus Evolution anyone?

- Ivan.

 

[Juha3]

Hello Juha3,

My credentials are fewer than yours.....
What document did that page come from? There are a few odd aspects of the M-82FN that I am interested in and perhaps I have the document you are referencing. I don't like to read through a bunch of Russian manuals unless I know I will find something.

From what we KNOW:
The critical altitude of the M-82FN was 4650 Meters.

From what various sources state:
The maximum speed has been given as low as 625 KPH and as high as 648 KPH.
The critical altitude for the La 5FN has been given to be as low as 5000 Meters and as high as 6250 Meters.

How do we reconcile all these?

Here is what I BELIEVE. (Emphasis on Believe but it seems to fit all the data points.)
With an engine making its best power at 4650 Meters, I believe a very good example of the La 5FN could reach 648 KPH at 5000 meters. This would be more typical of expectations for ram effect.
By 6000 Meters, its speed may have dropped to 635 KPH which is also pretty reasonable.
If you believe that speeds were 10 KPH slower at each altitude, I won't argue. Production quality did vary quite a bit.

- Ivan.

Hello Ivan
The docu, unfortunately I cannot recall where I got it, my memory is not as good as it was say 30 years ago and as a pensioner my procedures have became more sloppy.

On La-5FNs, I must disagree, Russian authors clearly state that those speeds are max. speeds, and because the altitudes varied the question is not speeds at certain altitude. Some tables show max speed for both stages and also max speed at 5,000 m, for some reason Soviet authorities thought that 5,000 m is an important altitude, usually the climb times shown in Soviet WWII docus are to 5,000 m. And in the attached table you see that the speeds at 5,000 m is lower than the max speeds for 2nd stage. There is also the La-5FN proto with its 648 km/h max. speed, it achieved 622 km/h at 5,000 m.

 

[Ivan1GFP]

Hello Ivan
The docu, unfortunately I cannot recall where I got it, my memory is not as good as it was say 30 years ago and as a pensioner my procedures have became more sloppy.

On La-5FNs, I must disagree, Russian authors clearly state that those speeds are max. speeds, and because the altitudes varied the question is not speeds at certain altitude. Some tables show max speed for both stages and also max speed at 5,000 m, for some reason Soviet authorities thought that 5,000 m is an important altitude, usually the climb times shown in Soviet WWII docus are to 5,000 m. And in the attached table you see that the speeds at 5,000 m is lower than the max speeds for 2nd stage. There is also the La-5FN proto with its 648 km/h max. speed, it achieved 622 km/h at 5,000 m.
View attachment 600837

Hello Juha3,

There is only one stage in the supercharger, so we are really talking about first speed or second SPEED.
First speed hit its critical altitude at 1650 Meters.
Blower shift to Second speed happens at 4000 Meters.
Second speed hits its critical altitude at 4650 Meters.

Now, this is for "Military Power" or 1000 mm Hg @ 2400 RPM.
Although the supercharger cannot provide any additional boost past 4650 Meters, do you happen to know if some of these tests ran up to 2500 RPM (Take-Off RPM) at altitude?
Is it possible the superchargers were different in the prototypes?

It just seems quite unusual for an aeroplane to make its best speed at 5700 Meters to 6250 Meters when its maximum engine power was achieved at 4650 Meters.
Anyone more knowledgeable care to comment?

- Ivan.

 

[Ivan1GFP]

Regarding the Tail Feathers on the P-39D versus P-39C:

P-39D actually did not come from the factory with the Fin Fillet.
The first model of the P-39 to come from the factory with the Fin Fillet was the P-39D-1 though many if not most P-39D were retrofitted with Fin Fillets later in their career.

- Ivan.

 

[pbehn]

Actually the P-39N was very competitive with anything in 1943, except possibly the Spitfire IX and the Merlin P-51 in the last month.

The early P-39s (D/F/K/L) would have been competitive with anything in 1942 had they not been 800+lbs overweight, as the AAF finally figured out. Except the two stage Spitfires.

If the P-39 had received the two stage V-1710-93 in early 1943, it would have been competitive with pretty much everything. Not nearly as heavy as the P-63 and much earlier.

This is simply not true. By 1943 the single stage Griffon Spitfire was in service, the Alisson engine P-51 was superior to the P-39. There is the Typhoon the P-47 how does it compare to the Hellcat and Corsair? A clipped and cropped late model Spitfire MkV was a good performer at low level on higher octane and boost, it would do a lot better if you take the cannons and armour out of it but that was specified military equipment, this discussion has been part of the P-39 history since the moment it arrived on UK shores, it is why they only did one mission from UK and all were then sent to Russia.

 

[Peter Gunn]

Actually 66 pages of me telling you that the 1942 P-39s (D/F/K/L) were way too heavy (836lbs) and could have climbed much better (1000fpm) if redundant/unneeded items were deleted, and showing you the official performance tests.

And you all telling me that the 1000fpm difference in climb between the two planes was from a slightly different propeller of the same diameter, an inch or two more length, a fin fillet, phantom CG issues that weren't there in the test planes, and other irrelevant mumbo jumbo.

And a few pages of your personal firearms.

ACTUALLY...

It's been a fair amount of those 66 pages of qualified guys from the aviation industry saying that what you have been proposing (over and over and over ad infinitum ad nauseam) isn't that simple of an equation. That you would quibble about "3mph" when the real issue is the 25 horsepower it takes to get that 3mph and what that means in combat, even though THAT was explained to you (more than once).

Even then I could probably take your arguments seriously except then you come off with:

Actually the P-39N was very competitive with anything in 1943, except possibly the Spitfire IX and the Merlin P-51 in the last month.

Are you seriously contending that the P-39 was a match for the FW-190 or Bf-109 in the skies over Western Europe? Man Eaker, Spaatz and Arnold must have been either dullards or totally in cahoots with Republic, Lockheed and North American to make sure Bell got screwed over.

Sorry, but the proof is in the pudding, how many missions did the P-39 fly for the 8th AF? Or the 9th?

I believe the RAF flew one (1) mission and said "Nyet" and shipped them to the Soviets, ah but that's right, the Brits were in on the conspiracy to add weight to it and make it a dog.

Tell me again of it's stunning record in the SWP as it handily brought down Zero's by the fistful.

All said and done, don't take this as a dislike for you, hell, you posts have kept me in stitches for while now but obviously there's no way to enlighten you, so the best I got is a shoulder shrug and a "whatever dude".

 

[Shortround6]

Just curious; when you all were discussing the weight differences between the P39C and D

Tail feathers were pretty much the same but the C had two .30 cal guns and ammo in the nose (a bit further forward of the .50 cal guns) so several feet in front of the CG .but these were shifted to the wings and one more added on each side, Weight went up but the wing guns and ammo are pretty much on the CG, probably didn't do much for roll response though.

 

[windhund116]

Not sure about exact numbers, but I was under the impression that the kill ratio for the P39 variants, in the SWPA was around 1:1 against Imperial Japanese Navy and Army air foes. In the same time frame the F4F Wildcat was around 5:1.

 

[GregP]

Hi Stig.

I'd really love to see a list of vetted German losses. I have an absolutely great list of German claims, both east and west, but have yet to see a vetted list of losses. Unless there is some reasonable check on it's accuracy, how would we know that this list with MANY fewer losses than Soviet claims wasn't "oversated," as the Soviet victories are allegedly so-overstated? Wouldn't the Germans have a vested interest in admitting fewer claims? Since we know the Germans built some 29,000 or more Bf 109s during WWII, and maybe 34,000 total including post-war, these had to be lost SOMEWHERE.

Not dismissing your link or your contention, just thinking about where the notion that many fewer Bf 109s were lost than claimed came from. The German operated as few as 19 He 100s and claimed they were in widespread squadron service ... to intinidate the world with propaganda. Why would we belive their loss figures are absolutely accurate? The Luftwaffe lied to Hitler about the level of their success for several years before he found out. Included in there are some loss figures that are well understated.

The Soviets claimed they destroyed more F-86s in Korea than we sent over. We KNOW how many were built, how many were sent, how many came back, how many we sold to other countries, and how many were still in service when we retired them, and the the Soviet Union and Chinese didn't shoot down as many Sabres as they later claimed. So, Soviet data is somewhat suspect, too. Is it likely that the overclaiming is limited to only victories, or is it more likely that losses were understated as well?

In the U.S.A., we only count losses in direct contact with enemy aircraft while in ongoing combat as combat losses. If some airplane got damaged, and then had an engine failure on the way home, we count that as an "operational loss," not a combat loss, even though the engine most likely would not have failed without the damage from combat. So, our loss figures, while pretty accurate in total, aren't exactly "squeaky clean" when it comes to combat losses in air-to-air combat, either.

Just saying we may never know what the real numbers were except to say that the data are a bit suspect.

 

[Juha3]

Hello Juha3,

There is only one stage in the supercharger, so we are really talking about first speed or second SPEED.
First speed hit its critical altitude at 1650 Meters.
Blower shift to Second speed happens at 4000 Meters.
Second speed hits its critical altitude at 4650 Meters.

Now, this is for "Military Power" or 1000 mm Hg @ 2400 RPM.
Although the supercharger cannot provide any additional boost past 4650 Meters, do you happen to know if some of these tests ran up to 2500 RPM (Take-Off RPM) at altitude?
Is it possible the superchargers were different in the prototypes?

It just seems quite unusual for an aeroplane to make its best speed at 5700 Meters to 6250 Meters when its maximum engine power was achieved at 4650 Meters.
Anyone more knowledgeable care to comment?

- Ivan.

Hello Ivan
Of course, 2 hours sleep and too much on 60-series Merlins lol!
Igor Kopilow in his article on La-5s in feeniks 3/2014 says that during 1944 there were improvements in the supercharger air intake.

 

[P-39 Expert]

Gen. Harmon was unhappy with the performance of the P-400 over Guadalcanal; 67th Sqd had been roughly handled in it's first engagement, and in consequent engagements, the inability to get up to the altitude of the incoming bombers. The main reason being that the P-400, originally intended for the British, were equipped with a high pressure oxygen system; 'no supply of high pressure oxygen bottles were available om Guadalcanal' so they were forced to operate at low altitude (p. 85 of the report). There were other issues as well, even if the oxygen supply problem was solved, Harmon (and Vandegrift) did not consider the plane suitable as an interceptor and out-classed by the Zero.

In the attachment I have highlighted the suggestion given Harmon that the P-39's enroute to New Caledonia could be stripped of some 1500 pounds (20% of it's operational weight, in the field ?!?) and pointed to Australia where ...'considerable success with P-39's against Zeros is being achieved'.

By Australia I guess was meant New Guinea, which I believe was the only scene of combat between P-39's and Zero's at this time. The P-39 units there were credited with 95 victories against Zero's (15 actual losses), so the percieved success was not all that 'considerable'.

Weight was actually only reduced by 600+lbs which allowed the P-39K to fight at 27000'. Best Japanese bombers G4M came in at 18000'-22000'.

 

[P-39 Expert]

This is simply not true. By 1943 the single stage Griffon Spitfire was in service, the Alisson engine P-51 was superior to the P-39. There is the Typhoon the P-47 how does it compare to the Hellcat and Corsair? A clipped and cropped late model Spitfire MkV was a good performer at low level on higher octane and boost, it would do a lot better if you take the cannons and armour out of it but that was specified military equipment, this discussion has been part of the P-39 history since the moment it arrived on UK shores, it is why they only did one mission from UK and all were then sent to Russia.

Please go to wwiiaircraftperformance.org and look at the P-39N climb numbers. Then look at the P-51A, Typhoon, P-47(1943), Hellcat, Corsair, Spitfire V, FW190 and Zero climb numbers. P-39N substantially outclimbed all those planes in 1943.

I never said to remove any cannons, only the wing .30cal MGs. Only armor I recommend removing is the nose armor.