XP-39 II - The Groundhog Day Thread (4 Viewers)

[wuzak]

Is it odd that the listed climb rate in both eth P-39C and P-39D tests are constant up to, basically, the critical altitude?

And that power is constant below that as well, according to the charts?

 

[BiffF15]

Many get shot down without realizing the opponent was there

From the gun footage I have seen, I think it could be easily argued that more than half had no idea they were being attacked until to late.

Cheers,
Biff

 

[pbehn]

From the gun footage I have seen, I think it could be easily argued that more than half had no idea they were being attacked until to late.

Cheers,
Biff

In the Battle of Britain it was much more than half, it was very difficult to make a kill when a lot of planes were in a fur ball, plus it is estimated up to 10% were hit by friendly fire or enemy fire not actually meant for them.... and then there were more than a few collisions too.

 

[BiffF15]

Biff, those teste were conducted at Wright Field by AAF staff whose only job was to test those planes under very strict testing standards and criteria. If some guys on a message board try to invalidate a test done 70 years ago then we have no basis for evaluating the differences in those planes. We must assume that the tests were conducted properly and the information is accurate. Otherwise, what's the point if we're making the rules up as we go along?

P39 Expert,

Realize that you are making up the rules as you go along with the P39C to D difference of 836lbs accounting for a 1000 fpm increase in climb.

"The basic differences between the P-39C and P-39D were armor, 2 more guns and ammunition (with an existing two relocated to the wings), and self-sealing tanks. The weight difference you keep harping on, "836 pounds," WILL NOT result in an extra 1,000 feet per minute climb difference. Period. A 12% reduction in weight does NOT give you a 37% increase in climb rate." GregP

I quoted and bolded Gregs' comment above to re-iterate what you are choosing to ignore. You are also giving no credit to those guys who were there and doing the fighting and or decision making. The US decided it didn't cut the mustard. Russia loved them. They also over boosted them (could walk home if it failed), and kept the war low which played into the P-39s strengths. Compared to it's contemporary Russian counterpart it was probably a step up, or the motor could take a thrashing that others couldn't (don't know but am making an assumption based on the testing that occurred regarding the actual limits of the V-1710).

Also my earlier post regarding the handling / spin characteristics of the P39 as compared to it's US contemporaries went unanswered. If the USAAC went to the lengths of making a spin video, including showing a crash, then there had to be something in its handling as compared to its counterparts. I've done spins, come down through the contrails in a tail slide, negative G stalls, a negative G guns track (very uncomfortable), near mid airs, and all sorts of fun (scary) stuff but after watching that video I would want a serious demo or 3 from an IP before attempting one.

The guys on here are trying to help, let them.

Cheers,
Biff

 

[Ivan1GFP]

Here's a photo of the arrangement. Don't think the 37mm horsecollar magazine fits in there, but a 20mm belt feed might.

I don't really think keeping the 37 mm with its penalties was such a good idea but if it had to be done.....
How about running the endless belt magazine UNDER the cannon instead of over it?
I also wonder if shifting the .30 cals a few inches forward would cause problems.

 

[GregP]

Hi Miflyer.

Yes, it was a "favorite" of low-altitude hot dogs and was quite a good aircraft below 10,000 feet MSL. I'm sure that the P-39 would have been a good mount for almost any low-altitude mission that wasn't out of range. But, if the fight was above maybe 12,000 feet, then they would have chosen some other aircaft ... IF there was a choice. If your unit was flying P-39s, then you flew a P-39 and figured out how to get the most out of it.

Some P-39 info:
1) Australia: 31st Pursuit Group, Michigan. 39, 40, 41 Squadrons. 1941. Then they went to Australia. Not great success.
2) New Guinea: 8th Fighter group. 35 and 36 Squadrons. 1942. 26 of 41 P-39s remained when they reached Port Moresby, most of them lost in accidents before combat was ever joined. Combat in Apr 42. Buzz Wagner evaluated the P-39 versus the Zero. The Zero out-maneuvered, out-climbed, and out-accelerated the P-39, but the P-39 was faster at sea level. He rated the P-39 as 10% better than the P-40 in everything but maneuverability. The flaws he listed included gun reliability, lack of engine armor, leaky propellers, weak undercarriage, poor performance above 18,000 feet (higher than often reported), and – most important – lack of range. The Airacobra could cope above New Guinea and Guadalcanal, but was out of the picture for most "next targets" due to lack of range. The Airacobras about held their own (kills and losses about even), but they were always outnumbered. By the end of 1942 the P-39 squadrons in V Fighter Command had claimed 80 victories but had lost a similar number of aircraft themselves at a cost of 25 pilots killed or missing.
3) Aleutians: 54th FG, Jun - Oct 42. Not much to say ... no enemy there.
4) Guadalcanal: P-400s. 67th FS. 22 Aug 42. Lost 10 of 14 P-400s in 4 days. Oct 42, 339th FS arrived with P‑39s. Unreliable guns. Jamming 37 mm cannons, usually after 2 – 3 shots. Lt. William Fielder scored 5 kills in a P-39 – only America P-39 Ace. Not much other successes.
5) Kwajalein Island: 318th FG, 46 and 77 FS. Phased out in 1944. Last P-39 groups in Pacific.
6) North Africa and Italy: 81st and 350th FG, 68th OG (PR). End of 1942. Lost 107 P-39s, mostly to ground fire. 20 air kills and about the same on the ground. Final kill 6 Apr 44.
7) Training: Most important advanced trainer inside U.S.A. At least we found a use for them.

 

[Stig1207]

The Airacobras about held their own (kills and losses about even), but they were always outnumbered. By the end of 1942 the P-39 squadrons in V Fighter Command had claimed 80 victories but had lost a similar number of aircraft themselves at a cost of 25 pilots killed or missing.

According to Claringbould they were credited with shooting down 95 Zero's, so one would think that they would have considered themselves as doing pretty well; that kills were well in access of losses, and much better than 'holding their own'.
Maybe they percieved that they were always outnumbered? There was not actually any real difference in numbers of available P-39's vs Zero's.

 

[XBe02Drvr]

Maybe they percieved that they were always outnumbered? There was not actually any real difference in numbers of available P-39's vs Zero's.

You can have just as many aircraft on strength as the enemy, but if he consistently manages to bring more aircraft to the engagement, you're outnumbered. Reliability matters.

 

[PAT303]

81 pages and you are all still arguing about how easy it is to turn a donkey into a war winning by simply removing a couple of .30 cals and some armor????.

 

[XBe02Drvr]

81 pages and you are all still arguing about how easy it is to turn a donkey into a war winning by simply removing a couple of .30 cals and some armor????.

Amazing, ain't it?

 

[buffnut453]

You can have just as many aircraft on strength as the enemy, but if he consistently manages to bring more aircraft to the engagement, you're outnumbered. Reliability matters.

It's not just a reliability issue. The force that's on the offensive can pick the time and location of their attack, so they can plan for how to mass their force. The defensive side is responsive, which presents challenges when it comes to massing force.

Basically, the defending side has 2 choices: maintain a standing CAP or try to scramble to respond. CAPs consume a lot of airframes (typically an entire squadron to maintain a 3-4 aircraft CAP.) and the continual flight hours eat through serviceable airframes very quickly. If you don't have standing patrols, then the challenge is scrambling large numbers of defensive fighters in a short timeframe.

Bottom line: it's easier to mass force for offensive ops than it is for defensive ops, which means defenders will often be outnumbered.

 

[P-39 Expert]

Many get shot down without realizing the opponent was there

Most never knew their opponent was there. 60%+ by many estimates.

 

[MIflyer]

Yes, it was a "favorite" of low-altitude hot dogs and was quite a good aircraft below 10,000 feet MSL.

Erich Hartman said, "At low altitude the P-39 performed like the 109."

 

[Stig1207]

You can have just as many aircraft on strength as the enemy, but if he consistently manages to bring more aircraft to the engagement, you're outnumbered. Reliability matters.

Sure, but over New Guinea, there was no one side bringing consistantly more aircraft to the fight than the other, mostly it seems to have been pretty even. Nor was one side offensive and the other only defensive; they attacked each other, 'tit for tat' as Claringbould calls it.
These were small scale operations, and the P-39's for most smart had the altitude advantage to due adequate forewarning by Coastal spotters. The P-39's were caught out on a few occasions where the spotters didn't see the attacking Japanese formations, but that was not the norm.

 

[Stig1207]

Erich Hartman said, "At low altitude the P-39 performed like the 109."

On the ground?

 

[P-39 Expert]

P-39 Expert, I am with you on respecting the tests as run at the time. But, in this case, we have one test that is markedly different from all the OTHER tests.

The basic differences between the P-39C and P-39D were armor, 2 more guns and ammunition (with an existing two relocated to the wings), and self-sealing tanks. The weight difference you keep harping on, "836 pounds," WILL NOT result in an extra 1,000 feet per minute climb difference. Period. A 12% reduction in weight does NOT give you a 37% increase in climb rate. All those differences were internal. They had no aerodynamic effect whatsoever. The only difference in the two planes was weight.

So, either the P-39C was operated at higher MAP than reported or the other P-39s were operated at lower power. There is no third option. If I'm going to say a test is recorded incorrectly, it makes a LOT more sense to me that ONE test (the P-39C) is misreported than all the rest of them (P-39D, et al) being incorrect. For all I know, the Allison in the P-39C test was "hot-rodded" by being ported and polished to give more power than normal. I DOUBT that, but there is SOMETHING wrong for sure. I hesitate to even question ONE test, but we have this wide discrepancy in climb rate that only shows up in the P-39C test. Same engine, same power below 10000'. Above 10000' the P-39C horsepower was actually slightly less.

Saying that 836 pounds accounts for it just isn't going to cut it because it doesn't account for it. The LEAST history-disturbing conclusion is that the P-39C test was run in some non-standard manner. Testing was standardized, that was the purpose of the tests, to accurately compare different models. Go to wwiiaircraftperformance and look at the Tactical Suitability Tests for the P-38, P-47 and Allison P-51. They all were deficient in climb and the recommended fix was to reduce all non-essential weight. Weight influences climb more than any other factor.

Expand above.

 

[MIflyer]

On the ground?

I have flown both taildraggers and nosegear airplanes and I can say with great confidence that the P-39 was vastly superior on the ground to the 109. According to reports, the 109 was one of the worst airplanes ever built for handling on the ground.

And the attitude the P-39 was sitting at on the ground meant it could still shoot targets. Supposedly there was a P-38 pilot who actually used to land, drive around, and shoot up Japanese airbases on the ground in the Pacific, but I never heard of any P-39's doing that.

 

[Stig1207]

I should have written parked on the ground, but anyway I just being funny (trying to).

 

[glennasher]

I should have written parked on the ground, but anyway I just being funny (trying to).

It's quite all right, I understood it immediately, and got a good chuckle out of it.

It's almost as funny as one member's deliberate obtuseness and refusal to understand facts.

 

[BiffF15]

Expand above.

P39 Expert,

Your ability to repeat something, while faced with information that refutes it, is truly something to see.

Good luck,

Biff