XP-39 II - The Groundhog Day Thread

[GregP]

Sorry Fubar57, my stopwatch broke and I don't know.

I'll guess its better than the top speed of a Vespa, though ... the old 2-stroke Vespa, not the modern one fitted with emissions crap. Maybe the Vespa would win if you put an expansion chamber on it ... but where O where would you put an expansion chamber on a Vespa? That's the question. Maybe if you shaped it like a question mark?

 

[XBe02Drvr]

A6M performance fell off at 20-22,000 ft, like the P-39's did at 18,000 ft. That 2-

P39 Expert replied:
With a little less weight (300lbs or so) P-39 would climb with a Zero.

Maybe on paper, or under flight test conditions. Doesn't mean it would respond comparably in combat. Even with a "weight watchers" P39, Zero has a significant weight advantage as well as a slight thrust advantage and a better L/D wing in the high teens altitudes, leading to better acceleration from cruise to combat, and better instantaneous "pop up" performance in response to a bounce. Steady state numbers derived from flight tests don't account for the dynamics of air combat.
Plus, the Zero pilots had already had plenty of experience fighting heavier western type aircraft in China, Philippines, Malaya, DEI, and Ceylon before they met P39s in NG.

 

[ThomasP]

Hey guys,

Thanks for the reply. The Japanese characters 零戦 do seem to mean 'zero fighter' via Google translate.

 

[P-39 Expert]

Hello P-39 Expert,



Bell made a lot of unsubstantiated claims to sell his aircraft.

It is quite astonishing to see this statement from YOU. You want us to believe your performance and handling claims when the trained test pilots, and combat pilots who actually flew the aircraft report something quite different.



Here you go again with the "40 mph faster than a Zero". The facts simply don't agree with you.
When a captured and beat to crap and rebuilt aircraft can hit 335 MPH in testing without emergency power, what do you think one that HASN'T been wrecked and rebuilt can do when its pilot chooses to use emergency power?
Your numbers don't add up.
These early P-39s also were equipped with engines that had a critical altitude at around 12,000 feet. They made their maximum speeds around 13,000 feet.

They also weren't carrying drop tanks for decoration. They were not going to have the range to do anything useful without drop tanks.



You have a very interesting view of history. Do you really believe those other types were not there in 1943? Some of those other types were already being replaced by aircraft with better altitude capability by 1943.

Another couple questions for you are: Would your hypothetical P-39N cruising at 30,000 feet be carrying a drop tank?
Would it be a P-39N with 120 gallons of internal fuel or only 87 gallons?
If it is NOT carrying a drop tank, then where would it be going at 30,000 feet where internal fuel would be sufficient for the mission?

Also, as GregP pointed out, just because an aircraft can get to 30,000 feet doesn't mean it can fight there. The A6M2 had a service ceiling somewhere between 35,000 feet and 38,000 feet depending on the information source but it most certainly wasn't a high altitude aircraft either.

- Ivan.

Double post.

 

[DerAdlerIstGelandet]

Sorry Fubar57, my stopwatch broke and I don't know.

I'll guess its better than the top speed of a Vespa, though ... the old 2-stroke Vespa, not the modern one fitted with emissions crap. Maybe the Vespa would win of you put an expansion chamber on it ... but where O where would you put an expansion chamber on a Vespa? That's the question. Maybe if you shaped it like a question mark?

That depends. Is that Vespa from 1942? When the war had only been going for a year?

 

[P-39 Expert]

Hello jmcalli2,

I referenced the report you listed because P-39 Expert was constantly claiming "40 MPH faster" when we were comparing the early P-39 and A6M2.
The P-39N was that fast in one test. Most references don't ist it as quite that fast.
As I commented recently, I am not claiming any version of the A6M was really particularly fast.

Regarding IIS 85, I am quite familiar. I have already quoted from it quite a few times.

- Ivan.

Attached please find a performance graph for the P-39K which had the same 8.8 supercharger gears as the P-39D. Also attached is a P-39D performance test. The numbers are virtually the same.

As you can see from the graph the top speed of the K model was 370mph up to 16000'. The A6M2 is commonly listed at 330mph at 15000' with speed falling off at higher altitudes at the same rate as the K. That's a 40mph difference at all altitudes.

The climb numbers on the chart and the report show that power was reduced from combat power (3000rpm) to normal power (max. continuous) when the 5 minute limit was reached. This limit was increased to 15 minutes in mid 1942, just after these tests. The red dots represent rate of climb at combat power 3000rpm. This closely approximates the A6M2 climb rate.

 

[XBe02Drvr]

This closely approximates the A5M2 climb rate.

Well of course, that was an open cockpit fixed gear monoplane of a little over 700 HP. Worthy opponent for the P39!

 

[GregP]

Vespa probably made from melted MC.200s ... or maybe melted CR.42s.

Oh, and ...

At 15,000 feet, the P-39D shows about 1,800 fpm on one curve above and about 1,550 fpm on the other, but I can't tell what the difference is between the curves … can't read the legend writing. The A6M5 Model 52 climbs at between 1,950 and 2,600 fpm at 15,000 feet in one report from wwIIaircraftperformance, so it outclimbs the P-39D handily at 15,000 feet, which is about the upper limit of where you'd want to fight the P-39D. The speed of the A6M5 Model 52 was anywhere from 300 mph to around 335 mph at 15,000 feet from the same report.

So, the P-39D, at full power might be able to slightly close or maybe slightly get away from the Zero but, when he DID close, the Zero would outperform him in climb and turn easily.

That is not a good place to be if you're flying a P-39D and the enemy knows you are there. At least, I would not want to be flying the P-39D in those circumstances if I had a choice. Might be OK if you are doing the ambushing.

 

[P-39 Expert]

Well of course, that was an open cockpit fixed gear monoplane of a little over 700 HP. Worthy opponent for the P39!

Thanks, I mistyped. Original corrected.

 

[P-39 Expert]

Vespa probably made from melted MC.200s ... or maybe melted CR.42s.

Oh, and ...

At 15,000 feet, the P-39D shows about 1,800 fpm on one curve above and about 1,550 fpm on the other, but I can't tell what the difference is between the curves … can't read the legend writing. The A6M5 Model 52 climbs at between 1,950 and 2,600 fpm at 15,000 feet in one report from wwIIaircraftperformance, so it outclimbs the P-39D handily at 15,000 feet, which is about the upper limit of where you'd want to fight the P-39D. The speed of the A6M5 Model 52 was anywhere from 300 mph to around 335 mph at 15,000 feet from the same report.

So, the P-39D, at full power might be able to slightly close or maybe slightly get away from the Zero but, when he DID close, the Zero would outperform him in climb and turn easily.

That is not a good place to be if you're flying a P-39D and the enemy knows you are there. At least, I would not want to be flying the P-39D in those circumstances if I had a choice. Might be OK if you are doing the ambushing.

Pardon me, I'm comparing the 1942 P-39s and A6M2. The A6M5 was later and should be compared to the P-39N of late 1942 early 1943.

 

[GrauGeist]

The A6M5 variant went into service mid-1943, supplementing the A6M3 that was produced between '42 and '43.

 

[P-39 Expert]

How fast did the P-39 climb with 300lbs of less weight?

300lbs lighter at 1.2fpm per pound would mean adding 360fpm to the values on the chart in my post #1006.

 

[fubar57]

"Would mean?" You're just guessing?

 

[DerAdlerIstGelandet]

300lbs lighter at 1.2fpm per pound would mean adding 360fpm to the values on the chart in my post #1006.

It his own factual method.

 

[P-39 Expert]

"Would mean?" You're just guessing?

Well, since I don't have my own personal P-39 that I can adjust the weight and test, yes I'm guessing.

The P-39C climbed 1000fpm faster than the P-39D. The C was 836lbs lighter than the D. 1000 divided by 836 = 1.2. The C and D were identical except for weight. Just guessing.

 

[Ivan1GFP]

Hello jmcalli2,

I was a bit busy earlier today when I was responding to your post, so I figured I go into a bit more detail now that I have a bit more time.

The problem the P-39 had in the PTO was in large part due to the USAAC being at the bottom of the learning curve in tactics and maintenance while the Japanese were experienced in both.
The Japanese had their logistics worked out, the USAAC did not.

The Japanese really didn't have any particular advantage in experience in terms of maintenance. Their types were just as new.
As for Japanese logistics, in some places it was pretty good. In places such as New Guinea, it was much worse than what the Allies were experiencing. The Japanese Army had it particularly bad. Anything past basic repairs needed to be shipped out because facilities did not exist in theater.

The P-39s were often sent up to intercept Japanese bombers flying at 20,000 ft. It would take 6-8 minutes for a P-39 to reach them, by which time the bombers would be gone. Meanwhile, the climbing P-39s would be bounced by A6Ms.

The biggest problem which P-39 Expert pointed out was that the early P-39 with a drop tank could not really get up past 17-18,000 feet. It also had very reduced performance past 20,000 feet even without a drop tank as noted from the IIS 85 Report you mentioned and I have quoted the section in a prior post.

Try reading P-39/P-400 vs A6M3 Zero New Guinea 1942 by Michael John Claringbould. It has some good combat accounts, some of which will say the P-39 and A6M were close in speed, some were the P-39 was faster, likely due to acceleration being close for the two aircraft. But the main reason to read the book is the in-depth look at combat records; the P-39 and A6M were even in the win-loss stats. That surprised me.

The P-39 had a speed advantage at just about every altitude. Sometimes it wasn't very large but speed isn't the only thing.
At low to medium speeds, the A6M in most models had a very significant Acceleration advantage. That is why the acceleration tests in IIS 85 were started at such odd speeds (generally only about 30-40 MPH below the maximum level speed of the A6M2).
When an aircraft is near its maximum speed, acceleration isn't going to be good.

As I see it, there are quite a few reasons why the Japanese pilots may not have done so well. Lack of communications and coordination is a major factor.

As for the A6M having a service ceiling of 35-38,000 ft, that didn't mean that it fought at that height.
Service ceiling means the rate of climb is 100 feet/minute.

I actually pointed out the same thing in a prior post when I commented that although the A6M2 had a service ceiling of 35,000 to 38,000 feet depending on the data source, that doesn't mean it was a high altitude fighter.

A6M performance fell off at 20-22,000 ft, like the P-39's did at 18,000 ft. That 2-4,000 ft made a difference.

This depends on which version of the A6M you are comparing. The A6M2 had a critical altitude of 4200 Meters which is not substantially higher than the early P-39 and performance past 20,000 feet was not so good. The A6M3 had a critical altitude in high blower of 6000 Meters (19,685 feet), so 20-22,000 feet was where it should have been performing best. Below that altitude, it was not as effective as the A6M2.

- Ivan.

 

[fubar57]

Well, since I don't have my own personal P-39 that I can adjust the weight and test, yes I'm guessing.

The P-39C climbed 1000fpm faster than the P-39D. The C was 836lbs lighter than the D. 1000 divided by 836 = 1.2. The C and D were identical except for weight. Just guessing.

So your numbers mean nothing then, just fluff.

 

[wuzak]

Well, since I don't have my own personal P-39 that I can adjust the weight and test, yes I'm guessing.

The P-39C climbed 1000fpm faster than the P-39D. The C was 836lbs lighter than the D. 1000 divided by 836 = 1.2. The C and D were identical except for weight. Just guessing.

Might need some more data points.

 

[wuzak]

At 30,000ft the P-39N had approximately 650hp at wide open throttle and 3,000rpm. That is War Emergency Power!

 

[windhund116]

Kanji 零戦 means Zero Fighter. "Reisen" is a contraction of Reishi Kikanjo Sentouki.

Reishi Kikanjo Sentouki