XP-39 and the Claims

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That looks like a 75 gallon steel tank - US manufacture.
 
GregP said:
You, me, or anyone else claiming something didn't happen is no proof one way or the other.
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But let's circle back to the beginning; who is claiming the XP-39 went 390 mph? That seems the logical place to start, since we can then look into their source material.

Otherwise.... as Wuzak says...
wuzak said:
You're looking for proof of something that didn't happen?
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A few books claim there is no documentation.

You do have the absence of documentation of any sort of rebuttal/complaint/argument from Bell to the NACA say to the effect "your wind tunnel says 340 mph, our flight test/s says 370-375 mph" let alone 390 mph.
We are not talking 5-10mph out of 400mph here , we are talking about a 50mph discrepancy. A 10-15mph discrepancy should have been able to be fixed fairly easily. Lower the canopy, fix (or at least improve) the radiator and oil cooler ducts and put some sort of adjustable outlets on the radiator, oil and inter-cooler ducts to limit airflow at high speeds.
 
Hi Admiral Beez,

When I look up the XP-39, the 390 mph is reported widely in many places. I didn't make the claim. In my library alone, it is reported by Ray Wagner in American Combat Planes and several others. Personally, I doubt the XP-39 went 390 mph on test flights, but I have no proof of it one way or the other. So, if you want to claim it didn't, the burden of proof is not on me to defend the published 390 mph claim that I didn't originally make, the burden of proof is on you and anyone else who wants to claim it didn't go that fast to actually refute it.

Either you doubt all the figures in these often-quoted references or you are cherry-picking the XP-39 to make a point for some agenda of your own. Making calculations from assumed numbers does not refute it. Who is to say how good your numbers are? You could get a 100% representative scale model in a wind tunnel, make it go 390 mph at 20,000 feet, and then extrapolate the horsepower required to do that, and compare the result with the Allison V-1710 installed or something similar.

Failing that, you are just like me, a person who doubts it went 390 mph but has no proof of same. To me, that seems like a lot of effort to lay to rest a claim made for ONE airplane that never saw combat. There were no other P-39 airframes that had the turbocharger system installed. I am unwilling to invest even $1 to refute a claim for one prototype airplane when there is no point in doing so. It is not particularly important to me or anyone else in here because it has no bearing on WWII since the turbocharged P-39 was not ever produced. In fact, it didn't even survive in turbocharged form; the XP-39 flew as the XP-39B without a turbocharger system installed. I like the unique looks of the P-39, but am not really a huge fan of the P-39 in any guise. I actually get to see the occasional P-63 in a Planes of Fame airshow, but I have only seen a P-39 fly twice. It was good to see one fly, but I am still not a huge fan of the type, likely due to early childhood impression that it wasn't very good. In point of fact, it WAS quite good below 12,000 - 15,000 feet. It just wasn't very good as a fighter above the mid-teens.

Good luck in your quest to find the truth. I have only seen published support for the 390 mph claim in my time of some interest in WWII planes, which is around half a century. I have seen the claim questioned in here, even fairly well questioned. But nothing that proves it never happened to me. So, while I am firmly in the corner of the people who doubt the 390 mph claim for the XP-39, I also do not have proof of it. Inserting a picture and saying, "just look at it, it could not go that fast!" doesn't cut it. Simply stated, I want proof it didn't go that fast because there are published claims it DID go that fast. Refuting them beyond a doubt goes WAY beyond someone saying it didn't happen because they say so.

Generally, I solve the proof problem by not bringing up the XP-39 speed claim in casual conversation. In my lifetime, including almost 15 years as a volunteer at the Planes of Fame Museum where we DO talk about WWII fighter planes often, nobody has ever brought up the 390 mph claim out of the blue. Not discussing it means that, for me, it has never come up before anywhere but in this forum. It isn't a problem I need to solve. But I would love to see it laid to rest with some proof that I can point to and say, "There, that proves it!". Until then, I doubt the 390 mph claim, but I cannot state exactly how fast it went from any personal knowledge.
 
If you go back to books/magazines/newsreels published in WW II (especially in the first few years) you can find all sorts of quotes or references to things like 400mph P-40s (and the 700mph dive speeds) which wound up repeated in a number of early post war books. Even William Green has had a number of his "facts" questioned and corrected over the years. Like the 109Ks with a pair of 15mm MG 151s in the cowl. Which has been repeated in other books by other authors and on may internet sites.
Also the number of "nicknames" that Axis troops were "supposed" to have called Allied aircraft because they were so terrified of them has been shown to be pretty much propaganda.

Bell lied about how fast the P-39 was to get French and British contracts. They had to specially modify a plane to get through an acceptance test. Why is it so hard to believe that somebody at Bell put out the 390mph figure as advertising/propaganda?

We have this chart:
http://www.wwiiaircraftperformance.org/P-39/P-39C_Chart-Bell_Aircraft-1400.jpg

which is dated 10-29-39 and "checked" on 2-7-40 and while it does say "plotted from tables" it does NOT say "estimated."
The XP-39 did not makes it's first flight until 11-25-39 (nearly a month after the date on the chart?) and that was a 15 minute flight.

The chart is supposed to be for a P-39C but a P-39C won't fly until Jan 1941. So obviously that chart was nothing but estimates.

Many of those authors were just going by common knowledge or what others had written. It was the best information they had at the time.

as for

GregP said:
Inserting a picture and saying, "just look at it, it could not go that fast!" doesn't cut it.
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go back and read the posts. Claiming that the P-39N went XXX speed using about the same amount of power and therefore PROVES the XP-39 could have done it doesn't cut it either as the two planes had very different drag numbers as a result of their different configurations,

Part of the contention is not about one airplane that never saw combat, it is about the often made claim that the NACA and AIr Corp Generals/officers Ruined the P-39 and the US could have had a much better fighter and done much better against the Germans and Japanese in 1942/43 if it wasn't for the stupidity of the NACA and those Air Corp officers.
 
Once again, you completely miss my point. I don't care either way if the XP-39 went 390 mph or not. It did not affect WWII and it was only one airplane. A calculated plot is an estimate of performance, not a test, and the P-39C is not the XP-39.

It is NOT hard for me to believe the XP-39 never went 390 mph. In fact, I believe it did not. What I lack is any proof either way. I have never seen an actual plot of the XP-39 flight performance speed envelope, but I DO have several references that make that claim.

But I will not jump on the bandwagon of saying something and ignoring the scientific method. To follow the scientific method, you ask a question, do background research, form a hypothesis, test your hypothesis with an experiment, analyze your data and draw a conclusion, and communicate your results. By "test your hypotheis," I mean disprove it. The statement might be, "The XP-39 went 390 mph in 1939." Can you disprove it? I can't. The method is NOT to state what you want and show some data supporting it. The method is to state something you don't believe and disprove it.

So far, all I see are people making a hypothesis statement that the XP-39 did not go 390 mph. I don't see anything resembling a test of the hypothesis and I especially don't see any analysis of the results or communicated results. All I see is speculation. Good in itself, but hardly conclusive.

And this ain't philosophy. We are talking about hard engineering facts. An opinion won't change what actually happened. It is difficult to find original XP-39 data either way, but very easy to find data that support lower speeds for non-turbocharged airframes that weren't the XP-39. I've never seen a production test of an actual P-39 that exceeded 400 mph in level flight, but I've seen NO DATA about actual XP-39 test flights. I HAVE seen some NACA wind tunnel reports on the XP-39 that may or may not be in the same configuration as test flown by Bell.
 
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P-39 Expert said:
And I still don't consider escort missions to Holland, Belgium and a sliver of France to be meaningful. Not when your main target is Berlin.
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What? Huh? Seriously?

So why is Berlin the only meaningful target? You do realize that the majority of strategic targets are not in Berlin right? You've got factories, munitions plants, ship yards, strategic materials, rail yards, stock yards, etc. from the French Coast to Berlin and back. I guess we should not have been bombing those meaningless ball bearing factories and steel mills hundreds of kilometers from Berlin. All those boys died on meaningless missions.

Sorry, but good thing you are an armchair general like the rest of us. Otherwise we would still be bombing Berlin today, while they keep building tanks, planes and munitions in France, Belgium, Netherlands, Stuttgart, Wilhelmshafen, Aachen, Franfkfurt, etc.
 
75 gal US Steel tank, then two 108 gal impregnated paper British tanks ~~ November/December 1943 for the P-47 shots.
The P-51B w/75 gal tanks used the same tanks as the P-47D tanks - combat tanks from US manufacture. The 355th Tank Farm gives a better perspective of rounded cigar vs tear drop design between 75gal and 108/110 gal tanks.
 

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How much does a 110 gallon drop tank weigh? I have gas weighing in at 6lbs per gallon so a 110 gallon drop tank would be 660lbs plus the weight of the tank. A little over the design of the P-39
 
pbehn said:
Holland and Belgium contained the Kammhuber line and airfields that protected the industrial area that is little more than a stones throw over the border. View attachment 579237
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Short rounds point is that the goal wasn't to bomb Holland into submission it was to bomb Germany. A fighter that can only escort to the edge of Germany is inadequate, as was proved in reality. The Spitfire is constantly castigated for this failing.
 
Reluctant Poster said:
Short rounds point is that the goal wasn't to bomb Holland into submission it was to bomb Germany. A fighter that can only escort to the edge of Germany is inadequate, as was proved in reality. The Spitfire is constantly castigated for this failing.
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Well yes, but you do what you can with what you've got, the Spitfire Mk IX was only castigated because of its range when aircraft with similar performance and longer range were available, up to that point it was used to B-17s on raids. If you take airforces out of it, there was a learning process by all involved, improving bombers and fighters, range and load and defence and function. Even if you just want to bomb Germany you have to drive air defence out of North France Belgium and Netherlands to maximise the number of routes into Germany, but as per my previous post the Ruhr area was a centre of German heavy industry and actually has more people than Berlin.
 


How do you prove that something didn't happen?

If you have documentation of test flights, or such, you can prove that something did happen. What documents spell out that something didn't happen?

It is impossible to prove that the XP-39 didn't go 390mph. It is only possible to prove that it did, but no direct evidence exists of that fact, as far as we are aware.

It is reasonable to conclude that the XP-39 did not go 390mph based on the lack of evidence that it did, and that the airframe was taken to NACA for remedial aerodynamic work a few weeks after first flight - the USAAC probably would not authorize that for a 390mph aircraft in 1939.
 

Well, lets see, we have.

1, no test report the XP-39 did fly 390mph.
2. reports of continued oil overheating and/or high temperatures causing at least one flight to be cut short.
3, At least one report of high coolant temperatures.
4, reports or accounts of modifications done to oil and radiator ducts. Which did not solve the problem
5, accounts of how the AAC wanted a new drive shaft installed in the plane because of vibration problems or worries if the engine misfired. Until new drive shaft was fitted engine rpm was restricted to either 2600or 2700rpm. The New drive shaft was not fitted until after the plane went to Langley. No full power flights?
6 time available.
a, first flight April 6th, 15 minutes.
b 2nd flight April 7th cut short due to oil temp
c. 3rd and 4th flights on April 22 total 47 minutes.
d 5th flight April 23, Nose wheel fails after manual lowering of landing gear, 1 hour 40 minutes total flying time in 5 flights.
e. accounts do not say what flying or tests were done in May of 1939. could have been some.
f. Plane is delivered to Langley on June 6th. After arrangements made at the end of April.
7, Langley claimed that the oil cooling problem was resolved or minimized during initial flight tests by using a higher drag duct than originally fitted.

So, if the XP-39 did do 390mph or anywhere near to it it had to be done in May, (none of the April flights were long enough to get to 20,000ft, do a high speed run and get back down on the ground again.) with a high drag oil cooler duct, a radiator that had problems (like at 350mph the radiator was supposed to have 16,900 cubic ft of air going through but only 10,250 cu ft was needed to cool the engine) and the engine was limited to 90% or less of rated rpm, unless the pilot disobeyed instructions.

I can't prove the XP-39 didn't hit 390mph but the chances of it are pretty slim. And if it hit 390 mph with all those problems it should have been a real rocket once they got fixed.
 
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