XP-39 and the Claims

[Reluctant Poster]

According to Bodie, the tests at Eglin were conducted by AAF.

Bodie makes a lot of unsubstantiated claims in his book. According to this report the tests were by Lockheed.
http://www.wwiiaircraftperformance.org/p-38/P-38J_performance_11march44.pdf

 

[Reluctant Poster]

Varsity - you REALLY need to pick up some good books about Fw 190 - there are tons of Internal (to the wing as defined below) four gun 20 and 20/30mm combinations from variances of the A-5 all the way through Fw 190D. The Fw 190 A-7 and A-8 variants had more internal firepower on board than any primary Allied fighter with 2xMG131, 4xMG151 - all under the skin - before adding pods- and before swapping a Mk 108 for MG 151/20mm.

What they sacrificed was range when compared to say a P-51-1-NA with 90 gal fuel cell in each wing.

You seem hung up on the definition of wing root versus wing. The Root Chord, wing root (as defined by the fuselage-wing interface) and the wing all the way out to the tip. Anything from the wing tip to the wing root chord is part of the wing. Any gun mouted internally between the upper airfoil surface and the lower airfoil surface is internal to the wing.

Here is an excellent illustration of some of the permutations of FW 190 armament
https://forums.eagle.ru/attachment.php?attachmentid=111393&d=1421221687

 

[fubar57]

Thank you for that

 

[drgondog]

I realize the K was not operational. I don't think it was ever contemplated that P-51 production should be halted, even though Bodie says the K tested a Eglin showed superior performance to the P-51 and P-47. The extant of the performance advantages of the K is probably a moot point considering it was still powered by an Allison that didn't like Northern Europe, had compressibility issues and a cockpit that was a nightmare for an inexperienced pilot.

Bodie was very much in love with the P-38. First the P-38K had a rate of climb from SL to 25000 feet that was greater than a combat loaded P-51B-1 or -5. That said, the flight tests of the P-51B-5-NA at 8500 pounds (versus 9100 fully loaded internally before the 85 gal tank was installed) was between 4300 fpm @6500 feet at 67" and 4600fpm @3500ft and 75" - With draggy wing racks and over 2000 fpm at 30K - which was more than K or J.

 

[varsity07840]

Biode makes a lot of unsubstantiated claims in his book. According to this report the tests were by Lockheed.
http://www.wwiiaircraftperformance.org/p-38/P-38J_performance_11march44.pdf

Pretty convincing.

 

[Reluctant Poster]

Here is an excellent illustration of some of the permutations of FW 190 armament
https://forums.eagle.ru/attachment.php?attachmentid=111393&d=1421221687

FW-190 A-6

 

[Reluctant Poster]

View attachment 578409

FW-190 A-6

Another one from
File:Fw 190 weapons arrangement.jpg - Wikimedia Commons

Note the Oerlikons in the outer positions

 

[Reluctant Poster]

Shortround alluded to the variety of blends that constituted 130 fuel. The attached paper clearly shows the immense number of base stocks used to produce 130 and the different proportions of various blending agents required to meet the 130 rating. Note that cumene, toluene and xylene are all aromatics.
The F-3 test was for lean mixture, while the F-4 test was for rich mixture.
I was confused at first but realized that a rich mixture rating of S+1.25 is the same as a PN of 130.

 

[jmcalli2]

The P-39N used a different radiator duct set-up, it used a different oil cooler, it had no intercooler and it no turbo hanging out the bottom. Plus the lower canopy and few other minor tweaks? The XP-39 had a much larger drag coefficient.
Claiming that the P-39N could do nearly 400mph with about the same amount of power as the XP-39 had so the Xp-39 should be almost as fast disregards these large differences in drag between the two airplanes.
The claim of 390mph in the time before Langley also disregards the chronic cooling problems the XP-39 had, both engine coolant and oil coolant.
The claim of 390mph in the time before Langley also disregards the documented problems with drive shaft that lead to a restriction on maximum RPM.
It would also make a complete lie out of the chart prepared by Langley showing the estimated speeds of the XP-39 as received, as modified by Langley keeping the turbo charger and as modified using the altitude rated non turbo Allison.
This chart indicates a max speed of 340mph at 20,000 with the speed dropping off towards sea level till it drops to just under 280mph.

If the XP-39 had gone anywhere near 390mph (or even 365mph) somebody could have told Langley "your wind tunnel/calculations are wrong and here is the proof".

Langley did estimate the XP-39 could have reached about 390mph at 20,000ft AFTER the modifications suggested by Langley were implemented. Modified radiator duct, modified oil cooler duct, modified intercooler, lowered Canopy, etc.

http://www.wwiiaircraftperformance.org/P-39/P-39N_level-speeds.jpg

 

[GregP]

Regarding post #81, Shortround, I mainly agree with your data except for the timeline.

I have seen original Allison correspondence regarding the aromatics via a friend who overhauls Allisons, and they fixed the jetting rapidly after they got some 20% aromatic fuel delivered to the factory. Before that, the issue could not be duplicated on the test stand, and they were scratching their heads because the engines were running fine in test. I regret to say I don't recall the date of the document because, at the time (some 8 years ago), it wasn't of any import to me as I was just trying to establish the facts.

The issue with lead separation in the intercooler did not happen exactly coincident with the aromatics and is a separate issue from the ethyl aromatics added to the fuel. It was about the increase in lead. Yes, it took some time to address, even partially.

I call it "British fuel" because the 8th Air Force P-38 fuel tanks were filled with fuel on airfields in Britain. I really have no idea of the source for the bowser trucks that fueled the P-38s and I hazard a guess you likely don't either. Could be U.S. supplied, could be supplied by Britain. But they didn't fill them up in the U.S.A. and then magically transport the P-38s to Britain. And the freighter convoys did bring fuel, to be sure, but they were mostly trying to stop Britain from starving. I imagine Britain supplied a lot of fuel to the early U.S. aircraft based there while we supplied a lot of food and other war material, at least early on. Regardless of the source, the P-38s were fueled with different fuel than the engines were run-in with back in Indiana at Allison, causing one major problem for the early P-38 squadrons until somebody thought to send a fuel sample to Allison consistent with the fuel actually being run in the field. When they DID send some and it was tried on the test stand, the issue showed up immediately. It is WAY easier to troubleshoot a problem when you can duplicate it in a running test engine than when you can't. You can't imagine they'd investigate a problem if the problem had not been reported, and there were some months where Allison simply could not replicate the engine failure problems because they were running fuel supplied locally and it ran fine on the test stand.

The date when U.S. fuel first had the aromatics bumped from 2% to a lot more is not the date when that reformulated new fuel started flying in combat. It is also not the date when someone thought to send some of it to Allison Engines in Indiana.

When they made new airplanes, they didn't show up in Europe right away. It took some time for them get built and accepted, get to training bases for pilots & mechanics, get some pilots & mechanics trained, and then prep the aircraft and personnel for transport and, finally, get all to Europe. When they got there, they weren't in combat immediately. They still had to work up to operational ready status on the new type.

Likewise, when they made new fuel, they didn't send it immediately to combat with the P-38 units. They'd first have to make it, run a preliminary test, transport it to a test unit, test it in service with the test unit, and then issue some to stateside units flying the P-38. If it performed well there (not always a given), then it could likely commence the process of being sent overseas, if enough was available for that at the time. I doubt very seriously that the fuel was allocated to P-38s in Britain as a first step in the distribution process. They were flying a LOT more P-38s elsewhere in North Africa, Alaska, the South Pacific, and in Conus units than they were in the UK at the time. When has the military EVER made the correct decision to deploy something to just the right place at just the right time? I'd say close to never. The closest I can think of prior to 1960 is when we got surprised in Korea by the MiG-15 and sent over some F-86's to Japan pretty quickly to be competitive. Prior to that, the military wasn't known for cutting-edge thinking and action in the logistics / deployment chains. It was much more of a case of "it'll eventually get there."

I've been posting about Allison engine and general P-38 issues for more than 10 years and have covered much of it many times in the past to little or no comment except for some nitpicking about details. In fairness, some of the nitpicking was correct, but usually ignored 95% of the post data. I could stand to review the P-38 timeline with the 8th Air Force if I want to talk about that subject other than from memory. But early use of the P‑38 in the ETO did see fuel-related issues, the early Allisons sent there did have manifold / intercooler issues that included both mixture problems and lead-separation, and they did have issues with freezing boost regulators and poor cockpit heaters. It took some time to get the factory informed of the issues, replicate them in test, come up with a fix, get them tested, get them into production, and then get them to the front lines. Nothing was overnight unless it was sitting on a counter waiting to be used. Unlikely at best.

The P-38J-25-LO and later models didn't really HAVE issues to speak of. The P-38J's were first delivered in fiscal year 1943, around September, which is not too far past when we started flying the P-38 overseas. But I doubt they got many to operational combat units before late 1943 to early 1944, particularly the P-38J-25-LO. It likely didn't hit actual combat service until mid-1944 or later. About the time the P-38 got "fixed," Doolittle had them drawn down in the ETO and by sometime in fall 1944, there was only one unit flying PR P-38s in that theater. Early J models were still seeing some fuel issues according to many sources.

The P-38J-25-LO and L engines ran well, the airframes had factory-fitted dive flaps so they could dive after anything without fear of not being able to pull out, they had hydraulic ailerons, they out-turned most of the opposition when flown in the correct part of the envelope, they had electric cockpit heaters, and they were being run on fuel that was anticipated by the engine factory. Were they perfect? No. By that time, there were newer, faster aircraft being flown by the enemy but, if they tangled with a competently-flown late-model P-38, it wasn't an easy fight by any means, and they flat weren't going to climb away from a P-38 very often.

None of this detracts from the fact that early P-38s (D, E, F, G, H) were basically not combat-ready as deployed and doesn't erase the issues that were experienced. I am not glossing over the problems that were seen. I am saying they were corrected in due time, but more time than users of the P-38 and even Lockheed were happy with. The only real timeline for correcting problems that users are satisfied with is immediately.

Lockheed did send Tony Levier over to Europe to show the service pilots that the P-38 wasn't a hard airplane to fly when flown by a pilot familiar with it. But that was in 1944, later than the early P38 escort period.

Your post #81 has good information in it as most of your posts do. But I am not sure your timeline as stated is exactly the way it went in the war. Might well be the timeline for when fuels were initially formulated, but lab fuel in a test beaker and fuel in the tanks of combat aircraft are two different animals.

Of course, my timeline could be a bit off, too. I confess I pay much more attention to the aircraft themselves than to the war itself, other than collecting data about it from recognized sources. Not saying you are wrong, Shortround, but perhaps your timeline isn't exactly spot-on, either. The issues I brought up were real according to many sources and the pilots who flew them. The exact timeframes may be plus or minus some months.

 

[Shortround6]

http://www.wwiiaircraftperformance.org/P-39/P-39N_level-speeds.jpg

And your point is???????
read what I wrote please, read the link/s to the Langley report.
and look at pictures.

XP-39 left side.

Large scoop for intercooler. balanced by a large scoop on the right side for the oil cooler.

Then you have the turbo and 4 waste gate pipes hanging out the bootom

And you have an incredibly lousy radiator set up in the wing. Outlet can be seen in top photo interrupting the port wing walkway. There was no adjustment for either the intake or the exit to control airflow, turns of the duct inside the wing were sharp and structural members obstructed airflow.

The tall canopy may have been the least of the aerodynamic problems.

It doesn't matter what the P-39N did (or any other model of the P-39) if these later versions had 2/3s the drag of the XP-39. In fact it only confirms the XP-39 could not have done what is claimed.

 

[Shortround6]

An old P-39 thread with a lot of pictures from the XP-39s time at Langley.

Bell P-39 Airacobra

edit, sorry guys, I forgot to say go directly to page 6.

Original coefficient of drag 0.0321

Coefficient of drag of a P-39 0.0217 from America's Hundred Thousand. I don't know where the Author got them.

The NACA spent a lot of time on the XP-39 trying different radiators, oil coolers and intercoolers. See the pictures so kindly provided johnbr.

 

[Zipper730]

Original coefficient of drag 0.0321

That would be this design...

Okay, so the intercooler is on the right side, the oil cooler is on the left side, with the radiator in the inboard left wing-root, with the airflow exiting out the top side of the wing? What are those small ports/scoops located just below the intercooler/oil-coolers, and the vents located next to the engine do?

Coefficient of drag of a P-39 0.0217 from America's Hundred Thousand. I don't know where the Author got them.

Which would be the upper image here. It looks like they were trying to refine the cooler scoops, and the covering of the turbocharger. What's the typical coefficient of drag for the P-40D/E, the Spitfire Mk.V, and P-38F come out to?

This figures seems pretty close to the V-1710 with 9.6 supercharger, but not the improved radiators operational aircraft and the top intake. It seemed the primary issue here was the fact that they 9.6 supercharger didn't work.

GregP , P-39 Expert

 

[Reluctant Poster]

The Bad British Fuel Myth was originated by Warren Bodie in his book "The Lockheed P-38 Lightning". Since the advent of the internet it has taken on a life of its own with various posters adding embellishments of their own such as "the lead was separating out in the fuel" "the fuel in the UK had a higher aromatic content" and other unsubstantiated statements.

The actual quote from Bodie is: "Gasoline available in the MTO obviously came from a different source, probably direct from the U.S.A. And it is well known fact that fuel in the United Kingdom was of poor quality. If you remember that the Allisons were not turbocharged in any fighters except the P-38s and that no Merlin had such supercharging, it becomes rather evident that fuel quality could easily have been one of the most important culprits."
"It is the authors opinion that British fuels furnished to the eighth Air Force were improperly blended at the time and the tetraethyl lead compound was separating out from the gasoline in the Allison manifold."

That's it, all pure speculation with no footnotes or historical references, nothing to back it up. In fact I have yet to see a shred of evidence indicating the fuel in the UK was of any lesser quality than elsewhere. There is however plenty of evidence to show that there was no significant difference.

It is instructive to note that the definitive book on the Allison "Vees for Victory" by Daniel Whitney does NOT mention Bad British Fuel anywhere in its text.

A good discussion of Britain's avgas supplies is presented in "Britain War Machine" by David Edgerton. There is a chapter that discusses Britain's sources of supply in some detail. As he notes "By the middle of the war nearly all of the aviation spirit, indeed nearly all the petroleum products, were to come from the USA"

Another good source is the Army Air Forces Historical Studies No 65 "Aviation Gasoline Production and Control which states:
"In addition, the British were asked to alter their fuel specifications to meet those of the U.S. Air Corps and Navy." (Dec 1941)

But let's ignore that, in the spirit of the underlying theme that the British were incompetent buffoons that couldn't do anything right, and assume their gasoline was inferior. That brings up the question of how much British fuel was there. The answer is: not much.

More than 85% of all high octane (or PN if you prefer) gasoline produced by the Western Allies (ie not including the USSR) was produced in the continental USA.
Before World War II the British had no oil industry to speak of. In 1938 (the last full year before the war) the only source of oil indigenous to the UK was Scottish shale oil, of which a total of 128,000 tons was produced. This represented 1.3% of the UK's total needs. In other words more than 98% of her oil was imported, making her the world's largest importer of oil by far. It should be noted that all shale oil was refined at the small refinery dedicated to the shale oil industry at Pumpherston in Scotland. This refinery did NOT produce avgas.

In 1939 Britain's first commercially viable oil field was discovered in Duke's Woods. Efforts were made during the war to develop these fields developed such that the total amount of UK oil produced had doubled by 1943, however demand had increased as well so UK contributions were still a drop in the bucket. Initially this crude oil was refined at Pumpherston, but later it was sent to the small Ellesmere Port lube oil refinery. Note that this refinery was also not equipped to produce avgas. In other words no avgas was produced using indigenous UK oil.
"The Production and Refining of Indigenous Oil in Britain" by B S Hoyle describes the history of the British oil industry prior to the discovery of North Sea oil. To get an idea of how insignificant UK production was, interesting to note that the UK oil fields produced about 3.5 million barrels of crude for the entire war which pales into insignificance when you realize the US was producing 3.8 million barrels A DAY in 1941.

Furthermore; in 1938 Britain was importing the majority of its oil as finished product. Half of the imports were in the form of what the British term motor spirit and aviation spirit (gasoline), a quarter in other refined products such a kerosene, diesel and fuel oil, with about a quarter arriving as crude oil.
There were only a 13 refineries in the UK ( vs ~400 in the US), 7 very small ones specializing in products such as bitumen (asphalt) and lube oils, the previously noted plant at Pumpherston and 5 larger ones (still small by US standards) relying on imported crude oil from Venezuela, the US and the Middle East. It is interesting to note that after the entry of the US into the war Britain actually shut down more than half of its refining capacity. Refinery throughput sank from 2,400,000 tons in 1938 to 908,000 tons in 1943!
Britain realized the importance of high octane avgas (PN of 100 or more) and placed a high priority on it. Since the British had no supplies of their and felt they could not rely on the neutrality leaning United States to sell them oil in a future war, they set up contracts with refineries in Aruba (Standard Oil of New Jersey), Curacao (Shell) and Trinidad using Venezuelan (and some Trinidad) oil. In addition the Anglo Persian Oil company (now BP) upgraded their large refinery in Abadan (Iran) and Shell added avgas capacity to their refineries in the Dutch East Indies.

Only one of the refineries in the UK was upgraded to produce 100 octane fuel (Stanlow). In addition 2 hydrogenation plants were built in the UK. The plant at Billingham used the same Bergius process used by the majority of German synthetic oil plants with one important difference; by the beginning of World War II it had switched from coal to creosote as its feedstock. The plant at Heysham hydrogenated gas oil (gas oil is the heavier faction produced by basic refining) that had been produced at the refinery in Trinidad. A planned third plant was canceled in favor of more US oil with the equipment shipped to Trinidad instead. Stanlow also used gas oil from Trinidad as its base stock.

After the US entry into the war there was a rationalization of the transportation of oil supplies to reduce the pressure on the limited number of oil tankers, many of which (approximately 10% of the fleet) had been quickly lost because of the US Navy's refusal to adopt the convoy system on the US east coast.

From "Aviation Gasoline Production and Control":
"For the sake of efficiency in distributing the insufficient supply, it was decided to allocate to the AAF the output of the Curacao and Trinidad refineries. This production was considered as a unit with the US Gulf Coat plants so as to relieve tankers for the Atlantic and Pacific ocean transportation. Thus arrangements were made to supply the AAF at Ponce in Puerto Rico and Jamaica from Curacao."

The Japanese graciously took the output of the Far East refineries, while much of Abadan's went to the USSR with the rest used in the Middle East and the CBI theater.

The 5 refineries producing avgas in the north east (Philadelphia, Linden NJ and Baltimore) were the closest supply to the UK but lost their source of crude oil from Venezuela. To compensate former product lines to the west were reversed to import crude from the mid-west. In addition, every oil tank car was gathered up and placed into dedicated trains transshipping Texas and Oklahoma crude to these refineries and barges were seconded to this service. The ultimate solution was to build the Big Inch Pipeline (completed August 1943) to transport the crude, but even this was not enough resulting in the construction of the Little Big Inch specifically to expedite the transport of finished product (primarily avgas) produced in Texas and Louisiana to the UK.

In 1944 the three UK plants produced approximately 3% of the Western Allies high octane production. Due to the combined bomber offence, the UK was by far the largest consumer outside of the continental USA, taking about 27% of the Western Allies production (again not including the USSR). This means less than 15% of the Avgas consumed in the UK (by both the RAF and USAAF) was produced in the 3 UK plants. In other words, the British couldn't begin to meet the RAF's needs, let alone supply the USAAF. Note that in late 1943 and 1944 Billingham was producing 150 PN which was never used in P-38s.

As noted in "Army Air Forces in World War II" by Craven and Cates Volume 2

"Virtually all of the gasoline used in the United Kingdom from 1942 to 1945 came from American sources. The British were responsible for gasoline supply to the Middle East and China –Burma –India theaters."




If British avgas was somehow "bad,' and there is not an iota of evidence to support this, the P-38 only had a 1 in 7 chance of receiving it. Judging by the enormous numbers of V-1710 failures someone must have been making a special effort to ensure the P-38 units were fueled exclusively with it.

To get an idea of the production imbalance in favor of the USA download the document "Official Munitions Production of the United States By Months, July 1, 1940- August 31, 1945" which contains a table showing the month by month production of avgas in the US as compared to foreign production. Official munitions production of the United States by months, July 1, 1940 - August 31, 1945. :: World War II Operational Documents
By the way, there's a lot of other fascinating material in this document.

In any event the basic premise of Bad British Fuel as the cause of the Allison failures is bogus. The Allison's problems were NOT limited to the ETO. This part of the myth was debunked by Daniel Whitney (author of Vees for Victory, the very comprehensive book on the V-1710) in the in his article "The Allison Time Bomb" in Volume 1 Number 2 of the "Torque Meter"
"Not long after the introduction of the P-38J pilots in all theaters began experiencing unexpected and sudden failures of their engines."


"The entire topic is further complicated because of the common impression that the failures occurred only in the ETO, so the problem "must have been poor quality British fuel" or the "low temperature at the high operating altitudes over the Continent."

He goes on to describe in some detail the problems experienced in the CBI.

The mode of failure was consistent. The outer most cylinders (1 and 6) received too rich a mixture, while the inner two (3 and 4) received too lean a mixture. The result was a failure of number 3 and 4 cylinders. This is can only be attributed to a flaw in the design. Looking at the intake manifold it is easy to see why. The air/fuel mixture has a straight shot into the number one cylinder while it has to make an abrupt 180 degree turn to reach the number 3 cylinder. The heavier than air fuel will tend to keep going in a straight line thus robbing the inner cylinders of enough fuel to avoid catastrophic consequences.

Due to the flow split and the two very tight elbows that I mentioned in a previous post, the fuel was separating out and pooling in the intake. This phenomenon was studied by the SAE in 1914! (the SAE paper is attached).

By the way the "Madame Queen" manifold is not a "turbulator" or a flow straighter (two diametrically opposed concepts) it is a second carburetor which uses its venturi to draw up and re-vaporize the fuel that has pooled at the bottom of the intake.

It should be noted that while the Allisons were blowing up at an incredible rate the RAF was at the same time engaged in the Battle of Berlin and as a consequent Merlins were flying thousands of sorties (>10,000) in four engine bombers to greater ranges without any reports of excessive failures. Not to mention the large numbers of sorties flown by R-1820s, R-1830s, R-2800s and V-1650s flying similar missions in that time frame. Applying Occam's Razor leads to the conclusion that the fuel wasn't at fault.

The venturi manifold was not designed in response to the crisis in the UK. The manifold had already designed and entered into production before the P-38 flew any missions over Germany. The first engines equipped with the new manifold were accepted by the AAF on November 28, 1943 at which time P-38 had only flown 7 missions over Germany and had only suffered 7 losses in total. Allison knew they had a problem before the P-38s went to the UK. As Dan Whitney notes "Allison had previously realized that operations in very cold conditions were causing fuel condensation and so had introduced the new venturi gas pipe as a fix late in the fall." (fall of 1943) . In Vees for Victory there are references to experiments being conducted on Allison engines in early 1943 to improve manifold design. As noted in this book the history of the development of the V1710 is a constant struggle to fix its fuel distribution problems. In fact the book states that the venturi pipe was designed as far back as December 1939 in an unsuccessful attempt to solve the even worse fuel distribution problems of the V-3420.

The fact that Allison had to resort to such a power robbing device shows how serious the problem was. It's ironic to note that at the same time that Rolls Royce was concentrating their efforts on cleaning up the intake tract to reduce pressure loses and therefore free up wasted horsepower, Allison was headed in the opposite direction cluttering up their intake with a loss inducing device such as a venturi.

Meanwhile, as Whitney notes, in January 1944 Lockheed instituted an accelerated test program on the opposite side of the earth in sunny, warm California. "The Battle of San Fernando Valley". The 3 P-38J-15's involved blew up 14 engines! At least 2 of these had the venturi intake. It should be noted that air temperature at 25,000 feet is just as cold over Southern California in the summer as it is in England in the winter. It's always cold at 25,000 feet, and any design that doesn't take that into account has failed.

In summary:

1. The amount of bona fide British oil was insignificant.
2. What relatively small quantities of British avgas that were produced met the same specifications as all avgas.
3. The P-38 suffered problems all over the world.
4. The problems had surfaced well before P-38s flew any missions over Germany
5. As noted in a previous post, aromatics were added to US produced avgas in order to increase production well before the Allison started blowing up over Europe

 

[drgondog]

An old P-39 thread with a lot of pictures from the XP-39s time at Langley.

Bell P-39 Airacobra

Original coefficient of drag 0.0321

Coefficient of drag of a P-39 0.0217 from America's Hundred Thousand. I don't know where the Author got them.

The NACA spent a lot of time on the XP-39 trying different radiators, oil coolers and intercoolers. See the pictures so kindly provided johnbr.

Hi Steve - I actually devote a lot of words re: Drag (surprise) in the new book. The Comparison table that I extracted was from NACA Advanced Confidential Report ACR L5A30, Roy Lange, February 1945, Pg 11. The tests were at the full scale wind tunnel at Langley for the P-40, P-38, F4F, F4U, F6F, P-63 and the P-51B. All a/c as received at Langley in stock condition. All inlets, exhaust stacks, gun ports, and Props removed - than added back one component at a time to obtain the Service Condition drag values.



The tests were run at 100mph at Sea Level and if you pull the Report you will see the slightly different RN due to the differences in Mean Aero Chord length of each wing.

NACA tested the P-63 which is cleaner than the P-39 due to the newer Low Drag wing = 0.0210 (vs 0.0209) of the P-51B for the UN-SEALED condition. After running 'unsealed' the respective values were 0.0171 vs 0.0173 - Note in propeller-less environment the advantage of the Meredith effect reduction to the drag of inlet scoop and flat plate effect is absent for the P-51B. This shows the nice aerodynamics achieved with the new wing and fuselage for the P-63.

For the casual viewer the relative CDtotal in Service Condition for P-40=0.0257; P-38=0.0293, F4F=0.0328, F4U=0.0284, F6F=0.0293, P-63=0.0210, P-51B=0.0209 (without benefit of cooling thrust obtained to offset the internal drag).

ADDED NOTE - after looking at Johnbr's excellent supply of XP-39/P-39 images, the CDhs I believe is the Total Calculated Drag Coefficient at the RN for the altitudes presented - which are significantly below SL Reynolds Number

 

[P-39 Expert]

You're digging too deep into '109 minutiae. The P-51 didn't need a new wing to accommodate an all .50 cal battery, four then six guns. The two nose guns P-36A evolved into the two wing gun P-36C and P-40 to the six guns P-40E without a new wing. The F4U evolved from a 2 wing gun prototype to a six .50 cal or four 20mm battery with the same wing. They all retained the same designation. The FW 190A8/R1 had four of its guns UNDER the wings not in them. Why was that?. The rest of the 190s you list had two of the guns (synchronized) in the WING ROOTS not in the WINGS. The original wing gun in the 190 was an MG 17. They were never able to increase the NUMBER of guns in the wing. Change in caliber was the best they could do. The P-39 wing could not accommodate a modern gun battery in the wings, hence the under wing guns as per the 109 and 190. The drag induced by the underwing guns on the 109 and 190 made them easy meat for Allied fighters. As far as the P-39Q goes, it didn't really matter. It was already a dog before the Q was introduced. Even the Soviets realized that and removed the gun tubs. Even Bell caught on and produced a batch of Qs without them.

P-39 was no dog especially by the time the N model was produced. Performance was so good that the AAF had to come up with something to retard it's performance so they added the podded .50 caliber MG. The Soviets removed ALL the wing guns, both .30s and the later .50s. Bell didn't "catch on", they built what the customer ordered/wanted. The Soviets didn't need wing guns and told the AAF as much.

 

[fubar57]

LOL!!!!

 

[DarrenW]

Coefficient of drag of a P-39 0.0217 from America's Hundred Thousand. I don't know where the Author got them.

Dean references this report in his book for that figure:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930092637.pdf

 

[drgondog]

P-39 was no dog especially by the time the N model was produced. Performance was so good that the AAF had to come up with something to retard it's performance so they added the podded .50 caliber MG. The Soviets removed ALL the wing guns, both .30s and the later .50s. Bell didn't "catch on", they built what the customer ordered/wanted. The Soviets didn't need wing guns and told the AAF as much.

Bell's time to introduce what the field commanders wanted was early 1942 before the field commanders knew what they wanted. The War Plans Division in late 1941 and 1942 posited battlefield air superiority while performing Fast Attack role - the reason the Mustang in the form of A-36 snuck its big nose in the AAF tent - despite Oliver Echols' resistance to NAA getting in the Pursuit game.

The limiting known factor for the P-39 was never speed or maneuverability at low/medium altitude - it was the lack of range and external stores. It was already 'written off' as a primary AAF Pursuit (as was the P-40) in 1942 for future procurement. Bell and Curtiss survived in 1942-43 because we had to fight with what we had and there weren't enough P-38/P-47s to backfill the battlefield CAS requirements. They also were augmented by Lend Lease to USSR and our Allies while improvements kept them competitive for low to medium altitude use.

The final straw was the success of the Merlin 'experiment' in mid 1942 when the CAS acolytes viewed the Merlin Mustang as the answer to the fast, load carrying, maneuverable, long range CAS fighter that could achieve air superiority - the reason it was painted in to replace the P-39 and P-40. Only a few visionaries understood the escort potential of the P-51B until early 1943 so there was no fight by Strategic Air proponents until mid 1943 after Blitz Week - all were destined to be TAC CAS and Recce in ETO.

The achilles heel for the P-39 from the inception was the wing. It was never conceptualized in 1937-1938 as anything but interceptor - and therefore had no room for growth for either internal fuel or external load and very little for internal armament. Price's decisions to encourage Bell to add wing armament capability was a desire to improve CAS effectiveness - not 'kill the program'

It is kind of silly to suggest that Maj/LtC Price, the AAF Materiel Command P-39 Project manager wanted to kill the P-39.

 

[varsity07840]

P-39 was no dog especially by the time the N model was produced. Performance was so good that the AAF had to come up with something to retard it's performance so they added the podded .50 caliber MG. The Soviets removed ALL the wing guns, both .30s and the later .50s. Bell didn't "catch on", they built what the customer ordered/wanted. The Soviets didn't need wing guns and told the AAF as much.

So, there was an AAF conspiracy to retard the performance of an aircraft they already bought? If it was such a world beater why didn't they replace those lousy P-38s with P-39Ns. I guess they did the same thing with the P-63.