Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (2 Viewers)

[MakerDude]

I have read a lot of the P-39 lend-lease.net articles and noticed that the soviets tended to use the p-39 slightly differntly than the west. Whereas most pilots in the west would shoot at 200+ yards, the Soviets would shoot at about 80 yards.

A US 37mm shell weighed 608 grams and contained 45 grams of Tetryl.
A 20mm Hispano shell weighed 130 grams and contained 10.2 grams of Tetryl (the were a number of similar shells). However the 37mm gun fired at 150-180 rounds per minute (book figure) vs the 20mm firing at around 600 rpm. A single 37mm shell was certainly destructive. the Problem was hitting the target with the low rate of fire gun (barges don't move very fast).

The Russians may have been impressed because the projectiles out of the 20mm ShVAK cannon went around 91-96 grams and contained 4.7 or 6.1 grams of RDX and aluminium.

For punching holes in armor you need velocity and the American 37mm didn't have a lot. The German 37mm used on the Stuka had about twice the potential energy with standard ammo and the Germans made AP rounds with tungsten cores. The US did not.

30mm of armor was generally considered the minimum needed to defeat 75mm HE ammunition from field guns or howitzers, this was generally the minimum specified for a "shell proof" tank (See British A10 for example) A 37mm HE round would have only a very small chance of disabling a tank with a single hit. AP shot for the field guns changed things. As did the proliferation of 37-47mm AT guns with high velocity AP rounds.

Hope that helps.

One of the reasons the Soviets were able to get more out of it was instead of firing at 200+ yards like the British and Americans they fired at about 80 yards. Alexander Pokryshkin there No 2 ace said it was easy to destroy your opponent, get to withing 80 yards pull the trigger and watch your opponent disintegrate. At that close range the low velocity of the 37mm and its low rate of fire become less important. The Soviets matched their tactics to their equipment.

 

[jmcalli2]

I would like to use the expertise of you other forum members to ask about more obscure aircraft.

For example, what do you have to say when comparing the P-39 vs the P-40? All I (think to) know so far:

- The US used the P-40, not the P-39.
- Both had poor high-altitude performance.
- The P-39 had the engine behind the cockpit and could field a big 37-mm gun in the front.
- According to wikipedia, the P-40 had the stronger engine.
- Also according to wikipedia, the P-39 was faster than the P-40, though this could easily be due to comparing different versions or altitudes. Otherwise, I would assume the P-39 to be preferred over the P-40.

- The US used BOTH the P-40 and the P-39.
- Both the P-40 and the P-39 used the Allison V-1710 except for a few P-40s that used the mid-altitude version of the Merlin V-1650.
- The P-39 was faster than the P-40.
- The aircraft were designed for different missions; the P-40 was a general purpose fighter while the P-39 was designed to an interceptor specification ( Both the P-38 and P-39 were designed to the same specification. The P-38 went with two engines to achieve the required performance while the P-39 tried to be the smallest single engine fighter possible to get there. The big cannon was part of the requirement. By the time the P-39 flew, the Army decided there was little threat from high level bombers and pulled the turbo from the P-39 to save weight. This limited the P-39's effectiveness to below ~18,000 ft, the same level as the P-40. )

 

[Shortround6]

The P-38 went with two engines to achieve the required performance while the P-39 tried to be the smallest single engine fighter possible to get there.

Most of the requirement/s were the same. However the requirement that led to the P-38 wanted one hour more endurance at the same speed/altitude (actually double from one hour to two hours) than the requirement that led to the P-39. It was the weight/bulk of the extra fuel that that made the P-38 so much larger. The specification might have been meet by single engine aircraft had a 1500hp single engine been available at the start of design. Such an engine was not available requiring the use of two 1000hp engines which made the proposed plane even larger.
What led to the P-39 was never intended to have the endurance of the requirement that led to the P-38.

By the time the P-39 flew, the Army decided there was little threat from high level bombers and pulled the turbo from the P-39 to save weight. This limited the P-39's effectiveness to below ~18,000 ft, the same level as the P-40. )

No, the turbo installation in the P-39 was a dog's breakfast (as was the original oil cooler and radiator) , and the turbo (and controller/s) were not ready for squadron use. The original XP-39 was never going to come near the projected/estimated performance numbers. The only way to get even close was to ditch the turbo, ditch the intercooler and totally redesign the oil cooler/radiator installation (putting them were the turbo had been).

 

[P-39 Expert]

We should always compare contemporary P-39s and P-40s. Those that were in production about the same time. P-39D/F and P-40E had the same 1150hp engines. P-39K/L and P-40L had the same 1325hp engines. The P-39M/N/Q and the P-40M/N had the 1200hp engines with the higher 9.6 supercharger gears for better altitude performance.

In every contemporary situation the P-39 was substantially lighter (7650#) vs the P-40 (8400#). That's about 750# difference. With both having the same engine the P-39 performance is always going to be better. Faster and particularly better in climb/ceiling. All the tests in Mike William's site confirm this, just impossible for it to be any other way. Maneuverability was supposedly very close, some give the edge to the P-40.

The Merlin P-40 was a substantial improvement and brought performance up to about exactly the same as a contemporary P-39D/F/K/L. Merlin had more power at the higher altitudes. Performance was not nearly as good as the P-39N. Performance in the Q was degraded by the gondola .50cal machine guns under the wings.

Range/endurance was about the same for both. The P-40 held more internal fuel but had a much higher allowance for take off and climb to 5000' than the P-39 making usable fuel closer to equal. The P-39's higher cruising speed at equal power settings made up for the rest.

 

[varsity07840]

The P-39k/L had an Allison. The P-40L had a Merlin.

 

[P-39 Expert]

The P-39k/L had an Allison. The P-40L had a Merlin.

The P-39k/L had an Allison. The P-40L had a Merlin.

Right. I was thinking K and I hit L. My bad.

 

[FLYBOYJ]

- The US used the P-40, not the P-39.

You're joking, right?

From Joe Baugher:

The following Fighter Groups operated the P-39 between 1941 and 1945, but in some cases only relatively briefly:

• 8th Fighter Group (35th 36th and 80th Squadrons
• 15th Fighter Group (12th 15th and 36th Squadrons)
• 18th Fighter Group (78th and 333rd Squadrons)
• 20th Fighter Group (55th, 77th, and 79th Squadrons)
• 21st Fighter Group (531st Squadron)
• 31st Fighter Group (39th, 40th, and 41st Squadrons)
• 33rd Fighter Group (58th, 59th, and 60th Squadrons)
• 52nd Fighter Group (2nd and 4th Squadrons)
• 53rd Fighter Group (13th, 14th, and 15th Squadrons)
• 54th Fighter Group (42nd, 56th, and 57th Squadrons)
• 56th Fighter Group (61st, 62nd, and 63rd Squadrons)
• 58th Fighter Group (67th, 68th, and 69th Squadrons)
• 318th Fighter Group (72nd Squadron)
• 332nd Fighter Group (99th, 100th, 301st, and 302nd Squadrons)
• 338th Fighter Group (305th, 306th, and 312th Squadrons)
• 343rd Fighter Group (18th Squadron)
• 347th Fighter Group (67th, 68th, and 70th Squadrons)
• 350th Fighter Group (345th, 346th, and 347th Squadrons)
• 354th Fighter Group (353rd, 355th, and 356th Squadrons)
• 357th Fighter Group (362nd, 363rd, and 364th Squadrons)
• 367th Fighter Group (392nd, 393rd, and 394th Squadrons)
• 372nd Fighter Group (407th, 408th, and 409th Squadrons)
• 473rd Fighter Group (451st and 452nd Squadrons)

P-39s were also used by the 342nd Composite Group (33rd Squadron) and the 59th Observation Group (488th, 489th and 490th Squadrons). The P-39 was also used by the 48th, 84th, 85th, 339th, 494th, 405th, 496th, and 478th Bombardment Groups in the training role.

 

[Greg Boeser]

You forgot 35th Pursuit/Fighter Group, (39th, 40th, 41st Squadrons)

 

[glennasher]

P-38s, P-39s, and P-40s were all used extensively in the Alaska campaigns, to move the Japanese off Attu and Kiska. While the Aleutians campaign wasn't a major operation, in the scheme of things, it was pretty important, nonetheless. They were used for armed recon, and for defense at the air bases scattered over the island chain, and to keep the Japanese at bay. The P-39s were highly valued up there.

 

[MIflyer]

By the time the P-39 flew, the Army decided there was little threat from high level bombers and pulled the turbo from the P-39 to save weight.

A common misconception, often repeated. I have even seen clueless but successful writers say something like, "In isolationist America the Army wanted to focus on ground attack aircraft to defend the beaches in case of an invasion." POPPYCOCK!

In reality the USAAF was totally focused on the turbo as a first stage supercharger for a a two stage system. They even tried the turbo on the P-36/40 airframe, to produce the XP-37 - and it worked, adding 50 mph speed at higher altitudes, as long as you did not want the pilot to be able to see anything from that cockpit way back in the tail.

Actually, stuffing that turbo in such a small airframe resulted in MORE drag and LOWER performance than the same airplane without the turbo. The high speeds quoted for the XP-39 were WITHOUT the turbo.

Now, as to why Allison did not produce a V-1710 with a two speed supercharger, which would have been incredibly easy for them, given the V-1710's removable accessory section, is something I have wondered about. Just about every other aircraft engine company in the word did do that.

 

[Shortround6]

Actually, stuffing that turbo in such a small airframe resulted in MORE drag and LOWER performance than the same airplane without the turbo. The high speeds quoted for the XP-39 were WITHOUT the turbo.

Actually the high speeds quoted for the XP-39 before the turbo was removed may have been the result of an over achieving sales dept

 

[GregP]

Hi Miflyer,

I worked in an Allison shop for several years. The owner has copies of several requests from Allison to the USAAF to develop an integral 2-stage unit, but none were approved for funding. Despite being bought by GM, Allison was essentially a small company, and did not have the funds or manpower to develop such a 2-stage supercharger system without backing from their largest customer.

When the 2-stage unit was not funded, they concentrated on delivering the contracts they had. The late-blooming auxiliary stage supercharger was a low-cost, company-funded effort to compete (basically a new case around the existing internal design of a supercharger plus a coupling shaft), but the Air Corps SHOULD have funded at least a trial engine or two using the 2-stage Merlin supercharger unit and an adapter. At least they could have seen what they were passing up.

Alas, it was not to be. If you needed to fight at 25,000 - 35,000 feet, you were forced to use a 2-stage Merlin / Griffon or 2-stage radial ... 2-stage in any case. Fairly poor planning in my opinion, but it happened that way as we all know. Allison never DID make the integral 2-stage supercharger we all wished they had made.

A separate thread might be very interesting on the development of a high-altitude version of the R-2800. In addition to supercharger issues, they had a major ignition problem. They even tried a pressurized ignition harness! It worked, but was never going to be reliable in the field, so they came up with low-voltage ignition and moved the coils out to the spark plugs to reduce voltage loss in the plug wires. But, that's another story.

Cheers.

 

[P-39 Expert]

A common misconception, often repeated. I have even seen clueless but successful writers say something like, "In isolationist America the Army wanted to focus on ground attack aircraft to defend the beaches in case of an invasion." POPPYCOCK!

In reality the USAAF was totally focused on the turbo as a first stage supercharger for a a two stage system. They even tried the turbo on the P-36/40 airframe, to produce the XP-37 - and it worked, adding 50 mph speed at higher altitudes, as long as you did not want the pilot to be able to see anything from that cockpit way back in the tail.

Actually, stuffing that turbo in such a small airframe resulted in MORE drag and LOWER performance than the same airplane without the turbo. The high speeds quoted for the XP-39 were WITHOUT the turbo.

Now, as to why Allison did not produce a V-1710 with a two speed supercharger, which would have been incredibly easy for them, given the V-1710's removable accessory section, is something I have wondered about. Just about every other aircraft engine company in the word did do that.

Turbo in the P-39 was totally unworkable, smart move to delete it to get the P-39 (and P-40) in production in time for U.S. entry into WWII.

AAF was focused on the turbo for the P-38 and P-47 which delayed their introduction into combat until Dec '42 and May '43 respectively. 1942 was fought almost solely by the P-39, P-40 and F4F for the USN. All three of these planes were grossly overweight as compared to British and Axis fighters. All three could have been lightened in the field to substantially improve their performance particularly in climb and ceiling.

Regarding the two SPEED supercharger, it was not really needed in the P-39 and P-40. Their single speed was high gear, a second speed would have been a low gear which would have provided a small increase in takeoff power at the expense of more weight and complexity. Takeoff power was already being increased from 1150HP to 1325HP with the -63 and -73 models of the Allison in mid '42. These were installed in the P-39D-2/K/L and the P-40K. Time limit for military power was also increased from 5 minutes to 15 minutes at that time.

The real payoff for high altitude performance was the two STAGE Allison-47 which was tested in the experimental P-39E in April '42. Unfortunately the P-39E was extensively redesigned with six .50cal machine guns AND the 37mm cannon and weight increased from 7650# to 8900#. High speed was improved to 386mph at 21,500' and ceiling increased to 35,000' but the single stage P-39N then in development was about that fast and climbed significantly better. So the P-39E was not produced.

A much easier and quicker fix would have been to just install the two stage -47 in a standard P-39D/F. The auxiliary first stage added 175# and the required 4 blade propeller another 75# for a total added weight of 250#. Add this to the normal P-39D at 7650# and the two stage P-39 would have weighed only 7900# as compared to the P-39E at 8900#. The extra 400HP at high altitude coupled with the 1000# weight savings would have made this plane a rocket. Performance would have been better than the P-38 and P-47. All this in mid'42. Oh well, hindsight is always 20/20.

 

[MIflyer]

I think you'd better forget about building any two stage supercharged engine without an Intercooler/Aftercooler. They tried no intercooler in the F-82 and had endless problems; the airframes set for years at the old Vultee plant in Downey with no engines because they could not get the V-1710's to run right.

And I guess I took too much thermodynamics in college and have had too much experience running tests with aircraft air to air HEX in test cells, but I find it incredible that no one but Stanley Hooker came up with the idea for an air to liquid aftercooler, thereby solving the space, drag, AND the control problem in one swell foop. Just for that they should not only knighted him but made him king of New Zealand or something. Actually the Merlin 61 was BOTH intercooled and aftercooled since the fluid picked up some heat between the stages as well as after them. Think what that approach could have done for drag reduction in the P-38, P-47, P-61, and B-29. But NO! Everyone could only think of air to air HEX for airplanes. The fact that Hooker, a theoretical aerodynamics expert could step outside his area of expertise shows just how brilliant he was.

 

[Shortround6]

AAF was focused on the turbo for the P-38 and P-47 which delayed their introduction into combat until Dec '42 and May '43 respectively

The P-38 was in combat or in combat areas in Aug of 1942.
July 31st the 27th squadron stays in Iceland as a defensive unit, relieved by the 50th Squadron Aug 26th and continues on to England.
Aug 9th two P-38s claim to Japanese flying boats in the Aleutian Islands.
Aug 22 the 67th squadron with a mix of P-38s and P-39s arrives at Henderson Field.
Aug 31st 164 P-38s have crossed the Atlantic by air.
P-38 recon planes were already in Australia.

All three could have been lightened in the field to substantially improve their performance particularly in climb and ceiling.

How???
remove armor?
Not fill fuel tanks?
Take out guns & ammo?
remove electric starters and fit smaller batteries?

a reason they were heavier than British and Axis fighters was that they carried more fuel and a heavier weight of guns and ammo. This heavier payload required a heavier structure which unit mechanics would have difficulty modifying.

 

[Acheron]

Two-stage superchargers were the ones needed to get high-performance at all altitudes, right? Sorry for my ignorance, but I was puzzled about some aircraft being better at high-altitudes than lower ones. At first I thought it was meant being relatively better higher up, but from what I read on wikipedia, it seems that certian supercharging schemes resulted in aircraft that were better higher-up in absolute terms, correct?

 

[pinsog]

Two-stage superchargers were the ones needed to get high-performance at all altitudes, right? Sorry for my ignorance, but I was puzzled about some aircraft being better at high-altitudes than lower ones. At first I thought it was meant being relatively better higher up, but from what I read on wikipedia, it seems that certian supercharging schemes resulted in aircraft that were better higher-up in absolute terms, correct?

Correct. Take an F4F Wildcat. 2 speed engines give about 1,000 hp at about 14,000 feet. The 2 STAGE engine gives about 1,000 hp at 19,000 feet. The result is that at 19,000 feet the 2 STAGE equipped plane is faster and climbs better giving it a significant advantage

 

[GregP]

Hi Archeron,

"Better" is relative. If you can maintain sea level horsepower as you go up, the airplane goes faster because there is less air density to produce drag.

But, a WWII fighter than can pull 6 - 8 gs down at 10,000 feet, even if only momentarily, can usually only make shallow turns at 25,000 feet + without stalling and losing significant altitude in recovery. The P-47 was one of the best way up high and was relatively not as good below 20,000 feet with regard to the performance difference with German fighters. That is, the German fighters were all pretty good in the 10,000 feet to 20,000 feet range and the P-47 was just coming into its best performance range when it got to 20,000 feet. It only got better versus the competition as the fight went up, at least until near the service ceiling.

The P-47 was not especially fast at low altitudes, but could maintain horsepower until way up high, so it gained in relative performance versus the opposition and was likely the best-performing fighter in mass production above 25,000 feet. I more or less discount the Ta-152 solely because they only delivered about 47 of them during the entire war and only two were still operating when the war ended (two Ta-152Cs, not the high-altitude H models). There were thousands of high-altitude P-47s from the P-47D-25-RE and onward in the series operating when the war ended. Of course, the U.S.A. wasn't being bombed on a daily basis so as to hinder production ... and that definitely made a huge difference continuity of the aircraft supply chain. If we needed, say, 25 new fighters, we could get them in a short time. Not so for the Luftwaffe from late 1944 onward. When the war ended there were a lot of essentially brand new fighters sitting about with no propellers and no fuel. There wasn't anywhere nearly as much of a fuel or propeller shortage as there was the problem of delivering the fuel and props to airfields and factories while being strafed by Allied fighters late in the war.

 

[Capt. Vick]

I remember watching one of those Dogfight programs about Guadalcanal on the history channel, where they use CGI to depict the battles. Well, they were interviewing a Wildcat pilot who said he went out with some Aircobras and since they stayed down low he felt they were the bare for him and his squadron mates.

 

[MIflyer]

It's ironic that the USAAC/F focused on high altitude turbosupercharged aircraft ever since the advantages were demonstrated by the famous Pikes' Peak Test in WWI, where legend has it GE employed a team of horses to pull a Liberty engine up to the top where the turbo demonstrated the ability to boost the output from the normal 230 hp at 14,000 ft up to 356 hp. That sealed the deal! If you had turbos you could climb higher and outperform everyone else. And this dream was realized when the Y1B-17 demonstrated the same top speed as the USN's F2A -at 10,000 ft higher.

The USN took note of this in a big way, realizing that the threat first demonstrated by Billy Mitchell had materialized - at least on paper in Wash DC. They had already built their first carriers and now needed something to compete with the B-17. The answer was a two stage mechanically supercharged engine in Grumman's reworked F4F.

The irony was that stuffing a turbo into a single seat fighter was not easy. It required two engines like the P-38 or a large two seat airplane like the P-47 was based on. So when the war started the USN, with its lower tech approach, which the USAAC had given up on with the XP-41, that was ready to fight at higher altitudes.