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

glennasher · Sep 14, 2020

GrauGeist said:
Several years ago, my friends and I were at the range and they were plinking at a 5/16" thick steel target with their .223s set up aboit 35 yards out.
It would ring like a bell with their hits. Being a smartass, I got out my 7x57 Mauser and took a shot. The target didn't move - ok, so I missed, no problem, took more careful aim and let fly. Again, nothing - I missed again??
Baffled, I went out and looked at the target. Scores of divots from the .223 impacts and lo and behold: two large holes near the center. The 7x57 passed through it like it was cardboard...

.30 caliber rounds can and will do damage.

In 5/16 steel, even a pistol load will ding the heck outa them. Back in the waybackwhens, I was casting bullets for a .41 Magnum revolver, and tried some of them (a fairly light bullet, even!) and it dimpled the heck out of the steel. We normally shot 9mm and .45 ACP at them, but since they were there, and I had that .41, I thought it might be interesting to see what happened. I quit after seeing how much damage that .41 did. The lead bullets were cast out of wheelweights, nothing special at all, and ran IIRC, about 190gr. I used the powder charge I normally used with 225gr. bullets, they weren't even a "hot" load.

GrauGeist · Sep 14, 2020

Acheron said:
Careful! I am an amateur, but I am stumbling over the 35 yards (32 meters). From the stories about the RAF gun convergence debate, typical engagement ranges seemed to be around 750 feet (~225 meters). Doesn't that make a considerable difference in how much energy the bullet will retain?

35 yards (32 meters) was a "for fun" distance at the gun range.

The point being, that the .223 (about 55 gr.) was just putting slight dents in the steel while making the target ring and dance and when I shot the target with my 7x57 (about 157 gr.), the target did not make a sound nor did it move. The bullet passed through it as if it were a paper target and this was a standard hunting round not an AP.

This illustrates the energy of a 7mm (.30) caliber projectile and while that was slightly tempered steel at close range, it would have easily penetrated and or damaged an aluminum structure at distances seen in aerial combat.

GrauGeist · Sep 14, 2020

P-39 Expert said:
And there are accounts from British pilots in the BoB of emptying their entire magazines of eight .30cal guns into a single He111 and watching it fly on to the target. Now I much prefer actual documented tests to anecdotal stories but if the .30cal gun was sufficient then the .50cal, 20mm, 30mm, 37mm guns would not have been developed. And the .30cal MG would have been used on AAf fighters, which it was not, except for the P-39.

Were they hitting the engines, wings and cockpit or were they emptying their entire magazines on the fuselage/tail?
What angle were they attacking at?
Were they even hitting it at all?

Plenty of evidence that .303s were effective (seen by wrecks scattered all over England) to question pilots reporting that they were not bringing down unarmored bombers after exhausting their entire loadout of ammo.

glennasher · Sep 14, 2020

Frankly, I'm surprised that the 5.56/.223 didn't zip right thru the steel. We had a saying "velocity penetrates steel" and it almost always worked. Even the piddling .17HMR will ding the heck out of steel, at only 2550fps/muzzle velocity. Then again, I've seen 5 ton truck tires at 200 yards with ball M193 (5.56) looking like a porcupine while still full of air, lol. Sometimes even 7.62mm NATO wouldn't penetrate those tires, so who knows?

jmcalli2 · Sep 14, 2020

Shortround6 said:
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.

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).

The path Bell took was to keep the power up at over 20,000+ feet. I'd read that the XP-39 hit 390mph at 20,000 ft even though the turbo was less than optimal. Power + altitude = speed because drag is less important in thinner air over 20,000 than at 12,000. NACA proposed reducing drag to get 400+ projected at 10,000 to 15,000 feet without the turbo. Since the P-40 was struggling to hit 340 at these altitudes and the XP-38 was over 400mph above 20,000 ft it seemed a no-brainer.

jmcalli2 · Sep 14, 2020

MIflyer said:
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.

The US was moving towards turobsupercharging because it promised "free" boost; no power drain to compress induction air, just energy that was being wasted. Despite the problems, it must be considered a successful step when you look at the P-38, P-47, B-17, B-24, B-29, B-32, and B-36.

GrauGeist · Sep 14, 2020

glennasher said:
Frankly, I'm surprised that the 5.56/.223 didn't zip right thru the steel. We had a saying "velocity penetrates steel" and it almost always worked. Even the piddling .17HMR will ding the heck out of steel, at only 2550fps/muzzle velocity. Then again, I've seen 5 ton truck tires at 200 yards with ball M193 (5.56) looking like a porcupine while still full of air, lol. Sometimes even 7.62mm NATO wouldn't penetrate those tires, so who knows?

The 5/16" plate wasn't mild steel, it had a slight temper to it, as it was a remnant from stock used for gussets on a Caterpillar's carapace - which is why it had a sweet ring to it when the .223s struck it!

GregP · Sep 14, 2020

Hi Jmcalli2,

We have entire threads about the XP-39 and almost nobody believes it really hit 390 mph. There doesn't seem to be any flight test data to surface that confirms that speed as yet.

I have a copy of a book with that data (390 mph) in it from 1946 and reissued unchanged in 1964. The book is, "U.S. Army Aircraft 1908 - 1946 SC-AEF-AAS-AAC-AAF, by James C. Fahey, published by Ship and Aircraft, P. O. Box 48, Falls Church, Virginia, 22046. The 390 mph claim is on page 33. The XP-39E is shown at 386 mph on the same page.

My copy must be from the 1964 reissue because there is a ZIP code in my copy and ZIP Codes were adopted in 1963.

MIflyer · Sep 14, 2020

jmcalli2 said:
The US was moving towards turobsupercharging because it promised "free" boost; no power drain to compress induction air, just energy that was being wasted. Despite the problems, it must be considered a successful step when you look at the P-38, P-47, B-17, B-24, B-29, B-32, and B-36.

Only the USAAF employed two-stage supercharged heavy bombers with high altitude capability as "the norm." While the USAAF heavy bombers took some heavy losses, the losses would have been crippling had they not had that capability. The USN used some B-17's and B-24's with that capability only because that was what was coming off the production line; on their dedicated USN version of the B-24, the PB4Y-2, they removed the turbos because they did not need that capability.

When the RAF needed some ECM aircraft they knew just where to go; they used B-24's and B-17's. The altitude capability enhanced the jamming coverage and also enabled them to better avoid a Luftwaffe that might be annoyed by their activities.

Oddly enough the USN, having introduced the two stage supercharged fighter to combat, abandoned the concept. The F7F and F8F used single stage supercharged engines, as did the last production Wildcat, the FM-2. After all, they had figured out that the only high altitude bombers they would encounter were on their side.

P-39 Expert · Sep 14, 2020

MIflyer said:
Only the USAAF employed two-stage supercharged heavy bombers with high altitude capability as "the norm." While the USAAF heavy bombers took some heavy losses, the losses would have been crippling had they not had that capability. The USN used some B-17's and B-24's with that capability only because that was what was coming off the production line; on their dedicated USN version of the B-24, the PB4Y-2, they removed the turbos because they did not need that capability.

When the RAF needed some ECM aircraft they knew just where to go; they used B-24's and B-17's. The altitude capability enhanced the jamming coverage and also enabled them to better avoid a Luftwaffe that might be annoyed by their activities.

Oddly enough the USN, having introduced the two stage supercharged fighter to combat, abandoned the concept. The F7F and F8F used single stage supercharged engines, as did the last production Wildcat, the FM-2. After all, they had figured out that the only high altitude bombers they would encounter were on their side.

The F8F and FM-2 were also lighter than their predecessors so they didn't need a two stage supercharger. The Bf109 and Zero were good at altitude with a single stage supercharger.

Shortround6 · Sep 14, 2020

The weight of the planes was only part of puzzle. The fact the F8F had an improved supercharger had a lot to do with it.

edit, not all single stage superchargers were the same and the state of the art in single stage superchargers did get better as the war went on. The improvements were not as dramatic as adding a 2nd stage but they did exist.

For the FM-2 the version of the Cyclone that was used in it offered 1000hp at 17,000ft which more than split the difference between the Cyclone in the Martlet I (1000hp at 13,500ft) and the P & W two stage engine in the F4F-4 and FM-1, 1000hp at 19,000ft. An empty FM-2 was over 300lbs lighter than F4F-4 so there was an advantage even before we start argueing about guns/ammo, etc.

The early F8F-1s got R-2800s that offered 1600hp at 16,000ft compared to the 1600hp at 13,500ft that the engines in the B-26 and Lockheed Venturas offered.
Late production F8F-1s got R-2800s that offered 1700hp at 16,000ft and F8F-2s wound up with single stage engines that gave 1600hp at 22,000ft.

Two stage engine in early F4Us and F6Fs gave 1800hp at 15,500ft and 1650hp at 22,500ft.

wuzak · Sep 15, 2020

P-39 Expert said:
The P-39D/F/K/L would have lost around 300# by deleting the four useless .30cal MGs in the wings (200#) and the nose armor (100#) which didn't protect anything. This increased climb by about 360fpm which would have allowed those early P-39s to outclimb the contemporary Zeros. P-39s already enjoyed a 40mph speed advantage up to 25000' over the Zero. The remaining 37mm cannon and two .50cal MGs left plenty of firepower as the Russians proved against the Luftwaffe.

P-39 Expert said:
Substituting a .50cal MG for the 37mm wouldn't have provided enough firepower and it would have screwed up the balance. Better to substitute a 20mm cannon with a bigger ammunition tray.

So, changing the 37mm for a 0.50" would have screwed up the balance, but removing 100lbs of armour from the forwardmost part of the fuselage would not?

P-39 Expert · Sep 15, 2020

wuzak said:
So, changing the 37mm for a 0.50" would have screwed up the balance, but removing 100lbs of armour from the forwardmost part of the fuselage would not?

Bell was able to maintain balance when the 20mm cannon was substituted for the 37mm cannon, a difference of 140# including ammunition. A .50cal MG with 200 rounds of ammunition would weigh about 140# for a difference of about 160# vs the 37mm cannon. So yes, they probably could have done it. Should have been able to remove the 100# of armor plate and maintain balance also with the 37mm.

But substituting a .50cal MG for either cannon would have been a substantial loss of firepower. The Navy calculated that a 20mm cannon was equivalent to three .50cal MGs. The substitution would mean only three .50cal MGs remained (actually only about 2.5 considering the loss due to synchronization of the original two). All the other AAF and USN fighters had at lease 4 .50cal MGs. Better to leave either cannon with the two synchronized .50s and have the equivalent of 4.5 .50cal MGs. Centerline fire of all three weapons helped also. Just my opinion.

MIflyer · Sep 15, 2020

I think that a .50 cal with late war API was at least as good as a 20MM for fighter vs. fighter WW2 combat.

Of course you would have to add weight forward to handle the CG problem. Add more ammo to the .50 cal and move some radios and the IFF from aft of the cockpit.
By the way, P-39's in the Pacific usually seem to have a box under the canopy aft of the cockpit. The radio compartment was aft of the engine, so I assume that extra box was the SCR-695 IFF.

Shortround6 · Sep 15, 2020

MIflyer said:
Oddly enough the USN, having introduced the two stage supercharged fighter to combat, abandoned the concept. The F7F and F8F used single stage supercharged engines, as did the last production Wildcat, the FM-2. After all, they had figured out that the only high altitude bombers they would encounter were on their side.

.Used in the F4U-5 postwar

P-39 Expert · Sep 15, 2020

MIflyer said:
I think that a .50 cal with late war API was at least as good as a 20MM for fighter vs. fighter WW2 combat.

Of course you would have to add weight forward to handle the CG problem. Add more ammo to the .50 cal and move some radios and the IFF from aft of the cockpit.
By the way, P-39's in the Pacific usually seem to have a box under the canopy aft of the cockpit. The radio compartment was aft of the engine, so I assume that extra box was the SCR-695 IFF.

View attachment 595126

Except that the P-39 was an early war airplane. How do you figure the .50cal with late war API was as good as a 20mm? Just curious.

MIflyer · Sep 15, 2020

Pilot reports of .50 cal API were very favorable. There were F6F's that shot down Vals with only one round.

Not a lot of room for radios in a P-39.

Peter Gunn · Sep 15, 2020

If I don't forget when I get back home, I have some pics in a book on the BoB I bought several years ago. In it there are several shots of LW bomber parts being hauled off for scrap with quite a few bullet holes in them. I'll scan it and post it if I remember, but the gist of it is this, you can clearly see in the photos which holes were made by the 20mm and which dents and paint scrapings were made by the .303's. I wouldn't call it a mike drop sort of evidence, just some food for thought.

I have no dog in this hunt, I wouldn't want to be shot at by any of the weapons discussed, but merely thought it might be of interest to the group.

Shortround6 · Sep 15, 2020

Ah, the wondrous American .50 cal

late war .50 about 800rpm with 43 gram bullet holding about 1 gram of incendiary material
20mm gun about 600rpm with 130 gram projectile holding 10 or more grams of incendiary or HE.

They have nearly identical muzzle velocities. The .50 has a better shaped bullet, the 20mm has more weight per unit of frontal area for better sectional density. Ballistic coefficient does favor the .50 but doesn't really come into play in an realistic air to air scenario (600 yds or under).

The M8 API was introduced in early 44. It was basically a copy of the Russian 12.7mm API round so there was no technical reason it could not have been introduced sooner for "what ifs"
However part of it's value was the incendiary ignited on impact as it was in the nose. It would give a flash on impact indicating the shooter was on target (tracer use was much diminished at this time) however very little incendiary material made it inside the aircraft if it hit anything substantial on the way in (or hit at bad angle).

I would note the examining wrecks or looking at wreck photos needs some interpretation. You can wind up with quite a bit of paint knocked off surrounding a rather small hole. You also have bullets hitting at rather oblique angles making large dents/scraps but no penetration when fired at long ranges. If you have a round "marking" then the bullet hit at a good angle, the more oval or elongated the hole/scrape the worse the angle.

and for instance.

supposed to have been shot down Friday 16th August 1940. in ~~Scotland~~

Edit, correction, crashed near Worthing in Sussex. No 19 Squadron was equipped with Spitfires with 20mm guns at this time but they were based at Duxford near Cambridge.

.303s? AA fire? The RAF had how many 20mm armed aircraft in August of 1940 in the ~~North of England and Scotland~~ South coast?

What made the bigger holes?

MIflyer · Sep 15, 2020

The US screwed up when we did not properly copy the MG-34. But I think we really screwed up big time when we did not scale up the .50 cal M-2 to 20MM. The US "experts" said it was not possible. But no one told that to the Japanese and they went ahead and did it. In the Smithsonian they have a sectioned US ,50 cal and a sectioned Japanese 20MM copy sitting side by side. Would have been nice to have the M-39 revolver 20MM in WWII but we copied the action from Mauser and did not get examples early enough.

Most 20MM guns in WWII were copies of the Orkelion, which had its drawbacks.

By the way "single shots" with the .50 cal M2 were possible because in some airplanes there were a few rounds between the ammo bay and the gun. After you were "empty" you could charge the guns and get one round in the chamber to fire. Line up very carefully behind that Val that is about to dive on that poor beat up DD. Pow! Boom! Flamer!

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

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