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

The 7100lbs is quite a trick.
Take a P-30D-1 and take out the wing guns (95lbs) and 115lbs of armor (leaving you with the armor & BP glass of a P-39C) and you get just over 6400lbs of tactical empty aircraft.

Now we can add fuel and ammo.

120 gallons of fuel is 720lbs OOPS, we are over 7100lbs.
118 gallons of fuel? OOPS we have no ammo.
160lbs worth of ammo (no .30 cal), we are down to 91 gallons of fuel

Oh yeah, forgot about about the 88lbs worth of ballast weights.
No problem, just don't put in any ammo for one of the .50 cal guns and leave out another 4 1/2 gallons of fuel.
well we can take out one 50cal since we don't have ammo for it.
and put back in about 12 gallons of fuel.

May I present you with the
Superfighter P-400
one 20mm with 60 rounds and one .50 cal with 200 rounds.
about a gallon less fuel than a Spitfire.

Yeah, I can see the British jumping all over that one.

Edit: If you take out one .50 cal and 200rounds of .50 cal ammo how much ballast do you have to put back in?

Peter Gunn said:

I appreciate the thoughts you guys, but thankfully it was kind of a big let down, not that I'm complaining mind you. I don't think the wind hit 35MPH but the vegetation got quite a dousing.

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Good news! you won't have to run the sprinklers for a few days.

Shortround6 said:

May I present you with the
Superfighter P-400
one 20mm with 60 rounds and one .50 cal with 200 rounds.
about a gallon less fuel than a Spitfire.

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With IFF?

wuzak said:

With IFF?

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Yes,
Unless some people believe that the British would have operated a fighter without IFF in the ETO in 1941/42 without IFF.
we could lighten the plane up a bit by going back to a radio like the P-39C used, barely able to communicate from Calais to Dover on a good day.

Those wimpy British sure ruined a good airplane, wanting cabin heat for flights over 20,000ft. A radio with more range than 10-20 miles, not wanting to get shot down by their own AA guns.

P-39 Expert said:

Wiki's information is from the Strategic Bombing Survey.

BoB has nothing to do with the P-39. Most all the information I quote on here is from wwiiaircraftperformance.org.

All if have said is that 109E fighter bombers couldn't get above 25000' so by definition they couldn't have fought at 30000'.

And I don't think there was a significant amount of combat at 30000'. Just my opinion based on capabilities of the planes involved.

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I suppose you mean
THE UNITED STATES STRATEGIC BOMBING SURVEY
Summary Report
(European War)
September 30, 1945?

at


You didn't specify which page and section, while such blanket references are common within some disciplines, at least most historians still insist on greater precision. I did not find the numbers you referred to, however i found this:

"Conventionally the air forces designated as "the target area" a circle having a radius of 1000 feet around the aiming point of attack. While accuracy improved during the war, Survey studies show that, in the over-all, only about 20% of the bombs aimed at precision targets fell within this target area. A peak accuracy of 70% was reached for the month of February 1945." Page 5.

You will notice the expression target area. As for the question what was targeted, consider this:

"In the latter half of 1944, aided by new navigational techniques, the RAF returned with part of its force to an attack on industrial targets
. These attacks were notably successful but it is with the attacks on urban areas that the RAF is most prominently identified." Page 3, my bold. And:

"As a rule the industrial plants were located around the perimeter of German cities and characteristically these were relatively undamaged." Page 4.

I know this is not the bob, but you were the one to introduce the word never and bring the fight down to RAF night bomber levels. As to fighter bombers not fighting above 25000 feet, that is possibly correct in a restricted sense of the word. They were only being bounced by planes flying higher. Originally it was not a question of fighting at 30000 feet, it was all about making you cringe. Anyway, in your restricted meaning of fighting, the great majority of Lancasters over Germany in 1943 were not fighting, they were merely motoring quietly around and burning out the harts of Germany's cities. Even when attacked, they often preferred to decline a fight with a cork screw manouvre. By the way a hint to what was targeted when RAF shifted from their admittedly abysmal early war 'precision' night bombing to area bombing is the introduction of the term 'de-housing'.

As others have explained, die Luftwaffe in 1940 possessed excellent navigational aids, more than enough to bomb a target the size of London during night. They did not there encounter the problems that RAF did over Germany with the restricted range of such aids on account of the earths curvature. In this face of the war the poor chaps indeed struggled to find the right city or, occasionally, even country. This is one important factor in bringing averages over the entire war down.

Shortround6 said:

The 7100lbs is quite a trick.
Take a P-30D-1 and take out the wing guns (95lbs) and 115lbs of armor (leaving you with the armor & BP glass of a P-39C) and you get just over 6400lbs of tactical empty aircraft.

Now we can add fuel and ammo.

120 gallons of fuel is 720lbs OOPS, we are over 7100lbs.
118 gallons of fuel? OOPS we have no ammo.
160lbs worth of ammo (no .30 cal), we are down to 91 gallons of fuel

Oh yeah, forgot about about the 88lbs worth of ballast weights.
No problem, just don't put in any ammo for one of the .50 cal guns and leave out another 4 1/2 gallons of fuel.
well we can take out one 50cal since we don't have ammo for it.
and put back in about 12 gallons of fuel.

May I present you with the
Superfighter P-400
one 20mm with 60 rounds and one .50 cal with 200 rounds.
about a gallon less fuel than a Spitfire.

Yeah, I can see the British jumping all over that one.

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And we go back to the fundamental question that has yet to be answered (despite being asked many, MANY times). If simply removing the wing guns and a few other bits and bobs resulted in a significant performance improvement, why wasn't that practice implemented more commonly across the US P-39/P-400 units? There is evidence that the wing guns were removed from a limited number of aircraft. However, the reaction wasn't "Wow! Removing those guns turned a pig's ear into a silk purse!"....it was more "Meh...it improved the old dog a little bit."

Despite removing the wing guns on some P-39s, the USAF still got rid of the P-39 from combat units as quickly as they possibly could. Why would they do that if the P-39 was such a competitive aircraft in 1942?

buffnut453 said:

Despite removing the wing guns on some P-39s, the USAF still got rid of the P-39 from combat units as quickly as they possibly could. Why would they do that if the P-39 was such a competitive aircraft in 1942?

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there are several reasons (in my opinion)
1. It wasn't competitive for much of 1942.
The P-39M and N don't start rolling out of the factory doors until late fall/early winter of 1942. Getting them to combat theaters takes several more months. Some units were still using P-39Ds (of different varieties ) in early 1943. The P-39K & L fall somewhat in between. FIRST delivery was in July of 1942, only 460 built of both models?
There were about 1760 (?) P-39Ds, P-400s and P-39Fs (D with a different prop) built.

2. P-39s used 3 different engines (or power ratings with several different "models" having the same rating) after the P-39C.

A. the 1150hp take off engine with the 8.80 gears.
B. the 1325hp take off engine with the 8.80 gears. Performance above around 12,000ft is pretty much the same. late Ds, and the K & L.
C. the 1200hp take off engine with the 9.60 gears, shows up in the M has performance improved by about 3-4000ft.

3. The US does not officially approve WEP ratings at low altitude until late 1942/ early 1943 in any engine. Despite what units might do at the local level.

testing a P-39M/N in late 1942 using WEP settings doesn't tell you what the planes in the Field were doing with their older engines and with throttle settings anywhere from standard limits to pressure readings having factory service reps 'cringing'.

BTW most of the later Weight charts have the P-39s carrying 300rpg for the wing guns instead of 1000rpg. this would save about 180lbs by itself. or just over 1/2 the weight of the four guns and 1000rpg. If the combat units have already taking out just about 180lbs then taking out another 170-180lbs might not show that big a difference???

Basically the vast majority of the P-39s in combat service in 1942 are the planes using the 1150hp engine with somewhat scattered unofficial "boosting" And it is this performance level that established the P-39s reputation for good or bad.

Shortround6 said:

A connection can be drawn between the BoB and the P-39/P-400 in that the P-39 was no longer wanted by the British not because the the BoB was already over ( and Russian being invaded when they showed up) but because the P-39 no longer met the tactical requirements of the British.

Operational altitudes had gone from 15,000-20,000 ft in the Battle of France to 25,000-30,000ft in the BoB in just 6 months.
The British had introduced the Hurricane II with the Merlin XX and the Spitfire V with the Merlin 45 many months before the P-400 showed up.

From Wiki " During a meeting held at the RAE at Farnborough on 17 February 1941 the Air Ministry asked "that a Spitfire should be provided with a pressure cabin capable of maintaining a pressure differential of 1 pound per square inch (69 hectopascals; 0.068 standard atmospheres) at 40,000 feet (12,000 m)."
Bolding is by me, this is 4 1/2 months before even the P-39C shows up in England. It is also about 2 1/2 months before Bell gets that tricked out 2nd production P-400 to barely make the qualifying speed for the contract.
The British were afraid that operational altitudes would continue to climb. It turns out that they didn't or at least not as fast as the British thought they would. Making aircraft work at 35-40,000 ft was somewhat harder than adding a very weak pressure cabin and small compressor. Germans found out the same thing.

But in the summer and fall of 1941 the threat of higher altitude combat was thought to be real and the P-400 wasn't going to work. The British also had more than enough lower altitude fighters. The P-400 wasn't even performing as promised.

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The high altitude Wellington which led to the Merlin 60 series came from Operational Requirement OR 94 which was placed in 1940. The prototype Spitfire Mk IX first flew in Sept 1941, so it was known well before that that planes would be going to higher altitudes. However without any change in altitude the RAF were having problems with pilots blacking out at circa 30,000ft even with oxygen supplies working. Even today no one can be examined to see if they will suffer from altitude sickness and it isnt all to do with low oxygen, but also the low pressure.

Greg Boeser said:

Now just think what mayhem those P-400s could have caused if they had been sent to Malaya to augment the Buffalos already there.
They've got to be better than tropicalized Hurricane Mk IIBs.

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Hayabusa fodder.

Shortround6 said:

there are several reasons (in my opinion)
1. It wasn't competitive for much of 1942.
The P-39M and N don't start rolling out of the factory doors until late fall/early winter of 1942. Getting them to combat theaters takes several more months. Some units were still using P-39Ds (of different varieties ) in early 1943. The P-39K & L fall somewhat in between. FIRST delivery was in July of 1942, only 460 built of both models?
There were about 1760 (?) P-39Ds, P-400s and P-39Fs (D with a different prop) built.

2. P-39s used 3 different engines (or power ratings with several different "models" having the same rating) after the P-39C.

A. the 1150hp take off engine with the 8.80 gears.
B. the 1325hp take off engine with the 8.80 gears. Performance above around 12,000ft is pretty much the same. late Ds, and the K & L.
C. the 1200hp take off engine with the 9.60 gears, shows up in the M has performance improved by about 3-4000ft.

3. The US does not officially approve WEP ratings at low altitude until late 1942/ early 1943 in any engine. Despite what units might do at the local level.

testing a P-39M/N in late 1942 using WEP settings doesn't tell you what the planes in the Field were doing with their older engines and with throttle settings anywhere from standard limits to pressure readings having factory service reps 'cringing'.

BTW most of the later Weight charts have the P-39s carrying 300rpg for the wing guns instead of 1000rpg. this would save about 180lbs by itself. or just over 1/2 the weight of the four guns and 1000rpg. If the combat units have already taking out just about 180lbs then taking out another 170-180lbs might not show that big a difference???

Basically the vast majority of the P-39s in combat service in 1942 are the planes using the 1150hp engine with somewhat scattered unofficial "boosting" And it is this performance level that established the P-39s reputation for good or bad.

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Agreed...the first really large-scale production variants (M or N) don't appear until quite late in the game, by which time there are better options available. Funnily enough we've been saying this for dozens of pages now but it still doesn't seem to register in certain quarters.

The other interesting thing about the P-39 are ongoing changes, throught its life, to strengthen the design. These changes were sometimes in areas that hadn't really seen an increase in load. Such beefing up of the airframe would increase empty weight but, more importantly, it perhaps suggests that there were some pervasive flaws--more charitably suboptimal compromises--in the design. Examples include:

P-39Q-15 Reinforced inclined deck to prevent .50 in (13 mm) machine gun mounting cracking, bulkhead reinforcements to prevent rudder pedal wall cracking, a reinforced reduction gearbox bulkhead to prevent cowling former cracking.

P-39Q-25 Reinforced aft-fuselage and horizontal stabilizer structure.


On top of that, we also see constant flip-flopping on the amount of armour protection (this doesn't include photo recce birds which had additional armour for the oil tanks and increased belly armour protection) and reconfiguration to maintain a safe CofG:

P-39D-BE Production variant based on the P-39C with 245 lb (111 kg) of additional armor, self-sealing fuel tanks

P-39N-1 Internal changes to adjust center of gravity when nose guns were fired.

P-59N-5 Reduced armour to from 231lb to 193lb.

P-39Q-1 Armour was increased to 231 lb.

P-39Q-5 Reduced armour to 193lb.

P-39Q-10 Variant with increased armor (228 lb).


To me, this all smacks of tinkering to eke out performance from an airframe that had no growth potential. When you compare it against the Spitfire, which doubled its max all-up weight, the P-39 simply struggled to perform throughout its life in comparison to other contemporary fighters.

buffnut453 said:

The other interesting thing about the P-39 are ongoing changes, throught its life, to strengthen the design. These changes were sometimes in areas that hadn't really seen an increase in load. Such beefing up of the airframe would increase empty weight but, more importantly, it perhaps suggests that there were some pervasive flaws--more charitably suboptimal compromises--in the design. Examples include:

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Wasn't Bell supposedly the "expert" in lightweight fighter design? The antithesis of Grumman, as it were.

well,

It didn't work quite as well as promised either.

Shortround6 said:

BTW most of the later Weight charts have the P-39s carrying 300rpg for the wing guns instead of 1000rpg. this would save about 180lbs by itself. or just over 1/2 the weight of the four guns and 1000rpg. If the combat units have already taking out just about 180lbs then taking out another 170-180lbs might not show that big a difference???

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Maybe I'm ignorant or naive, but it seems to me that removing 70% of one's ammunition in a fighter plane is 1) a tacit admission that the plane cannot do the job as designed and 2) requires much better gunnery from the pilot in order to approach the hit-ratio of a full ammo load-out.

Is there something in the equation I'm missing here?

Shortround6 said:

well,
View attachment 631643
It didn't work quite as well as promised either.

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Beat me to the punch on this as well. What I think is funny how it resembled a concept design that led to the P-39

FLYBOYJ said:

Beat me to the punch on this as well. What I think is funny how it resembled a concept design that led to the P-39

View attachment 631646

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Several of the Army's "lightweight fighter" submissions looked similar.
The Douglas XP-48 was along those lines, too (paper only, never built).

Thumpalumpacus said:

Maybe I'm ignorant or naive, but it seems to me that removing 70% of one's ammunition in a fighter plane is 1) a tacit admission that the plane cannot do the job as designed and 2) requires much better gunnery from the pilot in order to approach the hit-ratio of a full ammo load-out.

Is there something in the equation I'm missing here?

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My opinion, somebody over speced the ammunition load. At full cycle rate they had 50 (five zero) seconds of firing time for the .30 cal guns. 300 rounds gives 15 seconds. The 20mm gun had 6 seconds. The 37mm with 30 rounds had 12 seconds. The .50 cals had around 20 seconds depending on actual rate of fire. Perhaps 300 rounds may not be enough, but anything over 500 rounds was probably too much.

Shortround6 said:

My opinion, somebody over speced the ammunition load. At full cycle rate they had 50 (five zero) seconds of firing time for the .30 cal guns. 300 rounds gives 15 seconds. The 20mm gun had 6 seconds. The 37mm with 30 rounds had 12 seconds. The .50 cals had around 20 seconds depending on actual rate of fire. Perhaps 300 rounds may not be enough, but anything over 500 rounds was probably too much.

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Did anyone in USA do studies of what happened in the BoB? It was recommended to only fire 303s in two second bursts. 50 seconds of firing in 2 second bursts is what happens in video games.

pbehn said:

Did anyone in USA do studies of what happened in the BoB?

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It's possible - the P-47 did get eight .50MGs, which seems to me that they were pretty serious about perforating anything on the receiving end...

GrauGeist said:

It's possible - the P-47 did get eight .50MGs, which seems to me that they were pretty serious about perforating anything on the receiving end...

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Well the British increased from 4 to 8 mgs before the war based on how many bullets it needed to take down a bomber in the time you could expect a plane to have it in its gunsight. The P-47 has the same number but obviously more hitting power, and about the same as a Spitfire with 2 x 20mm canon and 4 x 0.303 mgs. My point was/is they didnt put 4 x 0.5" guns and more than twice the ammunition, just as when the P-51B/C changed to P-51D they didnt put more than 50% additional ammunition they put an extra gun with a similar amount of ammunition. You can always say a plane can be taken down with one bullet, but the more bullets hit the more likely you are to have success, if the time on target is short, you have to hit with more bullets. If you need to fire at things for 50 seconds, the things you are firing dont work.