XP-39 II - The Groundhog Day Thread (2 Viewers)

buffnut453 said:

I believe the only significant difference was in the sizes of populations, not in the degree or extent of mechanical expertise. Circa 1940, the US had a population of 132 million while the UK had just 48 million

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This is where we disagree. I'm convinced that it's an equation in two variables: size of population, and degree of mechanization of that population. Admittedly, nobody worldwide was overly prosperous during the 1930s, but the US, not as depleted and run down by the great world war as the rest of the industrial world, had experienced a booming and prosperous "roaring twenties". Cars, trucks, tractors, motorcycles and even motorboats spread through the population to an unprecedented degree, promoting familiarity with mechanical things on a broad scale. Then along came the depression, and the wherewithal to replace damaged or worn out machinery wasn't there, so folks had to get their hands dirty and coax a few more miles, a few more furrows, a few more fishing trips out of the old girl.
In answer to the question:

buffnut453 said:

"Pre WW2 how many people had even driven a car let alone knew how they worked?"

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the answer is "a significant majority of the population".

FLYBOYJ said:

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Thank you Joe. That saved me an awful lot of searching

XBe02Drvr said:

is "a significant majority of the population".

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"Circa 1940, the US had a population of 132 million while the UK had just 48 million."

Certainly a greater ratio of cars to people in the USA in 1940.
26.5 million on the roads for the USA.
1.34 for Great Britain.

1940 British and European Car Spotters Guide

I don't have it to hand but I believe a book by James Dunnigan

Jim Dunnigan - Wikipedia

went over the american advantage in one chapter. It may have been How to Make War

The US did have a much higher per capita ownership of cars/trucks and radios than any other nation in the world. This means that out of every 100 (or 1000) recruits brought into the service (army, air force, navy) the US had a higher percentage of drivers and low grade mechanics than any other country. It certainly does not mean that every US recruit could drive or change a spark plug or change a radio tube in a radio.

I think you will find that while the British Army was the first to be fully motorized (no more horses except in ceremonial units) The car ownership in the UK by private citizens was significantly lower than in the US. Germany, for all it's propaganda, was even lower.

for the US car ownership between 1927 and 1940 varied from 192 (in 1933) to 245 per 1000 people.

Fact #962: January 30, 2017 Vehicles per Capita: Other Regions/Countries Compared to the United States

as for farm tractors

so by 1940 the US had 1.5 million tractors in use on farms. Yes the US was much larger in population than most other countries, but many of those military age men (18-40) even from rural areas had at least some exposure to cars, or tractors or engines of some sort.

Not saying that other countries had no exposure, just less as percentage of population. This does not make american troops smarter, just better educated or experienced with some mechanical equipment.

And American kids loved their "Jalopies" - Bill Overstreet even had whitewalls on his P-51

It would seem as of the date of Wagner's letter/report (May 1942) none of the P-39s weapons systems was near a desired standard of reliability and/or serviceability.
The 37mm was not reliable and difficult to cock/reload in the air.
The .50 cal guns had problems with the firing solenoids.
The .30 cal guns were difficult to cock/reload in the air.

This may have influenced the pilots into keeping whatever guns they had on the theory that out of three different guns systems, something might go off (and continue to go off) when the trigger was pulled.
later P-39s may have gotten much better. However the question for 1942 is when did each gun system actually get better.
If you lose one .30 out of four your total firepower doesn't take much of a hit, Losing the 37mm or a .50 makes a more significant difference.

It also seems, based on Wagner's report, that his 8th PG pilots were dogfighting with the Zeros they encountered (although head on attacks were mentioned) and boom and zoom tactics were yet to be adopted.

XBe02Drvr said:

.....Then along came the depression, and the wherewithal to replace damaged or worn out machinery wasn't there, so folks had to get their hands dirty and coax a few more miles, a few more furrows, a few more fishing trips out of the old girl.
In answer to the question:
the answer is "a significant majority of the population".

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Hello XBe02Drvr,

The same thing happened again more recently in history though not in the United States.
Does anyone remember what it looked like in Cuba when Americans started visiting again a few years ago?
Many of the cars on the roads were from the 1950's. That was the last time the Cubans could import American cars and there weren't any more coming after that. When you can't get replacements, you learn to keep the ones you have running. It was a beautiful sight for the antique car buff.
Of course there were also a bunch of hulks sitting on the side of the road in various places.

- Ivan.

FLYBOYJ said:

It also seems, based on Wagner's report, that his 8th PG pilots were dogfighting with the Zeros they encountered (although head on attacks were mentioned) and boom and zoom tactics were yet to be adopted.

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It's awfully hard to boom and zoom when you can't get above your enemy. Not enough warning time plus a lackluster rate of climb makes for unpleasant interception geometry. And booming and zooming an opponent with the acceleration and initial climb rate of a Zero in your lead sled can be an unhealthy practice.

FLYBOYJ said:

View attachment 597124

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Two missions, right? One under 1000' and the other at 23000'. The performance above 18000' is probably with drop tank, this is what the performance charts in wwiiaircraftperformance.org show.

buffnut453 said:

I'm not arguing that less weight doesn't improve climb or ceiling. Clearly you're not reading what I'm writing...or you're deliberately misunderstanding it because you don't like the case I'm making.

I'm questioning whether the weight was necessary or not. You have consistently stated that the wing 30 cals and some amount of armour plate were unnecessary. That view is entirely contradicted by the man on the spot, Boyd Wagner, who clearly thought the 30 cals were necessary and he also asked for more armour plate for the engine. In short, the things you claim as unnecessary were deemed by the commander on-the-spot to be necessary.



And you've assiduously ignored the RAAF example of 453 Sqn which reduced the weight of their Buffalos. None of those pilots, with the exception of the Squadron CO, had ANY combat experience prior to 8 Dec 41 and yet they made the weight reduction modifications around Christmas time 1941.

Again, if inexperienced Aussies could do it with the Buffalo, why didn't USAAF squadrons make similar changes with the P-39 when they were in combat for several months? The only logical explanation is that the people on the spot in PNG and Guadalcanal thought that the "extra weight" of wing 30 cals and armour plate was NECESSARY and not "useless."

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In a later report Wagner criticized the reliability of the .30s.

P-39 was a liquid cooled plane, most vulnerable spot on any liquid cooled engine is the coolant radiators. Hard to armor coolant radiators. Nose armor is what should have been deleted. Almost half the weight of the total armor plate/glass protecting the propeller reduction gear that was not armored on the P-38, P-40, P-47 or P-51.

Again, removing just these two items (nose armor and .30calMGs) would have saved 300lbs, increased climb rate by 360feet/minute and combat ceiling to 29000' (at 3000rpm). That climb increase would have made the early P-39s climb faster than the early Zeros. Speed advantage and climb advantage. P-39 could then attack from above.

Again, I have no idea why the AAF chose to retain these items. Russians immediately removed the .30s on virtually all their P-39s and had great success against the Luftwaffe.

GrauGeist said:

Bill Overstreet even had whitewalls on his P-51

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Whitewall tyre (tire!) P-51s look awesome!

Shortround6 said:

US car ownership between 1927 and 1940 varied from 192 (in 1933) to 245 per 1000 people.

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In 1940 the average US family consisted of 3.76 people,* meaning 1000 people consisted of 265.9 families, who owned 245 cars that year.
I'd say that was a pretty high exposure rate to automotive technology. This may be off by a little, since the cars/1,000 number probably includes corporate and public sector fleet cars, taxicabs, etc. IE:Total passenger car production.
*US Census figures

XBe02Drvr said:

This is where we disagree. I'm convinced that it's an equation in two variables: size of population, and degree of mechanization of that population. Admittedly, nobody worldwide was overly prosperous during the 1930s, but the US, not as depleted and run down by the great world war as the rest of the industrial world, had experienced a booming and prosperous "roaring twenties". Cars, trucks, tractors, motorcycles and even motorboats spread through the population to an unprecedented degree, promoting familiarity with mechanical things on a broad scale. Then along came the depression, and the wherewithal to replace damaged or worn out machinery wasn't there, so folks had to get their hands dirty and coax a few more miles, a few more furrows, a few more fishing trips out of the old girl.
In answer to the question:
the answer is "a significant majority of the population".

Click to expand...

Graeme said:

"Circa 1940, the US had a population of 132 million while the UK had just 48 million."

Certainly a greater ratio of cars to people in the USA in 1940.
26.5 million on the roads for the USA.
1.34 for Great Britain.

1940 British and European Car Spotters Guide

Click to expand...

Shortround6 said:

I don't have it to hand but I believe a book by James Dunnigan

Jim Dunnigan - Wikipedia

went over the american advantage in one chapter. It may have been How to Make War

The US did have a much higher per capita ownership of cars/trucks and radios than any other nation in the world. This means that out of every 100 (or 1000) recruits brought into the service (army, air force, navy) the US had a higher percentage of drivers and low grade mechanics than any other country. It certainly does not mean that every US recruit could drive or change a spark plug or change a radio tube in a radio.

I think you will find that while the British Army was the first to be fully motorized (no more horses except in ceremonial units) The car ownership in the UK by private citizens was significantly lower than in the US. Germany, for all it's propaganda, was even lower.

for the US car ownership between 1927 and 1940 varied from 192 (in 1933) to 245 per 1000 people.

Fact #962: January 30, 2017 Vehicles per Capita: Other Regions/Countries Compared to the United States

as for farm tractors
View attachment 597136
so by 1940 the US had 1.5 million tractors in use on farms. Yes the US was much larger in population than most other countries, but many of those military age men (18-40) even from rural areas had at least some exposure to cars, or tractors or engines of some sort.

Not saying that other countries had no exposure, just less as percentage of population. This does not make american troops smarter, just better educated or experienced with some mechanical equipment.

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Thanks for the responses, gents. I'm replying-to-all to save time and coalesce my response into a couple of key thoughts that apply to all.

There are 2 fundamental flaws in the proposed concept of US mechanical superiority. The first is that other countries had a similar proportion of working-age men engaged in agriculture compared to more technical industries (e.g. Shortround's comment about "many of those military age men (18-40) even from rural areas had at least some exposure to cars, or tractors or engines of some sort."). The second, and far more significant, is the creation of a false dichotomy where car ownership/awareness of the internal combustion engine is directly correlated with technical awareness/proficiency.

In the 1930s, the UK had a greater proportion of men engaged in industry rather than agriculture compared to the US (figures for 1940 agriculture/industry: US - 18.5/23.4; UK 10%/36%) (Sources: US , UK). Almost all that industrial output required mechanics of some sort or other, whether maintaining pit engines, factory steam plants, machinery or whatever (e.g. one of my cousins who died in WW1 worked in a brewery but his job was maintaining a steam engine).

Even in rural areas, lower tractor ownership did not equate to a lack of technical expertise. The internal combustion engine was not the only means of providing automotive power, particularly in rural areas. In the UK, a great many farms were still using steam traction engines well into the 1930s. Many of these engines were decades old and required replacement parts to be hand-made/fettled by the owner or the local blacksmith (maybe that's where the workforce came from to hand-make all those Merlin engines? ).

I come from a working-class industrial town and there were literally hundreds of mechanical firms supporting the town; everything from metal forging to glassmaking to toolmaking and machining. Almost the entire town built, operated or maintained mechanical systems of one sort or another. To suggest that, somehow, these men were technically bereft because they couldn't drive and hadn't operated an internal combustion engine is ludicrous. To cite a personal example, my family only got its first car in the early 1950s. However, my three uncles collectively built the car from multiple boxes of bits. My family was dirt-poor working class but my uncles were all sufficiently technically-minded to build a car from components, and two of them had been driving for well over a decade when they made the car...but they'd never owned a car before.

My fundamental gripe is the over-emphasis of car ownership on the penetration of technology within society. America had certain factors which promoted the internal combustion engine. However, the absence of those factors did not make other populations any less technically savvy/aware, percentage-wise across the workforce.

P-39 Expert said:

Nose armor is what should have been deleted. Almost half the weight of the total armor plate/glass protecting the propeller reduction gear that was not armored on the P-38, P-40, P-47 or P-51.

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There you go again, removing weight from the front of the plane, despite being told repeatedly by virtually everyone here that's not an acceptable solution for weight and balance reasons. You could probably get away with it by loading all your nose mounted guns to their maximum capacity, then disconnecting the firing circuits so they can't further lighten the nose. Any way you slice it, you've got to have that weight up there, unless you can relocate some heavy items from behind the engine to the nose compartment, or delete them completely.
This isn't rocket science. The folks who built, maintained, and flew this bird knew this stuff. If there were feasible ways of fixing this issue that didn't trample on USAAF's fetishes they would have thought of them long before your time. The Russians, not slaved to the same fetishes, did exactly that. And it served them well.

buffnut453 said:

In the 1930s, the UK had a greater proportion of men engaged in industry rather than agriculture compared to the US (figures for 1940 agriculture/industry: US - 18.5/23.4; UK 10%/36%)

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Very interesting. What doesn't show here is that with it's vastly greater land under cultivation, and its relatively cheaper cost (in real terms) of farm machinery, US agriculture was significantly more mechanized in terms of machines/farm worker and raw numbers of agricultural machinery than any other nation. So ratios of agricultural/industrial employment aren't necessarily clear cut indicators of likely technical familiarity and experience.
I've taught two Iranians, an Iraqi, and a rural Kenyan to fly, none of whom had much experience with machinery of any kind until adulthood and arrival in the US. Smart guys all, but not technically minded. Visualizing mechanical relationships, understanding airflow, and comprehending such basic physics as gas behavior or gyroscopic properties was a real challenge, despite their well schooled English.

XBe02Drvr said:

Very interesting. What doesn't show here is that with it's vastly greater land under cultivation, and its relatively cheaper cost (in real terms) of farm machinery, US agriculture was significantly more mechanized in terms of machines/farm worker and raw numbers of agricultural machinery than any other nation. So ratios of agricultural/industrial employment aren't necessarily clear cut indicators of likely technical familiarity and experience.

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I entirely agree, but then that's rather my point. Different countries had different factors that drove automation and technology in different directions, or which had differing scales of impact on different industries.

Take the fishing industry, for example. As a proportion of US employment, it was probably quite small. Comparatively, the fishing industry in Britain was much more significant, given it is a small island nation with a smaller population. Now consider the thousands of coastal fishing villages in the UK, each with it's fleet of boats. By the 1930s, these were mostly powered vessels which the crew knee how to maintain. Again, it's not automotive or a tractor...but it required technical and machinery understanding that impacted the UK much more than the equivalent industry in the US.

P-39 Expert said:

Again, removing just these two items (nose armor and .30calMGs) would have saved 300lbs, increased climb rate by 360feet/minute and combat ceiling to 29000' (at 3000rpm). That climb increase would have made the early P-39s climb faster than the early Zeros. Speed advantage and climb advantage. P-39 could then attack from above.

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again, nose armor weight and balance/CG issues.

All three guns systems had issues in May of 1942.
Yanking the .30s may not have been good idea. Not all of the 30s are going to crap out at the same time.

Russians noted the 37mm (at least early ones) were unreliable. They got better later.
The "fix" for the .50 cal may have been relatively easy. Wagner says the firing solenoids weren't powerful enough. New (improved) solenoids could be fitted to existing guns. Please note that the recharging of the .50 cal guns was still a manual affair.

the .50 gun receivers are coming back into the cockpit. the red flags are attached to the cocking/recharging handles. the cylinders sticking back with the slot are the firing solenoids.

P-39 Expert said:

Again, I have no idea why the AAF chose to retain these items. Russians immediately removed the .30s on virtually all their P-39s and had great success against the Luftwaffe.

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You are rearward projecting. Russians pulled .30 cal guns in late 1942 or in 1943 on later P-39s. How many fixes/modifications to the 37mm and .50 cal guns had been done?
Russians were used to light armament and had often resorted to using less than the designed armament to improve performance.
I don't know what the russians got for a rate of fire out the .50s in most of their planes. The British were getting under 500rpm out of the .50s in the AIrcobra I (P-400 and 212 to Russia)
which is about the only commonly known number.
If the 37 packs it in and you have no wing guns you have about 15 rps of .50 cal, assuming they stay working.

Again relaibilty of the gun installations in the spring/summer of 1942 may have been lower than at later times. Making the extra .30 cal guns more important.

XBe02Drvr said:

There you go again, removing weight from the front of the plane, despite being told repeatedly by virtually everyone here that's not an acceptable solution for weight and balance reasons. You could probably get away with it by loading all your nose mounted guns to their maximum capacity, then disconnecting the firing circuits so they can't further lighten the nose. Any way you slice it, you've got to have that weight up there, unless you can relocate some heavy items from behind the engine to the nose compartment, or delete them completely.
This isn't rocket science. The folks who built, maintained, and flew this bird knew this stuff. If there were feasible ways of fixing this issue that didn't trample on USAAF's fetishes they would have thought of them long before your time. The Russians, not slaved to the same fetishes, did exactly that. And it served them well.

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Bell said in writing that the nose armor plate was not needed for ballast/balance on the P-39M. The M was an early model with the same weight and weight distribution as previous and later models. They were able to balance the plane with larger (heavier) propellers and different nose cannons that differed in weight by 140lbs. Bell designed the P-39 to take larger (heavier) three blade and four blade propellers and an auxiliary stage supercharger behind the engine that weighed 175lbs. They certainly were able to maintain proper balance with any or all of these items installed. The nose armor certainly could have been deleted and balance maintained.

If you remove the 100lb nose armor you don't need to relocate an item from behind the engine to the nose compartment. That would make the nose heavier than the tail. You could delete the item behind the engine to balance the plane, or move it to the center of gravity right behind the pilot above the engine. The IFF radio in the tail cone could have been deleted (some other planes didn't have it) or moved up right behind the pilot. If deleted you just saved another 130lbs. The Soviets deleted this radio (and the .30MGs) and reduced the weight of their P-39s by about 330lbs. They kept the nose armor and didn't have any CG problems.

Planes fly better if they are slightly nose heavy compared to slightly tail heavy. Neither is ideal but nose heavy but nose heavy doesn't bring out the problems quite as quickly.

The P-39 was NOT designed to have auxiliary supercharger behind the engine. Where is this story coming from?

You had the XP-39 with turbo UNDER the engine.
XP-39B with turbo taken out and radiators/oil coolers under the engine.
Same airframe rebuilt.
YP-39s and P-39Cs with the same layout out as the XP-39B

When/where was the P-39 with an auxiliary supercharger behind the engine?

The XP-39E was designed to use the Continental ?-1430 engine which was much longer than the Allison, fuselage was almost 2 feet longer than standard P-39. This gave plenty of room for the Allison with the auxiliary supercharger behind it. Bell never tried to stick a two stage Allison in a normal P-39 airframe, if I am wrong please provide photo's. drawings, or memo, letter of it being done. Not somebody just suggesting it.