XP-39 II - The Groundhog Day Thread (1 Viewer)

[SaparotRob]

My point is that applying the American situation to other countries is inappropriate. Equally, applying the situation in the UK to that in Italy is equally futile. The industrial revolution occurred at different times at different regions. Equally, levels of technical awareness varied greatly...but to suggest the US had greater technical savvy because farmers had Model Ts is taking things much too far (IMHO).

I don't think XBe02Drvr was saying Americans were/are more technically savvy (I know I wasn't), but that Americans were more habituated with rudimentary tech than most other nations as a whole.

 

[BiffF15]

MODE O.T. ON

View attachment 597215

The newspaper, which was the main press journal of the Italian Communist Party, says:

Eternal glory to the man who most of all did
for the liberation and progress of humanity
and​

View attachment 597217

Stalin's work is immortal!
Long live his invincible cause!​

Not only I had the dubious privilege of being born and live in the Nation that had the largest Communist Party in the Western world, but also in the Nation with the largest Communist Party in the world after the Soviet Union.

Almost one in three Italians voted until 1989 for the Communist Party and, considering that there were over thirty million voters in Italy, this meant more than ten million Communist votes.

I imagine that it is very difficult for an American or a British to understand how the propaganda of such a strong Communist Party was: everything had been invented in the Soviet Union, from radio to condensed milk and the Party newspaper every day gave the news of some amazing discovery made by some Soviet scientist. The Italians were divided in two: those who believed in it and who would have been ready to swear on what "L'Unità" said, and those who had been vaccinated and instead did not believe a single word of it. In 1989 we saw who History proved right.

Elmas,

The above bolded statement caught my attention. I fixed it in the following sentence, made more US appropriate...

Every single statement, or even word, in these times, made by The Main Stream Media, had to be strictly viewed with a large does of WTF...

MODE O.T. OFF

Cheers,
Biff

 

[P-39 Expert]

Hello P-39 Expert,

The P-39M was one of the Mid Production versions, about the same as the P-39N.
The engine was the V-1710-83 with significantly better altitude performance than the earlier models with the V-1710-35 and V-1710-63. It carried a bigger propeller (11 feet 1 inch) with different reduction gearing because the engine had the altitude performance to use it. Earlier models had a 10 feet 4 1/2 inch propeller.

What could be done with this engine is not indicative of what would work with earlier engines.

What change in nose cannons made a difference of 140 pounds?

- Ivan.

The M was an earlier model, 7000 more N/Q models would still be produced out of 9500 total.

The larger propeller was introduced with the 167th N model. Reduction gear was the same 2:1 as the D-2/K/L that used the -63 engine.

The 37mm cannon weighed 300lbs with ammo, the 20mm 160lbs with ammo. Difference 140lbs.

 

[buffnut453]

I don't think XBe02Drvr was saying Americans were/are more technically savvy (I know I wasn't), but that Americans were more habituated with rudimentary tech than most other nations as a whole.

My use of the term tech savvy reflected exactly what you stated more elegantly as "more habituated with rudimentary tech.". I just couldn't be bothered typing long words like habituated and rudimentary with my fumble-thumbs.

 

[Ivan1GFP]

Hello P-39 Expert,

The M was an earlier model, 7000 more N/Q models would still be produced out of 9500 total.

It depends on how you want to group things. Most books I have count the L through N models as the "Mid Production" series. There were about 240 M models produced and about 2000 N models produced.

The larger propeller was introduced with the 167th N model. Reduction gear was the same 2:1 as the D-2/K/L that used the -63 engine.

This is still different from the 1.8:1 reduction gear originally used on the P-39C/D/F series. The propeller on the M was 11 feet 1 inch diameter. The N model changed the reduction gear ratio to 2.23:1 and used either a 11 feet 4 inch or 11 feet 7 inch propeller. The Q used a 11 feet 7 inch propeller.
The early series propellers on -35 and -63 engines were almost always 10 feet 4 1/2 inch regardless of whether they were Curtiss Electric or Aeroproducts manufacture.

The 37mm cannon weighed 300lbs with ammo, the 20mm 160lbs with ammo. Difference 140lbs.

This is a cool little bait and switch you are trying to pull here. There were plenty of P-39 models armed with the 37 mm cannon before the M model came along, notably the C, D, F, J, K and L.
To say the M had cannons weighing 140 pounds more is a pretty poor argument when the majority of US service models already carried the same gun as the M.

- Ivan.

 

[SaparotRob]

My use of the term tech savvy reflected exactly what you stated more elegantly as "more habituated with rudimentary tech.". I just couldn't be bothered typing long words like habituated and rudimentary with my fumble-thumbs.

A full tenured professor at Brooklyn College said I was the best B.S. artist he ever met.

 

[SaparotRob]

But no better than a B.S. artist from any other nation.

 

[gordonm1]

I've read here the P40 was lengthened for the higher powered engines/speed giving more torque. I'm not sure how this played out with the P39? No changes?

Also any comparison on what actual metals were used on each plane? Duralum or something? steel?

 

[FLYBOYJ]

Lighter P-39 would have taken about 3 hours of maintenance crew's time at a combat base. Remove the wing .30s and their mounts, chargers, heaters and ammo boxes, and the nose armor plate. While you're at it remove the IFF radio and save another 130lbs. Still have the voice radio.

Having worked on many aircraft (to include warbirds) I can somewhat agree with your field removal of some the equipment to save weight, 3 hours of maintenance is a bit skewed unless you're going to just hack the items mentioned out, not plug rivet holes and possibly leave wire bundles.

The 1.2feet/minute climb per pound of weight saved comes from wwiiaircraftperformance.org. Compare the climb rates of the P-39D and the P-39C at their different weights. C climbed 1000fpm faster than the D and weighed 836lbs less, making each pound of weight improve climb by 1.2fpm. I know the C model did not have self sealing tanks and armor plate but it had the exact same engine, propeller and aerodynamics as the D model. Only difference in performance was the weight.

Your linear calculation does not address weight and balance of the items removed. If you're lucky enough to make the aircraft slightly tail heavy, it will fly faster but be more unstable, something already plaguing the P-39. You're comparing the C and D models and by your own post, no armor and no self sealing tanks. So you're making your point with performance numbers from an aircraft that was really not capable of entering combat????

 

[FLYBOYJ]

Also any comparison on what actual metals were used on each plane? Duralum or something? steel?

I think you will find both aircraft were constructed of similar material (24T, mild steel where required)

 

[MiTasol]

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.

Sorry Shortround but that is not correct. The cylinders sticking back with the slot are actually the buffers (shock absorbers)

The American 30 cal, 50 cal and 20mm solenoids look like this and mount on the side of the gun.

These pictures show them mounted on the P-39 wing guns.

The Brit .303 solenoids look like this and mount on the bottom of the gun

 

[MiTasol]

the red flags are attached to the cocking/recharging handles.

The "red flags" are, in fact, the cocking handles.

Again from the manual

Note items 20 and 60

 

[wuzak]

It depends on how you want to group things. Most books I have count the L through N models as the "Mid Production" series. There were about 240 M models produced and about 2000 N models produced.

Only the N and Q models followed the M. That would suggest the M was a later production version!

The Q was in production 8 or 9 months after the M.

 

[MiTasol]

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.

You have obviously never done weight and balance on a real aircraft, or actually worked on a P-39, or you would know that much of what you wrote above is not correct. Worse still, as many of the pilots on the forum will tell you, a stall caused by aft CG on many aircraft is stable meaning you cannot regain control. Regardless of power or control inputs the aircraft remains stalled and drops like a brick with almost zero forward speed. I have gone to two funerals caused by this mistake. Both pilots had carefully calculated there gross weight CG but forgot to check their low fuel, low speed, gear down CG.

You will note in your own writing that the Soviets removed the IFF to compensate for the removal of the 30 cals. There is nothing else heavy back there to remove except the oil tank and that is aft of the fuselage joint line. There is a tie down kit but that weighs about 5 or 6 lbs so is not going to help. Yes you could move the oil tank (and coolant tank) into the wing leading edge like the Hurricane did but that introduces all sorts of other problems. And you can remove the radios from above the engine (they and the engine are actually aft of the CG which is just above 2 = fuel, 9 = guns and 10 = wing ammo in the diagram the below and all forward of the CG) but where would you fit them?
\

On any aircraft if you remove 100lb from the very front of the aircraft you must compensate by removing weight from the rear.
If the weight you remove aft of the cg is only 50 lb then it must come from twice the distance from the CG that the removed weight was. etc etc etc

I have never seen anything from Bell saying the designed the P-39 to take the ASB used on the P-63. The coolant tank takes up all that space behind the engine on a P-39 and there is also structure there, including the fuselage bolt line, that would prevent an ASB being fitted. Find a flying example near you and go visit it as soon as restrictions allow. The lack of free space in that powerplant will surprise you and clearly show that there is no way it could fit an ASB.

They did design it with a turbo but that went under the engine.

This diagram shows the engine and supercharger outline but does not show the starter or generator or any of the mass of plumbing and "small" parts that extend from the rear of the engine. The oil tank is aft of the bolt line but the bulkhead is shaped to allow part of it to extend into the engine bay. There is no way an ASB would fit there.

 

[Shortround6]

MiTasoll

Thank you for the correction and the photos/pages.

 

[XBe02Drvr]

MiTasoll

Thank you for the correction and the photos/pages.

I was writing a similar treatise on weight and balance, but MiTasol's was way better.
Thanks, MiTasol !

 

[Ivan1GFP]

Only the N and Q models followed the M. That would suggest the M was a later production version!

The Q was in production 8 or 9 months after the M.

Hello Wuzak,

Your timing is probably correct, but there are other factors.
1800 P-39G models were originally ordered. None were actually built.
Instead, the contract for the G models was distributed in small batches into the K, L, M, and N (large batch) which don't differ much except in fairly minor detail and so are considered the same mid production series.

As for Letter designations in the P-39, in other fighters such as the P-47D, the degree of change between one Letter designation in the P-39 and the next was often less than that from one production block and the next in other fighters.
Look at how many versions were simply because the propeller was from a different manufacturer.

- Ivan.

 

[windhund116]

Thought some may like this photo. Lineup of some USAAF fighters used in SWPA action.

 

[SaparotRob]

Is there a date on that photo?

 

[windhund116]

No date on photo. Would be 1942-43, because of type of USAAF roundels?