XP-39 II - The Groundhog Day Thread

[glennasher]

I think the best solution would be to scrap the whole idea of the P-39.

 

[P-39 Expert]

I think the best solution would be to scrap the whole idea of the P-39.

Sure, in hindsight the AAF should have pushed development of the P-51 from the beginning. Then we wouldn't have needed the enormously expensive and complicated P-38 and P-47 either. But remember the earliest P-51 to see combat was in England for the British in April 1942 as the Mustang I. It was useless for anything but ground attack and reconnaissance. Top speed was 370mph at 13000' but climb was only 1980fpm at only 11000' and combat ceiling (1000fpm climb) was only 21000'. At that altitude speed had dropped to 357mph.

Of course in this scenario the two stage Allison V-1710 should have been pushed forward at a faster rate also. The V1710-47 was tested in the XP-39E in April 1942. This engine had the variable speed hydraulic clutch and generated its full 1150HP at 21000'. Simply move the carburetor from the auxiliary stage to its normal position on the engine and critical altitude is up to 25000'. Another three months to get into production and debug any glitches and a two stage P-51 would have been in production in July 1942. Combat by the end of '42. A year later the two stage Packard Merlin P-51 would have been in production. Hindsight is wonderful.

But what to do between Pearl Harbor and the end of 1942? Without the P-39 we would have been stuck with the P-40E. Top speed in the 340mph range at 13000'. Combat ceiling (1000fpm climb) 17000'. Literally could not reach 20000' in clean condition in a combat scenario. No chance against the contemporary Zero, 109 or 190.

Early P-39D/F/P-400 could have easily weighed 7100-7200lbs with performance of 375mph and climb of 2500fpm at 20000' by mid Very competitive/superior to the SpitfireV and Me109F. Armor plate/glass with self sealing fuel tanks and cannon/heavy machine gun armament. Totally wasted by AAF mismanagement.

 

[Ivan1GFP]

Hello P-39 Expert,

Here is a table with armour locations and weights:

The 100lb nose armor plate was unnecessary since it protected the reduction gear which was not armored in any other AAF/Navy planes. P-39 already had armor plate directly in front the pilot mounted on the bulkhead separating the cockpit from the armament bay.

British clearly specified way too much armor plate/glass for the P-400. Total weight was 265lbs as compared to 111lbs for the contemporary P-40E.

The nose armor plate was present whether the nose cannon was 37mm or 20mm. The 37mm was 140lbs heavier than the 20mm so Bell obviously had the ability to adjust the COG.

Completely agree that the Gearbox Armour was unnecessary for PROTECTION.
As for presence of the armour plate regardless of the 20 mm or 37 mm cannon installation, please observe that the Gearbox Armour varies a bit in weight depending on version. The need for protection certainly would not vary, so it suggests that it was there for balance. Note items 4, and 5 as well. Those pieces would work together to compensate pretty well for the reduced weight of the 20 mm cannon.
This additional armour appears to be the means that Bell compensated for the CoG results of replacing the cannon.

As for whether this quantity of armour was necessary other than for balance, consider that the RAF at the time had actual combat experience with modern aircraft while the US Army did not.

The armor for the oil tank weighed only 29lbs and was absolutely necessary as it protected the oil tank and engine from the rear.

The Soviets were easily the most successful operator of the Airacobra. In their testing of spin characteristics of the Airacobra, they chose to remove the oil tank armour from 4 of the 5 test aircraft. They actually retained the wing armament for more of the aircraft. They obviously deleted the wing guns on most of their operational aircraft, but I do not know if the oil tank armour was retained.
The problem wasn't so much the weight of the armour as the location which was very far aft of the CoG.

Regarding the P-39M Bell stated that the nose armor plate was not necessary for balance. The need to adjust weights for the COG was obviously a design necessity since from the beginning the P-39 was designed for larger heavier propellers (both 3 and 4 blade) and the possibility of the mechanical auxiliary stage supercharger located aft of the engine as used on the Allison -47 and -93.

It sounds like the P-39M may have had a heavy enough propeller to compensate. I know that some other items of equipment were moved around in later versions to make the aircraft less sensitive to CoG changes when loads were expended.

The only factor that kept the early P-39 from being competitive with the contemporary SpitfireV and Me109F was excessive weight. This was easily corrected by deleting unnecessary armor plate (specified by the British) and the useless .30cal wing guns. The lighter P-39 had self sealing fuel tanks, armor plate/glass and cannon/heavy machine gun armament.

There were other issues with the early P-39 that made it generally inferior to the Spitfire V and Me 109F.
The obvious issue is a lack of sufficient altitude performance. Later versions improved on that, but everyone else improved as well.
The other issues are a lack of control harmony. The roll rate of the P-39 was distinctly slow. The elevators were overly sensitive. (This is from NACA Reports and a few pilot accounts.)
Deleting the 30 cal wing guns might have been a good idea but it didn't leave enough gun power remaining.
Now, one might argue that the Soviets did this and they were successful, but the Soviets were generally satisfied with fairly lightly armed fighters with one MG and one Motorcannon. The Soviets also had much faster firing MGs than most other countries did.
The early .50 BMG installed in the cowl of the Airacobra had a particularly low firing rate and synchronizing for firing through the propeller wasn't going to help. The 37 mm gun was powerful but had poor ballistics and with 30 rounds was only good for 12 seconds of use.
For pure air to air use, the armament of the P-39C may have made better sense.

- Ivan.

 

[P-39 Expert]

Hello P-39 Expert,

Here is a table with armour locations and weights:View attachment 596327



Completely agree that the Gearbox Armour was unnecessary for PROTECTION.
As for presence of the armour plate regardless of the 20 mm or 37 mm cannon installation, please observe that the Gearbox Armour varies a bit in weight depending on version. The need for protection certainly would not vary, so it suggests that it was there for balance. Note items 4, and 5 as well. Those pieces would work together to compensate pretty well for the reduced weight of the 20 mm cannon.
This additional armour appears to be the means that Bell compensated for the CoG results of replacing the cannon.

As for whether this quantity of armour was necessary other than for balance, consider that the RAF at the time had actual combat experience with modern aircraft while the US Army did not.



The Soviets were easily the most successful operator of the Airacobra. In their testing of spin characteristics of the Airacobra, they chose to remove the oil tank armour from 4 of the 5 test aircraft. They actually retained the wing armament for more of the aircraft. They obviously deleted the wing guns on most of their operational aircraft, but I do not know if the oil tank armour was retained.
The problem wasn't so much the weight of the armour as the location which was very far aft of the CoG.



It sounds like the P-39M may have had a heavy enough propeller to compensate. I know that some other items of equipment were moved around in later versions to make the aircraft less sensitive to CoG changes when loads were expended.



There were other issues with the early P-39 that made it generally inferior to the Spitfire V and Me 109F.
The obvious issue is a lack of sufficient altitude performance. Later versions improved on that, but everyone else improved as well.
The other issues are a lack of control harmony. The roll rate of the P-39 was distinctly slow. The elevators were overly sensitive. (This is from NACA Reports and a few pilot accounts.)
Deleting the 30 cal wing guns might have been a good idea but it didn't leave enough gun power remaining.
Now, one might argue that the Soviets did this and they were successful, but the Soviets were generally satisfied with fairly lightly armed fighters with one MG and one Motorcannon. The Soviets also had much faster firing MGs than most other countries did.
The early .50 BMG installed in the cowl of the Airacobra had a particularly low firing rate and synchronizing for firing through the propeller wasn't going to help. The 37 mm gun was powerful but had poor ballistics and with 30 rounds was only good for 12 seconds of use.
For pure air to air use, the armament of the P-39C may have made better sense.

- Ivan.

Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39. Pretty impressive considering less than 5000 were delivered to them. Combat P-39s retained the oil tank armor and virtually all deleted the useless .30cal wing guns TO REDUCE WEIGHT and improve performance. All were fully combat capable at over 8000 meters (26500'). And they considered the 37mm cannon and twin .50cal MGs to be optimal armament for air to air combat. The 37mm cannon destroyed most all planes with on hit.

If the nose gearbox armor was unnecessary for protection then it should have been deleted along with the unnecessary oxygen tank protection. It was ARMOR. If not needed it should have been deleted. Bell had ways to adjust the COG including moving the IFF radios from the tail cone to above the engine right behind the pilot. Or removing it altogether like the Soviets did. Or other ways to adjust COG.

ONLY reason P-39 altitude performance was insufficient was WEIGHT, and then only on the earlier D/F/K/L models. Reduce the weight and altitude performance improves greatly. Roll rate and control harmonization was just fine. Was Chuck Yeager's favorite plane, until he got the two stage P-51B in 1944.

 

[Shortround6]

I would note that the Americans used a low pressure oxygen system 400-450psi in the bottles.
The British used a high pressure system, so far I have not found what pressure they were using.
When I was a fireman with 2200psi air bottles we considered 400-500psi to be empty.
Filling bottles (much like scuba tanks) was done in a steel cylinder to hold the bottle in case of mishap.

Perhaps the British high pressure bottles posed a higher risk to the aircraft if punctured?

 

[P-39 Expert]

I would note that the Americans used a low pressure oxygen system 400-450psi in the bottles.
The British used a high pressure system, so far I have not found what pressure they were using.
When I was a fireman with 2200psi air bottles we considered 400-500psi to be empty.
Filling bottles (much like scuba tanks) was done in a steel cylinder to hold the bottle in case of mishap.

Perhaps the British high pressure bottles posed a higher risk to the aircraft if punctured?

Valid point, but it ruins my theory that the Brits made the P-400 too heavy to get out of the contract.

 

[Ivan1GFP]

Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39. Pretty impressive considering less than 5000 were delivered to them. Combat P-39s retained the oil tank armor and virtually all deleted the useless .30cal wing guns TO REDUCE WEIGHT and improve performance. All were fully combat capable at over 8000 meters (26500'). And they considered the 37mm cannon and twin .50cal MGs to be optimal armament for air to air combat. The 37mm cannon destroyed most all planes with on hit.

Hello P-39 Expert,

That number of "less than 5000" accounted for over half the total production of the P-39.
The Soviets initially had their issues with the P-39 as well, but they spent the time to iron out the bugs.
The main reason why their pilots liked the Kobra was because it was generally reliable and worked as advertised unlike many of their domestic designs especially early in the war when the first lend-lease aircraft arrived.
Their battles tended to be at very low altitude where the Airacobra was very good and considerably better than than the early Yak and LaGG fighters even when things were working right.
As for being "combat capable" over 8000 Meters (26500 Feet), I wonder what that is in comparison to?
Is it compared to Soviet fighters which may be believable or against German fighters which would be wishful thinking?
You can strip off a couple hundred pounds, but if the engine can't supply enough power, performance is still going to be rather poor.

As for stripping off the .30 cal wing guns, Soviets preferred centrally mounted armament. They stripped off the wing guns from their P-40 Tomahawks as well which only left the two .50 cal cowl guns WITHOUT a motorcannon.

If the nose gearbox armor was unnecessary for protection then it should have been deleted along with the unnecessary oxygen tank protection. It was ARMOR. If not needed it should have been deleted. Bell had ways to adjust the COG including moving the IFF radios from the tail cone to above the engine right behind the pilot. Or removing it altogether like the Soviets did. Or other ways to adjust COG.

I believe a better way to consider the nose armour on the Airacobra was as "permanent ballast".
Many aircraft have this kind of thing. Removing it may make the aircraft lighter, but also makes it unsafe to fly under certain conditions.
If you really believe that it is possible to remove the Gearbox armour and other "unnecessary" nose armour from the P-400, I suggest you take the chart from the P-39Q manual and see where the CoG would end up with moving around the items you are proposing.
Just keep in mind that the stability becomes unacceptable in the early Airacobra when stores are expended.
This is corroborated by numerous pilot accounts.

ONLY reason P-39 altitude performance was insufficient was WEIGHT, and then only on the earlier D/F/K/L models. Reduce the weight and altitude performance improves greatly. Roll rate and control harmonization was just fine. Was Chuck Yeager's favorite plane, until he got the two stage P-51B in 1944.

A better reason for lack of altitude performance for those models was engines that had a critical altitude in the 12,000 - 13,000 Feet range.
NACA report L602 describes the control issues.
Chuck Yeager was an expert pilot and expert pilots can often overcome the idiosyncrasies of an aeroplane.

- Ivan.

 

[muskeg13]

The Airacobra (P.39) "This was a very inferior fighter aircraft at all times during the war. Its maneuverability, speed, dive and climbing qualities were were poor. It was one of the easiest of the Allied fighters to shoot down."

Galland, Adolf. Generalleutnant. The Luftwaffe Fighter Force: The View from the Cockpit (p. 25). Skyhorse. Kindle Edition.
The Luftwaffe Fighter Force: The View from the Cockpit (p. 217). Skyhorse. Kindle Edition.

 

[wuzak]

Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39. Pretty impressive considering less than 5000 were delivered to them. Combat P-39s retained the oil tank armor and virtually all deleted the useless .30cal wing guns TO REDUCE WEIGHT and improve performance. All were fully combat capable at over 8000 meters (26500'). And they considered the 37mm cannon and twin .50cal MGs to be optimal armament for air to air combat. The 37mm cannon destroyed most all planes with on hit.

If the nose gearbox armor was unnecessary for protection then it should have been deleted along with the unnecessary oxygen tank protection. It was ARMOR. If not needed it should have been deleted. Bell had ways to adjust the COG including moving the IFF radios from the tail cone to above the engine right behind the pilot. Or removing it altogether like the Soviets did. Or other ways to adjust COG.

I notice that of all the things you state the Soviets took out of the P-39 to improve performance, the nose armour was not one.

 

[P-39 Expert]

I notice that of all the things you state the Soviets took out of the P-39 to improve performance, the nose armour was not one.

Correct. But they did remove the IFF radio in the tail cone that weighed 120lbs. That should have been enough to throw the plane totally out of balance. Like I have said before, the P-39 was designed from the beginning to be able to be balanced with different weights both fore and aft.

 

[P-39 Expert]

The Airacobra (P.39) "This was a very inferior fighter aircraft at all times during the war. Its maneuverability, speed, dive and climbing qualities were were poor. It was one of the easiest of the Allied fighters to shoot down."

Galland, Adolf. Generalleutnant. The Luftwaffe Fighter Force: The View from the Cockpit (p. 25). Skyhorse. Kindle Edition.
The Luftwaffe Fighter Force: The View from the Cockpit (p. 217). Skyhorse. Kindle Edition.

He never ran into Alexander Pokryshkin.

 

[P-39 Expert]

Hello P-39 Expert,

That number of "less than 5000" accounted for over half the total production of the P-39.
The Soviets initially had their issues with the P-39 as well, but they spent the time to iron out the bugs.
The main reason why their pilots liked the Kobra was because it was generally reliable and worked as advertised unlike many of their domestic designs especially early in the war when the first lend-lease aircraft arrived.
Their battles tended to be at very low altitude where the Airacobra was very good and considerably better than than the early Yak and LaGG fighters even when things were working right.
As for being "combat capable" over 8000 Meters (26500 Feet), I wonder what that is in comparison to?
Is it compared to Soviet fighters which may be believable or against German fighters which would be wishful thinking?
You can strip off a couple hundred pounds, but if the engine can't supply enough power, performance is still going to be rather poor.

As for stripping off the .30 cal wing guns, Soviets preferred centrally mounted armament. They stripped off the wing guns from their P-40 Tomahawks as well which only left the two .50 cal cowl guns WITHOUT a motorcannon.



I believe a better way to consider the nose armour on the Airacobra was as "permanent ballast".
Many aircraft have this kind of thing. Removing it may make the aircraft lighter, but also makes it unsafe to fly under certain conditions.
If you really believe that it is possible to remove the Gearbox armour and other "unnecessary" nose armour from the P-400, I suggest you take the chart from the P-39Q manual and see where the CoG would end up with moving around the items you are proposing.
Just keep in mind that the stability becomes unacceptable in the early Airacobra when stores are expended.
This is corroborated by numerous pilot accounts.



A better reason for lack of altitude performance for those models was engines that had a critical altitude in the 12,000 - 13,000 Feet range.
NACA report L602 describes the control issues.
Chuck Yeager was an expert pilot and expert pilots can often overcome the idiosyncrasies of an aeroplane.

- Ivan.

P-39s were not low altitude planes. Even though the -85 engine's critical altitude was only 15000', service ceiling was 38500'. About the same as contemporary (1943) Corsairs, Hellcats, Thunderbolts, Lightnings and Me109s. Better than FW190 and Typhoon. Would outclimb all those planes up to 25000'.

Earlier P-39s with -39 or -63 engines had good altitude performance (for 1942) if weight was kept down like the Russians did. Unfortunately the AAF did not.

 

[Peter Gunn]

Hello P-39 Expert,

Here is a table with armour locations and weights:View attachment 596327



Completely agree that the Gearbox Armour was unnecessary for PROTECTION.
As for presence of the armour plate regardless of the 20 mm or 37 mm cannon installation, please observe that the Gearbox Armour varies a bit in weight depending on version. The need for protection certainly would not vary, so it suggests that it was there for balance. Note items 4, and 5 as well. Those pieces would work together to compensate pretty well for the reduced weight of the 20 mm cannon.
This additional armour appears to be the means that Bell compensated for the CoG results of replacing the cannon.

As for whether this quantity of armour was necessary other than for balance, consider that the RAF at the time had actual combat experience with modern aircraft while the US Army did not.



The Soviets were easily the most successful operator of the Airacobra. In their testing of spin characteristics of the Airacobra, they chose to remove the oil tank armour from 4 of the 5 test aircraft. They actually retained the wing armament for more of the aircraft. They obviously deleted the wing guns on most of their operational aircraft, but I do not know if the oil tank armour was retained.
The problem wasn't so much the weight of the armour as the location which was very far aft of the CoG.



It sounds like the P-39M may have had a heavy enough propeller to compensate. I know that some other items of equipment were moved around in later versions to make the aircraft less sensitive to CoG changes when loads were expended.



There were other issues with the early P-39 that made it generally inferior to the Spitfire V and Me 109F.
The obvious issue is a lack of sufficient altitude performance. Later versions improved on that, but everyone else improved as well.
The other issues are a lack of control harmony. The roll rate of the P-39 was distinctly slow. The elevators were overly sensitive. (This is from NACA Reports and a few pilot accounts.)
Deleting the 30 cal wing guns might have been a good idea but it didn't leave enough gun power remaining.
Now, one might argue that the Soviets did this and they were successful, but the Soviets were generally satisfied with fairly lightly armed fighters with one MG and one Motorcannon. The Soviets also had much faster firing MGs than most other countries did.
The early .50 BMG installed in the cowl of the Airacobra had a particularly low firing rate and synchronizing for firing through the propeller wasn't going to help. The 37 mm gun was powerful but had poor ballistics and with 30 rounds was only good for 12 seconds of use.
For pure air to air use, the armament of the P-39C may have made better sense.

- Ivan.

Hi Ivan,

Good post, in reading and looking at the chart, I was considering the P-400, so correct me if I'm wrong but my aerodynamically untrained eye sees the if you were to remove armor plates:
1 @ 95.45 lbs
4 @ 35.01 lbs
5 @ 27.60 lbs
---------------
158.06 lbs <-- total weight reduction
=========

If you remove that much weight from the nose from an airplane that we're talking does not eject casings or even links to try to keep the CoG from getting too askew, how will said removal of armor help?

The whole "British added weight to kill the P-39/400" line that some (not you obviously) tout seems a bit disingenuous to say the least. Apparently I've used that word (disingenuous) twice now whilst describing the P-39...

My general feelings, not directed at you Ivan, just as an observation is this:
I've seen mention of other contemporary fighters and their armor schemes mentioned. I think it warrants mentioning that for sake of argument, the Hellcat got what nickname again? I do believe the F6F was somewhat easy to fly if memory serves, the Airacobra... not so much.

 

[P-39 Expert]

Hi Ivan,

Good post, in reading and looking at the chart, I was considering the P-400, so correct me if I'm wrong but my aerodynamically untrained eye sees the if you were to remove armor plates:
1 @ 95.45 lbs
4 @ 35.01 lbs
5 @ 27.60 lbs
---------------
158.06 lbs <-- total weight reduction
=========

If you remove that much weight from the nose from an airplane that we're talking does not eject casings or even links to try to keep the CoG from getting too askew, how will said removal of armor help?

The whole "British added weight to kill the P-39/400" line that some (not you obviously) tout seems a bit disingenuous to say the least. Apparently I've used that word (disingenuous) twice now whilst describing the P-39...

My general feelings, not directed at you Ivan, just as an observation is this:
I've seen mention of other contemporary fighters and their armor schemes mentioned. I think it warrants mentioning that for sake of argument, the Hellcat got what nickname again? I do believe the F6F was somewhat easy to fly if memory serves, the Airacobra... not so much.

I'm not Ivan but thought I would reply anyway.

The whole "British added weight to kill the P-39/400" is my theory and mine alone as far as I know.

Regarding removing the armor from the nose, #4 and #5 were removed from all the other P-39 models. Removing #1 has always been my idea. 265lbs of armor is way too much for a small fighter as evidenced by the P40E having only 111lbs and the SpitfireV and Me109F having much less also. The Hellcat had only 200lbs of armor plate/glass and it had a 2000HP engine.

P-39 in all forms was an extremely easy airplane to fly. Tricycle landing gear made taxi, takeoff and landing much easier than taildraggers that were blind forward. Would turn inside any plane not made in Japan or named Spitfire, including the Hellcat. Would not tumble unless all nose ammo was expended, and then only on purpose.

 

[Ivan1GFP]

Hi Ivan,

Good post, in reading and looking at the chart, I was considering the P-400, so correct me if I'm wrong but my aerodynamically untrained eye sees the if you were to remove armor plates:
1 @ 95.45 lbs
4 @ 35.01 lbs
5 @ 27.60 lbs
---------------
158.06 lbs <-- total weight reduction
=========

If you remove that much weight from the nose from an airplane that we're talking does not eject casings or even links to try to keep the CoG from getting too askew, how will said removal of armor help?

Hello Peter Gunn,

The Airacobra at least with the 37 mm cannon had the reputation of longitudinal instability when the ammunition in the nose was expended. Apparently this was the situation even though cases and links were retained, so your conclusion regarding the consequences of removing nose armour is the same as mine. The aeroplane is lightened but becomes unsafe to fly.
I know that early models of the P-38 Lightning also had a similar issue. If no ammunition was carried, there needed to be ballast in the nose.

The whole "British added weight to kill the P-39/400" line that some (not you obviously) tout seems a bit disingenuous to say the least. Apparently I've used that word (disingenuous) twice now whilst describing the P-39...

As you say, I don't believe it was a matter of intentionally adding weight but more partial versus full ammunition and fuel loads and some added equipment. I also don't believe the switch to a 20 mm cannon was the best idea. The 37 mm already had a short duration of fire (12 seconds). The 20 mm had twice the ammunition load but four times the firing rate so the duration was only 6 seconds.
I believe a bigger problem was that British testing used throttle settings that were lower than what was used in the US and the requirement for snow filters.
For British testing, the Take-Off setting was determined to be 44 inches Hg and 3000 RPM.
For Speed runs, the maximum throttle setting was 42 inches Hg and 3000 RPM.
With a lower throttle setting, the critical altitude should have been increased over what was achieved with US Airacobras, but it was actually the same (13,000 feet) which suggests that there was some kind of intake restriction.
For Climb tests, 2600 RPM and 37 inches Hg was used
Even the "Take-Off" setting used was only the typical "Military" setting used in US service.
No test used the War Emergency setting which should have been available.
Under these conditions, it isn't a big surprise that the performance achieved was less than impressive.

My general feelings, not directed at you Ivan, just as an observation is this:
I've seen mention of other contemporary fighters and their armor schemes mentioned. I think it warrants mentioning that for sake of argument, the Hellcat got what nickname again? I do believe the F6F was somewhat easy to fly if memory serves, the Airacobra... not so much.

The P-39 was actually very easy to fly. Take-Offs and Landings were particularly easy. Visibility was excellent. Ground handling was excellent except that it had a tendency to overheat with prolonged running on the ground.
Control response was quick though ailerons were a bit heavy.
It developed a reputation for being a "Hot Ship" while P-40s with similar straight line performance didn't have the same reputation.

Regarding Armour, I had hoped to save this discussion for a new thread, but here goes:
Everyone seems to be hung up on the quantity of armour carried by an aircraft on the assumption that more armour means that the aircraft is "tougher" and harder to shoot down.
A year ago, I also was of the same opinion, but since then, I came across a discussion / explanation that made a lot more sense. Redundant structures and surplus structural strength, and designs that locate critical components in protected areas is much more important that the amount of armour carried. Realistically, even aircraft such as the Hellcat, Corsair, or Thunderbolt don't carry armour except to protect critical areas. Most of the airframe is unprotected. Certain aircraft such as the N1K2 Shiden-KAI had a reputation for toughness but actually carried no armour at all. Other aircraft such as the A6M were strong enough under normal conditions but didn't have enough redundant and surplus strength to hold together when major structures were damaged.
Having cockpit armour and self sealing fuel tanks is great but it doesn't make much difference when the whole wing comes off with a few hits.

- Ivan.

 

[Ivan1GFP]

P-39s were not low altitude planes. Even though the -85 engine's critical altitude was only 15000', service ceiling was 38500'. About the same as contemporary (1943) Corsairs, Hellcats, Thunderbolts, Lightnings and Me109s. Better than FW190 and Typhoon. Would outclimb all those planes up to 25000'.

Hello P-39 Expert,

I seem to remember that Shortround6 gave a pretty good description of why the P-39 didn't have a lot of use in the ETO for the escort missions that required fighters. As for comparison for altitude performance, it isn't just a matter of being able to reach a decent service ceiling. Even the A6M2 and La 5FN could do that. It is a matter of surplus power and performance when it got to typical altitudes for engagement in the theater.

Earlier P-39s with -39 or -63 engines had good altitude performance (for 1942) if weight was kept down like the Russians did. Unfortunately the AAF did not.

The Soviets also did a few things with those early P-39 that were not going to be acceptable in US service. They were typically using throttle settings beyond the War Emergency settings other services used. To them, it was acceptable to have to replace engines after a few flights. The whole aircraft was likely to be lost after a couple months anyway.
The problem with extra high throttle settings is that it only works as long as the supercharger can supply enough boost to allow it. If you read through the report on tests of Koga's A6M2, the P-39 used in those tests tried the same thing with 70 inches Hg at Take-Off. Even with just 52 inches Hg (WEP), the supercharger could not maintain boost past 4500 feet.

The Soviets didn't mind a fighter with ONLY two MG and a Cannon. That was pretty typical of their other fighters though the cannon was bigger than most of theirs.
For the US, that standard of armament was more typical of a tiny lightweight fighter such as the P-77.

- Ivan.

 

[P-39 Expert]

Hello P-39 Expert,

I seem to remember that Shortround6 gave a pretty good description of why the P-39 didn't have a lot of use in the ETO for the escort missions that required fighters. As for comparison for altitude performance, it isn't just a matter of being able to reach a decent service ceiling. Even the A6M2 and La 5FN could do that. It is a matter of surplus power and performance when it got to typical altitudes for engagement in the theater.

Surplus power was pretty good, P-39N would still outclimb a 1943 Thunderbolt at 25000'.



The Soviets also did a few things with those early P-39 that were not going to be acceptable in US service. They were typically using throttle settings beyond the War Emergency settings other services used. To them, it was acceptable to have to replace engines after a few flights. The whole aircraft was likely to be lost after a couple months anyway.
The problem with extra high throttle settings is that it only works as long as the supercharger can supply enough boost to allow it. If you read through the report on tests of Koga's A6M2, the P-39 used in those tests tried the same thing with 70 inches Hg at Take-Off. Even with just 52 inches Hg (WEP), the supercharger could not maintain boost past 4500 feet.

Yes the Soviets burned up their engines quickly by using full power continuously at low altitudes. But above the critical altitude this was a non-issue since that high MP could not be obtained.

The P-39D-1 used in the A6M2 test comparison weighed 7850lbs, one of the heaviest P-39s made. 70"HG was way over takeoff power of 44"HG, so sure it backfired. Even at that weight it climbed with the Zero until 14500' when the 5 minute limit was reached and it had to go to normal power (2600rpm). The 5 minute limit was increased to 15 minutes in mid-42 and at 3000rpm it would have stayed with the Zero on up to service ceiling.

The Soviets didn't mind a fighter with ONLY two MG and a Cannon. That was pretty typical of their other fighters though the cannon was bigger than most of theirs.
For the US, that standard of armament was more typical of a tiny lightweight fighter such as the P-77.

Standard for newer AAF and Navy fighters was 4x.50calMGs. P-51A/B/C, FM2 and F8F Bearcat all used 4x.50cal. 20mm cannon and 2x.50cal provided more firepower than 4x.50cal and 37mm and 2x.50cal had even more firepower than that. With centerline fire instead of converging fire from wing guns.

- Ivan.

 

[Ivan1GFP]

Hello P-39 Expert,

Surplus power was pretty good, P-39N would still outclimb a 1943 Thunderbolt at 25000'.

This really isn't saying very much. The Thunderbolt didn't climb particularly fast at any altitude.

Yes the Soviets burned up their engines quickly by using full power continuously at low altitudes. But above the critical altitude this was a non-issue since that high MP could not be obtained.

Above the Airacobra's critical altitude generally wasn't where the battles were happening.

The P-39D-1 used in the A6M2 test comparison weighed 7850lbs, one of the heaviest P-39s made. 70"HG was way over takeoff power of 44"HG, so sure it backfired. Even at that weight it climbed with the Zero until 14500' when the 5 minute limit was reached and it had to go to normal power (2600rpm). The 5 minute limit was increased to 15 minutes in mid-42 and at 3000rpm it would have stayed with the Zero on up to service ceiling.

Do you have evidence that the P-39D-1 used in the test against A6M2 actually was loaded to 7850 pounds?
They didn't actually back off to 44 inches Hg. In one test, they backed off to 52 inches Hg. In another test they ran at 55 inches Hg. These are War Emergency settings or above for the D-1. The A6M2 also had an "Overboost" setting but that was never used.
One of the things that was discovered in these tests was that the A6M2 really wasn't a particularly fast climbing aeroplane. It just had a very good zoom climb and climbed at a very steep angle. Another problem was that the automatic mixture control apparently didn't work in the rebuilt carburetor. The carb originally was designed to prevent negative G flooding but that feature was not restored on this captured A6M2 either.
Note also that the P-39D-1 could not continue these tests past 25,000 feet because it was low on fuel (!)
That DOES say something about lack of range, doesn't it?

Standard for newer AAF and Navy fighters was 4x.50calMGs. P-51A/B/C, FM2 and F8F Bearcat all used 4x.50cal. 20mm cannon and 2x.50cal provided more firepower than 4x.50cal and 37mm and 2x.50cal had even more firepower than that. With centerline fire instead of converging fire from wing guns.

The single 20 mm cannon and 2 MG does provide greater firepower but only for 6 seconds. After that, you have only two synchronized .50 cal HMG with a rather low ammunition load. One of the main advantages of the 4 gun Wildcats versus 6 gun versions was that the ammunition load and duration of fire was much greater.
For the 37 mm, it would be 12 seconds, but there you also have a cannon whose trajectory isn't remotely close to the .50 cal.
As for "newer" fighters, most of them went to MORE .50 cal guns. With the exception of the P-38, just about everything else used a uniform battery of guns. As for the F8F, although the gun count was lower, the gun used was the M3 which had a higher rate of fire.

Another interesting note regarding acceleration tests against Koga's A6M2 was that the majority of the tests were contrived to show that the US fighters had greater acceleration. This was done by picking a "cruising speed" to start that was usually only about 30-40 MPH below A6M2's maximum level speed. Aircraft don't accelerate quickly when they are near their maximum speed.
I wonder how these drag races would have gone had they started at 120-150 MPH?

- Ivan.

 

[Stig1207]

Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39.

By it self, this does not tell us much in regard to the combat performance of the P-39; aces scores are based on claims and the accuracy of those claims could vary a lot.

Based alone on the bomber gunners claims in the ETO, you could reasonly argue that a long range fighter was unnecessary since the losses inflicted on the Jagdwaffe by the gunners were so heavy that the Germans would not be able to withstand that amount of attrition!

 

[windhund116]

Based alone on the bomber gunners claims in the ETO, you could reasonly argue that a long range fighter was unnecessary since the losses inflicted on the Jagdwaffe by the gunners were so heavy that the Germans would not be able to withstand that amount of attrition!

I have never heard that argument. I thought bomber crew attrition rate, especially 8AF, were high --- when not escorted.