glennasher
Senior Airman
I think the best solution would be to scrap the whole idea of the P-39.
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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.I think the best solution would be to scrap the whole idea of the P-39.
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.
The armor for the oil tank weighed only 29lbs and was absolutely necessary as it protected the oil tank and engine from the rear.
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.
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.
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,
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.
Valid point, but it ruins my theory that the Brits made the P-400 too heavy to get out of the contract.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?
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.
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.
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.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.
He never ran into Alexander Pokryshkin.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.
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,
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.
Hi Ivan,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.
I'm not Ivan but thought I would reply anyway.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.
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-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.
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.
Surplus power was pretty good, P-39N would still outclimb a 1943 Thunderbolt at 25000'.
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.
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.
Soviets loved the P-39. Half their top aces and scores of 20+ victory aces flew the P-39.
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!