SHOULD the P39 have been able to handle the Zero? Was it training or performance?

[wuzak]

Okay, look at your photo of the P-39C. Says it weighed 7075# and made 379mph at 13000'. The British only got 359mph from theirs because they weighed 7850#. That's 775# lighter. But the real performance gain was in climb. That little P-39C at 7075# would climb at 3720fpm up to 12000'. How fast would the SpitV climb at that altitude? About 3000fpm or 750fpm less. The P-39C was faster and climbed faster than the SpitV.
Now, that P-39C didn't have self sealing tanks or armor plate/glass necessary for combat. The tanks added 260# and the armor added 240# so now we're up to 7575#. But wait, we can deduct 300# because the self sealing tanks reduced fuel capacity by 50 gallons, 100# by removing the two .30 caliber MGs in the nose and another 100# by deleting the nose armor (too far from pilot for protection) leaving us back at the original 7075# that gave the 379mph/3700'climb. Now the P-39C is faster than the SpitV, climbs faster, carries 20 gallons more gas, easier to land and is heavily armed/armored. This plane was available from July 1941 and was the plane the Army should have purchased.

You need to be careful when comparing fuel capacities of UK and US aircraft in gallons. That is because the UK quoted in UKG and the US quoted in USG, the UKG being 20% greater in volume than the USG.

Note also that British tests generally corrected their flight test results back to 95% of normal take-off weight (ie, normal ammo and fuel load, etc., not overload).

 

[wuzak]

Back to the two speed supercharger, the disadvantage was that in low gear power started to decline almost right away as the plane gained altitude and the air began to get thinner, so by the time you reached the shift point (11500') power was lower. Then you shifted into high and power steadily increased up to the critical altitude (18500') when it began to fall off again (just like low gear). This resulted in a sawtooth performance curve for both the engine and airplane. The Allison didn't have that problem (especially with the auto boost control) as it made 1325HP at takeoff and maintained that figure up to 8000' where it began to decline due to the thinner air.

The single stage V-1710's power curve follows the same shape as the V-1650-1, but without the second gear.

The reason for this is that the throttle causes a pressure loss and a reduction in efficiency of the supercharger. So the power rises as altitude increases, the throttle progressively opening to maintain the required boost level, until the critical altitude/full throttle height where the engine makes its peak rated power. The power then, pretty much, falls off a cliff.

The difference for the V-1650-1 is that when the power begins to fall off, another gear can be engaged. Note that the change point is determined by when the high gear has the same power as the low gear. Once in high gear the throttle has to be closed again, to prevent overboosting, and is, again, progressively opened until critical altitude/full throttle height. Hence the sawtooth shape.

The advantage in the 2nd speed can be seen in the Merlin XX (of which the V-1650-1 was a derivative) and Merlin 45. They were essentially the same, except for the supercharger drive. The XX had the 2 speed drive, low speed (Medium Supercharged gear or MS, in British jargon) had a lower ratio than the 45's single gear and high speed (Fully Supercharged, or FS, gear) had a higher ratio than the 45. Thus the XX had more power at low altitudes and high altitudes, with the 45 basically having the advantage around its full throttle height (~18,000ft).

 

[P-39 Expert]

You need to be careful when comparing fuel capacities of UK and US aircraft in gallons. That is because the UK quoted in UKG and the US quoted in USG, the UKG being 20% greater in volume than the USG.

Note also that British tests generally corrected their flight test results back to 95% of normal take-off weight (ie, normal ammo and fuel load, etc., not overload).

Right, the Spit held 100 American gallons and the P-39 held 120 American gallons.

 

[P-39 Expert]

The British were desperate for fighters in 1941 as Russia was desperate for the British to put pressure on Germany. However those fighters had to be superior in every respect to the Spitfire MkV, some fighter sweeps over France with Mk Vs resulted in no aircraft returning home. Being equal to the MkV was of no use at all because that was in no way good enough. To be any use at all the P39 had to be the equal of the P51A and Spitfire MkIX and it wasn't.

The British sure accepted a lot of P-40s, and they were in no way comparable to the SpitV or P-51A.

 

[P-39 Expert]

I would note that by the time the P39 was coming into service (fall of 1941) the 109E was on the way out and the 109F was equiping more squadrons every month. WHile the 109F may not have turned any tighter than the 109E it could sustain height or speed in a turn much better than the 109E.

I also have doubts about pulling 750lbs of armor out of a P-39. according to the weight tables there wasn't over 275lbs to begin with. Not to mention that an empty P-39D-2/P-400 weighed about 5550-5600lbs, basic weight (empty equipped) with guns, armor, radio, and oxygen was 6330-6420lbs.

Now perhaps you could save 750lbs (or close to it) by taking out the four wing guns (and their ammo) the armor and about another 100-130 worth of stuff (no oxygen over the Owen Stanleys? No radio? leave out 20 gallons of gas?)
I have no doubt that the pilots and crews did strip stuff out of the planes, however the weight saved by stripping the armor seems to be abut as exaggerated as the some of the air to air victories.

There was only 240# of armor in the P-39, but 100# of that could have been saved by removing the nose armor. Pilot was still protected by armor plate and glass right in frot of him.

 

[P-39 Expert]

Talk about ~20 mph difference P-51A vs. P-39N - 385-398 mph vs 409-415. Kinda points out how unfortunate it was that Allison didn't managed to put the reliable version of the V-1710 with 9.60:1 drive for supercharger. Here is the gun-less, well prepared P-39C with the 'faster' S/C making 406 mph: link.
The P-39Q, sans gun pods, was supposedly able to beat 400 mph. Sometimes the -85 engine was stated as with rated altitude at 15500 ft, no ram. We know that P-39s were succesful in post-war racing, despite some of competitors boasting twice the horsepower.

BTW - the comparison between the Fw 190A and P-39 is a tricky thing. We know that, in winter of 1941/42, the Fw 190A1 and A2 were good for 400+ mph at 17000-18000 ft, with full weapon set up and protection for both pilot, fuel and oil system. P-39C will not cut it performance-wise, it's protection is also lacking. It will pass another 10 months before the P-39M can do 375 mph at 15000 ft, by what time the Fw 190A3 makes 410 mph at 20000 ft. Where the P-39 shines is between sea leavel and 10000 ft.

The "faster" supercharger with 9.6 gears was installed in the P-39N, N and Q. Comparison with the FW190A and P-39M is in post #148. Official German govt document with official US govt figures on P-39N superimposed. Official govt docs, not 70 years of heresay.

 

[tomo pauk]

The British sure accepted a lot of P-40s, and they were in no way comparable to the SpitV or P-51A.

P-40 was available earlier and in greater quantities than the P-39, let alone the P-51A that entered the service with RAF by June 1943.
The P-40 was a better fighter than Hurricane, thus it was no wonder the P-40s ended up in North Africa. Not in UK by any meanigful numbers, though.

The "faster" supercharger with 9.6 gears was installed in the P-39N, N and Q. Comparison with the FW190A and P-39M is in post #148. Official German govt document with official US govt figures on P-39N superimposed. Official govt docs, not 70 years of heresay.

People are frying you exactly because you endeavoured in heresay when claiming that British were trying to weasel out from P-39 situation.
I know that M, N and Q versions got the 9.60:1 drive for the S/C. Unfortunately, that S/C drive was 10 months too late.
My point is/was that P-39 managed to best the Fw 190 a year too late in the altitude band that was well suited for the Eastern front, but couldn't do it in the ETO where a good performance at altitude was needed. On the other hand, the Fw 190As from mid-1943 were able to use greater manifold pressure = more power = more speed, the P-39N/Q from that time is a very 'niche' fighter.
Post #148 does not contain a comparison, comparisons include much more than speed figures.

 

[pbehn]

The British sure accepted a lot of P-40s, and they were in no way comparable to the SpitV or P-51A.

Yes, and after the first shipment all P-40s were delivered with armour and BP glass. The P-40 was not used as a fighter from UK but in recon and then only for 29 sorties. The P-40 was in service in North Africa and replaced the Hurricane. The P-39 was more of the same and arrived much later with serviceability issues. The P-40 as Tomahawk and Kittyhawks remained in service until tropicalized Spitfires started to replace them in 1942, but this is just after the P-39 started to arrive in UK.

Most of your "case" is just a trick with time lines. A comparison with the Bf 109E may give some information but the Bf 109F was arriving in service from October 1940. By the time any P-39s could have been in service in any numbers the Spitfire was being tropicalised and replacing the P-40 in Africa. Similarly you bring the time line of the Typhoon forward to make a political point about the British not needing the P39. In 1941 to 43 the British and the Americans needed front line fighters, no one gave a stuff who made them or what they were called but they had to do the job. While the Hurricane could remain in service to the end of the war in ground attack, in terms of taking on front line fighters it was obsolete in 1940, the P39 was pretty much the same.

 

[Shortround6]

There was only 240# of armor in the P-39, but 100# of that could have been saved by removing the nose armor. Pilot was still protected by armor plate and glass right in frot of him

Perhaps you are right, on the other hand

British could have saved weight on the Whirlwind by getting rid of the armor in front of the ammo drums for the 20mm cannon.
Many British fighters had a piece of armor in front of their 20mm belt boxes and heavy dural behind and or on top of the belt boxes.

Just maybe the the gearbox armor was doing double duty and not only protecting the gear box but keeping small bullets out of 37mm ammo?

one of the 37mm shells going off inside the feed way could ruin your whole day.

Not to mention the the P-39 had a few issues with center of gravity. Like not supposed to be flown without ammo for the nose guns unless ballast was carried?
Yanking the nose armor without yanking a similar weight from the rear of the plane at an equal distance is going to increase your accident rate.

 

[P-39 Expert]

View attachment 486062
Perhaps you are right, on the other hand
View attachment 486063
British could have saved weight on the Whirlwind by getting rid of the armor in front of the ammo drums for the 20mm cannon.
Many British fighters had a piece of armor in front of their 20mm belt boxes and heavy dural behind and or on top of the belt boxes.

Just maybe the the gearbox armor was doing double duty and not only protecting the gear box but keeping small bullets out of 37mm ammo?

one of the 37mm shells going off inside the feed way could ruin your whole day.

Not to mention the the P-39 had a few issues with center of gravity. Like not supposed to be flown without ammo for the nose guns unless ballast was carried?
Yanking the nose armor without yanking a similar weight from the rear of the plane at an equal distance is going to increase your accident rate.

Exactly what I was saying, all that armor plate and glass weighed 240# but that gear box armor in the nose was 100# of that. No other fighters had armor there (unless there was a liquid tank there), and it really didn't protect the pilot much since he already had the forward armor plate and the windshield armor glass directly in front of him. It would have been a CG/balance issue though, but that could have been offset by moving the radio equipment from the tail cone up to right behind the pilot above the engine. Look closely and lots of P-39s have moved the radio equipment there.

 

[P-39 Expert]

Yes, and after the first shipment all P-40s were delivered with armour and BP glass. The P-40 was not used as a fighter from UK but in recon and then only for 29 sorties. The P-40 was in service in North Africa and replaced the Hurricane. The P-39 was more of the same and arrived much later with serviceability issues. The P-40 as Tomahawk and Kittyhawks remained in service until tropicalized Spitfires started to replace them in 1942, but this is just after the P-39 started to arrive in UK.

Most of your "case" is just a trick with time lines. A comparison with the Bf 109E may give some information but the Bf 109F was arriving in service from October 1940. By the time any P-39s could have been in service in any numbers the Spitfire was being tropicalised and replacing the P-40 in Africa. Similarly you bring the time line of the Typhoon forward to make a political point about the British not needing the P39. In 1941 to 43 the British and the Americans needed front line fighters, no one gave a stuff who made them or what they were called but they had to do the job. While the Hurricane could remain in service to the end of the war in ground attack, in terms of taking on front line fighters it was obsolete in 1940, the P39 was pretty much the same.

 

[P-39 Expert]

No trick time lines. Different planes. Two different P39s, the older ones with the 8.8 supercharger gears (P-39D, F, K and L) and the later ones with the 9.6 gears (P-39M, N and Q). The 9.6 gears gave an additional 100HP at all altitudes. The improved 9.6 gears were available in production P-39s starting with the M in November 1942. Over 7000 were the improved M, N & Q of the 9500 total produced. The N and Q were the primary models supplied to the Russians. The charts in post #148 compare the N introduced in Dec 1942 with the FW190A6 introduced in June 1943. Apples to apples time-wise, both fully loaded, these are the official Luftwaffe charts for speed and climb with the official US Army figures for the P-39N superimposed. The FW was a little faster above 5km altitude in override boost with C3 injection (war emergency) for one minute, but the P-39N was just as fast as the FW's "combat" rating which is column #2. The climb chart shows the P-39N substantially outclimbed the FW AT ALL ALTITUDES. Pretty much a wash vs the Luftwaffe's premier fighter.
And below 5km altitude (16500') the P-39Ns advantage in both speed and climb is huge. Now, please let me hear from all you "two speed" and crankshaft experts about how big an advantage low gear is. As you can see from the charts the two speed supercharger results in a "sawtooth" speed and climb curve while the single speed P-39N develops its maximum power at 3km (10000') and then gradually declines from there up to the combat ceiling. Most historians would have you believe that the Allison engine fell off the mounts and the plane tumbled to earth after crossing 12000'. This was a much better plane than history gives credit for.

 

[Peter Gunn]

*SNIP*

This was a much better plane than history gives credit for.

That's why there are so many P-39 aces in the USAAF and RAF...
Sure, over the steppes of Russia at low altitude and overboosting the engine, VVS pilots did well with it. Again, a niche fighter, the Germans on the western front and the Japanese were no so obliging to stick to low altitude combat.

Wasn't it George Welch that supposedly said the best thing about the P-39 was the twelve hundred pounds of pilot armor behind him?

I think in this instance, history has given credit where it is due.

 

[pbehn]

No trick time lines. Different planes. Two different P39s, the older ones with the 8.8 supercharger gears (P-39D, F, K and L) and the later ones with the 9.6 gears (P-39M, N and Q). The 9.6 gears gave an additional 100HP at all altitudes. The improved 9.6 gears were available in production P-39s starting with the M in November 1942. Over 7000 were the improved M, N & Q of the 9500 total produced. The N and Q were the primary models supplied to the Russians. The charts in post #148 compare the N introduced in Dec 1942 with the FW190A6 introduced in June 1943. Apples to apples time-wise, both fully loaded, these are the official Luftwaffe charts for speed and climb with the official US Army figures for the P-39N superimposed. The FW was a little faster above 5km altitude in override boost with C3 injection (war emergency) for one minute, but the P-39N was just as fast as the FW's "combat" rating which is column #2. The climb chart shows the P-39N substantially outclimbed the FW AT ALL ALTITUDES. Pretty much a wash vs the Luftwaffe's premier fighter.
And below 5km altitude (16500') the P-39Ns advantage in both speed and climb is huge. Now, please let me hear from all you "two speed" and crankshaft experts about how big an advantage low gear is. As you can see from the charts the two speed supercharger results in a "sawtooth" speed and climb curve while the single speed P-39N develops its maximum power at 3km (10000') and then gradually declines from there up to the combat ceiling. Most historians would have you believe that the Allison engine fell off the mounts and the plane tumbled to earth after crossing 12000'. This was a much better plane than history gives credit for.

You are still doing exactly the same thing. By December 1942 the RAF had the Spitfire Mk IX Typhoon and the Mustang Mk 1 in service in numbers, they were used at Dieppe. The P-39N may have been something in UK arriving in numbers in UK in 1939, by the end of 1942 in addition to the RAF aircraft the USA was introducing the P-47 and P -38 the time had passed.

 

[P-39 Expert]

You are still doing exactly the same thing. By December 1942 the RAF had the Spitfire Mk IX Typhoon and the Mustang Mk 1 in service in numbers, they were used at Dieppe. The P-39N may have been something in UK arriving in numbers in UK in 1939, by the end of 1942 in addition to the RAF aircraft the USA was introducing the P-47 and P -38 the time had passed.

P-39N was comparable to the Typhoon in speed and superior to the Typhoon in climb. The Spitfire IX had a two stage engine (two superchargers) for it's high altitude capability. I never said the P-39N was comparable to the SpitIX. Would have been superior to the SpitIX with the Allison V-1710-93 mechanical two stage engine that went into the P-63. The -93 was in series production from March 1943 and the first P-63 wasn't ready until October, so that -93 should have been installed in the P-39 immediately in March. 1800HP WEP at 22000' compared very favorably with the Merlin 61 in the SpitIX and P-51B.
P-38 didn't enter combat until December 1942 in the older and less capable F and G models and the P-47 didn't enter combat until May 1943 with the 8th Air Force in England. These new turbocharged "superplanes" weren't without their faults. The P-47 couldn't climb and the P-38 couldn't dive. Neither could maneuver with a FW or Messer, much less a P-39N.

 

[Elmas]

I'm always puzzled how some posters in this forum refer only to maximum speed, climb rate, manifold pressures and so on and of an airplane completely ignore things like (from Wiki, just for a quick reference)

Angular momentum - Wikipedia

Moment of inertia - Wikipedia

that are essential to judge the behaviour of a plane.

I can imagine the behaviour of a P-39, all ammunition spent, when a Pilot had to pull energetically the stick to come out from a dive, one or two Me-109 on his tail. I know that some Italian Pilots described the experience as hair raising, and some British too, I can imagine, from the use the RAF did of the plane. Russian Pilots I don't know, but probably they were used to things like Russian Roulette…

 

[Peter Gunn]

One might ask oneself if the V-1710-93 with attending supercharger setup would fit in the P-39. The P-63 is two feet longer after all. But in reality, you're going off into flights of fancy to prove an un-provable point.

Cheers.

 

[pbehn]

P-39N was comparable to the Typhoon in speed and superior to the Typhoon in climb. The Spitfire IX had a two stage engine (two superchargers) for it's high altitude capability. I never said the P-39N was comparable to the SpitIX. Would have been superior to the SpitIX with the Allison V-1710-93 mechanical two stage engine that went into the P-63. The -93 was in series production from March 1943 and the first P-63 wasn't ready until October, so that -93 should have been installed in the P-39 immediately in March. 1800HP WEP at 22000' compared very favorably with the Merlin 61 in the SpitIX and P-51B.
P-38 didn't enter combat until December 1942 in the older and less capable F and G models and the P-47 didn't enter combat until May 1943 with the 8th Air Force in England. These new turbocharged "superplanes" weren't without their faults. The P-47 couldn't climb and the P-38 couldn't dive. Neither could maneuver with a FW or Messer, much less a P-39N.

And again the same thing, pushing the time line back for one aircraft but not another. By the end of 1943 the P51B/C is in service, you are a few months away from the Tempest being in service. The P 47 arrived in January, it takes months to get into service, that is also true for any engine produced in USA as you quoted, they must be made, shipped, installed, tested shipped and tested again. Both the P47 and P-38 whatever their faults could fight at range and altitude which is where the combat would be in the near future. The Spitfire MkXII with Griffon engine was superior by 14MPH to the Mk IX at low level but found targets hard to find. The LW would just climb away above 20,000ft where it ran out of lungs, it needed a two speed two stage supercharger the first of which flew in Jan 1943.

 

[tomo pauk]

No trick time lines. Different planes. Two different P39s, the older ones with the 8.8 supercharger gears (P-39D, F, K and L) and the later ones with the 9.6 gears (P-39M, N and Q). The 9.6 gears gave an additional 100HP at all altitudes. The improved 9.6 gears were available in production P-39s starting with the M in November 1942. Over 7000 were the improved M, N & Q of the 9500 total produced. The N and Q were the primary models supplied to the Russians. The charts in post #148 compare the N introduced in Dec 1942 with the FW190A6 introduced in June 1943. Apples to apples time-wise, both fully loaded, these are the official Luftwaffe charts for speed and climb with the official US Army figures for the P-39N superimposed. The FW was a little faster above 5km altitude in override boost with C3 injection (war emergency) for one minute, but the P-39N was just as fast as the FW's "combat" rating which is column #2. The climb chart shows the P-39N substantially outclimbed the FW AT ALL ALTITUDES. Pretty much a wash vs the Luftwaffe's premier fighter.

Fw 190 was probably LW's premiere fighter, the Bf 109F/G climbed better, though.
Please note that P-39N that can out-climb the Fw 190As was the model with less fuel, 87 US gals (72.44 imp gals), so the weight was down by 200 lbs vs. the models with 120 US glas. The C3 injection override boost was allowed for 10 minutes, and was option at lower altitudes, typically 3000 ft and lower. The 'simple' overboost was allowed for both supercharger gears, on the other hand.

And below 5km altitude (16500') the P-39Ns advantage in both speed and climb is huge. Now, please let me hear from all you "two speed" and crankshaft experts about how big an advantage low gear is. As you can see from the charts the two speed supercharger results in a "sawtooth" speed and climb curve while the single speed P-39N develops its maximum power at 3km (10000') and then gradually declines from there up to the combat ceiling. Most historians would have you believe that the Allison engine fell off the mounts and the plane tumbled to earth after crossing 12000'. This was a much better plane than history gives credit for.

P-39 usualy does not receive a bad rap here. Like every other A/C, it have had it's good and bad sides.
Let's imagine for a moment that P-39 is outfitted with a 2-speed drive for the S/C. We'll use a brand new gearing, with, say, 10:1 drive for high gear, and 8:1 for low gear. Should be making military power of 1100 HP at 17000 ft, and 1200 HP at ~10500 ft? WER of 1400 HP at 11000 ft, and 1600 HP at 2000 ft; take off 1400 HP. Net result 400 mph with 120 gals and full wepon set up, with increase in climb rate at all altitudes and shorter take off distance.

P-39N was comparable to the Typhoon in speed and superior to the Typhoon in climb. The Spitfire IX had a two stage engine (two superchargers) for it's high altitude capability. I never said the P-39N was comparable to the SpitIX. Would have been superior to the SpitIX with the Allison V-1710-93 mechanical two stage engine that went into the P-63. The -93 was in series production from March 1943 and the first P-63 wasn't ready until October, so that -93 should have been installed in the P-39 immediately in March. 1800HP WEP at 22000' compared very favorably with the Merlin 61 in the SpitIX and P-51B.
P-38 didn't enter combat until December 1942 in the older and less capable F and G models and the P-47 didn't enter combat until May 1943 with the 8th Air Force in England. These new turbocharged "superplanes" weren't without their faults. The P-47 couldn't climb and the P-38 couldn't dive. Neither could maneuver with a FW or Messer, much less a P-39N.

Typhoon was faster at most altitudes.
P-39 + 2-stage V-1710 is a non-starter, unless the fuselage internals are reworked. Let's recall that even the post-war racing P-39s were still outfitted with 1-stage engines, despite the potential for much greater power offered by 2-stage versions.
2-stage V-1710s installed on P-63 were good for 1120-1300 HP at 22000 ft (no ram) 1800-1850 was available at low level. chart
Too much 2-stage V-1710s gathering dust inn 1943? Install them on the P-51s, those at least can bring war to the enemy.
Nobody will put the P-38 or P-47 in the box tagged 'perfect fighters', even if they were much more useful than P-39s or P-40s.

 

[Shortround6]

We also have the flight of Fancy in which the engines with 9.60 gears get an extra 100np at all altitudes.
They did not. For take-off and military power they were limited to 1200hp instead of 1325hp. And WEP was also dropped. Strong warnings were issued about exceeding the book boost limits as the 9.60 gears heated the intake charge more than the 8.80 gears and at the same pressure level was actually skating much closer to the detonation limit.
This is the classic trade off a single speed supercharger makes that the automatic boost control can do nothing about.