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

[Shortround6]

It is, the P-39 chart at Zeno's doesn't have the percentages filled in but we know it can't be zero

Just pointing out that test results don't always reflect service results, especially in very different climate conditions. ALL planes are going to be degraded somewhat, some may be degraded more than others.

 

[krieghund]

The part of the document encompassing the US airplane engines (open the picture in separate tab for hi-res):

View attachment 233020

Whole document:

http://www.enginehistory.org/ModDesig/SecI.pdf

Is there something that indicates the altitudes are with or without RAM?

 

[Shortround6]

As a check try the Hurricane II test report;

Hurricane II Z-3564 Trials Report

That particular test machine held 8.8lb boost to 20,800ft in level flight at 3000rpm.

While climbing at 2850 rpm the full throttle height was 15,700ft for 9.4lbs and 16,500ft for the same 8.8lbs used in level flight. A problem with the pressure control or normal tolerance?

In another test of the Merlin XX in a Hurricane reported in the a book on the Merlin by the Rolls Royce Heritage trust the "9lbs" boost was held to over 20,000ft in level flight.

 

[wuzak]

As a check try the Hurricane II test report;

Hurricane II Z-3564 Trials Report

That particular test machine held 8.8lb boost to 20,800ft in level flight at 3000rpm.

While climbing at 2850 rpm the full throttle height was 15,700ft for 9.4lbs and 16,500ft for the same 8.8lbs used in level flight. A problem with the pressure control or normal tolerance?

In another test of the Merlin XX in a Hurricane reported in the a book on the Merlin by the Rolls Royce Heritage trust the "9lbs" boost was held to over 20,000ft in level flight.

What are you saying SR?

The FTH was 20,800ft in FS gear.

 

[Shortround6]

With RAM, in level flight at full speed and in the Hurricane II......YES.

Since the amount of RAM is dependent on speed the 20,800 ft altitude ONLY works for the INTAKE of the Hurricane AT 246mph ASI.

Going to a hypothetical Spitfire with a Merlin XX you have a different air scoop, inlet duct which may affect things, for good or bad. You also have extra speed which should give an even higher FTH .

Dropping to climb speed of 142 mph ASI for the Hurricane is what drops the FTH in climb.

Sticking the Merlin XX in a Mosquito will give different results as will sticking it in Lancaster.

Different air scoops/inlet ducts and different speeds.

This is why the engine makers rarely included RAM altitudes in their specification sheets.

Also please note that if the plane was cruising at 20,800ft at 170mph ASI and opened the throttle to accelerate, it would not have 8.8-9lb boost available UNTIL it had accelerated to 246 mph ASI.

and any maneuver, even a 1.5 "G" turn that bled speed would also cause the manifold pressure to drop.

 

[wuzak]

Ok, understood.

 

[tomo pauk]

Is there something that indicates the altitudes are with or without RAM?

Yep, click on the 'Introduction' link posted here.

 

[krieghund]

Here's the charts for the P-39D with two engine options

 

[P-39 Expert]

Correct on the lack of EW, they didn't have radar in New Guinea until August 1942. Hard to intercept Bettys at 22000' if you don't know they are coming.
Regarding P-39 drop tanks, most used the 110 gallon external tank. Made fuel management easy, you had 120 gallons internal and 110 external, so when you ran your drop tank dry it was time to head back to base. If you encountered combat and dropped your external tank, you headed for home after that combat.

The P-39 (among many Allied airplanes) have had several issues that were hampering it's better score vs. Zero.
The crucial thing could easily be the lack of dependable early warning systems in areas where the P-39s were operating during 1942. As seen in ww2 in all theaters, the fighters, no matter how good, need sufficient time to warm-up, take off and climb to the suitable altitude.
Next thing would be the pilot's tactics experience - P-39 should flatly lose the vs. Zero in turning fight, and Zero's pilots were the best in the world in 1942.
Then we go to the engine limitations: the single speed V-1710 was, during the 1st half of the war, a dog above 15000 ft. The airframe issue would be the loopsided layout of the engine intake, much reducing the ram effect. That should steal couple of thousands HP/feet from the already low engine power/altitude. The Japanese bombing runs were conducted at higher altitudes, and their Zeros have had two-speed superchargers, so the Zeros would be the ones to dive at P-39s, not vice versa. Another airframe issue would be the low fuel quantity, giving the P-39 pilot two uneasy choices:
- drop the tank and engage what is close (and that might be the Zero coming to get him), leaving it without fuel to chase speedy Japanese bombers
- leave the drop tank on, and risk to be shot down since one is slow unviedly with the DT
Having the DT attached also lowers the rate of climb, not a good thing if the bombers Zeros are close.

 

[P-39 Expert]

I agree the P39 had flaws, but it was much faster then the Zero and could easily out dive the Zero. The F4F had nothing on the Zero except being tougher and yet it fought the Zero to about a draw while the P39 didn't do as well. How can that be explained?

Navy pilots were better right out of flight training. They had 600 hours of pilot training where the Army pilots graduated with only 200. All that "landing on a ship", navigation, etc. Those Navy pilots were living proof that the better pilot wins over the better plane, because there wasn't much worse a plane during that period than the F4F. Barely the same top speed as a Zero but abysmal climb and turn, and a very narrow landing gear. They beat the Zero with boom and zoom tactics, if you were above the Zero you made a diving pass and then converted your dive speed to altitude by climbing back up above. If the Zero was above you, you dove away and when out of range climbed back up above and made a diving pass. No turning with the amazingly maneuverable Zero, ever. Just dive away, your Wildcat was stressed to take it, the Zero was not. By the way, the Army pilots caught up with the Navy pilots as they gained more experience, but right out of flight school ( and almost all Army pilots were) the Navy was better.

 

[P-39 Expert]

The table for the V-1650-1 lists the critical altitudes in the wrong column, under 'with ram', instead under 'no ram'.

The columns are correct, the two figures are for low and high gear. You took off in low and shifted to high at about 11500' for military (full) power. The Allison had a single speed supercharger so there was no shifting. Two speeds was not better than the Allison single speed. Low gear was a safety measure simply to keep the pilot from overboosting the engine at take off. Allison just told the pilot not to exceed a certain amount of boost at takeoff and the throttle had a "take off" stop about halfway up. Just set the throttle at the takeoff stop and it was the same as "low gear" in a two speed. Then as you climbed you gradually opened the throttle above the "take off" stop to maintain power as the air got gradually thinner the higher you went. Then when you reached critical altitude (12000' in the early engines, 15000' in the later) power gradually declined up to the ceiling, just like every other engine.

 

[P-39 Expert]

Thank you for the graph.

This seems to show that the P39 will outperform the F4F up to 24,000 feet or so. I'm having a hard time believing that it was the P39's performance as much as it was a training issue considering the F4F was around 1 to 1 against the Zero. I think if I was given the choice, I would choose the P39, at least I had the option of running if things didn't work in my favor.

The graphs are correct except the early P-39 was about 10mph faster than shown. So it was faster than the F4F at all altitudes. And keep in mind that not much combat took place above about 26000' (8000 meters) in either the Pacific or European theater. B-17s and B-24s flew at 25000' so you needed about another 1000' or so to intercept or escort them. Specialized reconnaissance planes flew higher, but combat planes didn't much go over 26000'.

 

[P-39 Expert]

The P-39 was not a "dog" at 12,000 feet but at 24,000 it needed full throttle to keep from stalling. In the early part of the New Guinea campaign, the P-39 was used as an interceptor against bombers with escorts coming over the target at altitudes over 20,000. They never were able to attain an altitude advantage during attempted intercepts and were constantly bounced by escorts coming down on them from higher altitudes. The 8th Pursuit(fighter)Group was decimated. At Guadalcanal lack of oxygen for P-400s was a mute point. They couldn't get to the same height as the F4Fs with or without oxygen.

Duane

Beg to differ. The P-39s (couple of squadrons) were all that stood between the Japanese and Port Moresby in May/June/July of 1942. The Japs flew multiple bombing missions daily (weather permitting) trying to knock out the P-39 bases and the P-39s kept them out. Problem was the early P-39 (carrying a drop tank) could only reach up to about 18000' before it's climb rate fell below 1000'/minute, and in combat that was excruciatingly slow. The Japanese Navy Betty bombers came in between 18000' and 22000'. There was no long range radar until August at Milne Bay. So these boys had to fly patrols or wait on the ground. And those patrols were at 22000' so it took a long time to get there, but they could do it. And flying around waiting for your opponent when you had no idea if he was even coming or not was wasting already incredibly scarce resources. After the radar arrived in August these pilots could perform the more conventional method of interception, getting a call from the radar station with altitude and direction of the incoming force with time to take off and climb above them to attack. Results (and the pilot's nerves) were much better with radar. Even with all these disadvantages the Army pilots were able to maintain a 1:1 kill ratio. Tough, smart kids.

 

[tomo pauk]

Welcome to the forum.

...
Regarding P-39 drop tanks, most used the 110 gallon external tank.
...

I'd politely ask for the source for that statement.

...
Those Navy pilots were living proof that the better pilot wins over the better plane, because there wasn't much worse a plane during that period than the F4F. Barely the same top speed as a Zero but abysmal climb and turn, and a very narrow landing gear. They beat the Zero with boom and zoom tactics, if you were above the Zero you made a diving pass and then converted your dive speed to altitude by climbing back up above
...

There was Buffalo and P-36 around, plus the CW 21. Hurricane was no better than better versions of the F4F - F4Fs weren't all the same in 1941/42.
F4F hardly beat Zeros by a wide margin.

The columns are correct, the two figures are for low and high gear. You took off in low and shifted to high at about 11500' for military (full) power.

The figures for the rated altitude were in the wrong cloumn. See for your self - there is a firm ~7500 ft worth of altitude advantage the V-1650-1 had over the early V-1710s. Or, more than 200 HP difference at 20000 ft, a 25% power more for the V-1650-1 there.
Granted, later V-1710s cut that difference in power to 15-20% above 15000 ft.

The Allison had a single speed supercharger so there was no shifting. Two speeds was not better than the Allison single speed. Low gear was a safety measure simply to keep the pilot from overboosting the engine at take off. Allison just told the pilot not to exceed a certain amount of boost at takeoff and the throttle had a "take off" stop about halfway up. Just set the throttle at the takeoff stop and it was the same as "low gear" in a two speed. Then as you climbed you gradually opened the throttle above the "take off" stop to maintain power as the air got gradually thinner the higher you went. Then when you reached critical altitude (12000' in the early engines, 15000' in the later) power gradually declined up to the ceiling, just like every other engine.

Let's not make advantage from a shortcoming. There was a reason why people all around the world were installing 2- , 3- or variable-speed drives for the superchargers on their engines when possible, despite the higher cost and more resources and manufacturing time needed. BTW - US pilots were listening to the USN/USMC/USAAC/AAF, not Allison or other engine maker.
Low gear enabled to the engine to have good power at low level, while retaining good power at high altitude. That, combined with bigger S/C on the V-1610, meant that it produced more power at most of altitude bands than any 1-stage V-1710.

 

[Stig1207]

Even with all these disadvantages the Army pilots were able to maintain a 1:1 kill ratio.

Is that 1:1 ratio against all enemy aircraft types?

 

[Shortround6]

I would note that a lot of people used single stage single speed superchargers and used some sort of restriction on the throttle for take-off and low altitude even if it was just watching the boost gauge (the British actual fitted a boost control mechanism, set the boost to 6lbs and the mechanism would hold that boost or at least not exceed it now matter how the pilot climbed and dived below full throttle height).
However since the problems in the engine with a single speed supercharger are that
1. you don't have the throttle plate/s fully open so there are "pumping losses".
2. The fast spinning impeller takes more power to drive.
3. The fast spinning impeller heats the intake charge more making it less dense and the higher temperature pushes it nearer to the detonation limit.

All put together the single speed engine is making much less power at low altitude than a two speed engine.
Sorry, not having to shift supercharger gears or saving on manufacturing costs is a bogus argument.
For the Merlin running on 87 octane gas the Merlin III with an 8.588 supercharger gear take off was 880hp at 3000rpm at 6 1/4 lb boost.
a Prototype engine with 7.32 supercharger gear was rated at 1000hp for take-off at 3000rpm and 6lbs boost and this was superseded by the Merlin VIII
using a 6.313 supercharger gear and rated at 1080hp at 3000rpm at 5 3/4 lbs boost.
Now the low gear MK VIII was using about 55% of the power to drive it's supercharger compared to the MK III Merlin and was also heating the intake charge proportionally less, throttle plate/s were also much closer to fully open.

overboosting engines well beyond manufactures recommendations was done, but usually only at the cost of shorter engine life. In fact the Flying Tigers started to pick up on the fact that while a severely over boosted engine often made it home it also showed a very noticeable tendency to fail on either the next flight or the one after.

Please note that early Allison engines (the long nose) used a crankshaft that did not have the heat treatment/surface treatments of later Allison crankshafts and would not tolerate severe abuse for any where near as long even if they would give hundreds if not thousands of hours of service if stress levels were kept to more moderate levels.

 

[P-39 Expert]

Is that 1:1 ratio against all enemy aircraft types?

Yes, all aircraft types. A twin engined bomber and an observation plane each counted one victory. Not all victories were against Zeros.

 

[P-39 Expert]

Welcome to the forum.



I'd politely ask for the source for that statement.



There was Buffalo and P-36 around, plus the CW 21. Hurricane was no better than better versions of the F4F - F4Fs weren't all the same in 1941/42.
F4F hardly beat Zeros by a wide margin.



The figures for the rated altitude were in the wrong cloumn. See for your self - there is a firm ~7500 ft worth of altitude advantage the V-1650-1 had over the early V-1710s. Or, more than 200 HP difference at 20000 ft, a 25% power more for the V-1650-1 there.
Granted, later V-1710s cut that difference in power to 15-20% above 15000 ft.

View attachment 485755



Let's not make advantage from a shortcoming. There was a reason why people all around the world were installing 2- , 3- or variable-speed drives for the superchargers on their engines when possible, despite the higher cost and more resources and manufacturing time needed. BTW - US pilots were listening to the USN/USMC/USAAC/AAF, not Allison or other engine maker.
Low gear enabled to the engine to have good power at low level, while retaining good power at high altitude. That, combined with bigger S/C on the V-1610, meant that it produced more power at most of altitude bands than any 1-stage V-1710.

Couple of things, not arguing that the 1650-1 made more power than the Allison, it did because it had a larger diameter impeller (supercharger). That is a fact.
But the two figures listed in the "Engine Ratings" column (below the Takeoff rating) are for low gear (1240hp/3000rpm/11500') and high gear (1120hp/3000rpm/18500'). Takeoff was in low gear (to not overboost the engine at low altitude where the air is thicker) and then manually shifted to high gear at 11500' with critical altitude being 18500' to draw in more of the thinner air at higher altitudes.
And the single speed Allison was in no way a disadvantage. Later models (starting with the 1325hp V-1710-63) were equipped with an automatic boost control or automatic manifold pressure regulator (same thing). The maximum boost (or manifold pressure) for the engine was preset and this gizmo mounted on the carburetor limited boost to at or below that preset amount. In other words you couldn't blow up (overboost) the engine at ANY throttle setting. This eliminated the need for two speeds, manual shifting or automatic shifting. And this device apparently worked very well and was very dependable since it was used on most all the engines Allison manufactured thereafter.
So, with no throttle management the pilot could set the boost control, firewall the throttle and not overboost the engine at any altitude. This eliminated a lot of pilot workload.
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.
Only real problem with the Allison was that the Army insisted on designing planes around it that just weighed too darn much. The P-39 weighed around 7650#, the P-40 weighed 8400# and the P-51A weighed about that also. 8400# divided by 1150HP is 7.3 pounds/HP. The Me109G6 weighed 6800# with a 1475HP engine or 4.6 pounds/HP. You can see the problem.

 

[P-39 Expert]

Since we are talking about the P-39, lets clear up a few inaccuracies that have perpetuated over the decades:
1. The XP-39 was not ruined by deleting the turbocharger. Turbo was deleted to get the P-39 and P-40 ready in time for WWII. Turbo was new and was the main reason that the similarly turbocharged P-38 didn't enter combat until the end of 1942. And the intercooler and oil cooler arrangements were not adjustable to let in more or less air as needed so they would not have worked in combat. Allison was coming out with engines that had higher critical altitudes and even one with a second stage supercharger that ended up going into the P-63.
2. The rejection of the P-39 and P-400 (export P-39) by the British was solely political and economic. They ordered those planes in 1940 when Hitler was about to invade France expecting a long war and needing more airplane production. They cancelled the order in late 1941 after France had fallen and the Battle of Britain was over. They no longer needed these planes since their own fighter production (Spitfire and Typhoon) was adequate with no threat of Nazi invasion. But the main reason for cancellation was these original orders were hard money purchase contracts and they no longer had the money to pay for them, and in the meantime Lend Lease had been enacted that would send them all the planes they wanted/needed for free. Why spend $millions on a plane when they were now free. So the British specified much more armament and weight on these P-39s so that performance suffered and they could weasel out of the contract.

 

[varsity07840]

The P-39 (among many Allied airplanes) have had several issues that were hampering it's better score vs. Zero.
The crucial thing could easily be the lack of dependable early warning systems in areas where the P-39s were operating during 1942. As seen in ww2 in all theaters, the fighters, no matter how good, need sufficient time to warm-up, take off and climb to the suitable altitude.
Next thing would be the pilot's tactics experience - P-39 should flatly lose the vs. Zero in turning fight, and Zero's pilots were the best in the world in 1942.
Then we go to the engine limitations: the single speed V-1710 was, during the 1st half of the war, a dog above 15000 ft. The airframe issue would be the loopsided layout of the engine intake, much reducing the ram effect. That should steal couple of thousands HP/feet from the already low engine power/altitude. The Japanese bombing runs were conducted at higher altitudes, and their Zeros have had two-speed superchargers, so the Zeros would be the ones to dive at P-39s, not vice versa. Another airframe issue would be the low fuel quantity, giving the P-39 pilot two uneasy choices:
- drop the tank and engage what is close (and that might be the Zero coming to get him), leaving it without fuel to chase speedy Japanese bombers
- leave the drop tank on, and risk to be shot down since one is slow unviedly with the DT
Having the DT attached also lowers the rate of climb, not a good thing if the bombers Zeros are close.

The A6M2 Model 21 Zero encountered by the P-39 in New Guinea did not have a 2 speed engine. That was introduced on the A6M3.