The P40 thread

[Farky]

I actually think that 56"/2400 setting was prohibited by the flight manual...

 

You are absolutely right, 56"/3000 rpm was prohibited by the P-40E flight manual. Well, at least in time when was this P-40 model used in combat. But what was possible is completely different thing.

 

 

"56"/3000" were "may not be used" (Page 32 in PDF) if there was no Manifold Pressure Regulator installed. However, the Handbook also mentions "Standard Emgergency Power" of 52"@3000 for 5 Minutes.

 

 

52"/3000 rpm was also prohibited by the P-40E flight manual, there is no such thing like "Standard Emergency Power" in any official flight manual or engine power table. As far as i know, USAAF (or everyone else around the world) didn't even use this term during WWII. And I am pretty sure, that use of this "Standard Emergency Power" (whatever it was) also requires Manifold pressure regulator installed.

[TXSailor_1]

If you even have minimal Knowledge of Engines and how the Whole "Air-Thing" works, shouldn't it be immediately obvious? 

 

Yeah... I guess 10 years of civil aviation, 4 years of military aviation, I don't really know anything about how this "air thing" works...

 

Conversely, I've never encountered an aircraft, real life or sim before, where application of full power instantly wrecks an engine. I can see overheating on takeoff if all radiators are closed, sure, but with radiators full open, thus cooling not an issue, and smooth application of power, the inability to push a throttle completely forward without immediate damage to said engine is absurd in my experience. 

[ZachariasX]

Yeah... I guess 10 years of civil aviation, 4 years of military aviation, I don't really know anything about how this "air thing" works...

 

Conversely, I've never encountered an aircraft, real life or sim before, where application of full power instantly wrecks an engine. I can see overheating on takeoff if all radiators are closed, sure, but with radiators full open, thus cooling not an issue, and smooth application of power, the inability to push a throttle completely forward without immediate damage to said engine is absurd in my experience. 

It has been debated whether the cues delivered by the engine are as would be expected from an engine that is run at severe overcompression and is predetonating. Personally, I think they should be such that you wouldn't have dared walking the throttle to 100% at take off.

 

One has to remember, that the planes here in BoX feature peculiarities that (for good reason) are not existent in todays aircraft, and if 56'' Hg MAP would go unpunished, you'd see a lot of very powerful P-40 in multiplayer...

[TXSailor_1]

It has been debated whether the cues delivered by the engine are as would be expected from an engine that is run at severe overcompression and is predetonating. Personally, I think they should be such that you wouldn't have dared walking the throttle to 100% at take off.

 

One has to remember, that the planes here in BoX feature peculiarities that (for good reason) are not existent in todays aircraft, and if 56'' Hg MAP would go unpunished, you'd see a lot of very powerful P-40 in multiplayer...

 

Yeah, some kind of indicator that SOMETHING isn't right prior to losing the engine would be nice. But I genuinely wonder whether such a situation even existed in real life. Time limits at max power were certainly common, but being completely unable to push the throttle full forward is something I have simply never heard of before. Unless you need to REALLY gingerly advance it, it seems impossible to go to full forward at all, and I can't imagine that being at all correct.

[6./ZG26_Klaus_Mann]

Yeah, some kind of indicator that SOMETHING isn't right prior to losing the engine would be nice. But I genuinely wonder whether such a situation even existed in real life. Time limits at max power were certainly common, but being completely unable to push the throttle full forward is something I have simply never heard of before. Unless you need to REALLY gingerly advance it, it seems impossible to go to full forward at all, and I can't imagine that being at all correct.

Well, 60"+ of Boost can cause Pre Ignition and Detonation pretty much instantly, and they will end your Engine very, very quickly if the Carb can't handle it. Especially on Take Off without Cooling Air in the Intake. It's like having the Supercharger of your Hot Rod set to too low gearing. You can't go full Throttle either in that case at the Risk of Splitting the Block. 

Your Manifold/Carb need to be able to reduce the Intake Temperature. If they get too Hot you have a Problem. And since they are thin Metal. the Heating up happens in a Matter of Seconds and KABOOOM, all of the Junk gets blown out at the Wrong End. 

 

You can go full forward at 12000@2600rpm/15000ft@3000rpm without Danger. At that Point the Supercharger can't give more than 37"@2600/42"@3000 respectively. 

Allison probably had a 10% Safety in their Calculations and Limited WEP Settings by Supercharger Drive Speed. The Turbo-Normalized Engines had a smaller Reduction Ratio, thus Turning Slower and were able to sustain higher Settings (60") than our Altitude Rated F3R. 

Apparently the Post P-40E models also received different intake Mainfolds and Carbs which allowed even higher Settings. 

Edited July 30, 2017 by 6./ZG26_Klaus_Mann

[BlitzPig_EL]

And yet, as I have posted repeatedly, US and Commonwealth units in North Africa and the Pacific were changing the supercharger gear ratios and running these same V1710 engines at 70+ inches of manifold for 15 to 20 minutes at low levels without blowing up the engines.

 

What is happening in the game is a less than ideal, no, it's a gamey solution, applied by the developers who read the manuals and took them at face value, which is nonsense as the manuals they translated for the VVS were pre war training manuals meant to keep engine repairs low, and not meant for front line combat aircraft.

 

So is it a simulation when you enforce engine settings that no one in combat used and made the consequences 100% fatal to the engine every time? 

Edited July 30, 2017 by BlitzPig_EL

[ZachariasX]

How much you can exceed boost before predetonation happens depends on your fuel quality (typically much better for the Americans in the Pacific) as well as on the athmosphere. So I'd be careful comparing what they supposedly did with the Russian steppe.

 

I'd welcome a thorough simulation of the predetonation. But we definitely should hear it happening.

[BlitzPig_EL]

The point is that the Allison V 1710 is a very rugged engine, and that is not portrayed, at all, in this sim.

[Farky]

And yet, as I have posted repeatedly, US and Commonwealth units in North Africa and the Pacific were changing the supercharger gear ratios and running these same V1710 engines at 70+ inches of manifold for 15 to 20 minutes at low levels without blowing up the engines.

 

 

They weren't changing supercharger gear ratios, they were just moving throttle lever during flight forward to get up to 70 inHg of MAP (in case of V-1710-F3R, P-40E engine) or reseting automatic manifold pressure regulators to 66 inHg in case of V-1710-F4R (P-40K engine).

[ZachariasX]

The point is that the Allison V 1710 is a very rugged engine, and that is not portrayed, at all, in this sim.

Yes, I don't doubt that. But predetonations also kill a rugged engine. How much it could take long term is also illustrated with the P-39 where it was clear from when on the engine started to "make metal". This also dependent on the quality of lubricants used. But we do know that the Allison as well as the Merlin can be pushed to 3000+ hp for short times as they do in the Reno air races. (Ok, they are heavily modified engines, but still the same block.)

 

It is also not clear what happens to a 1940 front line Allison engine run at 70'' Hg. How many sorties until it is broken? In game, we have always an unlimited suply of aircraft, all being pristine new. We never decrease squadron readyness by flying at high boost...

 

But by all means, *we should hear the engine suffering* if handled wrong. Not just a gauge pointing at a value, then no more power.

[BlitzPig_EL]

Just re read the Allison document about pushing the 1710 to high boost, and yes, I made a mistake saying they changed the gear ratios.   That is mentioned later in the document as something done by the factory to later model engines for more performance at higher altitudes.

[Field-Ops]

...

But by all means, *we should hear the engine suffering* if handled wrong. Not just a gauge pointing at a value, then no more power.

 Definitely need some more audible feedback in this aspect, before engine is damaged beyond repair. 

[chris455]

Yeah... I guess 10 years of civil aviation, 4 years of military aviation, I don't really know anything about how this "air thing" works...

 

Conversely, I've never encountered an aircraft, real life or sim before, where application of full power instantly wrecks an engine. I can see overheating on takeoff if all radiators are closed, sure, but with radiators full open, thus cooling not an issue, and smooth application of power, the inability to push a throttle completely forward without immediate damage to said engine is absurd in my experience. 

This. ^

The point is that the Allison V 1710 is a very rugged engine, and that is not portrayed, at all, in this sim.

Also this ^

[StickMan]

I don't think it was the engine that couldn't handle those pressures, it was the fuel that was available at the time period. So yes, detonation will occur at very high compression with the fuel available at the time period we are in, in this game. Detonation can kill an engine very quickly if not instantly.

 

150 grade fuel didn't start getting tested until 43'. It wasn't until 150 grade was available did the Allison power plants get approved to run at higher pressures and then only for limited times according to the USAAF.

Edited July 30, 2017 by GeneralZod

[TXSailor_1]

I don't think it was the engine that couldn't handle those pressures, it was the fuel that was available at the time period. So yes, detonation will occur at very high compression with the fuel available at the time period we are in, in this game. Detonation can kill an engine very quickly if not instantly.

 

150 grade fuel didn't start getting tested until 43'. It wasn't until 150 grade was available did the Allison power plants get approved to run at higher pressures and then only for limited times according to the USAAF.

 

But the key question is, since the aircraft was designed prior to 150 octane, one would expect that the aircraft was NOT designed with 150 octane in mind. Thus, it was NOT designed to allow the throttle level to demand powers that would instantly destroy the engine. Again, I don't have documents to back this up, that's just something that is unheard of to me. I'm very well used to time limits on power settings (And FWIW those limits are based on flight hour flown, i.e., a certain power setting can be run for 15 minutes, then you must fly at a lower setting for an hour, then you get another 15 minutes of that power...) but I have NEVER heard of 'Push lever forward, instant kill engine'. 

[BlitzPig_EL]

The high boost pressures I referenced were used before the end of 1942, and hence before the availability of 150 octane fuel.

 

Here is a screenshot of part of the first page of the Allison document, note the date.

 

 

Knock yourselves out.

Edited July 31, 2017 by BlitzPig_EL

[indyscout]

Hey all, pretty new to the p40 topic and I was wondering if someone could point me to a run down of the issues with the p40. Is the general consensus that the p40 is not worth purchasing in its current state?

[19//Moach]

I have to add another voice to the clamor here, indeed: 

 

the current model of the P40's engine is simply unacceptable to the standards set by everything else in this game at this point.

 

 so many elements have come such a long way since development started, engines in general now seem crudely out of place, as if belonging to a different, less attentively developed game.

 

 

the P40 stands in the very core of this new pressing need, as there are multiple reports, and plenty of evidence which fully contradict what happens in the sim under such high-power running conditions.  

 

 

 

with the new FMs coming in, it is expected that this plane should become at least aerodynamically sound, to a point where it's airworthiness (let alone it's usefulness as a combat aircraft) is less of a contradiction...

 

but even then, it will remain so that the legendary toughness of the Allison V-1710 has its memory disrespected by representation of it as an unreliable, fragile and wholly inadequate powerplant.  

 

 

an overhaul of engine simulation would be the next step I'd hope to see prioritized.  a next step in development for engines, much like there is to be for FMs, is clearly due in order to bring that aspect of the game up to par with the rest of what we have in it.

Edited July 31, 2017 by 19//Moach

[19//Moach]

Hey all, pretty new to the p40 topic and I was wondering if someone could point me to a run down of the issues with the p40. Is the general consensus that the p40 is not worth purchasing in its current state?

 

 

issues: 

 

 - until the new FMs are in (late next month) - the plane exhibits such instability that it may be considered unairworthy.  this is in contrast to its historical reputation of a stable gun platform, and makes it critically handicapped in combat (especially online)

 

 - the plane suffers from a violent, physics defying onset of an absurd "full rudder stall" (aka: The Death Slide) - which makes it prone to departing controlled flight even before the wings have reached their critical stall angle, caused by simply exceeding a 12° sideslip maximum. this is not mentioned in any wartime publications, instead, many have brought up research which all but denies it having ever been a factor.  a yaw stability issue is known about the plane, but no sources even hint at a such extreme consequences to sideslip angles

 

 - the under-damped pitch and yaw moments, combined with excessive roll coupling make for a pilot workload which is alien to fixed wing aircraft, just to maintain directional control. this increases the rudder problem to an extreme problem, as the erratic swaying motion (wobble) that results from even minor lack of cross-axis coordination is enough to exceed the controllability envelope, leading to a deadly full scale spin

 

 - the engine is severely limited by a cartoon-like depiction of engine limits taken from pre-war handbooks at face value. that means power settings in excess of levels determined for maintenance considerations will incur extreme physical consequences.  this behavior is fully incorrect, as multiple sources have indicated it could tolerate substantially higher loads

 

 - this engine model is governed by a timer-based system which ensures catastrophic mechanical failure once time runs out.  this time is linearly proportional to the level of power generated along arbitrarily defined "modes" (i.e. 50% into "combat mode" yields 2x total "combat time" before sudden failure).  there is no indication on temperature gauges or any other means for a pilot to determine how close to disaster he is.

 

 - without the ability of developing power levels as those reported by combat veterans with this airplane, it becomes surely impractical to use this airplane in air-to-air combat. it is outclassed in maneuverability and speed even by enemy bomber types, requiring exceptional tactics and above all, luck in order to achieve any victory whatsoever

 

 - other technical issues include an unhistorical tendency of engine overcooling. on the ground, it should overheat at idle with rads open, yet it overcools even with rads fully closed, despite of weather. the startup procedure is also animated incorrectly, performing corrective steps for overuse of the primer pump as though these were part of the normal sequence. this is such that engine starts will take twice as long as they would have in reality.

Edited July 31, 2017 by 19//Moach

[indyscout]

Thanks for the run down Moach, sounds like I'll hold off on picking up the p40 until some of those issues are addressed.

[StickMan]

Let's for a moment consider being able to run the power plant at 70" hg for prolonged periods of time in game. From everything I've read about the P40 it wasn't a particularly stellar performer. Certainly it was capable and as with many aircraft it could be deadly in the right hands. From my limited time with it it does seem to reflect that in game, IMO. When I've flown to it's strengths I've certainly scored victories with it. It's performance seems to match what I've read when it's properly managed, to me.

 

Another point to consider is maybe those that were highly successful with the P40 such as the Flying Tigers were successful because they pushed the powerplant beyond what others were willing to do. A fact that I would think they would want to share and would be better documented if true.

 

If the devs actually changed the engine to run high boost for prolonged periods would it cause the P40 to over-perform in game unrealistically? That's the real question. Unfortunately we wouldn't know until it was actually changed.

Edited July 31, 2017 by GeneralZod

[19//Moach]

(...)

 

If the devs actually changed the engine to run high boost for prolonged periods would it cause the P40 to over-perform in game unrealistically? That's the real question. Unfortunately we wouldn't know until it was actually changed.

 

 

nobody is asking for it to be extended unrealistically - much the contrary. realism is the key word here

 

the engine issue most often raised is not of being able to abuse the engine longer because of combat inadequacies. it is of how the current limits contradict many historical claims that it could be done without the consequences found in the game.  

 

if the engine was over-performing, the issue would be just as critical, but to the opposite effect.

Edited July 31, 2017 by 19//Moach

[JtD]

... but I have NEVER heard of 'Push lever forward, instant kill engine'.

Now you did. Welcome to early supercharged engines!

[StickMan]

nobody is asking for it to be extended unrealistically - much the contrary. realism is the key word here

 

the engine issue most often raised is not of being able to abuse the engine longer because of combat inadequacies. it is of how the current limits contradict many historical claims that it could be done without the consequences found in the game.

 

if the engine was over-performing, the issue would be just as critical, but to the opposite effect.

Agreed, if it is proven that it could take some "balls to the wall" handling of the throttle then certainly it should be modeled. However in my experience it already can. So how much time are we talking about? I've firewalled the throttle on various occasions although never for more than several seconds or so.

 

I do find your previous post and assessment a bit harsh on our current P40.

I've been able to out turn just about anything at low to medium altitude and I've found it to be very stable at combat speed with a very light touch of the stick to keep it in check. It is a poor climber as it was historically. As such, never try to go vertical with a 109, that is akin to a suicide attempt. It also loses power at high altitude due to its single stage blower but it performs exceptionally well in a dive. I find this to be it's strongest asset in game as diving on an unsuspecting bandit can make for an easy kill. With its well mannered dive and hard punch of 6 .50cals it has made quick work of enemy planes for me this way.

 

Not to say it doesn't have room for improvement. Its obviously getting improved upon in the next patch. I just found what you posted slightly unfair, in some aspects.

Edited July 31, 2017 by GeneralZod

[Herne]

Thanks for the run down Moach, sounds like I'll hold off on picking up the p40 until some of those issues are addressed.

 

I've been flying this bird a lot lately, and really enjoying it. It takes some getting used to, I find it takes a little practice looking after your engine, and you constantly adjust throttle with altitude.

 

My understanding is that most american and even japanese superchargers of the era work in a similar fashion, so it's all good practice for the upcoming Battle of Midway. 

[[CPT]Pike*HarryM]

From everything I've read about how the Russians used these planes they would run them at high-power and they would simple lose power over time as they wore out. So if there were not a spare engine you would be stuck with a "dog" until you did, that was the punishment. In this game you grab a fresh plane each sortie, so you are punished in the short term not the long term. I think loss of power (most of the time) instead of engine blowing up would be more realistic.At max RPM maybe more chance of throwing a rod or some other catastrophic failure.

[6./ZG26_Klaus_Mann]

Well, if you set the Quick Missions Difficulty to "Unbreakable" the Engine will not Die. A speed Test at Full Throttle here results in up to 585kph on the Deck. With Manual Pitch you can set it to 3300rpm and get 615kph on the Deck. 

 With Full Power available there would be no other Word than Stellar.

[ZachariasX]

Well, if you set the Quick Missions Difficulty to "Unbreakable" the Engine will not Die. A speed Test at Full Throttle here results in up to 585kph on the Deck. With Manual Pitch you can set it to 3300rpm and get 615kph on the Deck. 

 With Full Power available there would be no other Word than Stellar.

It shows to me that predetonation as such is not modelled. The engine just "dies". If there was predetonation, power output should decrease significantly once that would set in (loudly with awful vibratons!!). If that was modelled as such, it would be more than pointless to open throttle beyond a "lethal" MAP, and we wouldn't really have this discussion.

[chris455]

Many here have spoken of improvements coming to the P-40 "in the next patch."

What did I miss?

Where is this documented?

Thanks in advance for any replies-

[JtD]

The general flight model overhaul has been announced for the next patch. The P-40 is expected to greatly benefit from that.

[ACG_KaiLae]

Adding to what has been previously stated here, that if you go off of the spec sheet for the game, a 110 will outturn a P-40 on the deck. This despite the fact that multiple combat reports from both allied and axis stated it was a better turner than the 109.

 

Waiting though to see what comes out of the patch before taking this up again.

[Boaty-McBoatface]

Well, if you set the Quick Missions Difficulty to "Unbreakable" the Engine will not Die. A speed Test at Full Throttle here results in up to 585kph on the Deck. With Manual Pitch you can set it to 3300rpm and get 615kph on the Deck.

With Full Power available there would be no other Word than Stellar.

 

That's an interesting experiment.

 

Does anyone know what power it would make at the full throttle 56mmhg boost? If it gets 585kph then I'm guessing that's near 2000hp.

[BlitzPig_EL]

A quick Wiki shows that the V 1710 -111 (F30R) gives the following performance.

• Power output:
  • Take-off: 1,500 hp (1,119 kW) at 3,000 rpm and 56.5 inHg (190 kPa) manifold pressure
  • Military: 1,500 hp (1,119 kW) at 3,000 rpm at 30,000 ft (9,144.00 m)
  • Normal: 1,100 hp (820 kW) at 2,600 rpm at 30,000 ft (9,144.00 m)
  • Cruising: 800 hp (597 kW) at 2,300 rpm at 30,000 ft (9,144.00 m)
• Specific power: 0.88 hp/cu in (39.3 kW/L)
• Compression ratio: 6.65:1
• Oil consumption: 0.025 lb/hp/hr (0.01475 kg/kW/hr)
• Power-to-weight ratio: 1.05 hp/lb (1.76 kW/kg)

Will dig through my books to try to find data for the -39 at 56 inches.

[Boaty-McBoatface]

So only 1500hp and it's faster than a fw190 and la5, despite much bigger airframe? 585kmh @ 1500hp, something is not right there.

[JtD]

Full throttle at sea level with our P-40E gives 65-70" boost. That's 1850hp, give or take.

[Boaty-McBoatface]

Full throttle at sea level with our P-40E gives 65-70" boost. That's 1850hp, give or take.

 

 

Just wondering, is there a certain way you figured that JtD?

 

Also, 65-70 inches HG is an insane amount of boost. That's like 32psi boost- double the spitfire maximum boost, or 2.2ata in the Bf109... nuts. 

Edited August 1, 2017 by temujin

[Stig]

I have already posted this in another P-40 thread, but I'll try again. An interesting viewpoint on the over boosting of the Allison. The highlighted bits are mine.

 

 

Allison approved a WEP rating of 1490hp at 56in MAP at 4300ft for the -39 engine.
They approved a WEP rating of 1580hp at 60in MAP at 2500ft for the -73 engine in the P-40K
The -73 engine had a few of it's components strengthened and also use 30% gylcol/70% water cooling.

Now maybe the Mid east pilots were pushing the engine to 66" on their gauges but they had no torque meters installed on the engine and I doubt the Mid east temperatures were corrected to the standard 59 degrees Fahrenheit which makes actual power output more than a bit doubtful.
Since the only production Allison engines to get to 1700hp were either turbo charged engines in the P-38 or the two stage mechanical supercharged engines in the P-63. The P-38L engines needed 150 PN fuel to reach 1700hp (70")and the P-63 engines needed water injection to go past 1500hp and 60-61" of manifold pressure and 100/130 fuel. They could hit 1850hp at sea level using 75"

And yet somehow in the field squadron pilots pulled 1780hp (measured how?) out of a -39 engine in a P-40E using 70" of MAP using a single stage supercharger, 100/130 fuel and no water injection.
Two stage superchargers as a general rule heat the intake charge less and require less power to drive.

Allison service reps did note instances of up to 66in used on the -73 engine and the Service reps in Australia did note use of 70" with the -73 engines. But power was not noted in the book I read.
Factory power graphs show the basic Allison with 8.80 gears just running out of the ability to flow enough air to get much past 61-62"mpa without either large amounts of ram (high speed level flight) or over revving the engine at sea level.

Edit. The change from 15 degrees C to 38 degrees C (59F to just over 100F) lowers the actual air density (weight of air per cubic_____) to 92.57%. Taking in the same cubic feet (or meters) of air per second or minute at the higher temperature will result in 92.57% of the power (in theory) of the "standard" temperature of 59F or 15C that most nations used as a standard. This is if the air pressure is standard.
This also means that a pilot could (boost control permitting and some US aircraft didn't have a automatic boost limiter) use 7-8% more absolute manifold pressure than "book figures" and yet only being making the "book" power numbers. Trying to get too tricking in gimmicking the boost control could land the pilot in trouble as the temperature at altitude (even 15-20,000ft) doesn't vary as much
as the temperature at ground/sea level around the world. Yes the temperature at 15,000 is higher in the tropics (or NA desert) than in England (or Ohio) but not the same difference you sea at ground level. Setting the engine up to "over" boost at sea level could very well result in too much over boost at an altitude of 9-10,000ft.

Now perhaps the North African and Australian figures were taken in their "winters" or cold snaps but pressure readings ( or max pressure seen by pilot while doing ?????) don't really translate into reliable power figures.

 

 

http://ww2aircraft.net/forum/threads/ww2-aircraft-more-successful-in-secondary-role.45311/page-8

 

[JtD]

Just wondering, is there a certain way you figured that JtD?

 

Also, 65-70 inches HG is an insane amount of boost. That's like 32psi boost- double the spitfire maximum boost, or 2.2ata in the Bf109... nuts.

Extrapolating the engine charts. Depending on which one you use, that's where you end up. For instance: read from chart at sea level, 42" ~ 1050hp, 51" ~ 1325hp, 60" ~1575hp --> estimated: 69" ~ 1800hp.

 

69+" would be achievable only with ram effect or in a high pressure environment, but would be achievable. Yes, that's an insanely high boost, and it's extremely stressful for the engine.

[ZachariasX]

I have already posted this in another P-40 thread, but I'll try again. An interesting viewpoint on the over boosting of the Allison. The highlighted bits are mine.

 

 

Allison approved a WEP rating of 1490hp at 56in MAP at 4300ft for the -39 engine.

They approved a WEP rating of 1580hp at 60in MAP at 2500ft for the -73 engine in the P-40K

The -73 engine had a few of it's components strengthened and also use 30% gylcol/70% water cooling.Now maybe the Mid east pilots were pushing the engine to 66" on their gauges but they had no torque meters installed on the engine and I doubt the Mid east temperatures were corrected to the standard 59 degrees Fahrenheit which makes actual power output more than a bit doubtful.

Since the only production Allison engines to get to 1700hp were either turbo charged engines in the P-38 or the two stage mechanical supercharged engines in the P-63. The P-38L engines needed 150 PN fuel to reach 1700hp (70")and the P-63 engines needed water injection to go past 1500hp and 60-61" of manifold pressure and 100/130 fuel. They could hit 1850hp at sea level using 75"And yet somehow in the field squadron pilots pulled 1780hp (measured how?) out of a -39 engine in a P-40E using 70" of MAP using a single stage supercharger, 100/130 fuel and no water injection.

Two stage superchargers as a general rule heat the intake charge less and require less power to drive.

Allison service reps did note instances of up to 66in used on the -73 engine and the Service reps in Australia did note use of 70" with the -73 engines. But power was not noted in the book I read.

Factory power graphs show the basic Allison with 8.80 gears just running out of the ability to flow enough air to get much past 61-62"mpa without either large amounts of ram (high speed level flight) or over revving the engine at sea level.

Edit. The change from 15 degrees C to 38 degrees C (59F to just over 100F) lowers the actual air density (weight of air per cubic_____) to 92.57%. Taking in the same cubic feet (or meters) of air per second or minute at the higher temperature will result in 92.57% of the power (in theory) of the "standard" temperature of 59F or 15C that most nations used as a standard. This is if the air pressure is standard.

This also means that a pilot could (boost control permitting and some US aircraft didn't have a automatic boost limiter) use 7-8% more absolute manifold pressure than "book figures" and yet only being making the "book" power numbers. Trying to get too tricking in gimmicking the boost control could land the pilot in trouble as the temperature at altitude (even 15-20,000ft) doesn't vary as much

as the temperature at ground/sea level around the world. Yes the temperature at 15,000 is higher in the tropics (or NA desert) than in England (or Ohio) but not the same difference you sea at ground level. Setting the engine up to "over" boost at sea level could very well result in too much over boost at an altitude of 9-10,000ft.

Now perhaps the North African and Australian figures were taken in their "winters" or cold snaps but pressure readings ( or max pressure seen by pilot while doing ?????) don't really translate into reliable power figures.

 

 

http://ww2aircraft.net/forum/threads/ww2-aircraft-more-successful-in-secondary-role.45311/page-8

 

When looking at the overboost capabilities, athmospheric conditions have a huge impact on possible boost rates regarding both power output and predetonation. I consider 10% difference a lot (as it is also referred to in you quote).It would be great if they were modeled and not just reflected by enige death. For all aircraft.

 

This is why I would never take 70'' Hg over New Guinea as 70'' over the steppe in a Russian winter. More like 60'' Hg (which is still a great lot) but the much lower quality of fuel and lubricants had to be considered (lowering max possible MAP further). Allowing such high overboost should require persistent damage in any type of career missions. Anyone pushing engines like that should end up quickly with an outfit of lemons.

 

Anyway, I expect a lot from the upcoming FM patch and I assume it will make it a lot easier to fly the P40 in a way that it doesn't bleed that great lot of energy during maneuveing. Even with 1300 hp the P-40 should be a handful for a 109F.

[BlitzPig_EL]

Please understand, I'm not advocating for 70" of manifold.

 

I posted that to show that the Allison V1710, as modeled in this sim, is so far from the reality of what it was capable of that using the word "simulation" and this P40 in the same sentence is laughable at best.

 

As the report said, pilots were running 70 inches for extended periods, whereas in our little bit of fantasy land you cannot get close to that for a few seconds before your engine has a catastrophic failure.

 

How long will "our" P40 run at 50 inches?  Or even 45?

 

 

I fear for the P39, and heaven help the F4F drivers in Battle of Midway.