P40: The underated underdog, or just behind the times

[fibus]

This is really good stuff in my opinion. It all rings true and now with the subject of allison engines so far away in time we will never know the complete truth.
One man I knew was an aeronautical engineer that worked at Wright during WW2 and had the assignment to inspect the manufacturing practices at subcontractors of aeronautical engines including the Allison. He was astounded, for instance, to see good connecting rods dropped into barrels or fitted with metal hammers.
Of course rubber mallets should be used and dropping rods atop another leads to nicks which can lead to failure of the part.
My conclusion about the Tomahawk is it was superior to the JAAF fixed wheel fighter aircraft it encountered and below 10,000 was equal to early Me/Bf 109's.
Both airplanes lacked good harmony of controls.
Coping with the Oscar and the Zero would take some care.
Tex Hill always considered the P 40 equal to Japanese aircraft and better in some ways but had to be used with correct tactics.

[PitLane]

In the early 40's Col. Chennault came to Curtiss in Buffalo to look at the P-40s with my Grandfather. Bill Pawley, president of the Intercontinent Corp. had meet with the VP of Curtiss, Burdette Wright and some others. The US government was having Curtiss divert "100" P-40s from the English contract to China. They had engines in them.

[Condora]

Hi guys!

New kid on the block here. Just fan of aircraft, would have tried to be a pilot or something aircraft-related, but since childhood I was as blind as a bat. And no radar.

Good pieces of info from some of you, and I'd like to see those pics of the "naval" P-51.

About the P-40, I believe that it would hardly be improved. It was based on a pre-war design, it had some drawbacks and qualities, but on WW II the industrial factor weighted a lot. As soon as someone came up with airplanes using new concepts, and/or easier to produce, the P-40 would be relegated to "secondary tasks".

That's basically what I think that happened to the Hurricane: reliable, tough, able to face the more advanced BF-109... but if you compare Hawker's Fury and Hurricane, you see that the Hurricane is a Fury with a new engine, canopy, and a wing removed.

The P-40 was not so outdated as the Hurricane, but the principle is the same: many airplanes based on early-30s concepts were not able to keep up with the new models, the better ones survived, even if "only" as all-round workhorses.

Cheers

[Elvis]

Originally Posted by Shortround6

While blueprinting can unlock "hidden" power in production car engines I would doubt that aircraft engines were anywhere as sloppy car engines to begin with.

Since both the British and the AVG sometimes pushed these engines to 58" of boost (and even 62" at 3200rpm) I think we can see were the "extra" power came from. THe AVG engines might have stood up to it better though

Some of the AVG parts were not simply "checked" but were actually remanufactured or modified from parts that DID NOT meet original specifications. THE AVG engines were assembled in a seperate building so there was no chance that these "reject" parts would end up in an American or British engine by mistake.

Originally Posted by Shortround6

I rather doubt that diesel engines were that sloppy either. Somethng else to consider is that clearances change as engines heat up. That famous diesel clatter when they are cold.
Aircraft engines being mostly alumininium have a greater co-effiecent of expansion than an iron engine would and considering their size compared to a car engine might use a different tollerance.

Rolls-Royce found that thier intial recomendations for valve tappet clearance were in error. The .020 used for both intake and exhaust was thought to close up as the engine got hot. it did on the exhaust side but the clearance actually got bigger on intake side and later engines change to .010 on the intake valves.
R-R did allow over boring an engine to elimate a step at the top of a cylinder but fitting oversized pistons was only alowed after the war and only for a brief period of time. cylinders were to be plated when possable and reground to bring then into spec.

Hey Shortround6, pull down your skirt, your inexperience is showing.

An engine is spec'd so that it will reliabily perform the task for which it was designed, regardless of the inginition system.
Yes, the Brits gain in performance is directly due to the increase of pressurization of the cylinders, but if you know you're going to do that, then you want to make sure the tolerances of the engine's affected parts are "spot-on", not just "close enough".
This is why they were "hand built" and why they were blueprinted.
Why else be so careful about assembly, if you weren't going to take the time to check each and every part.
Large rocker arm clearances are an indication that the engine's builder forsees the engine operating at high cylinder tempretures for an abnormally long period of time. This means the metal parts will expand to the point that they will exceed the normal clearances, so the manufacturer/builder allows for the prolonged heat by increasing the gap.
However, actual practice can sometimes show this is unneccesary and will thus rescind that spec and return either to the normal spec, or a lessened gap that may still be greater than the normal spec.
"Diesel Clatter" has nothing to do with the moving parts of the engine.
Its a condition commonly referred to as "engine knock" and it never does go away, or even lessen.
This condition exists in a diesel engine because it is not a "spark ignition" engine.
Instead, it compresses the air so tightly, it heats up to the point to where it can actually burn fuel, when atomized.
The same condition exists when a spark ignition engine "knocks". The air in the cylinder is actually hot enough to burn the a/f mixture after the intake valve has closed and the piston has begun to compress the mixture, but before the spark goes off.
Cylinder pressure in a spark ignition engine typically runs in the 90-150 psi range, but in a diesel engine, it can exceed 400 psi (thus the astronomical c.r.'s).
This puts a great increase in the load a diesel engine sees, and why those engines tend to be built a lot heavier than a non-diesel engine.



Elvis

[Shortround6]

Originally Posted by PitLane

In the early 40's Col. Chennault came to Curtiss in Buffalo to look at the P-40s with my Grandfather. Bill Pawley, president of the Intercontinent Corp. had meet with the VP of Curtiss, Burdette Wright and some others. The US government was having Curtiss divert "100" P-40s from the English contract to China. They had engines in them.

There was quite bit of finagleing going on with some of those contracts. The US was quite willing at times to give up some of it's "slots" in a production run in return for planes of a later model to be delivered at a later date. THe airframe manufacturer did not buy the engines from the aircraft engine makers. THe goverment bought the engines and had them shipped to the aircraft factory where they were fitted before the complete plane was delivered.
SO, yes the planes would have been delievered with engines (and spares sent along crated) but how the engines were paid for or how the engines came to be during production runs might be different than what appears at first glance. Please note that China didn't get into the lend lease act until April of 1941 so again some finagling was needed to cover contracts.

[Clay_Allison]

Originally Posted by Shortround6

"The reason Performance didn't change much with the change to the Merlin was because that Merlin was setup similarly to the Allison, i.e., single stage/single speed supercharger."

No, the Merlins used in the P-40 had single stage TWO speed superchargers.

They used 8.15 and 9.49 gear sets and were rated at 1240HP at 11,500ft and 1120hp at 18,500ft using 9lb of boost ( 48")compared to the later P-40 Allisons which gave 1125hp at 15,500ft at 7.25lbs of boost (44.5in)

The Merlin was rated at 1300hp for take off compared to the late Allisons 1200hp.

Going to the TWO stage Merlin design of supercharger would have ment an extra couple of hundred pounds of engine weight NOT INCLUDING the Liquied radiator for the aftercooler. This radiator has to be placed somewhere and will add at least some drag.

THE question is not weither it could be done but weither the improvement was worth the effort and the delay or interuption in production.

In my opinion it definitely was, the two stage supercharger is the only good way to get decent horsepower at altitude. Without that, it's a one-legged man in an ass-kicking contest. I'd throw out the pilot armor plate to make up the weight if it had to be done.

[Shortround6]

Originally Posted by Elvis

Hey Shortround6, pull down your skirt, your inexperience is showing.

An engine is spec'd so that it will reliabily perform the task for which it was designed, regardless of the inginition system.
Yes, the Brits gain in performance is directly due to the increase of pressurization of the cylinders, but if you know you're going to do that, then you want to make sure the tolerances of the engine's affected parts are "spot-on", not just "close enough".
This is why they were "hand built" and why they were blueprinted.
Why else be so careful about assembly, if you weren't going to take the time to check each and every part.
Large rocker arm clearances are an indication that the engine's builder forsees the engine operating at high cylinder tempretures for an abnormally long period of time. This means the metal parts will expand to the point that they will exceed the normal clearances, so the manufacturer/builder allows for the prolonged heat by increasing the gap.
However, actual practice can sometimes show this is unneccesary and will thus rescind that spec and return either to the normal spec, or a lessened gap that may still be greater than the normal spec.
"Diesel Clatter" has nothing to do with the moving parts of the engine.
Its a condition commonly referred to as "engine knock" and it never does go away, or even lessen.
This condition exists in a diesel engine because it is not a "spark ignition" engine.
Instead, it compresses the air so tightly, it heats up to the point to where it can actually burn fuel, when atomized.
The same condition exists when a spark ignition engine "knocks". The air in the cylinder is actually hot enough to burn the a/f mixture after the intake valve has closed and the piston has begun to compress the mixture, but before the spark goes off.
Cylinder pressure in a spark ignition engine typically runs in the 90-150 psi range, but in a diesel engine, it can exceed 400 psi (thus the astronomical c.r.'s).
This puts a great increase in the load a diesel engine sees, and why those engines tend to be built a lot heavier than a non-diesel engine.



Elvis

You are quite right. I pulled a major mistake and a boneheaded comment about the diesels.

But that is no reason to join me

Yes the British did overboost their Allisons compared to the USAAF and Allison recommendations at the time. BUT the AVG were not British and their engines were not British contract engines. I am not sure how the Allison factory workers who assembled the engines in Indianapolis in the spring of 1941 would KNOW how the engines would be operated by the AVG in combat STARTING in Dec of 1941, 6-9 months later.

THE Chinese engines were "hand built" becasue they were doing things like " fitting steel inserts that were plated to fit oversize tapped holes, connecting rod bearings altered to fit slightly undersized crankshafts, and dozens of other similar fixes were made"

THe point about the Merlin compared to the diesel is that each manufacturer decides what clearences are needed by their engine when running at temperature and how they are going to get them. THe fact that an engine may show different tolerences or clearances when cold compared to a totally different type of engine should not mean that the engine is question is "sloppy" or loose. I may have read more into the statement than was ment but I am tired of reading about how much better American Merlinis were than British bult ones and other such nonsense.

BY the way, are you getting those cylinder pressures with a compresion gauge?

they seem to be just a little low for pressure once the fuel starts to burn.

[Shortround6]

Originally Posted by Clay_Allison

In my opinion it definitely was, the two stage supercharger is the only good way to get decent horsepower at altitude. Without that, it's a one-legged man in an ass-kicking contest. I'd throw out the pilot armor plate to make up the weight if it had to be done.

Well, the pilots might not agree with you.

The P-40 suffers from two problems when trying to compeate against the 109.

One is that the 109s engine used lower boost to make it's power so that a single stage supercharger can supply enough boost several thousand feet higher than the more highly boosted American and British V-12s.

THe other problem is the much greater weight of the P-40. Even using the weight of the light weight P-40N you have a combat weight of 7,725lbs compared to the weight of a 109 F at about 6400lbs or an early 109G at 6800lbs. Now with 1300-1355hp at just over 18,000ft for the German engines you have power to weight ratio of 4.92-5.02. For the P-40 to equel this it needs an engine that will provide 1545hp at 18,000ft or little above. You need the Allison to provide almost 40% more power than it did originally and to do this several thousnad feet higher than it did. while this performance was avialable later it might not have been available in Jan of 1942. You are going to need every HP of a Merlin 60 series engine.

The Spitfire gained about 900lbs between the MK V and the Mk IX of which only about 250lbs are artributed to the DRY weight of the two engines. Pulling the armour won't come close to cover the weight of the COMPLEATE installation even if there were several hundred pounds not included in the engine change.

[Clay_Allison]

Originally Posted by Shortround6

Well, the pilots might not agree with you.

The P-40 suffers from two problems when trying to compeate against the 109.

One is that the 109s engine used lower boost to make it's power so that a single stage supercharger can supply enough boost several thousand feet higher than the more highly boosted American and British V-12s.

THe other problem is the much greater weight of the P-40. Even using the weight of the light weight P-40N you have a combat weight of 7,725lbs compared to the weight of a 109 F at about 6400lbs or an early 109G at 6800lbs. Now with 1300-1355hp at just over 18,000ft for the German engines you have power to weight ratio of 4.92-5.02. For the P-40 to equel this it needs an engine that will provide 1545hp at 18,000ft or little above. You need the Allison to provide almost 40% more power than it did originally and to do this several thousnad feet higher than it did. while this performance was avialable later it might not have been available in Jan of 1942. You are going to need every HP of a Merlin 60 series engine.

The Spitfire gained about 900lbs between the MK V and the Mk IX of which only about 250lbs are artributed to the DRY weight of the two engines. Pulling the armour won't come close to cover the weight of the COMPLEATE installation even if there were several hundred pounds not included in the engine change.

That's why in another thread I suggested that the US should have taken over development of the Griffon when the brits dropped it and skipped the Merlin, putting the Griffon in instead with an 11' five-blade prop.

[Shortround6]

Originally Posted by Clay_Allison

That's why in another thread I suggested that the US should have taken over development of the Griffon when the brits dropped it and skipped the Merlin, putting the Griffon in instead with an 11' five-blade prop.

And do what with it when?

Early Single stage two speed Griffons were rated at about 1730HP at 750ft and 1490HP at 14,000ft. at 12 lbs boost. (54") They weighed about 1800lbs. By the time this engine got to 20,000ft it might give you 1275HP? Merlin 45s in MK V Spitfires could give 1230Hp at 18,000ft and weighed 400lbs less.
THese weights do not include radiators, coolant, oil, oil coolers or propellors.

You would just have to develop the Griffon with a TWO stage supercharger about 6 months faster than the British developed the Merlin with it's two stage supercharger.

By the way, the Allsion -73 in the P-40 K was rated at 1550HP at sea level for WER at 60" of boost.

[Clay_Allison]

Originally Posted by Shortround6

And do what with it when?

Early Single stage two speed Griffons were rated at about 1730HP at 750ft and 1490HP at 14,000ft. at 12 lbs boost. (54") They weighed about 1800lbs. By the time this engine got to 20,000ft it might give you 1275HP? Merlin 45s in MK V Spitfires could give 1230Hp at 18,000ft and weighed 400lbs less.
THese weights do not include radiators, coolant, oil, oil coolers or propellors.

You would just have to develop the Griffon with a TWO stage supercharger about 6 months faster than the British developed the Merlin with it's two stage supercharger.

By the way, the Allsion -73 in the P-40 K was rated at 1550HP at sea level for WER at 60" of boost.

probably better to dig up the "original (P-40 what-if)" thread than have the same discussion in two different threads.

[Elvis]

Originally Posted by Shortround6

BY the way, are you getting those cylinder pressures with a compresion gauge?
they seem to be just a little low for pressure once the fuel starts to burn.

Which engine are you referring to? The gas engine or the diesel?


Elvis

[Shortround6]

Originally Posted by Elvis

Which engine are you referring to? The gas engine or the diesel?
Elvis

Both.

If we are talking about a cylinder pressure of say, 120lbs that can be acchieved by an engine with an EFFECTIVE (after the valves close) compresson ratio of 8 to 1. Not including any pressure rise due to the increased temperature of the gas.
A diesel at 20 to 1 would have 300psi again not including the pressure from the higher temperature.

IF these were the peak presures the engine wouldn't run. The pressure on the piston on the down (power) stroke would only equel the the work needed to compress the the gas (the air, air fuel, what ever non- liquied is in the cyllinder) with nthing left over to overcome friction let alone give you any power at the shaft.
You do know what BMEP and IMEP mean don't you?
And they are far from the peak pressure in a cylinder.

Shall we each lower our skirts now?

[Elvis]

Shortround6,

No, we shant.
However, it just occurred to me that the figures I quoeted could be a little misleading, in that we've been discussing aircraft engines this whole time, yet I quote automotive figures (at l;east with the gas engine figures).
Granted, the application shouldn't matter under natural aspiration, however, I did not state that the figures were aggregate for general automotive applications, and in that sense I apologize for not doing so.

...and no, those pressures are not "out-of-line" and yes, they were achieved with a compression gauge.



Elvis