P40C vs A6M2 (1 Viewer)

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Time to jazz up this section I collected this comparison along time ago, there was to be a comparison no2 bf109E vs spitfire mk1 but I never found it.

Enjoy

Nice! How about the other numbers?
 
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Something not generally known was the Tomahawks flown by the AVG had hand assembled engines. The P40's of the AVG had 1 or 2 hundred more horsepower than the P40's of the AAF at that time. In its area of operations it was the best fighter aircraft.
 
Something not generally known was the Tomahawks flown by the AVG had hand assembled engines. The P40's of the AVG had 1 or 2 hundred more horsepower than the P40's of the AAF at that time. In its area of operations it was the best fighter aircraft.

I would like to see some real documentation of this. I have no doubt that the AVG used "hand assembled engines" but then so did every other aircraft of the time. Robots or trained gorillas being in rather short supply in 1940 ;)

aircraft engines were built to rather tighter tolerances than car engines to begin with. While the engines for the AVG, being built of reworked "scrap" parts may have had a bit more care than normal in their assembly it is a little hard to figure out were an extra 100-200hp was hiding in the regular engines. If you run an engine at a given rpm (3000) and at a given manifold pressure you have a fixed amount of fuel air going into the engine for potential power. A certain amount goes out the exhaust, a certain amount goes to the radiator and oil coolers, a certain amount drives the accessories and supercharger, a certain amount is lost to friction and a certain amount is left to drive the propeller. Power lost due to friction is gotten rid of by the cooling systems. The Friction in the Allison was studied (as it is in all large scale engines) by turning the engine over with electric motors with various parts installed and removed. Like turning the crankshaft over with the pistons and piston rods removed to figure out the friction in the main bearings. They even knew how much extra friction was caused by fitting stronger valve springs that increased the friction of the cam followers on the camshafts.
The Friction in an early Allison was on the order of 120hp or less. No matter how carefully you assemble the engine you cannot make it friction free. There is no "extra" 100-200hp to be had.

What you can have is an engine that stands up to abuse better, the AVG was known to use higher boost pressures that the US army or Allison recommended at the time. In some instances they may have used higher than recommended rpms too. That will give "extra" power but does shorten engine life.

The Allison had a funny habit of not failing right away when abused. It had a tendency to continue to operate 'normally for several more hours before failing. This meant the engine failed on the second or third flight after the one in which it suffered the abuse which made it rather hard for field units to pinpoint the actual cause of the failures.
 
Hi Shortround6,
There are a few things that can be done to improve power without actually reducing friction on the engine:
Port matching, smoothing and porting intakes,
Hand fitting all the gaskets,
Boring the cylinders oversize and fitting larger pistons and rings,
Decking cylinder heads or blocks to raise compression slightly,
Custom valve jobs,

Align honing and hand fitting bearings would probably noticeably reduce friction.

While all the engines of the time were hand assembled, I don't believe it would have been normal practice to hand fit all the parts.

- Ivan.
 
There are a lot of 'tricks' that can be used on car engines in so called "stock" classes that don't really apply to supercharged aircraft engines.

1. Boring the cylinders oversize and fitting larger pistons and rings-bigger/heavier pistons and rings threw the balance off. Does anybody have any information about oversized pistons for Allisons? Merlins and aircooled engines replaced worn cylinders with original sized ones
2. Decking cylinder heads or blocks to raise compression slightly -compression in a supercharged engine was the enemy of power-it limited allowable boost. The Allison used about a 10% higher compression ratio than the Merlin to begin with and this limited the amount of boost that could be used. raising the compression ratio is counter productive.
3. Custom valve jobs? Cutting down on the valve seating area (narrowing the seat?) might decrease the time between valve jobs. Narrow seats also hinder the heat flow from the valve to the seat and head and for exhaust valves anyway may cause them to run hot. While these were, in a sense, high performance engines they were also built for durability and reliability. Hot spots in the cylinder head, hot exhaust valves/seats also limit allowable boost.
Allisons used 4 valve heads with pent roof combustion chambers. One might think that they were aware of breathing restrictions to begin with. They knew how much power fitting backfire screens cost them.

Aircraft engines did start out hand fitted. The Merlin by R-R started out that way but Ford of England (not Packard) were the ones who tightened up the tolerances of the parts to allow for true mass production. Allison started with had fitting, when you are building only a few engines a month their is no other way. BUT, there is a world of difference between car engines of the time and aircraft engines. Cadillac, who made a lot of parts for Allison found that while it took 29 separate operations to make a connecting rod for one of their cars it took 86 operations to make a connecting rod for the Allison. The rods were polished all over and then shotblasted to prevent fatigue failures. 20% of the Allison work force were inspectors.

I can easily believe these put out more power than standard engines, the question is how much more and 100-200 more than a the standard 1040hp is just a bit too much to be believable. I don't know what Allisons procedure was at that time but at some point during the war each and every engine was subject to a 7 hour run on a dyno and, no matter how it performed it was taken apart, re-inspected-magnafluxed-reassembled and run for two more hours before being preserved and packed for shipment. That should have take care of any low performing engines

.
 
Hi Shortround6,

I think the problem here is that you are assuming that US inspection standards were used for the equipment on these planes and that was certainly NOT the case.

Curtiss used this contract as an opportunity to get rid of old parts that were not suitable for the current standard being accepted by USAAF. Some planes had .30 cal MGs, some had .303s. Fuel tanks were whatever was left over. Fuel selectors were did not include a drop tank even though such would have been "standard" on the P-40Cs in this serial number range. The plumbing for drop tanks was typically not installed either.
This is quoted from memory of a couple articles I was reading.

Knowing that the engine blocks were all rejects would suggest that the folks doing the assembly KNEW they would have improvise and make do. They knew before even starting that these engines would not meet US standards, so I don't see why any of those practices that might reduce durability and running time in the long run would not be used anyway.

Folks like the British who were running Allisons in Africa already knew that the engine would take a lot more boost than the manuals specified, so the basic design was fairly sturdy. If someone bumped the compression up a bit and reduced that margin, who cares? It wasn't like a US inspector would complain. With a particular block or head, the casting flaw that caused the rejection might force you to do that or not use the part at all.

Perhaps folks who had to hone or bore out a cylinder / sleeve to be able to use it at all never bothered with oversized pistons at all. The ring tension would be a bit low, but in the short run, that is a bit more power at the cost of longevity. Even some of the US muscle cars back in the 1960's did that kind of thing.

Perhaps some of the builders with nothing better to do decided to try to balance all the pistons and con rods? Deburr all the oil passages?

Everything I am suggesting here is pure speculation, but when you have a bunch of good mechanics put on a task, there is a lot that CAN be accomplished. Then again, there were probably engines in this batch that didn't work all that well or started tossing parts as soon as they were run hard.

- Ivan.
 
Hi Shortround6,

I think the problem here is that you are assuming that US inspection standards were used for the equipment on these planes and that was certainly NOT the case.

Curtiss used this contract as an opportunity to get rid of old parts that were not suitable for the current standard being accepted by USAAF. Some planes had .30 cal MGs, some had .303s. Fuel tanks were whatever was left over. Fuel selectors were did not include a drop tank even though such would have been "standard" on the P-40Cs in this serial number range. The plumbing for drop tanks was typically not installed either.
This is quoted from memory of a couple articles I was reading.

Guns are government furnished equipment. Curtiss could not just stick in whatever guns were laying around as Curtiss didn't own the guns.
Knowing that the engine blocks were all rejects would suggest that the folks doing the assembly KNEW they would have improvise and make do. They knew before even starting that these engines would not meet US standards, so I don't see why any of those practices that might reduce durability and running time in the long run would not be used anyway.

In some cases the blocks were rejected because of over sized stud holes. These were "fixed" by drilling them out and fitting inserts (bushings) with the proper threads or by drilling out and re-tapping to take a larger stud. Some crankshafts with out of spec bearings were used by grinding the bearing slightly undersized and hand fitting a bearing to match. The mechanics assembling these engines were not "hot rodding" them, they were simply trying to build good engines using parts that had failed to meet specs at some stage in the manufacture/inspection process.

Folks like the British who were running Allisons in Africa already knew that the engine would take a lot more boost than the manuals specified, so the basic design was fairly sturdy. If someone bumped the compression up a bit and reduced that margin, who cares? It wasn't like a US inspector would complain. With a particular block or head, the casting flaw that caused the rejection might force you to do that or not use the part at all.

The time line doesn't this explanation. First British squadron in NA to use P-40s is equipped in April of 1941. First combat is May 14th, first victory in June 8th. In June of 1941 they are unloading the AVG Tomahawks in Rangoon. June 24th is when the last of the 150 Chinese contract engines (100 for installation and 50 spares) are finished. Not much time for the factory people to realize how much abuse the combat squadrons were subjecting the engines to. On Aug 11th the third Tomahawk squadron in NA becomes operational.


Perhaps some of the builders with nothing better to do decided to try to balance all the pistons and con rods? Deburr all the oil passages?

Nothing better to do? Allison was behind schedule delivering engines as it was, that is why they were using the non-spec parts to begin with. Allison piston had normal tolerance of .030lbs on a weight of 3.70lbs. That is total spread not plus or minus 0.030lbs. It turns out their were over sized pistons but when used in combination with standard pistons in the same engine the weight difference could not exceed 0.040lbs.
How much closer to want to balance these things? we are talking about 1% or under here.
These are aircraft engines, oil passages should have been deburred to begin with.

Everything I am suggesting here is pure speculation, but when you have a bunch of good mechanics put on a task, there is a lot that CAN be accomplished. Then again, there were probably engines in this batch that didn't work all that well or started tossing parts as soon as they were run hard.

- Ivan.

If there were any that didn't run well it doesn't seem to be noted, at least none that hadn't seem some extra abuse before they tossed any parts. airplane engines were built to much higher standards or tolerances than car engines to begin with, at least in proportion, so there isn't as much room for "blueprinting". If, for example, you allow a piston diameter to vary by + or - .005in on a 4in piston or the same on a 5.5in piston which is actually the tighter tolerance or which has the higher variation as a percentage of the base dimension.

That 0.030 tolerance in piston weight is 13.6 grams. For a high performance Chevy 489 cu in piston with a weight of 570 grams the tolerance in proportion would be 5 grams or less. Honda civic racing pistons can get down to around 235grams for a tolerance of under 2 grams if held to the same standard. Yes, race shops can do much better but those big Allisons weren't put together so sloppy that fitting better matched parts (blueprinting) was going unlock 10-20% more power.
 
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The fact is however, that the AVG seldom if ever met the A6M in combat.

When was this photo taken?

japanese-zero-captured-by-flying-tigers.jpg
 
From the deep radiator of the P-40 which is not an early B or C, it has to be an E, M, N ...
I would guess 1943 or later. I believe that this shows one of the Zero's that was rebuilt by the Chinese with the extra cooling louvres behind the cowling.
 
Sometime after October 1942. See
Untitled Document.
The AVG was disbanded in July 1942, so the P-40 in the background is a 23d FG. Note US Army NCO standing near the tail of the A6M; you would not have seen such with the AVG.
 

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