Spitfire V Versus P-40E

wuzak · Jul 16, 2020

GregP said:
Not sure the British lied about anything, but their flight reports generally limited the Allison to some lower boost than was used in combat while the Merlins in their tests were boosted to what WAS used in combat. That isn't exactly a lie since the test conditions were printed in the reports.

I'm sure that the boost used in tests were the recommended boost levels, which may have been exceeded on the front lines (at very low altitudes).

wuzak · Jul 16, 2020

soaringtractor said:
The shitfire Mk V and the P40 E matched up in time line, produced at about the same time and this proves why the Brits thought the P40 was the BEST AVAILABLE fighter of the time when they came to North American to see IF North American would build the {40 for them.

That'd be why the kept Spitfire V for themselves and farmed out the P-40s to the colonies and secondary fronts.

The British (and French) considered the P-40 to be the best available fighter from the USA. And in production.

soaringtractor said:
It also would explain why 14,000 p40's were built in WWII and kept in production right to close to the end of the war.

The P-40 was produced long past its use by date, as was the Hurricane.

In any case, it was useful as an advanced trainer.

Schweik · Jul 17, 2020

wuzak said:
I'm sure that the boost used in tests were the recommended boost levels, which may have been exceeded on the front lines (at very low altitudes).

Actually that isn't true, most of the tests, at least the ones we have access to, were done at low boost of 45" Hg, vs. the approved max of 54" - 57" Hg for most Allison variants, and 60" for Merlin. Basically it was the same issue as with the Spit. Performance differed greatly depending on the amount of boost used.

Greyman · Jul 17, 2020

Approved max when, is the key question I think.

Kevin J · Jul 17, 2020

wuzak said:
That'd be why the kept Spitfire V for themselves and farmed out the P-40s to the colonies and secondary fronts.

The British (and French) considered the P-40 to be the best available fighter from the USA. And in production.

The P-40 was produced long past its use by date, as was the Hurricane.

In any case, it was useful as an advanced trainer.

Being a bit negative, aren't we?

Schweik · Jul 17, 2020

Greyman said:
Approved max when, is the key question I think.

By mid 1942 generally

MIflyer · Jul 17, 2020

A P-40E pilot in the PI wrote that when the Japanese attacked he jumped in his airplane and took off, desperately trying to get out from under the rain of bombs. He looked at his manifold pressure gauge and was horrified that it only read about 15 inches. Clearly there was something badly wrong with the engine and he figured he was sunk. But as he sped away from the airfield and climbed for altitude he was surprised to see the pressure gauge go DOWN further, eventually beginning to show a pressure in the 50's. He had shoved the throttle forward and the engine, lacking an automatic manifold pressure regulator, had responded by producing manifold pressure so high that the gauge needle went past the top end and started another trip around the dial.

MIflyer · Jul 17, 2020

wuzak said:
The P-40 was produced long past its use by date, as was the Hurricane.

In the book "They Flew Hurricanes" an RAF pilot describes his frustration with why it was so long that they got nothing but Hurricanes in the Western Desert and on Malta rather than any Spitfires. "They have five thousand Hurricanes in the U.K. and they have nothing else to do with them."

In the P-40 training manual it is stated that they no longer send P-40's overseas and they have been replaced in combat zones by P-38's, P-47's, and P-51's but that they made great trainers.

Even the Mexican and Brazilian units we equipped and sent overseas got P-47's.

Kevin J · Jul 17, 2020

MIflyer said:
In the book "They Flew Hurricanes" an RAF pilot describes his frustration with why it was so long that they got nothing but Hurricanes in the Western Desert and on Malta rather than any Spitfires. "They have five thousand Hurricanes in the U.K. and they have nothing else to do with them."

In the P-40 training manual it is stated that they no longer send P-40's overseas and they have been replaced in combat zones by P-38's, P-47's, and P-51's but that they made great trainers.

Even the Mexican and Brazilian units we equipped and sent overseas got P-47's.

The Brits need the Tornado in service in 1942 for overseas use but powered by a P&W-2800. The Aussies need the Boomerang in service in 1942 with a GE B-2 turbo in it as per the CA-14A.

Schweik · Jul 17, 2020

MIflyer said:
A P-40E pilot in the PI wrote that when the Japanese attacked he jumped in his airplane and took off, desperately trying to get out from under the rain of bombs. He looked at his manifold pressure gauge and was horrified that it only read about 15 inches. Clearly there was something badly wrong with the engine and he figured he was sunk. But as he sped away from the airfield and climbed for altitude he was surprised to see the pressure gauge go DOWN further, eventually beginning to show a pressure in the 50's. He had shoved the throttle forward and the engine, lacking an automatic manifold pressure regulator, had responded by producing manifold pressure so high that the gauge needle went past the top end and started another trip around the dial.

This became increasingly common in both the Pacific and the Med, and the Allison company responded by hardening some parts in the engine (crank shaft and crank case among others) to better endure higher pressure. Eventually they moved the normal boost limit from 45" Hg to 54" and then ultimately 57" or 60" (P-40K) but this took a while to filter back to the flight manuals, and in some cases never did. 45" became the military power setting and 57" the WEP.

It echoes changes made to official boost settings for other aircraft like the Spitfire.

Schweik · Jul 17, 2020

MIflyer said:
In the book "They Flew Hurricanes" an RAF pilot describes his frustration with why it was so long that they got nothing but Hurricanes in the Western Desert and on Malta rather than any Spitfires. "They have five thousand Hurricanes in the U.K. and they have nothing else to do with them."

In the P-40 training manual it is stated that they no longer send P-40's overseas and they have been replaced in combat zones by P-38's, P-47's, and P-51's but that they made great trainers.

Even the Mexican and Brazilian units we equipped and sent overseas got P-47's.

That depends what time period. They were still using P-40s actively on the front line in Italy, Burma, and the South Pacific in 1944. And they were still scoring victories.

MIflyer · Jul 17, 2020

I believe the last RAF P-40 pilot KIA was in 1945. So they hung onto the tough old birds almost to the very end. The Dutch in the East Indies were still flying them against insurgents in 1947. The P-40 made a much better dive bomber than any mark of Spitfire. P-51 pilots flying short range ground attack missions in Korea often wished they had P-40's instead.

A friend of mine knew a WWI pilot who had worked at Allison before he went back into the service in WWII. He said that they ran the V-1710's up to 80 inches manifold pressure on the factory test stand and the only problem was that the bolts holding it down started breaking. Merlins modified for racing often use V-1710 piston rods because they are stronger.

Funny thing was that the P-40M, built exclusively for the British Empire, was the first to incorporate an automatic manifold pressure regulator, but one of the RAF comments was that you can disable the regulator and get better performance out of it.

And yet there are people today that will tell you that if you exceed 60 inches HG with a V-1710 or a V-1650 the whole engine will dismantle itself within seconds - or that you will gain no extra performance by overboosting it at lower altitudes..

Schweik · Jul 17, 2020

60" became standard for the V-1710-73 (standard on the P-40K)

The P-40M was basically designed to be a fighter bomber and had a higher gear ratio so that it's critical altitude was up around 14k ft instead of 12k ft like the V-1710-39 on the original P-40D/E (Kittyhawk I and Ia for the Brits). But this also meant that it wasn't as safe to boost the engines so high down low, which Allison warned about in their famous memo.

The confusing thing for the British was that they designated both the P-40K and P-40M as "Kittyhawk III" but they had very different performance. The P-40K peaked at around 12,000' ft but could be boosted to 70" apparently, down around 3,000' or lower (and officially to 60" up to about 7,000 ft) whereas the P-40M was probably safest at around 57" especially down low... which is still pretty good performance but it's not quite the beast that the P-40K was. The K models were in demand and British and Australian pilots mentioned "stealing" certain Kittyhawk III's from units that had them. Bobby Gibbes described an incident in which he was piloting a "stolen" Kittyhawk III and jumping ahead of a squadron of Kittyhawk II's (P-40F) he was leading to shoot down a Bf 109 that was flying over them.

Another American pilot described in a letter to his family a running fight he had with two Bf 109s as he was fleeing back to his base, in which he managed to stay ahead of them and eventually shot one of them down by sticking to 60" Hg boost. It's unclear if he was in a P-40L or a P-40K, as his units had some K models at the time due to a shortage of the Packard-Merlin 28 engines.

Schweik · Jul 17, 2020

One other point worthy of note, the RAF stopped using P-40s as front line fighters by the end of 1943, and in 1944 they were using them just as fighter bombers. They did still occasionally get victories when defending themselves against Axis attacks but the rate dropped off a lot, most of their losses were to flak. The Americans had some fighter groups that continued with P-40's in the MTO until May or June of 1944 by which time they were being replaced with P-47s and later in turn, P-51s.

The USAAF continued using P-40s in Burma until early 1945. In the Pacific they were gradually replacing them with P-38s but it took a long time, some units (I think two of the three squadrons of the 49th FG for example still had P-40s until late 1944). The Australians transitioned to Spitfire VIII in 1944 and the New Zealanders to Corsairs, but by that time they were kind of out of the fight.

GregP · Jul 17, 2020

I can tell you from personal experience working in an Allison shop that 57" and 3000 rpm are conservative for the V-1710.

Tractor pull guys turn them at 4000 rpm with no damage, but most of these guys have the crankshaft with 12 counterweights. We had one guy turn his at 5000 rpm by "mistake." It is installed in a race car and he was paying attention to a scantily-dressed lady instead of his starting technique and accidentally started it at wide open throttle! Yes, it broke, but no catastrophically. They have no trouble and no damage from running at 75", but that should include a run time. I would not want to run one at 75" for 30 minutes unless I was trying to save my own life, but a burst of power at 75" for a few minutes would not be out of line.

There is nothing "delicate" about a V-1710 Allison. It is a solid, good-running engine.

The best engines in the fastest at the Reno National Championship Air Races are not really "Merlins." Yes, they have a base Merlin engine, usually a transport engine, but the parts are diverse. Most of the really fast "Merlins" use Allison V-1710 G-series pushrods, custom pistons, modern ignitions, and a host of modern engine technology to produce 3,850 hp at 3400 or 3600 rpm and 140+ inches of MAP. They can do this for about 2 - 3 laps and then need to cool down a bit or else they tend to throw a scrap iron fit.

Schweik · Jul 17, 2020

I think the main issue with the WW II engines was the supercharger gear ratio. Higher ratio allowed better performance at higher altitude but it out more strain at lower altitude. Reno air races are done pretty low right?

At 70" Hg a P-40 was a beast. That is almost 40% more power than in the test in the OP.

pbehn · Jul 17, 2020

A testing establishment runs the tests its clients wants them to run, to give the results they want. An aircraft testing establishment wasn't a bunch of petrol heads seeing how fast they could make things go.

Schweik · Jul 17, 2020

I'm not alleging any conspiracy.

PAT303 · Jul 18, 2020

Schweik said:
This became increasingly common in both the Pacific and the Med, and the Allison company responded by hardening some parts in the engine (crank shaft and crank case among others) to better endure higher pressure. Eventually they moved the normal boost limit from 45" Hg to 54" and then ultimately 57" or 60" (P-40K) but this took a while to filter back to the flight manuals, and in some cases never did. 45" became the military power setting and 57" the WEP.

It echoes changes made to official boost settings for other aircraft like the Spitfire.

Boost pressure was governed by fuel octane/Performance number ratings not the engine it'self, hardening of parts was mainly for increased wear resistance to extend overhaul times.

Greyman · Jul 18, 2020

PAT303 said:
Boost pressure was governed by fuel octane/Performance number ratings not the engine it'self ...

Not if the aircraft had no automatic boost control -- which most US fighters were lacking in the first couple of years.

Altitude and throttle setting (accidental or intentional) played a starring role in those cases.

Spitfire V Versus P-40E

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Major

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Tech Sergeant

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