Ki-84 Hei vs TA-152H vs F8F-2 vs P-51H

tomo pauk said:

Racing P-39s were faster than racing Super Corsairs. Both types have had souped-up engines, IIRC 2000+ HP for the Cobra I and II, ~4000 HP for the Super Corsairs.

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And the Modified P-39s were lighter, faster and were better performers around a closed course. Racing these warbirds in a modified form will not give an accurate comparison as to their "combat" capabilities.

This is one of the few pieces that go into these racers in detail

FLYBOYJ said:

And the Modified P-39s were lighter, faster and were better performers around a closed course. Racing these warbirds in a modified form will not give an accurate comparison as to their "combat" capabilities.

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You have me scratching my head trying to remember where I've discussed the combat capabilities of a racer aircraft.

tomo pauk said:

You have me scratching my head trying to remember where I've discussed the combat capabilities of a racer aircraft.

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We've had this discussion several times on here over the years.

FLYBOYJ said:

This is one of the few pieces that go into these racers in detail

NX92848 | This Day in Aviation

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Great read, thanks!

mig-31bm said:

I have a question, for P-51H chart, what are 90 in Hg represent? Why that not in Ta-152, F4U-5 or F8F-2 chart

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Do someone know the answer for this?

FLYBOYJ said:

And the Modified P-39s were lighter, faster and were better performers around a closed course. Racing these warbirds in a modified form will not give an accurate comparison as to their "combat" capabilities.

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The Lighter part is debatable.

There is a Break down of weights in Birch Matthews book "Cobra".

While all the military equipment disappeared the increased fuel tankage (even in non-self-sealing fuel bladders), the P-63 prop, and the addition of a considerable quantity of water/methanol plus and extra oil cooler all contributed to bringing the weight of the racer to 7,749lbs for take-off.
The racers held 248 gallons of fuel and 100 gallons of the Water/alcohol mix. Granted they got a lot lighter as the race went on

mig-31bm said:

I have a question, for P-51H chart, what are 90 in Hg represent? Why that not in Ta-152, F4U-5 or F8F-2 chart

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90in Hg is the Manifold Absolute Pressure (MAP). It is equivalent to +30psi boost in the British nomenclature.

The reason it doesn't appear on the other charts is because the others could not use that boost. And the Ta 152H used a different measurement unit.

Shortround6 said:

The Lighter part is debatable.

There is a Break down of weights in Birch Matthews book "Cobra".

While all the military equipment disappeared the increased fuel tankage (even in non-self-sealing fuel bladders), the P-63 prop, and the addition of a considerable quantity of water/methanol plus and extra oil cooler all contributed to bringing the weight of the racer to 7,749lbs for take-off.
The racers held 248 gallons of fuel and 100 gallons of the Water/alcohol mix. Granted they got a lot lighter as the race went on

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Agree. Actually the Max T/O weight for a P-39Q was over 8000 pounds IIRC, normal gross I think was about 7500 pounds

*EDIT - According to the book "The Air Racer" By Charles Mendenhall, Empty weight for the 2 Cobra racers were 5578 lbs empty, 7886 lbs gross.

With or without nose armor?

SaparotRob said:

With or without nose armor?

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It didn't need the nose armour - the IFF was removed.

I have posted this here before, but it might seem like a good place to repost it. Enjoy.

P.S. Some units are gauge pressure and some are absolute pressure. The Germans uses ata (techniccal atmospheres).

1 standard atmosphere = 14.696 pounds per square inch (psi) = 760 mm Mercury (mm Hg) = 1.01325 Bar or 101.325 Pascals.

1 technical atmosphere (ata) = 14.223 psi = 735.557 mm Hg = 0.981 Bar.

OK. I'm done.

wuzak said:

90in Hg is the Manifold Absolute Pressure (MAP). It is equivalent to +30psi boost in the British nomenclature.

The reason it doesn't appear on the other charts is because the others could not use that boost.

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How come?, I thought the F8F-2 and F4U-5 were both designed much later compared to P-51H?

mig-31bm said:

How come?, I thought the F8F-2 and F4U-5 were both designed much later compared to P-51H?

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Air cooled R2800s vs the liquid cooled Merlin.

wuzak said:

Air cooled R2800s vs the liquid cooled Merlin.

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I see, so the air cooled engine can't use booster right?

mig-31bm said:

I see, so the air cooled engine can't use booster right?

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Not as much.

mig-31bm said:

I see, so the air cooled engine can't use booster right?

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See Greg's chart.
Anything over 14.7lbs (rounded up) or 29.92 in or 1.0 ata or 760mm is using boost.

How much can be is dependent on a number things, like the fuel, the capacity of the supercharger system, the strength of the engine parts and the ability of the cooling systems to keep the engine within temperature boundaries.

First, this is a complex subject, worthy of several books.

1) Radial engines generally turn slower than inline engines. Not always, but usually in aircraft.
2) According to the perfect gas law: pv = nrT, where p = pressure, v = volume, n = number of moles of material, T = Temperature, r = constant depending upon units. As you compress a gas, it gets hotter. You can only get to a certain pressure inside the cylinder before the air-fuel mixture heats up enough ignite whether or not the spark plug has fired. When you reach this temperature, you get detonation. The spark plug fires when it gets to just the right position to produce the best power. Detonation can happen before that time and cause the engine to lose power and even self-destruct.

3) As the Octane or performance number rating increases (anything up to 100, like 92-Octane fuel, is generally an Octane number; anything over 100, like 100/130 fuel, is a performance number usually called a "grade," as in 130-grade fuel) in a fuel, the higher the pressure can be before detonation. It doesn't make more horsepower, but allows the engine to develop more pressure before bad things happen, which generally means more horsepower CAN be produced if the engine is tuned correctly. Just changing the fuel to a higher number does not produce more power without corresponding changes to the ignition.

Most radials were limited to 45" - 60" inches of Mercury for boost. Most likely vales were around 50" - 56".

Most inline engines were limited to lower boost levels until some development allowed running them harder with some confidence. Allisons started the war off at 42" - 44", were increase to 57" mid-war, and were running 75" by the end of the war, sometimes up to 80". Merlins were roughly similar but usually were running a bit more boost earlier. By the end of the war they were hitting 90" Mercury for short durations. Today at Reno ,they get 130" - 140" with a LOT of changes and extreme tuning. They aren't really "Merlins" anymore.

An engine is basically an air pump, Yes, it has an air-fuel mixture but, if you can get more air through the engine, you produce more power. Atmospheric pressure is all that pushes the air-fuel mixture into the cylinders in a normally-aspirated engine. It is capped at 14.7 pounds per square inch at sea level (normal air pressure). But, air pressure drops as you go up. At 20,000 feet, you have about half the air you have at sea level. So, if you add a supercharger (compressor driven by the engine mechanically) or a turbocharger (compressor driven by the engine's exhaust), you can increase the amount of "push" to get more air into the cylinders. The amount of pressure over ambient air pressure is called "boost" and is usually figured in inches of Mercury, millimeters of Mercury, or sometimes inches or millimeters of water, depending on who is doing the measuring.

Basically, you can hold off the altitude at which the amount of air the going into the cylinder starts to drop off from the amount at sea level. That means the aircraft can go higher before it starts to lose power, but is generally more complicated and heavier, too.

Sorry if I assumed wrongly that a basic explanation was needed. I'm sure it can be said better, too. No insult intended.

GregP said:

Most radials were limited to 45" - 60" inches of Mercury for boost. Most likely vales were around 50" - 56".

Most inline engines were limited to lower boost levels until some development allowed running them harder with some confidence. Allisons started the war off at 42" - 44", were increase to 57" mid-war, and were running 75" by the end of the war, sometimes up to 80". Merlins were roughly similar but usually were running a bit more boost earlier. By the end of the war they were hitting 90" Mercury for short durations. Today at Reno ,they get 130" - 140" with a LOT of changes and extreme tuning. They aren't really "Merlins" anymore.

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It isn't about the radial layout vs the in-line layout.

It is about air cooling vs liquid cooling.

In terms of air-cooled radials, the one that could take the biggest boost was the R-2800. Usually in concert with copious amounts of ADI - water/methanol injection.

Of the liquid cooled in-lines the Merlin, Griffon and V-1710 all ended the war capable of very high boost pressures. The 2 stage Merlin and Griffon could go to +25psi boost (81 inHg MAP) without ADI. The V-1650-9 could go to +30psi boost (90inHg MAP) with ADI, the Merlin RM.17SM (which didn't go into production) could go to +30psi without ADI.

The V-1710 used ADI on the 2 stage engines, mainly because they didn't have an intercooler. But they also used ADI on the turbos to get that 75 inHg MAP.

The only other liquid cooled engine in the Western Allies' armoury was the Sabre. They didn't put a lot of boost into that until late in the war/post war.

SaparotRob said:

With or without nose armor?

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Years down the track, newbie forumers will look back at these old threads and go, "what the eff were they on about with nose armour 'n stuff?" Then they'll reach the epic P-39 thread and collectively go "aaaaaaah... geddit now..." with a knowing smile or grimace, depending on the reaction it invokes.