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

[BiffF15]

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.

They will need the patience of Job to get through the hundreds of pages needed to get to that "aaahh" moment.

 

[wuzak]

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.

They will be armed with previously unknown archival documentation that proves that a P-39 has been demeaned unfairly in the years since WW2.

 

[nuuumannn]

They will be armed with previously unknown archival documentation that proves that a P-39 has been demeaned unfairly in the years since WW2.

Of course! They can use the all pervading cover story that Flat-earthers, moon landing discreditors and COVID/Vaccine deniers all use when presenting their evidence; they read it on the internet...

 

[nuuumannn]

The irony of this is that by taking part in this forum, we are all "reading it on the internet"

 

[Tkdog]

Going back to the original question. Air superiority where? For what purpose? You don't just send a fighter out to, well, fight. There has to be a mission - even if it is just find the enemy and shoot them down. There has to be an objective gainer by doing that.

The fighters you list are shaped by the objectives they were designed to address. How close those design objectives align with how they would actually be used plays as much, or more, of a role in their success as technical details.

Bearcat is going to be as useful defending bombers over Germany. The Mustang is going to need significant changes to fly from a carrier.

 

[mig-31bm]

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.

No iam very greatful for your explaination

 

[wuzak]

Bearcat is going to be as useful defending bombers over Germany.

Flying from eastern France or western Germany?

The Bearcat would be better as a bomber interceptor for Germany.

The Mustang is going to need significant changes to fly from a carrier.

Yes it would.

 

[Tkdog]

I missed a "n" a "t" and a "'". Because my dog demanded I admire her new toy as I was trying to type my earlier response. Despite this, she is a very good dog.

I meant to type that a Bearcat would not be as good as an escort over Germany. Had not thought of it as a defender there, but that is a good point.

 

[SaparotRob]

The bacon is for your dog.

 

[WARSPITER]

You could also throw the Hawker Fury in this mix.

 

[mig-31bm]

You could also throw the Hawker Fury in this mix.

Uhh you mean this?

 

[WARSPITER]

No. This one.....

Source - Internet

 

[Schweik]

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.

Brilliant summary, thank you for that.

 

[Schweik]

How about one of these in the mix?

 

[GregP]

Love the Tigercat. Here is a clip of one at the Planes of Fame Airshow.

 

[tommayer]

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.

Question: I thought boost was anything over ambient. Running 30 inches at 5000 msl is running about 5 inches of boost. An R-985 at 36.5 inches @ sl is running 6.58 " boost as per your post, but the same engine @ 30 inches @ 8K is making approx 8 inches of boost. Or have I been thinking about this wrong for 55 years?

 

[GregP]

You are correct, tommayer.

Boost is anything over ambient.

On a standard day at sea level, that would be 29.92 inches of Mercury or 14.696 pounds per square inch or 760 mm Hg (Bar, ata, inches of water, etc.). Ambient is called normally aspirated and the atmosphere is the only thing pushing air into the cylinders. Boost is when you have a compressor (turbocharger or supercharger) helping to push air into the cylinders. Since an engine is basically an air pump, pushing in more air at the correct air-fuel mixture generates more power, more energy (heat).

Cheers.

 

[Dash119]

You could throw in a Hornet / Sea Hornet too...

 

[Shortround6]

Question: I thought boost was anything over ambient. Running 30 inches at 5000 msl is running about 5 inches of boost. An R-985 at 36.5 inches @ sl is running 6.58 " boost as per your post, but the same engine @ 30 inches @ 8K is making approx 8 inches of boost. Or have I been thinking about this wrong for 55 years?

You are not wrong.

Sorry I wasn't clearer.

 

[wuzak]

Question: I thought boost was anything over ambient. Running 30 inches at 5000 msl is running about 5 inches of boost. An R-985 at 36.5 inches @ sl is running 6.58 " boost as per your post, but the same engine @ 30 inches @ 8K is making approx 8 inches of boost. Or have I been thinking about this wrong for 55 years?

The British used boost in psi rather than MAP as their standard. The boost was the amount of pressure above standard seas level pressure.

So +18psi boost would be 32.7psi MAP at any altitude.