They will need the patience of Job to get through the hundreds of pages needed to get to that "aaahh" moment.
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They will need the patience of Job to get through the hundreds of pages needed to get to that "aaahh" moment.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.
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.
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...They will be armed with previously unknown archival documentation that proves that a P-39 has been demeaned unfairly in the years since WW2.
No iam very greatful for your explainationFirst, 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.
Bearcat is going to be as useful defending bombers over Germany.
The Mustang is going to need significant changes to fly from a carrier.
Uhh you mean this?You could also throw the Hawker Fury in this mix.
Brilliant summary, thank you for that.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.
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?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.
You are not wrong.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?
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?