Demo P-51 and Spitfire Top Speed

[David603]

You are right. The first Mustang, the P51A, was fitted with an Allison engine, which was good enough at low altitude but lacked supercharging and therefore had poor performance at high altitude. The plane in the demo is the later P51D Mustang which had an American built version of the Rolls Royce Merlin engine.

[Marchochias]

Originally Posted by David603

You are right. The first Mustang, the P51A, was fitted with an Allison engine, which was good enough at low altitude but lacked supercharging and therefore had poor performance at high altitude. The plane in the demo is the later P51D Mustang which had a Rolls Royce Merlin engine.

A Merlin equipped P51D could easily exceed 400 mph in level flight, right?

I can't even get past 250 in the game, though. Am I missing something with the throttle controls? WEP seems to make no different from 100% thrust with acceleration.

[David603]

Easily go past 400mph is probably overstating performance, since the Mustang D had a top speed of around 390mph at low level. The weight of the rockets will also be slowing you down.

However 250mph does seem rather low, so here is a little experiment to try. Get up to a decent altitude, and then dive until you do reach 400mph. Then see if you can hold this speed in level flight. If not, see what speed you can maintain.

[SleepTrgt]

Originally Posted by David603

Easily go past 400mph is probably overstating performance, since the Mustang D had a top speed of around 390mph at low level. The weight of the rockets will also be slowing you down.

However 250mph does seem rather low, so here is a little experiment to try. Get up to a decent altitude, and then dive until you do reach 400mph. Then see if you can hold this speed in level flight. If not, see what speed you can maintain.

ive come close to 375 Mph level flight.

[Marchochias]

Originally Posted by SleepTrgt

ive come close to 375 Mph level flight.

At what altitude? Was this with speed from a dive, or just gaining speed by going level?

I tried bringing the P-51 to 20 000 feet and diving, it reached 492 mph in the dive but the speed dropped off quickly after levelling.

The highest I could reach at very low altitude was 280 mph.

Does anyone know if the speed indicator is showing true airspeed or indicated airspeed?

[TexRoadkill]

If they fly at the same speed no matter what the altitude then they must be using true air speed. If it they were using IAS then you would probably see the speed closer to 400-500 mph when flying under 10,000 ft.

[IceFire]

I haven't finished the download yet but if BoP is doing things right then the speed you're seeing listed is called Indicated Air Speed (IAS). The top speed of aircraft that you see published in books and so forth is listed in True Air Speed (TAS). The Mustang will top out at 437mph TAS (D model) or 439mph TAS (B/C models) in the 25,000 feet range where the difference between IAS and TAS will be quite high. At sea level IAS and TAS are the same.

The difference is that air at higher altitudes is thinner thus the measurement will be different for speed. TAS corrects for that difference and measures your actual speed across the ground.

[Marchochias]

Yeah I know what IAS and TAS are, I just didn't know which one IL-2 BOP is using because it doesn't specify.

Since the maximum speed is so much lower at sea level, how fast was a P-51D supposed to be able to go at sea level or very close to it?

Also, do you know what the "WEP" throttle setting is? I'd never heard of such a thing before.

[DigitalMan]

Originally Posted by Marchochias

Also, do you know what the "WEP" throttle setting is? I'd never heard of such a thing before.

War Emergency Power. Pilots referred to it as pushing the throttle "through the gate." It would burn up fuel pretty quickly, but since we have unlimited we can push the throttle through the gate forever in the game.

[IceFire]

Originally Posted by Marchochias

Yeah I know what IAS and TAS are, I just didn't know which one IL-2 BOP is using because it doesn't specify.

Since the maximum speed is so much lower at sea level, how fast was a P-51D supposed to be able to go at sea level or very close to it?

Also, do you know what the "WEP" throttle setting is? I'd never heard of such a thing before.

Try this: http://www.wwiiaircraftperformance.o...stangtest.html

According to the top test a standard P-51B Mustang operating at 60.5" Manifold Pressure reaches 363 MPH TAS at 5000 feet. Thats the lowest altitude they test for on that one. There are a variety of other tests available but they use higher pressures in the engine and better grades of fuel. Have a look...but be warned there's lots of information

WEP is war emergency power. On the Mustang it'll include a bump up in boost pressures as well as water injection to keep the engine from exploding.