IAS/TAS (split)

On page 110 of the manual, there is a graphic with the IAS of the P51 at different heights. As it goes higher, it decreases. But shouldnt the true air speed be higher than the indicated?

You have less dense atmosphere, so the plane should have to fly faster to have the same lift at lower altitudes...

Back on topic, I will wait for a few videos, maybe some multiplayer footage to think about it.

My birthday is on 4th of May, so it is kinda early.

Maybe someone gifts it to me :D

IAS will get less as you go higher, TAS will increase... but at some point the air will start getting too thin and propeler will be less and less effective so eventually aircraft will start loosing forward speed and start stalling.

The graph in question doesn't show TAS. It shows max IAS per altitude.

This isn't about lift, it's about Max Indicated Airspeed. ;)

The graph in question doesn't show TAS. It shows max IAS per altitude.

 

This isn't about lift, it's about Max Indicated Airspeed. ;)

Why does the IAS decrease that much? The pitot tube that is used for measuring the pressure and calculate the IAS. But as the atmosphere becomes less dense, the wings itself have less resistance at the same TAS. So you fly faster, to have the same lift as at lower altitudes. But when you fly faster, the pressure in the tube itself should increase again, showing a higher IAS.

On a different topic, I would gladly buy P51 right now if you tell me that the next module will be the F/A18C! :)

Simplified:

Pitot tube measures pressure. This is your IAS. Think of it like this:

IAS: The amount of air molecules passing you per unit time.

TAS: The VELOCITY of air molecules passing you.

As you can see, IAS and TAS really doesn't have much at all in common. Things change a lot when these values change and you cannot take one as a simple substitute for another.

Two bad things which can happen as TAS increases: Compressibility, due to approaching the speed of sound, and aeroelasticity, or flutter. Both are potential killers and must be avoided.

The speed of sound depends on temperature only. As you climb at a given IAS, your Mach number increases due to increasing TAS. As you hit a certain Mach number, you will get local supersonic flows over the airframe. This creates shock waves and drastically changes the pressure distributions, can cause flow separation (stall), rudder lockups, reversal of the controls and various other nasty phenomena. Google Mach tuck for a particularly evil killer.

Aeroelasticity/flutter is when the inertial and elastic properties of the airframe finds resonance with the aerodynamic forces, setting up often severe vibrations in rudders or other structures. The onset of flutter depends on TAS rather than IAS, meaning the flutter IAS decreases with altitude. As flutter sets in, you can go from flying along fat, dumb and happy to falling down without wings in less than a second - and everything may seem fine until you just edge past that critical airspeed.

Cheers,

Fred