Tas

[Olendirk]

Hi!

This is my first topic, im new and an atpl student so hello to everybody. Id like to stay close to this network because the topics are really helpful.
Well, i have a simple question:
Why is the TAS increasing with altitude?do i have to accelerate the aircraft when i get up there?

Thanks !

OD

[oxford blue]

Well, in simple terms, IAS is not really a speed, although we call it one. It is a measure of how much air resistance you are meeting. We calibrate the instruments so that, in a standard atmosphere at sea level, the amount of air resistance is expressed in the same units as the speed you are going at.

As you climb, the air gets thinner. There are less air molecules per cubic metre. To experience the same amount of air resistance (that is, to keep the IAS the same), you have to fly faster through this thinner air. That faster true speed is your TAS.

Normally, you don't have to accelerate to maintain your IAS. But by maintaining your IAS and being in thinner air, you will get a higher TAS.

Hope this helps.

All the best.

[Olendirk]

So I get up there, the TAS rises because of the thinner air and i keep my IAS?

thats correct?

[pa28biggles]

Yes, you keep IAS constant, and your TAS will increase.

[Olendirk]

So i get faster and so its more effiecent to fly higher without having to increase the IAS?

[peb]

If you keep your IAS constant while you are climbing your TAS will increase and you Mach too. And opposite when your are descending.

If you keep your TAS constant while you are climbing your IAS will decrease and your Mach will increase. And opposite when your are descending.

If you keep your Mach constant while you are climbing your IAS will decrease and your TAS will decrease. And opposite when your are descending.






If you climb with a constand IAS you will be limited by the MMO. The same when you are desending, if you keep a constand Mach you will be limited by you VMO.
Usualy you climb with constand IAS up to 25.000 feet and then you will keep a constand Mach. And opposite when your are descending.

[Send Clowns]

So i get faster and so its more effiecent to fly higher without having to increase the IAS?

Only at the levels at which your engine and propellor (or turbo jet) are efficiently producing the thrust to keep the IAS. Eventually the limit will become, as suggested above, the maximum operating mach number as the local speed of sound (LSS) reduces and true airspeed (TAS) increases, so increasing mach number (ratio of TAS : LSS).