IAS and TAS

[RTHolmes]

so the ASI (speedo) on the instrument panel displays IAS, and a red mark for TAS. What is the TAS mark useful for?

afaik the key speed related stuff for ACM (Vmax, acceleration, turn rates etc) depends on IAS not TAS, so isnt TAS irrelevant? doesnt even figure in navigation (Ground Speed is used here). or am I missing something?

[Anaxogoras]

You need to know TAS to figure out ground speed, i.e. add or subtract the speed of the wind.

[hammer]

...doesnt even figure in navigation (Ground Speed is used here). or am I missing something?

In the flat world of AH, TAS = ground speed. Factor in the low level we normally fly, and that would be essentially true for a spherical world, too.

Regards,

Hammer

[Wedge1126]

What is your ground speed if you are flying straight up at 200 mph TAS?

[moot]

Zero... y=c.

[uptown]

What is your ground speed if you are flying straight up at 200 mph TAS?

 

[Wedge1126]

Zero... y=c.

I agree, but that's not what E6B says.

Although, I don't know what you mean by "y=c". I'm assuming y is the vertical component of velocity, but I don't know what c is. Speed of light?

[moot]

As in constant.. Plotting an airplane's purely vertical movement with y as vertical position and x as horizontal position gives you a constant x position.
I've wondered about the E6B too..

[Mace2004]

TAS has little use in AH.  In RL it's used in some performance calculations such as turn radius and total energy where you're looking at acceleration of a mass and, as others have mentioned, to determine wind and time to go. 

TAS is your actual distance over time within an airmass while IAS is not really a "speed" but a measurement of the impact pressure of the air on the airframe expressed in MPH (or Knots).  It is computed such that IAS will equal TAS at sea level on a standard day but it changes with altitude and temperature.  Conversion factors are used to compute TAS from IAS based on your pressure altitude and outside air temperature.  That's what the E6B is replicating.

For what we do IAS is the number that tells us most about what's important to us, i.e., how our airplane will perform.

[BnZs]

TAS has little use in AH. 

The little red needle is pretty useful for avoiding compressability at very high altitudes.

[RTHolmes]

isnt the onset of compression dependent on IAS rather than TAS? ie pressure differentials again?

[Anaxogoras]

isnt the onset of compression dependent on IAS rather than TAS? ie pressure differentials again?

Not all aircraft that experience high speed control problems are suffering compression.  For example, the 109 and A6M suffer the opposite of compression: there is too much air flow over the control surfaces.  The P-38G/J, on the other hand, suffers true compression where the controls would feel perfectly light, but wouldn't do a damn thing to control the plane.

[Slate]

   What happened to Wind in AH? We used to have a windspeed in the game enviroment. 

[Murdr]

isnt the onset of compression dependent on IAS rather than TAS? ie pressure differentials again?

No, compression is related to critical mach.  Mach number is TAS divided by speed of sound.  What the speed of sound (mach 1) equals is dependent on the tempature and air density you're flying in.

At 30k, which one of these numbers indicate you better watch your speed?  250 mph IAS = 406 TAS = Mach .60

At 4k in the game Mach .60 = 420 IAS = 450 TAS.

[Anaxogoras]

Oh!  I stand corrected.  Is this accurately represented in the game?  I haven't noticed TAS being the factor for compression, it always seemed like IAS.