why the speed is not consistent

[SUHANG]

nullHi guys, as attached picture. What my speed exactly is? on the HUD, the speed is 279, but if you look at the left DDI, the seed shown around the aircraft simple is 546T and  568G. And if I press F2 and look at the bar at the bottom of the screen, the speed is  So what is my speed is 255. So what exactly is my speed? 

And one observation, the higher the altitude, seems the lower the speed you can get on given the same throttle power. Is that the real case and why?

 

By the way, I want to jett the external oil tank, I choose the store on the jett dail and push the L1 & R1 on the jett panel, but after I puse the red button of Jett, nothing happend. Can someone explain this?

null

[Lace]

All of the above are correct.  

 

IAS is pitot static derived - what the instruments actually read

CAS is IAS corrected for instrument errors - how fast the aircraft actually feels like it is flying

TAS is CAS corrected for temperature/pressure and is the same as GS in zero winds conditions

GS is the speed at which you are actually covering ground - useful for ensuring an accurate time-on-target

 

At low level, there are lots of air molecules, so a fast indicated speed.  As you get higher, your IAS/CAS will be lower, as the air is less dense, and there are fewer air molecules hitting the aircraft.  The aircraft will feel 'mushy' even though you might be covering ground at a high speed. 

There are some online calculators is you google it, which can give you an understanding on how they are all related.

[rob10]

And you need MASTER ARM armed to use selective jettison.

[SUHANG]

thanks for the above reply. Problem solved. Solute.

[Brun]

I think it helps to think of IAS as an indication of aerodynamic performance rather than simply speed. Near the ground they're closely related but as you have noticed, become more divergent with increasing altitude.