Hi

 

I have these two questions that may have been asked before but I don't have a clear answer.

 

1. How come the speed on the PFD is not even close to either GS or TAS on the ND?

For example, I could see often TAS is 430 nd GS is 480 but on the PFD it registers as 290 and sometimes even as low as 259

 

2. How come the scale on the ND is always half of that set . i.e. 360 is 180, 80 is 40 and so on. Some one mentioned its due to the resolution on your FSX.

 

These issues do not affect my flying per se. Just curiousity.

 

Thanks

 

Bill

1. Because of that: http://en.wikipedia.org/wiki/Density_of_air, and therefore the measured speed up  there (the actual air pushed through a small tube) is not the actual speed but only the IAS - Indicated Air Speed (TAS - True Airspeed and GS - Groundspeed are calculations out of numerous factors).

 

2. Has nothing to do with resolution. when you set eg 80 thedistance from your airplane symbol to the top is 80nm, half of it (so half way down your ND or better to say the left inboard Display Unit DU) is 40nm.

 

3. you have to sign your post with your full name in this forum.

1. ... and though it might not tell you how fast you are going from one point to another the IAS is the aerodynamic speed. It governs lift and drag. Therefore it is more important when flying.

Thank you Chris and Lasse for the quick responses

 

Bill Hagag

1. ... and though it might not tell you how fast you are going from one point to another the IAS is the aerodynamic speed. It governs lift and drag. Therefore it is more important when flying.

Important as far as making sure you're at a high enough speed such that you aren't going to stall or overspeed, but other than that, when you're at the higher cruise altitudes, you'd be using Mach.