Target airspeeds don't add up

[alexis99 124]

I just noticed this when adjusting the F-14 radar.

 

So, in the F-14 Avionics:

There's a TargetTAS  which I assumed is the speed of the locked Target.

There's also a TargetClosure, which I assume is the speed at which you and the target are coming together.

 

Now when I lock a target by radar, and synchronise the visual target with the radar target, I get the box at the bottom right which identifies the target and confirms some of the figures displayed on the radar.

Altitude is correct, Target range is correct, but hey wait a minute what is this discrepency with the Target Speeds?

According to the radar, my Target was travelling at around 550Kts; whereas on the bottom right display, it was travelling at 330 Kts.

 

Am I misunderstanding what the figures mean, or is there some fault in the maths?

 

 

[Caesar 305]

I'm assuming this is the older SF-1 Tomcat, but the difference is likely KTAS vs KIAS.  The boxes on the player screen show KIAS, while the radar shows KTAS.  For an example of the delta between the two, I did a little demo in this thread:

 

http://combatace.com/topic/85255-change-aircraft-speed/?hl=kias&do=findComment&comment=685776

 

Post #14.

 

Hope this helps.

[alexis99 124]

Thank you, that helps very much. And so did your demo thread.

 

It's definitely the KTAS vs KIAS, because it occurs in all aircraft. The patchwork screen grab below is from the F-35A

 

 

The Own-plane box shows its airspeed to be 538 Kts, and this is matched by the HUD speed readout. So these are KIAS.

The Target Box shows the MiG to be doing 328 Kts; but the radar shows 349Kts, as does the HUD Radar repeater.

So Own-plane box, HUD Speed readout, Target box are all KIAS

Radar, HUD Radar repeater are both KTAS.

 

I wonder why there should be these differences, when you can't switch between KTAS and KIAS?

 

Anyway, I noticed the altitude discrepency too:

 

The Own-plane box gives barometric altitude, which is 10702 ft as agreed by the boxed HUD altitude readout. (On this HUD, the Radar Altitude is followed by an "R" and below the boxed barometric altitude.)

 

The Target altitude, according to Radar is 3900 ft, the HUD Radar repeater gives a more accurate 3982, but is basically in agreement. These are barometric readouts.

The Target box, however, shows 955 ft (AGL) which is clearly radar altitude. The flight was done over Scandinavia so the discrepency between barometric and radar altitudes are quite marked.

 

I found this all quite fascinating, so many thanks for pointing me in the right direction.