Ground Speed

[Scottish Wings 2]

Hello folks,

Would some one be able to explain how to obtain Ground Speed?

Thank you...

[scottb613 1,188]

Hi Stuart,

I'm not sure if you're talking in P2ATC or just in general... Just about any GPS including the default has the ability to display ground speed ??? It's the one speed that is easiest to determine as it's not affected by atmospheric pressure, density, or temperature.

Years ago - while in flight training - I made a flight planning spreadsheet that calculated GS among other things - so we can talk about the math too if that's what you're interested in...

Regards,
Scott

[Scottish Wings 2]

59 minutes ago, scottb613 said:

Hi Stuart,

I'm not sure if you're talking in P2ATC or just in general... Just about any GPS including the default has the ability to display ground speed ??? It's the one speed that is easiest to determine as it's not affected by atmospheric pressure, density, or temperature.

Years ago - while in flight training - I made a flight planning spreadsheet that calculated GS among other things - so we can talk about the math too if that's what you're interested in...

Regards,
Scott

Thanks for the reply Scott. It was under the P2ATC context I am most intetested in, as one of the flight plan inputs asks for GS. Wasn’t sure where this comes from when planning a flight...I am also just generally interested in all this sort of stuff so any help is really appreciated...👍

[scottb613 1,188]

Hi Stuart,

I have a whole ritual I go through to realistically plan a flight... I use a FltPlan.com (RW Flight Planner that welcomes FS users as well) to start with as it provides me with several things...

• Realistic ATC Routing
• Performance Profiles (Speed/Fuel) for just about every GA and BizJet Aircraft out there
• Flight planning legs with weather that includes groundspeed

https://fltplan.com/

Regards,

Scott

[scottb613 1,188]

Hi Stuart,

Ahh - disregard - sorry - I don't see GS on the output...

Regards,

Scott

[Dave-Pilot2ATC 870]

Groundspeed is equal to True Airspeed (TAS) minus the headwind component of the wind. 

For P2A purposes, let's say your expected TAS at a particular altitude from the route planner is 400 kts and you are traveling in an Easterly direction like KSAN to KPHX.  Winds at altitude are expected to be out of the West at 40kts.  An estimated groundspeed, without doing any trigonometry or using a calculator would be 440 kts.

If you were doing a real flight plan, you would use the E6B calculator, or some other means, to get the estimated groundspeed for each leg of the flight.  But for P2A purposes you are just providing an estimate of the average groundspeed for the full flight so P2A can make the initial calculation of the TOD.

Then, once you're flying, P2A uses actual Groundspeed to recalculate the TOD periodically so by the time you reach it, it will be fairly accurate. 

It's also worth noting that when planning a descent, GS is an important component.  Let's say you are at 14000 ft during the descent when all of a sudden ATC starts giving you vectors that will cut distance off your planned descent path.  You could increase your rate of descent, but that might not be enough, or it might cause your passengers discomfort.  In addition, or instead of increasing rate of descent, you can slow your airspeed early.  So maybe immediately slow to 200 kts instead of waiting until 10000 ft to slow to 250 kts as would be normal practice.

Hope that helps.

Dave

[Scottish Wings 2]

9 hours ago, scottb613 said:

Hi Stuart,

Ahh - disregard - sorry - I don't see GS on the output...

Regards,

Scott

No worries....

[Scottish Wings 2]

8 hours ago, Dave-Pilot2ATC said:

Groundspeed is equal to True Airspeed (TAS) minus the headwind component of the wind. 

For P2A purposes, let's say your expected TAS at a particular altitude from the route planner is 400 kts and you are traveling in an Easterly direction like KSAN to KPHX.  Winds at altitude are expected to be out of the West at 40kts.  An estimated groundspeed, without doing any trigonometry or using a calculator would be 440 kts.

If you were doing a real flight plan, you would use the E6B calculator, or some other means, to get the estimated groundspeed for each leg of the flight.  But for P2A purposes you are just providing an estimate of the average groundspeed for the full flight so P2A can make the initial calculation of the TOD.

Then, once you're flying, P2A uses actual Groundspeed to recalculate the TOD periodically so by the time you reach it, it will be fairly accurate. 

It's also worth noting that when planning a descent, GS is an important component.  Let's say you are at 14000 ft during the descent when all of a sudden ATC starts giving you vectors that will cut distance off your planned descent path.  You could increase your rate of descent, but that might not be enough, or it might cause your passengers discomfort.  In addition, or instead of increasing rate of descent, you can slow your airspeed early.  So maybe immediately slow to 200 kts instead of waiting until 10000 ft to slow to 250 kts as would be normal practice.

Hope that helps.

Dave

Thanks for the reply, this really helps!