Jump to content
Sign in to follow this  
pve

Average speed

Recommended Posts

Hi All

 

XML in FSX

 

Is there any vars. that can help to get average speed for a non direct course to a waypoint with changing speeds. It's easy to get if you use constant speed and direct course but maybe can't be done with XML.

 

Thanks


Paul EGLD

Share this post


Link to post
Share on other sites

If you need this info before the flight I assume you have the flight plan data available (leg distances and speeds) and you can use a formula to get the average speed?  If only needed after the flight keep track of the overall distance and time and divide.

Share this post


Link to post
Share on other sites

Hi Tom

 

 Yes that would work OK but I am trying to get the average updated during the flight without keeping to a flightplan.

 

I thought of doing it by taking lat/long positions at minute intervals and get distance & ET from that but not sure of the maths required to get overall realtime average accurate.


Paul EGLD

Share this post


Link to post
Share on other sites

Ok... first... I have to state that unless the course leads to the waypoint... you can't arrive at the waypoint and thus time to the waypoint would always be infinite.

 

So... not certain you're saying what you actually mean.


Ed Wilson

Mindstar Aviation
My Playland - I69

Share this post


Link to post
Share on other sites

Hi Ed

 

OK I haven't described it correctly.

 

This for FMC flight log page giving various info. like T/O time, current enroute time, fuel used etc. 

 

It also gives current avg. TAS & GS.  and  AIR DIST / GRD DIST traveled from departure point. These are values I am trying to get. 

 

Thanks


Paul EGLD

Share this post


Link to post
Share on other sites

Ah... those averages have nothing to do with waypoints.

 

Essentially while in flight the FMC is sampling the TAS and GS and computing the aircraft's average TAS and GS.

 

The way most avionics systems do this is that they have a definition of start of flight. Once it sees that, it starts to track TAS and GS and calculate the aircraft's average.

 

As for air distance and ground distance... that too is linked to the definition of start of flight.


Ed Wilson

Mindstar Aviation
My Playland - I69

Share this post


Link to post
Share on other sites

That all strait forward but do you know how it calculates the aircrafts averages?


Paul EGLD

Share this post


Link to post
Share on other sites

Uh... you know how to find the average of a set of values?


Ed Wilson

Mindstar Aviation
My Playland - I69

Share this post


Link to post
Share on other sites

Yes

 

how does the the RW FMS get the basic over the ground distance information? 


Paul EGLD

Share this post


Link to post
Share on other sites

All FMS systems get positional information... from a GPS, an INS... something that knows where the aircraft is. Many also utilize a triangulation method involving multiple navaids.

 

To be crystal clear... averaging speeds is completely separate from calculating distances of air vs ground. Are you wanting me to give you formula for calculating the distance values?


Ed Wilson

Mindstar Aviation
My Playland - I69

Share this post


Link to post
Share on other sites

Yes please, That would be most helpful


Paul EGLD

Share this post


Link to post
Share on other sites

In short, you need to track the following values:

1 - Average TAS.

2 - Average GS.

3 - Average TAS for current waypoint.

4 - Average GS for current waypoint.

5 - Ground distance.

6 - Air distance.

7 - Ground distance for current waypoint.

8 - Air distance for current waypoint.

 

For Average TAS and Average GS simply do the following once per second:

 

avg_tas_total = avg_tas_total + tas.
avg_tas_count = avg_tas_count + 1.
avg_gs_total = avg_gs_total + gs.
avg_gs_count = avg_gs_count + 1.
avg_gs_waypoint = avg_gs_waypoint + gs.
avg_gs_waypoint_count = avg_gs_waypoint_count + 1.
avg_tas_waypoint = avg_tas_waypoint + tas.
avg_tas_waypoint_count = avg_tas_waypoint_count + 1.
With those values you can figure everything else out.

 

1 - Check to see if waypoint has sequenced.
    If so, then reset the following:
      a. distance_ground = distance_ground + distance_ground_waypoint.
      b. distance_air = distance_air + distance_air_waypoint.
      c. average_gs_waypoint_count = 1.
      d. average_tas_waypoint_count = 1.
      e. average_gs_waypoint = gs.
      f. average_tas_waypoint = tas.
2 - Calculate great circle distance from prior waypoint to aircraft current position.
3 - Store in distance_ground_waypoint.
4 - Calculate average_gs = average_gs_waypoint / average_gs_waypoint_count.
5 - Calculate average_tas = average_tas_waypoint / average_tas_waypoint_count.
6 - distance_air_waypoint = distance_ground_waypoint * (average_tas / average_gs).
7 - Calculate overall_average_gs = average_gs_total / average_gs_count.
8 - Calculate overall_average_tas = average_tas_total / average_tas_count.

Ed Wilson

Mindstar Aviation
My Playland - I69

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
×
×
  • Create New...