How to use your GPS

There are two pages below with information that will help you to get the most out of your GPS whether you are flying in competitions or cross country.

 

GPS in Competitions

All competitions now use 3D GPS tracks for flight verification so if you want to enter a comp you have to have one and you better know how to use it. 3D means the GPS records height data in the track log. Make sure yours does.

You should know how to:

  • Add a waypoint by hand.

  • Define a route and activate it

  • Clear the track log and change track log settings.

  • Change the track sample rate

  • Change the interface mode.

  • Change the batteries (in flight if necessary)

  • Modify the track display

  • Mark a waypoint

  • Turn track recording off and on.

  • Change the display contrast

  • Set the coordinate system.

Registration

At registration for the comp (or on line before the comp if they are well organised) you will get your GPS loaded with the waypoints to be used in the comp. These will usually be prefixed by S (for start), T ( for turn point) or G ( for goal), and then a number to identify it and sometimes a short name. An additional waypoint is usually loaded containing your pilot registration number. If you get an unofficial download from another competitor you could will end up with their number on your flight. May not be a big problem for you but better to point it out to the scorers when you submit the flight.

If you wish to keep the waypoints you have stored in your GPS then download and save them to a computer and clear out you waypoint list before the comp. There are a number of reasons for this:

  • The scoring software has to read through all of the waypoints to find the one containing your pilot number. That slows things down.

  • You run the risk of having one of your waypoints overwritten by the comp ones (or vice versa).

  • When defining the task you have to scroll through a long list of irrelevant points to find the right ones. Not only slower but there is a great possibility of selecting the wrong one.

The Task

The task for the day will be given as a route with a start point, possibly one or more turn points and a goal. You will have to enter these as a route in your GPS by selecting the points from the list provided. The start time is often only 15 mins after the briefing so the less time you spend putting in the route the more time you have to think about how you are going to get around it. Always check that you get the same total distance for the task as shown on the task board.

The launch window will define the earliest and latest times you can takeoff to fly the task. If you take off outside those times your flight won't count in the comp.

The start can be from takeoff, or on entry to or departure from a defined cylinder after a defined time (think of a beer can sitting on the waypoint, you have to be in it).

Each turnpoint will also have a cylinder radius defined on the task board. You have to record at least one track point within this distance of the waypoint before going on to the next one. By setting a route the GPS will tell you how far and in which direction the next one is. If you are lucky the organisers will also have told you some landmark for the turnpoint as well. If your track points are recorded at 15 sec intervals then you had better make sure you are inside the cylinder for at least 15 secs to be sure of getting a point recorded. If your GPS doesn't tell you when you have entered the cylinder then you can set the rings on your map page to the same radius and zoom in when you are getting close to the waypoint to make sure you get the track point in there. A faster sample rate as on the bigger garmins or the competino/compeo is an advantage because you can spend less time in the cylinder.

Garmins have a bad habit of skipping waypoints on a route in tasks that zig-zag. So if the task requires you to fly to T 1 then T2 then back to T1 again before going to T3 the garmin will assume you have already made T1 the first time and will point you straight to T3. In zig-zag tasks rather than setting a route you can select the waypoints manually while flying and use the GOTO function to avoid accidentally skipping any.

 

Goal (Yipee!)

Goal can be either a line or a cylinder. If you get to goal ( lucky you) fly over the line or in to the cylinder and lose height away from the goal line before you find a safe landing place. If possible turn off your GPS or track recording to prevent overwriting any of your flight. AND DON'T USE TRACK/SAVE ON A GARMIN. If you have to turn your GPS on again for retrieve then turn off the track recording. Leave it set to wrap and remember to turn it on again before the next task.

Now make sure you report back by the deadline and sign out. Don't turn you GPS on until it is ready to be plugged in to the PC for download and do have your pilot number stuck on the GPS where the scorer can see it.

After the download, leave your track there until the next day, just in case there are any problems with it.

 

Overnight, charge your batteries.

 

Next day before you launch:

  • Clear the old track log

  • Make sure track recording is on

  • Clear the old route, enter the new one and activate it.

  • Switch on just before launch, and if you have to move launch sites then clear the track log again.

  • Write the route down where you can see it in flight.

Also read GPS in XC flying.

 

GPS in XC Flying

Pilot

Before going flying you need to know how to do the following things with your GPS.

  • How to enter your takeoff as a waypoint.
  • How to set your GPS to use GOTO takeoff.
  • How to modify display options to show ground speed, bearing and distance.
  • How to change pages.
  • Define the sample rate.
  • Zoom in to see your track at 400m resolution.
  • Set the datum to WGS84 or NZ Geo49.
  • Set the coordinate format to Deg mm.mmm
  • Set units to km/hr, km, meters.

Before takeoff

  • Mark your position as a waypoint. Just accept the default identifier ( eg 001 on a garmin) and set GOTO on that point.
  • Clear your track memory
  • Make sure the track recording mode is "wrap when full". If it is off you won't record any track, and if it is set to "stop when full" it will fill up and stop recording. At least in wrap you always get the last flight if you forget to clear out the old ones.

Now you have two choices depending on what you want the GPS track for, full log of flight or thermal tracking.

  1. Full track log for a XC flight.
    • Set the sample rate long enough to record your whole flight. The XC comp rules say a maximum of 30 secs between recording points, I suggest 15 secs max.
    • Leave it turned off until just before takeoff.
    • Provided you set the GOTO your takeoff position before turning it off you only have to press enter to reactivate it again after switching on. You can check this by watching what happens as you fly off down wind. It should point straight back at takeoff and show increasing distance.
    • Use the ground speed to tell you what the wind is doing at your altitude. Flying at trim speed (say 37km/h) watch the ground speed as you change direction. Simple subtraction will tell you what the wind component is and you can turn 30 deg or so either side of a line to see which way gives you the fastest ground speed down wind. Instruments like the competino and compeo do this for you while you are circling. Saves a bit of grey matter for thinking about where the next climb is going to be.
    • Report your position to the retrieve driver by giving your distance and bearing from take off. If you are getting low and think you will land soon then try to get one message in before you land.
    • After landing mark/enter your position then SMS this to your retrieve driver.
    • If you want to preserve your track log for flight verification then either turn it off now, or turn off recording mode. DO NOT USE TRACK/SAVE ON A GARMIN. IT WILL LOSE INFORMATION AND MAKE THE TRACK LOG USELESS FOR VERIFICATION.
  2. Using the track log to find lost thermals
    • For this you need a high sample rate, one or two seconds, so make sure you have enough memory to record the whole flight or use a separate GPS.
    • Turn it on before take off and set the map page to a zoom of about 500 meters.
    • You can see how the thermal tracks as you turn and follow it noting how the circles are stretched down wind.
    • If you fall out of the back of the thermal just head back to your last turns shown on the display. Most of the time the thermal will still be there waiting for you.
    • Don't get in to watching your GPS too much. Focusing on the GPs will distract you from looking for signs of lift, keeping watch on other gliders and an eye on the ground.

Retrieve

  • Set the GPS to GOTO take off and report your position ( :km from take off on bearing of:) every 10km or so to the retrieve crew so they can track your progress.
  • Once you land send an SMS with your GPS coordinates and a brief description.

Retrieve driver

  • When you receive GPS coordinates by SMS do a mark enter on your current location and then edit the current location to match the provided corrdinates.
  • Phone or SMS back to the pilot to confirm if he still needs pick up, or hitching, or got a lift, or walked away from position given.
  • Ask for any helpful directions to get there, obvious landmarks, power lines etc.
  • Confirm the pilot has a radio on the right frequency.
  • Plot the coordinates on your map (you do have one don't you?) and make a plan of how to get there.
  • Check your fuel.

Another handy use for your GPS

  • Find out your real trim speed.
    • Fly in to wind, hands up with no speed bar, and look for the GPS to show the minimum ground speed. Take note of this speed.
    • Now turn and fly downwind, hands up etc, and find the max ground speed. Take note of that speed.
    • Trim speed is found by adding the numbers together and dividing by 2. Eg min grnd speed 20kph, max grnd speed 55kph, then trim speed = (20 + 55) / 2 = 75 / 2 = 37.5 kph.

 

Also read GPS in Competitions