Tips & Tricks on Using GPS

This page is intended to help you to choose and set up a GPS receiver to record skydives for later evaluation with Paralog based on what works best for me. Most of this information is specific to the unit I am using, but can be easily transferred to all the other units on the market. There is more in-depth information available out there, especially in Scott Campos' great book on wingsuit flying 'Skyflying - Wingsuits in Motion' or in several threads on DZ.com.

This page will not tell you how to use your unit as most devices come with a detailed manual which describes all the necessary steps. So does Paralog. Use it!

The Receiver

FlySight Note: With the introduction of the FlySight, a GPS logger and real-time audible indicator designed from the ground up for wingsuit pilots, all off-the-shelf GPS loggers became obsolete from a skydiving point of view. We can only highly recommend it!

Wintec WBT-201 My current favourite is the Wintec WBT-201, a matchbox sized, logging GPS receiver. It has a built-in battery which is rechargeable throught the USB port. Data can be downloaded through USB or BlueTooth. Example tracks recorded with this unit can be seen in my logbook. Wintec WBT-201 The unit is the same size as an audible, so you can simply put the unit into the secondary(!) audible pocket of your helmet or you can mount it on the back of your helmet using a Neptune quick release bracket. Others have succesfully used pouches sewn onto the back of their Z1 or onto the back of an armwing.

Set Up

Enable WAAS/EGNOS, enable recording of tracks and set the recording interval to 1 sec. If your unit has a barometric altimeter, disable it, as they do not cope well with our descent speeds.

For the Wintec WBT-201, use the following settings (using the latest version of TimeMachineX, or even better, uCenter provided by uBlox, the makers of the GPS module used in the Wintec):

  • Under GPS Setting/SBAS, check "Enable", "Apply Integrity Information", "Apply SBAS...", and "Ranging...". Also, "1 Channel", and either "Auto" or "WAAS" for the US, "Auto" or "EGNOS" and "Allow Test Mode" for Europe (Click "Set" when done).
  • Under GPS Setting/Navigation Setting, select "5 - Airborne under 1g", and "3 - 3D only". Select "Enable RAIM" (Click "Set" when done).
  • Under Log Settings, select "Time" button and set Cond 1 for 0 to 2000KMH. and Cond 2 to 1 sec (Click "Set" when done).

See this thread on how to set up your unit to log more than one point per second.

Update: The Wintec WBT-201 has been replaced with the WBT-202. Use the 'WBT_Tool' on the unit's SD-Card to configure its settings and use the mass storage device (MSD) mode to acces the logs.

Preparing for the Jump

Each morning, turn on the unit and have it acquire a good fix for 15 mins to reduce the TTFF. Clear the track memory and turn the unit off again.

Before boarding the plane turn on the unit and have it acquire a good fix for 1-2 mins. Clear the track memory and turn the unit off again. For the next 30 mins. the unit will do a hot fix, which will usually last only 15 secs.
Update: With the modern sensitive units with their large track buffer, simply leave the unit turned on during the whole flight.

On Jump Run

Turn the unit back on on the 2 min call. Place the unit close to a window with a clear view of the sky (i.e. not a window under the wing). The unit will usually acquire a solid fix within 30 secs and keep it while you walk to the door.
Update: With the modern sensitive units with their large track buffer, simply leave the unit turned on during the whole flight.

During Freefall/Canopy Flight

Keep the receiver oriented towards the sky. Mounting the ForeTrex on the mud flap or the main lift web will result in poor data.

After Landing

Turn the unit off before you walk back to the hangar. Do not save the track to memory! On some units, this will reduce the resolution and strip the elevation data. Some units even strip the timestamps!

Downloading

Connect the unit to your computer: The ForeTrex 101 requires a special cable which needs to be purchased seperately from Garmin. If your computer does not have a serial port, you need a USB-Serial adapter as well. The WBT-201 can be connected with the supplied USB cable or Bluetooth, the WBT-202 and FlySight with the supplied USB cable. See this blog on how to use a WBT-201 with OSX/Linux.

Turn the unit on and download the tracks. Paralog will split the saved tracks, crop superfluous data before and after the track, extract the usual jump details like exit and open altitude, delay, etc. as well as horizontal and vertical distances and speeds, glide ratio, course, etc. and save the converted tracks into its logbook.

Analyzing the Jump

Every downloaded track can be analyzed individually using Paralog's jump profile chart and jump profile details view.