A Data Driven Approach to Aerobatic Flight Debriefs 12/12/2016

My goal with this project is to see if video replays and Google Earth dynamic track replays add value for debriefs of aerobatic flights. This is a work-in-progress. At the moment, I'm focusing on finding the best GPS solution (more on that below.) If you have better ideas how to do this, please let me know bill@billwitzig.com

So, far I can say that this has been useful for...

Here is an example

This is a video replay showing the track of an aerobatic flight displayed in Google Earth. This track is the IAC 2017 intermediate known sequence flown in a Christen Eagle. The acro box is a IAC 1000m box, with the 50m buffer included. The vertical extent of the box is 700m - the intermediate height limitations from the IAC rulebook. However, since this wasn't flown in NOTAM'd airspace, I adjusted the base of the box to 3500 ft-MSL.

2017 Intermediate Known

Keep in mind, this is a video replay I recorded while manipulating the Google Earth image. The results are more meaningful is you are the one "flying" through the earth view to debrief your flight. If you want to view thiis flight (or one of your flights) directly in Google Earth, you'll need to save the .kml files to your local file system and then open them directly from Google Earth. For example, here are the files for the acro box and the flight track for the flight shown above.

link to create the Google Earth kml aerobatic box

Cockpit Video of the Same Flight

How to view GPS tracks in Google Earth

Most GPS units save their track logs either as a .gpx or a .kml file and Google Earth will display both. So getting your flight track into Google Earth is simple, just save your track to your computer and open the file in Google Earth. You can also open the file on a text editor and edit attributes of the track (such as line thickness or color) manually. Both types of files use an xml data format, so the data are human readable. Details of the xml tags can are described on Google's kml reference, but here's one example: If your track data is extended to the surface, which is not that useful for aerobatics, you can change this by opening the .kml file in a text editor and changing <extrude>1</extrude> to <extrude>0</extrude>.

GPS Devices I've Used

Garmin Virb: The advantage of the Virb is that it saves video, barometric altitude and accelerometer data in addition to GPS position. The Virb video editing software also allows you to put virtual gauges on the video output which you can see in the video earlier on this page. The biggest disadvantage of the Virb is that altitude data lags the latitude/longitude data considerably. I'll discuss how to correct this later.

Garmin GPSmap 60Cx: This device is small and easy to use, but the data rate is far too slow to be useful for aerobatics.

iPad: On non-aerobatic flights I've used an iPad with foreflight, both with the internal iPad GPS and with a stratus as a GPS source. When paired with the stratus, GPS data are recorded at 10Hz, with the internal iPad GPS the data rate is 1Hz. I haven't tried the iPad during aerobatics yet, so I don't know if it overcomes the lagged baralt limitation of the Virb.

Processing GPS data

As I said earlier, you can import GPS tracks directly into Google Earth. However, the lagged baralt data created by the Garmin Virb needs to be corrected or else your acro flight path will not look like what you actually flew. The Virb uses barometric altitude and this lags the GPS x-y position considerably (it looks like about 5 seconds during vertical maneuvering). To correct this, I open the .kml file as an xml table in a spreadsheet, shift the altitude data by 5 seconds and then create a new .kml file. The Virb records position data at 1Hz, but it also records accelerometer data and this is done at 10 Hz, so when I tweak the altitude data, I also strip out the 10Hz accelerometer data.