my main question is why all data is gone with 21% if I didn’t have enough
battery fair enough but it should have recorded up to when the
battery died!
The Spark's
battery predictions are based on RTH speed and distance from home point, and assume a normal batttery discharge curve.
It does not account for a headwind on the return flight, or reduced
battery life due to cold temperatures. While the cold is a seasonal problem, headwinds are an issue all year round. You have to be especially careful when flying away from home with the wind at your back, because it means your Spark will get away from you much faster than normal, and will take much longer to come back.
That, and as you've noticed, RTH has problems with trees. You need to make sure you have the RTH height set for the obstacles (trees, buildings, hills, power lines, water towers, etc) so it will go up and avoid them. Note that if there's wind, it's pretty much always going to be blowing faster at higher elevations.
This is all hindsight advice now, but you have some things to learn from this experience, to prevent it from happening again.
- make sure RTH height is set appropriately for your terrain
- assume lower
battery life when it's cold (don't wait for the low
battery warning which is based on warmer temps)
- don't fly far away on windy days (don't fly out farther than you can SEE your drone, not just "LOS")
- return using manual flight if you are concerned about not making it back - fly as low and fast as you safely can
For now you will need to get the exact last known gps coordinates and go out there with a gps and start your search there. Work your way slowly directly back toward your home location. It may have detected a tree and gone up to go over it, and unfortunately exhausted its
batteries when trying to go over the tree and so landed on top of the tree. This could make retrieval challenging even if you're a good climber
