Drone Crash on Min Speed Testing

I am testing minimum speed of our drone to check its Min and Max speed survivability. Soon it reaches its minimum speed, drone loses all controls and even it doesn’t take any command on manual takeover. It doesn’t give any fail-safe warning and crashes rolling nose down. This has happened twice.

Can you please check from the log and guide.

Drone Type: Fixed Wing Twin Motor Propulsion
Autopilot: Cube

Log File Download Link: https://www.dropbox.com/s/ntsyujletjw2ayc/2019-06-30%2011-38-58.bin?dl=0

Looks to be a simple stall with no recovery.
You can see that once it hits the stall, altitude starts to drop quickly, but elevator and rudder go to near max, with no increase in throttle.
By the time you hit manual it was too late.

Stalls are nearly impossible to recover automatically, best way is to avoid them at all costs. This means installing an airspeed sensor and setting a minimum flight speed during auto modes that is 20% over your determined stall speed.

Don’t forget stall speed increases when you bank in a turn.


Most likely it is the FBW Min that is the problem, our drone stalled at a speed of approx 10m/s and the value for FBW Min is set to 9m/s, even below the stall speed instead of 20% higher. It should be around 15 m/s. Will check results in next flight.

Dont forget that you are using gps speed only, meanwhile your aircraft uses airspeed to judge its stall speed. If you have a slight tailwind then your ground-relative stall speed increases.

We have airspeed sensor installed.