Hi everyone,
I am experiencing a critical issue during hand-launch with my fixed-wing UAV(X-UAV Talon) and Pixhawk Cube Orange, I would really appreciate some insights from the community.
The Issue:
During hand-launches in Stabilize (and sometimes Mission/Auto) mode, the aircraft frequently suffers a violent crash immediately after leaving my hand. Instead of climbing, the aircraft rolls hard left straight into the ground.
The aircraft behaves inconsistently during hand launch.
Sometimes the launch is completely successful, and the aircraft flies normally for the entire flight.
However, on other flights, immediately after leaving my hand, the aircraft suddenly performs one of the following:
Rolls aggressively to the left and crashes.
Rolls aggressively to the right and crashes.
Pitches nose-down immediately after launch and impacts the ground before gaining altitude.
The failure happens within the first few seconds after release.
The strange part is that the direction is not consistent. Sometimes it rolls left, sometimes right, even though nothing has changed between flights.
Additional Observations
Another issue is that during successful flights in Stabilized mode, when I release the transmitter sticks:
Sometimes the aircraft continuously drifts to the left.
On other flights, it continuously drifts to the right.
Again, the direction changes between flights.
Log Files:
I have all flight logs .ulg, CSV and .tlogs and can upload them if needed.
2026-06-30 12-19-48.tlog (680.0 KB)
Launching Talon is not very easy, most probably (without looking at .bin) you stall it on launch, so it drops wing, when the wing drops, the stabilize mode gives even more counterinput (on the dropped wing you get aileron down, so that aggravates the stall). It does not matter what mode you are in.
What you should try is to launch the plane much harder, and almost parallel to the ground. That is the key.
Drifting after launch probably is not related to the crashes/stall issues you had.
And you should upload -bin file.
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Hi Michail,
Thank you so much for taking the time to reply and for the launch technique advice! Regarding the log file: I actually switch between using ArduPilot and PX4 depending on the flight. For this specific flight, I was running PX4 (with QGroundControl), which is why the system generated a .ulg file instead of a .bin file. However, the .ulg contains all the high-rate flight and sensor data equivalent to a .bin.
I have uploaded the .ulg file to Flight Review so it’s easy to analyze. Here is the link:
(I have also attached all the files, including the flight video, here if you prefer analyzing them in PlotJuggler or another tool).
Could you please take a quick look at the ULog data when you have time? I’d really appreciate your expert eye on whether the data confirms the launch stall, or if there might be an underlying sensor/stabilization anomaly explaining the inconsistent drifting.
Thanks again for your help!
That is definitively not a stall issue (although launching is not very good).
I do not understand much the data formats, but from the video it looks like it could be that the controls are inverted, and that the PIDs for roll are set very low. The plane continues to bank to the left very slowly, but progressively. If you have these two conditions, inverted controls and low PIDs that would you would get.
That would also explain that your plane sometimes goes to one side or the other.
But, if you did have succesful flights, then, this would not be the case. Unless you switched to manual.
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