Fixed wing - Descent rate and Altitude

Hello Experts,

We are currently experiencing a few issues while using a fixed wing model with PX4 & QGC. Our use case is to use the fixed wing UAV for photography at low altitudes using autonomous way point mission.

Mission is as follows : Auto take off followed by way point navigation and reach a pre determined destination. After reaching a pre determined destination, descend to a low altitude and take pictures, climb to a predetermined altitude, return to home and auto land. While executing this, we are facing the following issues

  1. While descending, the UAV is not reaching the required speed. We manipulated the variables "FW_T_SINK_MIN (min descent rate), FW_T_SINK_MAX (max descent rate), FW_AIRSPD_TRIM (Cruise speed) & FW_AIRSPD_MAX (Max airspeed allowed) ”” to achieve the descent rate but this doesn’t seem to be working. We gave an input of 10 m/sec but we achieved a max of 4 m/sec.
  2. The UAV is not descending to the required altitude. While testing, we observed that the UAV deviates from its course before it reaches the required altitude, takes off and goes to a loiter mode (I guess this is to prevent an inadvertent crash?) . Need help with the options to modify to ensure that the UAV reaches the altitude and takes off without crashing.

If anyone has any input on how we can achieve this, it would be greatly appreciated.
Thanks

We can send the logs if anyone can help look at them

Have you received a reply yet on this issue ?

I have a different case scenario where I would like to know how to slower the response of my V-Tail plane ailerons and ruddervator in order to avoid any drastic flip during mid flight !! If you know which PID parameter to adjust under QGC ( px4 stack) , appreciate your feedback.

Hi Sibu,
I haven’t received any response to the topic yet. We are trying to tweak various parameters to see which one is causing the issue. Hope some expert points us in the right direction. No luck yet.
Thanks