Hi all,
Can you please help me understanding the cause of crash that happened to my VTOL
3.5m wingspan just after take off in q_loiter mode
here is the crash bin file link:
The link requires permissions.
thanks
no permissions needed now; sorry
Hello please watch the video,we have upside down V tail plane and it falls down after taking off,can you please suggest what parameters for PID and so on to set?
You can see the video via this link - IMG_4566.MOV - Google Drive
Plane design issue. CoA is in front of CoG. You can see how the tail comes down after the initial impulse has veered off. Then it hangs on the propeller, stalls, torque rolls and finally comes down tail first.
Edit: Honestly I don’t get what you try to achieve and why it should work out.
Why do you throw that plane in Q-Loiter instead of FBWA or TKOFF mode?
I also see no method of counter torque if it would be a Tailsitter VTOL.
Looking at the video only, I do not agree that there is clear plane design issue at all and that you can conclude that CG is too far back. What I see is a relatively stable flight trajectory where the nose goes slowly up and up until the plane stallsand falls. Basically, the conclusion is that FC did not keep up the airspeed, or that it tried to climb too hard or did not react to the increasing pitch . But that is unlikely CG issue.
To me the indication is that during stall, the fuselage overtakes the wing by yawing.
It reminds me of some 24H race at NĂĽrburgring where it started to rain and all the Porsche 911 crashed into the wall backwards because the engine has the biggest inertia.
EDIT: That one in 2016, started to rain, grain and then race was terminated.
Looking at the bin file, I see a problem in the sense that GPS data and roll and pitch data do not seem to agree at all (altitude seems to be correct, but the speed graph is not)…Not sure why. In any case there are clear indiciations of the FC induced oscillations in pitch.
I agree on that, and it could be that rudder is insufficient… The angle at which rear stabilizer attached is around 30 degrees, leaving very little rudder effect
What I noticed in the graph is that there was an abrupt yaw change to 0 degrees after 2 seconds of flight which coincides with the beginning of cartrwheeling. That yaw change seems to indicate a problem with yaw sensing, not that it was a consequence of the loss of control. However, no RCoutputs changed as the result of it, i.e. FC ignored the yaw becoming 0… The whole bin file is really a mystery for me…
There is also the thing that RCIN frantically seems to do things, which are interpreted differnetly in the QLoiter mode. Notably, I noticed high throttle input, but throttle controls altitude, not power, so that is one way the FC thought that it should increase the pitch?
The short answer why the plane crashed is because it was launched in Qloiter mode, but what exactly happened is a mystery…
Thank alot for your replay;
Im using X7+ as FC , F9P RTK for GPS and H 16 pro for control.
I’m traying the plane for the second time. it was stable in q_loiter mode for the first time.
But in the second I take off normally and the i try to move forward in q_loiter mode at that time i loose control and the plane crash. i hope to understand what exactly the problem.
Greeting
Why do you have QLoiter mode at all?
QLoiter is for VTOL planes only… I begin to think that the setup of this plane is totally wrong…
You MUST make first flights in Stabilized Mode or Manual Mode. If you do not know how to fly planes, Manual mode could be more complicated, so use Stabilized, If you know how to fly planes, Manual Mode is safer.
You start tests with Manual, then Stabilized, then FBWA, then FBWB, then the Loiter.
Never start with Loiter! And you have QLoiter, which has nothing to do with your plane.
if you mean by “moving forward” applying more throttle, in QLoiter mode throttle controls altitude, not power, and since your plane seems not configured correctly, that was the result.
Thankyou Michail_belov for your replay;
In fact my plane is VTOL 4+1 fixed wing, and i just finish building it and start traying it in quadplane_stabilize mode after the setup , the result was good, the plane is very stable and it follow the coammand without any problem. Then i switch to quadplane_loiter mode also the first test was excellent and the behaviour was correct when i move the plane in that mode forward, backward, right and left using roll and pitch axes (not the throttle) from the radio control.
but the second test was a failure, as i describe before.
Greeting
If you flew in Loiter mode the first time, and in QLoiter Mode the second time, than it is almost certain that this was the cause of the crash. I do not understand how you managed to fly at all in QLoiter mode, because it is supposed to control only the hover motors, which are not present, so maybe you have setup the plane incorrectly.
1 Like
Hello,
I never flew the VTOL in loiter mode, just for the beginning of tests i follow the Ardupilot instructions, this is an extract from ardupilot document:
“Normally, it’s best to start by tuning the Rate Roll/Pitch P in QSTABILIZE mode then move onto tuning altitude hold in QHOVER mode, then QLOITER (which often needs no tuning) and finally the waypoint navigation performance in Auto mode.”
@Foued_Ammar Is the video posted by @AR_AM the flight you recorded in your logfile ?
If so, how can you throw the airplane into the air in a Q mode with missing quad motors?
Rolf
If I understand it correctly, Q…modes are for the VTOL part, i.e. they control motors which point upwards, i.e. for hover, not for flying straight.
I feel that you may have a mixup between QLoiter and Loiter Modes!
You still can (partially) setup a plane with Q Parameters without hover motors, but you can not use any Qmodes without motors.
On your previous flights you either flew in Loiter mode (which is also extremy difficult not to crash on the first flight) or, if you used Qstabilize, Qhover, or Qloiter, you must have: A. completely miswired the thing (like putting one hover motor output to the forward main motor, and B. a lot a lot of luck if you flew “succesfully”.
2 Likes
Hello and thanks alot for your replay,
This video will explain to you what i mean by testing the VTOL in quadplane_stabilize and quadplane_loiter mode before going further to test it as fixed wing in cruise mode or auto mode after the transition.
Either I am totally lost or you are totally lost…
Your video of your plane which crashed does not have VTOL motors installed. How do you test Q_Stabilize and Q_Loiter mode if you do not have motors?
And in your crash, with the only forward motor you have you do not have any way of flying VTOL modes, i.e. those beginning with Q… Your logs show clearly that you had QLoiter mode on. That means that without your VTOL motors you could not fly correctly at all! You flew probably because one of your VTOL motor outputs was connected to the front facing motor… And I am not sure how you have wired the servoes for elevator-rudder.