I need to precisely understand the transition flow, including all the potential scenarios. I’m a bit confused about the bit 19 of the Q_OPTIONS role.
The Transition section of the ArduPlane manual says that the bit 19 of the Q_OPTIONS is relevant only for tiltrotors:
Blockquote
for tiltrotors only: if bit 19 of Q_OPTIONS is set and Q_TRANS_FAIL is not zero, and if the groundspeed is greater than 1/2 of AIRSPEED_MIN, then the transition to fixed wing will immediately complete.
However, in the parameter description it is only stated that:
CompleteTransition-to fixed wing if Q_TRANS_FAIL timer times out instead of QLAND
So my question is if this bit is only relevant for the tiltrotors? And why if yes? What is the point of this parameter and its relation to the Q_TRANS_FAIL_ACT ( Quadplane transition failure action) with the “Warn only” choice? Does it have anything to do with the motor tilt operation and its timeouts in both ways (tilting to and from horizontal motor position?)
I fly only VTOL planes with non-tilting horizontal motors. So can I use this option that reaching the half of the AIR_SPEED (without the airspeed sensor) will complete the transition without waiting for the transition timeout?
Q_OPTIONS bit 19 applies to tilt motors because upon reaching Q_TRANS_FAIL, it allows the aircraft to make the decision to tilt the motors the rest of the way, or switch back into VTOL mode. Tilt motor transitions require the aircraft to reach AIRSPEED_MIN at an intermediate tilt angle (Q_TILT_MAX). If the motors don’t tilt far enough, it may never reach AIRSPEED_MIN.
A quadplane with separate lift and cruise motors is not expected to have these issues, because you have direct control over the forward motor (if switching to FBWA) or it will use TKOFF_THR_MIN or TRIM_THROTTLE in auto modes, which is expected to have plenty of power to accelerate the aircraft.
Thank you very much for your answer and confirming that it is relevant only for tiltrotors. However, I don’t understand the logic behind it. It is stated in the docs that this is useful when launching into headwind. And here I don’t understand what is the difference between tiltrotors and planes with conventional horizontal propeller. OK, the tiltrotors need more time for re-orienting the motors before they can contribute to the horizontal thrust. But not every conventional VTOL plane will have “plenty of power” as you say.
I fly (among others) FIMI Manta (converted to non-tilting configuration) and a Sonic Baby VTOL conversion, and both of them are relatively light and have not very powerful horizontal motors, Manta is also quite fast so sometimes these planes indeed have problems with completing the transition before reaching the time limit when the headwind is strong and there is no airspeed sensor. I can assume that there is plenty of airspeed as the launch is into headwind and the horizontal motor has been working. And what happens then if the transition fails?
This sets the mode that is changed to when Q_TRANS_FAIL time elapses, if set. See also Q_OPTIONS bit 19: CompleteTransition if Q_TRANS_FAIL
But the choices are only QLAND and QRTL, so if I started the transition by switching from QLOITER into FBWA and it times out, will the aircraft be left in FBWA? Or fall back to QLOITER? I think that the latter one is true, but can anyone confirm this?
What I would want to achieve is: after timing out Q_TRANS_FAIL, leave the plane in FBWA (force the transition to be successful even if the AIRSPEED does not confirm this). If for some reason the accumulated airspeed would be below the stall airspeed and the plane would stall, the VTOL assist would kick in. But I assume that reaching full horizontal thrust (which I confirm by telemetry) provides enough airspeed nevertheless.
If there is no parameter for this functionality, I suggest that it could be the 19 bit for non-tiltrotors, or yet another bit.