this page says when airspeed sensor failed and airspeed is too high, plane will lose altitude very fast and speed will try to gain. but there is no solution of this. will changing mode to FBWA help to solve this problem?
do FBWA mode use airspeed sensor…? controlling plane with joystick in FBWA mode will help dealing with this problem?
and above page says when airspeed sensor failed and airspeed is too high, plane will slow down and crash. but how about VTOL? it doesn’t say about that.
will Q_ASSIST activated when the speed is too slow?
how things will be going to when I turn of Q_ASSIST by set Q_ASSIST_SPEED to 0? will it crash?
and I wonder about the solution of this failure.
This is not a simple topic, because there are several options on what to do if an airspeed sensor fails. You can have the autopilot revert to synthetic airspeed and even let it go back to measured airspeed if it recovers. There are settings for maximum allowed discrepancy between GPS ground speed and measured airspeed as well.
I have a VTOL with airspeed sensor and I noticed that transitions to forward flight are much better with airspeed sensor as the transition speed is detected better. When in fixed wing mode, you have to manage and treat the airspeed sensor just the same way as with any fixed wing airplane with the considerations on the previous paragraph. I haven’t seen much use of the airspeed sensor during VTOL hover modes. It may be used for weathervaning, to help it hold in place in a windy day. Either way, with an expensive VTOL airplane, you need to do some field testing before sending it 50km over open sea
@Truth_T It’s a good idea to use two airspeeds. In my experience, when one airspeed fails, the EKF will use the other. If you only have one airspeed, the EKF will also jettison the airspeed after detecting an airspeed failure; but it could still crash.
That was neither cynical nor ironic. If dangerous flight control results from the faulty measurement and Arduplane does not detect the faulty airspeed sensor itself, this is the only way to save the plane. Except switching to manual mode, which one BVLOS rather not routinely mastered via FPV. FBWA can work, but it does not have to work if the speed is measured much too low with a partially blocked pitot tube and the control surfaces therefore have much too wide deflections and shake the aircraft. I speak from my own experience from almost seven years of flying with airspeed sensors.
We fly VTOL planes in 1+ hour BVLOS mapping missions and failing airspeed sensor is very common thing to happen if the plane encounters freezing conditions (blocked by snow or ice buildup).
This is how we are dealing with the possibility of airspeed failure:
Plane is 7,5 kg quadrotor VTOL, stall speed about 10m/s. Target airspeed during mission is 20m/s. Maximum real wind speed for our mapping missions is 8m/s.
This should give autopilot some headroom to maintain at least safe-ish airspeed. But as usual, your mileage may vary. For us this has completely cured crashes caused by unrecoverable stalls during tight turns with bad airspeed data. Q assist cant really save tip stall condition. MIN_GNDSPD prevents plane from stalling before ASPD_OPTIONS can do its magic and disable the sensor because of speed mismatch. Typical blockage causes airspeed readings to go up to 30+m/s while ground speed tries to dip to single digits.
But in real world it doesnt make much difference or could even be worse than not having heated pitot tube. Why? Because in our climate freezing conditions come and go more or less randomly. We prefer not to fly at all if there is such weather but things can change fast. Loosing airspeed is “great” early warning to RTL before plane is too iced up it does not want to fly anymore.