Aircraft does not prevent stall in AUTO or RTL mode

ArduPlane Plane 4.6
1

Hello
I discovered problem how Arduplane TECS controls airspeed of my plane in AUTO/RTL modes. It makes absolutely no effort to prevent stall. I performed test which is visible in the video where I disabled motors during RTL mode and the aircraft tried to maintain altitude disregarding the airspeed. The airspeed dropped below AIRSPEED_MIN=14 m/s and AIRSPEED_STALL=12.5 m/s and resulted in stall. Although my aircraft does not have physical airspeed sensor, the displayed estimated airspeed is not very wrong. What can I do to make aircraft to pitch down in this situation?

1980-01-09 17-35-26.bin.param (19.2 KB)

I also uploaded the parameters I used.

2

That’s the expected behavior.

Install airspeed sensor or enable using synthetic airspeed (highly experimental).

3

Check the TECS_SPDWEIGHT. Default is 1, but for this you might consider pushing it up towards 2. Go up in steps about .1 or .2 at a time and make sure it doesn’t cause any other issues.

4

That won’t work without airspeed sensor (or enabling experimental “use synthetic airspeed”).

5

Stall prevention, for example, increases speed or the turn radius if you try to fly too tight a turn at too low a speed. See the detailed description in the WIKI:

TECS isn’t intended for engine failure. You can use a “dirty” workaround to force TECS to make the plane descend with negative pitch during an engine failure by changing TECS_PITCH_MAX and TECS_PITCH_MIN via a LUA script—for example, to match best pitch for optimal glide performance.

6

If I switch on synthetic airspeed, what is the probability that this will cause the aircraft to crash? Does it affect FBWA mode?

7

Greater than 0 :sweat_smile:.

I personally haven’t used it. FBWA throttle control won’t be affected (it is manual anyways) but control surfaces gains may be.

8

So I tried to enable synthetic airspeed and it solved the problem. Not only it does not stall in RTL/AUTO mode but it also resolved other problem I had that aircraft most of the time flied much faster than necessary in AUTO mode.

9

The plane was flying as fast as it was configured to.

See TECS (Total Energy Control System) for Speed and Height Tuning Guide — Plane documentation

Some failure modes of synthetic airspeed are mentioned here Airspeed Parameters Setup — Plane documentation

As noted in TECS documentation throttle parameters must be configured even when using airspeed control.