Every time when airspeed sensor is activated and you try RTL the plane starts to descent and would hit ground if not switched to manual and saved.

(Use AS sensor) When I set RTL at 50m the plane starts descent with nose pitch 0°

(Don't use AS sensor) When I set RTL at 50m the plane starts climbing with nose pitch 10-15° and goes straight to the target altitude.

If you dont use the airspeed sensor everything is fine. What is causing this? This problem has existed quite long know and many people have written about it.


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And I was thinking to buy the AS sensor for my 2m glider.

But now I am afraid I need to wait until other people will provide the answer.

I wonder if this is in any way related to the issue that without GPS lock airspeed and pitch readings become negatively correlated. I added a comment on the issue list and pointed to this post.

Hello Veikko,

We have the same problem, we noticed that the throttle cuts immediately after turning to RTL. It can be seen clearly on the graphs attached the altitude and throttle and in the other the airspeed and groundspeed (less sensitive) to the change in throttle and altitude.

In this flight the plane crashed, i tried to recover it changing to manual but it was too late. Have you tried the altitude control algorithm to non-airspeed? another question is about the altitude you set for RTL, where can modify and the numbers are in centimeters or meters? I ask this because there are many places where you can modify it like in the advanced parameters list in configuration or in the flight data tab /actions tab but they don´t seen to have an effect on the flight. I also found a parameter in flight data tab/status/targetaltd100 and targetalt, do you have any idea what are they?

Tomorrow i will unable the airspeed sensor and see if that helps in RTL mode. Have you tried to fly a waypoint mission? does it flyght well or the RTL problems also affects the auto mode?  

hope we can solve this problem soon cause is very important to return safely to lunch in emergencies.




I forgot to upload the second graph. here it is.



Today I was flying some short test missions and had the same problems as you described.  The aircraft would descend in RTL or AUTO mode when the airspeed sensor and use airspeed boxes were checked on the hardware configuration page.  I too would like to know what is causing this.

The indicated airspeed on the HUD display appears to be accurate.

Thank you.

Bret C

What is your THR_MAX set to?  From looking at the graph it seems like it might be set to zero (bad).  Or possibly you haven't increased THR_MIN from the defaults (you want something at least high enough to keep the plane flying).

I just installed my A/S sensor and ran into this issue. Has anyone found a solution?

Anyone? Surely there is an answer somewhere. Is this possibly related to the leaking pitot tube issue?

I have noticed an issue with my newly arrived AS sensor. It's all over the map. It varies from 5-9 mph sometimes 11 mph just sitting. The first thing I noticed was it would vary with it's orientation. [ I'm speaking about the circuit board and chip not the tube] Then yesterday I finally noticed that if I squeeze the little board it works perfect. It floats around 0-1 mph. Rock solid and consistant. Blow on the tube it works great. Stop blowing and bam right back to zero. Stop squeezing and it's back to highly inaccurate. So there is certainly and issue with the board / chip. I carefully pushed on each solder connection, both mine and the factory solder joints, and it made no difference. I was thinking of trying just putting some silicone around the chip?? It seems like it has two 1/2's.. might be leaking between them? I have ask to return it for another one however so will wait before I try that. But at any rate it does not inspire a great deal of confidence. Personally I will only use min max throttle,,, no AS for flight control. I noticed two boxes in the hardware section on MP. One is enable and one is use? I wish I knew if I had it enabled checked but not 'used' would the amp not use any of the AS data for flight control? It would then only be in the HUD for reference? Sorry to ask a question in another persons thread but it seems relevant to the subject. 

@Richard Kennedy
The 3DR AS datasheet states that the error of the instrument reduces with the square of the pressure. This means that when static, the error is quite large, but as soon as it starts moving, even if only a few m/s, the error dramatically decreases and the value will lock solid even below that it was bouncing around when stationary. Also, if you increase the pressure by pressing on on the pitot, again, the error decreases just as you described

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