Loosing lots of height


I installed an APM in my Experimental Airline Peace Drone. The plane flies really steady with its long rear wings, in Manual mode its a pleasant plane to fly.

The issue I have is related to the initial turn the plane makes when switching to RTL, it looses a lot of height. by a lot I mean close to 30m of height. and then once the turn is completed, it gains the height, it only looses the height in that particular turn, cause once the plane reaches me and loiter it doesn’t loose height in the turns. First I thought its a setting in the apm in the amount of elevator its allowed to use, but why doesn’t it loose height when loitering above me. it doesn’t make a sharper turn when I switch to RTL

I tried this from really high, and rather low. so low I had to switch to manual to recover before it hit the ground, bottom line is if I’m lower than the height it looses it will hit the ground, but once that particular turn is completed, the plane doesn’t loose height in the turns.

I do think this is just a setting I’m missing because it only on that particular turn.

It sounds like you were flying significantly below your desired cruising speed when you engaged RTL. The firmware will dive to pick up speed with the default settings. Look at the throttle, speed and ‘TECS_SPDWEIGHT’ related parameters.


I looked at the log files but cant find the logs on the flights it did this… I’m going to clear the log files and fly it again this weekend, and will post it then…

I understand the reason why the plane cruise speed might be lower set value, but the motor is so strong it doesnt need to drop the nose to gain speed, and surely not so much that it would cause a crash…

Also make sure your airspeed sensor is well calibrated.

Hi Johan. Please post both your tlog and dataflash log once you have flown again. I’m curious to have a look why you are losing altitude.
Thanks, Grant.


I cant seems to download the Telemetry logs…

I think I manage to fix the “drop in height” now… one of the multirotor guys at the field changed a few settings, and now it seems like its not dropping height anymore in the initial turn. if the plane is higher than the set return height , it would cut the motor and glide to the height and then apply power so sustain the height.

but … i was told I’m loosing GPS satellites and its caused by the 433mhz telemetry unit… I should either remove it or move the antenna…

I’m a little worries about that, cause I’m busy installing an openlrs receiver… I fly FPV and want to use 433mhz for control and 1.2ghz for video. and I want to use the APM purely for the RTL option.

1.2 GHz is GPS frequency. That’s the problem.

OK… More flying been done this week and I dont know… this is scaring me a little on the board…

could you please tell me what the board actually do once the RTL is selected?
meaning… does is check height before starting to turn? cause the moment I select RTL it turn, instantly… it doesn’t even attempt to fix height till the turn is completed… mine is still loosing height in the initial turn… I’m off to flying it again. I don’t have the telemetry radio installed atm, so there isn’t telemetry logs.

but the time from realizing it drops, I have to select manual and recover… its 0.5 of a second to 2 seconds.
so I hope the log files make sense… I’ve opened the case and covered the barometer with some dark foam. I truely hope this is the problem and not anything else… I have a cheap Hobby copy and it does almost the same thing… it also doesnt gain height before turning, but the drop in height issnt as much as this one, and I have a 3D printed case over the HK clone. so maybe its letting less light getting to the barometer.

Johan, we really need logs to analyse your issue. Both tlog and dataflash please. The plane shouldn’t be dropping height - it doesn’t happen when I enable RTL so you either have found a bug we need to fix or there is some incorrect configuration.
Thanks, Grant.

The timestamp on your files indicate your clock is set wrong. Seems to be 1980?
Thanks, Grant.

Your altitude error is going crazy. Have a look at the graph I attached. I haven’t ever seen an altitude error that bad - off by 100m!!!
Are you flying with an APM2.5? I could only fine one magnetometer so I presume you are. What GPS are you using?
Your getting some serious interference from something. Is the APM covered or exposed to the light. The baro has problems if its subjected to direct sunlight.
diydrones.com/group/arducopterus … e=activity
Perhaps when it turns it faces the sun and goes crazy?
Thanks, Grant.

Hi GMorph

Thanks for the reply… I have shielded my board with some foam, and it does seem to be better now…
When I open the battery cover the altitude does differ a lot.

but now that the APM seems to be sorted, the plane almost need replacement. lol.

I’ve got a plane like that. But enough tape, hot glue and BBQ skewers seems to keep it flying :slight_smile:
Thanks, Grant

I have a new APM, and a different plane… same issue…

I’m confused… I set the RTL hight at 200m, hopeing the plane will attempted to instantly gain height once RTL is enabled. But still once RTL is initiated the plane cuts throttle, and starts to dive, not steeply or anything.

I have to give full up elevator when putting to plane to RTL, till the first initial turn is complete, the plane will then automatically start gaining height and return home.


I have the same problem : "once RTL is initiated the plane cuts throttle, and starts to dive for 1~2 second ,and gained altitude again after turn done"
Have anyone sloved this diving issue ?