APM2 crash video - throttle too low

As you can see in the video my SkyEye was gradually losing height pretty much continuously. It should have been about 70 feet above the fields and trees within my sight but dropped out of sight pretty quick. Somehow it clipped a fence (near the beginning of the video) and flew on. There are a few other near misses with tree tops as you’ll see.

I am sure it is speed related. The throttle seems very low compared to other flights and you can see it’s not moving that fast. The crash is a gradual dive into a field with long grass - luckily no damage. At the point of crash it should have been 20 meters above the ground and I confirmed that on the elevation graph in Mission Planner.

I’ve calibrated my speed sensor (about 2 weeks ago) and checked the tubes running from it which are OK. It was a very still day with just a 3mph breeze.

Any ideas?

youtu.be/doeo81ekqjU (video only 2 minutes)



This is a very common problem with planes, and there is a very very easy fix.

I have asked so many times for help, and it always looks like the plane looses altitude in the initial turn once you engaged RTL…

I hope the link works.


But there is an option to set the APM to use elevator for height and throttle for speed, and to disable the mix between the two… this issnt the optimum solution but it works on Bixlers and some of my foam planes.

so set ALT_CTRL_ALG to 1… That will tell the APM to control pitch and throttle with the non-airspeed algorithm. That is a bit simpler to tune.

Have you flown a few batteries in AUTOTUNE?
are your plane a bit heavy?
is it overpowered?
are you airspeed set to a reasonable flying speed?

autotune fix most of the initial issues most people have. then a heavy plane needs to fly a little faster and your flying airspeed might be set lower than your current stall speed. so the plane think its flying fast enough and doesnt apply more power and only up elevator to keep height, it wouldnt know to apply more power, and just loose height till it hit the ground.