Help - Dive when auto selected

I have a flying wing with Pixhawk 2.1 on board, I have programmed missions before with Mission Planner without incident. On this occasion however, every time I program a mission, when I try it out I get an instant dive with power applied. I cant see whats going on from the logs but I’m inexperienced at decoding the logs. Any ideas from you experts what * may have got wrong? (I did use ‘relative’ option for altitudes.).

All comments and help greatly appreciated.*

As always, we would like to see a log. My guess is that your airspeed sensor is not calibrated and your aircraft is attempting to keep itself from stalling even though it is probably already at an adequate airspeed.

Funny you should say that, I had just about reached a similar conclusion when I found the Airspeed sensor was enabled and this aircraft doesnt have one. Would that manifest itself in this behaviour? Manual flight is fine but as soon as auto enabled, dive to the ground?

Thank you for your reply.

yes, that is exactly what it would do, as it would think airspeed is low, so it will dive to gain speed

It should actually refuse to arm if airspeed sensor is configured but not found, shouldn’t it?

depends on the airspeed sensor, eg. if setup as analog then it can’t tell it isn’t there