Add fixed-wing takeoff mode without lateral navigation requirement

[sfuhrer]

Solved Problem

GNSS and magnetometer sensors are susceptible to disturbances on the ground. With bad heading and position estimation, the auto takeoff mode doesn't work reliably, which can lead to crashes or failsafe actions being executed. The current navigation loss failsafe for fixed-wings is Descend, which is dangerous to trigger while still being close to the ground.

Solution

Add a new flight mode Takeoff without navigation. It is currently only implemented for fixed-wing vehicles (even only for non-runway takeoff ones), and keeps most of the normal fixed-wing takeoff behavior with one big difference: instead of doing lateral guidance to fly to a takeoff waypoint or to keep course of ground constant, this new mode simply commands a 0° roll setpoint until the takeoff altitude is reached.
After reaching the takeoff altitude the flight mode automatically switches to Hold (Loiter).

This mode is also used to fall-back to from the normal Takeoff mode should during the takeoff procedure the navigation become invalid. It then proceeds with climbing, and gives the pilot more time to take over.

Changelog Entry

For release notes:

Feature: Add fixed-wing takeoff mode without lateral navigation requirement

Alternatives

Test coverage

In progress

[ryanjAA]

Pretty cool :)