RTL Mode (Return To Launch)¶
In RTL mode the plane will return to its home location (the point where the plane armed - assuming it had GPS lock) and loiter there until given alternate instructions (or it runs out of fuel!). As with AUTO mode you can also “nudge” the aircraft manually in this mode using stick mixing (assuming the RTL was not a result of RC failsafe).
The target altitude for RTL mode is set using the ALT_HOLD_RTL parameter in centimeters. When initiated below ALT_HOLD_RTL, Plane will immediately climb at maximum allowable rate to reach that altitude, if above, it will descend in a linear manner versus distance to home, reaching that altitude at the home loiter point.
The loiter radius at home is determined by RTL_RADIUS, if it’s non-zero, otherwise WP_LOITER_RAD is used. Clock-wise or Counter-Clock-wise circling can be set by positive or negative values for the radius.
Additionally, in firmware versions 4.0.6 and later, by setting RTL_CLIMB_MIN to a non-zero value, the plane will climb that many meters, limited in bank angle by LEVEL_ROLL_LIMIT degrees until the additional altitude is reached, then begin the above return to home action from that altitude.
To prevent the vehicle from turning until the return atlitude is reached, if below that value(ALT_HOLD_RTL + RTL_CLIMB_MIN), set bit 4 of the FLIGHT_OPTIONS bitmask.
Alternatively, you may configure the plane to return to a Rally Point, rather than the home location.
It is possible to setup an Automatic Landing to be executed when entering RTL. See Using DO_LAND_START for details. You must have setup your vehicle to properly do a automatic landing, of course.
“Home” position is always supposed to be your Plane’s actual GPS takeoff location:
It is very important to acquire GPS lock before arming in order for RTL, Loiter, Auto or any GPS dependent mode to work properly.
For Plane the home position is initially established at the time the plane acquires its GPS lock. It is then continuously updated as long as the autopilot is disarmed.
This means if you execute an RTL in Plane, it will return to the location where it was when it was armed - assuming it had acquired GPS lock.
Consider the use of Rally Points to avoid returning directly to your arming point on RTL