Return Flight Mode (RTL)

The Return flight mode (also known as "Return to Launch") causes the vehicle to return to its home position where it may then either wait (hover or circle) or land.

  • This mode requires GPS.
  • This mode is automatic (RC control is disabled by default except to change modes).

The specific behaviour for each vehicle type is described below.

Multi-Copter (MC)

A copter/multi-rotor will first ascend to the RTL_RETURN_ALT altitude and then fly to the home position in a straight line (if already above RTL_RETURN_ALT it will return at its current altitude).

When it arrives at the home/launch position it will rapidly descend to the RTL_DESCEND_ALT altitude. It will then hover for the period defined in RTL_LAND_DELAY before landing.

The RTL_LAND_DELAY is provided to allow time for landing gear to be deployed (this is triggered automatically). By default this period is short so that the vehicle will simply slow and then land immediately. The parameter can also be set so that the vehicle will hover indefinitely.

The RTL behaviour can be configured using the parameters below.

Parameter Description
RTL_RETURN_ALT Minimum RTL return altitude in meters (default: 60m). The vehicle will ascend to this altitude before returning. If already above this value the vehicle will return at its current altitude.
RTL_DESCEND_ALT Altitude at which the vehicle will slow or stop its initial descent (default: 30m)
RTL_LAND_DELAY Time to hover at RTL_DESCEND_ALT before landing (default: 0.5s). If set to -1 the system will loiter at RTL_DESCEND_ALT rather than landing.
RTL_MIN_DIST Minimum distance to trigger rising to a safe altitude. If the system is horizontally closer than this distance to home it will land straight on home instead of raising to the return altitude first.

Fixed Wing (FW)

A fixed-wing aircraft behaves the same as a multicopter on the return trip (respecting the same parameters). The only difference is that on arrival the vehicle will, by default, circle above the home position rather than hover/land. If RTL_LAND_DELAY is set to -1 the vehicle will land as described in the topic: Landing (Fixed Wing).

The following additional parameters affect RTL on fixed wing:

Parameter Description
NAV_LOITER_RAD The radius of the loiter circle.

VTOL

A VTOL follows the RTL behavior and parameters of Fixed Wing when in FW mode, and of Multicopter when in MC mode. A VTOL in FW mode will always transition back to MC just before landing (ignoring NAV_FORCE_VT).

© PX4 Dev Team. License: CC BY 4.0            Updated: 2017-11-22 18:46:59

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