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docs(navigator): clarify multicopter Return behavior (#27610)

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Sijia
2026-06-10 12:28:43 +08:00
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docs/en/flight_modes/return.md
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@@ -17,9 +17,9 @@ The following topics should be read first if you're using these vehicle types:
- Flying vehicles can't switch to this mode without global position.
- Flying vehicles will failsafe if they lose the position estimate.
- Mode requires home position is set.
- Mode prevents arming (vehicle must be armed when switching to this mode).
- Mode prevents arming (vehicle cannot be armed while this mode is selected).
- RC control switches can be used to change flight modes on any vehicle.
- RC stick movement in a multicopter (or VTOL in multicopter mode) will [by default](#COM_RC_OVERRIDE) change the vehicle to [Position mode](../flight_modes_mc/position.md) unless handling a critical battery failsafe.
- RC stick movement in a multicopter (or VTOL in multicopter mode) will [by default](#COM_RC_OVERRIDE) change the vehicle to [Position mode](../flight_modes_mc/position.md) unless prevented by the active failsafe state.
- A VTOL will return as MC or FW based on its mode at the point the return mode was triggered.
In MC mode it will respect multicopter parameters, such as the landing "cone".
In FW mode it will respect fixed-wing parameters (ignore the cone), but unless using a mission landing, will transition to MC mode and land at the destination after loitering at the descent altitude.
@@ -40,9 +40,7 @@ This topic covers all the possible return types that any vehicle _might_ be conf
The following sections explain how to configure the [return type](#return_types), [minimum return altitude](#minimum-return-altitude) and [landing/arrival behaviour](#loiter-landing-at-destination).
<a id="return_types"></a>
## Return Types (RTL_TYPE)
## Return Types (RTL_TYPE) {#return_types}
PX4 provides four alternative approaches for finding an unobstructed path to a safe destination and/or landing, which are set using the [RTL_TYPE](#RTL_TYPE) parameter.
@@ -169,7 +167,7 @@ In this case the vehicle follows mission waypoints, which we assume are planned
The return altitude for a fixed-wing vehicle or a VTOL in fixed-wing mode is configured using the parameter [RTL_RETURN_ALT](#RTL_RETURN_ALT) (does not use the code described in the next paragraph).
The return altitude for a multicopter or a VTOL vehicles in MC mode is configured using the parameters [RTL_RETURN_ALT](#RTL_RETURN_ALT) and [RTL_CONE_ANG](#RTL_CONE_ANG), which define a half cone centered around the destination (home location or safety point).
The return altitude for a multicopter (or VTOL vehicle in MC mode) is configured using the parameters [RTL_RETURN_ALT](#RTL_RETURN_ALT), [RTL_CONE_ANG](#RTL_CONE_ANG), and [RTL_MIN_DIST](#RTL_MIN_DIST), which together define a half cone centered around the destination (home location or safety point).
![Return mode cone](../../assets/flying/rtl_cone.jpg)
@@ -178,22 +176,19 @@ The return altitude for a multicopter or a VTOL vehicles in MC mode is configure
If the vehicle is:
- Above [RTL_RETURN_ALT](#RTL_RETURN_ALT) (1) it will return at its current altitude.
- Below the cone it will return where it intersects the cone (2) or [RTL_DESCEND_ALT](#RTL_DESCEND_ALT) (whichever is higher).
- Outside the cone (3) it will first climb until it reaches [RTL_RETURN_ALT](#RTL_RETURN_ALT).
- Inside the cone:
- Above [RTL_DESCEND_ALT](#RTL_DESCEND_ALT) (4) it will return at its current altitude.
- Below [RTL_DESCEND_ALT](#RTL_DESCEND_ALT) (5) it will first ascend to `RTL_DESCEND_ALT`.
- Outside of the radius defined [RTL_MIN_DIST](#RTL_MIN_DIST) (3) it will first climb until it reaches [RTL_RETURN_ALT](#RTL_RETURN_ALT).
- Below the cone and within [RTL_MIN_DIST](#RTL_MIN_DIST) it will climb to return at the cone intersection altitude (2), up to [RTL_RETURN_ALT](#RTL_RETURN_ALT).
- Inside the cone (4, 5) it will return at its current altitude.
Note:
- If [RTL_CONE_ANG](#RTL_CONE_ANG) is 0 degrees there is no "cone":
- the vehicle returns at `RTL_RETURN_ALT` (or above).
- If [RTL_CONE_ANG](#RTL_CONE_ANG) is 90 degrees the vehicle will return at the greater of `RTL_DESCEND_ALT` and the current altitude.
- The vehicle will always ascend at least [RTL_DESCEND_ALT](#RTL_DESCEND_ALT) for the return.
- If [RTL_CONE_ANG](#RTL_CONE_ANG) is 90 degrees the vehicle will generally return at its current altitude when close to the destination. The return altitude may still be constrained to avoid flying too low while approaching the destination.
## Loiter/Landing at Destination
Unless executing a [mission landing pattern](#mission-landing-pattern) as part of the return mode, the vehicle will arrive at its destination, and rapidly descend to the [RTL_DESCEND_ALT](#RTL_DESCEND_ALT) altitude, where it will loiter for [RTL_LAND_DELAY](#RTL_LAND_DELAY) before landing.
Unless executing a [mission landing pattern](#mission-landing-pattern) as part of the return mode, the vehicle will arrive at its destination, and rapidly descend to the [RTL_DESCEND_ALT](#RTL_DESCEND_ALT) altitude (if above that altitude), where it will loiter for [RTL_LAND_DELAY](#RTL_LAND_DELAY) before landing.
If `RTL_LAND_DELAY=-1` it will loiter indefinitely.
The default landing configuration is vehicle dependent:
@@ -221,12 +216,12 @@ The RTL parameters are listed in [Parameter Reference > Return Mode](../advanced
| ----------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| <a id="RTL_TYPE"></a>[RTL_TYPE](../advanced_config/parameter_reference.md#RTL_TYPE) | Return mechanism (path and destination).<br>`0`: Return to a rally point or home (whichever is closest) via direct path.<br>`1`: Return to a rally point or the mission landing pattern start point (whichever is closest), via direct path. If neither mission landing or rally points are defined return home via a direct path. If the destination is a mission landing pattern, follow the pattern to land.<br>`2`: Use the mission path to landing while skipping DO_JUMP and other non-position mission items if a landing pattern is defined, otherwise fast-reverse to home with the same traversal rules. Ignore rally points. Fly direct to home if no mission plan is defined.<br>`3`: Return via direct path to closest destination: home, start of mission landing pattern or safe point. If the destination is a mission landing pattern, follow the pattern to land. |
| <a id="RTL_RETURN_ALT"></a>[RTL_RETURN_ALT](../advanced_config/parameter_reference.md#RTL_RETURN_ALT) | Return altitude in meters (default: 60m) when [RTL_CONE_ANG](../advanced_config/parameter_reference.md#RTL_CONE_ANG) is 0. If already above this value the vehicle will return at its current altitude. |
| <a id="RTL_DESCEND_ALT"></a>[RTL_DESCEND_ALT](../advanced_config/parameter_reference.md#RTL_DESCEND_ALT) | Minimum return altitude and altitude at which the vehicle will slow or stop its initial descent from a higher return altitude (default: 30m) |
| <a id="RTL_LAND_DELAY"></a>[RTL_LAND_DELAY](../advanced_config/parameter_reference.md#RTL_LAND_DELAY) | Time to wait at `RTL_DESCEND_ALT` before landing (default: 0.5s) -by default this period is short so that the vehicle will simply slow and then land immediately. If set to -1 the system will loiter at `RTL_DESCEND_ALT` rather than landing. The delay is provided to allow you to configure time for landing gear to be deployed (triggered automatically). |
| <a id="RTL_MIN_DIST"></a>[RTL_MIN_DIST](../advanced_config/parameter_reference.md#RTL_MIN_DIST) | Minimum horizontal distance from home position to trigger ascent to the return altitude specified by the "cone". If the vehicle is horizontally closer than this distance to home, it will return at its current altitude or `RTL_DESCEND_ALT` (whichever is higher) instead of first ascending to RTL_RETURN_ALT. |
| <a id="RTL_CONE_ANG"></a>[RTL_CONE_ANG](../advanced_config/parameter_reference.md#RTL_CONE_ANG) | Half-angle of the cone that defines the vehicle RTL return altitude. Values (in degrees): 0, 25, 45, 65, 80, 90. Note that 0 is "no cone" (always return at `RTL_RETURN_ALT` or higher), while 90 indicates that the vehicle must return at the current altitude or `RTL_DESCEND_ALT` (whichever is higher). |
| <a id="RTL_DESCEND_ALT"></a>[RTL_DESCEND_ALT](../advanced_config/parameter_reference.md#RTL_DESCEND_ALT) | Altitude above the destination used for the final descent before landing or loitering (default: 30m). |
| <a id="RTL_LAND_DELAY"></a>[RTL_LAND_DELAY](../advanced_config/parameter_reference.md#RTL_LAND_DELAY) | Time to wait at `RTL_DESCEND_ALT` before landing (default: 0.5s) - by default this period is short so that the vehicle will simply slow and then land immediately. If set to -1 the system will loiter at `RTL_DESCEND_ALT` rather than landing. The delay is provided to allow you to configure time for landing gear to be deployed (triggered automatically). |
| <a id="RTL_MIN_DIST"></a>[RTL_MIN_DIST](../advanced_config/parameter_reference.md#RTL_MIN_DIST) | Within this distance from the return destination, the return altitude is calculated from the "cone" rather than directly from `RTL_RETURN_ALT`. |
| <a id="RTL_CONE_ANG"></a>[RTL_CONE_ANG](../advanced_config/parameter_reference.md#RTL_CONE_ANG) | Half-angle of the cone that defines the vehicle RTL return altitude. Values (in degrees): `0`, `25`, `45`, `65`, `80`, `90`. Note that `0` is "no cone" (always return at `RTL_RETURN_ALT` or higher), while `90` indicates an almost vertical cone, so the vehicle generally returns at its current altitude when close to the destination. The return altitude may still be constrained to avoid flying too low while approaching the destination. |
| <a id="RTL_APPR_FORCE"></a>[RTL_APPR_FORCE](../advanced_config/parameter_reference.md#RTL_APPR_FORCE) | [VTOL FW only] If set, home or rally-point RTL destinations are only considered when a valid VTOL approach loiter is defined for that landing location. Mission landing patterns are unaffected. |
| <a id="COM_RC_OVERRIDE"></a>[COM_RC_OVERRIDE](../advanced_config/parameter_reference.md#COM_RC_OVERRIDE) | Controls whether stick movement on a multicopter (or VTOL in MC mode) causes a mode change to [Position mode](../flight_modes_mc/position.md) (except when vehicle is handling a critical battery failsafe). This can be separately enabled for auto modes and for offboard mode, and is enabled in auto modes by default. |
| <a id="COM_RC_OVERRIDE"></a>[COM_RC_OVERRIDE](../advanced_config/parameter_reference.md#COM_RC_OVERRIDE) | Controls whether stick movement on a multicopter (or VTOL in MC mode) causes a mode change to [Position mode](../flight_modes_mc/position.md) (unless prevented by the active failsafe state). This can be separately enabled for auto modes and for offboard mode, and is enabled in auto modes by default. |
| <a id="COM_RC_STICK_OV"></a>[COM_RC_STICK_OV](../advanced_config/parameter_reference.md#COM_RC_STICK_OV) | The amount of stick movement that causes a transition to [Position mode](../flight_modes_mc/position.md) (if [COM_RC_OVERRIDE](#COM_RC_OVERRIDE) is enabled). |
| <a id="RTL_LOITER_RAD"></a>[RTL_LOITER_RAD](../advanced_config/parameter_reference.md#RTL_LOITER_RAD) | [Fixed-wing Only] The radius of the loiter circle (at [RTL_LAND_DELAY](#RTL_LAND_DELAY)). |
| <a id="MIS_TKO_LAND_REQ"></a>[MIS_TKO_LAND_REQ](../advanced_config/parameter_reference.md#MIS_TKO_LAND_REQ) | Specify whether a mission landing or takeoff pattern is _required_. Generally fixed-wing vehicles set this to require a landing pattern but VTOL do not. |