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Fixed Wing Loiter Modes - Orbit and Figure 8 (#26194)
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Hamish Willee
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<img src="../../assets/site/position_fixed.svg" title="Position fix required (e.g. GPS)" width="30px" />
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The _Hold_ flight mode causes the vehicle to loiter (circle) around its current GPS position and maintain its current altitude.
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The _Hold_ flight mode causes the vehicle to loiter around its current GPS position and maintain its current altitude.
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The mode supports a [number of distinct loiter modes](#loiter-modes), which are triggered using different QGC controls or MAVLink commands.
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These allow loitering with circular and figure 8 flight paths.
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:::tip
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_Hold mode_ can be used to pause a mission or to help you regain control of a vehicle in an emergency.
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It is usually activated with a pre-programmed switch.
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It is usually activated with a pre-programmed RC switch.
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:::
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::: info
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@ -24,24 +27,80 @@ It is usually activated with a pre-programmed switch.
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:::
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## Technical Summary
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## Loiter modes
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The aircraft circles around the GPS hold position at the current altitude.
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The vehicle will first ascend to [NAV_MIN_LTR_ALT](#NAV_MIN_LTR_ALT) if the mode is engaged below this altitude.
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### Default Loiter
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RC stick movement is ignored.
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The aircraft circles around the position at which the mode was triggered and maintain its current altitude.
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The loiter radius is set by the parameter [NAV_LOITER_RAD](#NAV_LOITER_RAD).
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Note that if the vehicle altitude is below [NAV_MIN_LTR_ALT](#NAV_MIN_LTR_ALT), it will ascend to that minimum altitude before circling.
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### Parameters
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The default loiter mode is entered when you switch to Hold mode without explicitly specifying any loiter behaviour.
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For example, if you switch to Hold mode using an RC switch, select **Hold** on the QGC flight mode selector, or activate the mode using the MAVLink [MAV_CMD_DO_SET_MODE](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_SET_MODE) command.
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### Orbit Loiter Mode
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<Badge type="tip" text="PX4 v1.12" />
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The aircraft travels towards a _specified_ orbit center position, then circles it with a given direction and radius.
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This behaviour can be accessed in QGroundControl by clicking on the map in Fly view, selecting **Orbit at Location**, and configuring the radius.
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The behavior can be triggered using the MAVLink [MAV_CMD_DO_ORBIT](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_ORBIT) command.
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Note that PX4 respects the specified centre point (`param5`, `param6`, `param7`), and the radius and direction (`param1`).
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PX4 ignores `param3` (Yaw behaviour) and `param4` (Orbits).
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The value of `param2` (velocity) is also ignored, but the speed can be controlled using the [MAV_CMD_DO_CHANGE_SPEED](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_CHANGE_SPEED) command (constrained between `FW_AIRSPD_MAX` and `FW_AIRSPD_MIN`).
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PX4 outputs orbit status using the [ORBIT_EXECUTION_STATUS](https://mavlink.io/en/messages/common.html#ORBIT_EXECUTION_STATUS) message.
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### Figure 8 Loiter Mode
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<Badge type="tip" text="PX4 v1.15" /> <Badge type="warning" text="Experimental" />
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The aircraft flys towards the closest point on a specified figure 8 path and then follows it.
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The path is defined by the figure 8 centre position, orientation, and radius of two circles.
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The feature is experimental, and is not present in PX4 firmware by default (on most flight controller boards).
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It can be included by setting the `CONFIG_FIGURE_OF_EIGHT` key in the [PX4 board configuration](../hardware/porting_guide_config.md#px4-board-configuration-kconfig) for your board and rebuilding.
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For example, this is enabled on the [default.px4board](https://github.com/PX4/PX4-Autopilot/blob/main/boards/auterion/fmu-v6s/default.px4board#L46) file for the `auterion/fmu-v6s` board.
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The behavior can be triggered using the MAVLink [MAV_CMD_DO_FIGURE_EIGHT](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_FIGURE_EIGHT) command (PX4 respects all the parameters).
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PX4 outputs the figure 8 status using the [FIGURE_EIGHT_EXECUTION_STATUS](https://mavlink.io/en/messages/common.html#FIGURE_EIGHT_EXECUTION_STATUS) message.
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::: info
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Figure 8 loitering is not currently supported by QGC: [QGC#12778: Need Support Figure of eight (8 figure) loitering by QGC](https://github.com/mavlink/qgroundcontrol/issues/12778).
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:::
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Figure 8 loitering is also available in the simulator.
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You can test it in [Gazebo](../sim_gazebo_gz/index.md) using a fixed wing frame:
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```sh
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make px4_sitl gz_rc_cessna
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```
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## Parameters
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Hold mode behaviour can be configured using the parameters below.
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| Parameter | Description |
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| -------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------- |
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| [NAV_LOITER_RAD](../advanced_config/parameter_reference.md#NAV_LOITER_RAD) | The radius of the loiter circle. |
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| <a id="NAV_LOITER_RAD"></a>[NAV_LOITER_RAD](../advanced_config/parameter_reference.md#NAV_LOITER_RAD) | The radius of the loiter circle. |
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| <a id="NAV_MIN_LTR_ALT"></a>[NAV_MIN_LTR_ALT](../advanced_config/parameter_reference.md#NAV_MIN_LTR_ALT) | Minimum height for loiter mode (vehicle will ascend to this altitude if mode is engaged at a lower altitude). |
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## MAVLink Commands
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The following commands are relevant to this mode:
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- [MAV_CMD_DO_ORBIT](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_ORBIT) - Switch to Hold mode and start the specified [Orbit loiter](#orbit-loiter-mode).
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Params 2 (velocity), 3 (yaw), 4 (orbits) are ignored.
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[ORBIT_EXECUTION_STATUS](https://mavlink.io/en/messages/common.html#ORBIT_EXECUTION_STATUS) is emitted.
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- [MAV_CMD_DO_FIGURE_EIGHT](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_FIGURE_EIGHT) - Switch to Hold mode and start the specified [Figure 8 loiter](#figure-8-loiter-mode).
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All params are respected.
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[FIGURE_EIGHT_EXECUTION_STATUS](https://mavlink.io/en/messages/common.html#FIGURE_EIGHT_EXECUTION_STATUS) is emitted.
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Note, other commands may be supported.
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## See Also
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[Hold Mode (MC)](../flight_modes_mc/hold.md)
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- [Hold Mode (MC)](../flight_modes_mc/hold.md)
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<!-- this maps to AUTO_LOITER in flight mode state machine -->
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