The flight modes determine who is in charge of controlling each one of the aircraft control channels. There are 5 different control modes and it is possible to combine them to create custom flight modes.
Modes editing panel
The options available are:
Automatic: the control channel is controlled totally by the autopilot.
RC: the control is totally carried out manually. The movements on the pilot stick imply directly movements on the servo linked to that control channel.
ARC: the autopilot aids the radio controller during the flight, i.e it could be considered as a mix between automatic and manual. The movements on the pilot stick are the input values on the control system, so the pilot commands a desired pitch, roll, IAS, heading and so on, and is the control system who is in charge of making the platform follow those commands.
Mix: in this mode, it is possible to select in which step of the controller will enter the pilot command. For example, the pitching of an aircraft is commonly controlled with 3 PID being: flight path angle, pitch and pitch rate. In the arcade mode the pilot command will be a desired flight path angle that enters as input of the whole control system, but in the Mix mode is possible to select where we want the command to enter, so the pilot command could be pitch (entering in the second PID directly) or pitch rate (entering directly on the third PID). The control system will take this input as a disturbance that it wants to discard because the final objective is to match the input of the first PID (a desired flight path angle in this case), so the Mix mode can be used to make small corrections when the aircraft is following a route for example, where we want it to move slightly towards a certain direction by introducing a value directly on the roll PID. The following figure shows how to select the Mix mode and the parameters that have to be configured: the variable to control (Desired Pitch in this case) and the gain applied on the stick command (it goes from -0.5 to 0.5 so in this case, a gain of 1 implies a Desired Pitch that can go from -0.5 rad to 0.5 rad).
Autotune: this mode has to be select when the user wants to find control gains automatically.
It is every common to find an automatic mode where all the dynamics are controlled by the autopilot. Likewise, the manual mode is completely controlled by the remote controller (rc). To change any of this options, click on the cell you would like to change and the next option will be set.