This is a short guide for setting up [ArduPilot](https://ardupilot.org/) on a flying wing. I use an Omnibus F4 that was previously set up for INAV (so motor on 1, elevons on 3/4), so most of this guide will be geared to that. If you use a different controller, your mileage may vary.
You should keep the [full list of ArduPilot parameters](https://ardupilot.org/plane/docs/parameters.html) open, for your reference while tuning.
## Hardware setup
The values in this section are specific to the Omnibus F4, but the settings aren't, so you'll usually need to adjust your outputs to your specific configuration but you probably won't need to skip many of the steps here.
- [ ] Connect GPS to UART 6 (SERIAL4). You don't need to do anything else for GPS, it should work out of the box.
- [ ] Connect Fport to a UART. I chose UART 3 (SERIAL2). If you want to use UART 1, you should set the RC input jumper to PPM on the F4 to disconnect the SBUS inverter from the pin.
- [ ] Set up the OSD (Mission Planner has a very nice UI for that). Keep in mind that ArduPilot's airspeed and windspeed estimation are quite good, so you may want to add those even if you don't have an airspeed sensor. You may also want to set up multiple screens, I use a potentiometer to switch between the four different screens of the OSD:
- [ ] Set up modes, possibly having switches override the mode channel to the mode you want.
What I do is set a given channel as the mode channel, and make that channel always output -100% on the radio. Then, I set up channel overrides for each switch, keeping in mind that overrides in OpenTX are executed in order (so the bottom override has the highest priority).
That way, I set MANUAL/ACRO/FBWA to be lowest priority (on the same switch), then CRUISE to override those, then LOITER, AUTO, AUTOTUNE in that order.
Finally, I add RTL to a switch on its own channel, with the highest priority of all overrides. I also add an override for that switch to the mode channel to -100%, so moving any other stick won't exit RTL mode as long as RTL is enabled.
## Auto modes
- [ ] Set `SERVO_AUTO_TRIM=1` so the aircraft trims itself while flying.
- [ ] Set `FS_SHORT_ACTN`/`FS_SHORT_TIMEOUT`/`FS_LONG_ACTN`/`FS_LONG_TIMEOUT`. I tend to disable the short action and set long to RTL.
- [ ] Set `RTL_CLIMB_MIN=30` so the aircraft climbs first before starting to return to home.
- [ ] Set `ACRO_LOCKING=1` to avoid drifting when you aren't moving the sticks.
- [ ] Change `AUTOTUNE_LEVEL` according to how aggressive you want the tune.
- [ ] Set `MIN_GNDSPD_CM` so the craft makes an effort to return even under high winds. WARNING: Might make throttle pulse or have other unwanted side-effects.
To tune the TECS, read the [TECS tuning guide](https://ardupilot.org/plane/docs/tecs-total-energy-control-system-for-speed-height-tuning-guide.html). It's very well-written and comprehensible. Note the maximum pitch up/down you want your plane to fly at (depending on the max vertical speed you want), and tune based on that.
- [ ] Fly in FBWA and see if you're gaining/losing altitude. Pitch up/down to fly level, check the pitch on the OSD, and use the formula `old_value+pitch*π/180` to get the new value (in radians).
