INAV's autoland approach explanation needed

[jaroszmm]

After my last flight where fog killed my LOS or FPV possibility to land and I had to crashland my plane in a nearby field and then look for it with GPS on my phone I started wondering about INAV"s autoland feature.
I do have some knowledge about it, remember trying it once or twice when it was still in a very beta state, but never actually used it. At the moment Marc helped me to set it up on my Nano Goblin, but I still haven't tried it out. And not until my last foggy flight I thought maybe it's time to figure out some stuff about it.

Now for the important stuff.
I am able to set up autoland in Arduplane, which IMHO is a bit easier to set up, because I can create a full approach pattern for a location avoiding trees, buildings etc, even make the final approach as a 500m straight line before touching down.
The drawbacks are that I can set up only one approach, no matter what wind direction is blowing at the field.

INAV allows to include wind direction into landing calculations etc, but what worries me is that triangular approach pattern (from what I remember 3 circles over safehome to determine wind direction and choose the proper runway) as it seems it is fixed and can't be modified.

I have no idea how high that triangle is flown. Also the transition into the final and touchdown. Basically I'm worried if I try it at my place the triange part will result in my plane hitting a tree or a building.

Could anyone draw here on the photo of my landing location (with some measurements) how would my plane behave over it, how will it land (it needs to go along the line from west to east) etc?

I know INAV won't let me create a custom approach pattern, which is sad, as it would be IMHO better to have a safehome with a nice approach pattern clearing any dangerous obstacles.

[b14ckyy]

Its actually all documented. https://github.com/iNavFlight/inav/blob/master/docs/Fixed%20Wing%20Landing.md

Look at the top down map image and the altitude phase graph below. The colors of the lines show the phases and it also explains the altitudes. The only thing I just realized, that we forgot to correct, is the approach length. That part actually starts at the purple line and not all the way to the left :D

[sensei-hacker]

I understand about the custom pattern. Maybe instead we could add a "land" option for a normal mission, something that would just kill throttle and put the plane in a glide / flare pitch angle. So if I understand correctly for me to clear the 25m trees I need 30m approach altitude?

That's a good idea. It was added in INAV 2.5.

The point types available are:
WAYPOINT, POSHOLD_TIME and LAND

More info:
https://www.daria.co.uk/mwptools/mission-editor/

[jaroszmm]

Something like that? First 5 WPs are 50m alt relative to launch, then I drop to 25 for WP6, 10 for WP7 and 2 for WP8, 1m for WP9 and 0m for LAND?

And if I understand properly I could in case of emergency hit RTH, allow plane to come back home, within first WP radius, enable mission and plane should follow that path and then "land" by itself or will it at the "land" WP go to the full autoland procedure?

[b14ckyy]

IIRC INAV will do a classic Circle landing if you do not apply approach directions to a landing waypoint or safehome.
So for that way that you show, it might be that INAV will go in a circle and level out below a given altitude threshold that is relative to the launch altitude.

A better way to do a "manual" waypoint approach would be to use the WypointUser Flags and Programming framework to switch the plane into Heading hold + Angle and override the throttle with a value of 1000. So it will glide down while keep its heading at a specific waypoint. Or you use the "Is Landing" as the trigger for that to switch out of WP mode and set Heading hold + Motor cut as a sticky function. I would probably go for the latter.

So if I understand correctly for me to clear the 25m trees I need 30m approach altitude?

to be 100% safe for the altitude of 25m on the trees you would need 1.5*25m approach altitude. So approach altitude of 38m. Then you will pass the trees at 25m or more for sure.

[jaroszmm]

So the "Is Landing" in programming tab is basically the exact moment plane hits the LDG WP and instead of going into circular land it forces itself to 1. Disable mission mode 2. immediately enable angle (for level flight) plus heading hold to keep the course 3. kill throttle to glide into the ground?

[b14ckyy]

correct. That should be easily doable via programming. you can even program a flare at a certain altitude with pitch override but better only with lidar.
you are rebuilding my test program that I made 2 years ago for the autoland concept :D

[jaroszmm]

Okay, so for today the plan is like that:

Set my mission on a switch and to autoload on boot.
I wonder about that last WP LAND, if this will trigger some weird landing thing or that programming stuff that @b14ckyy mentions should work.
Or I could remove the LAND WP and just disarm the plane when I see it on approach towards me :D I mean, we are still talking about a situation where we have full RC link control.
Also I deleted any safehomes I had just to make sure they won't interfere.