Using sonar as "radio altimeter"

If I am correctly informed the Ardupilot for planes currently does not support sonar sensor for height measurements ( though the Arducopter and ArduRover do). Has it not been considered for ArduPlane?

I imagine it would allow for much more sophistication in flare control for auto landings. Especially in situations where the plane will not land at the launch site (altitude known) but at other location (e.g. race point).

The sonar height would also be really useful for certain low level flight scenarios, e.g. flying FPV a few meters above water, particularly when it is calm.

Furtermore the sonar height could be utilized for flight phase identification / verification, which in turn can be utilized for control and protection logics (for landing gear status, ground spoiler / brake chute arming, speed target, etc…). Pretty much the way it’s done in advanced full scale aircrafts (using radio altimeters). :geek:

Hi Snurre,
I’ve been experimenting with sonar for APM:Plane and posted my first results yesterday.
See this thread on drones-discuss
I’m planning on adding sonar support for a future release. There are a few issues though:
[ul]doppler shift on due to high relative speed of plane and ground
prop wash
only seems to trigger reliably at below 4.5m
doesn’t work at all on grass (needs solid surface)
Cheers, Tridge

I’ve also tried the sonar sensor and ran into problems mainly it gave a lot of false readings as speed built up and wouldn’t work over grass. I’ve got a microwave range sensors (used in shops, etc to open doors when people approach) on order.

Hi Tridge and @priseborough

Yes, I just discovered this as an GitHub issue… so it has been on the agenda for a while.
I must confess my own encounters with sonar on the ArduCopter multirotor was very discouraging. I never got it to work well, due to many reasons. It´s like it needed several tech workarounds and a good deal of black magic to make it work.
But in theory it is awsome :laughing:

Paul, I look forward to learn about the experiences from the microwave sensors.