Bubble level

I’ve noticed a handful of planes have bubble levels mounted to the top of the airframe. What is the purpose of this?

Hi There,
to make sure that the craft is armed on a level surface so that accelerometers/compass are calibrated properly and don’t cause an immediate flyaway by being armed on a incline.
(some folks are working on fixes that would make this caution unnecessary except during calibration…)


ps if telemetry/MinimOSD active no need for bubble level as this is covered in the displays

It’s more likely to be for checking centre of gravity as you tell the apm/pixhawk what level flight is when you do the initial accelerometer calibration. That’s the time the airframe has to be truly level.

I’ve taken off from a few different places with various inclines and I’ve never had a flyaway, and my plane is usually upside down when armed as it’s armed as soon as I plug in the battery.