Getting only vertical component from accelerometer

Question

Suppose we have a 3.axis accelerometer in an aircraft. I would always need to know what is the vertical component of acceleration (towards the earth) no matter how the aircraft is orientated. I know I can do this if I incorporate additional gyro sensor. But suppose we don't have it - is it possible to get only vertical accelearation some other way? Maybe with the use of additional magnetometer?

Answer 1

I would not recommend it for an airplane and I say it is an ugly hack but you can do something with an accelerometer.

The accelerometer readings are the direct measurement of the orientation assuming that the body's acceleration in the Earth's frame of reference is negligible and the body is not rotating fast. Basically this is what you asked for, this gives you the vertical component of the acceleration (aka gravity).

This is not too useful due to the assumptions.

Magnetometers would not help, it would only help you to find where North is but it won't remove the need for the above assumptions.

There are applications where the accelerometer and magnetometer readings together are enough, without the gyros. It is the case when the body is static and the task is to measure its orientation. I have implemented such an application and worked really nicely.