# RMS Lift

Hi,

I have a time vs lift Coefficient vector, and it looks periodic when vortex shedding on an obstacle through a transversal flow is placed.

How do I calculate the rms of that lift coefficient?

Hi,

I guess your question is not about how to calculate the root mean square of a scalar signal (which is well explained on e.g. Wikipedia), but rather how to calculate the rms of a vector signal. This is a tricky question since RMS can only be performed on a scalar signal, so you need to figure out what scalar quantity you want to get out of your vector.

It’s hard to make any suggestions without knowing why you would want the RMS lift. It doesn’t help that I don’t really know any aerodynamics. Anyway here are three suggestions, where I’ll assume that the lift vector is called a:

1. You could take the RMS of the magnitude of the lift, |a|
2. You could take the RMS of the component of the lift which is normal to the surface being lifted, a_n
3. You could take the RMS of each spatial component of the lift separately, a_x, a_y, and a_z

I hope this is useful in some way!