I am currently reading up on inertial measurement in aircraft systems. Euler angles are one of the concepts I am a bit confused with. In an Euler angle-rate matrix there seem to be 3 parameters: p, q, and r. From what I understand about this we are talking about 3 values that each represent the rotation around an axis with reference to a base/mount.
My question is, does each of the parameters p, q, and r represent a particular axis? If so, what do each of the parameters represent (in terms of either x, y, and z or pitch, roll, and yaw)?
Here are some references to what I've been reading through: