Hi Balazs
The ZHAW (Switzerland) identified the airframe stability parameters in manual flight by analyzing the Paparazzi flight logs. The airframe resonance frequencies can be measured by flying nicely trimmed straight and level and giving a short manual disturbance in the according axis.
To measure the pitch resonance frequency you give a short impulse on the elevator and then measure the frequency of the airplanes nose going up and down. That works same for the yaw axis using the rudder. The roll axis is a bit more difficult, as it is not stable on many airframes and the oscillation mixes with the other axes.
Regards
Reto