I'm given to understand that the RAP test is used to identify any new natural frequencies of helicopter with the spray kit installed compared to helicopter without the kit. In order to demonstrate compliance with applicable requirements (FAR-27 & AC27-1B) the exercise should demonstrate that the new frequencies are not shifted towards helicopter rotating element frequencies (main rotor, tail rotor and others) and their harmonics. The research I have managed to conduct so far suggests that a transducer is attached to the various elements. This in turn is connected to a spectrum analyser. The attaching parts are then tapped (hammer?)and the resulting vibrations recorded by the spectrum analyser. This is beyond the scope of our normal activities hence the potential requirement for a specialised organisation.