Noise of counter-rotation propellers with nonsynchronous rotors

Counter-rotating propeller rotors, when run at different speeds, give rise to a noise spectrum-splitting phenomenon whose rotor-alone and interaction tones can be discriminated. Tabular data are presently given for such a rotor system, indicating mode behavior with frequency near the blade passing frequency and at twice that frequency. The mode-splitting behavior is found to constitute a powerful technique for noise source diagnoses in counter-rotating propellers.