1. The Helicopter;Gregory,1976
2. The Helicopter;Gregory,1976
3. Theory of self excited mechanical oscillations of helicopter rotors with hinged blades;Coleman;NACA Report 1351,1957
4. The mechanical instability and forced response of rotors on multiple degree of freedom supports;Brooks;Ph.D. Thesis, Princeton University,1961
5. Helicopter ground resonance;Hooper;Aircraft Engineering,1959