1. W.G. Bousman, D.L. Sharpe, R.A. Ormiston, An experimental study of techniques for increasing the lead-lag damping of soft inplane hingeless rotors, 32nd Annual National V/STOL Forum of the American Helicopter Society, Washington, DC, May 1976.
2. T.K. Caughey, M.E.J. O'Kelly, General theory of vibration of damped linear dynamic systems, Dynamics Laboratory, California Institute of Technology, Pasadena, California, June 1963.
3. R.P. Coleman, A.M. Feingold, Theory of self-excited mechanical oscillations of helicopter rotors with hinged blades, NACA Report 1351, 1958.
4. An experimental investigation of the stability of a bearingless model rotor in hover;Dawson;J. Amer. Helicopter Soc.,1983
5. Ground and air resonance characteristics of a soft inplane rigid rotor system;Donham;J. Amer. Helicopter Soc.,1969