1. 1) http://www.theorator.com/bills108/s309.html
2. 2) http://www.eurocopter.com/jrotor/69/friendcopter.html
3. 3) Caradonna, F. X., Kitaplioglu, C., McCluer, M., Baeder, J., Leishman, G., Berezin, C., Visintainer, J., Bridgeman, J., Burley, C., Epstein, R., Lyrintzis, A., Koutsavdis, E., Rahrier, G., Delrieux, Y., Rule, J. and Bliss, D.: A Review of Methods for the Prediction of BVI Noise, AHS Technical Specialists Meeting for Rotorcraft Acoustics and Aerodynamics, Williamsburg, VA, October 1997.
4. Free-Vortex Filament Methods for the Analysis of Helicopter Rotor Wakes
5. 5) Brentner, K. S. and Jones, H. E.: Noise Prediction for Maneuvering Rotorcraft, AIAA Paper 2000-2031, 2000.