WASET
    H. Bouadi and  M. Tadjine,  Nonlinear Observer Design and Sliding Mode Control of Four Rotors Helicopter.   journal   = {International Journal of Aerospace and Mechanical Engineering}, [online]. World Academy of Science, Engineering and Technology.
    July 2007, vol. 7(7). 329 - 334
    [viewed 25 April 2024]. Available from: https://publications.waset.org/pdf/1748.