Sharif Digital Repository

It is well-known that helicopters descending fast may enter the so-called Vortex Ring State (VRS), a region in the velocity space where the blade's lift differs significantly from regular regions and high amplitude fluctuations are often present. These fluctuations may lead to instability and, therefore, this region is avoided, typically by increasing the horizontal speed. This paper researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel experiments. Moreover, we propose that the so-called Windmill-Brake State (WBS) or autorotation region should also be avoided for... 

Minimum variance control is an established method in control of systems corrupted by noise. In these cases, as it is not possible to directly control the actual value of the system variables, one aims to reduce the variations instead. However, when the system noises are non-Gaussian, this approach fails because non-Gaussian noise cannot be characterised by simple measures such as variance. In these cases, the Entropy is proposed as a generalisation of the variance measure and the control objective becomes that of minimising the Entropy. Previously a limited form of this problem has been solved using first order Newtonian methods. In this paper, the control objective is first expanded to also...