Comprehensive System Identification of Ducted Fan UAVs - Cal Poly

Figure 4.4 – Simulink GUI Generated SweepOf note from Figure 4.4 is that the sweep does not have a fade in and fade outtime associated with it as was seen in Chapter 2, Figure 2.1. This is due primarily to thefact that for a 300 second sweep, the amount of energy going in to the system in the lowfrequency region needs to be high. In a piloted sweep, there is usually plenty of lowerfrequency data due to doublets and natural oscillation by the pilot. The parameters forthis sweep can be seen as entered in the GUI in Figure 4.3.From the start, sweeping the vehicle proved to be problematic within Simulink.The simulation environment is isolated and protected from naturally occurringoscillations and energy other than that of the sweep entered. Also, by the nature of thesimulation, all coupling is hard-wired directly into the simulation. This means that theaddition of noise to break up off-axis coupling will still show high degrees of correlationto on-axis inputs.The RUAV class of vehicles analyzed all use spinning propellers inside a duct forlift. With small vehicle inertias and very high speed propellers, gyroscopic couplingoccurs between pitch and roll. The angular momentum of the spinning propeller will- 108 -