Comprehensive System Identification of Ducted Fan UAVs - Cal Poly

cause a pitching moment to be exerted on the vehicle when its angular momentum vectoris moved in roll. The reverse is true if moved in pitch; a rolling moment is produced. Thiseffect is apparent in the stability derivatives M p and L q . Due to sign conventions instandard helicopter coordinate systems, M p will be a positive value and L q will benegative. It is these gyroscopic effects that make simulating a sweep through the vehicledifficult. They directly correlate the roll and pitch controls and make it difficult forCIFER, or any identification tool to determine which input is creating which output. Thiswas seen when the MAV vehicle was flight tested. The actual flight test data revealedcorrelation and cross-control coherence between the roll and pitch commands. This isshown in Figure 4.5.1COHERENCE0.60.20.1 1FREQUENCY (RAD/SEC)10 100Cross Coherence between Pitch and RollFigure 4.5 – MAV Flight Test Cross Coherence between Pitch and Roll controlsIt is readily evident that there is a large amount of coherence at some gyroscopic modebetween 2 ~ 7 rad/sec.- 109 -