Comprehensive System Identification of Ducted Fan UAVs - Cal Poly

Figure 3.14 shows how increasing the fan speed increases the pitching moment.By fitting lines to the data for 0 to 20 knots, a linear representation of the pitchingmoment derivative is obtained for this low speed condition. This is shown in Figure 3.14as dashed lines. The slopes of these lines are the dimensional derivatives. They aresummarized in Table 3.12. Figure 3.14 also shows that some critical velocity may existwhen the derivative will actually swing to negative. This is seen in the 1800 RPM case tobe around 70 fps.Table 3.12 – Pitching Moment Derivatives and Solotrek Fan SpeedFan Speed(rpm)Pitching Moment Derivative M u⎛ft-lb⎞⎜ ⎟⎜ft ⎟⎝ sec ⎠1,800 1.0342,200 1.3762,600 1.9333,000 2.589This wind tunnel testing was the extent of identification work completed for the Solotrekvehicle.- 47 -