An Integrated, Modular Simulation System for Education ... - Cal Poly

frequency analysis is a oscillation of the controls starting at a low frequency thenprogressing to as high a frequency as the pilot can attain without exceeding strict safetylimits. The maneuver is called a CHIRP. Note that in figure 30 the input the magnitudestays constant while in the output the magnitude drops off. This is characteristic for adamped second order system. On the right of the figure is the Frequency plot (bode plot)processed by CIFER. Compare the bode plot from CIFER to the bode plot in Figure 29.Note that in the Figure 29 the magnitude line breaks down and then stays slanted. In theCIFER plot the magnitude line breaks back up. This is incorrect. However notice thethird coherence plot. Coherence is a measure of the linearity of the system, the accuracyof the output data at the corresponding frequency. The same frequency where thecoherence plot breaks downward is the frequency that the magnitude breaks upward. Thecoherence plot tells the user that where the magnitude breaks upward the data is nolonger valid. CIFER is also able to fit a low order [first or second order] transfer functionto the bode plot. The original transfer function was obtained by doing a second order fitto the frequency data within the frequency range where the coherence was at or close toone. Given a complete set of control inputs and outputs, CIFER can create a full set ofdimensional stability derivatives and state space model.To demonstrate the procedure for creating, converting moving and processingCHIRP data using CIFER a Simulink model was created to produce the time history filesand several programs were created to save and convert the output data to a format CIFERuses for input.CIFER requires a binary file with a separate file for each control and response.Each file contains a column of numbers representing the position of the control or theacceleration or angular rate of the airframe. To demonstrate the procedure for collecting79