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An analysis of numerical methods for extracting aerodynamic coefficients from dynamic test data has been conducted. The emphasis of the analysis is on the effects that random measurement errors in the data and random disturbances in the system have on the accuracy with which the coefficients for linear and nonlinear systems can be determined. Both deterministic and stochastic methods for extracting the coefficients and determining their uncertainties are considered. The deterministic technique considered, due to Chapman and Kirk, provides excellent estimates of both linear and nonlinear static pitching moment coefficients for the range of measurement efforts and system noise considered. Somewhat less accurate estimates of pitch damping coefficients are obtained. The stochastic approach considered demonstrates the feasibility of using an extended Kalman filter, with a parameter augmented state vector, for determining the values of the aerodynamic coefficients and their uncertainties from noisy dynamic test data. Parameter estimates obtained from the extended filter compare favorably with previously obtained results using deterministic techniques. Estimates of the parameter uncertainties provided by the filter are generally superior to those obtained with deterministic techniques particularly when system noise has corrupted the data.

1Eight Keys to Eden

By Mark Clifton

When Earth loses contact with the colony planet Eden, an expedition is sent to find out why. Even though the planet has been determined to have no hostile properties, the second expedition is astonished to find no evidence of the colony. The colonists are spread out, naked, wandering dazed among the bushes, with no sign of any of the technology they brought from Earth. - Summary by Dale Grothmann