Real-Time Aerodynamic Parameter Estimation Without Air Flow Angle Measurements

Frequency-Domain Method for Automated Simulation Updates Based on Flight Data

“…The detrending can be done using a batch method, where leastsquares estimates of the bias and linear trend with time are removed from the time series, or using a high-pass filter with break frequency set to 1∕T Hz, where T is the maneuver time length in seconds. The latter procedure has been used successfully for real-time parameter estimation in the frequency domain [13].…”

“…The estimated parameter covariance matrix is [10] Σâ Eâ − aâ − a T σ 2 P T P (13) where the fit error variance σ 2 can be estimated from the residuals v z − Pâ (14)…”

“…It is well known that angle of attack and sideslip angle data can be reconstructed using kinematic equations and measurements of translational accelerations, attitude angles, airspeed, and angular rates, and that the resulting reconstructed time series generally have bias and trend errors because of unknown initial conditions, steady wind, and bias errors in the measurements used for the data reconstruction [10,13]. However, because frequency-domain methods are not affected by bias and trend in the measured data, using frequencydomain methods for the modeling enables the use of reconstructed data for explanatory variables such as angle of attack and sideslip angle.…”

“…However, because frequency-domain methods are not affected by bias and trend in the measured data, using frequencydomain methods for the modeling enables the use of reconstructed data for explanatory variables such as angle of attack and sideslip angle. This idea was first conceived and used in [13] to solve the important practical problem of real-time aerodynamic parameter estimation without air flow angle measurements. The same idea can be applied for simulation updates using flight data in the frequency domain.…”

“…In contrast, conventional frequencydomain methods that employ frequency responses are inherently limited to linear dynamic models. Additionally, recent work on dynamic modeling in the frequency domain without air flow angle (alpha/beta) measurements [13] is used to enable simulation updates without air flow angle measurements in the flight data. This capability can be very important in situations where air flow angle measurements are of poor quality or are nonexistent, such as low-cost flight-test programs or dynamic modeling for rotorcraft in hover.…”