Simulation and Flight Evaluation of a Parameter Estimation Input Design Method for Hybrid-Wing-Body Aircraft

Abstract

As part of an effort to improve emissions, noise, and performance of next generation aircraft, it is expected that future aircraft will make use of distributed, multi-objective control effectors in a closed-loop flight control system. Correlation challenges associated with parameter estimation will arise with this expected aircraft configuration. Research presented in this paper focuses on addressing the correlation problem with an appropriate input design technique and validating this technique through simulation and flight test of the X-48B aircraft. The X-48B aircraft is an 8.

Frequency Response Estimation for Multiple Aircraft Control Loops Using Orthogonal Phase-Optimized Multisine Inputs

“…Note that the number of excitations must equal the number of system inputs to be able to compute the matrix inverse in Equation (11). This process produces an unbiased estimate of the frequency response for an open-loop system from closed-loop data.…”

“…Figure 5a shows the resulting outer elevator to pitch rate frequency response. The solid markers correspond to the JIO estimates, computed with Equation (11), and match the true system dynamics, which are drawn with a solid red line. The open markers were computed with the direct approach in Equation ( 9) and were incorrect due to the correlated elevator deflections.…”

“…In traditional tests for aircraft system identification, one input of interest is excited at a time in a sequential manner, while the output measurements are observed and recorded. Examples include the Rockwell-MBB X-31A [9,10], the Boeing X-48B [11][12][13], the Grumman X-29A [14], the Bell XV-15 [15], and the Learjet LJ-25D [16]. For instance, when identifying the closed-loop dynamics, the pilot longitudinal stick could be used for one maneuver, then the pilot lateral stick could be used for a second maneuver, and lastly the rudder pedals could be used for a third maneuver.…”

Flight Test of Orthogonal Square Wave Inputs for Hybrid-Wing-Body Parameter Estimation

“…Prior research has involved using aerodynamic models to reduce the number of parameters being estimated in order to de-correlate inputs. 3 Other research has used time separation to de-correlate inputs 2 or sine waves that are mutually orthogonal in the frequency domain. 4 This paper presents an approach that uses square wave inputs that are mutually orthogonal in the time domain.…”

“…Isolating the aircraft response due to each control surface becomes difficult with large numbers of nearly coplanar control surfaces operating in a closed-loop flight control system. 2 Due to correlation problems, analysis of these aircraft will require advances in parameter estimation tools and methods to enable validation of aerodynamic models, simulations, and control laws.…”