It is common for aircraft to encounter atmospheric turbulence in flight tests.Turbulence is usually modeled as stochastic process noise in the flight dynamics equations.In this paper,parameter estimation of nonlinear ...It is common for aircraft to encounter atmospheric turbulence in flight tests.Turbulence is usually modeled as stochastic process noise in the flight dynamics equations.In this paper,parameter estimation of nonlinear dynamic system with both process and measurement noise was studied,and a practical filter error method was proposed.The linearized Kalman filter of first-order approximation was used for state estimation,in which the filter gain,along with the system parameters and the initial states,constituted the parameter vector to be estimated.The unknown parameters and measurement noise covariance were estimated alternately by a relaxation iteration method,and the sensitivities of observations to unknown parameters were calculated by finite difference approximation.Some practical aspects of the method application were discussed.The proposed filter error method was validated by the flight simulation data of a research aircraft.Then,the method was applied to the flight tests of a subscale aircraft,and the aerodynamic stability and control derivatives were estimated.All the estimation results were compared with the results of the output error method to demonstrate the effectiveness of the approach.It is shown that the filter error method is superior to the output error method for flight tests in atmospheric turbulence.展开更多
This paper presents the power-off, lateral-directional wind tunnel tests on the fixedwing, 19-passenger aircraft model developed within the Italian PROSIB project. The concept is an innovative small air transport airp...This paper presents the power-off, lateral-directional wind tunnel tests on the fixedwing, 19-passenger aircraft model developed within the Italian PROSIB project. The concept is an innovative small air transport airplane with distributed propellers and hybrid-electric powerplant. By measuring the aerodynamic forces and moments, the experimental investigation focused on the estimation of the power-off stability and control derivatives, highlighting the effects of the aerodynamic interference. Tests included a belly-mounted pod, simulating a battery storage unit, and two distinct empennage configurations: a body-mounted(low) horizontal tail and a T-tail(high). Numerical analyses were also used to further highlight the role of aerodynamic interference in the generation of forces and moments. For instance, wind tunnel data have shown a beneficial effect of the belly pod on the aircraft directional stability(+13%), but were in contrast with the results of numerical analyses(-30%). The measured sidewash depends also from the empennage layout, not only from the vertical tail planform area. Simulations confirmed an excessive directional stability with respect to the directional control in the ratio of 1.65, suggesting that such class of airplane should have a larger rudder chord ratio or a horn balance. Combined tests at different angles of attack and flap deflections revealed some issues on the lateral stability of the model, which are related to the velocity circulation on the wing in high-lift conditions counteracting the effective dihedral of the model's layout. The collected dataset of aerodynamic derivatives will serve as reference for a next experimental investigation on the aero-propulsive effects and provide useful information to researchers and professionals involved in similar design studies.展开更多
基金supported by the National Natural Science Foundation of China(No.11802325)。
文摘It is common for aircraft to encounter atmospheric turbulence in flight tests.Turbulence is usually modeled as stochastic process noise in the flight dynamics equations.In this paper,parameter estimation of nonlinear dynamic system with both process and measurement noise was studied,and a practical filter error method was proposed.The linearized Kalman filter of first-order approximation was used for state estimation,in which the filter gain,along with the system parameters and the initial states,constituted the parameter vector to be estimated.The unknown parameters and measurement noise covariance were estimated alternately by a relaxation iteration method,and the sensitivities of observations to unknown parameters were calculated by finite difference approximation.Some practical aspects of the method application were discussed.The proposed filter error method was validated by the flight simulation data of a research aircraft.Then,the method was applied to the flight tests of a subscale aircraft,and the aerodynamic stability and control derivatives were estimated.All the estimation results were compared with the results of the output error method to demonstrate the effectiveness of the approach.It is shown that the filter error method is superior to the output error method for flight tests in atmospheric turbulence.
基金funded by the Italian PROSIB (Propulsione e Sistemi Ibridi per velivoli ad ala fissa e rotante-Hybrid Propulsion and Systems for fixed and rotary wing aircraft) project PNR 2015-2020 ARS01_00297 led by Leonardo S.p.A
文摘This paper presents the power-off, lateral-directional wind tunnel tests on the fixedwing, 19-passenger aircraft model developed within the Italian PROSIB project. The concept is an innovative small air transport airplane with distributed propellers and hybrid-electric powerplant. By measuring the aerodynamic forces and moments, the experimental investigation focused on the estimation of the power-off stability and control derivatives, highlighting the effects of the aerodynamic interference. Tests included a belly-mounted pod, simulating a battery storage unit, and two distinct empennage configurations: a body-mounted(low) horizontal tail and a T-tail(high). Numerical analyses were also used to further highlight the role of aerodynamic interference in the generation of forces and moments. For instance, wind tunnel data have shown a beneficial effect of the belly pod on the aircraft directional stability(+13%), but were in contrast with the results of numerical analyses(-30%). The measured sidewash depends also from the empennage layout, not only from the vertical tail planform area. Simulations confirmed an excessive directional stability with respect to the directional control in the ratio of 1.65, suggesting that such class of airplane should have a larger rudder chord ratio or a horn balance. Combined tests at different angles of attack and flap deflections revealed some issues on the lateral stability of the model, which are related to the velocity circulation on the wing in high-lift conditions counteracting the effective dihedral of the model's layout. The collected dataset of aerodynamic derivatives will serve as reference for a next experimental investigation on the aero-propulsive effects and provide useful information to researchers and professionals involved in similar design studies.
