Abstract
Flow over an aircraft at high angles of attack is characterized by a combination of separated and vortical flows that interact with each other and with the airframe. As a result, there is a set of phenomena negatively affecting the aircraft’s performance, stability and control, namely, degradation of lifting force, nonlinear variation of pitching moment, positive damping, etc. Wind tunnel study of aerodynamic characteristics of a prospective transonic aircraft, which is in a canard configuration, is discussed in the paper. A three-stage experimental campaign was undertaken. In the first stage, a steady aerodynamic experiment was conducted. The influence of a reduced oscillation frequency and angle of attack on unsteady aerodynamic characteristics was studied in the second stage. In the third stage, forced large-amplitude oscillation tests were carried out for the detailed investigation of the unsteady aerodynamics in the extended flight envelope. The experimental results demonstrate the strongly nonlinear behavior of the aerodynamic characteristics because of canard vortex effects on the wing. The obtained data are used to design and test mathematical models of unsteady aerodynamics via different popular approaches, namely the Neural Network (NN) technique and the phenomenological state space modeling technique. Different NN architectures, namely feed-forward and recurrent, are considered and compared. Thorough analysis of the performance of the models revealed that the Recurrent Neural Network (RNN) is a universal approximation tool for modeling of dynamic processes with high generalization abilities.
Highlights
Modern transport airplanes use angles of attack close to stall during take-off and landing.Different trigger factors such as possible pilot mistakes, equipment faults and atmospheric turbulence and their combinations can cause loss of control, stall and spin
Many intensive studies are aimed at modeling of aerodynamics in the extended flight envelope in order to support investigations of aircraft dynamics, control system design [2] and to provide realistic pilot training using ground-based simulators in upset conditions [3,4]
Flow over an aircraft at high angles of attack is complicated by the dynamics of flow separation and reattachment, the development and breakdown of vortical flow, and their interaction with dynamics of the aircraft
Summary
Modern transport airplanes use angles of attack close to stall during take-off and landing. Where α is the angle of attack, x0 describes the steady dependency of x on α, and τ 1 and τ 2 are characteristic times of the flow structure development This approach was shown to be effective in accurate prediction of the unsteady aerodynamic effects, including unsteady flow over an airfoil with separation [18], a delta wing with vortex breakdown [19], and a maneuvering fighter aircraft [17]. One of the paper contributions is application of the phenomenological approach used in [17,20,21,27] in order to take into account nonlinear effects due to the complex canard-wing vortex flow in the nonlinear pitch moment coefficient model This model is used as a benchmark model and compared with the results obtained for the NNs. As concerns the phenomenological state-space model of unsteady aerodynamics, an ordinary differential equation is utilized to describe the effects associated with delay of the vortical flow formation. The results of the experimental data simulation using both the state-space and NN models are presented and compared
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