Unsteady Aerodynamic Modeling in Roll for the NASA Generic Transport Model

Abstract

Reducing the impact of loss-of-control conditions on commercial transport aircraft is a primary goal of the NASA Aviation Safety Program. One aspect in developing the supporting technologies is to improve the aerodynamic models that represent these adverse conditions. Aerodynamic models appropriate for loss of control conditions require a more general mathematical representation to predict nonlinear unsteady behaviors. In this paper, a more general mathematical model is proposed for the subscale NASA Generic Transport Model (GTM) that covers both low and high angles of attack. Particular attention is devoted to the stall region where full-scale transports have demonstrated a tendency for roll instability. The complete aerodynamic model was estimated from dynamic wind-tunnel data. Advanced computational methods are used to improve understanding and visualize the flow physics within the region where roll instability is a factor. Nomenclature

Hybrid Wing Body Model Identification Using Forced-Oscillation Water Tunnel Data

“…This approach allows for the inclusion of nonlinear behaviors and unsteady behaviors. The method takes advantage of indicial models that have been successfully applied to both transports and fighter aircraft over many years [5][6][7][8][9][10][11][12][13][14][15] . An advantage of the method is that the models retain conventional static and dynamic terms but replace conventional acceleration terms with indicial functions.…”

Upset Dynamics of an Airliner Model: A Nonlinear Bifurcation Analysis

“…[11] suggests that it may arise from wing stall or flow fields emanating from the forebody. There is ongoing research to establish whether wing stall is the probable cause for roll asymmetry [48]. The very small difference in alignment angles between the two engines was incorporated into the engine model on the basis of measurements from the 5.5% scale flight vehicle.…”

Aerodynamic Modeling for Poststall Flight Simulation of a Transport Airplane

“…The phenomenon of wing autorotation is the result of the development of asymmetric flow separation over the wing, which is induced by angular rotation around velocity vector V. The task of aerodynamic modeling requires the availability of suitable aerodynamic data and an appropriate structure of the aerodynamic model. Current efforts in aerodynamic modeling for transport airplanes in the extended flight envelope [4][5][6][7][8][9][10][11][12] largely rely on previously established modeling principles for combat aircraft [13][14][15][16]. The latter have generally been based on the use of wind-tunnel data from static, forced oscillation, and rotary balance tests [13][14][15]; free-spin tests in vertical wind tunnels [7,13]; and large-scale free-flight model tests [17].…”

“…The effect of unsteadiness of the motion is in some ways similar to that of the Reynolds number; for example, the increase in the maximum lift coefficient is proportional to the rate of change of the angle of attack _ α [18]. To capture unsteady aerodynamic effects due to delays in the development of flow separation, a number of phenomenological modeling methods have been proposed [8,9,[22][23][24]. Phenomenological modeling describes empirical relationships between the aerodynamic coefficients and motion parameters of the airplane.…”

“…A nonlinear unsteady aerodynamic modeling approach is beyond the scope of this paper; however, the reader can find examples of phenomenological aerodynamic models identified using test data from wind tunnels and CFD simulation results in Refs. [9,22,25,26].…”