Aerodynamic Modeling for Real-Time Flight Dynamics Simulation

Abstract

A low-order prediction method for post-stall aerodynamics of multiple-wing aircraft configurations was developed at NC State during 2003-06. The method is suitable for implementation in vortex lattice formulations. For post-stall conditions, it relies on the modeling of the trailing-edge flow separation due to stall using an appropriate camber reduction, or a “decambering”, at the section’s trailing-edge. The method uses an iterative approach to determine this decambering at all sections of the configuration, while ensuring that the boundary conditions are also satisfied everywhere. Recent work has resulted in speed improvements in the method and the coupling of the aerodynamic prediction with equations of motions for flight dynamics, resulting in the ability to simulate the aircraft flight dynamics at nominal and post-stall flight conditions faster than real-time. Current efforts are focused on validation of the low-order method at post-stall conditions using computational fluid dynamics studies of airfoils, wing, and configurations. Traditionally, simulations of flight dynamics make use of either linearizations and the use of aerodynamic stability derivatives [1] or the use of look-up tables generated for a given aircraft. Developing aerodynamic models in this fashion is configuration specific, and very often the models are only valid for a limited range of operating conditions. This paper presents the current status of an on-going effort at NCSU on augmenting linear aerodynamic prediction methods for use in real-time simulation of post-stall flight dynamics of multiplewing aircraft configurations. The post-stall prediction method is based on a decambering approach [2], developed at NC State in 2006 and made significantly faster [3] in 2008 using lift-distribution superposition principles. Given the instantaneous aerodynamic inflow angles and the angular-velocity components, the post-stall method predicts the aerodynamic forces and moments on the aircraft without the use of any empiricism. Inputs to the aerodynamic prediction method include planform-geometry details and lift, drag, and moment curves for all the airfoil sections including post-stall information. This paper, and previous studies have demonstrated the use of decambering in faster than real-time flight simulation. One aspect of the low-order aerodynamics that has not been explored in previous work is validation. Validation, focusing on the stall and post-stall regimes, is introduced in this paper. Due to the lack of experimental and computational post-stall aerodynamic data in the literature, CFD studies tailored for validation have been initiated in the current work. The current effort uses the NASA TetrUSS CFD package for this purpose. This paper begins with background on the decambering concept, and how it is applied in three dimensional aerodynamics. The recent efforts attempting to validate and improve the method using computational tools are discussed. Finally, results from real-time simulation are presented as well as future work directions for this effort.