Technological advances in areas such as battery technology, autonomous control, and ride-hailing services, combined with the scale-free nature of electric motors, have sparked significant interest ...

Tilt-Wing eVTOL Takeoff Trajectory Optimization

This paper focuses on full six degree-of-freedom aerodynamic modeling of small unmanned aerial vehicles at high angles of attack and high sideslip in maneuvers performed using large control surfaces at large deflections for aircraft with high thrust-to-weight ratios. Configurations, such as this, include many of the currently available propeller-driven radio-controlled model airplanes that have control surfaces as large as 50% chord, deflections as high as 50 deg, and thrust-to-weight ratios near 2∶1. Airplanes with these capabilities are extremely maneuverable and aerobatic, and modeling their aerodynamic behavior requires new thinking because using traditional stability-derivative methods is not practical with highly nonlinear aerodynamic behavior and coupling in the presence of high prop-wash effects. The method described outlines a component-based approach capable of modeling these extremely maneuverable small unmanned aerial vehicles in a full six degree-of-freedom real-time environment over the full...

Real-Time Flight Simulation of Highly Maneuverable Unmanned Aerial Vehicles

Impact of uncertainty in airfoil characteristics on wind turbine extreme loads

This paper presents selected results from an ongoing effort to develop an aerodynamic database from Reynolds-Averaged Navier-Stokes (RANS) computational analysis of airfoils and wings at stall and post-stall angles of attack. The data obtained from this effort will be used for validation and refinement of a low-order post-stall prediction method developed at NCSU, and to fill existing gaps in high angle of attack data in the literature. Such data could have potential applications in post-stall flight dynamics, helicopter aerodynamics and wind turbine aerodynamics. An overview of the NASA TetrUSS CFD package used for the RANS computational approach is presented. Detailed results for three airfoils are presented to compare their stall and post-stall behavior. The results for finite wings at stall and post-stall conditions focus on the effects of taper-ratio and sweep angle, with particular attention to whether the sectional flows can be approximated using two-dimensional flow over a stalled airfoil. While this approximation seems reasonable for unswept wings even at post-stall conditions, significant spanwise flow on stalled swept wings preclude the use of two-dimensional data to model sectional flows on swept wings. Thus, further effort is needed in low-order aerodynamic modeling of swept wings at stalled conditions.

/pdf/a-cfd-database-for-airfoils-and-wings-at-post-stall-angles-2u0mv6ct78.pdf

A CFD Database for Airfoils and Wings at Post-Stall Angles of Attack

This paper summarizes the status of ongoing NASA research supported over the past eight years to advance computational capabilities for modeling civil aircraft loss of control due to airframe damage or wing stall The research is motivated by a desire to exploit the capabilities of computational methods to create augmented flight simulation models that improve pilot training for such loss-of-control scenarios Flight of aircraft with either airframe damage or operating near and beyond the stall boundary encounters additional nonlinear aerodynamic influences on stability and control from dynamic motions that, if not included in flight simulation models, may lead to incorrect pilot responses In the present work, both low- and high-fidelity computational methods are explored for analyzing such nonlinearities The challenge of creating nonlinear reduced-order models from high-fidelity computational data is also addressed At the beginning, few guidelines were available for computing or modeling the dynamic s

Computational Aerodynamic Modeling Tools for Aircraft Loss of Control

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.

Justin L. Petrilli

Papers

A CFD Database for Airfoils and Wings at Post-Stall Angles of Attack

Computational Aerodynamic Modeling Tools for Aircraft Loss of Control

Aerodynamic Modeling for Real-Time Flight Dynamics Simulation