Decambering

Abstract: A cooling fan formed of two sheet metal layers joined to a centrally contained spider arm. The configuration of the resulting blade is streamlined or an airfoil in cross section. In constructing the fan the surface pieces are normally spaced from the central support arm and during assembly are forced together and joined to the arm. The resulting stress imposed on the leading and trailing edges of the surface sheets reduces vibratory stresses in the blade. In one embodiment the trailing edge of one of the sheets is permitted to slide along the surface of the other sheet when the other sheet is decambering due to centrifugal and aerodynamic forces generated by rotation of the fan. The result is to vary the moment arm of the restraining forces imposed on the decambering trailing portion of the flexing sheet, thus giving better control of the decambering rate of that sheet.

Abstract: The present invention relates to a device for de-cambering paper conveyed from a fixing station and presenting a convex or concave cambering caused by the fixing operation, the cambering direction being parallel to that of the paper transport. The decambering device contains one adjustable element (12) intended to eliminate the convexity, combined with an adjustable element (2, 4, 6, 8) designed to eliminate the concavity. The paper to be de-cambered runs through both elements.

Abstract: T HE simplicity and utility of Gurney flaps have resulted in a sustained research effort to characterize their behavior. Studies have elucidated effects of their length [1–5], location [6], orientation [6], and shape [7,8]. The impact of a Gurney flap is analogous to a conventional trailing-edge lift-augmentation device, primarily, a shift in the zero-lift angle of attack. This is accomplished through the flap functionally increasing aft camber, and thus, turning of the wake flow. The flap causes a finite pressure difference at the trailing edge (maintained through base suction imposed by a vortex street shed from the flap extents [9]) with final pressure recovery occurring in the wake. Consequently, a Gurney flap does not increase the adversity of the upper-surface pressure-recovery demands placed on the boundary layer. Thus, unlike a conventional trailing-edge flap, the stall angle is generally not reduced. An analytic study by Liu and Montefort [10], using thin-airfoil theory, showed that the lift increment and shift of the zero-lift angle of attack of a Gurney flap are dependent on h∕c . The experimental correlation of this result is well documented [1,2]. In addition to the shift of the zero-lift angle of attack, the Gurney-flap data have also indicated an increase in the lift-curve slope of the lifting element [2–4,11,12]. It has been suggested that the slope increase is due to windward-side boundary-layer thinning with incidence causing an effective increase in flap length [11]. The flap can also attenuate the adversity of the suction-surface pressure recovery, yielding a reduction in displacement thickness and, consequently, viscous decambering of the section with incidence. Because of the continuing interest in Gurney flaps, it would be useful to the community to have a simple relation that can estimate the lift augmentation resulting from theGurney-flap addition suitable for conceptual analysis. In this Note, a semi-empirical equation is presented that allows lift estimates accounting for both the zero-lift angle-of-attack shift and the increase in the lift-curve slope. After presentation of the expression, experimental data are analyzed to establish the required empirical constants. Subsequently, numerous comparisons with sectional and wing data are presented to validate the equation’s utility.

Abstract: A multidisciplinary research e.ort that combines aerodynamic modeling and gain-scheduled control design for aircraft flight at post-stall conditions is described. The aerodynamic modeling uses a decambering approach for rapid prediction of post-stall aerodynamic characteristics of multiple-wing con.gurations using known section data. The approach is successful in bringing to light multiple solutions at post-stall angles of attack right during the iteration process. The predictions agree fairly well with experimental results from wind tunnel tests. The control research was focused on actuator saturation and .ight transition between low and high angles of attack regions for near- and post-stall aircraft using advanced LPV control techniques. The new control approaches maintain adequate control capability to handle high angle of attack aircraft control with stability and performance guarantee.

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.