Decambering

Abstract: Apparatus and method for squaring and decambering at the assembly plant, and shimming at the job site, a thin metal door frame wherein the frame becomes an integral part of its own setting jig until installation, after which the semi-permanent setting jig is removed. Temporary jigs are used in the method to set the minimum door width tolerance and to square the frame elements.

Abstract: A recently developed post-stall aerodynamics prediction method has been improved for use in real-time simulation of aircraft flight dynamics. The aerodynamic prediction method models the boundary layer separation due to stall using an effective decambering on each wing section. The aerodynamics of the configuration is rapidly calculated using superposition of stored lift distributions, which allows the the method to be used in real-time flight simulation even for post-stall conditions. For a given aircraft state vector, the method predicts forces and moments on the configuration. This aerodynamics method is coupled with flight-dynamics equations of motion (EOM) such that the complete aerodynamics is solved at each time step of the solution of the flight EOM. At the current stage, the approach does not handle the effects of bodies, propeller-wash, and wake interference. These are to be incorporated in follow-on work.

Abstract: This paper presents a methodology for flight dynamics simulation inclu ding three-dimensional unsteady and post-stall aerodynamics. This is accomplished by integrating a decambering viscous correction into a linearized unsteady vortex lattice method. Coupling the aerodynamic model with the nonlinear rigid-aircraft equations of motion results in a low-order, medium-fidelity framework for flight dynamics simulation. The numerical studies first evaluate the im portance of unsteady aerodynamic effects on the dominant aircraft modes, illustrating the errors incurred on the prediction of the short period when quasi-steady approximations are employed. Next, the combined impact of unsteady and post-stall aerodynamics is assessed on a maneuvering aircraft. Furthermore, the framework is expected to be a suitable design-oriented tool for flight con trol synthesis and to incorporate aeroelastic modeling. I. Introduction High fidelity aerodynamic models implemented in the form of l ook-up tables [1‐3] are commonplace in certified flight simulators and training devices. Force and moment inf ormation for these look-up tables is commonly developed using some combination of the following techniques: Computational Fluid Dynamics (CFD), experimental testing of models in wind tunnels (static and dynamic), and/or experimental flight testing. Both CFD methods and data from experiments are capable of representing forces and moments in the nominal flight regime, where aerodynamics are expected to be linear, and beyond this range where significan t amounts of flow separation exist (aerodynamic stall). The primary disadvantage of using these high-fidelity repre sentations of forces and moments is the significant effort required to develop the look-up table. Each expected operating condition, defined not only by the aerodynamic inflow angles but also three components of angular rates, derivatives of these rates, and other explanatory variables as desir ed, must be run as a CFD or experimental test case to develop the look up table. It is often not feasible to perform such an extensive study due to limited resources, or because the required level of detail is simply not available at early conceptual design stages. The methodology presented in this research represents a departure from the high-fidelity approach discussed above. A medium fidelity aerodynamics model is considered, based on an unsteady vortex lattice method (UVLM) [4, 5] with a post-stall model based on iterative decambering [6, 7]. The UVLM is a fully unsteady, three-dimensional aerodynamic method, which is very accurate as long as potentialflow conditions are satisfied [ 8] ‐ in practice this requires low speed, attached flow. Howeve r, with increasing angles of attack, the boundary layer on the upper surface of a wing thickens and finally separates. If separation occurs, then potential-flow predictions deviate from the real viscous flo w. The underlying idea of the decambering methodology is that this mismatch due to the boundary-layer displacement thickness and separation can be related to an effective change in the chordwise camber. In other words, the goal is to match the potential-flow solution to the viscous one by introducing a decambering variable, which is effectively a camber correction ‐ it can also be seen as a rotation of the airfoil, modifying the effective angle of incidence to fit vi scous data. This idea has been around for several decades, but most recent progress can be found in Refs. [6, 9‐12]. While the scheme relies on a 2D airfoil data, 3D effects can be incorporated by accounting for the aerodynamic interference among all lifting-surface airfoils. This can be easily done on the UVLM, for instance, when enforcing the boundary conditions. A strip-theory philosophy for engineeringlevel predictions of wing aerodynamics at high angles of attack has been extensively adopted before [13‐17], leading

Abstract: The ability of low-order aerodynamic prediction methods, such as the vortex lattice method, to predict the force and moment characteristics of arbitrary wing geometries, including those with sweep, is well established for pre-stall conditions. Approaches to augment such methods by modeling the flow separation as an effective reduction in camber has allowed extension of the predictive capability to stall and post-stall conditions for unswept wings. Such approaches assume locally two-dimensional flow and use airfoil lift curves for the wing sections to provide the decambering corrections. For swept wings, spanwise pressure gradients cause tipward transport of the separated flow, resulting in modified stall behavior, with attached flow in the inboard regions and excessively separated flow outboard. As a result of this behavior, use of airfoil lift curves in the application of the decambering approach to swept wings results in poor prediction of stall characteristics. This paper explores the use of modified lift curves for the sections of swept wings, with modifications derived from analysis of RANS computational results. When these modified lift curves are used in the decambering approach, the low-order predictions for the swept wings are seen to agree well with RANS CFD predictions. The results indicate that the strip-theory approach is still applicable for swept wings provided the effect of spanwise redistribution of flow separation is correctly taken into consideration. This success provides impetus to develop an entirely predictive version of the low-order method.

Abstract: An automotive fan having flexible curved blades of resilient material which decamber as rotational speed increases in which an integral portion of each blade, having a mass of the order of 2 percent to 40 percent, preferably 8 percent to 10 percent, of the remainder of the blade, extends continuously along substantially the entire trailing edge of the blade and is folded upon itself at the trailing edge on the upstream side of the blade, thereby rigidifying and weighting the trailing edge to reduce vibration and noise and to assist the decambering of said blade at a predetermined rate.