Pitching moment

About: Pitching moment is a research topic. Over the lifetime, 3213 publications have been published within this topic receiving 38721 citations.

Flutter Stability of a Detuned Cascade in Subsonic Compressible Flow

Abstract: A mathematical model is developed to predict the unsteady aerodynamics of a detuned two-dimensional flat plate cascade in subsonic compressible flow. Aerodynamic detuning is introduced by nonuniform circumferential spacing and chordwise offset. Combined aerodynamic-structural detuning is accomplished by replacing alternate airfoils with splitter blades. A torsion mode stability analysis that considers aerodynamic and combined aerodynamic-structural detuning is developed by combining the unsteady aerodynamic model with a single degreeof-freedom structural model. The effect of these detuning techniques on flutter stability is then demonstrated by applying this model to a baseline unstable 12-bladed rotor and detuned variations of this rotor. This study demonstrates that detuning is a viable passive flutter control technique. Nomenclature A = cascade A airfoil index a — freestream speed of sound B - cascade B airfoil index CL = lift coefficient CM - moment coefficient C, = ratio of chord length of cascade B to cascade A CA = chord length of cascade A CB = chord length of cascade B ea = elastic axis location k - reduced frequency a>c/W n = airfoil index os - chordwise offset of cascade B relative to cascade A

CFD Analysis of the F/A-18E Super Hornet during Aircraft- Carrier Landing High-Lift Aerodynamic Conditions

Abstract: The goal of the current study was to determine if computational fluid dynamics is capable of accurately predicting the forces and moments on the F/A-18E Super Hornet at the high-lift aerodynamic conditions usually encountered during carrier landing. Past F/A18E computational studies have mainly focused on wind-tunnel scale calculations with the results being compared to existing wind-tunnel data. The calculations for this study were conducted at full scale and the results were compared to F/A-18E sim data where possible. The computational geometry included all of the flaps, control surfaces, shrouds and gaps usually present on the actual aircraft. During this study, static calculations were completed at various F/A-18E conditions along the path of an untrimmed longitudinal stick doublet maneuver. These calculations represent small, medium and large trailing-edge flap deflections. The results were compared to F/A-18E sim data. In addition, several static calculations were conducted for the F/A-18E trimmed with two different sets of control laws at three different longitudinal stick positions. Once again, these results were compared to F/A-18E sim data. Finally, a study was conducted to determine the effect of the trailing-edge flap deflection, aileron deflection and angle of attack on the F/A-18E forces and moments. A wide range of trailing-edge flap deflections was considered. Overall, the comparisons between the computational results and the sim data were favorable. However, the correlations for the pitching moment indicate that there is room for improvement. Traditionally, accurately predicting the pitching moment on the F/A-18E has been very challenging.

Measurement of Aerodynamic Forces on an Oscillating Airfoil

Abstract: : A literature survey was conducted to determine the state of the art of measuring and predicting aerodynamic characteristics of oscillating airfoils. Aerodynamic forces on a two-dimensional NACA 0012 airfoil oscillating sinusoidally in pitch were measured by two techniques. The forces were obtained from pressure measurements and by means of strain gage balances. Pressure measurements were made on the airfoil oscillating in pitch about the quarter-chord point at various mean angles of attack. Strain gage balance readings were obtained for models with pitch axis located at 25, 37, and 50 percent chord points oscillating about various mean angles. Direct force measurements were employed in an effort to obtain drag data. Instantaneous pressure distributions are presented for representative oscillating conditions.

Kinematics and aerodynamics of the velocity vector roll

Abstract: The velocity-vector roll is defined as an angular rotation of an airplane about its instantaneous velocity vector, constrained to be performed at constant angle of attack (AOA), no sideslip, and constant velocity. Consideration of the aerodynamic force equations leads to requirements for body-axis yawing and pitching rotations that must be present to satisfy these constraints. Here, the body-axis rotations and the constraints are used in the moment equations to determine the aerodynamic moments required to perform the velocity-vector roll. The total aerodynamic moments, represented in the reference body-axis coordinate system, are then analyzed to determine the conditions under which their maxima occur. It is shown, for representative tactical airplanes, that the conditions for maximum pitching moment are strongly a function of the orientation of the airplane, occurring at about 90 deg of bank in a level trajectory. Maximum required pitching moment occurs at peak roll rate and is achieved at an AOA in excess of 45 deg. The conditions for maximum rolling moment depend on the value of the roll mode time constant. For a small time constant (fast response) the maximum rolling moment occurs at maximum roll acceleration and zero AOA, largely independent of airplane orientation; for a large time constant, maximum required rolling moment occurs at maximum roll rate, at maximum AOA, and at 180 deg of bank in level flight. The maximum yawing moment occurs at maximum roll acceleration and maximum AOA and is largely independent of airplane orientation. Results are compared with those obtained using conventional assumptions of zero pitch and yaw rates and show significant improvement, especially in the prediction of maximum-pitching-moment requirements.