Sign ConventionChordwise moment, + tip toward trailing edge. Flap deflection, + trailing edge down. Flatwise moment, + tip up. Pitch link load, + in tension. Torsion moment, + leading edge up.

Neural network relationships between the full-scale, experimental hub accelerations and the componding pilot floor vertical vibration are studied. The present physics-based, quantitative effort represents an initial systematic study on the UH-60A Black Hawk hub accelerations. The NASNArmy UH-6OA Airloads Program flight test database was used. A "maneuvereffect-factor 0,'' derived using the roll-angle and the pitch-rate, was used. Three neural network based representation-cases were considered. The pilot floor vertical vibration was considered in the first case and the hub accelerations were separately considered in the second case. The third case considered both the hub accelerations and the pilot floor vertical vibration. Neither the advance ratio nor the gross weight alone could be used to predict the pilot floor vertical vibration. However, the advance ratio and the gross weight together could be used to predict the pilot floor vertical vibration over the entire flight envelope. The hub accelerations data were modeled and found to be of very acceptable quality. The hub accelerations alone could not be used to predict the pilot floor vertical vibration. Thus, the hub accelerations alone do not drive the pilot floor vertical vibration. However, the hub accelerations, along with either the advance ratio or the gross weight or both, could be used to satisfactorily predict the pilot floor vertical vibration. The hub accelerations are clearly a factor in determining the pilot floor vertical vibration. potation MEFManeuver effect factor, Equation The present study is the first systematic effort that considers hub accelerations in a quantitative manner, and attempts to identify numerical relationships between the hub accelerations and t?e fuelage vibrations. Also, this study was undertaken to obtain a better understanding of the basic dynamics underlying the main rotordependent fuselage vibration and the associated hub accelerations. The present study builds up on previous neural network studies that were conducted at NASA Ames in the areas of rotorcraft performance, acoustics, and dynamics (Refs. 2 to 8).Flight test data from the NASNArmy UH-60A Airloads Program (Refs. 9 and 10) were used in this study.Reference 4 studied the neural network based modeling of the UH-60A peak, 4P pilot floor vertical vibration (PW) for real-time applications. In Ref.

An analytical study is presented regarding the unsteady skin friction drag of an oscillating airfoil exposed to a fluctuating free stream speed. Both laminar and turbulent conditions are covered in the analysis. The unsteady potential flow pressure and velocity distributions required for the subsequent boundary layer analysis are obtained by an approximate development. The time-dependent boundary layer is solved by a finite difference scheme. It was found that depending on the values of the phase difference between free stream fluctuations and airfoil oscillations, reduced frequency, and amplitude of free stream fluctuations, the drag can either lead or lag the free stream.

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