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This paper describes a study in which structural optimization techniques are used to minimize the /i/rev vertical hub shears in forward flight, subject to aeroelastic stability constraints in hover and frequency placement constraints. A special technique is used to build a sequence of approximate inexpensive to solve optimization problems, the solutions of which converge to the solution of the exact expensive to solve optimization problem. Blade configurations with both straight and swept tips, and single-and double-cell cross sections are analyzed. The results show that the approach used in this study is very efficient and produces improved designs with a very small number of blade aeroelastic analyses.

The paper presents a study of the flight dynamics of an articulated rotor helicopter carrying a suspended load. The aircraft model includes rigid body dynamics, individual flap and lag blade dynamics, and inflow dynamics. The load is a point mass with a single suspension point. Results were obtained for load masses of up to 2000 kg, with load-tohelicopter mass ratios of up to 28%, cable lengths from 3 to 8 m, turn rates of up to 16 deg/sec, and advance ratios of up to 0.3. The load affects trim primarily through the overall increase in the weight of the aircraft; the influence of cable length is negligible. Substantial coupling can occur between the Dutch roll and the load modes. Because of this coupling, the Dutch roll damping can decrease with a deterioration of handling qualities. The effects on the phugoid are very small. A suspended load modifies the roll frequency response by adding a notch to the gain curves and a 180-degree jump in the phase curves at the pendulum frequencies of the load. The changes in bandwidth and phase delay are small. Notation a L Absolute acceleration of the suspended load, Eq. (4). D Aerodynamic force vector acting on the load, Eq. (6). F H Force applied by the load to the helicopter, Eq. (8). f L Vector of load equations of motion, Eq. (7). i B , j B , k B Unit vectors of the body axis coordinate system (Figure 1). i G , j G , k G Unit vectors of the gravity axis system; the k G vector is directed along the vertical. i H , j H , k H Unit vectors of hook coordinate system (Figure 1). l Cable length. m Mass of the suspended load. n T Load factor. p, q, r Roll, pitch, and yaw rate of the helicopter. R H Position vector of the suspension point with respect to the aircraft CG, Eq. (2). R L Position vector of the load with respect to the suspension point, Eq. (1). S L Equivalent flat plate area of the suspended load. x H , y H , z H Components of the position vector of the suspension point with respect to the aircraft center of mass (Figure 1). Greek Symbols and Subscripts θ L , φ L Coordinates of the suspended load (Figure 1). θ F , φ F Pitch and roll angle of the fuselage. µ Advance ratio.

This paper presents an inverse simulation methodology based on numerical optimization. The methodology is applied to a simplified version of the slalom maneuver in the ADS-33D helicopter handling qualities spec-

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A special fmite element for the modeling of a swept tip rotor blade is derived. The swept tip blade undergoes moderate deflections in flap, lag, and torsion. The nonlinear, partial differential equations of motion are discretired using a Galerkin Cite element method. Tip sweep introduces flap-torsion and lag-axial couplings, and may lead to aeraelastic instabilities associated with frequency coalescence. When frequency coalcsccnce does not occur, sweep is usually stabilizing. A comparison of the approximate model of a swept tip blade (using a blade with straight elastic axis and offsets of aerodynamic centers of gravity) with the exact swept tip model developed in this paper indicates that the approximate model can produce inaccurate results for the case of hingeless rotor blades.

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