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.

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An ef cient technique is described to calculate the sensitivities of bandwidth and phase delay (de ned according to the ADS-33 speci cation) and poles of a helicopter with respect to the blade torsion stiffness GJ. The technique is based on the derivation of expressions for the sensitivities using chain rule differentiation of appropriate portions of the equations of motion. Two con gurations are studied, similar to the Eurocopter BO-105 and the Sikorsky UH-60. The study shows that the semi-analytical sensitivities are in excellent agreement with the corresponding nite difference-based sensitivities and that they are far less sensitive to step size. For the BO-105 con guration, phase bandwidth, gain bandwidth, phase delay, and poles are only weakly nonlinear functions of the torsion stiffness GJ, and therefore, linear approximations are accurate for broad variations of GJ. The same is mostly true for the UH-60 con guration, except that move limits are recommended for linear approximationsto the phase delay at low GJ. The new technique is computationally very ef cient. The additional cost of calculating the sensitivities is 4% of that of a complete linearized analysis, regardless of rotor con guration and ight speed. The gure is expected to apply also to sensitivities with respect to ap and lag stiffness. Nomenclature A= state matrix A nr = state matrix in nonrotating frame B = control matrix B nr = control matrix in nonrotating frame C = output matrix D = distance from level 1 boundary in ADS-33 requirement charts E I 2 , E I 3 = blade lag and ap bending stiffnesses G.i !/ = frequency-responsematrix G J = blade torsion stiffness M t , M l , M f = elastic moment components acting on the blade section p = generic design parameter p, q, r = fuselage roll, pitch, and yaw rates T = multiblade coordinate transformation matrix u = control vector v, w, Á = blade elastic displacements x = state vector y = output vector µ G = geometric pitch angle of the cross section (pitch control angle plus builtin twist) ¿ p = time delay ! BW = bandwidth