Flight Dynamics of an Articulated Rotor Helicopter with an External Slung Load

Abstract

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.

Trajectory control of a class of articulated aerial robots

“…The position dynamics is decoupled and results in the standard form (10). The relation (11) is the Legendre transform from momenta µ " B ω L and ν " B 9 r L to velocities.…”

“…A related problem studied previously deals with the dynamics of helicopters with external slung loads (e.g. [10]). …”

Dynamic Stability of a Helicopter with an External Suspended Load

“…The state space model derives from the full-state linearization and condensation to fuselage states of the nonlinear rigid blade model used in Ref. 12. The main helicopter characteristics are reported in Table 1.…”

“…Since the focus of the analysis is on low speed and the suspension line has a negligible weight with respect to the load, the cable is modeled as inextensible, weightless and does not contribute to drag (Ref. 12).…”

Effects of Automatic Flight Control System on Chinook Underslung Load Failures

“…A more recent study of (Cicolani, Kanning& Synnestvedt, 1995) developed a comprehensive approach for slung-load modelling where generic simulation models for a tandem helicopter capable of carrying load in single or multiple points with one, two or more helicopters were investigated. (Fusato, Guglieri & Celi, 2001) developed a body-flap-lag model to study the flight dynamics of a single-rotor helicopter carrying a single-point suspended load, showing that the load affects trim primarily through the overall increase in the weight of the aircraft; the influence of cable length was negligible. (Stuckey, 2002), using the equations of motions developed by (Cicolani, Kanning& Synnestvedt, 1995) and an open-loop control for pilot modelling, developed a piloted simulation model for a tandem helicopter capable of carrying a mixed density slung loads.…”