A review of airship structural research and development

Airship dynamics modeling: A literature review

A new dynamics modeling approach is proposed for flexible airships, which integrates the flight dynamics, structural dynamics, aerostatics, and aerodynamics. In particular, a comprehensive aerodynamic computation is presented, including the potential-flow aerodynamics, the viscous effects, the forces on the fins, the forces on the hull due to the fins, and the axial drag. The coupling between flexibility and aerodynamics is incorporated through the local velocity of the deformed airship. The resulting dynamics model is represented by a single set of nonlinear ordinary differential equations, describing the rigid-body motion, the elastic deformation, and the coupling between them. This model has been implemented and used to simulate the Skyship-500 airship. Simulation results demonstrate the effects of structural flexibility on the aerodynamic and dynamic characteristics of the vehicle. These results reveal that strong coupling exists between the roll rotation and the bending deflection in the lateral plane, and that the natural frequencies of the airship in air are much lower than those in vacuum. In addition, the nonlinear dynamics model is numerically linearized to investigate the aeroelastic stability of the airship.

/pdf/dynamics-modeling-and-simulation-of-flexible-airships-3q5zqoh7qp.pdf

Dynamics Modeling and Simulation of Flexible Airships

An aerobot for global in situ exploration of Titan

Study on static and dynamic characteristics of an axial fan with abnormal blade under rotating stall conditions

LTA Aerodynamic Data Revisited

The application of complex coordinates to the study of the dynamic characteristics of the tip-pathplane of a helicopter rotor is considered. The coordinates describing rotor blade motions can be transformed from individual blade flapping angles to linear combinations of flapping angles. Two of the transformed coordinates can be interpreted as describing the tilting motion of the tip-path-plane. In a stationary reference frame, these two new coordinates are coupled. However, by defining a set of complex coordinates, for near hovering flight these two coupled differential equations can be combined into a single second-order differential equation describing the tilting motion of the tip-path-plane. This formulation provides a convenient and natural framework for investigation of the response characteristics of fully articulated and hingeless rotors. Considerable insight into the influence of various physical parameters on the behavior of the tip-pathrplane can be gained. The approach is illustrated by consideration of the transient and frequency response characteristics of the tip-pathplane and the influence of flapping feedback. An extension of the root locus method is described which makes the investigation of flapping feedback convenient. Nomenclature! a - rotor blade lift curve slope b = number of blades A(s) = transfer function c = rotor blade chord Ci = rotor hub rolling moment coefficient, positive for right roll, Ci = L/pKR2(VR)2R Cm — rotor hub pitching moment coefficient, positive nose up, Cm = M/pirR2(QR)2R Cmz = complex rotor hub moment coefficient, Cmz— Cm + iCi /i = rotor blade flapping moment of inertia j = constant of proportionali ty between complex inflow and complex rotor aerodynamic hub moment coefficient KH = gain parameter associated with integral flapping feedback Kp,e = parameters associated with proportional flapping feedback mz — dimensionless aerodynamic moment acting on rotor blade due to forward speed. Effect of cyclic pitch, angular rates and flapping not included p = rotor blade natural frequency in flapping divided by rotor rpm, also roll rate nondimensionalized by rotor rpm, positive roll right q = pitch rate nondimensionalized by rotor rpm, positive nose up

Complex Coordinates in Near Hovering Rotor Dynamics

A series of experiments were conducted with a dynamically scaled free-flight model of a unique hybrid heavylift vehicle, the Aerocrane, to determine its stability and control characteristics. A theoretical model was developed to predict these characteristics which showed very good agreement with experiment. The results of a study of the precision hover capabilities of the Aerocrane, based on this theoretical model, are described. It is shown that the precision hover capabilities are similar to those predicted for helicopters which can lift a comparable payload.

Stability and Control Characteristics of the Aerocrane Hybrid Heavy-Lift Vehicle

References 1 Fry, B. L. and Zabinsky, J. M., "Feasibility of V/STOL Concepts for Short-Haul Transport Aircraft" CR-743, 1967, NASA. 2 Marsh, K R., "Study on the Feasibility of V/STOL Concepts for Short-Haul Transport Aircraft," CR-670, 1967, NASA. 3 "Study on the Feasibility of V/STOL Concepts for ShortHaul Transport Aircraft," CR-902,1967, NASA. 4 "Study of Aircraft in Short Haul Transportation Systems," CR-986,1967, NASA. 5 "Technical and Economic Evaluation of Aircraft for Intercity Short-Haul Transportation," Federal Aviation Agency-Air Defense System-74, Vol. I, II, and III, April 1966. 6 "A System Analysis of Short-Haul Air Transportation," TR 65-1, Flight Transportation Laboratory, Massachusetts Institute of Technology, Aug. 1965.

H. C. Curtiss

Papers

LTA Aerodynamic Data Revisited

Complex Coordinates in Near Hovering Rotor Dynamics

Stability and Control Characteristics of the Aerocrane Hybrid Heavy-Lift Vehicle

Dynamic stability of V/STOL aircraft at low speeds

LTA aerodynamic data revisited