Air Cushion Vehicle Research Articles

Simple active aerodynamic suspension systems for high-speed ground vehicles

The feasibility of using active aerodynamic surfaces to improve the vertical ride quality of a tracked air cushion vehicle is investigated analytically with a six-degree-of-freedom linear model. Two aerodynamic fins actively control the pitch and plunge steady-state acceleration response of the passenger compartment to harmonic guideway excitations. For speeds of 200 and 300 mph, the choice of simple acceleration feedback signals sensed at the passenger compartment e.g. results in an acceptable ride quality. This is attained by practicable angles of attack and reasonable torques for the aerodynamic surfaces.

Response of Air Cushion Vehicles to Random Seaways and the Inherent Distortion in Scale Models

The heave, pitch, and roll equations of motion for an Air Cushion Vehicle are derived. The dynamic response to a random seaway is predicted from the linearized perturbation equations and compared with experimental tests of a subscale dynamically similar model operating in a towing tank. Frequency domain seakeeping analysis to determine acceleration response, frequency of bow slamming, structural loads, and relative motion between two craft is demonstrated. Because the atmosphere is not scaled during subscale model tests, an appreciable dynamic distortion is reflected in lift system physical parameters. This scaling problem is discussed and avenues of further subscale model experimental research are suggested.

Dynamic Whip of Elastically Restrained Plate Strips to Rapid Transit Loads

A plate strip of infinite length and constant width is cantilevered on a uniform elastic support along one edge and free along its opposite edge. A normal line load of constant intensity applied across its width travels along the strip at constant speed. Using plate theory, steady state solutions for the flexural waves are derived in terms of the generalized Fourier integral. Superposition is used to simulate responses to distributed transit loads. Results are applicable to the design of cantilevered guidance panels for air cushion vehicles and also in the design of the metal plates for the linear induction motors sometimes used to power these vehicles.

Reduction of TACV Power Requirements by Multiple-Stage Air Cushions

This paper shows that the power required for levitation for tracked air cushion vehicles can be significantly reduced by the use of multiple stage air cushions. A mathematical model for these air cushions is developed, and the air cushion pressures obtained from the model are compared with experimental pressures. It is shown that one of the most significant features of multiple stage air cushions is their inherent roll stability as opposed to an inherent instability for conventional air cushion designs. This inherent roll stability allows a significant reduction in the power required for levitation for tracked air cushion vehicles.

Accomplishments and future tasks in off-road transportation

In the first public lecture in a series on “Transportation Technology and Environment” at Carleton University, Ottawa, Canada, in late 1971, Dr. Bekker describes the development of the rationale now accepted for selecting vehicle design parameters at the conceptual stage. As examples of contemporary off-road vehicle development, he mentions tracked articulated vehicles and lunar roving vehicles. The need for rational, systematic thinking in modern vehicle design is stressed. A warning is given not to be lulled into trying to apply air cushion vehicle design criteria, originally developed for seagoing operations, to land operations. Dr. Bekker also identifies the need for laboratory simulation of ACVs operating over land, and reminds his audience that ecological considerations can no longer be ignored in vehicle design.

Tracked Air Cushion Vehicle Suspension Models: Analysis and Comparison

ABSTRACT In this paper several dynamical models of fluid suspensions for tracked air cushion vehicles are analyzed and compared. Specifically, the models considered conform to: a fifth-order linear suspension, a nonlinear configuration with a constant supply pressure, a nonlinear model with compressor characteristics, and a sixth-order nonlinear model with a supply duct connecting the compressor to the cushion chamber. Nonlinearities included in the analysis are the flexible-skirted cushion capacitance, cushion entrance and exit orifice restrictions, feeding system duct fluid capacitance, and compressor pressure-flow characteristics. Temporal responses are obtained for guideway and external force inputs. Back flow conditions under which the supply compressor can stall are examined. It is shown that the general behavior resulting from linear analysis is in many respects similar to that obtained from the nonlinear analysis. Thus, a linear model could provide a good initial basis for a preliminary design and...

AIR CUSHION VEHICLES—NEW TECHNOLOGY IN THE NAVY

AbstractIn 1970 the U.S. Navy undertook another major effort in air cushion vehicle technology. While the SES 100, a rigid sidewall craft, was being built, two Navy contracts were signed under the Amphibious Assault Landing Craft Program to design and build a fully amphibious air cushion vehicle. Although the major Research and Development effort in the AALC Program in support of the craft was performed by the two contractors, the Navy also undertook some research effort.This paper discusses Research and Development effort in the AALC Program addressed by the Navy, major ACV technologies—their importance to craft performance and direction for future R & D effort—and outlines the basis for the ACV design criteria development.

Design Loadings and Structural Considerations for Tracked Air Cushion Research Vehicle

Simple analyses of vehicle responses to operating conditions are used as the basis for determining the types of loading significant for structural design of the Tracked Air Cushion Research Vehicle (TACRV). A brief development is given for the methods used to determine the magnitude of cushion applied loads along with the internal reactions and load paths associated with the several suspension configurations. Although the choice of materials and conservative design safety factors tend to preclude fatigue problems for the test vehicle, a brief analysis is given to indicate some potential fatiguecritical areas in tracked air cushion vehicle (TACV) prototypes designed to higher stress levels.

The Acceleration of an Air Cushion Vehicle Under the Action of a Propulsor

This paper presents the solution for the motion of an air-cushion vehicle (ACV) starting from rest under the action of a propulsor of given thrust-speed characteristics. The wave resistance is based on linearized potential theory, while the aerodynamic drag components are assumed to be strictly quasi-steady. The problem is treated in two different ways: calculating the wave resistance in a truly unsteady manner, and on the simplified quasi-steady basis. The results show that the shape of the propeller characteristics has only a minor effect on the velocity pattern. However, the effect of overloading the ACV is shown to have crucial effects on its ability to surpass the critical depth hump. In this respect, the simpler quasi-steady calculations lead to unnecessarily pessimistic estimates of the acceleration margin. Under certain circumstances in relatively shallow water, the quasi-steady analysis would suggest that the ACV could not overcome the critical hump, while the more elaborate unsteady calculations show that it has indeed adequate power to reach its final cruising speed.

Nonplanar wings in nonplanar ground effect.

THE search for new high-speed ground transportation water and rough terrain vehicles has spread in many directions. One of these directions involves the use of aerodynamic lift to support and stabilize a high-speed vehicle above a planar or nonplanar (regular or irregular) ground surface. The ram wing and the terrafoil are the most popular names associated with this mode of transportation. A ram wing can be described as a vehicle which is geometrically similar to a large low-aspect-ratio airfoil flying close to the ground and is subject to aerodynamic ground effects. A detailed description of a terrafoil vehicle is presented in Ref. 1. In general, it can be described as a tandem winged vehicle subject to close ground effect and which aerodynamically interacts with a surface or guideway to achieve static and dynamic stability. The ram wing and terrafoil concepts for multiterrain travel have several advantages over other proposed guided and multiterrain vehicles, such as the air-cushion vehicle. Among these advantages are: 1) the utilization of ground augmented dynamic lift at high speeds, 2) the reduction in induced aerodynamic drag due to the presence of ground effect, 3) the reduction of wave and spray drag over water since these vehicles will in general (and particularly at high speeds) fly appreciably higher than the corresponding air-cushion vehicle, 4) the elimination of momentum or sink drag, which is the equivalent of induced drag for a wing, 5) the capability of being integrated with a captured air-bubble lift augmentation system, and 6) the capability for negotiating obstacles or drastic changes in height above the ground to facilitate travel over very rough terrain. There have been, however, some major difficulties impeding the development of these vehicles for use in highspeed surface transportation. One of these difficulties has been the absence of analytical or numerical methods for determining the flowfield about completely arbitrary nonplanar wings in the presence of any arbitrary nonplanar ground situation. Another difficulty stems from the fact that there has been a lack of investigations into the static and dynamic stability characteristics of three-dimensional wings in arbitrary ground effect. It is, therefore, the purpose of this investigation to develop a suitable numerical method for solving the problem of completely arbitrary lifting wings flying in the close proximity to arbitrary planar or nonplanar ground. A fu-

Guideway Camber and Three-Stage Passive Suspension for Improved Tracked Air Cushion Vehicle Ride Quality: Part II of a Parametric Study

Two means of providing a high quality air cushion ride at high speed using simple passive suspension systems are investigated. The inclusion of the proper amount of camber in guideway beams is shown to greatly reduce both low and high speed heave accelerations. A three-stage passively suspended vehicle including two degrees of pitching motion is shown to eliminate the high speed peak in accelerations present with two-stage vehicles. The effects of secondary and tertiary damping, of the vehicle to span length ratio, and of guideway camber on the ride quality of this vehicle are investigated. Coupled with cambered guideway beams, the three-stage passive suspension system appears to be an attractive alternative to active suspension systems.

Dynamic Interactions of High Speed Tracked Air Cushion Vehicles With Their Guideways: Part I of a Parametric Study

The vehicle-guideway system is modeled as an arbitrary number of lumped, doubly-sprung vehicle mass systems traveling in tandem along simple supported beams. The vehicle load is transmitted to the guideway as a time-varying uniform pressure compatible with vehicle motion. Effects of the dimensionless system parameters on vehicle heave acceleration, and guideway deflections and bending moments at high vehicle speeds are evaluated. Results for a vehicle which includes pitching motion compare favorably with those for a vehicle without pitch where the front and rear masses are uncoupled. By proper choice of parameters, passenger compartment heave accelerations can be minimized, although to keep this acceleration below 0.05g for vehicles traveling 100–300 mph requires systems with low vehicle to beam mass and frequency ratios as well as low vehicle lower to upper mass ratios. The benefits of distributed air cushion pressure to vehicle and guideway design are shown. Also, if the ratio of lower to upper vehicle mass is low, a constant moving pressure conservatively predicts the guideway response.

39. Cushion mechanics of a peripheral jet ACV in hovering flight over water: A. Jaumotte, A. Kiedrzynski, P. Spehl and P. Waterkeyn.Hovering Craft and Hydrofoil, 11 (2), 6–17; (1972) 7 ref., 18 fig.

This paper proposes a new schematic model of a jet-curtain for hovering flight over water. The theoretical analysis is made for perfect (nonviscous) fluids. The numerical results of this analysis are compared to the experimental results given by a bi-dimensional full-scale model. Referring to this comparison and to the observation of the flow patterns on the real model, the theoretical analysis is qualitatively extrapolated to the region of viscous fluids. The presence of the double jet-curtain effect in flight over water is verified. The mechanism of spray generation and the feature of the vortex pattern in the vicinity of the peripheral jet are explained. The results of the analysis allow the evaluation of the performances of the perpheral-jet air cushion vehicle in hovering flight over water.

Design and Development of an Air Cushion Vehicle Amphibious Assault Landing Craft

The U. S. Navy has recognized a need for substantial improvement in the performance and cost effectiveness of ship-to-shore movement of personnel and material. Coupled with this is a desire to provide additional flexibility of operation. These requirements can be achieved through the use of the air cushion vehicle concept. The paper presents the principal characteristics, together with the underlying design and development philosophy, of a 165-ton craft designed to meet the Navy's requirements, which is at present in the construction phase.

42. An experimental air cushion vehicle for the primary transportation of raw forest products: H. G. Murchinson.Hovering Craft and Hydrofoil, 11 (4), 23–26 (1972); 2 ref., 2 fig.

42. An experimental air cushion vehicle for the primary transportation of raw forest products: H. G. Murchinson.Hovering Craft and Hydrofoil, 11 (4), 23–26 (1972); 2 ref., 2 fig.

47. Air cushion vehicles for personal rapid transit: H. R. Ross.Hovering Craft and Hydrofoil, 11 (2), 12–25 (1972); 14 ref., 14 fig.

47. Air cushion vehicles for personal rapid transit: H. R. Ross.Hovering Craft and Hydrofoil, 11 (2), 12–25 (1972); 14 ref., 14 fig.

35. Data acquisition for a tracked air cushion vehicle: A. L. Niblett.Hovering Craft and Hydrofoil2 (6), 8–11 (1973).

35. Data acquisition for a tracked air cushion vehicle: A. L. Niblett.Hovering Craft and Hydrofoil2 (6), 8–11 (1973).

The Wave Resistance of an Air-Cushion Vehicle in Steady and Accelerated Motion

This paper deals with the theoretical wave resistance of an air-cushion vehicle (ACV) traveling over water of uniform finite or infinite depth, in steady or unsteady motion. Referring first to steady motion, it is shown that the unrealistic oscillations in the wave resistance curve at low Froude numbers found by previous workers can be eliminated by using a smoothed-out pressure distribution rather than one with sharp edges studied exclusively in the past. The main result of unsteady motion calculations is that the peak wave resistance in shallow water, even in moderately accelerated motion, is appreciably less than the corresponding steady-state value. An interesting feature of unsteady motion is that besides wave resistance there is another mechanism transferring energy to the free surface, which is here called the dynamic sustention power. Contrary to intuition, the wave resistance in unsteady motion over finite depth sometimes becomes negative at supercritical Froude numbers before finally vanishing at infinite speed.

Paper 2. Problems and Requirements of Directional Stability, Control and Manoeuvrability; High-Speed Craft

The problems of stability and control of high-speed craft are somewhat different for the various vehicle types. The first part of this paper briefly compares characteristics of air-cushion vehicles and planing craft. This is followed by a more detailed discussion of the problems and requirements of hydrofoil craft.

A Comparative Study of the Nonlinear and Linear Performance of Vehicle Air Cushion Suspensions Using Bond Graph Models

A nonlinear analytical model for the dominant low-frequency dynamic behavior of flexible-skirt air cushion suspensions is developed using bond graph notation. The model includes nonlinear fluid source and orifice characteristics, and modulation of cushion fluid capacitance and sealing gap fluid resistance by changes in geometry and cushion pressure. Bond graphs are presented for the fully nonlinear cushion and for the linearized small perturbation case. Both the nonlinear and linearized equations for the heave dynamics of an air cushion vehicle are developed and solved by machine computation for a realistic range of operating conditions. By comparing the linear and nonlinear solutions, it is concluded that the linear model is suitable for the preliminary design and optimization of air cushion vehicle suspensions. The full nonlinear simulation is prudent, however, to check a tentative design for the effects of unusually large guideway irregularities or external load disturbances.