In order to study the propulsive performance of a side-wall ACV over calm water, towing tank tests were carried out. The purpose of the present investigation is to determine the effects of model weight and side-wall depth on drag, and to consider how the measured drag can be broken down into its components. Obsevation and measurement of wet area on the inside of the side-walls was made with a fibre-scope apparatus. The wave making drag and the hydrodynamic drags such as the side-wall frictional drag and water contact drag of skirts are more significant than the aerodynamic drag. Two drag humps are found at Fn=0.6 and Fn=0.38. It is noted that the hump drag at Fn=0.6 is caused by the wave drag, however, the hump drag at Fn=0.38 is caused not by the wave drag but the skirts drag. An increase in the model weight causes an increase of skirts drag at Fn=0.38 especially. A significant wetting and scooping action of the rear skirts occurs at Fn=0.38. The nose up moment and the significant water contact drag of skirts should be attributed to this scooping action by the rear skirts. Above the primary hump speed the drag of the model increases as the side-wall depth is increased. However, at the secondary hump speed (Fn=0.38) these conditions are reversed. The breakdown of measured drag into components shows that the increased drag appearing with the increased side-wall depth is caused by an increase in the frictional darg of the side-wall itself. The reason skirts drag increases at the secondary hump speed for models with shallower side-walls is considered to be that the heave height is reduced because of the leakage of cushion air through the trough of the wave.
The purpose of the present investigation is to evaluate by experiment the theoretically predicted wave-making drag of ACV. The calculated wave drag of an ACV model according to the NEWMAN POOLE theory is compared with the wave drag calculated from the wave pattern measured along a longitudinal cut (NEWMANSHARMA method). The measured wave drag shows close correlation with the theory except at low speeds. For Fn<0.5 the experiment do not show the hump drag predicted by the theory. Why wave pattern drag has no drag rise at slow speeds seems to be reasonably explained by HOGBEN'S interpretation which pointed out the wave steepness limitations on Hovercraft wave drag.
This paper deals with the effect of forward speed on the front and ambient pressure of a peripheral-jet air cushion vehicle. The experiments are conducted with a twodimensional rectangular-shaped model in a moving ground wind tunnel. The peripheral-jet air is brought into the model through ducts at either side. The static pressure distribution, on the both side plates and on the front, rear and bottom surfaces of the model, have been measured in this experiments. The results are summarized as follows: (1) At subcritical speed, the semi-emperical analysis has been performed by applying the horizontal momentum balance at the reverse jet flow region of the front of the model. Calculated front pressure agree well with the experimental results. (2) The front pressure at subcritical speed increases as the jet momentum coefficient decreases, i.e. when the wind velocity is increased. (3) At near critical and supper critical speed, the front pressure coefficients are approximatly 1.0. (4) The wake pressure coefficients are nearly equal to -0.85.
Some experimental results are reported in this paper for a simplified peripheral jet GEM. The first phase concerns the flow pattern around the GEM, where the tuft-grid method has been used. Many instructive photographs are obtained which show a single horseshoe vortex around a GEM. The second phase contains measurements of pressure distribution on the GEM upper surface, The external drag is obtained by integrating the pressure distributions. Significant (about one-third) reduction of parasite drag has resulted from the influence of the peripheral jet over a wide speed range; inspection of the pressure distribution shows that the drag reduction occurs both at the front and rear of the GEM.
In the first part of the paper, an experimental study on heaving ACV is reported, where the limits of the application of the conventional quasistatical and linear theory are also shown. In the second part, a method is proposed to estimate the effects on heaving motion of the characteristics of fans, motors or engines and duct. whict supply the peripheral nozzle with air, and it is concluded that the effects are important while they have been frequently overlooked by many researchers. Finally, a method for analyzing the overall characteristics of the heaving motion including the effects of fans, etc, is proposed within the limit of the quasistatical and linear assumption. The agreement of the theoretical estimates with the experimental results is good enough to be used for the practical purposes
In this paper, dynamic characteristics of an ACV (Air Cushion Vehicle) over the irregular ground are investigated. The flow model derived in part 3 is developed for the dynamic motion by taking account of the changes of the cushion volume due to heaving motion or traveling motion over undulating surfaces. Digital simulations based on this model are carried out in several cases, and dynamic lift augmentations under the constant amplitude excitation over the smooth and undulating ground are measured by experiments and compared with the results obtained by the simulations. The experiments show a little greater values in damping, but the coincidence with computations seems to be reasonable.