Nonplanar wings in nonplanar ground effect.

Abstract

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-