Pitch Stability of an Unpowered Ground Effect Vehicle

Abstract

The ground effect regime was first utilized in the early 1900’s with the advent of transatlantic flight. Aircraft such as the Dornier DO-X would fly close to the surface of the water in order to increase its payload and range. Since that time, research has been periodic with the largest resurgence of ground effect interest in the 1960’s. The Russian government became involved in developing aircraft designed solely for ground effect flight. The design of these aircraft was difficult due to the inherent problems that exist within ground effect. There are natural instabilities that occur, especially in the longitudinal direction that are antagonized by shifting payload weights. Past researchers have handled the unique design requirements of ground effect through the usage of high-tail devices which operate outside of ground effect and power augmented ground effect which artificially generates the lift force through the use of thrust vectoring. The Center for Industrial Research Applications (CIRA) has developed a single passenger, unpowered, subsonic aircraft that relies on gravitational forces for momentum. AirRay combines the benefits of ground effect i.e. the increased lift and decreased induced drag, with a unique approach to maintaining stability. The design of AirRay faced many challenges as a result of flying in the ground effect regime, similar to those found in the prior efforts. These include natural instabilities, primarily in the longitudinal direction, that cause the glider to want to pitch up. In addition the size requirements for a single rider to maximize maneuverability, as well as the potential for updrafts on a downhill slope are added constraints to the design of the ground effect vehicle. These issues, and others, are the subject of current study. This paper has focused on the most important aspect of the design, longitudinal stability. This research has shown positive results with respect to the effectiveness of slots, on passively controlling the movement of the center-of-pressure at varying angles of attack. The 40 degree slot located at 20% of the chord line was most advantageous in stabilizing movement. These results indicate a craft can be designed that can be stable and function in the majority of the flight conditions that have been specified.