Aerodynamics of a Lifting System in Extreme

Aerodynamics of a Lifting System in Extreme

This book is dedicated to the memory of a distinguished Russian engineer, Rostislav E. Alexeyev, who was the first in the world to develop the largest ground effect machine – Ekranoplan. One of Alexeyev’s design concepts with the aerodynamic configuration of a flying wing can be seen on the front page.

The book presents a description of a mathematical model of flow past a lifting system, performing steady and unsteady motions in close proximity to the underlying solid surface (ground). This case is interesting for practical purposes because both the aerodynamic and the economic efficiency of the system near the ground are most pronounced. Use of the method of matched asymptotic expansions enables closed form solutions for the aerodynamic characteristics of the wings-in-ground effect. These can be used for design, identification, and processing of experimental data in the course of developing ground effect vehicles. The term extreme ground effect, widely used through­out the book, is associated with very small relative ground clearances of the order of 10% or less. The theory of a lifting surface, moving in immediate proximity to the ground, represents one of the few limiting cases that can be treated analytically.

The author would like to acknowledge that this work has been influenced by the ideas of Professor Sheila E. Widnall, who was the first to apply the matched asymptotics techniques to treat lifting flows with the ground effect.

Saint Petersburg, Russia February 2000

1.1 Some Definitions

This book discusses the aerodynamics of vehicles, that utilize the favorable effect of the proximity to an underlying surface upon their performance. Al­though this underlying surface may be not only land, but also water, snow, or ice, it will be called ground.

In what follows, the ground effect is understood as an increase in the lift-to-drag ratio of a lifting surface (a wing) moving close to the ground. For an appropriately designed lifting surface, this phenomenon exhibits it­self at distances from the ground less than the chord of the wing, but the most advantageous range of ground clearances normally lies below 25% of the chord. The term extreme ground effect, widely used throughout the book, is associated with very small relative ground clearances under 10%. This latter range is characterized by a significant increase in the efficiency of the lifting system and is expected to be operational for the lifting systems of the next generation of the craft.

Ekranoplan (a wing-in-ground-effect vehicle) can be defined as a vehicle with an engine and heavier than air that is designed to fly close to an un­derlying surface for efficient utilization of the ground effect. At present many terms exist to designate such a craft, namely, ekranoplan, wing-in-ground – (WIG) effect vehicle, wing-in-surface-effect ship (WISES), flaircraft, ground effect machine (GEM), etc.