A review is given of current methods in theoretical aerodynamics which are useful in the design of aircraft wings for subsonic and transonic speeds. These are of two basic types:

• (A) direct methods for calculating the flow over a givenwing shape. In the design process, these can be used to obtain a rapid estimate of the effect of a specified change in wing shape. The most practical methods of this type make use of the viscous/inviscid interaction technique; some recent methods are described and examples are given of their use, both in two and three dimensions, including comparisons with experiment.

• (B) inverse methods in which the shape is calculated explicitly, as a result of either (a) specifying the surface pressure distribution on the wing, or (b) requiring that some suitable ‘target’ function, usually the drag/lift ratio, shall be a minimum. At present, these methods are restricted to inviscid flow.

Several examples of both ‘pressure’ and ‘optimisation’ methods are discussed, and their advantages and limitations considered.

A mathematical model is presented of the aircraft program flight along a predetermined trajectory, with or without a specified speed history. Moreover, the aircraft is constrained to coordinated turns, which implies zero value of sideslip angle. The final equations of program motion are derived as a set of differential/algebraic equations. The aircraft control input ensuring the exact realisation of program constraints results from the transient dynamic solution of the equations of program motion. A simple numerical illustration is included.

The design of guided missile systems presents a wide spectrum of problems to engineers in numerous disciplines which range through aerodynamics, electronics and signal processing. Of all the tasks involved in the design process, perhaps the most difficult is the integration of the various technologies into a complete, harmonised system. IMPACT is a computer program which was developed to address the system design aspects of homing guidance missile systems. The aim of this paper is to describe the engineering philosophy and theoretical background to the IMPACT program.