The book begins with harmonic motion in which concepts like phase angle, amplitude and velocity response functions of systems are illustrated using complex numbers. The main emphasis is on the harmonic motion under external stimulus of periodic forces.

The problem: changing biosphere; Crop ecosystem responses to climatic change; Mitigation strategies; Economic and social impacts.

A method is presented for the calculation of rotor downwash in hovering and vertical flight. The blade is represented by a lifting line. The rotor wake is simulated by a vortex sheet and a series of rolled-up root and tip vortices, similar in form to that of a classical fixed-wing. The concept of rectangularization of the rotor wake is used in obtaining a formula for the normal component of induced velocity. Wake contraction based on experimental data is introduced into the calculations. Numerical calculations have been performed for two rotor configurations, viz. S.58, and a model rotor. Computed induced velocities and blade loadings are compared with the available flight data. The comparison shows the present simple method yields satisfactory results. (Author).

Between 8 September and 9 October 1985 the author attended the Eleventh European Rotorcraft Forum in London, and visited ten research establishments in England, West Germany, and the USA. The main purpose of the overseas visit was to investigate rotor wake modelling methods currently used. A report is given on the forum attendance and discussions held at the establishments, together with a general review of rotor wake modelling.