In 1973, automatic flight controls is one of the most exacting fields of technology, requiring a balanced combination of art, science and human understanding, and the efforts of large project management teams backed by adequate resources to bring any new concept to fruition.

Today's systems derive almost entirely from the technology of the past 25 years, and hence it is little known that there was some activity in automatic flight control for fixed wing aircraft as long ago as 1873, some 30 years before the world-changing events at Kittyhawk and when mechanical flight was still confined to balloons and a few rudimentary gliders.

The purpose of this paper is to study the random vibration of linearly elastic, lumped-mass systems containing non-linear damping, to ideal stationary Gaussian white noise excitation.

The following practical examples of systems with non-linear damping are quoted. A random vibration absorber with (velocity)2 damping, (velocity)2 damping in an aircraft oleo pneumatic undercarriage, and spar cap beam dampers in which damping is produced by relative motion between friction surfaces during beam deflection. In the first two examples optimum system parameters are determined in order to minimise the mean square response. In the third case the root mean square acceleration of a beam with spar cap damping is determined experimentally, the results being compared with Caughey's theoretical results.

The deterioration in the performance of NACA submerged intakes in the presence of a boundary layer has been established in Ref. 12, where a correlation of experimental data, obtained from wind tunnel tests on models, is presented. The purpose of this paper is to provide a prediction method which will allow the efficiency of these intakes to be estimated outside the range for which experimental data exist.

I am pleased to have the honour of presenting the 18th Henson and Stringfellow Memorial Lecture. The subject of helicopter modelling is certainly appropriate because of the pioneering experiments that Henson and Stringfellow carried out with steam-powered plane models more than 50 years in advance of the Wright brothers. Although true powered flights were not quite achieved, these models were notable for excellence in overall design, the efficiency of their small steam engines, and their ultimate influence in later developments that culminated in the first successful aeroplane. Although not as well known, models were also extensively employed in the early development of the helicopter and have since become almost indispensable for advancing helicopter technology. The main emphasis of this lecture will be devoted to the diverse ways in which small-scale helicopter models are presently employed in advancing this technology. To best accomplish this objective, I have chosen specific examples of helicopter models to illustrate their versatility and wide range of application. The presentation of these models will also serve a secondary purpose—to demonstrate the advanced level of technology that now exists for producing these sophisticated and fascinating models.