The aim of this presentation is to provide a survey of civilian VTOL activities in the United States. However, because of space limitations, attention can be focused on only a few topics. Nevertheless, it is believed that a representative picture of technical and organisational activities, current and future trends, and problems is presented.

The unique capability of vertical-lift systems (permitting take-offs and landings from restricted areas) generates a special market for these aircraft, because the needs of carrying both people and goods cannot be fulfilled equally well by other modes of transport. In this respect, the helicopter, which at present is the only operational VTOL concept, has demonstrated that a demand for its services, especially in such fields as offshore oil rig support, business flying, crane operations, etc, generates its own momentum of spontaneous growth, which should become quite visible from this presentation.

The important thing in the land battle is to overpower your opponent by out-manoeuvring him and then hitting him with all the weapons at your disposal. Clubs, swords, spears, brickbats and arrows, or rifles, machine guns and artillery or nuclear, chemical and guided weapons, the principles are the same:

• (a) Seek the enemy out.

• (b) Move into position.

• (c) Destroy him in battle.

The first task is therefore surveillance and target acquisition. This is a task which requires a soldier to get into a position to observe and discover where your enemy is and what he is doing. Most sensible enemies hide behind hills to keep out of harm's way, in order to conceal their future intentions. Therefore one of our basic problems is to find out what goes on behind the hill.

The attitude of a spinning satellite, specified in terms of the three Eulerian angles, is related to the angular velocity components in body-fixed co-ordinates by three coupled first-order non-linear differential equations. In general, these equations, being complex, are not amenable to analytical techniques. This study presents a new analytical approach to the analysis of these equations by first reducing the problem to the study of a single second-order non-linear differential equation and then establishing its equivalence with a second-order linear differential equation for the case of the satellite spinning with constant angular velocity components. The solution of this equivalent linear equation is then used to obtain the Eulerian angles.

Two papers by Dixon described a digital computing technique for the structural optimisation of a cantilever beam. This technique applied Pontryagin's Principle to the problem, and computation was effected using a modified Kutta-Simpson integration technique and the Rosenbrock hill-climbing method. Dixon's second paper, in which he revised his earlier work, cited the hybrid solutions of the authors for comparison with his own results. This comparison of the results obtained from the digital and hybrid methods showed a slight, but significant, difference which indicated the need for further verification.

The mathematical analysis of the induced velocity components of a screw propeller has occupied the attention of fluid dynamicists for many years. Early approaches to the problem concentrated mainly on momentum and blade element theories, neither of which are capable of providing a detailed knowledge of the flow field, except at the propeller plane or the boundary of the fluid. The early vortex theories also suffered from equally significant, but less severe, limitations and such methods were found to be completely unsatisfactory for many applications. In particular, the development of the ducted propeller for the propulsion of supertankers and VTOL aircraft has demanded a highly detailed knowledge of the flow field, especially around the propeller tip.

For the engineer, the “Concorde challenge” could be defined as follows:

A passenger carrying aircraft twice as fast as the existing aircraft and at least as safe.

When the jets came out 20 years ago, there was a sudden increase of the speeds used up to then, but their envelope stopped at the limit where the difficulties associated with very high speeds start