High-speed aircraft often develop separation-induced leading-edge vortices and vortex flow aerodynamics. In this paper, the discovery of separation-induced vortex flows and the development of methods to predict these flows for wing aerodynamics are reviewed. Much of the content for this article was presented at the 2017 Lanchester Lecture and the content was selected with a view towards Lanchester’s approach to research and development.

In this paper, we examine some of the physics behind Vertical Take-Off and Landing (VTOL) flying machines, and some of the emerging technologies that are driving the recent upsurge of new VTOL projects. The paper attempts to put these into context by examining some of the projects that have been publicised over the past couple of years, particularly those that transition from hovering into wing-borne flight. Although much progress has been made, there still needs to be significant breakthroughs in technologies, particularly battery technology, before the dream of fast, quiet and environmentally friendly inter-city VTOL aircraft can be realised.

I must start by thanking the Royal Aeronautical Society for the invitation to present this 27th Lanchester Memorial Lecture. It is an honour and a privilege to follow in the footsteps of the distinguished scientists and engineers who have given the first 26 lectures in this series. These lectures have included many outstanding reviews of a wide range of different topics and I am very conscious that they have set a standard that I, for my part, will find difficult to match. I hope, however, that by choosing a topic that has only been mentioned in passing in just a few of the previous lectures, I will be able to make my own distinct, individual contribution to this tribute to the memory of a man who was not only a great scientist and engineer and talented musician but who, by his writings as long ago as 1907, still carries a message for us today in 1987.

For all who are specialists of one kind or another, it is a very healthy exercise to read books written by scientists or engineers of the calibre and breadth of F. W. Lanchester. He was at the same time truly a pioneer of flight, an expert in fluid mechanics, in flight mechanics, in the practical, and (well ahead of his time) in the military applications of flight, in the novel use of materials, and an inventor of devices and mechanisms. However, it was with particular surprise that I found, on studying the literature under the name F. W. Lanchester, a book published in 1935 entitled Relativity and two earlier papers on the subject published in 1921. Lanchester had met Minkowski in 1908 at the house of his friend Carl Runge, the applied mathematician, at Göttingen, and following a discussion with Minkowski had taken such an interest in the field that he was able to make these early English contributions.

Perhaps the most important property that makes such pioneers is the courage to think truly new thoughts. His fascination with the new philosophy in physics may be easily understood in terms of this bold style of thought.

I felt indeed very honoured when I was invited to deliver the 30th Lanchester Memorial Lecture. I immediately started reading Frederick W. Lanchester's famous and impressive work ‘Aerodynamics’ published in 1907. It was very interesting to read but of course there was nothing to be found about delta wings at supersonic speeds, which I had offered to talk about, partly because I had studied this for the last 5–10 years and partly because Sweden had been developing delta winged military aircraft since 1948 or so. I also know of course that Great Britain had made impressive progress at the same time particularly Dietrich Küchemann and the group around him. I could therefore expect and fear to have a competent and critical audience to face.

From the first, let me nail my colours firmly to the mast by quoting Beethoven’s eventual dedication of the “Eroica” Symphony. For this particular Lanchester Lecture we are “to celebrate the memory of a great man”. My meaning here, I hasten to add, has none of that bitter intention of the Republican Beethoven who, so the story goes, having ripped out his earlier dedication to Bonaparte then substituted those words to commemorate the man once revered but who had recently proclaimed himself Emperor of the French. My intention is that we celebrate the memory of a man whose thinking remains as alive, as vital, as the day he set pen to paper. Each day of our lives we see his vision made manifest reality in the vapour trails of the Big Jets high overhead. And to borrow such a dedication seems appropriate since, not only was Lanchester a great admirer of Beethoven’s music, but also Lanchester’s largeness of spirit, his grandness of vision, his capacity for unremitting sheer hard labour put him in the heroic mould.

Lanchester was undoubtedly a great British engineer. He died just 47 years ago, at which time the name Lanchester could be seen on the front of some motor cars, but many knew little about the great contributions that Frederick William Lanchester had made to both mechanical and aeronautical engineering.

Whether Lanchester was interested in automobile aerodynamics or not, the subject combines two of his great loves. He designed and built petrol-engined cars, and his 1898 machine won the RAC’s Gold Medal (Fig. 1). As might have been expected, the drag coefficient of this vehicle is not recorded.

In pondering on a subject for this, the fifteenth, memorial lecture, I hoped to find something that might reflect the spirit of Frederick William Lanchester's work. But first of all, I tried to learn a little more of the man himself: his history and the design of events that agitated his enquiring mind. Most of what I discovered only emphasised my own unworthiness to contribute to his memory. For I am a member of Imperial College, and it was from that Institution that Lanchester left, disenchanted, in his third year without taking his degree. Worse still, I hold the Zaharoff Chair of Aviation; in one of my distinguished predecessors, Lanchester was later to discover a fierce opponent to his theory of the lifting wing and to his equally remarkable vortex theory of the propeller. It was only in another sphere, that of the Aeronautical Research Council, that I was able to establish a happy bond between us.

‘In offering to the public the first instalment of the present work, the author desires to record his conviction that the time is near when the study of Aerial Flight will take its place as one of the foremost of the applied sciences, one of which the underlying principles furnish some of the most beautiful and fascinating problems in the whole domain of practical dynamics.’
F. W. Lanchester — Preface to Aerodynamics (1907).

Frank Lanchester was born in 1863 and died in 1946. He lived through, and contributed significantly to, an astonishing expansion in aerodynamic knowledge and understanding. When he was a very small child, the Aeronautical Society of Great Britain was formed. Arguments about the underlying principles of aerodynamics were abundant, and manned powered flight was some 40 years into the future. When he died aerodynamics was well-established, codified and central to efficient aircraft design. Transonic flight through jet propulsion had almost been achieved.

Tonight, once again, we honour the memory of Frederick William Lanchester, one of the great pioneers of modern engineering, born in 1868 died in 1946. We keep his memory alive by exploring how his ideas and concepts have flowered into maturity, and by reminding ourselves that his example, philosophy and strength of purpose are still relevant in today’s world. I suppose each of us reacts individually to the life and work of a great man.

F. W. Lanchester obtained his first technical education at the Hartley Institute in Southampton, later to become the University of Southampton, during the years 1886–89. His autobiography describes in vivid terms the primitive nature of the workshop and apparatus available. He would indeed be shocked at the wealth of modern equipment now encountered in engineering departments of a University. At the same time, no one can possibly say that this lack of equipment influenced his pioneer spirit or his extraordinary clarity of thought, not only in the fields of aeronautical and automobile engineering, but also in subjects as diverse as the musical scale, poetry and even relativity.

Some remarks are first made on the pertinence of the topic chosen for a lecture dedicated to Dr. Lanchester. A brief historical review is then given of the development of University teaching and research activities in Aeronautics from the early years of the Century to the present. An imaginary but typical modern University Department of Aeronautical Engineering is described with particular reference to numbers of students, staff, laboratory equipment and budget. Some of the many research topics to which the Universities have made and are making important contributions are then discussed briefly. These are to illustrate the scope and tendencies of University research against the background of current developments in Aeronautics. Among the subjects referred to are such topics as the structure of the turbulent boundary layer and the measurement of skin friction, flow Separation phenomena, boundary layer drag and heat transfer at high speeds, aeroelasticity, the application of matrix methods to structural analysis using digital Computers, structural damping, secondary flows in propulsion machinery, the rotating stall and jet noise.

The paper concludes with some general remarks on the relationships between the Universities, the Government Research Establishments and the Industry and on the future of University research. The importance of maintaining on the one hand the independence of the Universities and on the other hand the closest contact between them, the Government Establishments and Industry is strongly emphasised.

By way of introduction, I suggest you consider for a moment of four aircraft as dissimilar as a small general aviation aircraft, a large transport such as the Airbus, a glider and finally a fighter aircraft such as the Tornado. As regards handling in the air of these widely differing flying machines, their most significant common quality is perhaps that they can all be flown by a human pilot.

In the definition of the desirable handling qualities of these aircraft, one might—in complete innocence—expect to find a description of such desirable qualities in terms of the behaviour, capabilities and limitations of the human pilot, which one would, of course, expect to be independent of class or category of aircraft.

Orbital manoeuvres by means of impulsive thrusts, such as those available with chemical rockets, are well known, but a different treatment is needed for the small, continuous thrusts that are typical of electrical propulsion systems. It is shown that with the aid of these small forces it is possible to change independently all the orbital elements of a spacecraft, and thus to proceed slowly from a given orbit to any other. For each manoeuvre there exists an equivalent velocity which depends only on the initial and final orbital states, and which can be related directly to the spacecraft propulsion parameters.

For any form of propulsion where the propellent acquires some or all of its energy from a separate energy source, as in electrical propulsion, it is found that optimum time-varying relations exist between the flow of mass and of energy, which may also be expressed in terms of the exhaust velocity and the thrust. In particular, the optimum exhaust velocity is shown to be an increasing function of time, related to the way in which the energy is released.

The practical realisation of electrical propulsion depends on the development of efficient propulsion units and of lightweight power supplies; these and other spacecraft components are discussed, and a number of examples of orbital manoeuvres are given, including close-Earth, far-Earth and lunar orbits. The paper concludes with a discussion of these orbital transfers in relation to their possible uses, including communication satellites and a test of relativity theory

I Consider it a great honour to be invited to deliver the First Lanchester Memorial Lecture, which, according to the instruction received from the Secretary of the Royal Aeronautical Society, should deal with Lanchester's personality and achievements. It is also a great pleasure for me to recall my personal contacts with this great man. On the other hand, I am not quite sure whether the decision of the Council, choosing me as the first Lanchester Lecturer, was really a wise one, since I am not in the best position to present a full biographical sketch of Lanchester. Somebody more familiar with Lanchester's automobile work, as, for example, Sir Harry Ricardo, would be more able to present a full picture of Lanchester's achievements. I must, therefore, restrict myself essentially to the treatment of Lanchester's contributions to the sciences of Aerodynamics, Flight Mechanics and Operational Analysis.

When I was invited to deliver the Lanchester Memorial lecture, I wondered why the great honour of being the first Frenchman selected for the celebration of the deeds of a great engineer was conferred on me. However, I am well aware that the Council of the Royal Aeronautical Society cannot make a mistake and there is good reason to choose, after so greatly famed professors, an engineer of the French Navy to illustrate, using a slightly different point of view, the influence of Lanchester on the development of aeronautics. This way, I do not have to apologise for a possible inadequacy which then would not be my own responsibility. I have only to do my best, so as not to betray the confidence of the Society.

Answering so plainly this first question, I had to find out how to fulfil my task. Possibly, my contribution to the intrepretation of the vortex sheets starting from the thin leading edges of a delta wing is more in the Lanchester line of thought than it is an extension of Prandtl’s inferences.

To be asked to give the Lanchester Lecture, on the topic of helicopters, is a great honour and just now a wonderful chance. We all know of Lanchester's basic contributions to our knowledge of the way in which lift is generated by the creation of a vortex system. For fixed wings the flow patterns are now known and the theories are in the third stage of refinement. But on helicopters, although it has been the topic of intensive research for fifteen years or more, the subject is much farther back. The results obtained are fascinating technically and pictorially and I would cheerfully discuss them for hours. But our understanding is far from complete and I have regretfully decided to throw away a wonderful chance and leave the topic to a less formal occasion.

The first question that a prospective lecturer of the august series in honour of Frederick William Lanchester should ask himself is the possible reason why he has been selected. I confess that for a considerable time I have been at a loss to understand this signal honour bestowed upon me. My mind ventilated a number of possible explanations starting from the evident but rather tenuous reasoning that both the eminent Mr. Lanchester and myself can show a connection with the leading Technological Institute of Britain, the Imperial College. But is this sufficient as a justification? I doubt it. Another path I tried to explore ventured along the intriguing intentional verbal slips and monumental sayings of Lanchester. Is it possible—I asked myself—that the wise Council of the Royal Aeronautical Society selected me on account of my undeserved reputation to have been in my Golden Youth an angry young man, an enfant terrible, and an early exponent of the anti-establishment criticism.

The Space Division of the North American Rockwell Corporation has developed a comprehensive computer-based heat transfer and thermal analysis capability especially for design support of the Apollo command module. The heat transfer analysis primarily centres about the solution of the diffusion equation using finite difference approximations. Since most problems encountered are non-linear in nature this approach has proved highly effective in producing accurate results economically. Recent studies, however, indicate that heat transfer problems are most successfully analysed by the finite element method. On the other hand, the finite element method in this field of application was not yet established when North American initiated this work. Lack of time does not allow a deserved discussion of this topic.

Longitudinal vortices have tremendous practical utility for flow control (control by vortices) and in some cases have exhibited tremendous potential for causing harm if uncontrolled (i.e. control of vortices is required). Vortex control has thus far been carried out via multitudinous approaches in an empirical fashion, aided by the essentially inviscid nature of much of longitudinal vortex behaviour. Further refinement and several applications of vortex flow control require knowledge regarding the detailed flow physics of longitudinal vortices such as transition, transitional flow regimes, turbulence structure and modelling, and interaction with shock waves, other vortices and surfaces. This paper summarises vortex control applications and extant techniques for the control of longitudinal vortices produced by bodies, leading edges, tips, and intersections.