Mesh generation is proving to be an important aspect of computational aerodynamics. Over the last few years the topic has received much attention. Methods based on the structured and unstructured philosophies both have their advantages and disadvantages. This paper discusses the possible benefits to be achieved in composite structured-unstructured meshes. An algorithm is described which can solve the Euler equations for inviscid flow on such meshes. Three applications of the composite approach are then described. The first example shows the use of regions of assembled triangles to improve the quality of flow results on a poor quality structured mesh. The second illustrates how geometrically complicated aerodynamic configurations can be treated by utilising local regions of unstructured mesh within a globally structured mesh. Finally, a method of mesh/flow adaptivity is described whereby a structured mesh is enriched in appropriate regions of the domain by the addition of meshes consisting of an assembly of triangles. The results show that distinct benefits can be obtained from this composite approach.

Drag-reduction performance of riblets on an axi-symmetric body was investigated using ARE’s High Speed Buoyancy Propelled Vehicle (MOBY-D) at high Reynolds number. Approximately 35% of the wetted body surface was applied with riblets in situ using BMT’s RIBCOATTM process, and net drag reductions between 0 and 3.0% were observed during the flight. The drag reduction increased toward the ascent as the vehicle acceleration decreased, indicating that the favourable effects that riblets have on the boundary layer structure may be susceptible to acceleration.

British Airways currently operates over 200 aircraft and the fleet continues to grow. These include twelve airframe types coupled to fifteen engine types. They represent most of the design and build philosophies that have been used over the last thirty years.

The aircraft range from the turboprop 748s through the latest 747-400s to Concorde.

The one feature which is common to all these aircraft is that they are maintained to standards which are defined to ensure maximum passenger safety and the best financial returns.

The ability to track time varying frequency and damping parameters using on-line versions of seven time domain system identification algorithms; Least Squares, Double Least Squares, Correlation Fit, Instrumental Variables, Instrumental Matrix with Delayed Observations, Extended Least Squares and Maximum Likelihood, is examined. Comparisons are made on results obtained from data generated from various simulated time varying systems, corrupted with both input and measurement noise, as a preliminary step before advancing onto real data. Only the Maximum Likelihood and Double Least Squares methods gave acceptable results on the most difficult data sets that were considered. The choice of an exponential weighting factor is crucial to the performance of the on-line methods when applied to data from time varying systems. The effect of assigning various values of the weighting factor is demonstrated. Further work is required to determine the optimum schemes for defining this parameter.

The lecture recalls great Manchester traditions in the mechanics of fluids and in related areas of mathematics which were brilliantly renewed from 1945 onwards through Sydney Goldstein’s work as Beyer Professor of Applied Mathematics. Goldstein brought to this important task not only his own personal distinction in those fields but also his great experience in leading interacting groups working in experimental and theoretical fluid dynamics with largely aeronautical objectives. The University has continued strongly to maintain these traditions.

The lecture celebrates also two fine pieces of research where gifted biologists have successfully used certain key mathematical ideas and methods in the mechanics of fluids to solve problems of importance in the field of animal locomotion. The first example is the work of C. J. Pennycuick, J. M. V. Rayner and G. R. Spedding in determining the character of the vortex wake behind a steadily moving bird in horizontal flapping flight. Typically, this takes the form of a “concertina wake” of fluctuating width but approximately constant circulation, exerting forces which are greater in the downstroke (which sheds a wide wake) and less in the upstroke (which sheds a narrower wake). Some notable advantages of the concertina wake are indicated.

Finally, work by Sir Eric Denton, Sir John Gray and Dr J. H. S. Blaxter on schooling behaviour in herrings and other clupeoid fishes is described. These fishes’ mechanisms for advantageously maintaining well coordinated motion of the school as a whole depend not only on eye vision but also on certain specialised organs admirably fitted to the sensing of hydrodynamic pressure fields (associated with the motions of other fishes) and of their lateral and longitudinal gradients.

A deliberate product strategy is usually aimed at creating a transport aircraft family on the basis of a common wing by stretching the fuselage. Due to this policy of high fleet commonality the costs for development, manufacture and maintenance can be reduced. On the other hand the wing designer has to choose an appropriate wing area for the maximum stretched version and try to find the best trade-off between design and off-design conditions.

A transonic wing however shows optimum performance at high loadings which are not achieved at entry into service with such a conventional fixed geometry wing. Variable Camber (VC) is offering an opportunity to achieve considerable improvements in operational flexibility, buffet boundaries and performance which allow a reduction in optimum wing size.

Significant drag reductions and increases of the buffet boundary were found from research work. This work led to the current concept where the trailing edge flaps and ailerons are used to modify the wing camber in cruise according to the lift demand.

An efficient VC system requires a change in design philosophy and several new constraints in the design problem were found to effect the extent of the supersonic region, the acceptable pressure gradients in the recompression zone and the required surface curvature. Theoretical and wind tunnel results are given as well as a discussion of the effects on the system design, loads, weight, handling qualities, propulsion integration and mission performance.

Variable camber will contribute an average reduction of 3 to 6% in fuel burn and enable the use of one wing for medium range and long range missions respectively. The introduction of VC will launch a new generation of intelligent airliners which will optimise their camber schedule throughout the entire mission. A further improvement potential due to leading edge camber devices and spanwise differential camber is emphasised.

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.

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.

A method for the numerical solution of the two-dimensional Euler equations on unstructured grids has been developed. The cell-centred symmetric finite-volume spatial discretisation is applied in a general formulation that allows the use of arbitrary polygonal computational cells. The integration in time, to a steady-state solution, is performed using an explicit, multi-stage procedure, with standard convergence acceleration techniques such as local time stepping, enthalpy damping and implicit residual smoothing. Accuracy of solution, in terms of minimising spurious entropy production, is achieved through careful treatment of the artificial dissipative terms near boundaries. Standard test cases for both subcritical and supercritical flows, including single- and multi-element aerofoils have been used to validate the method.

The buffet characteristics of a supercritical aerofoil were investigated in the High Reynolds Number Two-Dimensional Test Facility of the National Aeronautical Establishment (NAE). The test was performed quite deep into the buffet régime. The buffet onset boundary was determined from the divergence of the unsteady balance normal force. Steady and unsteady pressure measurements were obtained for shock-induced separation with reattachment as well as fully separated flows. For flow conditions where discrete shock wave oscillations occurred, ensemble-averaging of the unsteady pressures determined the propagation velocity of the pressure wave induced by periodic shock motion. A model of the self-sustained oscillatory shock motion due to shock-boundary layer interaction was formulated. Broad-band cross-correlations of the pressure field determined the downstream convection velocities of the turbulent eddies of separated flows.

Aspects of numerical simulation of aircraft program flight along a predetermined trajectory are presented. An emphasis is laid on the problem of describing the required trajectory by means of a succession of defined points. A spline function method is used for interpolation and smoothing routines. Some numerical illustrations of aircraft trajectory flight simulation (only planar motion) are demonstrated and discussed.

Europe has a long tradition in the technical innovation and production of new advanced aeronautical concepts. However the talent to transfer these technical advances into a commercial success was missing. With the creation of Airbus Industrie and pooling of resources for a common product, the concept of a technically very advanced aircraft family which is competitive in the world market has been successfully applied. New technology remains a constant challenge and this paper describes the main axis of research and new technologies which are of interest for future application in civil transport aircraft. A general review is given of the main improvement potentials in aerodynamics, propulsion systems, airborne systems and new materials.

Travellers flying into Paris would not connect the famous 100-year-old landmark, the Eiffel Tower, an immense and complex structure of open ironwork, 300 m high, with the aerodynamics of their streamlined modern aeroplane. The unexpected association between the two is Gustave Eiffel — ‘le magicién de fer’ — builder of the Tower in 1889, who pioneered much of the experimental research needed by the designers of the first aeroplanes, in the period from 1903, when he was in his ‘70s, until the time of his death aged 90 in 1923.

Post-Second World War generations of aerodynamicists are also probably unaware that Eiffel was the source of many of the basic results they use, since no modern textbooks refer to his researches of 70 years ago; yet nearly half of his obituary notice in the Times of 29 December 1923, headed ‘M. Eiffel — A Great Engineer’ referred to his aeronautical research using his Tower and his wind-tunnels. In order to appreciate how Eiffel came to embark on his new activities at such a late age we must look briefly at his first career, which established him as one of the most distinguished structural engineers of the 19th century, and the political scandal which brought it to an end.

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 unsteady loads on two wings, one exhibiting a trailing edge separation, the other a leading edge separation have been measured. It has been found that there are differences between the two wing loads, one having a large scale viscous-inviscid interaction producing high loads at a low frequency.

Eigenstructure assignment has been widely used in the past for the synthesis of flight control systems in the time domain. The method, although offering a straightforward way of determining static compensators which satisfy the specifications in terms of desirable time response characteristics, lacks the property of guaranteeing stability margins like the linear quadratic regulator (LQR) methodology. The present paper analyses the performance-robustness properties of eigenstructure assignment against the standard LQR in order to define a loop transfer recovery procedure similar to that of the LQG/LTR. Two applications are described in which helicopter flight controllers are synthesised by eigenstructure assignment and possess robustness properties comparable to those of similar quadratic regulators and yet resulting in a simpler compensator structure. The applications are chosen to correspond to two flight conditions reflecting the aim of generality of the comparison.

The evaluation of aircraft flying qualities has always required a high level of integration between airplane dynamic response and human operator properties. Today, the linear pilot-aircraft behaviour is a mature technology summarised by the publication of the military specifications MIL-STD-1797.

The present paper outlines the contribution of pilot modelling techniques to such endeavour and their use as a tool in the prediction of aircraft handling qualities characteristics by verifying their output in a Neal-Smith criterion framework. The objective is to complete the understanding of handling qualities in the linear part of the flight envelope (such as tracking) and to initiate work in the large amplitude manoeuvres. The results have produced an interactive computer aided software useful for pilot-in-the-loop analysis.

A finite element analysis has been carried out to simulate the effect of birdstrike on concave curved metal stiffened panels representative of engine intakes. A simplified static analysis approach was adopted including the effects of non-linear material response and large displacements. Loading was by means of an equivalent pressure derived from experimental results of bird impacts on rigid plates. Good agreement was obtained between predicted and measured bird impact velocities to cause penetration of the structure for a range of panel thicknesses, curvatures and impact angles.

Experiments at transonic speeds have been performed on several boat-tailed afterbodies and sting combinations with a view to assessing sting corrections to the measured afterbody drag at transonic speeds. Measurements made included afterbody total drag and base pressure in the Mach number range of 0.6-1.0 and Reynolds number range of 8-9.5 x 106. Correlations of base pressure and boat-tail pressure drag for the sting diameter and flare effects have been proposed using dimensional arguments. The correlations provide quick and reliable estimates for corrections that can be applied to the measured zero-lift drag of axisymmetric bodies with either contoured or conical boat-tailing.

A numerical method, based on the panel technique, has been developed for calculating the time-averaged separated flow about a wedge. The mathematical model, with constant vorticity in the wake, gives an infinite extension of the wake and constant base pressure while incorporation of the dispersion of vorticity in the wake into the mathematical model leads to its finiteness and non-uniform under-pressure. Experimental tests have been conducted in a low speed wind tunnel on models haying different wedge angles. The theoretical and experimental results agree closely for different configurations and specific values of dispersion factors. However, the agreement for base pressure is poor.