The mutual interaction between the main rotor and tail rotor wakes is central to some of the most problematic dynamic phenomena experienced by helicopters. Yet achieving the ability to model the growth and propagation of helicopter rotor wakes with sufficient realism to capture the details of this interaction has been a significant challenge to rotorcraft aerodynamicists for many decades. A novel computational fluid dynamics code tailored specifically for rotorcraft applications, the vorticity transport model, has been used to simulate the interaction of the rotors of a helicopter with a single main rotor and tail rotor in both hover and low-speed quartering flight, and with the tail rotor rotating both top-forward and top-aft. The simulations indicate a significant level of unsteadiness in the performance of both main and tail rotors, especially in quartering flight, and a sensitivity to the direction of rotation of the tail rotor. Although the model thus captures behaviour that is similar to that observed in practice, the challenge still remains to integrate the information from high fidelity simulations such as these into routine calculations of the flight dynamics of helicopters.

Before enlarging on the main subject of this paper, it will be helpful to clarify some fundamental conceptions of various rotor drive configurations.

In the past the original shaft-driven helicopter presented two major problems to the designer. These were first: the necessity to choose between either some torque balancing device or a multi-rotor layout and, second: the necessity of a large reduction gear box, the weight of which seemed to become prohibitive with increasing all-up weight of the design. Big helicopters with either single rotor/tail rotor configuration or multi-rotor configuration, are flying successfully and prove that these afore-mentioned problems, although still in existence, were mastered in an admirable way. Nevertheless, in the old days the words “ tip. drive ” had a magic sound to the harassed designer.

A conventional inverse simulation does not accommodate control constraints; hence for aggressive manoeuvring flight conditions, where control inputs are close to the limits, these algorithms lose some of their applicability. A modification of the conventional inverse simulation technique that accommodates the onset of physical limits or constraints is proposed in this paper. In this way a process of constraints handling is incorporated into the inverse simulation algorithm. Therefore, the aim of this paper is to demonstrate that conventional inverse simulation can be improved in terms of the realism of the results by applying a predictive capability for applications involving manoeuvring flight. The paper gives details of the development of the predictive inverse simulation algorithm and helicopter model used and, by presenting examples of results calculated for pop-up and lateral realignment manoeuvres demonstrates that a ‘receding horizon’ predictive approach offers improvements in the realism of inverse simulation results.

There are many examples in his two Alice books where Lewis Carroll, perhaps unwittingly, provides analogies with the world of reality. The lines quoted above are often used to portray the rapidly changing scenario in which we struggle to maintain the status quo of our social and political lives. The same is true in the world of structures: the scenario continually shifts as we discover new hazards which threaten our products. Aircraft speeds have increased, operators have demanded longer service lives, new materials have been introduced with their own susceptibilities, and so we must develop more comprehensive design requirements and better design techniques to ensure that each new aircraft maintains the existing standards of airworthiness—or at least the standards we imagine to exist.

As individuals, those who have been born and bred and nurtured in the long, unique and formative tradition of the British people may justly claim a pride in their scientific and technical achievements over the years which cannot be claimed in such measure by any other nation. It is a claim they can make as proudly this very day as they could have done over the past three hundred years.

In the main, this paper is concerned with but a small, although not unimportant, part of the scientific achievement of the Seventeenth, Eighteenth and Nineteenth centuries. It was a period, in Great Britain, of such giants as Isaac Newton, James Watt, John Dalton, Robert Boyle, Henry Cavendish, Michael Faraday, Charles Darwin, Clerk Maxwell, W. J. M. Rankine, Lord Kelvin, Lord Rayleigh, Sir Charles Parsons, Prescott Joule, C. G. Stokes, Osborne Reynolds, Sir J. J. Thomson, C. Babbage, F. W. Lanchester, and so many others whose ideas and achievements have changed the face of the world in this Twentieth century of application.

The aerodynamic interaction between a wing and a couple of propellers in tractor configuration is investigated by means of a model based on the lifting line concept and under the assumption of quasi-steady incompressible motion of inviscid fluid. The ways the propellers influence the wing performances, particularly the induced drag, are analysed. It turns out that the lift increase and the possible drag reduction depend strongly on the direction of the blade rotation and on the propeller distances from midspan, and result from two main effects: the direct propeller induction on the wing and the modification of the lift distribution along the span. An additional nonlinear (mixed) contribution affects the drag but has only negligible influence on the lift. The described model allows one to evaluate separately all these effects and helps understanding their influence on the global modification of the wing performances.

In a recent paper(1) Collar discussed some aeronautical applications of linear differential equations with variable coefficients. Part of the paper deals with the approximate solution:

of the differential equation

This asymptotic approximation, which dates back at least to Liouville, has an interesting history(2). It is widely known as the WKB approximation because of its use in quantum theory by Wentzel, Kramers and Brillouin. It has been applied to compressible flow by Imai(3).

While very useful it breaks down at the zeros of n(t) and there are problems in joining solutions passing through such points. Recently(2,4,5) extensions of the approximation which circumvent this difficulty have been developed. This note deals with the extension due to Bailey.

This approximation can be developed from the equivalence of equation (2) and the Riccati equation: —

The performance of hypersonic vehicles in the take-off stage considerably influences their capability of accomplishing the flight tasks. This study is aimed at enhancing the take-off performance of a cruise aircraft using the improved chimp optimisation algorithm. The proposed algorithm, which uses the Sobol sequence for initial population generation and a function of the weight factors, can effectively overcome the problems of premature convergence and low accuracy of the original algorithm. In particular, the Sobol sequence aims to obtain a better fitness value in the first iteration, and the weight factor aims to accelerate the convergence speed and avoid the local optimal solution. The take-off mass model of the hypersonic vehicle is constructed considering the flight data obtained using the pseudo-spectral method in the climb phase. Simulations are performed to evaluate the algorithm performance, and the results show that the algorithm can rapidly and stably optimise the benchmark function. Compared to the original algorithm, the proposed algorithm requires 28.89% less optimisation time and yields an optimised take-off mass that is 1.72kg smaller.

A technique is developed that can be used to predict the effects of battle damage on the aerodynamic performance of an aircraft’s wing. The technique is based on results obtained from wind tunnel tests on a NASA LS(1)-0417MOD aerofoil with simulated gunfire damage. The wind tunnel model incorporated an internal cavity to represent typical aircraft construction and this was located between 24% and 75% of chord. The damage was simulated by circular holes with diameters between 20% and 40% of chord. To represent different attack directions, the inclination of the hole axis relative to the aerofoil chord was varied between ±60° pitch and 45° of roll. The aerofoil spanned the wind tunnel to create approximate two-dimensional conditions and balance measurements were carried out at a Reynolds number of 500,000 for incidences, increased in 2° increments, from –4° to 16°. Surface flow visualisation and pressure measurements were also carried out. For a given hole size, the increments in lift, drag and pitching moment coefficients produced trends when plotted against the difference between the upper and lower surface pressure coefficients on the undamaged aerofoil taken at the location of the damage. These trends are used as the basis of the predictive technique. The technique is used to predict the effects of a previously untested damage case, and these are compared with wind tunnel tests carried out on a half model finite aspect ratio wing. For all coefficients the trends in the predicted data are similar to experiment, although there are some discrepancies in absolute values. For the drag coefficient these discrepancies are partly accounted for by limitations in the technique, whilst discrepancies in the lift and pitching moment coefficients are attributed to limitations in the aerofoil test arrangements.

Most modern aircraft employ discrete ailerons for roll control. The induced drag, rolling moment, and yawing moment for an aircraft depend in part on the location and size of the ailerons. In the present study, lifting-line theory is used to formulate theoretical relationships between aileron design and the resulting forces and moments. The theory predicts that the optimum aileron geometry is independent of prescribed lift and rolling moment. A numerical potential flow algorithm is used to evaluate the optimum size and location of ailerons for a wide range of planforms with varying aspect ratio and taper ratio. Results show that the optimum aileron design to minimise induced drag always extends to the wing tip. Impacts to induced drag and yawing moment are also considered, and results can be used to inform initial design and placement of ailerons on future aircraft. Results of this optimisation study are also compared to theoretical optimum results that could be obtained from morphing-wing technology. Results of this comparison can be used to evaluate the potential benefits of using morphing-wing technology rather than traditional discrete ailerons.

The potential to recover waste heat from the exhaust gases of a turboprop engine and produce useful work through an Organic Rankine Cycle (ORC) is investigated. A thermodynamic analysis of the engine’s Brayton cycle is derived to determine the heat source available for exploitation. The aim is to use the aircraft engine fuel as the working fluid of the organic Rankine cycle in order to reduce the extra weight of the waste heat recovery system and keep the thrust-to-weight ratio as high as possible. A surrogate fuel with thermophysical properties similar to aviation gas turbine fuel is used for the ORC simulation. The evaporator design as well as the weight minimisation and safety of the suggested application are the most crucial aspects determining the feasibility of the proposed concept. The results show that there is potential in the exhaust gases to produce up to 50kW of power, corresponding to a 10.1% improvement of the overall thermal efficiency of the engine.

In this review paper, several take-off techniques of different species of animal flyers and gliders, both extinct and extant, are analysed. The methods they use vary according to animal group and size. Smaller animals, such as insects, rely on the use of transient aerodynamic techniques or the use of stored elastic energy. Medium-size flyers such as birds, bats, and other mammal gliders initiate flight by a jump which involves leg and wing movement coordination. The largest animals to fly, the extinct pterosaurs, are believed to have used a combination of aerodynamic and mechanic techniques in order to become airborne. The information presented here can be used as a resource for novel biomimetic unmanned aircraft design.

The aerodynamic modelling is one of the challenging tasks that is generally established using the results of the computational fluid dynamic software and wind tunnel analysis performed either on the scaled model or the prototype. In order to improve the confidence of the estimates, the conventional parameter estimation methods such as equation error method (EEM) and output error method (OEM) are more often applied to extract the aircraft’s stability and control derivatives from its respective flight test data. The quality of the estimates gets influenced due to the presence of the measurement and process noises in the flight test data. With the advancement in the machine learning algorithms, the data driven methods have got more attention in the modelling of a system based on the input-output measurements and also, in the identification of the system/model parameters. The research article investigates the longitudinal stability and control derivatives of the aerodynamic models by using an integrated optimisation algorithm based on a recurrent neural network. The flight test data of Hansa-3 and HFB 320 aircraft were used as case studies to see the efficacy of the parameter estimation algorithm and further, the confidence of the estimates were demonstrated in terms of the standard deviations. Finally, the simulated variables obtained using the estimates demonstrate a qualitative estimation in the presence of the noise.

Graphite is a material with unique high-temperature properties. Its strength and modulus increase with temperature up to about 2000-2500°C., in which range it exhibits a higher strength than any known material. The development of new types of graphite (such as pyrolytic graphite, deposited from the vapour) and impregnated graphites, are both significant to future technology. The highly-oriented pyrolytic graphites in particular, with their marked thermal and mechanical anisotropy, and their superior mechanical properties (60 x 103 lb./in.2 strength at 2750°C, with 60 per cent ductility) offer distinct possibilities, particularly in composite structures. Graphite sublimes directly from the solid to vapour phase at 3700°C. at atmospheric pressure. As the sublimation energy is high, it is, at least in theory, a very efficient ablating material. It also has a high creep resistance. Surface reactions limit its value, particularly in oxidising environments, and coatings, or other methods of surface protection, are of high importance. The modulus of graphite is low, being about one-half of that for lead at room temperature, increasing with temperature to a maximum in the region of 2200°C. The properties vary in detail from one type of graphite to another, and with the direction in which measurements are made. Graphite has a low density (about 2·0) and is comparatively cheap, so that its low temperature limitations (zero ductility at room temperature) may be offset, at least in part, by a re-appraisal of the design factors. It can be joined and fabricated fairly readily, and appears to be a material of great value to advanced high-temperature projects in the future, where composite assemblies of various kinds will be essential.

The problem of a non-planar wing of finite span very close to the ground is considered by the method of matched asymptotic expansions. This method is based on the work of Widnall and Barrows, in which a planar wing very close to the ground was examined in detail. A simple analytic solution, to first-order approximation, is obtained for a non-planar wing which is uncambered. Expressions for the lift coefficient, induced angle and induced drag coefficient, which are valid for small ground clearance and moderately small aspect ratio, are derived for the case when the configuration of the wing projected onto a transverse plane normal to the free stream is elliptic. The problem of the optimum lift distribution around the wing and the rolling-moment coefficient for the inclined flat wing are discussed.

The distribution of camber and of aerofoil angle of attack is given analytically for an optimally loaded non-planar wing, to first-order approximation. Moreover, it is seen that, to first-order approximation, the aerodynamic forces given for the small aspect ratio are independent of the wing planform and depend only on the wing configuration at the trailing edge projected onto a transverse plane.

Vibration characteristics of a linearly tapered cantilever beam and a shaft have been studied by using the lumped inertia force method; a linear displacement distribution is considered over each element. The results are compared with some of those in the literature and with experimental observations. These comparisons indicate that, even using a few elements, a reasonable degree of accuracy can be obtained in the natural frequency, although it is essential to consider more elements in order to determine mode shape accurately.

Non-symmetric response of elastic shells to localised impact loads is studied. Closed-form solutions for the response to four particular kinds of pulse shapes are given. Experimentally measured values of the strain response of a cylinder to impact loads are obtained which compare satisfactorily with theoretical predicted values.

Throughout the course of a flight mission, a range of aerodynamic conditions, including design-point conditions and off-design conditions, are encountered. As the bypass ratio increases and the fan-pressure ratio decreases to reduce the engine’s specific fuel consumption, the engine diameters increase, which results in an increase in the nacelle weight and overall drag. To reduce its weight and drag, a shorter nacelle with a length-to-diameter ratio $L/D = 0.35$ is investigated. In this study, an adaptive cokriging-based multi-objective optimisation method is applied to the design of a short aero-engine nacelle. Two nacelle performance metrics were employed as the objective functions for the optimisation routine. The cruise drag coefficient is evaluated under cruise conditions, whereas the intake pressure recovery is evaluated under takeoff conditions. The cokriging metamodel are refined using an effective infilling strategy, where high-fidelity samples are infilled via the modified Pareto fitness, and low-fidelity samples are infilled via the Pareto front. By combining parameterised geometry generation, automated mesh generation, numerical simulations, surrogate model construction, Pareto front exploration based on the non-dominated sorting genetic algorithm-II and sample infilling, an integrated multi-objective optimisation framework for short aero-engine nacelles is developed. Two-objective and three-objective test functions are used to validate the effectiveness of the proposed framework. After the optimisation process, a set of non-dominated nacelle designs is obtained with better aerodynamic performance than the original design, demonstrating the effectiveness of the optimisation framework. Compared with the kriging-based optimisation framework, the cokriging-based optimisation framework outperforms the single-fidelity method with a higher hypervolume value at the same number of iteration loops.

In this paper, a novel thrusting manoeuvre control scheme is proposed for a small spacecraft which is based only on the gimbaled thrust vector control (TVC) system. The spacecraft structure is composed of a body and a gimbaled thruster where common attitude control systems such as reaction control system (RCS) and spin stabilisation are not employed. A nonlinear two-body model is considered for the characterisation of the gimbaled-nozzle spacecraft where the gimbal actuator provides the only active control input. The spacecraft attitude is affected by a large exogenous disturbance torque which is generated by a thrust vector misalignment from the centre of mass (CM). To achieve some performance goals in the both transient and steady-state modes, a new control scheme is derived based on the combination of two linear and nonlinear controllers. The proposed method ensures the attitude and thrust vector stability during an impulsive orbital manoeuvre while eliminating and rejecting an exogenous disturbance torque. The numerical simulations illustrate the applicability of this method for using in a small spacecraft and its efficiency in sustained operation.

When a non-uniform stream flows through a cascade of compressor blades a three-dimensional secondary motion is generated in the outlet stream. This motion, which consists of a spanwise re-orientation of the Bernoulli planes, together with the effects of vorticity components in the stream direction, may be predicted theoretically. In this paper experimental results obtained on a 6 in. chord cascade are reported. The experimental and computed outlet angles are compared and the discrepancies are explained qualitatively. Additional particle track and visualisation experiments were designed to investigate the local blade flows and the effects of the nose vortices.