The transfer matrix method of structural analysis is applied to the problem of beams subjected to large deflections by dividing the beam into a large number of uniform sections and applying elementary bending theory to each section. The solution using this method is compared with the theoretical solution of Bisshopp and Drucker for large deflections in uniform cantilever beams. The method has also been applied to uniform and tapered cantilever beams at various angles to the horizontal under vertical point loading and the results compared with experimental data obtained from laboratory measurements.

This paper studies the rotor aeromechanics in descending flight using a nonlinear flexible multibody dynamic analysis code, DYMORE. A freewake model is included in DYMORE to improve the rotor wake modelling. The wind-tunnel test data of the Higher-harmonic Aeroacoustics Rotor Test (HART) II rotor, with and without higher harmonic pitch control (HHC), and the flight test data of the full-scale utility helicopter rotor in descent are used for the aeromechanics correlation at an advance ratio of 0·15. The blade-vortex interaction (BVI) airloads are reasonably predicted for both the HART II and utility helicopter rotors, although some BVI peaks are missed on the advancing sides for both the rotors. The flap deflections and elastic torsion deformations at the blade tip are fairly correlated against the measured data of the HART II rotor. The correlation of blade structural moments for both HART II and utility helicopter rotors are not as good as the lift predictions; however, a reasonable prediction is obtained for the utility helicopter rotor.

The aim of this work is to develop a calculation model based on the method of characteristics making it possible to study the effect of the stagnation pressure of the combustion chamber on the 2D and axisymmetric minimum length nozzle design giving a uniform and parallel flow at the exit section. The model is based on the use of the real gas approach. The co-volume and the intermolecular interaction effect are taken into account by the use of the Berthelot state equation. The effect of molecular vibration is considered in our model to evaluate the behaviour of gas at a high temperature. In this case, the stagnation pressure and the stagnation temperature are important parameters in our model. The resolution of the algebraic equations is done by the finite difference corrector predictor algorithm. The validation of the results is controlled by the convergence of the critical section ratios calculated numerically as obtained by the theory. The mass and the thrust are evaluated to improve the efficiency of the nozzle. The comparison is made with the high temperature and perfect gas models. The application is made for air.

This paper deals with the problem of fault-tolerant control (FTC) for redundant multirotor unmanned aerial vehicles (UAVs) subject to actuators failures. A fuzzy logic approach is used to solve the constrained control allocation problem by adjusting the components of the multiplexing vector once a motor failure is detected. This fuzzy logic allocation problem is tuned using the Bacterial Foraging Algorithm (BFA), a powerful bio-inspired optimisation technique. The effectiveness of this approach is illustrated through real experimental application to a hexarotor UAV, where up to two motors failures are considered.

In this paper, a new type of fixed-wing vertical take-off and landing, unmanned aerial vehicle (UAV) has been designed. Thrust-vector direct force control has been introduced in three axes to make UAV exhibit superior manoeuverability in transition flight. Considering the characteristics of UAV's dynamic model, which are non-linear, non-affine, and have redundant input, a two-stage progressive optimal control allocation method is developed, which can optimise position and attitude control in synthetical, and motivate effectors to generates desired force and moments. A task-oriented weight selection scheme is proposed to make objective function suitable for different tasks and flight conditions. In addition, a general constraint strategy is designed to guarantee the feasibility of optimal allocation results, which can largely reduce the onboard computation time. Simulations show that UAV can adjust flight attitude and use control effectors in an optimal way, and demonstrating satisfactory tracking of low-speed high-manoeuver flight paths.

In ref. 1, an extension of the Kantorovich variational method of minimising a functional is discussed. The extension is based on an iterative technique wherein functions derived from the solution of sets of simultaneous ordinary differential equations are used again in cyclic order to obtain an improved solution. It is conjectured that if the iterative procedure is continued indefinitely, the functional will be close to its correct value, and so also will the associated function. The method given in ref. 1 is a generalisation of the iterative technique for minimising a double integral given by the writer in ref. 4, although in this work the iterations are carried out in the first approximation of the Kantorovich method and convergence is obtained in the usual manner of Kantorovich. Like ref. 4, ref. 1 uses the classical torsion problem of a rectangular bar as an illustrative example. Each shows that accurate Prst approximation solutions can be obtained and ref. 1 goes on to show that, for this particular problem, the derived functions are unique and are not dependent on the initial choice for part of the function.

A theoretical study is made of the aerodynamics of wings executing simple harmonic oscillations. The wings considered are slender and infinite-simally thin; they may have curved leading edges and be cambered, but their cross sections must be straight lines. The value of the reduced frequency is assumed to be such that the flow is governed by the two-dimensional Laplace equation.

Leading-edge separation is simulated by a line vortex joined to the leading edge by a cut. The strength and position of the vortex and the values of the generalised forces can be determined by the theory. Results have been calculated for flat delta wings and a flat gothic wing; they are in reasonable agreement with experiment.

In this paper, a Gaussian process regression (GPR)-based novel method is proposed for non-linear aerodynamic modelling of the aircraft using flight data. This data-driven regression approach uses the kernel-based probabilistic model to predict the non-linearity. The efficacy of this method is examined and validated by estimating force and moment coefficients using research aircraft flight data. Estimated coefficients of aerodynamic force and moment using GPR method are compared with the estimated coefficients using maximum-likelihood estimation (MLE) method. Estimated coefficients from the GPR method are statistically analysed and found to be at par with estimated coefficients from MLE, which is popularly used as a conventional method. GPR approach does not require to solve the complex equations of motion. GPR further can be directed for the generalised applications in the area of aeroelasticity, load estimation, and optimisation.

This investigation surveyed the potential and established outcomes for future 19-passenger fixed-wing commuter transport aircraft concepts employing battery-based Voltaic-Joule/Brayton motive power systems with no additional electrical energy drawn from generators mechanically coupled to thermal engines. The morphological approach was that of a tri-prop (two on-wing podded turbo-props and one aft-fuselage mounted electric motor configured as a pusher-on-pylon installation). A Battery System-level Gravimetric Specific Energy (referred to as “battery energy density”) of at least 500 Wh/kg yielded 39%, 25% and 10% block fuel reductions for 150-nm (Design Service Goal), 430-nm (85th percentile) and 700-nm (maximum range) stage lengths, respectively. All quoted comparisons are against a suitably projected turbo-prop only year-2030 aircraft. In contrast to the reference Beech 1900D, block fuel reductions of up to 44-49% were predicted, which could facilitate a significantly lower deficit in relation to the Advisory Council for Aviation Research and Innovation in Europe (ACARE) Strategic Research and Innovation Agenda (STRIA) 55% target for year 2030. This investigation also indicated that, in the future, suitably flexible hybrid-electric architectures could be fashioned allowing possibility for the aircraft to complete any required city-pair operations (within the legitimate payload-range working capacity) irrespective of exchangeable batteries being available at a given station. Finally, it was also established, assuming such a tri-prop morphology, Normal conducting machines delivering maximum shaft power output of 1.1 MW would be required.

The aim of this paper is to determine the mathematical relationship (model) between control deflections and structural deflections of the F/A-18 modified aircraft in the active aeroelastic wing technology program. Five sets of signals from flight flutter tests corresponding to the excited sources were measured by NASA Dryden Flight Research Center. These excitation inputs are: differential ailerons, collective ailerons, collective stabilisers, differential stabilisers, and rudders. The signals to be used by the model are of two types: control deflection time histories and corresponding structural deflections on the wing and trailing-edge flaps. We choose to use the subspace identification method based on reconstructing the observability matrix in order to identify the nonlinear multi-input, linear-in-the-states, multi-output system. We identify models (input/output characteristics) by applying this method for a number of sixteen flight conditions for which the Mach number varies from 0·85 to 1·30 and the altitudes vary from 5,000ft to 25,000ft. Very good results are obtained with a fit between the estimated and the measured signals and a correlation coefficient higher than 90%.

Flying under degraded visual environments is a challenging task in helicopter operations. The brownout phenomenon, caused by the rotor downwash on a dusty or sandy underground has caused several critical incidences and accidents in the past. In contrast to an extensive free wake analysis of the rotor vortices, this paper presents a computer graphical solution to simulate brownout conditions. The animation approach builds upon a particle system with a basic aerodynamic assumption of a permanent ground vortex and additional turbulence. The created brownout effect module is a part of the RealTime Image Generator software, used in DLR’s ground based helicopter flight simulator. The object oriented structure of the underlying application programming interface OpenSceneGraph facilitates the development of a generic effect interface for future improvements. An overview of the developed module, the particle system engine and the physical dependencies is provided. To overcome the challenge of capturing the visual realism, a pilot test course with brownout typical tasks is presented. Criteria focussing on the visual and physical parameters are defined to build up a questionnaire. It is used to improve the visual standard and to meet the future pilot’s needs.

A nonlinear aeroelastic model capable of assessing arbitrary morphing manoeuvres and calculating the associated morphing energy requirement is presented in this paper. The aeroelastic model consists of a close coupling between a corotational beam element, accounting for geometric nonlinearities, and a Weissinger method aerodynamic model, containing the Prandtl-Glauert correction for high-subsonic Mach numbers. The morphing deformations are discretised into three distinct morphing modes; fold morphing, twist morphing, and shear morphing, because of which virtually any morphed shape can be achieved, given a proper distribution of the three modes over the wing. The proposed aeroelastic morphing framework is used to design morphing winglets, and it has been shown that morphing winglets can improve the performance of fixed winglets significantly for regional airliners.

Aeroelastic phenomena of stall flutter are the result of the negative aerodynamic damping associated with separated flow. From this basis, an investigation has been conducted to estimate the aerodynamic damping from a time-marching aeroelastic computation. An initial investigation is conducted on the NACA 0012 aerofoil section, before transition to 3D propellers and full aeroelastic calculations. Estimates of aerodynamic damping are presented, with a comparison made between URANS and SAS. Use of a suitable turbulence closure to allow for shedding of flow structures during stall is seen as critical in predicting negative damping estimations. From this investigation, it has been found that the SAS method is able to capture this for both the aerofoil and 3D test cases.

This paper examines the design of a composite helicopter rotor blade to meet given cross-sectional properties. As with many real-world problems, the choice of objective and design variables can lead to a problem with a non-linear and/or non-convex objective function, which would require the use of stochastic optimisation methods to find an optimum. Since the objective function is evaluated from the results of a finite element analysis of the cross section, the computational expense of using stochastic methods would be prohibitive. It is shown that by choosing appropriate simplified design variables, the problem becomes convex with respect to those design variables. This allows deterministic optimisation methods to be used, which is considerably more computationally efficient than stochastic methods. It is also shown that the design variables can be chosen such that the response of each individual cross-sectional property can be closely modelled by a linear approximation, even though the response of a single objective function to many design parameters is non-linear. The design problem may therefore be reformulated into a number of simultaneous linear equations that are easily solved by matrix methods, thus allowing an optimum to be located with the minimum number of computationally expensive finite element analyses.

Minimisation of airframe mass reduces the costs of materials and manufacturing, as well as fuel consumption and atmospheric emissions. Fast, reliable analysis tools are required during preliminary design, when many alternative configurations and load cases are considered. The modelling and computational costs of finite element analysis are avoided by employing exact strip solutions of the governing differential equations, using the Wittrick-Williams algorithm to solve the resulting transcendental eigenproblems of buckling and vibration. This paper reviews recent enhancements to the exact strip method for analysis and optimum design of aerospace structures, using the specialist software VICONOPT. Lighter composite panels can be designed by obtaining reliable estimates of the reduced postbuckling stiffnesses when loaded in compression and shear. Further advances include discrete optimisation of layer thicknesses to allow for practical composite manufacturing constraints, vibration constraints, and a newly extended multi-level interface combining finite element analysis of a whole wing with exact strip postbuckling design of individual panels.

The title of this paper clearly has a wide scope. None will dispute the presence of many problems in aircraft development. It was suggested in the first place that this paper might take the form of a description of the workings of a chief designer's mind when a new aeroplane is conceived. Such a paper would deal largely with technical considerations, such as choice of engines, wing loading, plan form and so on.

The diversity of uses to which the modern aeroplane is put gives rise to great differences between types. A jet fighter, for example, will be influenced by considerations far removed from those controlling the design of a long—range civil transport. To attempt to cover in detail such a wide field would result in an encyclopaedia rather than a paper; to tackle it in general terms would beget a vagueness lamentably devoid of interest.

Therefore, it has been thought wiser to attempt an assessment of some of the more fundamental problems confronting aviation.

Although a numerical solution of the turbulent boundary-layer equations has been achieved by Mellor and Gibson for equilibrium layers, there are many occasions on which it is desirable to have closed-form expressions representing the velocity profile. Probably the best known and most widely used representation of both equilibrium and non-equilibrium layers is that of Coles. However, when velocity profiles are examined in detail it becomes apparent that considerable care is necessary in applying Coles's formulation, and it seems to be worthwhile to draw attention to some of the errors and inconsistencies which may arise if care is not exercised. This will be done mainly by the consideration of experimental data. In the work on constant pressure layers, emphasis tends to fall heavily on the author's own data previously reported in ref. 1, because the details of the measurements are readily available; other experimental work is introduced where the required values can be obtained easily from the published papers.

The paper uses the conventional nine-noded Lagrangian element for studying transient linear response analysis of composite stiffened shells. An improved version of the stiffener modelling has been used in which the stiffener can be placed anywhere inside the element. For the first time, concentric or eccentric stiffeners have been used for composite stiffened shells for solving the transient dynamic response of these structures. These are not available in existing commercial packages. Different types of time dependent loading such as short duration air-blast loading, suddenly applied uniformly distributed step loading and sinusoidally harmonic loading have been considered in this paper. The results of stiffened composite cylindrical shells and doubly curved shells with different boundary conditions and various laminate orientations have been presented for eccentric stiffeners. Parametric studies considering different variables have also been carried out.

The research paper addresses the problem of estimating aerodynamic parameters using a Gauss-Newton-based optimisation method. The process of the optimisation method lies on the principle of minimising the residual error between the measured and simulated responses of the system. Usually, the simulated response is obtained by integrating the dynamic equations of the system, which is found to be susceptible to the initial values, and the integration method. With the advent of the feedforward neural network, the data-driven regression methods have been widely used for identification of the system. Among them, a variant of feedforward neural network, extreme learning machine, which has proven the performance in terms of computational cost, generalisation, and so forth, has been addressed to predict the responses in the present study. The real flight data of longitudinal and lateral-directional motion have been considered to estimate their respective aerodynamic parameters. Furthermore, the estimates have been validated with the values of the classical estimation methods, such as the equation-error and filter-error methods. The sample standard deviations of the estimates demonstrate the effectiveness of the proposed method. Lastly, the proof-of-match exercise has been conducted with the other set of flight data to validate the estimated parameters.

This paper concerns aircraft system identification and, in particular, the process of aerodynamic model structure determination. Its application to experimental data from unmanned aerial vehicles (UAVs) is also described. The procedure can be particularly useful for determining an aerodynamic model for aircraft with unconventional airframe configurations, which some unmanned aircraft tend to have. Two model structure determination techniques are outlined. The first is the well-established stepwise regression method, while the second is an adaptation of an existing frequency response approach which instead utilises maximum likelihood estimation. Example applications of the methods are presented for two data sources. The first is a set of UAV flight test data and the second is data recorded from dynamic wind tunnel tests on a UAV configuration. For both examples, the model structures determined using stepwise regression and maximum likelihood analysis matched one another, suggesting that the maximum likelihood approach and the chosen thresholds for its statistical metrics were reliable for the data being analysed.