How much is known about high altitude clear air turbulence? Sufficient to show that aircraft may, with little or no warning, experience bumpiness which the pilot would describe as “ moderate ” or, on occasions, “ severe,” at altitudes up to at least 40,000 feet, thus including altitude bands where commercial jet aircraft will be flying during the next few years. The phenomenon, therefore, is of significance to airline operators and the requirement is for the aircraft commander to be supplied with sufficient information to enable him to avoid such turbulence, or to provide him with adequate warning so that crew and passengers can be properly prepared for it. This does not imply that there is evidence to suppose that clear air turbulence may be of such severity as to affect the safety of a flight. It is important, however, to take good care of the passengers and their comfort is an essential consideration.

Recent work by Tsitas and Kingston(1) has demonstrated that an 8kg 6U CubeSat can be designed to perform Earth observation missions equivalent to those of 50-150kg microsatellites. Their design is reviewed and its commercial potential is compared to the 156kg RapidEye spacecraft. Three other commercial applications of this design are described. These are: a standard spacecraft for space scientists and astronomers; the spacecraft component of an N nation 5 spectral band disaster monitoring constellation and a night imaging satellite. Nanosatellites should now be considered for commercial missions previously thought to require microsatellites.

Recent advances in two lifting surface methods are reported. The present subsonic constant pressure method improves upon the program robustness of the doublet lattice method. The present unified supersonic-hypersonic method extends the range of applicability of lifting surface theory to the Newtonian limit. Based on a uniformly-valid series formulation, the method accurately approximates the non-linear thickness effect, whereas this effect is neglected by the linear theory and overestimated by piston theory. In fact, the present results generally agree well with the trends of several Euler solutions. Among other findings, cases computed by the unified method confirm that the effect of thickness is to reduce the supersonic flutter speed.

A simulation study was conducted in order to investigate the influence of vortex deformation on wake encounter characteristics. Wake vortices tend to be strongly deformed during the decay process, depending on the atmospheric conditions in terms of turbulence and thermal stratification. For quantification of the influence of vortex deformation, encounters of an aircraft of the ‘Medium’ category behind a generator aircraft of the ‘Heavy’ category were simulated with straight vortices and with realistically deformed vortices derived from large-eddy simulations. All relevant parameters that influence the encounter characteristics, such as encounter angles and positions, were varied within a wide range. In order to cover all kinds of vortex deformation, encounters with different vortex ages from 16-136 seconds were simulated. Hence, all relevant phases during the vortex decay from nearly straight and wavy vortices to vortex rings were considered.

The parameter variation study revealed that on average the impact on the encountering aircraft is less with deformed vortices than with straight vortices of comparable strength. Especially with vortex rings, the encountering aircraft is exposed to a much smaller impact. However, the results also show a larger aircraft response during encounters with wavy vortices just prior to vortex linking. The maximum aircraft response with wavy vortices is stronger than with straight vortices of comparable strength. Also, the strongest encounters occur under greater encounter angles with deformed vortices than with straight ones.

From necessity, military aircraft often operate in a highly fatigue damaging environment and history has shown in lost lives and aircraft the consequences of failure to appreciate fully the usage environment. The need for robust and cost effective structural usage monitoring of military aircraft to ensure operations are conducted within acceptable levels of risk is paramount. Furthermore, increased economic pressures require ever-inventive methods to be employed to maximise the lives of military fleets; structural usage monitoring will be a key asset in this drive. A highly cost effective indirect structural health and usage neural network (SHAUNN) monitoring system is proposed. A SHAUNN uses regression relationships determined by artificial neural networks to predict stresses, strains, loads, or fatigue damage from flight parameters. Within this paper the development of a SHAUNN monitoring system is described. Flight parametric data, captured during Operational Loads Measurement of the Royal Air Force Dominie TMk1 aircraft have been used to predict stresses at the key structural location in the wing, using mapping relationships determined by artificial neural networks. A framework for the development of the SHAUNN monitoring system is discussed and the basic architecture of the multilayer perceptron artificial neural network is described. It is concluded that this technology could provide the basis for an accurate, cost-effective structural usage monitoring system and further work to investigate the prediction of ground – based stresses in the wing is recommended.

The paper presents a method for constructing a set of vertical flight path segments, that would compose an aircraft's vertical flight envelope, by using an aircraft performance model. This method is intended to be used for aircraft flight plan prediction and optimisation algorithms. The goal is to reduce the volume of recurring segment performance computations currently required for flight plan prediction or optimisation. The method presented in this paper applies to a free-flight scenario. The flight-path segments composing the vertical flight envelope belong to one of the unrestricted climb, constant-speed level flight, step-climb and continuous descent segments, performed at the consigned climb, cruise and descent speed schedules and at the consigned air temperature values. The method employs an aircraft model using linear interpolation tables. Nine test scenarios were utilised to assess the performances of the resulting flight envelopes as a function of the number of cruise altitudes and descent flight paths. The set of evaluated performance parameters includes the range of total flight times and still-air flight distances, and the vertical profiles describing the minimum and maximum flight times, and still-air flight distances. The advantages of the proposed method are multiple. First, it eliminates the need for repetitive aircraft performance computations of identical vertical flight plan segments, and provides the means for quick retrieval of the corresponding performance data for use in the construction of a full flight plan. Second, the vertical flight path look-up structure and the vertical flight-path graph describe a set of vertical flight paths that consider an aircraft's and flight plan's configuration parameters and cover its maximum flight envelope. Third, the look-up structure and the graph provide the means for rapid and clear identification of the available options for constructing a flight-plan segment, as well as for detecting the points associated with changes in the flight phases, including climb, cruise, step-climb and descent.

A considerable amount of theoretical investigation has been undertaken recently, into the stress concentrations arising in the vicinity of cut-outs in aircraft pressure cabins. Papers which analyse the stress concentrations around circular, elliptical, and square reinforced cut-outs, under various loading conditions have been presented by Mansfield, Hicks and Wittrick.

In all of these investigations, the problem of the cut-out in a cylinder has been reduced to a problem of an infinite plane sheet containing a hole, and the effects of the curvature have been generally assumed to be insignificant.

The Swiss Airforce is operating F/A-18C/D Aircraft since 1997. Since the aircraft’s structural design is different from the version operated by the US Navy it was necessary to carry out a structural integrity study (ASIP) which was done by The Boeing Company in St. Louis. To validate this study a full scale fatigue test facility was build at RUAG and operated from 2003 to 2005. When operating this facility difficulties were encountered with the aerodynamic loads data provided by Boeing (insufficient, not well documented, questionable data). As a result RUAG looked for alternative methods to provide the aerodynamic loads, and a large investment was made in the development of a Computational Fluid Dynamics (CFD) tool. The Navier Stokes Multi Block (NSMB) solver, which was developed in an international collaboration, was adopted. In a first phase the code was validated by comparing results of CFD calculations with wind-tunnel results, results from literature and flight test data results. In the second phase, discussed in this paper, a Fluid Structure Interaction (FSI) tool was developed to permit unsteady aero-elastic simulations. Particular attention is focused on the vertical tail since this component of the F/A-18 fighter is very sensitive to fatigue due to unsteady loads generated by buffeting phenomena.

It has almost become a tradition in recent years to begin a paper on boundary layer by paying a tribute to the great Prandtl and his famous paper in which he introduced the conception of boundary layer into Fluid Dynamics.

The year 1954 is, however, not only memorable to mark the passing of fifty years since Prandtl's classical demonstration of the effect of boundary layer suction on the flow pattern around a cylinder; it is also memorable because in 1954 most convincing demonstrations of practical applications of boundary layer control for aircraft have taken place. I am referring, in particular, to the demonstrations with the Attinello flap in the United States which mark the introduction of one form of boundary layer control as an engineering and practical reality.

It was pointed out in ref. 1 that various interpolation techniques could be used to develop elements (for the matrix displacement method) of increasingly more complex characteristics both as far as geometry and specification of strain are concerned. A number of authors have examined this problem in detail and attention is drawn to the excellent work of Bogner, Fox and Schmit on plate elements, and to the elegant paper by Pestel. Over a number of years the ISD at the University of Stuttgart has investigated the application of interpolation functions and has developed within the ASKA language a number of corresponding elements.

The next generation of civil large aero-engines will employ greater bypass ratios compared with contemporary architectures. This results in higher exchange rates between exhaust performance and specific fuel consumption (SFC). Concurrently, the aerodynamic design of the exhaust is expected to play a key role in the success of future turbofans. This paper presents the development of a computational framework for the aerodynamic design of separate-jet exhaust systems for civil aero-engines. A mathematical approach is synthesised based on class-shape transformation (CST) functions for the parametric geometry definition of gas-turbine exhaust components such as annular ducts and nozzles. This geometry formulation is coupled with an automated viscous and compressible flow solution method and a cost-effective design space exploration (DSE) approach. The framework is deployed to optimise the performance of a separate-jet exhaust for very-high-bypass ratio (VHBR) turbofan engine. The optimisations carried out suggest the potential to increase the engine’s net propulsive force compared with a baseline architecture, through optimum exhaust re-design. The proposed method is able to identify and alleviate adverse flow-features that may deteriorate the aerodynamic behaviour of the exhaust system.

An analysis is presented of the output of a pressure probe, comprised essentially of four yawmeters, which was designed to yield vorticity information.

It is shown that if the probe is utilised in flows which have vorticity dominated by variation of either the direction or the magnitude of the velocity then the probe output may be easily related to vorticity. It is argued that such flows should be readily recognised, and they include many situations of interest involving vortex flows, boundary layers and wakes.

Earlier work had already demonstrated that the probe is useful in exploring regions of predominantly streamwise vorticity. The present work shows a result with the probe used in a boundary layer flow where the vorticity is nearly normal to the local flow.

Use of the probe in unsteady flow is briefly examined.

This paper describes a detailed experimental investigation of turbulent heat transfer in a radially rotating tube with particular reference to its application to the design of cooled turbine rotor blades. The paper focuses on the strategy adopted, the description of the apparatus used, the method of data processing and a selection of measurements which illustrate the manner by which Coriolis force and centripetal buoyancy force interactively affect the local heat transfer along the leading and trailing edges of the tube.

As well as re-confirming the fact that Coriolis force and centripetal buoyancy have a significant influence on the forced convection mechanism present due to the through flow, a number of new experimentally-based observations are presented. An empirical correlation, which is physically consistent, has been developed which permits the interactive effect of Coriolis force and centripetal buoyancy on forced convection to be evaluated and quantified.

The work has been motivated by the need to understand the general effect of rotation on the performance of the internal cooling airways used in gas turbine rotor blades.

The flying wing supersonic transport is simply a straight wing of high aspect ratio and of sufficient size to contain passengers comfortably. Such a wing can be steered to different sweep angles and thus adapted to efficient flight over a range of Mach numbers.

The writer demonstrated such a wing by flying models at the First International Congress in the Aeronautical Sciences. The potential advantages of such a flying wing were discussed by G. H. Lee of Handley Page Aircraft at a subsequent Congress. The present paper gives recent studies of flight stability, efficiency and operational problems. It is suggested that by limiting the Mach number to twice current jet speed fuel efficiency approaching that of present day subsonic transports could be achieved. This goal would probably also require the development of variable bypass engines.

Wind tunnel data have been obtained from a flapped tanker wing and receiver aircraft model at varying vertical separation and the results compared with theory. In the aerodynamic model, the tanker wing is represented by a pair of horseshoe vortices from the wing and flap tips and an allowance is made for the self-induced vertical displacement of the trailing vortices at the receiver aircraft position. The aerodynamic loads on the receiver are determined by the vortex-lattice method and lifting-line theory, although an approximate method is used to determine the side force on the fin. Data were obtained from open and closed test sections in order to estimate the wind tunnel boundary interference effect. In the longitudinal case, significant differences were obtained between theory and experiment. Two reasons for the differences are the assumption that the trailing vortices are fully rolled up and the neglect of viscous decay of the vortices. The lateral aerodynamic interference was determined by banking the tanker wing and displacing it sideways and by yawing the receiver aircraft model. In the case of the rolling moment due to sideways displacement, which is the most significant lateral aerodynamic interference term, the wind tunnel boundary interference is highly significant and the difference between theory and experiment is large due to incomplete roll up of the trailing vortices. The theoretical and experimental trends are similar although the theory overpredicts the rolling moment due to bank and sideways displacement while the corresponding side force and yawing moment are underpredicted. As in previous tests using an unflapped tanker wing, the effect of the sidewash due to the tanker wing on the receiver in yaw is found to be relatively insignificant.

For a simple undamped vibrator driven by a force whose frequency varies linearly with time, simple algebraic expressions are derived which give values for the maximum amplitude performed by the vibrator and for the frequency of the driving force where the maximum displacement occurs. Driving forces of both increasing and decreasing frequencies are considered.

A method of calculation is developed to compute the overall performance of a multi-stage axial compressor, from a knowledge of the individual stage characteristics, by a “stacking” technique. Compressor models are designed and their overall performance calculated. These results are compared to show, qualitatively, the effect of alterations in design and stage performance on overall performance and to find how compressors should be designed for optimum performance.

A study of the laminar boundary layer on a yawed infinite wing in a compressible fluid is made. A method is presented for the investigation of compressibility effects by direct solution of the linearised equations of motion, first considerably simplified by the extension of a transformation due to Illingworth and Stewartson, which assumes a heat-insulated surface and a fluid of unit Prandtl number and a coefficient of viscosity which is proportional to the absolute temperature. As an example of this procedure the boundary layer near a stagnation point is calculated. The simplifications necessary for an extension of the momentum method, which is available for a yawed infinite wing in an incompressible fluid, are discussed, and this method is recommended for a first evaluation of the effect of compressibility.

Hypersonic conical flows over delta wings are treated in the thin-shock-layer approximation due to Messiter. The equations are hyperbolic throughout, even in regions where the full equations are elliptic, and have not hitherto been solved for flows with attached shock waves. The concept of the simple wave has been used to construct a class of solutions for such flows; they contain discontinuities in flow variables and shock slope but, for the case of flow over a delta wing with lateral symmetry, agreement with results of numerical solutions of the full equations is good. The method is applied to plane delta wings at yaw, and to wings with anhedral and dihedral. For the flow at the tip of a rectangular wing, it is shown that two distinct solutions may be constructed.

A new integral equation, and the corresponding boundary-element method, is presented for the aerodynamic analysis of compressible, subsonic, potential flows around bodies in arbitrary motion, with applications to helicopter rotors in hover. The formulation is closely related to that introduced by Morino for the aerodynamic analysis of aircraft: in that paper, the surface of the aircraft is assumed to be in arbitrary motion with respect to a frame of reference that moves in uniform translation. Such a formulation is very useful for the analysis of aircraft undergoing small oscillations with respect to a reference configuration. However, for the analysis of more complex motions (e.g. helicopter rotors in forward flight), it is more convenient to use a frame of reference that moves in arbitrary motion (in particular, for the case of a body moving in rigid-body motion, a frame of reference rigidly connected with the body).