Plume interference effects on the axisymmetric flowfields around powered missiles are investigated using computational techniques. The study is mainly to understand the physics of the plume-induced shock and separation particularly at high plume to exit pressure ratios with and without shock-turbulent boundary layer control methods. Mass-averaged Navier-Stokes equations with the RNG k-ε turbulence model are solved using a fully implicit finite volume scheme and time-marching algorithm. The shock position and extent of separation was found to be dependent on the freestream Mach number and plume pressure ratio. Rounding the tail or a groove on the surface near the tail moved the shockwave downstream of the tail fin which should enhance the control of the missile.

There is a need for consistency between aviation safety targets – target levels of safety (TLS). Consistent ‘risk philosophy’ ensures that resources can be allocated in areas where they will be most beneficial in reducing the number of potential accidents and fatalities. Many existing aviation targets were devised decades ago, have not been brought up to date to take account of the considerable improvement in the sector’s safety performance, and are not targeted at some specific future year. It appears feasible to construct consistent and up-to-date sets of TLSs covering the full range of aviation needs, in particular for air traffic management. However, this requires significant, more demanding, changes to some TLS values. One caveat to note is that the safety of ‘loosely coupled’ aviation systems may be better described and managed by the Health and Safety Executive version of risk assessment rather than by a TLS approach.

The present paper concerns the response of a following airplane to a pair of wing tip vortices left by a leading aircraft, represented by the Hallock-Burnham model, including the effect of vorticity decay between the two aircraft. The effect of vorticity is evaluated in terms of the induced rolling moment and also the lift loss; these specify the roll acceleration and the downward acceleration, respectively. The corresponding two response equations can be put into the same dimensionless form, and integrated using exponential integrals. This specifies the roll rate and sink rate as a function of time; besides the latter, the bank angle and altitude loss, are also plotted, all also as a function of time, for all combinations of leading and following aircraft in five classes. These are the three ICAO weight categories of light, medium and heavy, plus two other cases, viz the special case of the Boeing 757, which requires larger separations distances, and the case of a future very large transport aircraft (VLTA) exceeding significantly the size of a Boeing 747.

It cannot have escaped notice, that in two months time we will celebrate the centenary of the first flight of a powered aircraft carrying a man. We rightfully acclaim ‘The miracle at Kitty Hawk’ for all that it has meant to our chosen profession, albeit outside our remit as a rotorcraft section.

There is however a significant 80th anniversary, which we can add to this centenary year. On 9 January 1923, a Cierva C-4 autogyro piloted by Lt Alejandro Gomez Spencer made an officially observed circular flight of over 4km (2·5 miles) in Madrid.

This important event brought the name of Juan de la Cierva to the fore on the International scene, and was subsequently to prove to be the key to the modern helicopter, an interesting lesson in technology in that, Cierva never set out to invent the helicopter, and never produced one himself.

Of equal significance is the fact that the Rotodyne represented an innovative application of the technology that Cierva began. Many would claim that the gyroplane has never been exploited to it’s full potential; maybe the Rotodyne gave us a foretaste of what was possible.

Experimental investigations were carried out to study the acoustic radiation from a rectangular wall mounted cavity in a confined supersonic flow. The free-stream Mach number was maintained at 1·5 and the cavity length-to-depth ratio was varied from 0·43 to 5·0. Acoustic measurements made on the top wall show jumps in the dominant frequency as the cavity behaviour changes from shallow-to-square-to-deep cavity. Numerical simulations of this unsteady two-dimensional flow using the commercially available software FLUENT have also been carried out. Unsteady pressure data at the same location in the flow field as the pressure transducers in the experiments was collected. FFT analysis of the unsteady pressure data was performed to obtain the dominant acoustic frequencies. The values for these dominant frequencies predicted by the numerical calculations agree well with experimental data. The numerical study also predicts the frequency jump observed in experiments.

In this paper we study large angle rotational manoeuvres of spacecraft. The problem of attitude control is formulated and solved through potential functions, thus simplifying frequent reorientation manoeuvres. A combination of gas jet and FEEP thrusters is employed in order to obtain short settling times while meeting stringent pointing requirements. In this way, spacecraft reorientation is achieved in two integrated steps by means of a discrete/continuous control law. Autonomous avoidance of undesired space orientations is obtained and constraints due to the solar array pointing requirements are satisfied. A case study is discussed where the methodology is applied to a large space telescope.

In flows over an ogive cylinder placed at incidence, it is well documented that a side force acts on the cylinder. However, little is known about the relation between the side force (CFy) and other force and moment components. In this note, the variations of three force and three moment components, acting on the ogive cylinder, with roll angle are measured simultaneously. The model was placed at four different angles-of-attack, namely α = 30°, 45°, 50° and 60° and the results show that in addition to CFy, the variation of CFz, CMx, and CMz with the roll angle also exhibit the square wave like behaviour at α = 45° and 50°, and with the same cross over φ positions, while CFx and CMy remain relatively constant irrespective of the roll angle. The magnitudes of CFx and CMy were found to increase with angle of attack and were thought to be due to the increase in normal frontal area.

Two aspects of hydrogen-air non-equilibrium chemistry related to scramjets are nozzle freezing and a process called ‘kinetic afterburning’ which involves continuation of combustion after expansion in the nozzle. These effects were investigated numerically and experimentally with a model scramjet combustion chamber and thrust nozzle combination. The overall model length was 0·5m, while precombustion Mach numbers of 3·1±0·3 and precombustion temperatures ranging from 740K to 1,400K were involved. Nozzle freezing was investigated at precombustion pressures of 190kPa and higher, and it was found that the nozzle thrusts were within 6% of values obtained from finite rate numerical calculations, which were within 7% of equilibrium calculations. When precombustion pressures of 70kPa or less were used, kinetic afterburning was found to be partly responsible for thrust production, in both the numerical calculations and the experiments. Kinetic afterburning offers a means of extending the operating Mach number range of a fixed geometry scramjet.

The dynamic behaviour of rotor blades is often modelled using onedimensional beam analysis with equivalent mass and stiffness properties to those of the full blade. Calculation of accurate elastic stiffness terms for these arbitrarily shaped sections with differing material properties is vital to this process. A method which produces these properties using standard finite element analysis codes is presented. The method is then compared with theoretical results for a simple rectangular section beam and case studies are performed on a composite laminate and box-section.

The problem of simulation models capable of predicting the aerodynamic instability of helicopter slung-load cargo containers and bluff bodies is addressed. Instability for these loads is known to depend on unsteady frequency-dependent aerodynamics, but simulation models that include the unsteady aerodynamics do not currently exist. This paper presents a method for generating such models using computational fluid dynamics (CFD) to generate forced-oscillation aerodynamic data and frequency domain system identification techniques to generate a frequency response from the CFD data and to identify a transfer function fit to the frequency response. The method is independent of the responsible flow phenomenon and is expected to apply to bluff-bodies generally. Preliminary results are presented for the case of the 6- by 6- by 8-ft CONEX (container express) cargo container. The present work is based on two-dimensional (2D) aerodynamic data for the CONEX side force and yaw moment generated by a forced oscillation in which frequency is varied smoothly over the range of interest. A first-order rational polynomial transfer function is found adequate to fit the aerodynamics, and this is shown to provide a good match with flight test data for the yawing motion of the CONEX.

While expansion deflection (ED) nozzles have traditionally been considered primarily for use as altitude compensating devices to improve the performance of single stage to orbit vehicles, they also offer the potential for enhancing high altitude propulsion systems. If intended to only operate in near vacuum conditions, the complexity of analysis and inherent risks involved in the ED concept are greatly reduced. An integrated approach to the design and performance analysis of such nozzles is presented, comprising a mixture of computational fluid dynamics, the method of characteristics, and a semi-empirical model to allow full analysis of the closed wake flow-field of an ED nozzle. While it is demonstrated that the influence of the parameters used to define the throat region is critical to the successful application of the ED nozzle, it is also shown that with careful design the weight savings possible are significant. The analysis method itself is flexible and rapid, and lends itself well to incremental improvements in accuracy as the flow under consideration becomes better understood.

Usually a fixed pitch propeller is designed to be optimal at cruise speeds. Thus the efficiency is quite low at takeoff or low speeds, as well as during other flight regimes. The present paper shows that by introducing a flexible element into the blade root, the propeller efficiency can be improved over a wide range of velocities. The flexible element reacts to root flap or torsion moments by changing the blade pitch at the root. The root flexibility and the pitch angles at the root at zero loads are chosen such that efficiency will increase during problematic regimes without decreasing the propeller thrust. In the case of straight blades the torsional moment at the root is too small to be used. In the case of swept blades this moment component is significantly increased and can contribute to the design of an optimal aeroelastically adaptive propeller.

Control activity is a recognised gauge of pilot workload and recent research has employed wavelet decomposition to classify discrete control actions into categories such as guidance and stabilisation. The aim of the present work is to extend the wavelet approach so that workload may be quantified through sets of rules based on appropriate control activity metrics. The rules are derived from data collected in piloted simulation trials of a variety of flying tasks involving a number of pilots and different helicopter configurations. Statistical tests are then applied which test the efficacy of the derived rules. The immediate aim of the research is to establish whether workload can be successfully predicted from control responses. The underlying goal however, is to be able to predict workload ratings from desktop simulations in order to provide indicative workload information at the design stage. The contribution of the current study to this objective is discussed.

This paper focuses on the design of a cascade within a cold stream thrust reverser during the early, conceptual stage of the product development process. A reliable procedure is developed for the exchange of geometric and load data between a two dimensional aerodynamic model and a three dimensional structural model. Aerodynamic and structural simulations are carried out using realistic operating conditions, for three different design configurations with a view to minimising weight for equivalent or improved aerodynamic and structural performance. For normal operational conditions the simulations show that total reverse thrust is unaffected when the performance of the deformed vanes is compared to the un-deformed case. This shows that for the conditions tested, the minimal deformation of the cascade vanes has no significant affect on aerodynamic efficiency and that there is scope for reducing the weight of the cascade. The pressure distribution through a two dimensional thrust reverser section is determined for two additional cascade vane configurations and it is shown that with a small decrease in total reverse thrust, it is possible to reduce weight and eliminate supersonic flow regimes through the nacelle section. By increasing vane sections in high pressure areas and decreasing sections in low pressure areas the structural performance of the cascade vanes in the weight reduced designs, is improved with significantly reduced levels of vane displacement and stress.

Modern high-speed aircraft, especially military, are very often equipped with single or compound delta wings. When such aircraft operate at high angles-of-attack, the major portion of the lift is sustained by streamwise vortices generated at the leading edges of the wing. This vortex-dominated flow field can breakdown, leading not only to loss of lift but also to adverse interactions with other airframe components such as the fin or horizontal tail. The wind tunnel and water studies described herein attempt to clarify the fluid mechanics of interaction between the strake and wing vortices of a generic 76°/40° double-delta wing leading to vortex breakdown. Some studies of passive control using fences at the apex and kink region are also described. Various diagnostic methods-laser sheet flow visualisation, fluorescent dyes, and pressure sensitive paints have been used.

The design methodology and performance of Loughborough University’s new 1·9m × 1·3m, indraft wind tunnel is discussed in the following paper. To overcome severe spatial and financial constraints, a novel configuration was employed, with the inlet and exit placed adjacent to each other and opened to atmosphere. Using a fine filter mesh, honeycomb, two turbulence reduction screens and a contraction ratio of 7·3, flow uniformity in the working area of the jet at 40ms-1 is shown to be within 0·3% deviation from the mean velocity, with turbulence intensity in the region of 0·15%. Working section boundary layer characteristics are shown to be consistent with that of a turbulent boundary layer growing along a flat plate, which originates at the point of inflection of the contraction. A maximum velocity of 46ms-1 was achieved from a 140kW motor, compared to a prediction of 44ms-1, giving an energy ratio of 1·42. Comparison between theoretical and measured performance metrics indicate differences between the way modules perform when part of a wind tunnel system compared to data gathered from test rigs.

The aeroelastic stability of a uniform, untwisted hingeless ‘smart’ helicopter rotor blade in hover has been analysed. The concept of a ‘smart’ blade is achieved by implementing a piezoelectric stack at an appropriate location along a host blade such that upon actuation it enters the load path becoming an integral part of the host structure. Thus, the stiffness characteristics of the rotor are altered causing modal damping augmentation of the blade. The perturbation equations of motion for the ‘smart’ blade that describe the unsteady blade motion about the equilibrium operating condition are obtained using Galerkin’s method. These differential equations with periodic time coefficients are analysed for stability utilising the Floquet method. Six different regimes of actuation are investigated, and a parametric study is carried out by considering six different design cases. It is shown that, compared to a ‘host’ blade the stability characteristics of the ‘smart’ blade are not affected adversely. In fact, a judicious design and actuation of the ‘smart’ spring has the potential of improving the stability boundaries of individual blades.

The effect of multigrid acceleration implemented within an upwind-biased Euler method for hovering rotor flows is presented. Previous work has considered multigrid convergence for structured single block rotor solutions. However, for forward flight simulation a multiblock approach is essential and, hence, the flow-solver has been extended to include multigrid acceleration within a multiblock solver. The requirement to capture the vortical wake development over several turns means a long numerical integration time is required for hovering rotors, and the solution (wake) away from the blade is significant. Hence, the solution evolution and convergence is different to a fixed wing case where convergence depends primarily on propagating errors away from the surface as quickly as possible, and multigrid acceleration is shown here to be less effective for hovering rotor flows. Previous single block simulations demonstrated that a simple multigrid V-cycle was the most effective, smoothing in the decreasing mesh density direction only, with a relaxed trilinear prolongation operator. This is also shown to be the case for multiblock simulations. Results are presented for multigrid computations with 2, 3, and 4, mesh levels, and a CPU reduction of approximately 80% is demonstrated for 4 mesh levels.

A two-dimensional vortex particle model is used for studying the development of the vortex wake generated by the wing of an aircraft in the Trefftz plane. Two-dimensional, finite-area vortex structures simulate the initial vorticity distribution at a near-field cross-section of the wing, as provided by either measurements or simulations. The code is used for studying the effect of weak or strong counter-rotating vortices on the development of an aircraft wake. Application in a three-vortex configuration, consisting of the tip and flap vortices, plus a weak negative vorticity sheet lying between them, supports the hypothesis of Graham that the merging of the tip and flap vortices is prevented, because in such an arrangement the counter-rotating vorticity sheet is wrapped around the primary vortices. The present results indicate that even in the far field the tip and flap vortices remain distinct and follow a helical trajectory with large-pitch and small-radius. The code is next applied to the two-vortex system of Savas’s triangular wing, in which the circulation of the flap vortex is comparable to that of the tip. Although a 2D analysis is inappropriate for stability analysis it is still useful for a quick qualitative investigation. Results indicate that the flap and tip vortices follow a helical trajectory with large-pitch but also very large radius. During one period, the flap vortex covers a span wise distance equal to the wing span. Such a flow has not been observed in flight or in laboratory tests. Actually, Ortega et al, who studied experimentally the triangular wing of O. Savas, found out that before concluding one full spiral, the vortices are literally destroyed (rapid spreading of their vorticity) by an instability mechanism.

Thirty-eight data sets from static tests of various 65° delta wings in many water and wind tunnels are compared with four empirical vortex breakdown location prediction methods and the results of two Navier-Stokes computations to assess their range of validity in pitch. Vortex breakdown is the sudden expansion and subsequent chaotic evolution of the otherwise orderly, spiraling, leading-edge vortex flow over the upper surface. Large fluctuations occur in vortex breakdown location at static test conditions making accurate experimental determination difficult.

The prediction methods do not account for the seemingly minor geometric details that vary between the models such as thickness, leading-edge bevel angle and radius, trailing-edge bevel angle, sting mounting, instrument housings, etc. These geometric variations significantly affect the position of vortex breakdown and degrade the accuracy of the predictions. The large changes in the flow produced by small geometric changes indicate that an efficient flow control strategy may be possible. Many of the data sets are not corrected for tunnel wall effects, which may account for some of the differences. Data presented herein are as published by the original authors, without additional corrections.