Two-dimensional potential flow expressed by means of the complex potential function uses Euler coordinates, i.e. a fixed point approach. However, there are many cases where the identical particle time is required, for example the settling time of suspended particles, heat convection (because in incompressible potential flow the heat and flow equations are uncoupled), and dispersion of fluid particles due to distortion.

In real variables the differential equation for the Lagrange time is generally too complicated because it involves two coordinates as functions of time. In the following a differential equation of single complex variable is derived.

The factors influencing survival in aircraft accidents can be classified into configurational, environmental, procedural or behavioural. New methodologies which have been developed in order to simulate emergency behaviour are introduced. A series of experimental programmes in which the new behavioural techniques are applied to configurational, environmental and procedural changes in the cabin are described. The results suggest that the techniques provide the behavioural and statistical data required for the assessment of design options or safety procedures for use in aircraft emergencies.

The rotorcraft has evolved considerably since the introduction of the first helicopters into civil and military service in the early post-war years. The latest generation of rotorcraft now entering production make use of sophisticated technologies and set new standards for performance, productivity and safety. The paper discusses the current state of rotorcraft technology and outlines potential improvements for the future.

As a prelude to the discussion of technology improvements, future market conditions and drivers are examined. Cost is highlighted as a major preoccupation for civil and military operators and cost-effectiveness and operational flexibility are noted as the key market requirements for the future.

A range of platform and system issues are reviewed and potential improvements discussed. Areas covered include

• • rotor systems

• • powerplant

• • transmission

• • fuselage structures

• • vibration reduction

• • flight controls

• • human machine interface

• • mission systems.

The potential for new rotorcraft configurations is considered with particular attention given to the evolutionary step of thrust and lift compounding, which offers a wider flight envelope for rotorcraft without the high cost of radical configuration change.

Finally, the need for an integrated approach to the rotorcraft design and development process is emphasised. The highly capable tools and techniques that are now becoming available are considered vital to future process improvements. It is foreseen that increased resources will be needed during the early stages of product development in order to produce first time designs that meet market requirements. The importance of technology demonstration as a means of providing technology maturity is discussed. It is concluded that demonstration programmes will need to be closely linked to market requirements in the future with costs shared between all sections of the rotorcraft community.

This paper addresses the problem of limit-cycle taming, which is defined in this paper as the use of nonlinear control laws to ensure that the limit-cycle behaviour of the system beyond the stability boundary is of a benign rather than a destructive nature. Specifically, we consider a one-parameter (denoted by λ) autonomous dynamic system having algebraic nonlinearities. We assume that the system has a stable solution, x = 0, for λ < λ0, and experiences a Hopf bifurcation at λ = λ0. Using a singular perturbation analysis about the stability boundary, it is shown that, using a simple nonlinear control law, limit-cycle taming is always possible in the neighbourhood of a Hopf bifurcation. The control system proposed for limit-cycle taming is fully nonlinear, and therefore does not affect the linear behaviour of the system (in particular its stability characteristics). Hence, limit-cycle taming may be used in conjunction with a standard linear active control (e.g. use of linear active control to increase the stability boundary). Applications of the theory to the problem of flutter are presented.

Some earlier investigations on the flows in S-shaped diffusing ducts suggested that the first bend was the primary source of pressure loss and engine-face flow distortion, e.g., Goldsmith. By increasing the curvature ratio (ratio of the duct curvature to the duct inlet cross-sectional diameter) of the first bend and by incorporation of a straight diffuser joining the end of the first bend and the inlet of the second bend, a significant improvement in the total pressure recovery at the engine face could be achieved (Fig. 1). A large proportion of the gain in the total pressure was attributed to the central straight diffuser. Results at a lower inlet speed (incompressible; inlet Reynolds number about 60 000) in the same ducts by Ho, Myring and Livesey(2) revealed the same trend as in the original high inlet speed reported by Goldsmith(1) (compressible; inlet Mach number from 0·4 to 0·8; inlet Reynolds number over one million). However, changing the curvature ratio in the first bend also changes the direction of the axis of the inlet plane, which should be aligned in the same direction as the axis of the exit plane (cf Fig. 1). Thus, the previous experiments were actually comparing ducts at different angles of attack relative to the axis of the exit plane; in relation to a typical jet aircraft intake installation. Hence, the effectiveness of the straight diffuser at zero angle of attack (relative to the axes of the inlet and exit planes) on the overall total pressure recovery in an S-shaped duct had not been assessed.

Non circular jets are emerging as a new class of passive control mechanism of jet flow. Jets issuing from non circular nozzles, rectangular, square, triangular, elliptic etc, are found to entrain several times more ambient fluid than equivalent axisymmetric nozzles. Non circular jets are generally referred to as non axisymmetric or three-dimensional jets. The increased entrainment of these asymmetric jets, particularly that of elliptic jets, has attracted the attention of many researchers. As asymmetric jets, multiple jets of different geometric configurations have also been proved to be effective in passive control of the jet flowfield. Multiple asymmetric jets may be expected to emerge as an effective method of passively controlling the jets. Many researchers have studied the flow field of single three dimensional jets and multiple circular or plane jets. But studies on multiple threedimensional jets are very limited. Pani and Dash studied the flowfield of three-dimensional single and multiple free jets. Their observed mean velocity distribution results were in agreement with the theoretical profiles.

The work reported here extends the work of Nikuradse on the categorisation of surface roughness. Nikuradse’s work considered pipe flow, whilst in this paper boundary layer flow is investigated. Important and fundamental differences between these two types of flow are shown. An experiment upon turbulent boundary layers over sandpaper-type roughnesses enabled a fluid-mechanic categorisation of these surfaces to be obtained for this flow. This is compared with some shape and size categorisations of the roughnesses from detailed measurements.

This paper describes the implementation of the DRA GVAM87 model in Modula-2, using the Hood design methodology, and the subsequent validation of the real-time model running on a personal computer. The work demonstrates that the execution speed of the model is not compromised while overall validity of the simulation is maintained. The model was interfaced with an existing simulation of the Sea Harrier head-up display (hud) in order to provide visual cues of the aircraft's motion during piloted flight.

A discussion is presented of innovative change in aerodynamics, in which the transformation of practical transonic aerodynamics by computational fluid dynamics is taken as a case study for the lessons to be learnt. The study focuses on the historic breakthroughs of Emmons and Murman and Cole in the calculation of transonic flows, and on the exploitation of these at the Royal Aircraft Establishment to provide industry with a new, and highly successful, tool for practical transonic wing design. It reaffirms the view that a first prerequisite for innovation is the active presence of individuals with clear vision and a spirit of adventure. Further, innovative work will flourish only if the climate is favourable, no matter how exceptional the individuals may be. The discussion concludes with remarks on opportunities for innovation in the treatment of Shockwaves, turbulent shear layers and complex practical configurations.

Results are presented from low-speed windtunnel tests on an isolated generic chined forebody with pneumatic methods of yaw control at high alpha. Measurements of forces and moments were made on the forebody at angles of attack in the range 0° ≤ ɑ ≤ 60°. Slot blowing through the chine edge at various angles and upper surface tangential blowing have been compared, and optimum configurations have been identified. The effects of forebody cross-sectional shape have also been investigated and have been found to be highly critical in determining blowing effectiveness. Limited flowfield visualisation is also presented in order to gain some understanding of the flow field characteristics.

The multidisciplinary problem of tail buffeting is solved using three sets of equations. The first set is the unsteady, compressible, full Navier-Stokes equations which are used for obtaining the flowfield vector and the aerodynamic loads. The second set is the coupled aeroelastic equations which are used for obtaining the bending and torsional deflections of the tail. The third set is the grid-displacement equations which are used for updating the grid coordinates due to the tail deflections. For the computational applications, a sharp-edged delta wing of aspect ratio one and a rectangular vertical tail of aspect ratio one placed in the plane of geometric symmetry behind the wing are considered. The configuration is pitched at a critical angle of attack (α = 38°) which produces asymmetric, vortex-breakdown flow from the delta wing primary vortices. The results show the effects of coupled and uncoupled bending-torsional responses and the effects of Reynolds number.

A computer assisted conceptual aircraft design methodology (CACAD) has been developed to size turbofan powered transport aircraft. New modules for predicting the maintenance costs of each airframe system and subsection of structure, were developed and incorporated into CACAD.

Many aspects of variable camber wing technology (VCW) were modelled. These included different types of drag saving due to chordwise, as well as spanwise camber variation. Models were also derived for mass, maintenance cost, and extra development cost increments for wing trailing edge devices, flight control, and hydraulic systems. These were incorporated into CACAD, and then a multidisciplinary trade-off study resulted in predicted savings of up to 3·5% in direct operating cost (DOC). The technology was evaluated for DOC improvement against a number of existing, future, and derivative aircraft, under different sensitivity conditions. Reliability, maintainability, and development (R, M&D) predictions were shown to be decisive in determining the feasibility of VCW technology. The study showed that long range, low to medium capacity, derivative aircraft are the most suitable applications for VCW technology.