Aerodynamics is one of the main fields of application for practical mathematics and the treatment of aerodynamic problems requires a thorough mathematical training. Whoever opens a modern book on aerodynamics will be surprised from the very beginning, that the phenomena within this very fugitive medium air may be expressed by formulas according to mathematical laws.

We must, however, never forget, that before a flow phenomenon can be mathematically analysed, physical reality must be understood by observation and experiment.

The mathematical treatment will always tend towards an approximate solution, as it is much too complicated to analyse a flow process exactly.

We have grown used to the idea that in the Middle Ages inventors produced several forerunners, either real or imaginary, of modern aerodynamic devices. The helicopter was designed, in principle, before Leonardo, while the rigid aerofoil, in the form of the plane-surface kite, achieved a remarkable degree of sophistication before the end of the sixteenth century. It has commonly been assumed that among these mediaeval inventions we should include some sort of three-dimensional kite, a precursor of Hargrave's box-kite, either in the form of a windsock equipped with wings, or in that of a primitive hot-air balloon, with or without additional lifting force provided by wings. I wish to examine the evidence for the existence of these objects, and to make a fresh assessment of the likelihood of their ever having flown.

In 1956 the Defence Research Board of Canada and Canadair Limited (a wholly-owned subsidiary of General Dynamics Corporation), agreed to sponsor jointly a study of V/STOL technology to determine the configuration of aircraft best suited to the support of ground forces. During the following year it was decided that for the transport role the tilt-wing/slipstream-deflection concept promises the best aircraft from the overall point of view. Subsequent analysis and flight experience have confirmed this, and have also demonstrated a high degree of compatibility between aircraft attributes and general requirements for support of surface forces.

This paper is intended to supplement a part of the paper by Mr. F. W. Armstrong on ‘The aero engine and its prospects—fifty years after Griffith’. It deals in more detail with Dr. A. A. Griffith's early ideas on the aerodynamic aspects of turbomachines.

Even with reasonably optimistic use of materials and operating temperatures it was essential in 1926 that very high component efficiencies were obtained to make the gas turbine competitive with the piston engine on fuel consumption. Griffith believed that efficiencies of over 90% could be obtained for the compressor and turbine components, if the correct attention was given to the aerodynamic design of the blades. His 1926 report on ‘An aerodynamic theory of turbine design’ showed how such high efficiency designs should be carried out and gave appropriate formulae for the compressor and turbine efficiencies.

Windtunnels are generally used for testing models of solid, aerodynamic objects, such as aircraft. The test articles are generally manufactured to have a representative external profile but provide sufficient strength to survive the harsh windtunnel environment without damage to the test article or tunnel. It is somewhat unusual, however, to test lightweight, high drag, fabric models (i.e. parachutes) in supersonic flow.

This paper describes the testing carried out on the parachutes for the Huygens probe, the techniques developed for the testing and the lessons learned.

Tests were carried out to characterise the drag coefficient of the parachute designs throughout the Mach range of 0.05 to 1.5, and the stability coefficients at incidences of up to 15° at low Mach numbers.

Currently there is renewed interest in the evaluation and reduction of steady wind tunnel wall interference, especially for large models.

Evaluation of previous predictions for perforated and slotted tunnels suggests that a hybrid slotted tunnel, ie a slotted tunnel with closed slats and perforated slots) should offer minimum corrections for upwash, flow curvature and solid blockage. This suggestion is confirmed by the present computer studies of a range of rectangular hybrid slotted tunnels.

The computer studies are for tunnel working section height to breadth ratios of 0·835 and 0·600 over the Mach number range from 0 to 0·85. Wings swept at 28° and 50°, with ratios of model span to tunnel breadth varying from 0 to 0·7, are considered. An idealised fuselage shape is used to predict solid and wake blockage corrections for the wall configurations selected on the basis of minimum upwash and curvature interference.

RANS models remain an attractive turbulence simulation method which could provide some open jet aerofoil interaction analysis at a fraction of the cost of a high-fidelity LES approach. The present work explores the potential and limitations of RANS in this context by simulating an open jet aerofoil noise experiment using the aerospace oriented Menter SST RANS model. This model’s tendency to transition at a critical Reynolds number lower than the experimental value was found to impact the boundary layer development. However, the introduction of a low-Re correction improved the prediction of surface pressure and skin friction, enabling the suction surface separation bubble to be captured. The free shear layer’s virtual origin characteristics exhibited sensitivity to the interaction with the aerofoil, which can be developed into a metric of the interaction. The main challenge for RANS was accounting for the rise in background disturbance level in the working section, which is caused by the high-turbulence intensity in the free shear layers.

In parallel with the work undertaken at the University of Southampton on the study of the noise from subsonic jets, a further investigation has been made into the noise from supersonic or choked jets. Whereas in the former case the noise is due to the turbulent velocity fluctuations and thus contains a wide spectrum of random frequencies, the latter case contains, in addition to this wide spectrum, noise caused by turbulence-shock wave inter-action.

Once the critical pressure ratio of a jet has been attained, i.e. that pressure ratio which produces sonic or supersonic flow in the jet pipe just before the orifice, the structure of the jet depends crucially upon the nozzle shape.

In this paper, we examine some of the physics behind Vertical Take-Off and Landing (VTOL) flying machines, and some of the emerging technologies that are driving the recent upsurge of new VTOL projects. The paper attempts to put these into context by examining some of the projects that have been publicised over the past couple of years, particularly those that transition from hovering into wing-borne flight. Although much progress has been made, there still needs to be significant breakthroughs in technologies, particularly battery technology, before the dream of fast, quiet and environmentally friendly inter-city VTOL aircraft can be realised.

The Surface Operations Simulator and Scheduler (SOSS) is a fast-time simulation of the airport surface used to rapidly develop and test new surface scheduling concepts. Gate conflicts present a challenge for surface scheduling. A late departure pushback or early arrival sharing the same gate can cause a gate conflict, which if left unmanaged, can lead to surface gridlock. Surface scheduling concepts that meter departures at their gates can increase the likelihood of gate conflicts. In real operations, hardstand areas are used to temporality park aircraft out of the way to avoid gate conflicts. New SOSS models and functionality for hardstand operations were developed to simulate gate conflict management approaches using hardstands to temporarily park either the arrival or departure out of the way of the other. Four gate conflict management approaches were simulated with surface scheduling and their effects on surface operations were compared. The four gate conflict management approaches each allowed a unique subset of resolution actions including early departure pushback, sending the departure to the hardstand, and sending the arrival to the hardstand. The gate conflict management approaches allowing arrivals to be sent to the hardstand were found to be most successful in resolving the gate conflicts and maintaining scheduler performance measured by takeoff time predictability.

The rotor sub-assembly of the high-pressure turbine of a modern turbofan engine is typically free to move downstream because of the force imbalance acting on the disc and blades following an un-located shaft failure. This downstream movement results in a change in the geometry of the rotor blade, tip seals and rim/platform seals because of the interaction of the rotor sub-assembly with the downstream vane sub-assembly. Additionally, there is a change in the leakage flow properties, which mix with the main flow because of the change in engine behaviour and secondary air system dynamics. In the present work, the changes in geometry following the downstream movement of the turbine, are obtained from a validated friction model and structural LS-DYNA simulations. Changes in leakage flow properties are obtained from a transient network source-sink secondary air system model. Three-dimensional Reynolds-averaged Navier-Stokes simulations are used to evaluate the aerodynamic effect from the inclusion of the leakage flows, tipseal domains, and downstream movement of the rotor for three displacement configurations (i.e. 0, 10 and 15 mm) with appropriate changes in geometry and leakage flow conditions. It is observed from the results that there is a significant reduction in the expansion ratio, torque and power produced by the turbine with the downstream movement of the rotor because of changes in the flow behaviour for the different configurations. These changes in turbine performance parameters are necessary to accurately predict the terminal speed of the rotor using an engine thermodynamic model. Further, it is to be noted that such reductions in turbine rotor torque will result in a reduction of the terminal speed attained by the rotor during an un-located shaft failure. Therefore the terminal speed of the rotor can be controlled by introducing design features that will result in the rapid rearward displacement of the turbine rotor.

For an augmented aircraft, it is shown that filter error method leads to improved identifiability of aerodynamic parameters from measurements that are affected by the feedback from the flight controller. Simulated lateral-directional data of an advanced fighter aircraft, obtained from a nonlinear six-degree-of-freedom simulator, are used for the purpose of analysis. The aircraft stability and control derivatives are estimated using filter error method and compared to the estimates obtained from output error method to ascertain the degree of improvement achieved in the identified derivatives. Identification results with output error method show that feedback causes a discernible offset in the estimated values of the derivatives relative to the reference parameter values. The filter error method helps to reduce this offset and thereby yield estimates that match better with the reference parameter values.

This paper describes a first attempt to establish the order of magnitude of finite aspect ratio effects for jet-flap wings. Lift, pitching moment, and drag results are presented from pressure-plotting measurements on a jet-flap model of aspect ratio slightly less than three. These experiments were complementary to two-dimensional tests carried out at the National Gas Turbine Establishment.

This paper investigates the issue of tracking control for a free-floating space manipulator with prescribed performance constraints, considering the inertia uncertainties, internal disturbances and input saturation. An inherently continuous adaptive controller is proposed by incorporating non-singular fixed-time sliding mode control, prescribed performance control (PPC), and auxiliary compensation. First, a modified non-singular fast fixed-time terminal sliding surface is constructed, which has a shorten convergence time than the conventional fixed-time sliding surface. Unlike the existing complicated PPCs, a simple structure controller is developed to satisfy prescribed performance constraints through a unique tangent-type PPC technique. The input saturation is then compensated adaptively by an auxiliary mechanism. The Lyapunov theory thoroughly validates the stability and fixed-time convergence of the closed-loop tracking system. With the suggested control scheme, the system states can converge quickly to a small neighbourhood around the origin within a preassigned time, while the position tracking error can be confined within a prescribed performance bounds even in the presence of input saturation. Compared to the existing tracking methods, the suggested control approach has the advantages of faster transient convergence, higher steady-state tracking precision, and stronger robustness. Simulation comparisons demonstrate the effectiveness and superiority of the proposed controller.

Tests were made in the N.A.C.A. gust tunnel to determine the effectiveness of a long-period dynamically overbalanced flap in reducing aeroplane accelerations due to atmospheric gusts. For two gust shapes, one gust velocity, one forward velocity, and one wing loading, a series of flights was made with the flap locked and was then repeated with the flap free to operate. The records obtained were evaluated by routine methods.

The results indicate that the flap reduced the maximum acceleration increment 39 per cent, for a severe gust with a representative gust gradient distance of 8 chord lengths and that, for an extreme gust shape (a sharp-edge gust), the reduction was only 3 per cent. The results also indicate that the flap tended to reduce the longitudinal stability of the aeroplane. Computations made of the effectiveness and the action of the flap were in good agreement with the experimental results.

The possibilities of a vertically-corrugated web as a means of reducing thermal stresses naturally have for some time been generally appreciated by designers. The stress relief to be expected is examined in some detail here. It is shown that quite shallow corrugations can be effective in reducing thermal stress and that a flange-to-web connection at corrugation-pitch intervals can offer substantial advantages over a more continuous type of connection. Arguments are presented to show why straight-sided corrugations are superior to curved ones.

The computer is seen as the greatest invention in history, in that it has a universality which transcends all other known inventions. It will ultimately be capable ot any process describable in terms ot an open or closed logical structure.

In a deterministic science such as aeronautics, it has clear capabilities in the solution of the equations governing fluid flow, structures, propulsion, navigation and so on. The speed and size of future computers, together with all sorts of new software techniques, will facilitate almost instantaneous solutions of any problems, within the next century.

There will be two major constraints on these developments which we can predict with confidence. The first is financial. The second is more subtle: there may develop sociological resistance to technological advances, especially to those wielding the power implicit in future generations of computers, and this carries important implications for scientists.

Gas turbine blades feature multi-pass internal cooling channels, through which relatively colder air bled from the compressor is routed to cool internal walls. Under rotation, due to the influence of Coriolis force and centrifugal buoyancy, heat transfer at the trailing side enhances and that at the leading side reduces, for a radially outward flow. This non-uniform temperature distribution results in increased thermal stress, which is detrimental to blade life. In this study, a rotation configuration is presented which can negate the Coriolis force effect on heat and fluid flow, thereby maintaining uniform heat transfer on leading and trailing walls. A straight, smooth duct of unit aspect ratio is considered to demonstrate the concept and understand the fluid flow within the channel and its interaction with the walls. The new design is compared against the conventional rotation design. Numerical simulations under steady-state condition were carried out at a Reynolds number of 25000, where the Rotation numbers were varied as 0, 0.1, 0.15, 0.2, 0.25. Realisable version of k-$\varepsilon$ model was used for turbulence modelling. It was observed that new rotation (parallel) configuration’s heat transfer on leading and trailing sides were near similar, and trailing side was marginally higher compared to leading side. An interesting phenomenon of secondary Coriolis effect is reported which accounts for the minor differences in heat transfer augmentation between leading and trailing walls. Due to centrifugal buoyancy, the fluid is pushed towards the radially outward wall, resulting in a counter-rotating vortex pair, which also enhances the heat transfer on leading and trailing walls when compared to stationary case.

Modern balances are rugged, sensitive and easy to read. A top-loading balance with a capacity of 1 kg and digital readout to 0.01 gm has been adapted for use as a micromanometer. A sketch of the arrangement is shown in Fig. 1. It will be seen that there is no modification to the balance itself, which can still be used for its normal laboratory function, and no calibration is required for pressure measurement provided the diameter of the fixed drum is known.

In any industry, success calls not only for a tool which is well adapted to its purpose, correctly maintained and efficiently used, but also for a tool which is unsurpassed by a better one.

This is also true of air transport. C. R. Smith (President, American Airlines Inc.) noted some time ago that an aircraft ceases to be efficient as soon as another aircraft becomes available that can do its specific job better. This axiom places emphasis on the selection of aircraft as one of the primary elements of success for airlines which, in order to survive economically, must have available the right number of aircraft of the right type at the right moment.

This is the result of two essential characteristics of air transport: intense competition and marginal profits.