Search results

A NUMBER of approaches to the calculation of rotor downwash have already been discussed. Broadly spsaking, the methods of Castles and DeLeeuw and Squire and Mangler are the same. In both methods the downwash at the rotor disk is assumed to be perpetrated in a helical downwash sheet which, as the slipstream, extends below the rotor to infinity. The downwash in the disk due to the bound vortices, and the additional downwash in the disk which is induced by the helical sheets in the slipstream (Castles and DeLeeuw substitute downwash rings for helices, in the interest of mathematical simplicity) is calculated, on the assumption of an infinite number of lightly loaded blades. The final results of Castles and DeLeeuw on the one hand, and Squire and Mangier on the other, are in very wide disagresment. This disagreement is principally due to the fact that, whereas the first investigation assumes constant circulation along the blade (ideal twist and taper), Mangier and Squire assume a ‘practical’ variation of the form likely to be encountered on an untwisted untapered blade. We conclude that the radial distribution of lift on a helicopter blade will have a profound effect on the downwash pattern: which in turn will affect the calculated lift.

THE paper reviews the problem of the influence of the walls of a closed tunnel in increasing the velocity in the neighbourhood of a model under test. It is shown that, for a perfect fluid, considerations of continuity suffice to establish an exact value of the mean interference velocity for any cross‐section of the tunnel. This mean interference velocity is expressed in terms of the perturbation velocity which would be caused by the same model in the absence of the walls. The linearized theory of subsonic compressible flow is applied and it is shown that the interference velocity for a small two or three dimensional model is increased in proportion to l/β3, where β=√(l—M2) and M is the Mach number. Interference caused by a body with a long parallel middle body, the influence of the wake from a model and of the boundary layer on the tunnel walls are briefly considered.

The literature on jets is extensive but scattered. A concise guide is needed, and this paper attempts (at the risk of over‐simplification) to summarise some of the available information, both theoretical and experimental (some of it obtained in the Department of Mechanical Engineering) on those jet properties which are important in engineering — velocity profile and decay, spread, entrainment and static pressure.

IN this paper an examination is made of some of the evidence on which the resistance law of a smooth flat plate with turbulent boundary layer is based. It is shown that a power index law for the resistance agrees with experiment quite as well as formula; involving logarithms. The suggested new value for the coefficient of

The data on round jets in still air and in a general stream are analysed to determine the spread of the jet and the decay of the axial velocity distribution. The temperature distributions for heated jets are treated in the same way. Methods of model test technique for jets and jet aircraft are discussed; it is shown that the jet momentum is the most important quality in the representation of hot jets. Illustrations of the effect of jets on neighbouring surfaces, including the Coanda effect, are given, and finally an examination of the effect of jets on aircraft stability is made.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued

This paper explores openness within new product development (NPD) projects. The purpose of this paper is to examine the impact of breadth, depth and partner newness on product innovativeness and product competitive advantage. The authors also seek to examine the contingent effects of the appropriability regime. The authors make suggestions to academics and practitioners based on the findings.

The authors use a structured survey instrument producing an empirical analysis of 205 NPD projects in the manufacturing sector in the UK. The authors use an ordinary least squares regression model to test hypothesised relationships between openness (breadth, depth and partner newness), product innovativeness, product competitive advantage and the appropriability regime.

The authors find that each of the three dimensions of openness, depth, breadth and partner newness, have a significant but differing impact on product innovativeness. Specifically, the study indicates that breadth has a positive effect but only in the presence of a strong appropriability regime, partner newness has a direct positive effect, and depth a direct negative effect. The authors also find that product innovativeness has a positive impact on product competitive advantage.

Further research should focus on replicating the findings in other countries, search for further moderating factors, such as the stage of the NPD process, and analyse the longitudinal impact of openness within NPD projects.

Organisations are encouraging managers to be more open in their approach to NPD. The authors’ findings suggest that managers need to think about the three dimensions of openness, breadth, depth and partner newness. Their engagement with each of these dimensions depends on the desired outcomes of the innovation project and the strength of patents.

The research extends the extant supplier involvement in new product development literature to examine the effect of up to 11 types of external actor in NPD projects. The authors test a new multi-dimensional measurement scale for the openness construct. The authors show that each dimension has a different relationship with product innovativeness.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Committee, Reports and Technical Notes of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.

The purpose of the present work is to develop a unified mathematical theory of the steady and disturbed motion of a helicopter with particular emphasis on the dynamical aspects of the problem. The helicopter is assumed to undergo arbitrary small disturbances in velocity and angular velocity from a steady rectilinear flight condition, and the rotor forces are calculated as generalized functions of the initial and disturbed velocities. A high degree of accuracy is maintained both in the retention, where necessary, of products of small quantities and in the retention of high powers of µ in the solution of the trim equations. The steady motion of the helicopter is discussed at length as a preliminary to a study of its dynamic stability. Part I deals with the general features underlying helicopter motion. The importance is emphasized of a three‐dimensional approach to the problem, and it is shown that a complete description of steady rectilinear motion demands the use of fifteen equations in eighteen parameters, the solution of which presents no real difficulty. A start is made on the analysis of rotor blade motion, and the geometrical aspects are discussed by means of a system of rotating vectors.

SUMMARY A detailed account is given of the aerodynamic and inertia forces acting on a rotor blade when the helicopter is undergoing arbitrary disturbance in velocity and angular velocity. A fairly generalized form is used for the downwash velocity. A principle is enunciated enabling the several second order terms of significance in the angle variables to be recognized and retained.