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The third term has been expressed as but in wind tunnel work it is often more convenient to measure were the omission of the dash signifies that the moment is now measured about a wind axis. The two quantities are very closely related and the measurement of one tells us almost as much as if the two were known. The latter, however, tells us either directly or indirectly what effect the addition of fin and rudder will have on the autorotation properties of the wings alone. The damping of fin and rudder being due essentially to the air flow meeting them at an angle on account of the rotation it should theoretically be possible to deduce this dynamic quantity from a simple static test of moment due to yaw angle. An experiment to test this was carried out several years ago but the static test did not give any approximation to the truth. This was ascribed at the time to the shielding of fin and rudder by the tail plane in the rotative experiment and subsequent work has amply confirmed this view. It is now known that shielding by the tail plane is by far the most important factor in determining the efficiency of the vertical surfaces at high angles of attack.

DEAR SIR,—I read with much interest Mr. J. H. Crowe's article on Longitudinal Stability, which was published in the March issue of AIRCRAFT ENGINEERING. It forms a useful summary of present‐day knowledge on the glider stability problem, but is rather misleading in the section devoted to the effects of slipstream.

School-university partnerships are enhanced by synergistic relationships. Positive outcomes increase when partners work across disciplines, focus on cultural competencies, and expand from local to global engagement. This chapter offers an overview of the Bradley Professional Development Schools (PDS) Partnership, a description of the Comprehensive Integrated Services Model, and a summary of current thinking about synergy and cultural competencies in relation to school–university partnerships. Through descriptions of various multidisciplinary PDS projects and partnerships, the chapter explores concepts such as emergent realities, cross-cultural, intercultural or global competencies, empowering learning culture, and global awareness, demonstrating how an comprehensive integrated services model that is holistic in nature sustains school–university partnerships in multiple and creative ways across local and global environments.

THE advantages and disadvantages of the fixed wing for gyroplanes are examined. On the simplest assumptions an expression for the percentage load taken by the fixed wing of a gyroplane is derived. The values so arrived at are compared with those found by experiment and the discrepancy between the two is explained in terms of the increased downwash at the centre of the disc of the gyroplane. It is shown that as much as 50 per cent of the weight of the aircraft can be taken by the wing at top speed with moderate wing area and the most suitable setting. The advantages of an adjustable wing from the point of view of rotor speed control are pointed oat. The Lift/Drag of the combination is raised by 2 over the L/D of the rotor alone. The stability of gyroplanes is discussed.

THE major problems connected with the development of satisfactory structural strength requirements have long since been solved. We have, in this country, an empirical system of specification which fulfils the fundamental criterion of any strength system, namely, that failures in the air through lack of adequate strength of any component of an aircraft are extremely rare. An analysis of civil accidents (Ref. 1) shows that about 6 per cent are due to this cause. This does not imply any reason for regarding even this small number with complacency, rather the reverse.

THE basic theory of stability has undergone no important modification since the publication of Professor G. H. Bryan's book on Stability in Aviation in 1911. The stability equations derived therein serve to‐day with the difference that axes and symbols have now been standardised and with the additional refinement of a non‐dimensional form of the stability equation introduced by H. Glauert. Due to the vastly increased knowledge of aerodrynamic characteristics, however, the stability derivatives are more readily assessable in any particular design case. This applies more particularly to longitudinal stability calculations which may, and indeed often arc, carried through with no wind tunnel tests available apart from a lift and drag curve for the aerofoil section used. There has also been some extension of the use of stability charts for deriving an approximate knowledge of the behaviour of the aeroplane when it receives a disturbance. These charts are exceedingly useful for obtaining periodic time and damping factor, but the assumptions on which they are based should be clearly realized.

THE increasing speed of modern aircraft has brought to the forefront the necessity for making a careful drag analysis of all aircraft in order to separate out the essential drag, that is to say the drag that is unavoidable, from the non‐essential drag. Most designers, we believe, now do this in order to see what progress is being made in the streamlining of their products. By this means we are enabled to see the relative importance of the drag terms and to arrive at a figure of merit. The ideally‐streamline aeroplane, though not at present a precise proposition, is like other ideals unattainable. It is the standard to which designers may aspire, but which they cannot achieve.

IN view of the interest taken in M. Mignet's “Pou‐de‐Ciel,” some notes on this peculiar wing arrangement may prove of interest. There are essentially three divergences from current practice in the layout of the “Pou.”

MUCH time and money have been devoted to the development of the helicopter, but the achievement of a practical machine is apparently not yet in sight. Some of the problems, indeed, have been solved; others await solution. In any discussion of the helicopter the subject naturally divides itself into five headings. First, there is the problem of the provision of adequate lift. This has for many years been solved, and an airscrew can now be designed that will give its predicted lift with a certain degree of confidence. On the practical side, helicopters have demonstrated that they can be built with a sufficiently light structure weight that modern power plants are adequate to lift the aircraft vertically upwards. The problem has also been investigated theoretically, and a relationship between disc loading and pounds per horse power established which should permit of any designer producing a helicopter that will lift itself. This fact cannot be too strongly emphasised in view of the fact that many inventors consider that the major problem is one of lift.

IT has been suggested from time to time that this case might conceivably arise for acrobatic aeroplanes and therefore a tentative investigation was undertaken. Although the results show that in certain cases extra loads are thrown on the structure over and above the designed loads, this must not be interpreted as meaning that an aeroplane is likely to fail under these circumstances, because certain basic assumptions have had to be made, the validity of which is doubtful. Further investigation is needed to supplement the somewhat scanty data that we have as to the existence of these gusts in the upper atmosphere and their magnitudes. Also the problem of the dynamics of an aeroplane in a terminal velocity dive with horizontal gusts has been entirely neglected although it is by no means improbable that the question of the stability of the machine has some bearing on the loads that are likely to build up as a result of gusts.