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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.

Experiments with Modified Tail Units.—Experiments have been performed with 1/15th scale models of the original single‐seater fighter and 1/20th scale models of the Bristol Fighter with a view to improving their spinning properties by redesigning the tail unit. The experiments with the fighter models were mainly directed at investigating the spinning characteristics of the original and deepened models to see whether the overall effects of the deepened fuselage and raised tail plane would bear out the encouraging conclusions drawn from the wind tunnel work. The scope of the experiments was somewhat limited, but all results indicated that slower and steeper spins and very much more rapid recoveries might be expected from the deepened fighter.

IT seems rather strange that while the general property of wing flaps of putting up both the lift and the drag of a wing at the same time has been known for many years, so little practical application of this result has been made until quite recently.

THERE is little doubt at the present time as to the great advance in safety which the invention of the automatic slot has brought to the aeroplane. It has been the means of overcoming one of its chief failings, the loss of stability and control at the stall. Automatic slots at the wing tips are themselves capable of converting an aeroplane which is unstable in roll at incidences beyond the stall into one which is definitely stable; at the same time the aileron control is increased and improved in that its application is not accompanied by so great an adverse yawing moment as for ailerons working on an unslotted wing. Further, if some form of interconnection between ailerons and slots is adopted, or some device (e.g. the “interceptor”), by means of which the action of the slot can be spoiled, a further big addition to the control at the stall can be made as well as further improvement in the shape of a reversal of the usual yawing moment. Whether such addition is desirable for all types of machine remains to bo seen; it may be that in certain types the automatic slots alone, without interconnection, will provide all the increase in stability and control at the stall which is required.

THE Spinning Panel of the Aeronautical Research Committee received an inquiry from the Society of British Aircraft Constructors as to whether it would be possible to formulate a set of simple rules for the use of aeroplane designers to guide them in making their machines safe from spinning. As a result, a report was prepared by Mr. Irving, of which the following is a summary, which represents the nearest approach that the Panel feels justified in making at the present time towards meeting the request put forward by the Industry. The Report contains a full statement of the aerodynamic and inertial properties of aeroplanes which, according to current views, are regarded as important in their effect on spinning qualities and a statement of the various combinations of properties which are today considered good or bad. Although the formulation of a complete set of rules is desirable, and may ultimately be possible, knowledge on the subject is not yet sufficiently complete to warrant the laying down of quantitative rules in a simple definite form.

THE outstanding property of the biplane to be described, as determined from model tests, is stability in roll up to angles of incidence in excess of 40 deg. (Fig. 8). This is achieved without any additional mechanism or parts, simply by the form and disposition of the wings. Maximum lift is slightly increased (Fig. 6) and there are minor advantages as regards coming in to land, aileron control and spinning.

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.”

IN the May, 1933, number of AIRCRAFT ENGINEERING there was published an article by Korvin‐Kroukovsky on the uncontrolled tail spin, in which one of the main points put forward was that during a spin both the body and the tail were very largely shielded by the wings. It was then argued from this that danger might be expected more especially in the low‐wing monoplane type and also the biplane with big forward stagger of wings. At the time there was very little direct evidence on the effect of wings on body and tail moment although an early report on the “ Bantam,” an unstaggered biplane which had spun into the ground, had shown pretty clearly that it was the tailplane which was responsible for the complete blanketing or even reversal of the fin and rudder in a flat spin, and that this could be remedied by raising the tailplanc.

THE purpose of this paper is to give some account of the work on spinning and the progress which has been made since S. B. Gates and L. W. Bryant presented their paper to the Society, which was published in more comprehensive form by the Aeronautical Research Committee as R. & M. 1001.

IN AIRCRAFT ENGINEERING for June, 1935, and in R. & M. 1715, the present writer and others described some experiments on a wing cellule model of a new form of biplane, the special advantage of which was stability in roll up to angles of incidence as high as about 40deg.; and it was suggested that if the results of the model experiments were borne out on the full scale such a type of biplane might with advantage be adopted for a light sporting machine with a view to minimising the risks due to the inadvertent stall.