It is now over a year since the Society had the pleasure of listening to Senor de la Cierva’s paper on the development of his new type of aircraft. In view of that paper it is unnecessary for me to enter into any detailed historical account, but I would like to recall to your minds just these few facts. The object which Senor de la Cierva had in view was to design some form of aircraft which would avoid loss of control on stalling and would at the same time facilitate the process of landing.

What may be termed broadly the medical aspects of flying are far more wide–reaching than is generally supposed, especially since such a term embraces both the physiological and psychological aspects of the subject. All the while, therefore, that man acts as the controlling and co–ordinating mechanism of the machine, the study of man in relation to his machine must occupy an important place in the progress of aviation. It is because this aspect of the subject has tended to be somewhat overlooked that I venture to address this Society again to–night.

In the first place I wish to consider what happens when a man learns to fly. As the result of information gleaned by his various senses he is taught, according to his aptitude, to perform or to try to perform certain arm and leg movements which will control the machine safely while it is in the air. To do this, however, in addition to perceiving, he must in certain circumstances display judgment before he acts, although, as he becomes more experienced in flying, he will automatically perform certain movements in response to certain sensations.

In the past the usual method of dealing with the articulated rod has been to treat the problem graphically. Although this method may be sufficiently accurate for a first approximation the inherent difficulties often lead to serious errors after the first few stages. A graphical method is always sufficiently accurate to determine the travel of a piston operated by an auxiliary rod ; but, the double differentiation of the displacement curve by graphical means (to obtain the acceleration curve), is not only inaccurate but a long and tedious operation.

To remedy this defect a Fourier's series has been developed which can be differentiated at sight and which gives a remarkable accuracy.

The geometrical properties of the mechanism have been analysed and thus equations are formed giving the resultant radial and tangential components at the crank pin, the bending forces and tensions on the master rod, etc.

We should like to preface our essay on the subject of spinning by mentioning the circumstances under which our investigations were carried out and the sources of our information. The Panel of the Aeronautical Research Committee which has been appointed to deal with all questions connected with the stability and control of aeroplanes was requested in 1924 to consider the urgent problems connected with the alarming accidents due to certain machines failing to retover from a spin. After the issue of a preliminary report on the situation by the Panel, the writers of this paper were asked to go into the whole question as far as existing information from full-scale and wind tunnel experiments would permit. We have had ready access to all available data, coming chiefly from Farnborough on the full-scale side, and from the N.P.L. on the model side.

The subject of “Line-squalls” is one which has not been entirely neglected in the proceedings of this Society, but it has not hitherto been treated in any degree of detail. Sir Napier Shaw, in a lecture delivered on January 7th, 1914, on the subject of “Wind Gusts and the Structure of Aerial Disturbances,” briefly cited the line-squall as a phenomenon involving a violent commotion in the atmosphere, illustrating his remarks by sketches and meteorological records relating to a well-marked instance on October 14th, 1912, at Aberdeen.

An investigation of channel wall interference with the object of verifying experimentally the accuracy of the results given by the theory developed by Prandtl and extended by Glauert. Tests were made, with cylinders and aerofoils, using the “ mirror ” method, for some ten different channel sizes. The results show :

1. 1. The presence of the channel walls results in an increase in the drag of a symmetrical body, such as a cylinder.

2. 2. Agreement with the theoretial corrections for incidence and drag for channels of reasonable size.

3. 3. The extent and nature of the wall interference effects on the aerodynamic characteristics of aerofoils in much restricted streams, beyond the limits of applicability of the theory.

From time to time attempts have been made to produce a dynamometer capable of measuring the power output of an aero-engine during flight at various atitudes. The type that has proved the most suitable up to date in flight tests is the Bendemann hub acting on the hydraulic principle which was originally designed in Germany. The principle has recently been tested in America with moderately satisfactory results, and experiments with a modified form of the apparatus are at present being conducted at the Royal Aircraft Establishment. The Bendemann hub and its accessories are somewhat complicated and are difficult to instal in a machine and to maintain in a serviceable condition, also the apparatus will not work properly at altitudes above 20,000 feet owing to increased viscosity of the working fluid at low temperatures.

The apparatus described below is simpler in construction, lighter and more robust than the Bendemann hub, and should be capable of giving equally good results irrespective of altitude; moreover, the work of fitting it to a Service machine would not be great and would not necessitate the employment of specially skilled mechanics.