In his recent lecture on “ Airship Mooring and Handling,” Captain Butcher refers to certain experiments carried out with the use of models in connection with three-wire mooring. It is, perhaps, useful to add some further details of these special experiments, which were conducted at the National Physical Laboratory.

Mention was made by Captain Butcher of the original or “ fixed ” three-wire system (see Fig. 1), which originated from the emergency mooring of R.9. Its defects lie in the occasional slackening and subsequent impulsive tightening of one or more of the mooring cables when the airship is riding in gusty weather. In the particular modifications introduced by the N.P.L., breakdown due to this contingency is eliminated.

The efficiency of all internal combustion engines is influenced to a large degree by the density of the charge prior to ignition. In the stationary engine operating at normal ground density, the variation in compression pressure throughout the range of working conditions is so small as to have no appreciable effect upon engine performance. In the aero engine, however, the conditions obtaining in flight are such as to produce wide variation in the suction pressure and therefore in the compression pressure due to changes in atmospheric density.

Table I has been prepared to show the variation in air pressure, temperature and density with height, the figures given representing the mean conditions obtaining in the south of England.

It is extremely difficult to obtain reliable data concerning the actual performances of German giant aeroplanes, and it will therefore be better for our purposes to confine ourselves to generalities without the use of actual figures, whose reliability may be open to question.

In the first instance as regards “ speed , ” we find within each of the two “ A ” and “ B ” type designs, that the speed diminishes as the number of motors increases. That is to say, a two-engined “ Type A ” aeroplane will have a greater speed than a four-engined “ Type A2 ” machine, with conditions as regards the horse-power loading and wing loading approximately the same.

Exactly the same rule is distinguishable in the case of the “ Type B ” machines. In the case of the “ Type A ” machines this result is obviously to be expected, firstly, on account of the extra head resistance introduced by an increased number of motors when exposed to the wind ; and secondly, on account of propeller “ interference ” and inefficiency.

The manoeuvres of getting off and landing are to me the beginning and the send of flight; they separate the sheep from the goats; the aristocrat of the flying world uses them for the display of his genius, leaving his would-be imitators to find what consolation they can in the amusement with which they innocently provide the onlookers.

In commercial flying the manoeuvres of getting off and landing are still the most obvious calls on the pilot's skill; and who shall deny the splendid response? But a determination to ease the pilot's task is not thereby for an instant to be excused. This, one of the most urgent problems before applied design to-day, lies in the conflicting requirements of ease and safety in getting off and landing and those of economy and usefulness in full flight. To assist in the statement of this problem is the object of my Paper. These are the manoeuvres perhaps about which most has been said, and, from the pilot's point of view, least written. Since first a heavier-than-air machine left the ground, they have never failed as a topic of conversation throughout the whole flying community; and this has tempted me to analyse them on the basis of my own experience and that of the many pilots I have known.

Introductory.—In the course of inquiries made recently by the Accidents Investigation Sub-Committee they were impressed by the fact that the various terms normally used to describe the characteristics of an aeroplane in regard to its stability or instability are incomplete and defective from a pilot's point of view. Not only did there appear to be differences in the meanings attached to the various stability terms by pilots and others, but in several cases the meanings were not in accordance with the definitions used in physical science generally. It appeared that a scheme of definitions could be drawn up which would be acceptable both to those interested practically and theoretically in the subject. Definitions are needed for discussions on stability and particularly in making more definite the information given by pilots when describing the behaviour of aeroplanes. It is felt that the definitions, if accepted on all hands, would lead to such observations during the life of an aeroplane as materially to assist the investigations of accidents.

The following note has been written partly by way of a commentary upon Dr. H. C. Watt's recent article, in the July number of the Aëronautical Journal, entitled, “ A Note on the Theories of Screw Propulsion,” and partly by way of an explanation of the apparent inconsistency of the “inflow” theory of the airscrew.

Consider an element of a propeller blade situated at a radius of x from the boss centre of the propeller and having an angle of ϕ between the chord line of the blade section and the plane of rotation. The form of the blade section is considered to be that of an aerofoil, of which the characteristics are known from wind channel experiments upon a model of the same geometrical form (Fig. I).

We wish to apply these wind channel data to the propeller blade element with rigorous consistency, i.e., as far as the two respective régimes of the propeller and the aerofoil permit.

The weather of the English Channel and South East Coast of England, like that of other localities in the British Islands, is well known to be variable and subject to rapid changes which take place sometimes with little or no warning. These changes are in places complicated by such factors as the general contour of the cliffs, an abrupt fall of the land towards the south, and the effects of evaporation taking place continuously over the channel, and giving such a well defined local character to changes of wind as to mask temporarily the indications of an approaching disturbance.

Much, however, can be ascertained by the study of the local cloud formation, wind structure, type of barometric curve, and temperature variation, and the following discussion of certain aspects of Channel meteorology is intended to explain the commoner variations of weather which occur in that area. The meteorological peculiarities of the Channel may be conveniently studied under the six separate headings of atmospheric depressions (primary and secondary), winds, mist and fog, thunderstorms, squalls and gales.

A proper treatment of the construction and properties of airship fabrics would require a book rather than an essay. In what follows, it is possible therefore to deal briefly only with the principal types of fabrics, classified according to the main functions of each, describing their structure and behaviour and the chief factors affecting their permanence when in service. There are, then three main classes :—

I. Fabrics for the envelopes of non-rigid airships.

II. Fabrics for the gasbags of rigid airships.

III. Fabrics for the outer covers of rigid airships.

In all cases low specific weight (expressed here in grammes per square metre) is clearly of the greatest importance.

I. Fabrics of this class must possess gas-holding properties, mechanical strength and pliability. The internal pressure (equal to about 30111ms. of water) which maintains the shape of the envelope sets up in its fabric considerable tension, and this is increased by the distributed weight of the whole ship.

In a recent article in “ Engineering ” the writer has given an account of the principles which govern the design of aeroplane control surfaces, making special reference to wing ailerons. Included in the information presented were data on the properties of wing ailerons of the ordinary unbalanced form, but varying in span and chord length and fitted to wing tips of different plan forms. From these data several conclusions of practical importance were drawn, some of them finding general application in the design of control surfaces, and it may be useful to give a résumé of these before proceeding to deal with the balancing of control surfaces.

(i) All ailerons and elevators become relatively inefficient for movements above about 15° to 20° from the normal position, owing to a sudden reduction in the slope of the curve relating moment on machine with angle of aileron or elevator. For movements up to about 15° or 20° the moment is nearly proportional to the angle.

In attempting to survey the growth and progress of the “ Giant ” aeroplane in Germany, it is first of all necessary to review the circumstances and conditions which determined and necessitated the direction of effort in this direction, and secondly, to indicate roughly the accessory circumstances peculiar to the conditions of the Central Empires during the war at the period when giant aircraft first began to appear, and to distinguish if possible the influence of these circumstances where they bear on development in a manner either conflicting or diverse from the conditions appertaining in Entente countries.

Such a preliminary survey is absolutely necessary in order to disabuse the mind of its natural tendency to compare the completed individual German giant aeroplane with its corresponding Entente type; and at the same time to prepare one of the various confusing and unexplained peculiarities which must tend to mislead, if the ruling circumstances are not first made clear.

I feel it a great honour to whave been asked by this Society to speak to you this evening on this subject. The question of the utilisation of airships for commercial purposes has attracted an immense amount of public attention during the past year. Unfortunately, owing to the high costs of running airships experimentally, the Air Ministry have been faced during this period with the necessity of having to abandon airships for military purposes, and also of having to cease their experiments on the use of these ships for commercial purposes. Fortunately it is inherent in the British temperament to give its greatest sympathy to a man when he is down, and for this reason, concurrently with the complete cessation of all airship activities, such stupendous ideas as the use of airships for linking up the Colonies have been put forward. The scheme for using aircraft on such an unprecedented scale for commercial purposes is so gigantic as to call for very grave and careful consideration.

In this lecture it is proposed to deal with the general aerostatical principles governing the flight of lighter-than-air craft, and also to describe briefly the various types of airships, with special reference to the rigid airship.

The future of lighter-than-air craft is undoubtedly dependent upon the development of the rigid airship, in which type of ship efficiency and performance increase at a greater rate than the gross lifting capacity.

To understand the working of a large airship it is essential to have a thorough grasp of the elementary aerostatic principles governing the flight of an ordinary free balloon, so it is proposed, first, to outline these principles and then to pass on to the non-rigid, semi-rigid and rigid types of airships, all of which are virtually balloons of varying type, rendered dirigible by the fitting of means of propulsion, and navigable by the introduction of controlling surfaces.