“Weight” is the key to everything that matters in aircraft construction. It is of paramount importance to performance, comfort and safety. Incidentally, it is also many a designer's excuse for any shortcoming on his machine.

Analysing the weight figures for an aircraft, one can classify them into three groups:—

1. 1. Weights over which the designer has no influence.—Namely, engines and accessories, airscrews, instruments, wheels and brakes, etc. This group represents about 35 per cent. of the empty weight of a normal commercial machine.

2. 2. Weights over which the designer has a limited influence.—Namely, fuel tanks and pipes, cowlings, engine controls, cabin equipment, upholstery and windows, heating, etc., which represents some 20 per cent. of the empty weight.

3. 3. Weights within the designer's influence.—Namely, wings, fuselage structure, tail unit, chassis, flying controls, etc., which represent about 45 per cent. of the empty weight.

From that memorable day in December, 1903, when Orville Wright made the first power driven flight, aeronautical engineers have directed continuous efforts towards improving the range of aircraft. The distance covered on that first flight was about 120 yards. At the present time the record for distance flown in a straight line stands at 5,012 miles, and as for duration, some unfortunate Americans recently succeeded in staying in the air for nearly 27 days and nights without landing. This latter record has little value beyond that of an endurance test of the engine, and possibly the physiological effects on the occupants of the aircraft. The long distance record, however, has a direct influence upon the design of both military and commercial aircraft.

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 formi by the Aeronautical Research Committee as R, & M. 1001.

Although it is distinctly possible that the aeroplane of the future will be unspinnable it is a fact that the great majority of present day aeroplanes are capable of taking up the spinning motion either inadvertently or by deliberate intent on the part of the pilot. If it were really true that all those aeroplanes which apparently require to be forced into a spin would J ever inadvertently fall into one, a considerable number could be definitely classed as safe by forbidding spinning on such aircraft.

The following paper does not pretend to be a complete and exhaustive survey of all the theoretical and experimental work which has been done up to the present on the subject of control beyond the stall.

It is confined to main questions and to a report of the practical research work upon which my colleagues and I have been engaged during the last two years.

In doing so I am well aware of the incompleteness of our research work and its methods, which aimed more at finding ad hoc than general solutions. The outlook of the engineer is different from that of the learned scientist. Not for him is the tranquil and contemplative atmosphere that surrounds purely scientific research work. If he breaks new ground he has neither time nor means to strive for a thorough, complete and general treatment of the particular problem he encounters. His work is limited by financial considerations; hampered by a rigid system of Works Orders; and by the lesser interest in so-called “unproductive” work which characterises industrial institutions. In short, from his point of view, the solution is infinitely more important than the theory or the methods by which it is obtained. A practical solution often presents itself automatically if the physical conditions of a particular problem are properly recognised, even if the degree of accuracy does not satisfy the rigid requirements of pure scientific research.

Aircraft engineering has been described as “ordinary engineering made more difficult.” Probably most of you will agree that our difficulties are often greater than those that confront other branches of the engineering profession, and that the chief source of them is our inability to forecast with entire confidence what air will do under any given circumstances. Our position in this matter is much better than it was, for instance, at the end of the war. During the last thirteen years we have seen the theories associated with the name of Professor Prandtl receive general acceptance, with a profound effect upon our attitude towards some of the most important practical problems of air-flow with which we have to deal, namely, those associated with the production of lift. The boundary layer, then little more than a scientific curiosity, has become a matter of common concern. It achieved a striking practical success in the rationalisation of the international tests of airship models, which led to a marked advance in our attitude towards the whole problem of scale effect. But in many respects we are still greatly hampered. In so far as there has been any advance in the pure hydrodynamical theory of the flow of viscous fluids, it is hardly too much to say that its practical effect has been negligible. What then are we to do?

Until recently an aeroplane undercarriage has generally been called upon to serve two purposes only :—

To absorb the energy due to the vertical velocity of the aircraft when landing;

To enable the aircraft to be flown off from, and manoeuvred over, ground which may be very rough or very soft.

To these requirements are now added a third :—

To absorb the energy due to the horizontal velocity of the aircraft by means of wheel brakes.

These three duties must be carried out with the minimum possible weight and head resistance, for the undercarriage must be as self-effacing in flight as it is all-important on the ground.

The problems connected with wheel brakes are very specialised in themselves and have a particular interest at the present time. For this reason it was decided to deal with them first, and later to turn to the more general aspects of undercarriage development.

Second in importance only to the problem of increasing the safety and reliability of aeroplanes is the question of reducing their head resistance. If aviation was to take its place as an established means of commercial transport the first essential was obviously to make it reasonably safe and certain, and the main energies of investigators and designers immediately after the War were directed to this object. Economy of operation, of which the reduction of head resistance is one of the major factors, was, by comparison, somewhat neglected. But in the last three or four years, with the safety and reliability problems essentially solved, more attention has been devoted to the reduction of drag.

In reviewing the progress that has been made, and the possibilities of further improvement, it is helpful to inquire what is the best we can hope for. We know that the generation of the lift required to carry weight in heavier-than-air aircraft is inseparably associated with a certain drag—the induced drag.

It is twenty years ago almost to the day since the world was saddened by the news of the death of one of its heroes—Wilbur Wright. The inspiring story of the successful attack made by the two brothers, Wilbur and Orville, on the age-long problem of human flight is too well known to be told at length here. But it is remarkable that the first flight by a motor driven aircraft on 17th December, 1903, was made only two years after Chanute, in a speech before the Western Society of Engineers, had felt compelled to use such cautious words as: “There is some hope that, for some limited purposes at least, man will eventually be able to fly through the air.”

My flight from List, Germany, to Chicago, via Greenland and Labrador, was made in July and August of 1931. I had previously made a similar flight to America in 1930 when I chose the south point of Greenland and became very much impressed by this magnificently interesting country. Ever since that flight I had a strong desire to explore this country more closely. My desire for a second flight became acute when we, in Germany, received the first reports of the British Arctic Air-Route Expedition, under the leadership of Mr. Watkins.

Their weather reports for our prospective flight were very favourable and I immediately set to work to organise my second venture.

Fire control has two phases, prevention and cure. Of these the first is obviously the most important, but equally obviously serious attention must be given to the second.

Great advances have been made towards the minimising of the fire hazard as it affects aircraft. Previously inflammable components have been replaced by ones of metal; tanks have been made much less prone to disintegrate in a crash, and the press has provided us with a non-inflammable fuel.

It is not my intention to-night, however, to deal with this aspect of the case; it has received a great deal of attention and is constantly before you as aircraft designers. I propose to elaborate the subject of curing those cases we are unable to prevent.

The subject of fire extinction has been curiously neglected scientifically. Recently, one must admit, some attention has been bestowed upon it, but attention of rather a haphazard nature.

During the past few years particular attention has been paid to the protection of metal parts of engineering structures of all kinds against corrosion. The problem of protecting metal structures against deterioration is now recognised as of primary concern both to users and to manufacturers. Corrosion prevention is an economic problem and its cost must be based on the cost of preventative measures compared with the loss directly and indirectly due to deterioration. In those sections of industry in which marked advances have occurred in corrosion prevention, the advances can be seen to be the result of close co-operation between the laboratory, manufacturers and users.

Since the Armistice the gradual development of the various types of aero engines, together with the abandonment of windmill driven accessories, has necessitated an increase in the number of auxiliaries incorporated in the engine structure, and the engine designers are to be complimented for the ingenuity and compact arrangement of the auxiliary drives and housings on present-day aero engines.

The auxiliary drives for valve operation, dual magnetos, oil pressure and scavenge pumps, water and petrol pumps, supercharger, turning, starting and gun gears, are usually grouped in a housing or housings at the rear of the engine, except that on the radial air-cooled engine the valve gear is arranged at the front and the water pump is unnecessary.

The aeroplane launching catapult is a means whereby in a very short distance the speed of an aeroplane can be accelerated from rest to that at which it becomes air borne.

Fundamentally the aeroplane launching catapult comprises a carriage on which is mounted the aeroplane to be launched, a motive plant which causes the carriage to travel at an increasing speed along a prepared track or structure and a means of arresting the carriage after the aeroplane has attained the necessary flying speed.

Some wind tunnel experiments have been made on a variable pitch airscrew which shall change its pitch automatically as V/nD changes. The change in pitch is operated by the resultant effect of centrifugal and aerodynamic forces.

Reduction in air density, e.g., due to increase in height, causes an increase in pitch.

In the event of engine failure the blades assume the position of minimum drag.

A tentative design for a model screw, together with tests thereon, are described, and it appears that if the friction in the bearings about which the change in pitch occurs can be made reasonably small, it should be possible to construct a satisfactory full-scale screw.

Due proportions being established, it can be said that the present time, as regards what has been called the “conquest of the air,” is comparable to that extremely remote epoch in which Nature for her part also solved the problem of flight.

Man arrived late in the history of his life at the realisation of locomotion in the air, but Nature also reached the same realisation only in a second stage of the evolution of living forms. The early animal species were all wingless, the development of the wings being the effect of a successive adaptation.

At present the number of fliers is very large.

From calculations of the zoologist Dödering, mentioned by the zoologist Zschokke, together with a large number of interesting data and information about animal flight in a very important book, we know that among 420,000 animal species at present existing at least 260,000 are able to move through air. As is seen, flight is a faculty widespread in Nature; from the figures some 62 per cent, of the species living to-day is adapted to aerial locomotion. If from these calculations we exclude water creatures, which give a small contribution of fliers (and moreover of a very poor quality), the ratio of the flying to the nonflying species rises to 75 per cent.

I wish to make it quite clear that any opinion expressed in this lecture is merely a personal opinion, and does not tend in any way to express the official view.

As a serving officer it has been necessary for me to obtain permission to give this lecture, and a copy of the proposed lecture has been submitted to the authorities, but this in no way implies that they are in agreement with the opinions expressed in the lecture.