Metal adhesives have been known to the Aircraft Industry for at least ten years, the Chrysler Cycle Weld process being among the earliest. Since then metal-to-metal bonding has been the subject of many papers, but no member of a firm of aircraft constructors is known to have lectured on the subject.

It is hoped, therefore, that this paper may prove a useful contribution to the workshop aspects of the method. The fundamentals of adhesion will be avoided and only brief reference will be made to the strengths of structures assembled by that means; those are matters for the physicist and aircraft designer.

The 822nd Lecture to be read before the Royal Aeronautical Society, “Progress Towards Hydraulic Serviceability,” was given by R. H. Bound, F.R.Ae.S., and H. G. Conway, F.R.Ae.S., on 15th March 1951 at the Institution of Civil Engineers, Great George Street, S.W.I. Major G. P. Bulman, C.B.E., F.R.Ae.S., President of the Society, presided at the meeting and introduced the lecturers, Mr. R. H. Bound, Technical Director of Dowty Equipment Ltd., and Mr. H. G. Conway, Technical Director of British Messier Ltd.

To be asked to prepare a paper for delivery to the Royal Aeronautical Society on the subject of the serviceability of a product with whose design the authors are closely associated, offers an excellent opportunity for a critical survey of the field, uninfluenced by commercial considerations and with the realisation that the admission of faults, where present, is essential for constructive consideration of the whole problem.

The hydraulic installation of an aircraft is now such an important and integral item of equipment that any steps which may be taken towards improved performance in serviceability would contribute notably to the operational success of transport and military aircraft. The degree of complexity required in modern aircraft hydraulic systems is such as to make impossible a completely fool-proof system. But consideration of factors which keep trouble within very small bounds is of vital importance.

In this paper the thrust of the turbo-jet engine is rigorously defined, and is divided into the three components front external, internal and rear external. The measurement of thrust in static tests and in flight is discussed. Current methods are critically examined and test methods are proposed. Special attention is given to a method of calculating flight performance from simple static tests with different nozzle areas. A convenient form of engine curves for static tests is shown and a method of flight testing is given.

Much has been written about planning and progressing as applied to manufacture, but there is a noticeable lack of information on its application to the design work which must precede construction.

It is in order to help fill this gap that the present paper has been written.

The paper deals with planning applied to the development of prototype aircraft from the time of submitting a tender up to the first flight of the first prototype.

It discusses the methods of estimating the lapsed time up to first flight, the design man-weeks likely to be expended, methods of measuring design progress and the cost of design changes.

The rational estimation and derivation of aerodynamic loading data is becoming of rapidly increasing importance in the design of modern aircraft. The great advances made in aircraft performance during the 1939-45 War, together with the generally detrimental effect of compressibility upon stressing loads, have combined to make the task of the structural designer much more difficult. A few years ago, the loads resulting from the often arbitrary stressing cases of A.P.970 (Ministry of Supply Air Publication 970, Design Requirements for Aeroplanes for the Royal Air Force and Royal Navy) were of relatively minor significance and furthermore, any inaccuracies in their estimation and derivation were covered almost always by the ultimate factor if the estimate were on the low side, while if the loads were conservative, the weight penalties and structural difficulties involved were small.

Measurements were made of the downwash effects behind two finite wings 3.1 percent, thick, having square and 20° raked tips respectively. The tests were conducted at a Mach number of 1.45 and a Reynolds number of 1.2 millions by traversing a yawmeter 1.62 chords behind the trailing edge of the finite wings.

In general, a maximum downwash of the order of ½° per degree of wing incidence was observed in that portion of the tip Mach cone behind the wing, and a maximum upwash of similar magnitude was observed in that part of the tip Mach cone situated outboard of the wing.

Thus it is apparent that these effects are large enough to affect the lift on any surface situated in the tip Mach cone behind a finite wing. In particular, placing the rear surface in the downwash region behind a finite wing, will tend to reduce the overall lift while placing it in the upwash region will tend to magnifiy the variations of lift initiated by the finite wing.

Recently published statistics give the impression that an excessively high percentage of non-carrier aircraft accidents investigated during 1948 were primarily due to human error. Further, an examination of available data covering the past decade gives the same impression in respect of all aircraft accidents occurring during that period. The figures quoted convey in fact the unpalatable implication that, although in nearly a half century of aviation great strides have apparently been made in increasing the reliability of the aeroplane, very little has been accomplished in reducing the element of human error in aircraft accidents. Why is this?

It has been claimed that the possibility of accidents in flying is inevitable by reason of the inherent conditions of flying which necessitate, besides reliance on the technical factor, considerable reliance upon the skill, judgment, memory, and physical and psychological conditions of the human being.

The dangers and other disadvantages of using air pressure in the strength testing of pressurised fuselages are reviewed. A technique in which water is used instead of air is described, and its advantages considered. References are made to future test methods, and particularly to the need for the application of pressure combined with aerodynamic and inertia loads.

The contraction of a wind tunnel should be free from adverse pressure gradients, since this might cause boundary layer separation.

A wall contour has been designed for a circular cross-section contraction using incompressible flow theory. This gave a favourable pressure gradient at the beginning of the contraction where separation is likely to occur.

Appendix I compares the theory with experimental results obtained from a model of a proposed supersonic tunnel of which the contraction is rectangular in cross-section and which has been based on the results obtained in this report.

The rate of ice accretion on an aircraft depends upon meteorological factors and aircraft characteristics. There are on the one hand atmospheric pressure and temperature; water content; droplet size; electrostatic conditions. On the other hand, there is the collection efficiency made up of aircraft component design characteristics such as size; shape; material; surface finish. Finally, there are aircraft flight variables such as speed; attitude; skin temperature; vibratory state.

Meteorologists are able to define potential icing intensity if they can forecast the ambient factors mentioned. The intensity may be defined as light, moderate, or severe, or by some such broad adjective, with reference to a hypothetical collector. Similarly, the air-worthiness authority, e.g. the Air Registration Board, must be satisfied that an aircraft can be operated safely in the appropriate meteorological conditions. Therefore the probable association of each meteorological factor with the others needs to be known.

A few years ago when high–speed aircraft were mentioned, speeds of 300 to 400 m.p.h. came to mind. The advent of jet propulsion has made those figures 100 per cent, out of date and today speeds are discussed more and more in terms of Mach number; for example, high–speed subsonic aircraft fly at Mach numbers of 0.85 to 0.90, aircraft are flying in the transonic region and supersonic guided missiles are proposed for speeds anywhere between M=1.5 and 2.5, i.e. ground level speeds up to 2,000 m.p.h.

It is proposed to review very broadly the suitability of propulsion units for these transonic and supersonic applications. What is the difference between ordinary power plants and those for high speed? The answer might be contained in another question—why are supersonic aircraft different from conventional types? The aerodynamicist will give an involved explanation concerned with compressibility, drag rise, shock waves, and so on.

Accidental dispersals of medically and agriculturally undesirable insects by sea and air transport are discussed, with attention to the relative importance of the roles of ships and aircraft. World-wide records of insects found on board aircraft and discovered to have been introduced at airfields are briefly reviewed, and consideration is given to ways of meeting the problem by insecticidal treatment and airport insect control. It is felt that the insecticidal treatment of aircraft, even when provided for by comprehensive international regulations and conscientiously undertaken, does not alone provide sufficient protection against insect introductions, and that greater attention should be paid to the preventive aspects of the problem, with particular regard to the control of insects of both medical and economic significance at international airports.

These notes are intended to summarise for the benefit of aeronautical students the basic requirements of nose-wheel steering hydraulic systems. The various factors which have to be considered are listed and representative solutions given.