The so-called Preferred or Standard Number Series is neither well-known nor often used in the British Aircraft Industry, perhaps because the series has not been published by the British Standards Institution or any other official body. Its use has much to commend it on the grounds of convenience and standardisation. Just as it is necessary for the international comprehension of science to standardise on basic symbols and terminology, so is it sometimes beneficial that numbers themselves should be widely used in the same manner.

The Series is published in France as the Renard Series, and also by the International Standards Association, using rounded off numbers to suit the metric system. The American Standards Association has published an American Standard differing from the I.S.A. table only in so far as certain values are rounded off to reasonable inch figures; included also is a table of more approximate fractional sizes.

The Journal in which Mr. W. Tye's Second Barnwell Lecture has been published (“ The Outlook on Airframe Fatigue,” May 1955 Journal) has now reached Australia. I felt that some comment was called for when I discovered that Mr. Tye had not mentioned the work done in Australia on the life of aircraft structures.

What I believe to be the facts are as follows. Australian concern regarding fatigue was awakened in January 1945, when a Stinson air liner VH-UYY crashed with the loss of ten lives. The analysis made by the C.S.I.R. Aeronautical Research Laboratory confirmed that it was caused by a fatigue failure in the welded tube of the primary wing structure.

Mr. H. A. Wills, in charge of structural and metallurgical research at the Laboratory, initiated a programme of fatigue tests on actual aircraft wings, designed to give factual answers to the problem of determining the safe life of aircraft structures. The basic idea that this could be done had been suggested in a paper by Bland and Sandorf0, and the Stinson accident provided the necessary urge.

Of all the treasures accumulated by the Society in the course of its long career, in some ways the most interesting is the oil painting depicting a river scene with a balloon overhead, which hangs in the Secretary's room. In spite of this I have never seen any account of it, and all trace of the means by which it came into the Society's possession seems now to be lost–unless by chance this note may catch the eve of someone still living who has knowledge of the facts. At first sight it seems to be merely one of the many fanciful pictures of a balloon ascent so common at the end of the XVIIIth century in the period immediately following the invention of the balloon, but some years ago I stumbled, more or less by accident, on certain facts that lift it out of the ruck. When I was, in 1924, collecting the material for my book, Aeronautical Prints and Draivinys, I came across an engraved portrait of Joseph Michel, the elder Montgolfier, joint inventor of the balloon.

The accompanying Report No. B.A. 1083 of the Royal Aircraft Establishment demonstrates generally that a moving body or rider plane can be associated with a fixed body or plane for altering the aerodynamic properties of the combination for various useful purposes, and in particular, that rotating cambered rider planes, when associated with the front edge of a fixed wing of standard section (see Fig. 11) “are definitely advantageous” in improving the gliding conditions, and that “by increasing the size of the rotors relatively to the size of the wings, this superiority is increased.”

Previous experiments at the N.P.L. with various types of wings fitted alternately—with optimum wing-tip slots and with rotors—have shown that rotors can give about the same degree of lateral stability as tip slots, but over a much wider angular range. Other experiments with better rotors than used at the N.P.L. have shown that a more powerful stabilising effect over a wider annular range is to be obtained with rotors than with slots.

This paper discusses a few simple ideas which may be supposed to form, consciously or unconsciously, a schematic basis for the servicing of given aircraft in given circumstances. It is not concerned with engineering technique but rather with the assumptions behind it.

The purpose of an aircraft's upkeep, by which is meant its servicing and maintenance in the widest sense, is to enable the machine to furnish the maximum output of flying work of the required kind and intensity. “Intensity” is used to mean an aircraft's rate of output of flying work in a calendar period.

For commercial aircraft the average intensity required is usually near the maximum that can be sustained at reasonable upkeep expense, because this tends to maximise net profit (or to minimise net loss if there is no profit) by lowering the overheads related to the capital cost of aircraft.

The behaviour of an elastic aircraft in flight may be divided into dynamic and static cases with an intermediate class of phenomena under the heading of stability. The dynamic category is concerned with flutter and divergence effects and since these are destructive when they occur they are naturally given precedence in the aeroelastic analysis of an aircraft.

Having eliminated these dynamic effects by suitable design it is natural to turn to the static case which assesses the manoeuvrability of the aircraft. With the advent of sweepback and the attainment of higher Mach numbers it becomes increasingly difficult to determine the behaviour of modern aircraft even when regarded as rigid.

When the writer undertook the preparation of this paper, he rapidly discovered that it was not easy to find any branch of the subject which had not already been dealt with exhaustively by far abler pens than his. One or two matters have, however, been chosen about which information is somewhat meagre or scattered, and which may not, perhaps, be familiar to the aircraft engineer.

First a review will be made of the various types of electronic engine indicator which have been developed up to the present time; this instrument is coming into prominence now, and although it has by no means reached a state of perfection, it is a valuable asset in the hands of the research engineer for the study of fuel problems and other minor points.

The 767th Lecture was read before the Royal Aeronutical Society on Thursday, 17th February 1949, at the Institution of Civil Engineers, Great Georgr Street, London, S.W.1. Dr. H. Roxbee cox, D.I.C., F.R.A.e.S., President of the Society introduced the Lecture Squadron Leader E. A. Harrop, O.B.E., A.F.R.Ae.S., R.A.F., of the Department ot the Air Member for Technical Services, Air Ministry, and a serving engineer officer of long experience in the Royal Air force.

The title of this paper could cover a number of interesting problems ranging from the ultrasonic scream from compressors and its (alleged) effect in producing “jet sickness,” to the noise from supersonic propellers but, since it is “in particular Jet Noise” which is under discussion, this paper deals entirely with that subject. Some new facts are presented, mostly obtained at my own firm, with the active encouragement of the Ministry of Supply, and some of their implications are discussed.

An Artificial Satellite set to start on a circular orbit round the Earth, will have to be given a known velocity, at right angles to the radius vector, which depends upon its distance from the Earth's centre.

It will, from the start, begin to spiral downwards towards the Earth, owing to the resistance of the atmosphere, but if it begins its path at a sufficiently high altitude, the decrease of height after one revolution will be small.

Should the initial “ tangential ” velocity be greater than the value calculated for a circular orbit, the satellite will, according to the text books, describe an ellipse instead of a circle; and, if at a sufficient distance for the air resistance to be at first ignored, will return after one revolution to the distance at which it started, this point being the perigee of the ellipse. It will never return to a point outside the starting point.