In accepting the invitation to address the Royal Aeronautical Society I am deeply conscious of the honour that has been paid to me and of the responsibility I have undertaken. My sense of responsibility flows from the realisation that I have been called upon to contribute from personal knowledge and experience to the great volume of recorded and authoritative opinion already contributed by these lectures.

I have chosen to address you on some international aspects of air transport because it is my firm belief that the lack of an enlightened multilateral code in an important field of international air transport is one of the more serious impediments to the full exploitation of the technical advances with which air transport has been presented in recent years.

Sources of noise in aircraft are discussed briefly with particular reference to the introduction of the turbo-jet engine.

An account is given of a particular investigation made in a Lancastrian aircraft fitted with both turbo-jet and reciprocating engines. The equipment by which the noise spectrum was analysed over, an extended frequency band is described.

The results are examined and the effects of the two types of engine on the noise spectrum are compared, under different representative conditions, in the forward and rear sections of the fuselage.

The pure bending of a rectangular beam about an axis parallel to a principal axis of its cross-section is well understood if its depth d is comparable in magnitude with its breadth b. The usual theory, noticing the geometrical fact that at any cross-section the longitudinal strains of filaments of the beam are proportional to the distances of the filaments from some neutral axis parallel to the axis of bending, postulates that the longitudinal stresses will vary in the same way.