The aeroelastic properties of modern aircraft are such that necessary calculations, of critical flutter speeds for instance, can be remarkably complicated. A flutter analyst requires an inordinate degree of skill and experience if he is to acquire a “sense of feel” in calculations. The difficulty of deciding how to adjust a critical flutter speed predictably by some structural modification is a typical outcome of this complication.

Although it is only the future that matters, the Centenary of this Society justifies a glance at the past—but what is one to look at? So much has happened.

There is one thing I must say at the outset—that I find it very difficult to believe that it has all happened. Cerainly what has been achieved could not possibly have been foreseen in 1914, and this leads me to something which I believe in very firmly indeed—that is, the futility of planning over a long period. Such planning must be on the most flexible basis possible.

The pressure distribution on the surface of an aerofoil section at near sonic speeds is not sensitive to small changes in free-stream Mach number, and the distribution at M0=1.0 is often referred to as the sonic-range pressure distribution. Attempts to predict this form of pressure distribution have met with some success in the past, the work of Spreiter and Alksne, using an approximate solution of the non-linear equations of transonic small-disturbance theory, being of particular note. Reference 1 demonstrated the application of this theory to a family of non-lifting, sharp-nosed aerofoils and found good agreement with experiment at free-stream Mach numbers close to unity.

It is a remarkable calibre of man who is attracted to aviation. Those enthusiasts who formed Britain's Aeronautical Society 100 years ago were optimistic visionaries. For they had to wait 37 years before man's first controlled powered flight. Very few of the members then, in 1903, are alive today. And this is also true of those other optimists who, inspired by the Wrights’ great achievement, have led the world during the past 63 years into the astronautic age.

After an interview with Mr. Handley Page, I began work for him in January 1916. My brother had been on design work on the 0-100 for many months under Mr. G. R. Volkert and Mr. F. Arcier, and when recommending me to Mr. Page he was told “I had better sack you and engage him”—however, we were both members of his staff for many years. The drawing office at Cricklewood Lane was cramped and had been stables. Handley Page wind tunnel work was first in charge of Mr. Boswell, and later Messrs. Reynolds, Widgery and Russell. I was fortunate in gaining wind tunnel experience and came to realise how keenly Mr. Page followed up the results (taking them home with him at weekends). For many months I was Mr. Page's Personal Assistant.

Handley Page wind tunnel work was first in charge of Mr. Boswell, and later Messrs. Reynolds, Widgery and Russell. I was fortunate in gaining wind tunnel experience and came to realise how keenly Mr. Page followed up the results (taking them home with him at weekends). For many months I was Mr. Page's Personal Assistant.

The purpose of this note is to present some recently acquired data showing the effects of variations in the open area of slotted liners on the pressures on a twodimensional aerofoil at sonic speed in the 36 inch X 14 inch transonic wind tunnel at the NPL. The basic slotted liners for this tunnel have eleven longitudinal slots, giving an open-area ratio (σ) of 0.091. Other slot openings are obtained by closing appropriate slots with “Sellotape.” Nine values of σ ranging from 0 to 0.091, were used in this investigation. A wall static-pressure orifice, sufficiently far upstream of the model to be unaffected by its presence (3-6 chords), was used as a reference pressure for tunnel speed. The relationship between the Mach number given by this reference pressure and the true tunnel Mach number (M0), at the model location, was obtained by careful calibration.