If the term ‘angle of incidence’, so frequently used in aeronautical discussions, could be confined to a single definite meaning, viz., the angle at which aeroplane and wind actually meet, much error and confusion would be averted. But many of the best writers use this term loosely and inexactly, with the result that their calculations and explanations of phenomena are thereby often rendered of little value, and students are misled.

If a plane be held stationary in a horizontal wind (Fig. 1), the angle of incidence A C D will be equal to the angle with the horizon. But if the wind have an upward trend, the angle of incidence will be increased to A C D2. A calculation based on the assumption that A C D still remained the true angle would, of course, be seriously in error.

It is my privilege to speak to you tonight on some aspect of the work of testing experimental aircraft, and in order to present my subject to you in as lucid a manner as possible, I am going to ask you to consider that we actually have a machine before us waiting for its first test.

We must assume that the cockpit arrangements have been approved before this, for so much has to be done that can only rightly be done as the machine is being built. The seat and rudder positions must be comfortable, windscreening good, view ample, engine controls handy, flying controls accessible, smooth and firm, petrol flow satisfactory and necessary instruments must be clearly visible. The first thing to be done is to weigh and balance the machine. From this we learn the total weight—the designer learns whether he has been clever or not—and then we chase that elusive spot the e.g. The wing position and tail setting have been designed with the e.g. in an assumed position, and if one weighing shows it to be seriously out, then before the machine can be flown it should be ballasted to bring it to the required balance. The flying controls should be carefully tested by the pilot. It is not sufficient to waggle the joystick and watch the ailerons and «levators move; very careful attention must be given to see that they move the right way.

Ever since I first began to study Aeronautics I have been annoyed by the vast gap which has existed between the power actually expended on mechanical flight and the power ultimately necessary for flight in a correctly shaped aeroplane. Every year, during my summer holiday, this annoyance is aggravated by contemplating the effortless flight of the sea birds and the correlated phenomenon of the beauty and grace of their forms.

In World War II when Spitfires and Mustangs and Messerschmitt 109s and other aeroplanes of that category were quite common, we were all aware of the troubles that these particular aeroplanes got into when starting to dive. When getting up to around 80 per cent of the speed of sound, the aeroplane starts shaking, buffeting we call it; some of them lost ailerons and tails and it proved to be fatal to some of the pilots. It was quite obvious to all people who have an engineering mind that something just was not quite right, especially in the speed range they were flying in those days.

I was both honoured and pleased to be invited to give this Mitchell Memorial Lecture. Aside from the personal gratification there were, and still are, two other substantial reasons for my satisfaction:

• (i) Mitchell, and his distinguished contemporary, Camm, are without doubt still the best-known names in British aircraft design. Both were heroes of my boyhood—I had not yet taken my eleven plus at the time of R. J. Mitchell’s death. Later, I worked for 16 years for and with Sir Sydney.

• This lecture therefore provides me with an opportunity formally to express the lifelong respect I have always had, in absentia, for R. J. Mitchell and his achievements.

• (ii) The Southampton Branch Committee were tolerably firm in their invitation: ‘Sea Harrier’, they said. Since at the time Sea Harrier was occupying —and still fills—over 75% of my professional lot, I was specially pleased with the choice of subjects offered.

Many space satellites consist of a pair of highly-flexible solar panels attached to a relatively rigid centre-body, the recently launched CTS is a good example. The panels supply electrical power to the communications equipment and attitude sensors which are usually mounted on the centre-body. It would appear that in the current generation of vehicles the flexure of the panels does not degrade the quality of the attitude control. This may not be so, however, in the next generation of satellites which will of necessity carry much larger solar panels. If the same high pointing accuracy is to be maintained in these vehicles and problems due to structural damage are to be avoided, then the flexure of the panels will have to be controlled.