The present Paper is a record of experimental work carried out with a view to overcoming the phenomenon of “ burbling.” As is well known, the total pressure on an aerofoil is the sum of the positive pressure on the under side and the negative suction on the upper. If this negative suction can be made to increase progressively with increasing angle of incidence to angles greater than heretofore, the maximum value of the aerofoil lift coefficient will be increased. The effect of such an increase on aeroplane design depends upon the magnitude of the increase and the extra structure weight of the device necessary to obtain it. The present method which, is now described has been evolved from experimental data, and an outline of the results is given below.

In a Paper which I read before the Royal Aeronautical Society in April, 1911—ten years ago—I attempted an analysis of the somewhat meagre results then available on the pressures on plane and curved surfaces moving through the air.