On 18 June, 1914 Lawrence, son of Elmer Sperry (founder of the Sperry Gyroscope Company) flew over a crowd assembled at Argenteuil, near Paris (Fig. 1). His aircraft was a Curtiss C2 flying boat and the purpose of the flight was to demonstrate the Sperry Gyroscopic Stabilizer in a competition organized by the Aero Club of France. It was a dramatic demonstration. On the first pass over the crowd Lawrence Sperry stood up and held both hands in the air whilst his mechanic, Emile Cachin, walked out on the wing and stood holding one of the struts. The lateral stability of the aeroplane was undisturbed, but the spectators were able to see the ailerons move to compensate for the engineer's weight. This performance was repeated several times and Sperry also demonstrated the automatic ‘volplaning’ function of the system which caused the aircraft to dive and regain speed in the event of an approach to the stall. The company was awarded a prize of 50000 francs as winner of the competition.

It is generally felt that by causing aircraft to follow accurate climb and descent paths the flow of traffic in terminal areas can be improved. This paper, which was presented at a meeting of the Institute held in London on 29 November 1972, with the President, G. E. Beck, in the Chair, discusses the special constraints involved in vertical plane navigation. These arise from difficulties in the accurate measurement of position, and the limitations of aircraft response. The need to fly at differing speeds and in various configurations, while minimizing passenger discomfort and external noise, is also considered.