Encyclopædia Britannica, Volume 30 — Aeronautics ​AERONAUTICS (see 1.260). Between 1909 and 1921, Aero- nautics, an infant to start with, had not grown as a child The engine, though once in advance, fell behind, and only now (1921) is again full of promise. They have since become the most usual bracing of British aeroplanes. They offer approximately one-eighth of the resistance of cable of the same tensile strength. Their metallurgy required careful study, and hence in other countries cable has continued to be used, frequently duplicated, the cables lying one behind the other with a wood " fairing " between them. Struts of streamline shape were in use at an earlier date. The bodies of aeroplanes have improved in form, the crew has been protected from wind pressure, and the spokes of wheels have been covered in with fabric. Of these, seven were at the National Physical Laboratory at Teddington, three 1 Report, Advisory Committee for Aeronautics, 1909-10, p. 38. 1 Report, Scale Effect Sub-Committee A. C. A., 1917-8, R and M, 374 ​ at the Royal Aircraft Establishment, Farnborough, and a number distributed amongst the private aeronautical firms of Britain. 1 America has a number of channels of generally similar type, 2 but with a unique example in one instance where the speed of the air current is very high. These have been continuously evolved up to the present day, and their dissemination has spread far and wide much acquired knowledge. 3 Reports of the Advisory Committee for Aeronautics to date, Jour, of the Royal Aeronautical Society. Reports of the National Advisory Committee for Aeronautics, United States of America. " Applied Aerodynamics," L. Bairstow. " Aeronautics: A Class Text," E. B. Wilson. " Aeronautics in Theory and Experiment," Cowley and Levy.  ​ The earliest steps in England, or indeed anywhere, to unify such standards were taken by the Royal Aircraft Factory at Farnborough in 1913. built-up stand pivoted about the propeller shaft axis, is held and the torque measured with a graduated bar and counterpoise. To vary the power absorbed at a given speed, the Fell type of Escargot (see figs. 19 and 19a), introducing Butterfly valves in the tangential outlets, was developed late in 1917. Restriction of the air outlet from the Escargot perforce reduces the work to be done by the fan on the air, which tends to rotate with the fan and so increase the speed of the engine to a corresponding degree. A power curve range is thus obtained comparable with that given by the Heenan and Froude brake. Curtiss was probably the most outstanding engine in America, and when the United States declared war in 1917 her need for high-powered aero engines became acute. In May 1917 it was decided, in confer- ence with the Allied Mission in the United States, to design and build the Liberty engine, of which an 8-cylinder model was completed for test on July 3 1917. This was not put into production, as advices from France indicated that demands for increased power would render it obsolete before it could be produced in quantity. Efforts were then concentrated on a 12- cylinder model, the first of which passed its so-hour test on Aug. 25 1917. Towards the end of the war the French made some use of navigational bomb sights, and the United States Government had a large number constructed, but so far as is known no such efforts were made elsewhere. For D.R. navigation on land aircraft use is often made of an instrument called an aero bearing plate. This was an adaptation of a marine bearing plate, or pelorus, having a transparent centre to admit of vertical observations of the ground, and having one or more longitudinal rods or wires which could be aligned parallel to the apparent earth flow so as to enable the drift angle to be read off. It was the conflict of opinion between the British and German delegates, as to the right of each State to the exercise of control and juris- diction in the air space over its territories, that prevented the completion of an International Convention by the conference held in Paris in 1910. By the first British Aerial Navigation Act (1911) power was taken to prohibit the navigation of air- craft over prescribed areas. Every aircraft of a contracting State has the right to cross the air space of another State without landing, subject to following the route fixed by the State, but if it passes from one State into another it must land, if required to do so by the regulations, at an appointed aero- drome. Every State has the right to establish reservations and restrictions in favour of its national aircraft in connexion with the carriage of persons and goods for hire between two points in its territory but is liable to reciprocity on the part of other States. A series of annexes to the Convention give detailed regulations with regard to the marking of aircraft (Annex A), certificates of air- worthiness (Annex B), log books (Annex C), lights and signals and rules of the air (Annex D), pilots' and navigators' certificates (Annex E), maps and ground markings (Annex F), the collection and dissemination of meteorological information (Annex G) and customs (Annex H). The Convention provides for the establishment of a permanent International Commission of Air Navigation, affiliated to the League of Nations, consisting of two representatives of the United States. The ship was then enlarged and a sister ship, " Nordstern," also constructed. Subsequent to the R33 class the British R36 and R37 were constructed to a generally similar design, of somewhat greater capacity and much improved detail. R8o, designed and con- structed by Vickers, embodied several entirely new features, but her size was so restricted by the dimensions of the construction shed that her performance was seriously handicapped. R38 made radical changes in features of design, and a clear and def- inite departure from German methods. The United States had contracted for its purchase.