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Aviation History
1919
1919 - 0264.PDF
UJLJZ^I aerodrome would be provided with suitable electric light sky signals to indicate the position of the landing ground to incoming ships at night, and the aerodrome would require to be provided with landing lights to indicate the position of the mooring tower and to give sufficient light to enable the ship to be moored. SECTION IX.—The Weather as Affecting Airship Service The elements of weather that have influence on airship travel are wind, rain, hail, snow and fog. It is not likely that rain, hail, snow and fog will of themselves have much influence on airship flying. With suitable rain-proof non-absorbent • outer-covering, the absorption of water and the consequent increase of weight are avoided. Hail and snow will not adhere to the ship's surface when in flight owing to the high speed through the air, and in any case, as the precipitation height is not usually more than 8,000 ft. they can be entirely avoided by flying above this height. Fog might give trouble in landing, but in flight the airship would be above the fog and not be affected by it. In landing suitable means would be taken to mark the landing place by means of captive balloons or kites, and strong searchlights could be used on the ground. At night the balloons would carry electric lights "with connection from the ground. Rain, hail, snow and fog are also generally local in their occurrence, and could in any case generally be avoided by a short deviation from route. Cross-Atlantic records indicate that on the main steamship routes fog sufficient to impede navigation does not occur on more than twelve days in the year. Wind.—The only important factor that need be taken into consideration is wind, but in most cases unduly strong winds can be avoided by flying at a higher level or sailing on a different course so as to avoid the storm area. As is well known there are at sea level, between certain clearly-defined latitudes, prevailing winds of constant direction, of which advantage can be taken by suitably laying out the course and route to be followed. Again, at the higher levels, there is at most latitudes a constant drift, of which advantage may be taken even if the winds at sea level are unfavourable. The following general facts which have been established from meteorological records all over the world have a great bearing on airship possibilities, viz :—1. Heavy storms, which are usually of a cyclonic nature, are known rarely to cover an area of more than 200 miles diameter. 2. The rale of progres sion of a cyclonic area is considerably less than the speed of air movement in the area. It is therefore obvious from the above that an airship would get clear of a cyclonic area by a deviation from her route of not more than 200 miles, and •once clear of the disturbed area would have no difficulty in getting and keeping away from it. Prevailing winds at sea level in the North Atlantic.—The prevailing winds north of the Equator may be clearly divided into two regions :—1. Between that part of the west coast of Africa between latitudes 300 N. and 150 N., and the American Coast from Florida to the Amazon. In this region the winds at the African coast blow from N.E. by N., and gradually become more easterly across the Atlantic, until at the American coast they are practically N.E. at the Amazon and practically E. at the Mexican Gulf. These winds are the trade winds of the old navigators, and are remark able for their steadiness and persistency, both as regards direction and speed. The speed of these winds averages 10-15 m.p.h., and varies little from season to season. These winds are favourable for flying from east to west. 2. Between the coast of the United States from Florida and as far north as Newfoundland to Europe, from the north coast of Spain to the north of Scotland. In this region at the American coast the prevailing winds blow from almost due W. in the winter months, veering S.W. in the summer months, and gradually change in crossing the Atlantic to S.W. on the European coast in winter and almost doe W. in summer. These winds are more variable than the trade winds, bnt are persistently westerly. Their speed is, how ever, more variable. The yearly average of the speed of these winds is 15 m.p.h., but they occasionally Wow up to 40 m.p.h., and heavy gales are not unknown m the winter months, but these are TMually of a local character. Records kept on the main Atlantic steamship routes indicate that on the average general winds of 40 m.p.h. and over do not occur •on more than 20 days per annum, and the total time of duration not more than 300 hundred hours in all. Practically all the storms of 40 m.p.h. and over occur N. of latitude -45^ N., that is, the latitude Bordeaux-Nova Scotia, and 60'per cent, of total number of storms in the winter months (November, December and January), only less than 10 per cent, in the summer months (May to August). The foregoing prevailing winds are clearly shown on the Atlantic Wind •Chart. Prevailing winds at higher levels.—Although, as stated above, precise information is available of the sea level pre vailing and periodic winds at various latitudes very Bttle co-ordinated work appears to have been done hi charting the prevailing and seasonal winds in the higher levels of the atmosphere. A great deal of work has been done in various localities in U.S.A., England and Germany, but very little is known of the winds at the higher levels over the great ocean tracts. There is no doubt a great necessity for inter national research on the predictions of weather conditions in the higher atmosphere, to enable advantage to be taken of these higher currents, if Atlantic flying is to become as common as Channel flying. At high altitudes, constant winds of from 30 to 40 m.p.h. are common, and if the prevailing directions of these are known to airship navigators, the duration of the journey could be considerably shortened, even by taking an indirect route, if advantage can be taken of these air currents. It is, however, undesirable to fly at great heights owing to the low temperature, but with suitable provision for heating there is no reason why flying at 10,000 ft. should not be common. SECTION X.—Airship Navigation The navigation of airships is similar in principle to that of steamships, but is made more difficult by much greater drift to be allowed for. The actual course of a ship being the resultant of its own forward speed and that of the motion of the air in which it is borne, it is impossible for the navigator to plot his true course relative to the earth unless he is aware of the motion of the air. When navigating over land he is able to determine the drift of his ship by observation of a suitable fixed point on the earth's surface, and adjust his compass course accordingly to give the desired true course Over sea, of course, no fixed point is available, so if the motion of the wind is not known, the course must be periodi cally corrected by astronomical observation and determination of his charted position. A reliable and effective method of navigation is, however, available with the wireless installation. If the ship is in communication with two stations they can determine the direction of the transmitted waves and signal to the ship its bearings, from which the position can be laid off on the ship's chart and the new departure determined. It is known that this method of direction was used by the German naval Zeppelin airships. SECTION XI.—Comparison of Airships and Aeroplanes for Long-Distance Transport Endurance.—The airship of 3,500,000 cubic ft_ capacity, specified in this paper for immediate use for trans-Atlantic transport, has an endurance of 80 hours at an air speed of 60 m.p.h., and can carry 15 tons of passengers and mails for an air distance of 4,800 miles at that speed. Also it would be quite a practicable proposition with present systems of design and materials of construction to build a rigid airship to carry 50 tons of passengers and freight for 10,000 miles at a speed of 80 m.p.h. as soon as developments in the demand for aerial transport justify the construction of the size of airship necessary. With a 40-ton all-metal aeroplane— which represents about the maximum size and most efficient weight-carrying type that could at present be constructed and handled—the maximum non-stop endurance of this machine would not be greater than 25 hours, carrying a load of passengers and mails of about 3 tons, at an air speed of 85 m.p.h., i.e., having a maximum air distance of 2,100 miles, and unless some radical new method of design is discovered, it is considered theoretically impossible to produce a machine on the present methods of construction even with fight metal structure throughout to give an effective range of more than 2,000 miles, and then only with a relatively very small passenger load carrying capacity. The advantage of the airship in these respects is due to the following characteristics. In the case of the airship the percentage of useful lift increases with the size of ship and the weight to power ratio decreases. In the case of the aeroplane the percentage of useful lift and the weight to power ratio increases but slightly with increase of size. It therefore may be definitely accepted that for voyages on which it is necessary to make a non-stop flight between points more than 2,000 miles distant the airship is far more econo mical, and further is the only means of aerial transport practicable. On the other hand, if flying oyer land with landing grounds provided at intervals of not more than t.ooo miles, the aeroplane can, of course, travel for indefinite distances, coming down at each landing ground for replenish ment of fuel and oil. It therefore appears inevitable that the airship will hold the field for long distance cross oceanu voyages, and the aeroplane will be used for routes which may be flow* in stages of a maximum distance apart of about 1,000 miles continuous flight. Carrying this de- 264.
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