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Aviation History
1917
1917 - 0658.PDF
that, instead of abusing the wind, we can use it. We can follow the main currents instead of fighting against them, and then we shall find them our friends. For instance, the route homewards from India during the greater part of the year will be far easier through Afghanistan, Russia, Germany, and by what I may call the northern route, than by a more southern course, for easterly winds or calms predominate. On the outward or eastward journey, however, the route is across France, by the Rhone Valley, where the wind is often north-westerly, sometimes called the " Mistral," to Marseilles, whence we shall go either across the Lower Alps to Italy, and follow the coast to the heel of Italy. Or we shall fly via Sardinia to Malta, whence by Tunis we get to Egypt. The alternative routes will be from Brindisi to Alexandria direct about 900 miles, or from Taranto to Malta. Thus the east- ward and westward routes to India, the Central European and Mediterranean, may be spread apart by 1,000 miles at their extreme point of divergence, and yet be the quickest routes and the cheapest to fly. In fact, wind will matter far more than mileage. In former days the trade winds dictated just the same sort of courses for sailing ships, and often the outward and homeward routes were half an ocean apart. So it will be in future. Eastern Routes as affected by Winds. Now let us take the outward Eastern route in detail and see how the winds will help on an average winter day. Starting, say, from Hendon or, perhaps, Croydon—for I assume that two great starting and landing places will exist for northern and southern routes to and from London—in the first flight Marseilles will be reached, where a descent for lunch will be made, the 600 miles—I give round figures— having been covered in about five to six hours. This portion of the route will be affected on about 80 per cent, of the days of the year, first by westerly and later by north-westerly winds, that is, either cross or negative and favourable currents. Next, some point near Taranto or Brindisi or at Malta itself will be the next stopping place. This part ot the journey will probably be done by seaplane in order to avoid the longer route round the Bay of Genoa and the leg of Italy. The prevailing wind over this section will be north-west to start with, and afterwards light airs from the south-westward will be encountered. The " mistral " often extends in a modified form on many days in winter to a point as far as the south end of Sardinia, where the most westerly current supersedes it. The winds on the first day will, therefore, be favourable on the average. On the second day, whether we start from Brindisi for Alexandria direct or fly via Malta and Tunis or Tripoli, a westerly wind will prevail as a rule near the African coast, though a moderate easterly wind is sometimes met with in the neighbourhood of Malta from September to April. On this second day's journey by evening you will have reached either some point between Malta and Alexandria on the Tripoli coast, or more likely Alexandria itself, only 850 miles from Malta. Egypt is situated in a region where calms or light winds predominate, with the exception of the disagreeable sand-laden " Khamseen," the strong westerly wind from the desert, which, however, is favourable to pro- gress eastwards. We then proceed eastwards over the Arabian desert, where calms and light winds are the rule, a state of atmosphere which prevails all the way to Karachi, except in the monsoon period, when the north-west wind is also in our favour. In the Persian Gulf the isobars for the greater part of the year show a prevalence of north-westerly currents, also favour- able. At Karachi in the winter, during the day, wind of considerable strength from the south-west is produced by the great difference of temperature between the Arabian Sea and the heated areas of the Sind desert behind it. Flying on south-eastward towards Bombay or north-eastward towards Delhi, there is no decided unfavourable current on the average. Thus we trace step by step, or rather anti- cyclone by anti-cycloae, isobar by isobar, the outward route to India. I have not time to examine in detail all possible routes, but on the homeward passage, the reverse side of these winds, favourable for flying eastward, is available. Every weather system, as I have explained, has a circular move- ment. There is no doubt about the prevalence of easterly and south-easterly winds throughout the monsoon period, lasting from the middle of May to the end of October, in all the country we should use for our westward journeys, through Afghanistan and through the neighbourhood of the Aral and Caspian Seas. Our first day's journey homeward takes us to Gurieff, following the average isobars. And once the corner of the Hindu Kush has been crossed at about 5,800 ft., the country all the way to England is marvellously flat, which JUNK 28, 1917. favours the absence of wind. I would remark here that absence of strong winds is a feature of inland flat countries, while mountain chains, especially when high and snow covered, are specially liable to storms owing to the sharp "changes of temperature producing local winds of considerable force. The next day we leave the head of the Caspian Sea, and arrive via Lugansk at Tarnopol near Lemberg. Here, again, we leave the mountain systems of the Caucasus, the Balkans, and the Carpathians to the south of our route. The next and third day we have to face the chances of westerly winds against us when approaching the North Sea and Channel, which, however, lose much of their force inland. From these, however, there will be no escape, except when an anti- cyclonic system exists over Scandinavia—a not uncommon winter and spring feature—which will give us easterly or north-easterly winds over Western Germany and Holland. The Wind our Friend. ^ After the detailed consideration of these two Eastern routes you will grasp the point at which I have been driving, namely, that the wind systems of the world can probably be made to serve the purposes of flying exceedingly well, and that, instead of winds being a disadvantage to flying as might at first be thought, they will assist us if properly understood. In fact, the existence of alternate high and low-pressure areas, with their respective and regular circula- tions of wind, will define far more than geographical conditions the chief air routes of the world. Of course, there will be special atmospheric conditions from time to time which will involve alteration from the average courses recommended for over-sea and over-con- tinental flying. There may be, to take a common instance in summer, an extensive " low " over France or over the mouth of the Channel involving strong easterly winds blowing from our western shores far out into the Atlantic to a point at which the Azores " high" is joined up with another " high " near the Atlantic coast. In such a case a seaplane could, with the probability of a favourable wind over the greater part of the passage, fly from County Kerry to St. John's, Newfoundland, in a shorter time and with less expendi- ture of petrol than by any other route. And in flying west- ward you will be sun-chasing. In our English latitudes of 51 to 55 the earth's motion does not exceed about 650 m.p.h., and though we shall not be able to fly quite fast enough yet round the planet to keep the sun over our heads continuously, still at 120 m.p.h. we shall lengthen our day very consider- ably. In the case of crossing the Atlantic there will be a gain of about 4 hours between Ireland and Newfoundland, which means that, leaving Ireland at 7 a.m. on a summer morning, if an average of no m.p.h. is maintained, you will reach St. John's in 16J hours actual elapsed time, from which four hours must be deducted in point of solar time. Thus you will leave Ireland after breakfast at 7 a.m. and reach Newfoundland at 7.30 p.m. by local time, in time for dinner. Coming eastward; your daylight, alas ! will be shortened by the same time, and, except in the summer months, a start before dawn or an arrival after sunset will be inevitable. But to return to the consideration of a western route as affected by weather conditions. Assuming again an exten- sive " low " situated between the West coasts of Scotland and Iceland, a common winter type of weather, while the Azores " high " has extended some way up the Bay of Biscay, then the passage to America may be more advisable by the Azores than by any more northern route. With wireless stations specially instituted for this purpose over the world's surface, and ships stationed at intervals over the sea to send wireless messages as to weather conditions, our fore- casts and weather charts of the future compared with those of to-day, good as they are, will be extraordinarily accurate, and be absolutely reliable except in the case of very suddenly formed small depressions local in their influence. I would mention before I leave the subject of the winds, that along the line of the equator there is a tendency to an easterly wind, sometimes north-east, sometimes south-east, at all times of the year. This tendency also will be useful. I cannot deal on the present occasion with other weather conditions such as fog, except to mention that fog exists chiefly in certain latitudes, and generally coincides with calm weather, or, at any rate, very light winds. Rain, snow and hail I disregard, for they will be negligible to the planes of the future, though large hailstones may be harmful to propellers or even wings ; but hailstorms are local, as a rule, and can be avoided. The ability also of aeroplanes to avoid or rise to a height above local disturbances will be the solution of many of these difficulties, for heavy precipitation, generally speaking, arises in levels lower than 10,000 ft. 658
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