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Aviation History
1916
1916 - 0155.PDF
FEBRUARY 24, 1916. f/TiGHT WIND FLYING. By J. H. FLYING in a wind is really very little more difficult than flying in calm air if one goes to work in the right way. The following notes may be of use to those whose flying, so far, has been confined to fairly calm weather. One would, naturally, not try to fly in a 40 m.p.h. wind before being able to fly in a wind of, say, 10 m.p.h., which all means, that to fly in anything of a wind, one must start at the bottom, which in this case is generally termed a " calm." Bumps and such like are soon not looked upon as quite so terrible as they used to appear. Meanwhile, as one increases in confidence, and attempts flights in winds of increasing velocity, it is not necessary to run any unusual risks. For instance, it is just as well to give your engine a good run before starting —and start right into the wind. After a time, having taken due caution all along, one finds it not at all hard to fly in most winds, bar hurri canes, &c. Having got to this stage, you will have noted that very frequently a wind of, say, 5-15 m.p.h.—as registered by the anemometer—is more tricky to fly in than a wind which may reach 25 or 30 m.p.h. on the ground, and you will realise that it isn't the strength of a wind which matters, within limits, but the extent of the departure of the gusts from its mean velocity, i.e., a fairly steady strong wind is preferable to a wind of lower velocity but in which the gusts are more marked. Having reached the stage of flying in a pretty strong wind, you will practically have acquired the habit of getting to work on any bump the instant it starts to appear—it's a good policy, and a habit which comes quite naturally. The nature of a wind at low altitudes is determined, to a very great extent, by the contour of the ground, so that one encounters eddies which tend to alter the path of a machine, and which have to be corrected in the ordinary way. For example, a railway embankment produces a most pronounced up and down current when there is a wind blowing across it. As the height increases the effect becomes more and more damped—at 2,000- 3,000 ft. the effect on the air of any ordinary obstruction on the ground is practically negligible. Most winds, which may be pretty bumpy near the ground, become fairly regular when the region round about 3,000 ft. is attained. Generally speaking, winds also increase in velocity as one gets higher. For example, on one occasion I started off in a wind of approximately 25 m.p.h.—according to the anemometer. At first, things were pretty rough, but I was making headway quite satisfactorily. As the machine got higher the ground speed decreased, until at about 3,000 ft. no progress to speak of was being made. At this height the air was very much better as regards bumps, while at 4,000 ft. it was pretty steady; but when at this height, heading directly into the wind, I was making no progress at all—in fact, was " standing still." As 5,000 ft. and 6,000 ft. were reached the velocity of the wind had increased again, so that I was, by that time, going back wards—very appreciably—which was not over pleasant, as I had to get back to my starting place. Now as to getting back—no progress could be made at 4,000 ft., so down to 3,000 ft.; here again no forward motion was apparent. At 2,000 ft. it was a bit better, but not good enough, so the return journey was made at about 1,200 ft.—and 155 MOORE. even then it took just on half an hour to cover about five miles—the pitot tube showing 60 m.p.h. The same thing happened on another occasion, but not in quite so pronounced a degree; still the machine was going well—backwards—at any altitude from 5,000 ft. to 8,500 ft. When starting a flight in a strong wind it would seem advisable to attain a fair altitude, say 300 ft.-400 ft., before attempting to turn. This is pretty general know ledge, but, as such, should not be disregarded just when it is necessary to apply it. Turning down wind, in really gusty weather, always carries with it the possibility of a drop—due, naturally, to the momentary loss of air speed which may be pro duced if a rear gust should strike your machine while turning. Drift is a very well-known feature when there is any wind about. Everyone has seen an aeroplane going along somewhat "sideways." Care should be taken when landing to put the machine head to wind if it is found that the machine is drifting, which effect, though easily noted when near the ground, is not quite so evident at a height. When about to land, the correct thing to do is to turn the machine into the draught—which is placing it head to the wind. The direction of a wind may vary at different alti tudes. If it is desired to know the direction of a wind near the ground when you are high up one can frequently get a good idea of this by having a look round for some smoke, which is an excellent guide. Turning to another little matter which may be of interest—a wind of any strength makes a big difference to the range which a machine may command when a glide is started from a given height. This can be seen fairly easily from the accompanying diagram; a few figures have been introduced which may make things a bit clearer. In general terms— If Gliding angle = 1 in r. Wind velocity » ± x m.p.h. Ground speed (in calm air) = k m.p.h. Height = h ft. then the increase [(ii) down wind] or decrease [(iii) head to wind] in the gliding range of an aeroplane hr x x AC represents the gliding path of an aeroplane (in still air), which in this case is taken as / in 4. At this angle the air speed of the machine is 4$ m.p..h. AEX AEi represent the velocity of the wind (IJ m.p.h., in this case, and which is supposed to be a steady wind) in the two directions shown—for the sake of comparison the resultant paths of the aeroplane AD and AF are shown on the same diagram. BC, BD, and Misrepre sent the ground speeds of the machine (i) in still air, (ii) when gliding down wind, and when (iii) gliding into the wind. [In order to put this in language somewhat pertaining to flying, this matter is set out at some length, and, needless to say, the conclusion is not arrived at by the shortest route.] tan a. = '25, i.e., a. = 140. BC = ^4Ccos a = 45 x -97 = 43*65. I.e., in still air machine's ground speed is 43*65 m.p.h. D 2
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