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Aviation History
1916
1916 - 0511.PDF
JBNB 15. ^I6- l/UGHf] THE RANGE OF FLIGHT AND RADIUS OF THE EFFECT OF OBLIQUE WINDS ON IN our issue of May 18th, we examined the effect on the speed and radius of action of an aeroplane of a wind blowing in a direction parallel to the line of flight This condition, however, seldom obtains in actual practice for more than a brief period; and generally, the direction of the wind is oblique to the course of the machine. Under these circumstances, the course of an aeroplane relative to [the ground will depend upon the velocity and direc tion of the wind and the speed and direction of the machine relative to the air through -which it is travelling ; and the pilot will turn the nose of the machine into the wind through some angle, the magnitude of which will depend upon the factors mentioned, to compensate for the effect of the wind. This angle will become less as the air speed of the aeroplane increases and as the velocity of the wind decreases, and the more the direction of the wind tends to coincide with the line of flight. A ! .si E V D Hk n c^ > Fig. 1. Ordinarily, before commencing a long-distance flight, a pilot determines his course from the map, and notes the position of some distant recognisable object or objects over which he must pass in travelling towards his destination. He sets the course pointer in the correct position, and, on getting into the air, places the machine on the course previously determined. The effect of a side wind, however, is to blow him off his course, and he therefore" turns the aeroplane into the wind, disregarding the compass entirely until he finds himself heading straight for the distant object which he located on the ground. He then notes the number of degrees through which he has turned the machine—that is, the angle between the lubber point and the course pointer. On passing over the object upon the ground, he momentarily places the aeroplane on the magnetic course and picks, up another landmark directly ahead; and then imme diately turns the machine into the wind through the angle he found necessary before reaching the first object, and finds whether or not the aeroplane is heading for the second objective. It is probable that, should the wind be constant in velocity and direction, a small reduction in the number of degrees can be made ; but by taking a succession of observations of this character on a series of distant points, a mean value is obtained, which, if the machine is turned off its magnetic course by this amount, will bring the aeroplane over its desired destination. When flying at night, in a strange country or in a haze or fog, or over the sea, however, the location of definite objects on the ground is at times impossible ; but given the true course, so long as the velocity and direction of the wind and the air speed of the aeroplane are known, it is possible to ascertain not only the angle between the true course and the axis of the machine, which is all that is necessary in order to fly towards the desired destina tion, but also the ground speed at which the flight is made, and' therefore the time at which the aeroplane should reach the end of its outward journey. The air ACTION OF AIRCRAFT. THE SPEED AND RANGE OF FLIGHT. speed of the aeroplane will be known before starting the flight, and can be checked by means of the air-speed indicator on the journey; while the direction and velocity of the wind can be approximately determined by observing the movements of clouds or other floating objects, if visible, at the height at which the flight s made, or by experience, or by flying up and down the wind. The closer the approximation to the true value, the more accurately can the allowance to be made for the effect of the wind be calculated and the nearer will the calculated ground speed be to the true speed; but it will be seen from Fig. 3 that an error of 10 per cent, in the estimated velocity and of io° in the direction oi the wind only produces a cumulative error of 2^ in tin: cal culated allowance for turning into the wind, and of 5 per cent, in the ground speed, for a wind velocity of 40 miles per hour at an angle of 90" from the true course, and an aeroplane speed of 100 miles per hour; and if any check can be imposed during flight, these values will be reduced accordingly. An error of 2^* in the course would take the pilot only about 4 miles to the right or to the left of his objective at the end of a 100-mile flight. Fi*. 2. Fig. 1 shows diagram, by means of which the direction and ground speed of an aeroplane of known air speed may be detennined graphically for a given velocity and 5" 1
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