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Aviation History
1914
1914 - 0001.PDF
Flight, January 3, 1914. ^ (7- ^\C( First Aero Weekly in the World. Founder and Editor : STANLEY SPOONER. A Journal devoted to the Interests, Practice, and Progress of Aerial Locomotion and Transport. OFFICIAL ORGAN OF THE ROYAL AERO CLUB OF THE UNITED KINGDOM. No. 262. (No. 1, Vol. VI.)] JANUARY 3, 1914. ["Registered at the G.P.0.1 L as a Newspaper. J fWeekly, Price 3d. L Post Free, 3Jd. Editorial Office: 44, ST. MARTIN'S LANE, LONDON, W.C. Telegrams: Truditur, Westrand, London. Telephone: Gerrard 1828. Annual Subscription Rates, Post Free. United Kingdom ... 15s. od. Abroad 20s. ad. CONTENTS. Editorial Comment: A Warning to Pilots Smuggling by Aeroplane The Hendon Aerodrome and its Work Men of Moment in the World of Flight : Pierre Chanteloup A Warning to Pilots. By Harris Booth Paris Aero Salon Royal Aero Club. Official Notices Eddies. By " Will o'the Wisp " From the British Flying Grounds Christmas Flying at Hendon Armchair Reflections. By The Dreamer Aeroplane Types. Wright Model E Aero Engines. By Granville E. Bradshaw British Notes of the Week ... Foreign Aviation News Models. Edited by V. E. Johnson, M.A. Made! Club Diary and Reports »3 '5 17 23 »5 EDITORIAL COMMENT. Elsewhere in this issue, Mr. Harris Booth " A Warning cajjs attention to what is apparently a Pilots " defect in the pitot tube type of air speed indicator which is used on aircraft to determine the speed of the machine relative to the air through which ic is moving, and he attributes the difference of opinion that exists at the present time as to the utility of an air speed indicator, as a safeguard against such accidents as may ultimately be caused through a pilot stalling his machine, to the incorrect reading given by the instrument. For the benefit of our readers who may not be conversant with the construction of the pitot tube type of indicator, it may be observed that it consists of a U tube partly filled with a suitable liquid, one limb of which is in communication with a small orifice facing the air stream, and the other limb with an orifice at right- angles to the direction of the flow of air. In still air, the level of liquid is the same in both limbs, since the atmospheric pressure acts upon each column; but in moving air, while the latter is unaffected by the velocity of the air passing by the orifice, the former is subjected to the pressure caused by the air impinging upon the mouth of the orifice. Thus, the difference in the level of liquid in the two limbs of the U tube is due to the forward velocity of the machine relative to the air; and from the fundamental formula for the flow of air, the head of liquid is proportional to the square of the velocity. There cannot be the slightest doubt concerning the accuracy of the instrument for measuring the speed of the air or of other fluids moving with uniform velocity, and it has been employed for this purpose in experimental and practical work all over the world; and provided that the plane containing the U tube is set at right- angles to the direction of motion and the apparatus is not subjected to a vertical acceleration—either positive or negative—it may be relied upon to give correct readings, even in gusty winds. But, if the forward velocity is accelerated or retarded from any cause, and the plane containing the U tube is in the direction of motion, the small quantity of liquid in the horizontal portion of the U tube will tend to lag behind, or be urged forward, by the accelerating force, thus destroying the accuracy of the instrument. Similar remarks apply should the indicator receive a vertical acceleration, but as Mr. Booth discusses this in his article, it is unnecessary to enter upon the matter in this column. It may be pointed out that the question of lag, due to the viscosity of the liquid employed in the instrument or to other causes, cannot enter into the matter; as apart from the fact that the vibration to which it is subject would overcome any such tendency, the magnitude of the alteration in the height of the column of liquid accompanying changes in velocity at ordinary flying speeds, is altogether too great compared with any lag that there may be. Thus, if the instrument is so graduated that a column of 8 inches represents a speed of ioo miles per hour, at 50 miles per hour the difference in the height of liquid in the two limbs would be 2 inches and at 60 miles per hour it would be 2 '88 inches. The arguments adduced by Mr. Booth in support of his contentions appear to leave little room for doubt as to the accuracy of his conclusions, which may be equally well applied to any form of indicator that is gravity controlled. In view, therefore, of the supreme importance of knowing the actual speed of the machine relative to the air, under many flying conditions, owing to the fatal consequences that may ensue should reliance be placed upon an B 2
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