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Aviation History
1912
1912 - 0160.PDF
importance in the design of any machine, and the power required must be reduced to a minimum for the most economical machine. We obtain loading by dividing weight of model by area of planes, and power by dividing weight of elastic by duration of flight. There is another formula which I have seen recently, viz. :— „„. . weight of machine x distance Efficiency = . • , .-—-. —:• * weight of elastic This introduces the force required to propel the model, together with weight propelled, and gives the highest efficiency for the greatest weight and least driving force, whereas the first formula gives the test value for greatest loading and least power. Another point in favour of the first formula is that measurements are scientific and do not suffer by local or accidental conditions, whilst the second may be increased or decreased by several conditions out ot the competitor's control. The machine flying against the wind is penalised, while one flying with the wind obtains false honours. A sudden gust may alter the direction and thus decrease the efficiency by reducing the distance (measured in a straight line). Swerving will, in the same manner, detract from the result; but should this be thus counted as lack of efficiency ? I think not, because direction would be under the perfect control of the pilot in a full-size machine. I should be glad of criticism or advice in this matter. STANLEY A. SEARS (Hon. Sec. Worcester M.Ae.C). Victoria Institute, Worcester. The "Gnat" Model. U49SJ To the description of my "Gnat" Tractor screw model in your issue of December 30th, and the remarks on same made by Mr. V. E. Johnson, may I be permitted to make the following reply through the agency of your correspondence columns. In the first place, in all my experiments with either single or twin screw tractor type models, the models, when not fitted with a fin .have always given the same results, despite the fact that they will glide well whether fitted with a fin or not. I will do my best to •describe* this fiction. When wound up and released the model travels about five yards quite nicely, then suddenly starts to go upward, turn a very small circle and dive downwards, nose first, without the slightest attempt to regain the horizontal, despite all kinds of stabilising angles on both main plane and tail. Of course, I do not go so far as to say that this action will apply to any model of this type, I merely state what has happened to my models, notwithstanding the fact that when making a twin tractor I am always most careful to have exactly the same weight of rubber to each screw, giving each the same number of turns, and as I always use carved wood screws the pitch is the same in each screw, so that the action should be exactly balanced ; yet with all these precautions I have not succeeded in obtaining a flight until a fin has been added, even if it be only of the most primitive description. For example, When making my first twin-tractor I took it for granted that I should not need a fin, owing to the action being balanced I therefore did not fit one. I wound this model up and released it, and to my very great sur prise found this same action as applied to the single screw machines. Again testing this thoroughly I decided to put on a fin of some sort, and having nothing more Suitable than a thin postcard I fitted this underneath the tail plane, and stiffened the front edge with a piece •of 20 s.w.g. soft iron wire. After adding this very primitive fin, the very first attempt at flight resulted in a flight of about 50 yards. Can Mr. Johnson explain this? Now, supposing that we were to convert this single screw into a twin, as proposed by Mr. Johnson, I have very great doubts as to " the result being that the length of flight would be considerably increased." I am afraid it will take time and a lot more co-operative experiment before we find out what really happens to this type of model and the cure for it; up to the present I have not yet succeeded in getting more than 50 yards with a twin-screw tractor monoplane, and I have certainly not touched anything unreasonable, in my designs, not having tried anything that is not reasonable and generally accepted practice, and I am .quite sure that the screws have not been at fault. I have a model (constructed since sending the description of my No, 8 model to you), 30 ins. overall length, 22 in. span, 6 in. diameter, 12 in. pitch, tractor screw, weight exactly 3 ozs. Number of turns obtainable 500 (length of rubber drive is only 20 ins.) This model has repeatedly flown from 120 to 130 yards. Now for an analysis. Tractor, 12 in. pitch; highest number of turns 500. The greatest distance this model could fly is obviously 500 ft. Now, the model flies 120 to 130 yards, or 360 to 390 ft., meaning a loss for slip of propellers and resistance of model of only 110 to 140 ft., 75 per cent, efficiency, which I think is quite on a par with the full- sized machine. I would like to say that only 3 yards 12 in. of fV -strip rubber was used to take this 3-oz. model its 130 yards. I think this is as good as any elevator leading and carved propeller com bination can do ; my reason for stipulating a carved propeller is because you cannot be absolutely certain what is the pitch of a bent wood or makeshift propeller, owing to the huge camber given to it in winding. A great advantage that the twin propeller elevator leading model has over the single-screw machine of either type, is the enormous pitch possible to put on the propellers with impunity, sometimes reaching as much as 34 in. pitch on a 2 ft. 9 in. frame, while to even approach this high pitch would be useless without an enormous span on a single screw machine. Finally, I will mention that the greatest distance accomplished with the No. 8 model described in your issue of December 30th was 100 yards not 150. As to speed, this was estimated by myself to be about 18-20 m.p.h. The run taken before rising was about four feet against a fairly strong wind off the grass on Blackheath ; I do not think the model would rise in a calm as the wheels are too far in front of the e.g. Brandon Street, S.E. J. H. DOLHTTLE. ® ® ® ® " The Aeroplane in War." SUCH is the title of a new book in which Mr. Claude Grahame- White and Mr. Harry Harper have collaborated, and as may be gathered deals with the use of Military aeroplanes. It will shortly be published by Mr. T. Werner Lawrie. ® ® ® ® IMPORTS AND EXPORTS, 19H-12. AEROPLANES, airships, balloons and parts thereof (not shown separately before 1910):— Imports. Exports. Re-Exportation, 1911. 1912. 1911. 1912. 1911. 1912. £ £ £ £ £ £ January... 1,196 <5l9 1,088 2,412 Nil Nil The Index to Vol. Ill of FLIGHT (1911) is now ready. Price 3d. (post free 4d.) of the Publishers, 44, St. Martin's Lane, W.C. Aeronautical Patents Published. Applied ror In 1011. Published February 15th, 1912. 2,194. J. W. BUCK. Flying machines. 4,165. G. MEES. Regulating speed and altitude of flying machines with gyro- scopically-acting stabilising propellers. 5,070. G. MEES. Differential-control of twin propellers. 18,311. M. REYMOND. Aerial propelling devices. I 9>354- t\ JAMIESON. Propeller for driving aerial torpedoes. 23,516. L. B. HOLLAND. Aeroplanes. 27,160. R. J. ISAACSON. Mounting aerial propellers. PRINCIPAL CONTENTS. ——f PAGB Editorial Comment ... ..,- ... ... 138 Military Aeroplanes and Vanity Fair. Tiie Paulhan-'I'atin Aero Torpedo (with Scale Drawings) 130 Impressions at the Paris Aero Show. By Dr. E. Valentin 142 Hydro-Aeroplanes-at Nice .. ^ 143 Discussion on Soaring Flight at the Aeronautical Society 144 Royal Aero Club Notes 146 Air Eddies. By " Oiseau Bleu " , 148 From the British Flying Grounds 150 Foreign Aviation News 152 Models. Conducted by V. E. Johnson, M.A 154 The Kite and Model Aeroplane Association 5 Progress of Flight about the Country 15 Correspondence 158 FLIGHT. 44, ST. MARTIN'S LANE, LONDON, W.C. Telegraphic address: Truditur, London. Telephone: 1828 Gerrard. SUBSCRIPTION RATES. FLIGHT will be forwarded, post free, to any part of the world at the following rates:— UNITED KINGDOM. ABROAD. s. d. s. a. 3 Months, Post Free ... 1 8 3 Months, Post Free... 2 9 6 „ ,, .-33 ° » .1 ••• 5 6 12 „ „ ... 6 6 12 „ „ ... 11 o Cheques and Post Office Orders should be made payable to the Proprietors of FLIGHT, 44, St. Martin's Lane, W.C., and crossed London County and Westminster Bank, otherwise no responsibility will be accepted. ICO
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