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Aviation History
1910
1910 - 0234.PDF
^HTJ Propeller Fastening. Provision has been made on the Green engine for the crank-shaft to be fitted either with a propeller or a tractor screw, a double-thrust bearing being the standard fitting on all engines (Fig. n). The propeller is built up on a flanged sleeve that slides over the end of the crank-shaft and is driven by keys. The sleeve is held in place by a nut on the end of the crank-shaft, which forces the opposite extremity of the sleeve hard up against the aforementioned thrust bearing. The inner ball-race against which this sleeve is thrust is itself loose on the shaft, but abuts against a solid collar. MARCH 26, 1910. It carries two rows of balls on opposite sides of a simple thrust collar, and these balls run in ring races that are contained in a screw-capped box forming an extension of the crank-chamber casting. When the crank-shaft is fitted with a propeller the thrust is transmitted direct to the crank-chamber casting by the direct abutment of the propeller sleeve upon the thrust-bearing. When, on the other hand, the crank-shaft is fitted with a tractor screw, the pull is transmitted to the crank-shaft through the nut on its extremity, and is transferred thence to the screw cap on the thrust-box via the collar on the crank-shaft itself. # ® ® ® AN AERODYNAMIC EXAMINATION PAPER. WE have received from Mr. L. Blin Desbleds, lecturer in aeronautical engineering at the Northampton Institute and the Polytechnic, what we believe is the first exami nation paper ever set on aerodynamics. It forms part of the aero-engineering course at the Polytechnic School of Engineering, and by reason of its general interest we reproduce the entire series of questions below :— INSTRUCTIONS. (Only SIX of the following ten questions to be attempted.) 1. Define the term "co-efficient of influence of aspect ratio " of a plane rectangular surface. What, according to Soreau's formula, is the greatest value which that co-efficient may have ? Can that value be attained in practice ? A plane surface, 24 metres span, and of depth 6 metres, moves in still air in a pterygoid aspect at a speed of 50 kilometres per hour at an inclination of 50. Calculate the pressure of the air on the surface. [K = 0*07 and L - 30J.] 2. If the area of the surface, referring to Lilienthal's table, be A square metres, and if it is moving at an inclination of 50 at a speed or v metres per second, calculate the lift and drift of the surface. 3. Explain briefly the " theory of equivalent plane surface" applied to curved surfaces. 4. Show, by means of sketches, how a low position of the centre of gravity of an aeroplane relatively to the centre of air pressure helps to maintain the lateral stability of an aeroplane when it is moving in a straight line, but tends to destroy that stability when the motion is along a curved path. 5. Comment on the following statement: "Of two aeroplanes which differ only in the outline of their sustaining surfaces, the one which has the worse ' sustaining quality ' can be made to move with the greater speed." 6. Show, by means of diagrams, how the longitudinal stability of an aeroplane is affected by the relative positions of the centre of gravity, centre of pressure, and point of propeller thrust (or traction). 7. What is the "dynamical thrust" of a screw-propeller? What, according to Arnoux' experiments, is the relation between the dynamical thrust of a screw-propeller and its stationary thrust ? 8. Explain why an aeroplane naturally falls a little when it takes a turning, and, also, in what way the unequal air-pressure, on an aeroplane's wings when it takes a turning, helps it to take that turning. 9. What, according to the experiments of the Aerodynamical Institute of Kutchino, is the direction of the pressure of the air on a plane surface moving at a small angle of inclination ? Prove that, if the air pressure is assumed to be perpendicular to a plane surface moving at a small angle of inclination, no serious error is introduced into the expression giving the lift of the surface ; but that the expression for the drift may be seriously affected by the assumption. 10. Explain the following terms which have been used by Drzewiecki in his theory of aerial screw-propellers: "modulus," "normal blade," "specific width," and " reduction ratio." A motor, of h.p. P, is driving a propeller at the rate of N revo lutions per minute ; if the pitch of the propeiler is p feet and its slip per cent, is s, find an expression for the efficiency of the pro peller, assuming that the resistance to the motion of the propelled apparatus is fi lbs. <S> <# & &lt;& PROGRESS OF FLIGHT ABOUT THE COUNTRY. (NOTE.—Addresses, temporary or permanent, follow in each case the names of the clubs, where communications of our readers can be addressed direct to the Secretary. We would ask Club Secretaries in future to see that the notes regarding their Clubs reach the Editor of FLIGHT, 44, St. Martin's Lane, London, W.C., by 12 noon on Wednesday at latest.) Birmingham Aero Club (165, HAMPTON STREET). AN arrangement has been made between this club and the members of the BoEanical Gardens, Edgbaston, to hold an exhi bition of model aeroplanes, light petrol motors, &c, on Saturday, May 21st. There will be two petrol-driven model biplanes giving short flights. In addition, there will be flights of the ordinary elastic-driven models. Entries are invited from all parts. Prizes in cash will be given to the value of ^30. Special prizes are offered for original designs. Coventry Aeronautical Society (18 and 19, HERTFORD STREET). ON Thursday March 10th, a second most interesting lecture was delivered bifore this Society by Mr. A. P. Thurston, B.Sc, on the subject of "Screw Propellers." The lecture was profusely illustrated with lantern slides of Sir Hiram Maxim's new machine, with which Mr. Thurston is interested, and also with a number of models of propellers which had been used for experimental purposes. In connection with the above club, a lecture by Mr. F. W. Lanchester has been arranged for Thursday, April 14th, at the Corn Exchange, Smithford Street, Coventry, the subject of which will be announced later. Dundee Aero Club (3, BALTIC STREET, DUNDEE). THE club is making excellent progress, despite the lack of interest in aerial locom >tion in this district. A meeting was held in Lamb's Hotel, Dundee, on Wednesday, 16th inst., and a competition was arranged for models, to take place on 16th ApriL The chairman of the meeting, Mr. J. H. Stewart, kindly offered a prize to be competed for. It was decided that we should see about a suitable place at once. Recent trials with models proved very satisfactory. One model, weighing 17 ozs., flew straight for 70 yards, and another of the same dimensions, but weighing only 12 ozs., flew 200 yards. We use plenty of elastic, with large propellers. Kite and Model Aeroplane Assoc. (27, VICTORY RD., WIMBLEDON) THE Council of this Association wish to call the attention of all model makers to the fact that a number of flying meetings will be held during the summer, in addition to the kite and gliding contests. A special feature will be an open competition for model machines on new and scientific lines, as the rules will be drawn up on quite different lines to those generally followed. The conditions will be finally settled at the next meeting, and will be sent out to members and those interested during the first or second week in April. Gentlemen wishing to join should send in their names at once to the Hon. Sec. The subscription is 5/. per annum, and 2s. 6d. per annum for members under 17 years of age. The Council also appeal to those interested to subscribe to the prize fund. Midland Aero Club (GRAND HOTEL, BIRMINGHAM). AT the meeting at headquarters on the 16th inst., Dr. Ratcliffe, F.R.S., was the lecturer, and dealt in a most interesting manner with the evolution of the aeroplane. He pointed out how many people tried to imitate the bird by flapping wings, and in this connection he showed a series of fifty photographs, showing one beat of a fly's wings from start to finish. He went on to show that the soaring flight of birds offered another solution and mentioned the long distances which the albatross can soar without moving its. wings. 232
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