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Aviation History
1911
1911 - 0489.PDF
JUNE 3, 1911. The freedom from vibration or " flutter" of both devices was very remarkable, due to the fact that the centrifugal force set up in the Substance of the vanes followed the lines of iorce of the discharging currents of air, and consequently was exactly opposed to the reaction thrusts. In the screw-propeller the lines of centrifugal force acting upon the blades are at right-angles to the air currents. One important fact ascertained from the experiments with the Vortex propeller was that the currents discharged from the Vortex not only leave at a tangent to the circle of rotation, but always take a course at right angles to the outer edges of the vanes. The dis charged currents, therefore, form a truncated cone, the angle of which is determined by the angle of the inverted cone formed by the revolving vanes. The most efficient angle for the purpose for which the propeller will be used is a cone of 90°, producing a truncated cone of similar angle for the discharging currents. The reactions against the latter thus give a thrust at an angle of 45" with the axis of rotation. As the vane system is symmetrical the thrusts of the reaction are also symmetrical, and the rectangular components of such thrusts may be expressed as follows, where N represents the number of vanes, and P the thrust on each:— N. P. cos 0 = the net resultant of the reaction thrusts along the axis of the shaft, which is relied upon for propulsion. N. P. sin 0 — a multitude of couples giving a turning moment in opposite direction to the motion of the shaft itself. The resultant of I/jjCHT] the turning moments acting upon the shafts of the two Vortex pro pellers shown in Fig. 17, when revolving in opposite directions, would apparently be a turning moment tending to rotate the body of the machine in the vertical plane about a horizontal axis some distance above such body. This moment would be neutralised by the formation of another and opposite turning moment due to the position of the centre of gravity of the machine being below that of the metacentre. It is obvious that, if each Vortex propeller be regarded as an isolated unit, without reference to the force of gravity, the value of the cos 0 resultant will not be affected by any inclination of the axis in either the vertical or the horizontal plane, and that when applied in opposition to gravity its maximum value will be when the axis is vertical. But in the application to a flying-machine of two such Vortex propellers revolving in opposite directions, the position of maximum efficiency will be that where the axes of the two propellers are inclined upwards at 45°, as shown in Fig. 17, where the body of the machine is represented in section by a circle. Like the wing of a fly, the efficiency of the Vortex propeller increases with the angular velocity of the vanes. Owing to the small size of the fly's wing a high speed of rotation is necessary to obtain the required angular velocity. The much greater length of the vanes in the case of a full-sized Vortex propeller would, it is computed, render unnecessary a higher speed than 300 or 400 revs, per iniii. <3 ® Lieut. Menard's Tour of France—Passenger Record Beaten. AFTER being delayed for some days by bad weather, Lieut. Menard was able to commence his long projected 3,000 kilom. tour around France on the 25th ult. Accompanied by Lieut. Do Hu, he started on his Henry Farman from Bouy at five minutes to three, and at a quarter to six, after having covered 238 kiloms. in 2 hrs. 50 mins., he landed at Chartres at a quarter to six in order to take on board more petrol. At a quarter past seven Vendome was reached, and a landing was decided upon in order to inspect the motor, which was not working at all well. Two hours and a quarter were, as a matter of fact, spent in making adjustments, and it was not till half-past nine that the aviators were in the air again. Chatellerault was passed about midday, and at a quarter past twelve a safe landing was made at Lacueit, close by Poitiers. The journey was a record one, and the last portion beat the world's records for a flight with passenger. The total distance covered during the morning was 600 kiloms. In consequence of some repairs being necessary, the journey was not resumed until Saturday last, when the two aerial voyagers, after fitting a new motor to the machine, left Poitiers for Rocheforte-sur- Mer, which was safely reached after about an hour and a half's flying. Lieut. Menard and his companion were to have continued their journey on Wednesday to Pau. America and the Gordon-Bennett Cup. IT is now practically certain that Weymann will be one of the U.S.A. representatives in the competition for the Gordon-Bennett Cup, and he will use a Nieuport monoplane. Another likely starter is Earle Overton, who has been making some good flights in America on a 70-h.p. Gnome-Bleriot. The name of Mr. J. V. Martin, who until recently was at Hendon, has also been mentioned, while the American Aero Club is asking American citizens at present in Europe studying aviation to communicate with them, with a view to being included in the team. ROUND FRANCE BY MILITARY AEROPLANE.—Lieut. Menard and his passenger, Lieut. Do Hu, who, on a military Henry Farman, is making a tour round France. On his first day's flight he easily beat the world s record for passenger-carrying across country. 491
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