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Aviation History
1910
1910 - 1052.PDF
The area of the interior hole of theannulus should be greater than the area of the open slots in the disc (in the tracing the areas are approximately i '68 to 73). The disc will tend to come to rest with the slots open, as this is the position of least pressure ; if owing to sudden fall in pressure it should stop with the slots closed it will creep round to the open position as the working pressure is reached. The rotating disc should be quite true, fairly light, and have a high moment of inertia to steady the note, and also prevent it sounding with short puffs of wind, which though slowing the aero plane would make the whistle suggest an increase of speed. It seems to me this might occur when descending in a spiral path, and coming round into the wind. It is of no use relying much on the pitch of the note given ; uuless it is low and so/t, it is generally a wild shriek, the presence or absence of which only can be taken as a sure index. If two warnings are required two sirens giving different notes and sounding at different pressures is probably the safest; they can have a common collecting funnel, but it is not so good. Probably the best arrangement would be one sight and one sound indicator, as the sight indicator can be easily tested with the finger before starting to see that it has not stuck, and would serve therefore as a standby ; this is not so with the sound instrument. If it is desired to make the instrument adjustable the distance piece and the screw-cap can be lengthened, and a sunk scale cover- able by the screw-cap added. The instrument can be tested upon a rotating arm. A 4 ft. arm at 220 r.p.m. =60 m.p.h. W. LANGDON-DAVIES. forward by the spring to such a distance that another port, arranged on another portion of the whistle, is uncovered, thus again allowing the whistle to blow. The device consists of a central brass tube, A, in one end of which [38] Herewith design and description of a speed-alarm. The complete absence of gearing, the compactness of the device, the ease of adjustment to any required speed, and the probable reliability of action, are points advanced in its favour. t. fp •' h\ • A *\ ' zx _-^*-^|^ii«^w'|:'''',,,'l<l ~ r /K \ 1 / H If the sails revolve, the other revolving parts must of necessity work in unison, accurately and smoothly. The sound produced by the contact of the needle and fretted collar will be immensely accentuated by the medium of the megaphone to which the needle is attached. Parts.—A, windmill blades; B, spindle ; C, springs and weights, actuated by centrifugal force; D, cylinder, threaded externally ; E, fretted collar, steel ; K, locking-nut; H, mega phone funnel, metal, carrying a thin metal disc, supporting needle, designed to vibrate freely. Action.—Rotary force causes the weights to fly outwards, draw ing cylinder, D, along spindle, B, until having attained the requisite speed, serrated collar, E, comes into contact with needle. The vibration of the disc supporting needle produces a musical sound of surprising volume. The object of the locking-nut is to adjust the serrated collar for any required velocity. Cambridge. W. J. STALLAN. [39] The accompanying drawing shows a device which, when attached to an aeroplane in such a position that it is exposed to the wind, will warn the aviator whenever his machine may be exceeding the maximum, or be falling below the minimum, of certain pre arranged maximum and minimum wind speeds, the device being so arranged as to emit a high or low note to indicate the maximum and minimum limits respectively. Principle.—An ordinary whistle, if blown into, will only sound if the holes provided for the escape of the imprisoned air be open. In the above device such a whistle is providedwith a funnel-shaped mouth to receive the air, and a disc is so arranged that the pressure of the wind, normal to its surface, will, on reaching a certain pre-determined maximum value, force the disc back against the action of a spring to such a distance that it uncovers the ports arranged on the whistle to permit the imprisoned air to escape, thus allowing the whistle to blow. On the wind pressure dropping below a certain pre-arranged minimum value the disc is forced is fixed the whistle, E, with funnel-shaped orifice, J, and which, at the other end, is soldered to a brass plate, F, for attaching to the aeroplane. The sleeve, B, which is concentric with tube, A, and which slides, over it, is formed of two pieces of brass tubing of equal length, with a flange on one end. These flanges butt together in the centre and are ground to a good fit. They are held together in this manner between the disc, C, and a separate recessed flange, D. The screws do not, however, pass through the flanges formed on the sleeves. The latter are thus free to revolve separately in either direction. The disc, C, is prevented from rotating by the small steel wire, I, which passes through a somewhat larger hole in the disc, and is securely fastened at both ends of the device. The disc, C, together with both portions of sleeve, B, can, therefore, slide along tube, A. This motion is opposed, however, by the compression in the helical spring, G. The tube, A, has two helical slots cut in it, as shown at L and M. The sleeve, B, which slides over tube, A, has two small holes drilled, one in each half, as shown at O and P. From an inspection of the drawing, it will be readily seen that when the wind pressure reaches a value high enough to force the disc, C, back to such a distance that the hole, O, in sleeve, B, comes over the slot, L, in tube, A, a passage is opened up for the escape of the imprisoned air in the tube ; hence the whistle will blow. It will also be seen that the further sleeve, B, is rotated in a clockwise direction, when viewed from the front, the further the disc, C, will have to be forced back by the wind to allow the whistle to blow. A pointer, Q, attached to the sleeve, B, moves over a scale arranged on the front of the disc, C, and graduated in m.p.h. By moving the pointer to different positions on the scale, the whistle may be adjusted to blow off at any desired maximum velocity. From Fig. 3 it will also be noticed that immediately the wind pressure falls so low as to allow the hole, P, in sleeve, B1, to come directly over a part of slot, M, a free passage will again be allowed for the air, and the whistle will again blow. Also the further this sleeve, B', is rotated in an anti-olockwise direction, viewed from the back, the lower the wind pressure will have to drop in order to allow the whistle to blow. Attached to this sleeve is also a pointer, which may be moved over a similar scale as that for the maximum velocity, only situated on the back of the disc. This is to adjust the whistle to blow at any desired minimum velocity. As the opening for the escape of the air at the minimum velocity limit is much further from the whistle itself than the opening when indicating maximum velocity, a much longer column of air is set in vibration. Hence a lower tone results. Victoria, Australia. H. ERNST. 1050
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