MESSRS. WHITELAW AND STIRRAT'S HYDRAULIC ROTARY ENGINES LATEST IMPROVEMENTS. We described about two years ago (see Mech. Mag. No. 903,) the hydraulic rotary engine originally patented by Mr. James Whitelaw, of Glasgow, and which has since obtained so much celebrity in the mechanical world; and we have now to lay before our readers a description of some important improvements which have been since invented and patented by the same gentleman in conjunction with Mr. James Stirrat of Paisley. Figs. 1 and 2 of the accompanying engravings represent an elevation and plan of the original engine in its present most improved state. The engine, it will be recollected, is worked by the pressure and reaction of a column of water. The main pipe a a, conducts the water which drives the machine into its arms from a reservoir or head on a higher level than the arms; b b b b are the arms which are hollow; the water passes into them at the centre part c, and escapes out at the jet pipes d d. The motion of the arms is communicated to e e, the main, or driving shaft of the machine, and by means of a wheel, pinion or pully, fixed on the shaft e e, its rotary motion may be communicated to any machinery which the water mill may be intended to work; ffff is a large bracket, which is fixed to the wall, or building, gg; this bracket supports the shaft e e. The tail race is marked h h. As the arms have a rotary motion, and the pipe a a is fixed to the building under it, there must be means provided to prevent the escape of water at the place where the main pipe meets the arms. A contrivance suitable for this purpose is shown in fig. 1. It consists of a ring i i, round the underside of c, the central opening or aperture leading into the arms, and of a part k k, turned cylindrical at the place where it fits into the bored part on the top of the pipe a a. The part k k has a groove turned round its outside, near to its bottom end. The groove is to be wrapped full of soft twine, in order to prevent the escape of water betwixt the pipe and the cylindrical part of k k. There is a flanch outside of the part k k, and rope yarn is wrapped round in the space betwixt this flanch and the top of the main pipe, for the purpose of keeping the top of k k in contact with the bottom of the "Let 1, 4, 9, (fig. 3) be a circle of the same diameter as that described by the centre of the jet pipes, and let this circle be divided into, say twelve equal parts, in the points 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and let the radius 1 w be also divided into twelve equal parts in the points a ce gik moqs and u. From each division on the circle draw a straight line to the centre w, and from the division at a, on the radius, draw from the centre w a portion of a circle till it cuts the radius 2 w in the point b. From the same centre w draw a portion of a circle through the second point c, till it cuts the radius 3 w in the point d. In this way continue to draw concentric arcs from the divisions on the radius 1 w, making each concentric arc to terminate in that radius immediately following the radius in which the arc formerly drawn was made to terminate. The points of intersection 1 b, d, f, h, j, l, n, p, r, t, u, and w, thus obtained, will be points in the middle of the breadth of the and a curved line traced through these points will be the curve of the middle of the breadth of the arm. After the curved line 1 d, l, r, w, is formed, any number of points in the curve lines, which form the sides of the arm, will be obtained in the following way. With was a centre draw such a number of concentric circular arcs passing through the curve line 1 d, l, r, w, as may give a sufficient number of the required points. Then, with a pair of compasses take a distance equal to four times the width of the outer end of the jet pipe, and set off that distance upon each such concentric arc, twice measuring, once upon each side of the curve 1 d, l, r, w, from the point of intersection of the arc and that curve. oi o The p marked off on one side of the curve line 1 d, l, r, w, are points in one side of the arm, and the points similarly marked off on the other side of that curve are points in the curve which form the other side of the arm; arm, on the other side of that curve, a distance equal to four times the width of the jet pipe, and in the same way the breadth of the arm at any other point will be found. If the arm be drawn in the manner now described, its depth, as also that of its jet piece, will be uniform throughout. In fig. 1, the depth of the arms and jet pieces are thus adjusted. The width of each jet pipe being, as before mentioned, onefourth of the length of the chord subtending the circular arcs which determine the width of the arm, if one-eighth of this chord be set off on each side of the circle 1, 4, 9, and a portion of a circle having w for its centre, be drawn from the outer end of the arm through each point so set off, and towards 12, it will coincide with the outer and inner sides of the jet pipe. In practice, the corners 13 and 14 (fig. 3) should be rounded off in the manner shown in fig. 2. "In cases where the machine moves so fast as not to allow time for the water leaving it to fall a distance equal to the depth of the arm, before the next arm comes up, the water which leaves the one arm will be struck by the other, and thus the machine will be in some measure retarded. When the machine moves at a speed slower than that of the water, this defect may, in most cases, be remedied by simply turning the outer extremity of the jet pipes a little outwards, in order that the water which leaves the one arm may be thrown outside the other. The width of the jet pipes in relation to that of the arms will be regulated by the velocity of the machine in relation to that of the water which works it. Thus, if the machine mes at the same speed as the water, the width of the outer end of each jet piece should be about one-third of the length of the chord subtending the arcs, which determine the breadth of the arm. The machine which we have just described should move at a speed about one-third slower than that of the water, and if the machine moves at about three-fourths of the speed of the water, the chord which subtends the arcs which determine the breadth of the arm should be two and a half times longer than the width of the jet pipe." The advantage of the present machine over that first invented by Mr. Whitelaw consists in its preventing more effectually the water from being carried round with the arms. Of this the patentees give the following very clear and satisfactory explanation: "Suppose, for the sake of illustration, that the centre of the jet-pipes move at a speed as great as that of the water issuing from them. In this case, the width of each jet-pipe will be about one-sixth of the width of the arm, its width being marked off on circular arcs, in the manner before mentioned. An arm of the kind represented in fig. 3, if its dimensions be as last given, will contain about as much water as will fill a straight arm running from the centre out to the jet-pipe, if the area of the cross sec tion of the straight arm be uniform throughout its length, and this area be six times larger than that of the jet-pipe. A straight arm having its cross sectional area six times larger than its jet-pipe will, in one revolu tion, expend about as much water as will fill the arm, the motion of the water through the arm being six times slower than its speed through the jet-pipe, and the radius of a circle being to its circumference nearly as one to six, the length of the arm being to the circumference described by its jet-pipe in the same proportion. But the capacity of the curved arm being the same as that of the straight arm, as much water as will fill the former will be the quantity required during one revolution of the machine. From this it is clear, that the water which is leaving the centre, w, at any instant when the arm is in the position shown in fig. 3, will, after the arm has made one revolution, be out at 1, the beginning of the jet-pipe. The cross sectional areas of the arm are so adapted to the curvature of the line 1 drw, that whenever any point, as p, in the arm, arrives at the point o, in the radius w 1, the water which left the centre when the arm was in the position shown in the figure, will also have arrived at or near the point o, and thus the water will flow from the centre of the machine out to the jet-piece in a straight line, or nearly so, when the machine is in motion." When a jet-pipe moves at a speed slower than that of the water issuing from it, the arm may have a greater capacity than it would have if the motion of the jet-pipe were as great as that of the water without carrying the water round with it; for when the speed of the arm is reduced, the speed of the water flowing through it may also be diminished. The kind of arm shown in figs. 1, 2, and 3 has an uniform depth throughout its length, and its cross section at any point is of a rectangular form; but it will be evident that each cross section of an arm and jet-pipe may be of a square, circular, or any other suitable form, provided the square, circular, or other form of arm has its cross sectional areas at the corresponding distances from the centre w, the same as the cross sectional areas of the kind of arm shown in figs. 1, 2, and 3. For working in tail water, the patentees recommend such a modification of the machine, figs. 1 and 2, as is represented in figs. 4 and 5. Here two circular plates are set apart from each other, at a distance equal to the depth of the arms, with curved division pieces to form the sides of the arms, and jet-pieces fixed betwixt the plates; the main shaft is fastened to the centre of the uppermost plate, and the opening for the water is in the centre of the plate which is undermost. If the arms or water spaces are beyond a certain width, the inner ends of the divisions placed betwixt the plates, will terminate in a sharp end before they reach the central opening. Betwixt the inner ends of the division pieces and the central opening, the top and bottom plates should be formed, in such a manner as to allow the water to flow from this opening out to the inner ends of the arms, at every point of its passage, with the same, or nearly the same degree of speed. This is managed by diminishing, from the central opening out to the inner end of the arms, the depth of the space which is betwixt the top and bottom plates. a a is part of the main shaft; the arms or passages for the water are marked bb; and c is the central opening for the water. Another machine, differing more materially from the first, is represented in figs. 6 and 7. In this machine the main pipe, a a, conducts the water from the reservoir bb; cc is the rotary part of the machine; this part is open at the top end, bb, where the water is admitted, and it has an opening at c c, its bottom end, to allow the water to escape after it has acted on the machine. To the inside of bb, c c, the plates or blades marked d d are fixed. These plates run from near the top of b b, c c, to the opening below, in a spiral direction, as shown in the figures. The main shaft or spindle, e e, is fixed to the blades, and to the part b b, c c, in the manner shown in fig. 7, in order that the motion which will be given to the part b b, c c, by the action of the water on the blades, may be communicated to the shaft e e. The bottom end, or foot, f, of the shaft turns in brasses, in the ordinary way, and its top end has a bearing at g. It will now be clear, that if the water be allowed to rush from the main pipe a a into the part bb, cc, it will, by its force against the blades, set them, and the parts in connexion with them, in motion; but the weight of the water will, during its descent along the spaces marked ʼn h, also act upon the upper inclined surfaces of the blades d d, and assist in keeping up the motion of the machine. Thus, one part of the force which keeps the machine in motion is derived from the momentum given to the water by the pressure of the column of water which is above the under end of the main pipe, and another part of this force is obtained by the weight of the water after it gets into the part b b, c c. The hydraulic engine we have last described is an improvement on the wellknown machine called the "Danaide;" the principal difference in the two machines is, that, in the "Danaide," the plates or blades which the water acts against are straight, and have a vertical position, while, in the new machine, the blades run from near its top end to the opening below, in an angular or spiral direction. ON THE MOTION OF A FALLING ARROW OR DART. BY CAPTAIN J. NORTON. Sir, It has frequently occurred to me, when a school-boy, practising with an arrow or dart of a peculiar form, that the arrow, in descending, after being thrown or shot perpendicularly into the air, instead of coming down with its point foremost, has turned on its side, and come to the ground spinning horizontally, so as to resemble the wheel of a jack. The arrow, which in its ordinary fall would reach the ground in the space of a second, by this rotary motion in a horizontal line occupies full a minute in its descent. I mention this fact in the hope that some of your numerous readers may be so good as to explain the cause, as, in the event of the art of flying ever coming into fashion, a knowledge of the cause of the arrow performing the horizontal motions of a wheel may be of practical use. The arrow I allude to was in the form of a flat spoon, having a notch about its centre, where it was found to balance, inclining towards its point, and was cast by means of a pliable stick, having a string at the end of it; a knot in the string fitted into the notch, and by bending the stick the arrow was discharged. Yours, &c., J. NORTON. MR. ZANDER'S TABLES OF THE SIX STEAMERS PLYING above bridge. Sir, The interesting notice of Mr. Zander's steam expansion and condensing systems in the two last Numbers of your valuable journal is accompanied by two useful comparative tables of the dimensions and performances of sundry steamboats; but in those tables there appears to me to be an error with regard to the area of the total effective paddle-board surface of each vessel, which, should my view be incorrect, I hope will call forth a reply from some of your able correspondents. I will take, for instance, the dimen sions given of the Era's paddles-length of the boards 5 feet, breadth 1 foot; number in each wheel 12; number of paddle boards immersed in the water in both wheels 5. Area of paddle-boards in both wheels, or total effective paddle surface 25 square feet. Now, it is to this statement, that the effective paddle surface is equal to the area of all the floats immersed, that I wish to invite attention. With paddle-wheels of the foregoing dimensions, in order that 24 floats in each wheel may be immersed, the dotted line of the accompanying figure must be a C the water line, cutting the floats cc at one-fourth their breadth, in which case the greatest depth of immersion, a b, would not exceed 1 foot 8 or 9 inches, which, multiplied by the breadth of the wheel (5 feet) gives an area of effective paddle-board surface for each wheel of 84 square feet, or 174 feet for both wheels, instead of 25 feet; for I cannot conceive that the boards immersed and moving behind each other so rapidly exactly in the same plane, increase the area of resisting surface which each presents, but merely maintain a constant action upon that area, as each board rises out of the water in succession. But I very much question whether the mean useful effect extends beyond the area of one paddle board in each wheel (or in this instance, of 5 square feet), for supposing the common paddle-wheel can be beneficially immersed to the depth ab of the diagram, its efficiency would be greater, by the direct action of boards of the same depth at a b, than by the oblique action of those in the position c c. If I am correct, several of the calculations in the tables referred to, would require reconsideration. I am, Sir, your obedient servant, October 27, 1842. |