Articoli correlati a Lessons & practical notes on steam
Sinossi
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1867 Excerpt: ...it receives the entire thrust of the shaft before the indication of the scale'is noted. Did the propeller and steam piston travel through the same distance in any given time, and were all the power applied to the piston transmitted to the water through the propeller, the total pressure upon the steam piston and the thrust of the propeller would be identical, but since such is never the case, we ascertain the theoretical thrust, thus: Total effective pressure on piston in lbs. x 2 length of stroke in ft. x No. of revols. per min. Pitch of propeller in feet x number of revolutions per minute. = Theoretical thrust in lbs. The difference between this and the actual thrust, shows the amount lost in friction of engines, propeller, and load, overcoming resistance to edge of propeller blades, working pumps, etc The loss from slip is independent of this. Strain upon a Screw Propeller-blade. We can best illustrate this by an example. Given, circumference of centre of pressure of a 3 bladed propeller, 30.9 feet; distance from hub to centre pressure 41 inches; pitch 22.5 feet; thrust 12T00 pounds: required, the strain upon each blade at the hub. SOLUTION. Let F G H be the development of the helix on a plane, draw B D at right angles to F H, and A E at right angles to G H. Trigonometri cally, we ascertain the angles at A and D to be each = 37 9', and at C and B to be each = 52 5', and the lengths of the lines A E, B D, to be relatively as 1.000 to 1.237. Now, inasmuch as the whole thrust can be supposed to be concentrated in the centre of pressure of the blade, and as the 12700 lbs. is in a line with the axis, it follows that, if the line A E represents the direction and amount of this thrust, the line B D, at right angles to the propeller blade at the centre of pressur...
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