The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

408 frictionless gear of the screw type for an exhaust-steam turbine of 300. B. H. P. running at 3,000 revolutions per minute; through this gear the power of the turbine is transmitted to the main propeller shaft driven by the reciprocating engine at a speed of 75 revolutions per minute. Such a high speed reduction is possible in this case, owing to the fact that the absence of friction between the work- ing parts allows such high circum- ferential 'velocities as would be quite unpracticable with mechanical gear- ing; besides, apart from the bearings, there is no' need for lubrication, and this is a point not to be depised. Un- like an electric motor, the revolving parts of the magnetic gear carry no winding whatever, so that the empty slots and helical grooves of both wheel and worm provide for a per- fect cooling. The three main parts of the gear are: The field magnet M, the laminated worm W, the wheel Vv. The Field Magnet. The field magnet, made of cast steel of high magnetic permeability, is of thé Manchester type; its top pole-piece is laminated in order to prevent losses and heating from hy- steresis and Foucault currents. The coils are wound with high conduct- ivity copper wire properly insulated. The worm is made up of iron stamp- ings fixed concentrically on two cast iron spiders, in exactly the same way as the armature core of a motor or dynamo. One end of the worm shaft is coupled to the turbine. The end- thrust is either entirely or partially balanced by that of the turbine. A thrust-bearing is shown at the other end of the shaft to take the unbal- anced thrust. The wheel, being sub- jected to a side-thrust due to the angularity of the teeth, partially re- lieves the thrust-blocks of the pro- peller shaft. The. wheel V has a hollow rim made up of sprockets of soft iron coarsely laminated; these sprockets have the same angle, width and pitch as the threads of the worm opposite which they move with a clearance of about %4 in. This wheel is keyed on the propeller shaft driven by the reciprocating engine at 75 rev- olutions per minute. To clearly un- derstand how the tangential pull on the rim of the wheel is obtained by means of apparently perpendicular lines of force it must be pointed out that the latter are not actually normal to the circumference of the wheel, but owing to difference in the degree of saturation of the iron sprockets due to a slight advance of the worm threads TAe MARINE REVIEW under load the lines of force cross the air gap at an angle, dragging the wheel in the same way as the armature of an electric motor is pulled back into the field when shifted along its center line. in the Magnetic Gear and Speed-Reduction. Losses The transmission losses are, the electrical energy necessary for excit- ing the magnetic field and the hy- steresis and Foucault-currents in the iron of the worm and wheel. Field Excitation. From experiments I have made, I found that a magnetic density of 15,- 000 lines per square centimeter are required to give a tangential force Gi 22 lb. per sq. in,-.of: iron "face: With. a total air-gap of one centi- meter, a number of ampere-turns equal to 800 X 15 = 12,000 is required for producing the necessary mag- neto-motive force; as there are two parallel magnetic circuits (wound in series) it will really be 24000 am- pere-turns, to which we must add 6,000 ampere-turns to overcome the resistance of the iron circuit, and this brings the total to 30,000 ampere turns. Let us now assume that the pressure of the electric supply is 120 volts, that the wire with which the coils are wound has a sectional area of 0.012 sq. in., to which corresponds an ohmic resistance of 0.2 ohms per 1,000 yd., and that we allow a cur- rent density of 1,000 amperes per sq. in., say 10 amperes for the section of our wire; then, 3,000 turns of such wire will be necessary to give the 30,- 000 ampere turns required. The length of each turn of wire being 2 yd., the total length of the electric circuit will be 6,000 yd., whose total resistance (at 2 ohms per 1,000 yd.) is 12 ohms. The. formula R = | = E, in which R is the resistance of the circuit, I the intensity of the cur- rent, and E, the electro-motive force, is yerined; 12 ohms X< 10 amperes -- 120 volts. The total electrical energy corresponding to these figures is: 10 amperes: X 120 volts = 1.200 watts. which is less than 1 per cent of the total power transmitted (300 H. P.). Loss Through Hysteresis. and Fou- cault Currents. Owing to the laminated state of the worm, and also the sprockets of the wheel, the loss through eddy- currents and hysteresis is very low and always less than 4 per cent of the total power, which, added to the 1 per cent of the field excitation, will October, 1910 give a total transmission loss of 5, per cent. The total weight 'of the 300 B. H. 'P. gear for reducing the speed from 3,000 to. 75 revolutions per minute is 11 tons, of which 2 tons for the worm with its shaft and bearings, 4 tons for the wheel and 5 tons of the field magnet. Comparing these fig- ures to electrical transformation, it would 'be in the latter case: One 250 K W dynamo at 3,000 R. P. M., 3 tons (approximately); one 300 H. P. motor at 75 R. P. M., 27 tons (ap- proximately); total 30 tons. The magnetic gear can run in both direc; tions if the turbine is reversible, if such is not the case, the excitation is cut off by means of a switch, and the reciprocating engine gives alone the reverse motion without the assistance of the turbine. Aerial Navigation Editor Marine Review :--It would not be at all surprising if among the clouds should soon pass beyond the experimental stage and as now being freely prophesied by many that such aerial vehicles will become mighty engines of destruction in times of war, being a method that any na- tion may adopt and put into opera- tion upon slight provocation, invad- ing any country by day or night, dropping most terrible explosives in- to great cities with the most destruct- ive effects. One can scarcely imagine any limit to the train of evils that would follow such a system of aveng- ing a real or fancied wrong and in- augurating a system of destruction for outside the bounds of so-called "civilized warfare." In view of the rapid development in the science of traveling through space at a desired height with its threatening possibil- ities and even probabilities, such con- ditions may speedily bring about an alliance between the principal na- tions of the earth declaring jor ar- bitration of all international ques- 'tions, clothing itself with ample pow- er to enforce the declaration, and thus turn this threatening engine of destruction into a channel that will entirely reverse its operation and ef- fect so as to work out the problem of universal peace between the nations of the earth through sane and civil- ized arbitration. James STONE. Cleveland, Oct. 10. The steamer Felix Carbray, for- merly the John C. Gault, owned by F. B. Chesborough, Emerson, Mich., will go to the coast this fall. navigation © . Sa a aN ah i Sg a a ah ee Ea ge a ai ase ia ale