US1108875A - Propeller. - Google Patents

Description

J. H. O. ALEXANDER.

PROPELLER.

AMLICATION FILED 00124, 1912.

Patented Sept. 1, 1914.

illillH WITNESSES: //v m/ r02 UNITED STATES PATENT OFFICE JOHN H. C. ALEXANDER, OFOAKLAND,CALIFORI'QIA.

PROPELLER.

Specification of Letters Patent.

Patented Se t-1,1914.

Application filed October 24, 1912. Serial No.v727,569l

To all whom it may concern: I

Be it known that I, JoHNvHL C.- ihLEXANr mm, a subjectof the King ofGreat Britain,

residing at Oakland, in the county of Alameda and State of California, have invented new and useful Improvements in Propellers,

of which the following is a specification.

My invention relates to screw propellers in a general way but-more particularly of the helix form which are employed forvarious purposes, such as, for instance, wlndmills, fans, vessels, flying machines, etc., and cons sts in providing a generalform for constructing the. blades thereof, whereby the sor d by the propeller is, imparted to the fluid or medium in which the propeller works, in such'a way as to produce the usefal result for which the propeller is intended and designed. y

In the construction of propellers it is obvi-i ous that, to secure the results that I have specified above, the form of the blade must hear at all points: such definite relationship to its velocity at such points that the fluid or column in the same plane normal to, the axis of rotation of the propeller; and the fluid or 7 medium acted upon or to'which themotion is imparted must, in order. to fulfil these conditions, leave the propeller in one direction only and with the same velocity throughout its entire body relative to the axis of the propeller.

It must further be evident that, in order to avoid a loss in efiiciency, the portion of the blade which first acts upon the fluid or medium acted upon or to be set in motion by the propeller, or through which the propeller is to pro ress. must be so formed and at such an ang e to a plane normal to its axis as to offer the least practicable resistance to its entrance and produce the least practi cable instantaneous acceleration and that this angle must be so modified from theadvancing edge to the trailing edgefof the blade, as to produce a gradual acceleration o the fluid or medium "acted upon and'that thisfmodifieation' must be such that the efgrefitest possible amount of the energy abarts of the column of In ot or words, there should 'fective pitch of the blade at any circular cross section concentric'with the propeller axis shallequalthe whole pitch of the propeller; divided by the angulai width of the blade at that section. Again, it is evident that if said column is t leave the propeller in one direction-only-anc that this direction 15 to be such as to utilize the power absorbed bythe propeller to the utmost, theform of the blade on any plane'normal to theaxis of revolution ofthe propeller must be s'uchpas to prevent. centrifugal action by the pi-opellay. and both this form and. the form of the blade at all scctionsparallel to the axis of rotationare embodied in my invention and the nature, characteristic features and seq )e of same will be readily understood from t e drawin herewithand forming a pa-rt l'ie rveiof. I iave sought to secure the greatest possible clearness in sliowin gmy meaning and intention by illustrating the methods of production of the actual form of my invention-as though it had no volume, 2'. e, no ac tual thickness of material, exceptingtwhere,

for the sake of clearness. I have indicated an actual hub des'ign'ated N. Since the'dynamic efliciency of the propeller is not dependent upon, nor is my invention concerned with, any other feature than the form thereof, sini'te'also the thickness of the various el mcnts of any propeller would vary with each'variation in size or other conditions to be met with in practice and since the form of the back of the blade in an actual propeller, designed on the lines prescribed by my invention, would be exactly similar to the, form of the front of the blade as I have shownit, ck} ceptmg the variations necessary to permit the inc usion of the material of construction between the two surfaces of the blade and what variation might be necessary to give the edges of the blade the best form for reducing resistance to the medium in which the blade is to operate, all of which variation shpuld, as far as possible, be made in the found the surface of the back of the blade excepting only the necessary filleting or reinforcing, added to therbla de where it joins the hub,'whic,h maybe on either or both sides I In the accompanying one sheetof drawing Figure 1, is a plan viewof" the propeller constructed according to myinvention: 2, is a vertical elevation taken on dotted line 10 yet Figu lgandi Eig.:3,-is

a view showing the increasing pitch curve assumed by the blade at cross sections, towit, 8 to t, u to o, and w to 00.

Referring to-Fig. 1, it will be seen thatthe blade may be formed either by the arc of a circle as indicated by the dotted line and indication of any selected radius r, on the advancing edge of element L or any suitable curve as, for instance, the one used for the I shall hereafter call the normal one in contradistinction to the reverse or backing direction, than any other point between it and the hub of the propeller, i. 6., that there shall be an increase in the angular advance from hub to tip and that whatever form is used, the peripheral-tip of the advancing edge, if produced to the peripheral circle, shall have greater angular advance, in the normal direction of rotation than any other portions of the blade.

The method of producing the form of the blade elements in the propeller, as shown articularl onFig. l, is as follows z-Havmg decide upon the form to be used for the advancing. edge of the blade element, the, itch of the propeller and the angular widt of the blade element, the axial travel of the generatrix in forming the surface of one blade element will be to the pitch of the propeller as the angular width of the blade decided, upon,

is to 360 degrees. Having determined this dimension-it is to be divided into any convenient number of parts, the only consideration being that there shall be enough such divisions as to produce sufiicient accuracy in the form of the curve of the surface of the blade between the trailing and advancing edges.

The peripheral circle is laid out to any scale and element K is produced by dividing an arc of the peripheral circle equal in length to the angular width of the blade element into as many parts as has been as above mentioned, to accurately produce the. curve in the blade element between the trailing and advancing the number so taken edges. In this instance, is eight.

The divisions are not equal but are a series in geometrical progression starting at the trailing edge of the blade element, so as to Oopioa of this patent may be obtained for five cents each, by

produce an increasing axial pitch from the advancing to the trailingedge of the blade; thus, (Ii-J) will be the first term and h-i the last term of the series, and the common multiplier used will be such as to produce the best curve which experience dictates and will vary with the medium to be acted upon by the propeller. The points, a, b, c, d, e, f, g, h, and z having been located on the peripheral circle are now joined to the center of the peripheral circle by the lines and angle or angles or by the arc or curve selected as the form of the advancing edge of the blade element, as shown, and the plan of the blade element viewed parallel to the axis of the propeller is now complete. iinv section can now be produced by the usual method of projection, as shown on Figs. 2 and 3. The lines 1, 2, 3,4, 5, 6, 7, 8 and 9, on Fig. 2, being equidistant parallel lines separated bv such intervals that the total distance between lines 1 and 9 to the scale used in,the figure bears the same ratio to the total pitch of the propeller to be designer, to the same scale, from the propeller form as the angular width of the blade element bears to 360 degrees, and is equal to the axial travel of the generatrix to the scale used, in forming one surface of one blade element.

. After the propeller is completed as above described, the edges may be rounded off .or otherwise shaped to present any desired outline, without affecting the efficiency of the blade form, except in so far as it decreases the blade area.

It is to be understood that my use of the word blade does not limit my invention to propellers having one blade, but simply refers to one of. any number of blades which may be used and which will. all be similar in all respects to the blade described.

Believing I have produced novel and useful improvements in this class of inventions, and having thus described the same to be understood and practised by those skilled. in the artto which the same appertains. what I claim is- An impeller having one or more blades, each blade having the form described by a generatrix forming part of a logarithmic spiral diverging from the axis to the periphery of the blade and entirely in advance of the radius which moves ina plane normal to the axis and sweeping the blade, and describing a helix of increasing axial pitch.

In testimony that I claim the foregoing I have hereto set my hand this 19th day of October, 1912.

JOHN H. C. ALEXANDER. Witnesses SHERIDAN FORBES, EMILY WiinsR.

addressing the Commissioner of intents,

Washington, D. G."

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