US1850476A - Propeller - Google Patents

Description

March 22, 1932. 1-1, ug 1,850,476

PROPELLER v Fi led May 1, 1931 SSheets-Sheet 2 March 22, 1932. H. M. RllS 1, 4

PROPELLER Filed May 1. 1931 3 Sheets-Sheet v$5 Patented Mar. 22, 1932 A uurrae stares PATENT. orrrca The present invention relates to propellers for ships and air craft and the ob ect of the invention is to provide a propeller so constructed that an even pressure is obtained at the entire pressure side of the propeller wing and that the slip becomes minimized.

The invention will be fully described in connection with the annexed drawings where Fig. l diagrammatically illustrates the construction of a propeller wing as seen from the side thereof.

Fig. 2 illustrates the same in plan view and Fig..- 3 the same as seen from the end. Figs. 4 and 5 illustrate diagrammatically the calculation of the exit angle of the pressure side.

Fi 6 is a view similar to Fig. 1 illustrating a m ed form ofconstruction.

Fig. 7 illustrates a pattern adapted to be used when making a model of the wing, and

Fig. 8 shows a ready propeller with three wings seen from the rear thereof.

According to the present invention the proeller is designed and calculated starting i rom the rear edge of the wings which edges in all cases are perpendicular to the propeller ams.

At first is drawn the propeller axis m-n and a line r-s perpendicular thereto, which latter indicates the rear edge of a propeller wing. The place 0 where these lines intersect becomes the centre of sphericalsurfaces on which the profile of the pressure side of the wing shall be laid. The rear edge of the propeller thus will lie in a section through an imaginary sphere the diameter of which is like the diameter of the propeller.

The diameter 0-1 of the propeller hub is now chosen and the circle portion Z -0 is drawn. Then are, preferably with equal distances therebetween, drawn a number of similar circle portions from the places 27, as shown, 0 always forming the center. The

distance between the circles is chosen at will, but the smaller said distance is the more co rect the shape'of the propeller will become.

The spherical surfaces represented by the circles 1- 7 are then intersected by a series of lines parallel to the line H and indicating 0 sections o-f through the propeller wing.-

The distance between the lines af is chosen at will, but also here the correctness of the wing obtained will be greater the shorter said distance is chosen.

Now there is chosen an exit angle for the tangent to the pressure face at the rear edge of the wing at point 1, and this angle forms the figure from which the entire calculation and construction is derived. Said angle is chosen relatively great for propellers which shall run fast and smaller for propellers running with less turns per time unit.

The corresponding angles for the other spheres 2-7 decrease with the distance from the axis m-n. However, they do not decrease proportionally with said distance. -I

have namely found that said angles should always correspond to the formula tga Jl z where R is the radius of the hub or the distance from the axis to the first sphere and a is the angle chosen at said sphere.

If the angle a is chosen to be 60 the angles, say at the points 3, 5 and 7 then will be 45, 37 40' and 33 10', as indicated in Fig. 4.

After the angles thus having been determined at the rear edgeof the wing for the several spheres are helices laid along the spheres the pitch or angle increasing with increasing distance from the axis mn.

' For sake of simplicity only one of these helices shall be described, namely the helice 2 on the sphere 3 where the exit angle is 45.

The distance between the section lines af may be calledy. From Figs. 4 and 5 will be seen that the point where the line a, intersects the line a lies at a distance it, from a lane a circle the radius 1'. of which is like the distance from the axis M to the point where the sphere 3 and the plane a intersect. The

central angle )8; of said chord is determined formula s by the equation I: 8m 5s ,7

If a great circle is laid through the point of intersection between a, and a (see Flg. 5) it will be understood that the chord decreases for the several section planes, and the general formula of the chord will be r,, sin 13..

If on the sphere 3 there is laid a number of great circles from the rear edge of the wing:

and forwardly (see Fi 2) with an angle therebetween corresponding to 3., the line 2 will pass through the intersections between said great circles and the section planes af. Thus the pitch will increase towards the front edge of the wing.

The several profile lines which maybe thus clibtaincd .are shown in projections at Figs.

In the embodiment of the propeller here aimed at a cylindrical hub is to be used. The profile of the wings pressure side is passed on to this cyli der by tracing circles with 0 as centre which pass throu h the intersection between the hub (dotted l1ne in Fig. 1) and the several planes a/. After the radii of said circles (or spheres) having been calculated by means of the formula where Ri is the radius of the hub Yn is the distance of the plane from 1-s, the exit angle for each sphere is determined by means of the reviously disclosed formula, whereby the points where the helices intersect the hub cylinder ma be calculated or designed.

- In the em odiment now described the pressure sidesof the wings are formed along lines 1 ing on spheres havin a common center in t e propeller axis. I that the pressure sides of the propeller wings may also with good result he laid along lines on spheres the centres of which do not correspond, but are situated in a plane through the rear edge of the wings.

The calculation and construction of the rofiellerwings is then effected in practicaly t e same manner as described above, only with the difference, that several circles are drawn the centres of which lie on the line H and the radius of which always is where R is the radius of the hub (0-1) and the exit angle chosen at the pointl (see Fig. 6) The distance between the centres of such circles is preferably always the same, as indicated in Fi 6.

However, t e angles at the several spheres ave, however, found 2-7 in this case decrease in accordance with another formula than disclosed above. In the latter case the exit angle shall in all distances from the axis M correspond to the r-J i where R is the distance from the axis and s is an expression expressed by the equation m (tg a fi 1? where R is the radius of the hub (0-1) and 01 the exit angle chosen at this point.

I have also invented a speclal method of preparing models to be used in the casting of pro ellers according to my invention. Such mo el is made u of plates the thickness of which is like the istance 3 between the planes On these lates are, by means of models marked 0 the points for the lines a in correct distances from the plane throu h the rear edge of the pro eller, whereupon t e surface of the wing is ormed in accordance with these points.

In Fig. 3 is shown such a model late for the section plane 0 in Fig. 1. At sai late is drawn up the line r& and then the ub, as

shown. Then are drawn circles c,--c with radii corres ending to the points in the lane a where the atter is intersected by the sp erea 27. Then from Fig. 2 are measured, on

the same circles c,c-,, the correspondin chord lengths from the line 18, whic lengths are marked off on the circles on the plate. 'By drawing a line through the points thus obtained the profile of the pressure side of the wing in the lane 0 is obtained.

' This plate is lai on the top of the third plate and under the fourth plate and marked ofi thereon. When all plates thus are marked off and formed in accordance with the markin s and are assembledso that all lines r-e coincide, the pressure surface is obtained with correct shape.

The thickness of the wings is chosen'in accordance with usual calculation of strength, &c., and the suction side is given the profile most corresponding to the profile of the pressure side.

Havin 7 now particularly described and ascertaine the nature of my said'invention and in what manner the same is to be performed I declare that what I claim is:

1. A propeller in which the pressure side of the wings are shaped along lines forming helices on spheres.

2. A propeller according to claim 1 in which the centers of the spheres are situated in a plane lying at right angles to the propeller axis.

3. A propeller accordin to claim 1 in which the centers of the'sp eres are situated in a plane lying at right angles to the prowhich the eiieh the heiiee incree messes peller axis and the rear edge of the wings ee-= incide withseid plane,

4, A propeller eccor to eleim 1 in which the spheres have flifierem'; radii en a common centre in the propeiler em's 5. A propeller according to cleim 1 which the spheres have like radii.

e. A propeller according to claim 1 in which the angle between as tangent to the reel? I pen, of the pressure side end the pieme oi? see-series eioeg theses-1' edge of the Willig &e= creeses ish the distance irom the prepeiies axis. Q

E. A. garepelier eecerding the claim i which the spheres have difierene radii we. the eagle between e tangent to she rear past 0 the pressure side we the plane ef reteztiete e my distance Tam she propeller eer respendsie th fermuie 1: 13 M16 cheese :2 8; pi Whisk per'ieneiiy ice cieeiess dies the ime more the proyeiler axis,

10. A propeller accereing Le claim ii in i which the spheses have like redii eni she an gie between a, tangent to the rear of the pressure side and the plane ofrocesion as my dlissence Efrem the propeller em's eerrespends with s ne formula where R is the distance frem said axis and. e

- is an expression defined by the equation '(l?=( Zga .R whereR is the radius of the hub and a; is the an is chosen at this point.

21 testimony whereof I' aflix m si wire.- 3 HANS MARTINIIS IIS.

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