US2648390A - Variable pitch screw propeller - Google Patents

Description

Aug. 11, 1953 E. DE LAGABBE VARIABLE PITCH SCREW PROPELLER 2 Sheets-Sheet 1 Filed July 30, 1947 Fig. 6

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VARIABLE PITCH SCREW PROPELLER Filed July 30, 1947 2 Sheets-Sheet 2 Fig. 9

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Patented Aug. 11, 1953 UNITED STATES PATENT OFFICE Application July 30, 1947, Serial No. 764,711 In France March 27,1945

Section 1, Public Law 690, August 8, 1946 Patent expires March 27, 1965 Claims. 1

This invention relates to variable pitch screwpropellers.

When in operation, a screw-propeller blade, or more correctly its spanwise axis, traces a helix, and each radial element of the blade axis traces a helical path the tangent of whose pitch angle-is inversely proportional to the radius. For efficient operation the blade must be so shaped that the blade-element at each radius is set at the appropriate angle of incidence to the helical path traced by that element. Since the pitch angles of the helical paths traced by the blade-elements depend on the advance per revolution, to which the tangents of these angles are directly proportional, a fixed pitch screw-propeller can only achieve a good efliciency at one value of the ad vance per revolution, which may be called the design value. At any other value of advance per revolution, the pitch angles of the blade elements necessarily dilTer from the optimum value at all radii. A. variable pitch screw-propeller achieves a nearer approach to optimum elliciency at all values of advance per revolution within its working range, since not only are the pitch angles of all the blade elements correct at the design value of the advance per revolution, but at other values of this parameter Within the working range the blade pitch angle at one radius, usually called the datum station, may be adjusted to the correct value by rotating the blade as a whole about its spanwise axis. However as the twist or" a rigid blade, which determines the difierence between the pitch angles of elements at different radii, is fixed, it follows that the result of rotating the whole blade adds or subtracts an equal amount to or from the blade pitch angles at all radii, whereas ideally the amounts to be added or subtracted should be approximately inversely pro portional to the radius.

To minimise the effect of errors so introduced the radius selected for the datum station is usual- 1y that of the part of the blade which does the most work, but even so, the errors are often great enough at values of advance per revolution notably different from the design value to lead to stalling of the blade elements furthest from the datum station, with a consequent marked loss of efficiency. In any case the efiiciency of a variable pitch propeller at any value of advance per revo lution differing much from the design value falls considerably short of the optimum attainable by a propeller with blades designed to have the appropriate twist for such a value of the advance per revolution. The main object of this invention is to provide a novel form of construction of (Cl. --1S0.24)

a screw-propeller, in which this disadvantage is largely overcome and whose efiiciency through-' out the working range of advance per revolution is made to approach the optimum more closely than is the case with the conventional variablepitch propellenby providing the screw-propeller with blades whose twist is controllably variable and with means for controlling the twist of the blades.

According to the invention, the blades of a screw-propeller each comprise at least two spanwise extending parts, of which one at least can be controllably twisted elastically to a greater or lesser degree to vary the incidence of such part relatively to the other spanwise extending part or parts to an extent which varies along the span, and thereby alter the effective twist of the whole blade.

The torsional stiffness of the controllably twist able blade-part or parts will normally be considerably inferior to that of the remaining part or parts of the blade.

Preferably the trailing portion of the blade is constituted by a controllably twistable part, this portion of the blade being well adapted to the purpose on account of its thinness and consequent torsional flexibility and because the aerodynamic bending moments are least in that region; but alternatively or additionally a controllably twistable part may be disposed in some other chordwise position, for example to form the leading portion of the blade, since it is evident that angular displacement of either the trailing or leading portion of a chordwise section of the r blade relatively to the remaining part will alter the ellective incidence, and pitch angle, of the whole blade-section.

To achieve controllable elastic twisting of spanwise extending blade part, such part may be rigidly secured to the relatively rigid spanwise extending part of the blade at the tip, or be integral therewith in the tip region, the twisting eiiort being applied at the root of the twistable blade-part.

In order to obtain a desired distribution of twist along the span of the twistable blade-part, when the twisting effort is applied, the torsional stifiness of this part may be made non-uniform along the span, this being achieved either by continuous variation of sectional shape or by non-uniformity of the modulus of rigidity, or by both; and for this purpose a composite type of construction embodying materials of differing modulus, suitably disposed to impart a prescribed distribution of torsional stiffness, may be employed.

To enable a variable twisting effort to be applied to a twistable blade-part, its root end mat be loosely rotatable in a socket formed in a member fast on a non-twistable part of the blade, means being provided for rotating the root end in its socket through a variable angle relatively to the non-twistable blade-part, which means may be independently controllable or operatively interconnected with mechanism for varying the pitch of the blade as a whole, so as to impose a prescribed relationship between pitch setting and effective blade twist. The mechanical means by which this operative interconnection is achieved may be of any convenient kind, examples of suitable mechanisms being hereinafter described.

The several spanwise extending parts of which the blade is composed and which are relatively movable to accommodate the varying twist applied by the controls to one or more of these parts may meet on a spanwise articular joint; or may be separated by a spanwise slot, which may be shaped in the known manner to operate as a lift-increasing or drag-decreasing device, by its action in suppressing separation of the boundary layer.

The nature of the invention Will be better understood and a preferred manner of carrying it into practice will be ascertained from the following description of a specific example, including certain modifications, with reference to the accompanying drawings, of which:

Fig. 1 is a view in elevation of a variable-pitch propeller blade according to the invention, showing its insertion in the hub partly in section;

Fig. 2 is a view in elevation of the blade tip, illustrating a modification;

Fig. 3 is a view in section on the line a-a of Fig. 2;

Fig. 4 is a view in section on the line bb' of Fig. 1;

Fig. 5 is a view similar to Fig. 4 illustrating another modification;

Fig. 6 is a view in section on the line c-c of Fig. 1;

Figs. 7 and 8 are schematic views looking in the direction of the spanwise axis, showing the blade parts in two different positions;

Figs. 9 and 10 are cross-sectional views of the part 2 of Figs. 1 to 5, illustrating different constructional methods;

Fig. 11 is a sectional view similar to Fig. 6, illustrating a further modification.

To shorten the description and to avoid unnecessary detail in the drawings, the pitch-varying mechanism, which may be of any convenient type, has been omitted. The specific features characteristic of this invention can be applied to variable-pitch propellers having any of the known or conventional types of pitch-varying mechanism.

Referring to Fig. 1, the blade comprises two spanwise extending parts or members I and 2 rigidly connected together in the tip region by an undivided part 3. The members I and 2 may be formed from a single-piece blade by splitting it to form a slot 4 separating member I from member 2; or these members may be fabricated separately and joined together at the tip by any convenient method of rigid jointing, such as welding, riveting, gluing, vulcanization or the like (according to the blade material used), a riveted joint being illustrated by way of example in Figs. 2 and 3. The cross-sectional shape of the flexible portion 2 of the screw propeller may vary continuously along its length.

The member I is rigidly fixed to a shank 5 (shown in Fig. 1) which is secured to upper and lower adapter members 23 and 23' respectively and which can rotate in the propeller hub 24 about the axis II) for pitch variation; and the adapter element 23 is provided with a socket containing a bearing in which the shank 6 of the member 2 can rotate about the axis II, which is preferably parallel to axis III, as shown.

On the inner end of the shank 6 is keyed a lever I carrying a cam-follower 8 engaging a cam 9 formed in the propeller hub, the generators of the cam-face being parallel to axis II. On changing pitch, the adapter 5 rotates in the hub about axis I0 carrying with it the member I and the follower 8 rolls on the cam 9, and thus imparts to the lever I and shank 6 a rotation about the axis I I, thereby forcing the element 2 to twist upon itself. The element I being of a size considerably larger than the element 2 has a rigidity to twisting such that it is practically not deformed when the element 2 is subjected to a twist.

If necessary, the degree in which the torsional stiffness of member I exceeds that of member 2 may be enhanced by making them of different materials having different moduli of rigidity, such that the material of member I has the greater modulus. In this way the assembly may be made to act approximately as though the member 2 were securely embedded at its tip, as would be the case if member I were infinitely stiff in torsion.

The member 2 by reason of its elastic twist acts as a torsion spring holding the follower 8 in engagement with the cam 9, but if in any position it is substantially unstrained torsionally and the follower therefore has a tendency to leave the cam, a spring such as spring I3 shown in Fig. 6 may be provided for holding the follower onto the cam.

The blade cross-section bb of Fig. 1 as shown in Fig. 4 illustrates an arrangement in which the members I and 2 meet on an articulated joint, whereas that shown in Fig. 5 illustrates an arrangement in which the members I and 2 are separated by a high-lift or drag-decreasing slot, in which case the axis II preferably passes outside the blade contour.

The disposition of the parts of the blade at two different pitch settings are schematically shown in Figs. 7 and 8. In Fig. 7 the follower B is riding on a high spot of the cam 51 and has caused the lever I to rotate the member 2 into a position relative to member I such that the blade section is highly cambered; in Fig. 8 the follower 8 rides on a low spot of cam 9, reversing the position of member 2 relative to member I and giving the blade section a reflex camber.

Two types of composite construction of the member 2 are illustrated in Figs. 9 and 10. In Fig. 9 the construction comprises a metallic portion I4 to which is bonded a moulded elastic material forming the portion I5. In Fig. 10 a portion 20 of cruciform section composed of one material presents recesses I6, II, I8, I 9 which are filled with another material having a different modulus of rigidity.

In the modification illustrated in Fig. 11, a lever 20 fast on the shank of member 2 and corresponding to lever 1 of Figs. 1 and 6 is pivotally connected at 2| to a link, whose other end is pivotally anchored to the hub at 22.

It will be evident that the operation of the last mechanism is analogous to that of the cam mechanlsm of Figs. 1 and 6 in imparting a variable twist to the member 2 and in varying its incidence relative to member 1 as the blade-pitch is varied.

Having now particularly described and ascertained the nature of this invention and in what manner the same is to be performed, I declare that what I claim is:

1. A variable pitch propulsion screw comprising a hub, a blade rotatably mounted in said hub, said blade having two spanwise extending portions, the first of which is a relatively rigid main portion and the second portion of which is a flexible portion disposed along said rigid portion, said flexible portion being non-deformably secured to and integral with the tip portion of said rigid portion, pitch varying means connected to the inner end of said blade for changing the pitch of said rigid portion, and means interconnecting the free end of said flexible portion of said blade with said propeller hub and said pitch varying means operable upon the change in pitch of said main portion of said blade to deform, by twisting, said flexible portion in conjunction with the varying of the pitch of the rigid portion.

2. A screw-propeller as claimed in claim 1, in which said flexible portion constitutes the trailing portion of the blade.

3. A screw-propeller as claimed in claim 1, in

I which said rigid and flexible portions are separated by a slot extending longitudinally of the blade axis, said slot terminating short of the tip.

4. A screw-propeller as claimed in claim 1, in which the flexible portion has a varying modulus of rigidity throughout its length and whereby the torsional stiffness of said flexible portion is non-uniform along its length.

5. A screw-propeller as claimed in claim 4, in which the cross-sectional shape of said flexible portion varies continuously along its length.

6. A screw-propeller as claimed in claim 4, in which said flexible portion is of composite construction and embodies materials having a differing modulus of rigidity to impart a predetermined distribution of torsional stiffness.

7. A screw-propeller as claimed in claim 1, including means for controlling the degree of twist imparted to said flexible portion.

8. A screw-propeller as claimed in claim 1, wherein a cam is provided on the hub of the screw propeller and a lever is fixed on the root end of said flexible portion cooperating with said cam.

9. A screw propeller as claimed in claim 1, wherein said rigid portion and said flexible portion are separated from one another by a longitudinally extending slot of lift-increasing or dragdecreasing form.

10. A variable pitch propulsion screw comprising a hub, a blade rotatably mounted in said hub, said blade having two spanwise extending portions, the first portion of which is a relatively rigid main portion and the second portion of which is a flexible portion disposed along said rigid portion, said flexible portion being non-deformabl secured to and integral with the tip portion of said rigid portion, pitch varying means connected to the inner end of said blade for changing the pitch of said rigid portion, and means interconnecting the free end of said flexible portion of said blade with said propeller hub and said pitch varying means, and a lever connected by a link with a pivot fixed on the hub of the propeller, operable upon the change in pitch of said main portion of said blade to deform, by twisting, said flexible portion in conjunction with the varying of pitch of the rigid portion.

EDMOND DE LAGABBE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,449,129 Pescara Mar. 20, 1923 1,656,019 Roberts Jan. 10, 1928 1,886,289 Miller Nov. 1, 1932 2,055,928 Hays Sept. 29, 1936 2,126,813 Reid Aug. 16, 1938 2,145,805 Ring Jan. 31, 1939 FOREIGN PATENTS Number Country Date 235,700 Switzerland Dec. 15, 1944 546,394 France Nov. 8, 1922 550,227 Great Britain Dec. 30, 1942 550,484 Great Britain Jan. 11, 1943

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