US2594160A

US2594160A - Variable pitch propeller with an axially movable hub

Info

Publication number: US2594160A
Application number: US758964A
Authority: US
Inventors: Hansson Oscar
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-05-17
Filing date: 1947-07-03
Publication date: 1952-04-22
Anticipated expiration: 1969-04-22

Description

0. HANSSON April 22, 1952 VARIABLE PITCH PROPELLER WITH AN AXIALLY MOVABLE HUB Filed July 5, 1947 Patented Apr. 22, 1952 OFFICE VARIABLE PITCH PROPELLER WITH AN AXIALLY MOVABLE HUB Oscar Hansson, Trollhattan, Sweden Application July 3, 1947, Serial No. 758,964 In Sweden May 17, 1946 2 Claims.

The present invention relates to air propellers having blades which may be adjusted to differ ent angular positions with relation to their own longitudinal axes. More particularly, the invention relates to that type of said propellers in which counterweights are provided for balancing the propeller blades in order that the blades may have a tendency to increase their pitch angle upon the rotation of the propeller, and in which the hub of the propeller is adjustably mounted on its shaft as to be able to be displaced thereon, a spring being inserted between the propeller shaft and the hub to counteract said displacement.

The object of the invention is to provide a propeller of this type the blades of which may adjust themselves automatically to such angular positions with relation to their longitudinal axes as to allow the propeller as a whole to automatically control its number of revolutions according to a predetermined characteristic as a function of varying admission of fuel to the motor and varying flight path speed of the aircraft.

An assential feature of the invention is that each propeller blade is connected at its root by means of appropriate connecting elements, as levers and links, to the propeller shaft or to elements carried thereby for positively turning the blades about their longitudinal axes as a result of an axial displacement of the hub on the propeller shaft, the air force component .as produced by the rotation on account of the pitch angle tending to displace the hub axially in order to turn all the blades about their own axis to a position corresponding to a reduced pitch angle, so that with suitably adjusted spring and suitably placed and dimensioned counterweights a balance may be obtained at the speed desired for various degrees of fuel admission, that is to say, at varying propeller thrust, between on the one hand the axial air force componentand the inertia force component of the blades with the counterweights and, on the other hand, the axially directed force as exerted by the spring on the hub.

In the accompanying drawing Figure 1 is part of an axial section of a two-bladed propeller embodying this invention. Figure 2 is an enlarged view of a detail. While in the drawing two propeller blades are shown it is to be noted that, of course, the number of blades may be greater than two without departing from the principle and scope of the invention. Since the propeller blades are all of the same design, one

of themonly is shown in detail. 7

propeller blade.

stream-lined profile.

With reference to the drawing, the numeral l designates the propeller shaft which may be either the motor shaft or a separate shaft geared to the motor shaft. Secured to the propeller shaft in any suitable way is a sleeve 2.

Slidably mounted on said sleeve so as to be easily displaced thereon is the hub 3 of the propeller. Said hub, however, is locked against rotation with relation to the sleeve 2 by the provision of coengaging ribs or

wings

4 and 5 on sleeve 2 and hub 3, respectively. The hub 3 is formed with a radially extending journal 6 for each On each such journal the respective propeller blade 1 is rotatably mounted at two points thereof, namely, by means of a journal bearing 8 at the outer end of the journal 6 and by means of a ball thrust bearing 9 at the inner or base end of the journal. To permit mounting of the'bearing 9 the root portion it) of the blade has screwed thereon a sleeve II the end of which facing the propeller shaft is formed with an inwardly projecting flange l2 forming a support for one race of the ball bearing. The other race of said bearing is held in place by means of a cone l3 screwed on the journal 6. Projecting from the flange l2 in any convenient direction is an arm [4 forming or carrying at its free end a journal l5 eccentric with relation to the journal 6. Said eccentric journal I5 is connected by means of a connecting rod IS with a journal I I provided at the outer end of an extension of the sleeve 21 which projects beyond the end of the propeller shaft.

In the drawing said journal I! is shown as positioned between a pair of ears 18 provided at the inside of a cover [9 for the sleeve 2, said cover being preferably threaded into the sleeve so as to be reliably held thereto. The cover l9 projects beyond the circumference of the sleeve so as to form a flange serving as a support for the outer end of a powerful coiled spring 20 surrounding the sleeve 2, the inner end of which bears against a flange of the sleeve 3. Thus, the spring 20 tends to displace the sleeve 3 in the direction towards the motor.

The cover 19 of sleeve 2 is further provided with a sleeve shaped extension 2| of reduced diameter. Slidably engaging this extension is a pin 22 secured to the apex of a stream-lined sheet metal housing 23 which encloses the entire hub structure so as to protect the articulations and the contact surfaces thereof against dust, while at the same time giving the hub a The housing 23 is closed at its wide end by an annular closure member 24 connected at its inner, periphery to the in or weights to turn in such a direction as to 7 increase the pitch angle, b, instead of, as the case would be if the blades had no counterweights, turning in a direction corresponding to a reduced angle of blade.

The lever arms [4 of all the blades are of the same length and form equal angles with their respective blades, and the connecting rods I6 belonging to the various propeller blades are also of the same length and, in case of a propeller having but two blades, they are arranged in an inverted symmetrical relation to the axis of the propeller. Thus, the propeller blades will always be simultaneously set to equally great angles 01).

The operation of the propeller described is as follows:

When the propeller is at rest the blade is held by the action of spring 20 on the hub '3 at its greatest angle of pitch. Said angle may be limited by a stop comprising, for instance, a projection 26 on sleeve 2 and a corresponding shoulder 21 on hub 3. As soon as the propeller startsrotating, dynamic ai forces appear resulting in aforwardly acting propeller, thrust. This propeller thrust acts in an opposite direction to that of the spring force and, consequently, tends to reduce the pitch angle; as a matter of fact,

this reduction takes place if the propeller is displaced in the forward direction on its hub. In addition, the action of the centrifugal force on the weights 25 and on the blades causes a turning moment on the blades with respect to their longitudinal axes which results from all of the centrifugal forces appearing and tends to turn the blades in such a direction as to increase the..pitch angle. The spring 20 should be so proportioned as to' allow the turning moment of the motor to produce suificiently great air forces for imparting to the propeller a certain forward displacement on its hub in a direction towards reduced pitch ance results between, ion the one hand, the action of the spring and the thrust of the propeller and, on the other hand, the forces resultingfrom centrifugal force moments, during a given moment of the motor at a given number of revolutions and a given flight path speed. r

7 It is desired in respect of an aircraft propeller that it should increase its speed as a result of an increased admission of fuel, that is to say, as a result of an increased motor moment, and vice versa. This is. true especially as far as starting and rising is concerned, since it is desired as a rule to obtain the greatest power of the motor possible during a few minutes, until the aircraft has attained a given altitude above ground.

It is also desired that, should the .motor cease working, the propeller may occupy an adjustment of the blades with a given suitable pitchangle in order that the air may cause the motor torotate at a given relatively low number of revolutions.

Hereinafter I shall prove mathematically that the above described construction results in a propeller capable of adjusting its number of revolutions automatically according to the characteristic one may desire at varying fuel admission and varying flight path speed of the aircraft. 7

The range of adjustment of the blade in respect of starting, rising and level flight amounts to about 20 and in respect of a range of this comparatively low value one may consider the lever arms on the blade roots as being of a constant length (or as varying rectilinearly with the pitch angle) and likewise consider the resulting inertia force moment acting on the blades as being constant (Or also varying rectilinearly with the pitch angle) 'as far as varying pitch angle is concerned.

The inertia force moment varies also with the 7 square of the number-of revolutions.

One may now assume, for instance, that the propeller is so designed that the lever arms I4 connected to the roots of the blades project at right angles to the propeller shaft when in their intermediate positions, so that they may be assumed to be approximately constant as to their length within the range of adjustment. One may also assume that the weights 25 are so placed and dimensioned that an intermediate set position of the blade corresponds to the apex of the inertia moment characteristic for the blade and that, as a result, the inertia moment may be assumed to be approximately constant irrespective of variation of the pitch angle 0b;

Let it be assumed that the length of lever arm i4 is L, the thrust of the spring 20 is Pe, the resulting counteracting moment on the propeller asproduced by the air forces is M1, the moment of the motor acting on the propeller is Mk, the scalar sum in respect of all blades of the inertia moment as exerted by the centrifugal forces on the blades about their longitudinal directions is Mm, the axial component of the dynamic air force actions on the propeller Ki and the thrust corresponding to said inertia moment is Pm, then the following equations are obtained at the state of dynamic balance:

If the number of revolutions of the propeller per second is indicated 11., then the following equationis obtained:

7 Mm kmJL 7 IV in which m is a constant of inertia without res gard to number of revolutions. 1

' Let it be assumed for one moment that the moment of the motor Mk is maintainedconstant and that the aircraft is caused due to a changed 7 sure), and the number of blades is indicated Nb,

then I obtain for Mk=constant, the following equations in which symbol 2 denotes summation:

R11 IM I =EN .Ap.B.AR.sin 6,,.R |M l=constant and , Ry K,=2N .ApB.AR.cos 0 Ru 2 cos 0,,

n.cos 0 from which at last follows i ki 13,. red

In the foregoing the symbol red is an abbreviation of reduced and symbol 0bm=the angle of blade at different adjustments within the range of angular variation in respect of that radius of blade, at which the term cos Him is equal to the arithmetic medium of cos 0 in case of the cross section of all blade elements at any position of blade desired within said range.

If the angle 01am is given in radians, then we may in respect of the spring write where kc and P6 are constants.

By approximation and reduction to a linear function in respect of fibm we may write K =K,,+g -0,,,,,=K,,k,.0,, (VII) R red cotg 0 and in which K1 represents the value of K1 in the middle range of adjustments.

In respect of the same central point, we then have from Equation VII:

Determining the moment of inertia Mmo at the same central point we have from Equation II:

(According to Equation IV) kmo T' From Equation III we then obtain by inserting the above expression Hence kmo It is desired that the number of revolutions ought to be independent of Him and that the number of revolutions ought to be increased with increased fuel admission (that is to say, with increased IMkI) This condition is satisfied by two equations obtained from the above equation, namely:

From these equations it is realized that by suitable adjustment of the spring and the weights carried by the blade roots the propeller may be caused to operate according to any characteristic desired.

It is to be carefully observed in the constructive performance that the lever arms of the blade roots should be properly dimensioned with rela- ,tion to frictional forces as well as with relation to the loading weights of the blade roots, as said arms affect the speed characteristic desired in the same degree and in the inverse proportion as the loading weights.

From the above description including the equations it is evident that the construction described permits obtaining a number of revolutions which is independent of the flight path speed or which may be dependent thereon according to a given law desired, and that this number of revolutions, as is always desirable, in-

on weights carried by the roots of the blades which in respect to these inertia forces overweigh the forces produced in the blades proper.

As to the constructional details modifications may, of course, be made within the scope of the invention, though they are not specified in the above description or illustrated in the drawing.

What I claim is:

1. An aircraft propeller of the type specified comprising a powerdriven shaft, a sleeve rigidly mounted on said shaft, a hub on said shaft, slidable bearing means on said sleeve and said hub for allowing the hub to slide axially on the sleeve, interengaging means on said sleeve and hub for locking said sleeve and hub against relative rotation, radially extending shafts rotatably mounted in said hub, a propeller blade fastened to each of said radial shafts, counterweights secured to said radial shafts in positions removed from the axes of said shafts for tending to turn the shafts and blades about their axes towards an increased angle of pitch under the action of the centrifugal force appearing as result of the rotation of the peller shaft resulting, from the axial air force component, a coil spring having its axis extending longitudinally of the axis of the driven shaft and engaging with its ends the sleeve and the hub, respectively, a lever and linkage mechanism connecting an eccentrically located part of the root end of each radial blade shaft to said sleeve for effecting during the operation of the propeller a balance between the axial air force component, the inertia force components in axial direction as caused by the blades and their counterweights on the one hand and the thrust on the hub resulting from the action of the spring on the other hand.

2. An aircraft propeller of the type specified comprising a power driven shaft, a sleeve rigidly mounted on said shaft and extending beyond the V free end thereof, a cover at the free end of said sleeve having an outwardly projecting flange, a hub mounted on said sleeve longitudinallyslidably, said hub and said sleeve having coengaging means for causing the hub to rotate with the sleeve while allowing it to slide axially in relation thereto, radially projecting integral journals on said hub, propeller blades having hollow shaft ends rotatably mounted on said radial journals, counterweights secured to said hollow shaft ends eccentrically in such positions as to tend to turn the bladestowards an increased angle of pitch under the action of the centrifugal force resulting from the rotation of the power driven shaft, a compression spring mounted on the extension of the sleeve'between the flange of the cover of the sleeve and the-respective end of the hub slidably mounted on said sleeve, for counteracting the a 8 axial displacement of the hub on the power driven shaft resulting from the axial air force component, a leverand linkage mechanism provided inside the extension of the sleeve connected between the cover thereof and the root end of the hollow shaft ends eccentrically of the axis of the shafts of the propeller blades'for effecting during the operation of the propeller a balance between the axial air force component, the inertia force components in axial direction as caused by the blades and their counterweights on the one hand and the thrust on the hub resulting from the action of the spring on the other hand.

OSCAR HANSSON.

REFERENCES CITED UNITED STATES v PATENTS Number Name Date 1,806,385 Bramson May 19, 1931 1,952,066 Havill Mar. 27, 1934 1,952,802 Havill Mar. 27, 1934 1,952,812 Mansson Mar. 27, 1934 1,977,031 I Zipay Oct. 16, 1934 2,008,865 Havill et a1 July 23, 1935 2,257,126 Rindfleisch Sept. 30, 1941 2,422,558 Korff June 17, 1947 FOREIGN PATENTS Number Country Date 21,067 Great Britain 1910 311,472 Great Britain May 16, 1929