US3565544A - Marine propeller - Google Patents

Abstract

A VARIABLE THRUST MARINE PROPELLER INCLUDING A HUB WITH A PLURALITY OF BLADES PIVOTALLY MOUNTED ON THE HUB FOR PIVOTAL MOVEMENT ABOUT AXES GENERALLY PARALLEL TO THE AXIS OF ROTATION TO THE HUB FOR MOVEMENT FROM A NESTED POSITION ADJACENT THE HUB TO AN EXTENDED POSITION. THE CENTER OF MASS OF EACH BLADE IS DISPOSED REARWARDLY OF THE PIVOTAL AXIS FOR THE BLADE RELATIVE TO THE DIRECTION OF ROTATION OF THE HUB SO THAT THE FORCE OF WATER ON THE BLADE WHEN THE BLADE IS ROTATING WILL WORK AGAINST THE CENTRIFUGAL FORCE ON THE BLADE DUE TO ROTATION OF THE HUB. AS THE BLADES PIVOT OUTWARDLY TOWARD THEIR EXTENDED POSITION, BOTH PITCH AND DIAMETER OF THE PROPELLER ARE INCREASED.

Description

D. J. MARSHALL MARINE PROPELLER Feb. 23, 1971 3 Sheets-Sheet 1 Filed Feb. 7, 1-969 M a .1 Z M J, M w W W J5 131"1971 D. J. MARSHALL 35 .544"

I MARINE PROPELLER 3 Sheets-Sheet 3 Filed Feb. 7, 1969 j 07. 3M ya/3M United States Patent Ofice 3,565,544 MARINE PROPELLER Don J. Marshall, Edgewater, Md., assignor to Goodall Semi-Metallic Hose & Mfg. (30., Philadelphia, Pa., a

corporation of Pennsylvania Filed Feb. 7, 1969, Ser. No. 797,393 Int. Cl. B63h 3/10 US. Cl. 416-89 13 Claims ABSTRACT OF THE DISCLOSURE A variable thrust marine propeller including a hub with a plurality of blades pivotally mounted on the hub for pivotal movement about axes generally parallel to the axis of rotation to the hub for movement from a nested position adjacent the hub to an extended position.-

The center of mass of each blade is disposed rearwardly of the pivotal axis for the blade relative to the direction of rotation of the hub so that the force of water on the blade when the blade is rotating will work against the centrifugal force on the blade due to rotation of the hub. As the blades pivot outwardly toward their extended position, both pitch and diameter of the propeller are increased.

The present invention relates to new and useful improvements in marine propellers and more particularly to marine propellers having means for fully automatic variation of both pitch and diameter solely dependent on the thrust requirements of the driven vessel under varying operating conditions.

The need for pitch variation has long been recognized, and the present state of the art includes many successful versions of such propellers. However these are normally dependent on extraneous mechanism, hydraulic, electrical, mechanical, or combinations of these, plus human surveillance and interpretation of hull operating conditions. They are expensive and complicated, require skilled operators, and periodic maintenance and care. As such, they offer nothing by way of assistance in the problems of pleasure boating and other small craft operation.

Due to the relatively narrow range of operating efiiciency of the internal combustion engine, and the relatively broad range of thrust requirements imposed upon the marine hull by such factors as varying loads, varying load placement, water absorption, degree of hull fouling, sea surface conditions, wind direction relative to course, etc., a fixed pitch and diameter propeller very often forces the driving engine to work under adverse conditions of overload or overspeed. Consider that these changing conditions can exist in a single given hull, and that it is a common practice to mount standard classes of engine on or in many differing sizes and forms of hulls, the problem of operating the engine at its optimum efliciency range is greatly multiplied. A particular example of this is in the inboard or inboard-outboard field, wherein a factory installed propeller is supplied with the engine. Rarely is this propeller of correct size for the hull on which the engine is mounted, and the owner usually must try out several propellers in order to arrive at efiicient and satisfactory performance. As a matter of fact, even after making a selection of propeller for his hull, the before-mentioned variations in operating conditions renders the chosen propeller inefficient under heavy loading or the presence of even minor hull fouling.

The loss of money to the supplying industry which must produce, catalog, and stock a multiplicity of propellers in dealerships around the world, and the loss of time and money to their customers through purchase of extra propellers in an attempt to meet this problem is considerable. Add to this the waste fuel, excessive engine 3,565,544 Patented Feb. 23, 1971 wear, and lost hull performance, and it becomes apparent that a more flexible means of boat propulsion is sorely needed.

It is obvious that the average boat owner cannot afford the high initial cost of the variable pitch propellers which are available in the present state of the art. As a matter of fact, the average pleasure boat owner does not want to be bothered by the extra chore of propeller pitch regulation in his already too few hours of pleasure time afloat. Indeed, to do so effectively, he would be obligated to purchase, as minimum instrumentation, an accurate speedometer, a tachometer, and a manifold pressure gauge, plus spending a good part of his cruising time in calculations of the data displayed.

The propeller of the present invention includes a hub and a plurality of blades pivotally mounted on the hub for free movement about axes generally parallel to the axis of rotation of the hub from a nested position parallel to the axis of rotation of the hub from a nested position to an extended position. The greater portion of the mass of each of the blades is rearward of its pivotal axis with respect to the normal direction of rotation of the hub. As the hub is rotated, centrifugal force will tend to cause the blades to pivot outwardly. However, this centrifugal force is opposed by the thrust on each blade created by the resistance of the water to the movement of the blade through the water. Thus, for any fixed resistance to movement of the boat and speed of rotation of the propeller, the blades of the propeller will reach an equilibrium position and the pitch of the blade will automatically change to compensate for variations in operating conditions of the boat.

There are numerous benefits arising from the blade having this particular type of construction. For example, when the boat is being started and the propeller is initially being rotated at relatively slow speeds, the blades will be pivoted inwardly toward their nested position preventing a sudden shock load from being exerted on the motor during start or during rapid acceleration from a slow speed. When the boat is being operated, the pitch of the blade will change with a change in load conditions of the boat to prevent overloading of the motor and keep the motor operating at its most efficient speed. Should cavitation occur for any reason during operation of the boat, for example, because of an extremely sharp turn or because of turbulent water, the blades will immediately pivot outwardly to increase the effective diam eter and pitch of the propeller, thus increasing the bite of the blades in the Water and eliminating cavitation. In addition, during operation vibration is substantially decreased because any imbalance in the propeller will be compensated for by movement of the blades to a balanced position. Further, during operation, should the blades hit the bottom, the blades will fold inwardly to their nested position decreasing the possibility of breaking the propeller. The blades are similarly folded inward should the boat be run through seaweed. A further advantage of the propeller of the present invention is that if the drive is put in reverse, the blades will automatically open outward to their fullest extended position, increasing the efiective area and thus the braking power of the blade.

In view of the above, it is an object of the present invention to provide a propeller having means to vary its diameter and pitch, fully automatically, to suit the varying power demands of the hull, thus permitting the driving engine to operate at a high level of efiiciency and constantly protect the engine from destructive overload or overspeed conditions.

Another object of the present invention is to provide a marine propeller which by varying its diameter and pitch will enable a single factory installed propeller on a given power unit to efliciently drive a relatively broad range of hull sizes, weights, and underbody forms.

A further object of the present invention is to provide a marine propeller which changes its pitch and diameter solely by sensing variations in hull drag so as to provide at all times the proper configuration assuring effiecient engine function under all operating conditions.

A further object is to provide a marine propeller which will eliminate the fixed ratio between hull drag and engine r.p.m., by constantly monitoring changing conditions and automatically varying its diameter and pitch.

Still another object is to provide an automatically variable marine propeller which will be simple and rugged in construction, maintenance free, and which is inexpensive to manufacture.

Still further objects and fuller uderstanding of the invention, its operation, and its advantages may be had by referring to the following description, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevational view of one form of propeller made in accordance with the present invention;

FIG. 2 is a rear view of the propeller of FIG. 1 showing in broken line the blades in their fully retracted or nested position, and in solid line the blades in their fully open or extended position;

FIG. 3 is a fragmentary sectional view through the hub of the propeller and one blade taken on line 33, FIG. 2;

FIG. 4 is a rear view partially in section showing the hub and one blade in its retracted position;

FIG. 5 is a sectional view taken on line 5-5, FIG. 4, showing the pitch angle of the working surface of the blade in its retracted position;

FIG. 6 is a view similar to FIG. 4 with the blade in its fully extended position;

FIG. 7 is a sectional view taken along line 7-7, FIG. 6, showing the pitch angle of the blade fully extended; and

FIG. 8 is a rear view partilaly in section of another blade form of the present invention showing a method of creating mass balance to rear in blades; and

FIG. 9 is a chart showing on a plot of engine speed v. boat speed the engine torque, hull drag and centrifugal force effect on the propeller blades.

Referring more specifically to the drawings and particularly to FIGS. 1 and 3 thereof, the propeller of the present invention includes a hub portion 10 adapted to be mounted on a drive shaft of a boat or engine in any conventional manner, for example, by means of a shear pin 12 and is plurality of blades 13 mounted on hub 10 for limited pivotal movement between a retracted and an extended position.

The hub 10 includes spaced apart forward and rearward flanges 14 and 15, respectively, with a tubular web 16 extending between the forward and rearward flanges and surrounding the shaft. In the present example, a plurality of flat abutment surfaces 17 as shown in FIGS. 4 and 6, are provided as means for the limitation of blade movement. Other conventional forms of stop such as lugs, shoulders, and etc., may be used, and if desired, may be faced with a resilient material to lessen drive train shock loads during starting and reversing operations.

The individual blades 13 are equally spaced about the periphery of the hub and include a mounting boss 18 at the inner forward edge of the blade, with the working portion of the blade projecting substantially radially outward from the boss.

In the embodiment of FIG. 1, the blade is generally L shaped with one leg of the L extending substantially radially outward from the boss and the other leg of the L shown at 13a, extending rearward relative to the normal forward rotation of the hub of a radial line from the center of shaft 11 through the mounting boss 18.

Other blade configurations may be used, reproducing are moment arm effect of the L shape by modification of the chordal section of said blades as shown in FIG. 8. In this form, the thickened section of an area redially outward of pivot 19 and rearward of a radial line through the center of the drive shaft and mounting boss serves the function of the rearward extending leg of the L shaped blade of the present embodiment. This thickening of section will hereinafter be called, by its function, mass imbalance.

The working face of the blades should be in the general form of a helix, subject to such refinements as cupping or spoonfacing. The side opposite the working face should be in general an ogival curve, modified as needed to create the above mentioned mass imbalance of the blade necessary to create the moment arm desired for pivotal motion, but in keeping with proper streamlining to obtain eflicient movement through the water and minimum turbulence.

In accordance with the present invention, each blade is mounted pivotally on the hub for limited pivotal movement between a retracted or nested position as shown in broken lines in FIG. 2 and as shown in FIG. 4, and an extended position as shown in solid lines in FIG. 2, and as shown in FIG. 6. This is accomplished in the illustrated embodiment of the present invention by providing a mounting pin 19 for each blade extending axially through said boss and both forward and rearward mounting flanges. If desired, conventional anti-friction bushings and thrust washers made of suitable non-corrosive materials, not shown, may be inserted within and fore and aft of each blade boss 18.

The mounting pin 19 is secured in Place in the flanges by any desired conventional device, such as a drive pin 20, as shown in FIG. 3. The axes of each of the mounting pins 19 are substantially parallel to the axis of hub 10 in the present embodiment, but may be offset slightly if desired to augment the function of negative blade rake as is fully explained hereinafter. It is essential that the mountinng pins 19 or equivalent pivoting means he placed radially outward from, and equally spaced about the center of rotation of hub 10, and in equal respective position from the blade limit stepping means, so that all blades will pivot outward under equal force, and to and from similar stop points, in order to achieve dynamic balance and maintain the same when held in its fully open or closed positions.

As centrifugal force expands the blades, there is a first effect pitch change derived from basic laws of mathematics. This occurs due to the fact that as diameter increases, there is a corresponding increase in the circumference of the inscribed circle of blade travel. The blade working surface, having a set pitch angle, but now traveling a greater linear distance per revolution, effects a pitch increase equal to the tangent of that angle multiplied by the increase in circumference expressed in inches.

There is a second effect pitch increase, simultaneous and cooperative with the above. FIGS. 3 to 7, inclusive, illustrated a forward reaching angle, or negative rake, of the blade working surface. The negative rake may be provided either by tilting the axis of the mounting pins 19 relative to the axis of the drive shaft 11 so that the blade is tilted forwardly from a line perpendicular to the axis of the propeller drive shaft or by tilting the individual blades 13 forwardly relative to the mounting boss of each bladeas shown in FIG. 3.

In the illustrated embodiment of the present invention, the negative rake to each blade is created by maintaining the mounting pins 19 parallel to the axis of the propeller drive shaft 11 by tilting the individual blade portions 13 forwardly with respect to each mounting boss 18 for each blade. This negative rake in the blade is converted to an increase in pitch angle as the blade is moved from its retracted position to its extended position.

The rake angle is provided in each blade when the blade is in the retracted or nested position. In this position, the negative rake angle or tilt of the blade has no effect on the pitch angle of the blade. This rake angle can be as shown in FIG. 3 wherein the working surface of the blade is tilted forwardly to provide a negative rake of, for example, 5 when the blade is retracted. The pitch angle of the blade when the blade is fully retracted is the angle X as shown in FIG. 5 which is the angle of the working surface along an arc drawn from the center of the drive shaft. When the blade is rotated to its fully extended position as in FIG. 5, the rake of the working surface then faces at least partially forward and the rake angle adds to the pitch angle to increase the pitch angle, for example to X +5 as shown in FIG. 7.

To understand the effect of this as related to blade expansion, one must visualize the inflow current passing, as it actually does, straight into and parallel with the plane surface of the blade; in FIG. 3 this is from the eye of the viewer toward the drawing.

Observe that the 5 rake angle which as drawn illustrates its relation to a perpendicular plane about the axis of hub when in the blade retracted position, will have zero effect in deflection of water mass rearward-to the left in this view. However, in expanded position, the blade being now rotated toward the viewer on axis 19, this rake angle will be seen by the inflow current as working pitch. It should be realized that this function occurs gradually, in cooperation with radial expansion, and that the two pitch increasing means are cumulative in effect.

FIG. 8 illustrates a modified form of hub and blade configuration of the present invention. In this form, the web 16a of the hub is cylindrical in form and is covered by a layer of elastomeric material 21. The blade includes a boss portion 22 pivotally mounted to the flanges of the hub by a mounting pin 23. The boss has arcuate projecting abutment surfaces 24a and 24b adapted to engage the elastomeric layer 21 on the web 16a to limit the inner and outer positions, respectively, of the blade. Mass imbalance of the blade is created by having the thicker and heavier portion of the blade rearwardly, relative to the forward direction of rotation of the hub, of a radial line drawn through the center of the drive shaft 11 and the center of the mounting pin 23.

When the propeller of the present invention is mounted on a boat shaft and rotated in the forward direction, as rate of rotation increases, centrifugal force increasing by the square of rate of rotation operates on the moment arm extending between the radial line through the center of the boss of the blade and the rearwardly disposed center of mass and biases the blades toward the extended position. This action is opposed by drag forces composed of normal blade drag and the variable hull drag. It is important here to realize that at low rate of rotation,

combined drag effect is greater than centrifugal force effect, but that as the rate of rotation increases, centrifugal force rapidly becomes superior. Blade expansion will then commence and will continue until hull drag, increasing sharply with increased speed and combined with increased blade drag will equal centrifugal force effect, at which time, blade diameter and pitch will assume a fixed value. (It is important to understand that although centrifugal force increases by the square of the rate of rotation which should mean that it will remain always superior to the linear increase of drag, there is a limiting factor imposed by the shortening of the moment arm as well as a lessening of the mass imbalance as pivotal movement progresses, enables drag effect forces to equal centrifugal force.

A more complete understanding of these functions may be had by reference to the attached graph of FIG. 9, in which the interaction of the various forces are depicted for a typical 60 hp. outboard engine, mounted on a planing hull, with the propeller of this invention installed.

. foreshortens the moment arm and the mass imbalance so that at the point coincidental with torque peak, all forces become equal and blade expansion is halted.

Reading further from this point we see drag falling off almost vertically with the centrifugal force effect remaining almost constant. This depicts the conditions existing during cavitation, and in this zone, blade expansion is immediate and maximum.

Thus hull resistance being the governing factor, in the case of a light fast hull, expansion will continue to greater degree and pitch and diameter will become fixed at a relatively high value. Conversely, with heavier loading or a larger or slower hull, blade expansion will be arrested earlier and pitch and diameter will become fixed at a relatively lower value.

Essentially, the pitch and diameter setting of the propeller of this invention is at all times governed by that law of motion which states that for every action there is an equal but opposite reaction. Thus, engine torque being the accelerating force biasing toward blade expansion, and combined drag components being the accelerating force biasing toward blade retraction, the blade will at all times assume a position at which the opposing forces are in equilibrium, this controlling the work potential of the propeller. Thus an engine driving this propeller will at all times be enabled to function near its point of highest efficiency, torque output, and optimum r.p.m. rate.

The propeller of this invention has many advantages.

First of these is a lessening of starting shock loads on engine and drive train. This is mainly due to the fact that in blade retracted configuration it is far too small a propeller for the driving engine and is thus capable of instant and easy acceleration, and also due to the fact that at the very inception of rotation, the hub mass is first moved, and then the blades. This is in sharp contrast to all other propellers where both the total mass and full work capability of the propeller are seen by the engine and drive train at instant of start.

Another shock lessening feature of this propeller is found in the fact that the blades are free to fold back at the instant of accidental impact with submerged objects and thus tending to fend them away and by shortening the moment arm subject to impact forces, decreasing the transferred force.

Still another advantage associated with the pivoting blades is the fact that such blades render a propeller essentially self-balancing so that moderate blade damage will not create the usual heavy vibrations. In the usual propeller, the entire blade mass is rigidly fixed to the hub and shaft. Any dynamic imbalance is thus transferred into the hull where serious damage may ensue. With the propeller of tln's invention, as the greater mass of the working blade is travelling in essentially free orbit about the hub, being thrown constantly outward against a wall of water which supports most of its weight, any change in mass causes the blades to assume a slightly altered path about the hub, transferring little if any of the mass effect to the hub.

Readily apparent is the economy of replacing only the blade or blades damaged by such impact, rather than the entire propeller.

A most important advantage is increased hull acceleration. As shown above, engine acceleration is almost in stantaneous. Blade expansion not taking place until the engine has reached a high level of power output, it is then in condition to drive the hull forward without the usual protracted period of slow laboring to attain full power.

It has been found that hull acceleration rate using the propeller of the present invention is considerably greater than when using a conventional propeller.

One of the most damaging duties imposed on a marine engine is slow trolling with a standard propeller which is normally designed for optimum function at high speeds. Even though throttled down, the engine is actually laboring, temperature goes up, lubrication pressure goes down, valve ports and spark plugs become fouled. With the propeller of this invention, as the throttle is closed down to trolling speed, r.p.m. drops, blade drag exceeds centrifugal force effect, and the blades retract to very low pitch values. Thus for any given trolling speed, engine r.p.m. rate is higher and the engine is relieved from heavy lugging and runs free and easy.

In emergency stopping procedures, at the instant of shaft reversal the blades immediately swing to full expanded position. Pitch and diameter are instantly boosted to values greater than the driving engine could possibly sustain in forward travel thereby increasing the braking effect.

The propeller of this invention acts to positively control runaway cavitation. This dangerous phenomenon can occur during normal operation in choppy seas, during period of high speed operation and in hard turns, always.

at times when it is least welcome. Its least effect is a sudden loss of all propuslion. Also, it can cause failure of propellers, shaft, strut and engine as r.p.m. rate instantly advances to a point far in excess of designed maximums. This form of cavitation is a function of air entrapment in the propellers inflow current or may occur when the negative pressure ahead of the blades exceeds the vapor pressure of the water. With all propellers in the present state of the art, the only means of control in this situation is an immediate throttling down of the engine, hopefully before damage has occurred.

With the propeller of the present invention, at the instant of inception of this cavitation, as blade drag immediately drops to zero, centrifugal force effect on the blades remaining constant, the blades instantly expand to maximum. As the working area of the propeller is thus increased, there is a reduction of negative pressures operating on the inflow current. Solid water fiow is immediately restored and normal r.p.m. rate is attained with no attention or action required of the operator.

Yet another advantage, much appreciated by boat owners who operate in weed infested waters, is the selfcleaning feature of the propeller of this invention. Normal practice in case of weed fouling is a repeated reversal of blade rotation in an attempt to throw off the fouling material. This is sometimes effective, but often the blades must be cleared manually. With the pivoting blades of this invention, simply closing the throttle will cause the blades to retract to the nested position, thus altering the sweep angle of the leading edge of the blades, allowing the fouling material to slide away.

From the foregoing it can be seen that the present invention provides a novel marine propeller having many proven advantages and in which the pitch and diameter can change automatically in response to changing operating conditions in order to more efiiciently satisfy these conditions.

While a particular embodiment of the present invention has been illustrated and described herein, it is apparent that various modifications can be made to this embodiment while still utilizing the disclosed invention.

I claim:

1. A variable pitch marine propeller comprising: a hub having a central axis of rotation for mounting coaxially on a rotatable shaft, a plurality of blades spaced apart around the periphery of said hub with each of said blades having a root portion disposed adjacent said hub, means providing a pivot connection between said hub and the root portion of each blade to permit said blades to pivot independently of each other for free swinging movement about axes substantially parallel to the axis of said hub between a nested position adjacent said hub and an extended position outwardly therefrom, each blade having its center of mass located rearwardly of a radial line through said axis of rotation of said hub and said pivot connection relative to the normal direction of rotation of said hub in both the nested and extended positions so that centrifugal force ap lied thereto upon rotation of said hub causes the blades to pivot, each of said blades having a working surface with a portion thereof inclined with respect to a plane normal to said axis of rotation, said surface portion subtending a pitch angle with respect to a line perpendicular to a radial line from said axis and in said plane, whereby upon rotation of said hub on its axis, an increase in its angular velocity causes the blades to pivot outwardly and the pitch of said propeller to increase, and a decrease in its angular velocity causes the blades to pivot inwardly and the pitch of said propeller to decrease.

2. A propeller in accordance with claim 1 wherein said working surface of each blade subtends a rake angle with respect to said normal plane and along said radial line when such blade is in its nested position, so that the pitch angle is increased and decreased in relationship to the respective outward and inward angular displacement of the blades.

3. A propeller in accordance with claim 2 including means on said hub cooperating with said blades to limit angular displacement of said blade.

4. A propeller in accordance with claim 1 wherein said pivot connection means comprises protrusion means extending radially outward on said hub and means disposed substantially parallel with said axis of rotation mounting the root portion of a blade between said protrusions.

5. A variable pitch marine propeller comprising: a hub having a central axis of rotation, a plurality of blades spaced apart around the periphery of said hub with each of said blades having a root portion disposed adjacent said hub, means providing a pivot connection between said hub and the root portion of each blade to permit said blades to pivot about axes substantially parallel to the axis of said hub between a nested position adjacent said hub and an extended position outwardly therefrom, each blade having its center of mass located rearwardly of a line through said axis of rotation of said hub and said pivot connection relative to the normal direction of rotation of said hub when said blades are in the nested position so that centrifugal force applied thereto upon rotation of said hub causes the blades to pivot, each of said blades having a working surface with a portion thereof inclined with respect to a plane normal to said axis of rotation, said surface portion subtending a rake angle with respect to a radial line in said plane and subtending a pitch angle with respect to a line perpendicular to said radial line in said plane, whereby upon rotation of said hub on its axis an increase in its angular velocity causes the blades to pivot outwardly and said pitch angle to increase, and a decrease in its angular velocity causes the blades to pivot inwardly and said pitch angle to decrease, so that the pitch of said propeller varies in response to the angular velocity of the hub.

6. A propeller in accordance with claim 5 in which the rake angle of each blade increasingly adds to the pitch angle of the blade as the blade pivots outwardly from the nested to the extended position, and means on said hub for cooperating with said blades to limit the angular displacement of sach blade on its pivot connection, whereby the maximum and minimum pitch angle of said propeller may be fixed.

7. A propeller in accordance with claim 6 wherein said blade displacement limiting means comprises: a pair of abutment surfaces diverging outwardly around said pivot connection on the root portion of each blade and an abutment surface on said hub disposed between the axis of rotation of said hub and said pivot connection, whereby.

the abutment surfaces on the root of each blade engage the abutment surface on the hub to limit the angular displacement of the blades.

8. A propeller in accordance with claim 7 wherein at least one of said abutment surfaces is covered with an elastomeric material to absorb shock of impact of the blade on the abutment surface.

9. A propeller in accordance with claim 5 wherein said hub has a pair of flanges spaced apart along its axis of rotation with said blade roots disposed therebetween, and said pivot connection means comprises an axle disposed substantially parallel with said axis of rotation between said flanges, whereby the angular displacement of the blades is in a plane substantially normal to the axis of rotation.

10. A propeller in accordance with claim 5 wherein the center of mass of each blade is located outwardly from said axis of rotation of said hub a distance greater than the radial distance between said axis of rotation and said pivot connection.

11. A propeller in accordanc with claim 5 in which the outward and rearward location of the center of mass relative to a center of pivotal movement of each blade 10 thereof is so positioned as to generate calculable centrifugal force upon rotation of said propeller.

12. A propeller in accordance with claim 11 in which the generated centrifugal force will operate to bias the blades thereof in a pivotal motion precessive of the direction of rotation of the hub.

13. A propeller in accordance with claim 11 in which the developed centrifugal force shall be in equality with drag normal to the blades thereof, when said blades are in a position between said nested and extended positions.

References Cited UNITED STATES PATENTS 1,435,791 11/1922 Baker 170160.52 2,134,660 10/1938 Everts 41689(UX) 2,282,436 5/1942 Taylor 170-16052 2,885,012 5/1959 Heintzelman 170--160.11 3,077,229 2/ 1963 Heintzelman 170-16011 3,358,773 12/1967 Oldberg 17O160.11

EVERETIE A. POWELL, JR., Primary Examiner US. Cl. X.R. 416-143

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