US2850105A

US2850105A - Propeller mechanism with means to vary the pitch change rate

Info

Publication number: US2850105A
Authority: US
Inventors: Roy H Brandes
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1953-06-26
Filing date: 1953-06-26
Publication date: 1958-09-02
Anticipated expiration: 1975-09-02

Description

, Sept. 2, 1958 R. H. BRANDES 2,850,105

PROPELLER MECHANISM WITH MEANS TO VARY THE PITCH CHANGE RATE 2 Sheets-Sheet 1 Filed June 26, 195:

INVENTOR. Roy HBEANDES ATTORNEY p 2, 1953 R. H. BRANDES 2,850,105

PROPELLER MECHANISM WITH MEANS TO VARY THE PITCH CHANGE RATE Filed June 26, 1953 2 Sheets-Sheet 2 IN VEN TOR.

)EoY/i BRANDES;

A TTOE NE Y United States atent PROPELLER MECHANISM WITH MEANS TO VARY THE PITCH CHANGE RATE Roy H. Brandes, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application June 26, 1953, Serial No. 364,374

Claims. c1. 170160.21)

The present invention relates to variable pitch propellers, and more particularly to a fluid pressure system for adjusting the pitch position of propeller blades.

Heretofore, fluid pressure systems for adjusting the pitch positions of propeller blades have been of two distinct types. In one type fluid pressure is developed by mechanically driven pumps during propeller rotation, and by electric motor driven pumps when the propeller is stationary. In the other type an accumulator is employed to store fluid under pressure developed bythe mechanically driven. pumps during propeller rotation, which stored pressure fluid may be used to effect pitch changes when the propeller is rotating slowly, or is stationary. This invention pertains to a system of the latter type and relates specifically to means for increasing the rate of blade angle change by increasing the flow capacity of a control valve when accumulator pressure fluid is employed to effect pitch adjustment. It has been ob served that the pressure potential of fluid available for pitch adjustment when the propeller is rotating at normal propeller angular velocities, is appreciably higher than the pressure potential of fluid stored in an accumulator, and, hence, if the same flow rate is employed when using accumulator pressure fluid as is employed when the propeller is rotating and the pumps are supplying fluid under pressure, the rate of blade angle change will either be excessive during propeller rotation, or inadequate when the propeller is stationary, or rotating at a low angular velocity. Accordingly, among my objects are the provision of a propeller pitch adjusting mechanism including means for varying the rate of blade angle change; the further provision of mechanism of the aforesaid character including means for automatically increasing the rate of blade angle change below a predetermined rotational speed of the propeller; and the still further provision of centrifugally actuated means for varying the flow capacity of a control valve in a fluid pressure system for adjusting the pitch position of the propeller blades.

The aforementioned and other objects are accomplished means responsive to the speed of propeller rotation for determining the maximum port area of a control valve available for directing fluid flow to a servo-motor to effect an adjustment in the pitch position of propeller blades in one direction. Specifically, the rate of blade angle change in the decrease pitch direction is varied by the mechanism of this invention to enable the propeller blades to be moved from the full feathered position to any blade angle position in the positive thrust range with the requisite rapidity. The mechanism comprises a twoposition stop operatively associated with a flow controlling valve for determining the maximum flow port area available for the flow of pressure fluid to blade angle changing means in a decrease pitch direction. The mechanism functions to restrict the rate of flow through the control valve to the pitch changing means in a decrease pitch direction above a predetermined rotational speed of the 'ice 2 propeller. However, when the speed of a propeller drops below the predetermined rotational speed, the mechanism is automatically operable to remove the restriction to thereby permit increased flow rates to the blade angle changing means in the decrease pitch direction.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings;

Fig. l is a perspective view of a variable pitch propeller incorporating the mechanism of this invention.

Fig. 2 is an enlarged fragmentary sectional view taken on line 2-2 of Fig. 1.

Fig. 3 is a view, partly in section and partly in elevation, taken generally along line 3-3 of Fig. 4.

Fig. 4 is a fragmentary .-vi ew taken in the direction of arrow 4 in Fig. 2.

Fig. 5 is a schematic diagram of a fluid pressure system for controlling a variable pitch propeller incorporating the mechanism of this invention.

With particular reference to Fig. 1, a variable pitch propeller is shown including a hub 10 having a plurality of radially extending blade sockets 11 in which propeller blades 12 are supported for rotation about their longitudinalaxes. An accumulator 13 is attached to and rotates with the propeller hub 10. A regulator assembly 14 is, likewise, attached to the hub 10 and rotates therewith. The propeller hub 10 is operatively con.

nected to a shaft 15, which is operatively connected to any suitable prime mover, not shown, for imparting rotation to the propeller assembly. The propeller construction may be generally of the type disclosed in the Blanchard, et al. Patents 2,307,101 and 2,307,102, wherein a fluid pressure system for actuating torque units disposed within the root sections of. the blades, is housed within the regulator 14. 1

The present invention is disclosed herein in conjunction with the propeller control system disclosed and claimed in copending application, Serial No. 273,806, filed February 28, 1952, in the-name of Moore, et al. now U. S. Patent No. 2,745,500 With particular reference to Fig. 5, a partially schematic and block diagram of the fluid pressure system disclosed in the aforementioned application is shown incorporatingthe two-position stop mechanism of the present invention. The fluid system includes a pump 20, which is mechanically driven during propeller rotation. The pump is disposed within the regulator 14, and has an inlet 21 and an outlet 22, which communicates through a check valve 23 with a conduit 24. The conduit 24 has branch conduits connected to a pressure control valve assembly 25. The pressure control valve assembly 25 controls the pressure potential of fluid within a high pressure conduit 26 in accordance with the demands of a pitch changing servomotor 27. As the specific construction and operation of the pressure control valve assembly 25 is disclosed in the aforementioned copending application, and forms no part of this invention, the operation thereof Will not be described in detail herein. The high pressure conduit 26 communicates with a feathering control valve assembly 28, which controls the flow of pressure fluid from the accumulator, or pressure storage chamber 13 through conduit 29. The high pressure fluid conduit 26 also communicates with a pressure reducing and accumulator charging valve assembly 31, one portion of which controls the flow of fluid to the accumulator 13 through the conduit 32, and another portion of which supplies reduced fluid pressure to conduit 33, that connects with port 34 of a speed sensitive valve assembly 35. The

3. high pressure conduit 26 also communicates with a supply port 36 of a servo actuated distributor valve 37.

The speed sensitive value includes a housing 100 having a chamber 38 within which a sleeve 39 is supported with port opening 40 by reason of the annular channel between

lands

42 and 43 of the plunger 41 so that low pressure fluid is always supplied to a passage 48 in the valve housing.

Land 42 of the plunger 41 controls the flow of low pressure fluid through port 47 of the sleeve to a passage 49 in the valve housing. Passage 48 is connected through a selector valve assembly, designated generally by the numeral 50, to a conduit 51, which communicates with a servo chamber 52 of the distributor valve 37, while passage 49 is connected through the selector valve assembly 50 to a conduit 53, which communicates with a second servo chamber 54 of the distributor valve 37. The function of the selector valve assembly will not be described in detail inasmuch as it forms no part of the present invention except for the fact that it is employed to control actuation of the servo-motor 27 to move the propeller blades 12 to the feathered position and back to apositive thrust position in the governed speed regime.

Lever 45 has associated therewith a movable fulcrum 55, about which the plunger 41 of the speed sensitive valve tends to move the lever under the urge of centrifugal force under the direction of arrow 56. Upward movement of the plunger 41 is opposed by a tension spring 57, one end of which is attached to the end of lever 45, and the other end of which is attached to the stationary valve housing 100 of the speed sensitive valve 35. The speed of propeller operation in the governor speed regime may be varied by adjusting the position of fulcrum 55, by which the mechanical advantage of lever 45 may be varied.

The lever 45 includes an abutment portion 58, which is adapted to engage a stop pin 59. It is apparent that when the thrust of spring 57 exceeds the thrust of centrifugal force in the direction of arrow 56, the spring 57 will pivot the lever 45 about the fulcrum 55 and move the plunger 41 downwardly relative to the sleeve 39, as viewed in Fig. 5. The stop pin 59 i carried by a lever 60, one end of which is pivoted at 61 to a portion of the speed sensitive valve housing 100, and the other end of which is schematically shown as carrying a weight 62, which is responsive to the thrust of centrifugal force. During normal rotational speeds of the propeller, the

thrust of centrifugal force in the direction of arrow 56 6 is sufiicient to maintain lever with its weight 62 against a stop 63 in opposition to the force of the spring 57. Thus, during normal rotational speeds of the propeller the lever 60 and the stop pin 59 are in the full line position, as shown in Figure 5. It will be appreciated that within the normal rotational speed range of the propeller, the propeller speed can be less than the speed setting of the governor valve, and hence the spring 57 will pivot the lever 45 about the fulcrum 55 so that the abutment portion 58 moves toward the stop pin 59. Moreover, if the rotational speed of the propeller is sufficiently below the speed setting of the governor, the abutment portion 58 will engage the pin 59, in' which instance the governor valve is supplying maximum decrease pitch flow to the servo motor 27 as determined by the stop pin 59.

However, if the rotational speed of the propeller drops below the normal rotational speed range, for instance below 600 R. P. M., the force of the spring 57 acting through lever 45 and abutment 58 on the stop pin 59 will overcome the thrust of centrifugal force in the direction of arrow 56, and the arm 60 with its weight 62 will be moved to the dotted line position of Figure 5. in the dotted line position, as shown in Figure 5, the weight 62 engages a second stop 64. When the lever 60 is in the dotted line position as shown in Figure 5, the lever 45 under the urge of spring 57 can pivot about the fulcrum 55 and thus move the plunger 41 downwardly as viewed in Figure 5 so that the governor valve will supply a greater decrease pitch flow to the servo motor 27.

Accordingly, when the rotational speed of the propeller is above 600 R. P. M. the maximum decrease pitch flow to the servo motor 27 is less than the maximum decrease pitch flow to the servo motor 27 when the rotational speed of the propeller is below 600 R. P. M.

The servo actuated distributor valve 37 includes a plunger having spaced lands 71 and 72 that cooperate with

ports

73 and 74, respectively. Port 73 is connected by a conduit 75 to an increase pitch chamber 77 of the servo-motor 27, while port 74 is connected by a conduit 76 to a decrease pitch chamber 78 of the servo-motor 27. The servo-motor 27 is shown schematically as including a cylinder within which a reciprocable piston 79 capable of fluid pressure actuation in either direction, is disposed. The piston 79 includes a rod portion 80, which projects through an end wall of the servo-motor cylinder and has formed thereon a rack 81. The rack 81 meshes with a blade pinion 82 such that reciprocable movements of the piston 79 will move the blade 12 about its longitudinal axis so as to vary the pitch position thereof. The

conduits

75 and 76 also communicate with the pressure control valve assembly 25 in a manner more fully disclosed in the aforementioned copending application, Serial No. 273,806. The conduit 75 also communicates with a constant leak valve assembly 83, the function of which is, likewise, disclosed in the aforementioned application.

The plunger 70 of the distributor valve 37 includes a cam surface 84 on which a cam follower 85 rides, the cam follower being connected by means of a rod 86 to the sleeve 39 of the speed sensitive valve. The cam follower 85 is maintained in engagement with the cam surface 84 by means of a spring 65. The plunger 70 also includes a servo piston 87 exposed to the pressure fluid in servo chamber 52 for effecting movements of the plunger 70 to the right, as viewed in Fig. 5. The opposite end of the plunger 70 is engaged by one end of a rocker arm 83 pivoted at 89, the other end of which is engaged by a piston 90 exposed to the pressure fluid in servo chamber 54. As piston 90 is of larger area than piston 87, it is apparent that a lower pressure potential in chamber 5i will be required to move plunger 70 to the left, as viewed in Fig. 5, than will be required in chamber 52 to move the plunger 70 to the right.

It has been observed that during propeller rotation at normal angular velocities, the pump 20 maintains a pressure potential between 1000 and 1500 p. s. i. in the conduit 26. However, when the angular velocity of the propeller drops below 600 R. P. M., the pressure potential developed and the flow produced by the pump 20 is insuflicient for effecting pitch changing movements of the blades 12 out of the feathered position with sufficient and drain, respectively, for unfeathering. Normally, the

accumulator 13 has suflicient storage capacity to supply enough fluid flow to move the blades throughout at least one complete range of pitch change movement, that is,

from the negative low angle to full feather and return. However, the pressure potential of fluid stored inthe accumulator is appreciably less than the" pressure developed by pump 20 during propeller rotation at normal speeds, it being established that the pressure potential of fluid stored in the accumulator is approximately 500 p. s. 1.

Consequently, it is manifest that as the rate of blade angle change is proportional to the quantity of pressure fluid flowing per unit time to the servo-motor 27, when the pressure potential of the fluid is decreased, the flow rate will, likewise, be decreased through a given size orifice, or port area. However, the flow rate, and hence, the rate of blade angle change, can be varied by varying the flow port area so that the same, or greater, flow rates can be achieved at reduced pressure potentials. result is accomplished in the present invention by the centrifugally actuated stop pin 59 for the speed sensitive valve plunger 41, to insure an adequate rate of pitch change when pressure fluid of reduced pressure potential, is being used to eifect pitch adjustment toward a decrease pitch position.

Referring again to Fig. 5, the full line 91 indicates the lowermost position, which the upper surface of land 42 of plunger 41 can assume with the stop pin 59 in the solid line position. These conditions obtain when the angular velocity of the propeller is above 600 R. P. M., for example. However, when the angular velocity of the propeller drops below 600 R. P. M., for example, the weight 62 will move the lever 60 about its pivot point 61 so that the stop pin 59 is moved to the dotted line position of Fig. 5, wherein the upper surface of land 42 of the plunger 41 may move to the dotted line 92. Thus, it is apparent that when the propeller is rotating about 600 R. P. M., the opening of port 47 to the passage 38 and drain port 66 is restricted, while below a rotational speed of 600 R. P. M., the port 47 may be opened fully to drain, as indicated by the dotted line 92.

Downward movement of the plunger 41 from the position shown in Fig. 5, results in movement of the plunger 70 to the right such that port 73 will be connected to drain through port 66 and port 74 will be connected to the supply port 36, inasmuch as the servo chamber 54 is connected to drain through conduit 53, passage 49 and ports 47 and 66, while chamber 52 is connected to the low pressure conduit 33 through conduit 51, passage 48 and ports 46 and 40. Thus, high pressure fluid from conduit 26 will be supplied to the decrease pitch chamber 78 of the servo-motor through conduit 26, while the increase pitch chamber 77 will be connected to drain through conduit 75 and ports 73 and 66. It will be observed that inasmuch as the area of piston 90 is appreciably greater than the area of piston 37, in restricting the drain flow from servo chamber 54, the plunger 70 may never reach a position Where port 74 is fully open. In actual practice the arrangement is such that the control port 74 is only opened sufliciently to produce a blade angle change rate of about per second in a decrease pitch direction with a pressure potential between 1000 and 1500 p. s. i. in conduit 26. Thus, if the pressure potential in conduit 26 falls to say 500 p. s. i. due to propeller rotation below 600 R. P. M., the restriction of port 47 in permitting flow from servo chamber 54 to drain will result in an inadequate rate of pitch change in the decrease pitch direction. However, below 600 P. M. the stop pin 59 will have moved to the dotted line position, thereby permittingthe port 47 to be fully opened whereby the low pressure fluid in servo chamber 52 will move the plunger 70 to a position where port '74 is substantially fully open. In this manner it has been observed that the rate of blade angle change with a pressure potential of approximately 500 p. s. i. can be increased to approximately 8 per second. In this manner the propeller blades can be moved out of the full feathered position and into any position of the governed speed regime with the desired rapidity, when This the propeller is stationary, "or rotating below a predetermined speed, for example, 600 R. P. M. Sleeve 39 operates in a follow-up relation with respect to the operation of plunger 41. Inasmuch as the valve assembly 35 merely controls the position of the distributor valve plunger 70, while the distributor valve plunger 70 controls the rate of blade angle change, it will be appreciated that when the pin 59 is in its downward position, the plunger 41 can move downwardly a greater distance thereby permitting the distributor valve plunger 70 to move to a position wherein port 74 is fully open. However, due to the follow-up relation between the plunger 41 and the sleeve 39, when the pin 59 is in its upper position, as shown in Fig. 5, the distributor valve plunger 70 cannot be moved to a position wherein port 74 is fully open to the supply port 36.

With particular reference to Figs. 2 through 4, the structural embodiment of the speed sensitive valve assembly 35 will be described. As is shown in Fig. 2, the housing 100 of the speed sensitive valve assembly 35 is mounted on the front plate of the regulator 14 so that the speed sensitive plunger 41 is located on a radius from the center of rotation and thereby responds to the thrust of centrifugal force in the direction of arrow 56. As is shown, the tension spring 57 has one end attached to the housing 100. and the other end attached to. the lever 45. The housing 100 includes a bifurcated plate portion llll to which the bifurcated end portion of the speed responsive weighted lever 60 is pivotally attached by trunnions 102 and 103. The lever 60 carries the stop pin 59, which limits the downward movement of the lever 45 in Fig. 2. The plate member 101 has secured thereto a pair of screw devices 104- and 105 having shims 106 between the threaded portion and the head portion to define the limits of movement of a cross pin Hi7 carried by the lever 69. As shown in solid lines in Fig. 3, the cross pin M37 is in engagement with the shims 106, which represents the position lever 69 will assume under the thrust of centrifugal force due to propeller rotation above 600 R. l M. When the speed of propeller rotation falls below 600 R. P. M., the lever 60, which includes suflicient mass so as to be responsive to centrifugal force, will move in a clockwise direction about its trunnions, as is viewed in Fig. 3, to the dotted'line position where the ends of cross pin 107 will abut the lower side of the headed portions of the screw devices 1% and 105. It is apparent that clockwise movement of the lever 60, as is viewed in Fig. 3, will lower the position of stop pin 59, thereby permitting the lever 45 to move downwardly a greater distance under the thrust of spring 57.

From the foregoing, it is apparent that the present invention provides means for automatically increasing the flow capacity of a valve mounted in a centrifugal field, when the rotating structure to which the valve is attached rotates below a predetermined angular velocity. In this manner, the flow rate in the decrease pitch direction can be maintained at the requisite value with reduced pressure potential when the propeller is stationary, or substantially stationary.

While the embodiment of the present invention as here- 1 in disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A fluid pressure system for controlling the pitch position of propeller blades including in combination, a rotatable propeller having blades mounted for rotation about their longitudinal axes, fluid pressure operated means operatively connected with the blades for adjusting the pitch position thereof in either direction, a source of fluid pressure for actuating the pitch adjusting means, valve means connected to the source and to the pitch adjusting means for controlling the application of pressure fluid to said pitch adjusting means for varying the pitch position of said blades in either direction, and centrifugally actuated means operatively associated with said valve means and operable to limit the maximum rate of pitch adjustment in the decrease direction above a predetermined propeller speed.

2. In combination with a variable pitch propeller having blades mounted for rotation about their longitudinal axes to different pitch positions, fluid pressure operated means operatively connected to said blades for adjusting the pitch position thereof in either direction, a source of fluid pressure for actuating the pitch adju. "Lg mean valve means connected with said source and with said pitch adjusting means for controlling the flow of pressure fluid from said source to said pitch adjusting means for adjusting the pitch position of said blades in either direction, and ccntrifugally responsive means rotatable with the propeller and operatively associated with said valve means for restricting the permissible rate of flow from said source through said valve means to said pitch changing means in a decrease pitch direction above a predatemined rotation of speed of said propeller.

3. In combination with a variable pitch propeller having blades mounted for rotation about their longitudinal axes to different pitch positions, fluid pressure operated means operatively connected to said blades for adjusting the pitch position thereof in either direction, a source of fluid pressure for actuating the pitch adjusting means, valve means connected with said source and with said pitch adjusting means for controlling the flow of pressure fluid from said source to said pitch adjusting means for adjusting the pitch position of said blades in either direction, said valve means including an element rotatable with the propeller and movable in response to the thrust of centrifugal force established by rotation of said propeltor and a pivotally mounted assembly rotatable with the propeller and movable in response to centrifugal force including a stop pin operative.y associated with said valve element for limiting movement of said valve element in one direction, the construction and arrangement being such that the rate of flow to the pitch adjusting means in the decrease pitch direction is restricted above a predetermined rotational speed of said propeller.

4. In combination with a variable pitch propeller having blades mounted for rotation about their longitudinal axes to different pitch positions, fluid pressure operated means operatively connected to the blades for adjusting the pitch position thereof in either direction, a source of fluid pressure for actuating the pitch adjusting means, valve means connected with said source and with said pitch adjusting means for controlling the flow of pressure fluid from said source to said pitch adjusting means for adjusting the pit-ch position of said blades in either direction, said valve means including an element rotatable with the propeller and mounted for movement in responseto the thrust of centrifugal force established by propeller rotation in one direction, a lever having an intermediate fulcrum point, one end of said lever being pivotally attached to said valve element, resilient means acting on said lever about said fulcrum point so as to oppose the thrust of centrifugal force on said valve element so as to move the valve element in the opposite direction when the for-cc of the resilient means exceeds the thrust of centrifugal force, and a stop assembly rotatable with the propeller and responsive to the thrust of centrifugal force, said stop assembly including means operatively associated with said lever for limiting movement of said valve element by said resilient means in opposition to centrifugal force, the construction and arrangement being such that the stop assembly contrOls the maximum permissible rate of flow to the pitch adjusting means in the decrease pitch direction so that at rotational speeds of the propeller above a predetermined angular velocity of, the flow to the pitch adjusting means from the source through the valve means is restricted in the decrease pitch direction, whereas below said predetermined angular velocity the flow from the means may be virtually unrestricted.

5. In combination with a centrifugally responsive valve assembly mounted in a centrifugal field and adapted to control the rate of fluid flow from a source of fluid prersure to a servo-motor, a centrifugally responsive lever pivotally attached to said valve assembly, said valve assembly including a reciprocable element, the position of which is affected by the thrust of centrifugal force, and a two-position stop pin carried by said lever and engageable with said element for limiting movement of said element in one direction, the construction and arrangement being such that the position of said stop pin varies between said two positions dependent upon whether the thrust of centrifugal force is more or less than a predetermined value.

6. In combination with a valve assembly mounted in a centrifugal field and including a reciprocable element movable in one direction by the thrust of centrifugal force, resilient means operatively associated with said element for opposing the thrust of centrifugal force, and a two-position stop assembly pivotally connected to said valve assembly in said centrifugal field including means coacting with said valve element for limiting the movement of said valve element in one direction, the construc tion and arrangement being such that the position of said last recited means varies dependent upon whether the thrust of centrifugal force is more or less than a predo termined value and thereby limits movement of said valve element by said resilient means.

7. In a variable pitch propeller, the combination including, a rotatable propeller having a plurality of blades mounted for rotation about their longitudinal axes to vary the pitch position thereof in both directions, mocha nism operatively connected to said blades for adjusting the pitch position thereof, and centrifugally actuated means operatively connected with the pitch adjusting mechanism for varying the maximum rate of pitch adjustment in one direction when the speed of propeller rotation is above a predetermined value from the maximum rate of pitch adjustment in said one direction when the speed of propeller rotation is below said predetermined value.

8. In a variable pitch propeller, the combination in cluding, a rotatable propeller having a plurality of blades mounted for rotation about their longitudinal axes to vary the pitch position thereof in either direction, mcchv nism operatively associated with said blade for adjusting the pitch position thereof in both directions, and means rotatable with the propeller and actuated by the thrust of centrifugal force, said means having operative connection with said pitch adjusting mechanism so as to increase the maximum rate of pitch adjustment in one direction below a predetermined rotational speed of the propeller.

9. In a variable pitch propeller, a rotatable propeller having a plurality of blades mounted for rotation about their longitudinal axes to vary the pitch position thereof in either direction, fluid pressure operated mechanism for varying the pitch position of said blades including, a source of fluid pressure comprising pressure developing means associated with and operable upon rotation of the propeller and an accumulator having connection with the pressure developing means so as to be charged thereby. fluid pressure operated motor means having connection with said blades for adjusting the pitch position thereof, and valve means having connection with said source and said motor for controlling the application of fluid pressure from the source to the motor means, and centrifugally actuated means operatively connected with said valve means for limiting the rate of application of fluid pressure to said motor means by said valve means in one direction above a predetermined rotational speed of said propeller to thereby limit the maximum rate of pitch change of said propeller blades in said one direction.

10. In a variable pitch propeller, a rotatable propeller having a plurality of blades mounted for rotation about their longitudinal axes to vary the pitch position thereof in either direction, fluid pressure operated mechanism for altering the pitch position of said blades comprising, a source of fluid pressure including pressure developing means associated with and operable during propeller rotation and an accumulator having connection with said pressure developing means so as to be charged thereby, fluid pressure operated motor means having connection with said blades for adjusting the pitch position thereof, and valve means having connection with said source and said motor for controlling the application of pressure 15 fluid from the source to the motor, and means rotatable with the propeller and responsive to the thrust of centrifugal force, said means having operative connection with said valve means so as to increase the permissible rate of application of pressure fluid to the motor means by said valve means in one direction when the propeller is stationary and the accumulator is supplying pressure fluid.

References Cited in the file of this patent UNITED STATES PATENTS 2,626,669 Moore et al. Jan. 27, 1953 2,640,555 Cushman June 2, 1953 2,661,806 Nims et a1. Dec. 8, 1953