US2462932A - Pitch changing mechanism - Google Patents

Description

1, 1949. J, ANDERSON PITCH cmmeme MECHANISM 4 Sheets-Sheet 1 Original Filed April 8, 19 5 INVENTOR L izrlznfizfiderann Z/Lmfj/zww ATTORNEY PITCH CHANGING MECHANISM Original Filed April 8, 1943 4 Sheets-Sheet 2 INVENTOR finE/Zrdwsan at: i f z;

ATTORNEY arch 1, 1%. J. E. ANDERSON 2,462,932

PITCH CHANGING MECHANISM Original Filed April 8, 1945 4 Sheets-Sheet 3 INVENTOR LlbfinEflndar-san ATTORNEY 1949.. J. E. ANDERSON PITCH CHANGING MECHANISM ori inal Filed April 8, 1945 Sheets-Sheet 4 5 11mm HWHJ H Q Y a L. 7/ Q m: u: A!

INVENTOR ujzz finEflndet'san.

wwzwzm ATTORNEY valve and a lubricating Patented Mar. 1

John E. Anderson, Portland, Conn; minor to United Aircraft Corporation, East'Bar-tiord, Com, a corporation of Delaware Continuation of application Serial No. 482,265, April 8, 1943. This application died July 26,

1946, Serial No. 686,298

12 Claims. (Cl. INF-160.33)

This invention pertains to aeronautical propellers, with particular reference to an improved pitch changing mechanism.

The invention is an improvement on the invention of Caldwell et al., Patent Number 2,308,488,

issued January 19, 1943. This application is a continuation of application Serial No. 482,265 of John E. Anderson filed April 8,1943, now abandoned.

One object of the invention is to provide a follow-up valve having one element thereof positively movable in response to pitch changes ofthe blades, and another element which may remain fixed, may be governor controlled, or may be manually controlled, all at the will of the operator.

Furthermore, if the propeller is operating with. the controllable element of the valve in fixedpitch position, and the blades tend to creep to higher or lower pitch positions, the valve functions to Prevent the creeping.

Each blade is provided with a pitch-changing hydraulic motor of the vane type. Fluid for the motors is provided by a high pressure pump having several cylinders and pistons rotating with the propeller hub. The fluid exhausts from the motors into the hub mechanism where it is used for lubricating purposes, and finally drains to sump.

Another object is to provide a control valve with cooperating ports and lands dimensioned to provide a leak through the valve when the lands on the control valve are centered with relation to the ports in the follow-up valve, in order to maintain pressure in the vane motors to keep the blades at required angles against the blade twisting moments.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate what is now considered to be a preferred embodiment of the invention.

Fig. 1 is a front view of the hub portion of an aeronautical propeller constructed according to the invention.

Fig. 2 is a sectional View on line 22 of Fig. 1. Fig. 3 is a' diagrammatic illustration of the hydraulic system mounted on the hub for changing the propeller pitch, and particularly illustrating the follow-up valve, a high pressure safety pressure-maintaining valve.

Fig. 4 is a longitudinal sectional view on an enlarged scale or the control valve shown in Figs. 2 and 3.

Fig. 5 is a view on'line 5-5 of Fig. 2 showing the control valve in section and the locations of a the safety valves.

Fig. 6 is a transverse sectional view on line B-.5 of Fig. 2.

The propeller has a hub i0 (Fig. 2) with three bladesoclrets (Fig. 1). l2, l4 and Ii supporting blades I8, 20 and 22 in a manner permitting the steel balls 32, the balls being inserted through holes 34 in the wall of the sockets while the blades are in loading position with the end of vane motor 38 against ,hub l0, after which the holes are closed by plugs 36 and the blades are moved outwardly to their operative positions.

The pitch changing vane motor 38 (Fig. 2) is located within the shank of each blade, and is particularly illustrated and described in United States application Serial No. 474,638 filed February 4. 1943,.by John'E. Anderson and Arthur N. Allen, J r., for Propellers.

Each motor has fluid conduits, as indicatedat 40-42, 44-45, and 4 850 (Fig; 3). Each con- 7 duit, is, in reality, also connected by passages,

not shown, to the chamber diametrically opposite the chamber to which it is shown tobe connected in the drawing. .The vane motors diagrammatically shown in Fig. 3 are indicated by the numerals 38a, 38b and 380; Each motor comprices a fixed inner member 58 having a pair of abutments 59, and an outer member 60 having av pair of vanes 8i and rotatable about inner membar 58 to change the pitch of the blades. The fluid connections to the motors lead from manifolds62 and'G4 (Figs. 2 and 3) extending around the propeller hub, and these manifolds are connected with the control valve generally indicated at 66, by channels 68 and m; The passages 52, 54 and 56 take care of leakage from the vane motors.

The blades are interconnected for simultaneous and coextensive movements by a three piece adjustable bevel gear 12 (Fig. 2), rotatably supported on a bearing 13' mounted in hub III coaxial with shait 24 and meshing with gear sectors secured to the shank ends of the blades, the sector for blade 20 being indicated at 14 (Fig. 2). Limiting positions of the propeller blades in their pitch -changing movements are determined by stop rings 16 and 18 (Fig. 5) cooperating with a member 80 rotatable with gear 12. V

Fluid for operating the motors is supplied by a pump generally indicated at 82 (Fig. 2) and illustrated and described in detail in United States application Serial Number 482,264, filed April 8, 1943, by John E. Anderson for Pumps for. hydraulic pitch changing mechanisms. The pump comprises an annular header 84 surrounding the rearward portion of the propeller hub and carrying circumferentially spaced cylinders-86 (Figs. 1 and 2) within each of which is a piston 68 operable by a connecting rod 89 the ends of which are engaged by sockets in the piston and in the outer race of a ring 90 supported by rollers on an eccentric rim 9| carried by a sleeve 92, and having gear teeth 94 engaged by the teeth of gear 238 of an auxiliary feathering-motor 242 (Fig. 8), which is flxedly mounted'so as'not to rotate with the propeller shaft 24. Thus rotation of sleeve 92' is Prevented except as controlled by motor 242. The pump casing includes an annular reservoir or sump 96 towhich areconnected the suction ports of all the pump cylinders, and also includes a pressure manifold 98 connected with the discharge ports of the cylinders.

Valve 66 (Figs. 2, 3 and 4), comprises three concentric members, the fixed outer bushing I00,

the slidable intermediate follow-up sleeve valve I02 and the slidable inner control valve I04. Bushing I is fixed in the propeller hub parallel cured at its ends in follow-up sleeve I02v limits the extent of longitudinal movement of valve I04 relative to the sleeve. Pin I55 is also used for ad- 'justing, the position of the control valve through threaded rod I50. The pin is kept from rotating by engaging holes in follow-up sleeve I02, which in turn is prevented from rotating by pin I46 in slots I41. To adjust the position of'the control valve screws I53 are removed, sleeve I49 is rotated a proper amount, and screws I53 are replaced.

Member I54 is movable by a pitch control mechanism, not illustrated, but which may be of the character illustrated and described in United States application Serial No. 664,640, filed April 24, 1946, by Perin and Richmond for Propeller control means, and assigned to the assignee of this application. In such an arrangement a .servo-motor-operated rack I58 (Fig. 2) imparts a slight rotational movement to member I54 to cause a relative movement between external spiral splines I51 provided on member I54 and corre-y sponding internal spiral splines I59 in an annular member I60 rigidly secured, by annular bracket I62, to the front end of the casing of engine 25.

Because of the spiral arrangement of splines I61 and I59 the slight rotational movement bf member I54 will cause a longitudinal movement I of this member proportional to the movement of to the'axis of-shaft 24. ,Follow-up valve I02 is.

in the form of a sleeve provided with end lands I06 and I08 and intermediate lands H0 and II2,

the adjacent lands being separated by annular spaces in the sleeve, which overlie ports H4, H6 and H8 in bushing I00. Connecting with the above annular spaces, follow-up valve I02 is provided with ports I20, I22 and I24 leading from the-interior to the exterior thereof, and control valve I04 l i's provided with spaced lands I26 and I28 which serve to control ports I20 and I24 in a manner tobe presently described.

Sleeve valve I02 is moved in accordance with the pitch changing movements of the propeller blade through connection with blade synchronizing gear 12 (Fig. 2). To gear 12 is secured a spur gear I21 -which, through an idler pinion I32, drives pinion I34 formed at one end of sleeve I45 (Figs.

3, 4 and 6) in which are two helical cam grooves I43, 180 degrees apart, Sleeve I45 rotates around an inner'sleeve I49 which is provided with diametrically opposed longitudinal slots I41 (Figs.

2 and 4). A pin I46 through the end of valve I02 passes through slots I41 with each end of the pin in one of the cam grooves I43. Sleeve I49 and its slots I41 are non-rotatable with respect to the hub, being integral with cap II which is secured to the hub by screws I53 (Figs. 1, 2 and 4). With the above structure in mind, it will be realized that rotation of gear I34'wi1l rotate cam I45. Cam grooves I43 engage the ends of pin I46 and therefore move the pin longitudinally along slots I41, and the pin will movevalve I02 with it. .Thus is established the control of follow-up valve I02 from gear 1'2, through gear Control valve I04 is connected through a screw threaded rod I50 (Figs. 2 and 4) with a ring I52 a straight-toothed rack I58 which engages teeth I64 provided on a portion of member I54, For the number of straight teeth in I54 plus the necessary rotational travel, the spiral teeth in fixed member I60 are removed. Movement of rack I59 may also be utilized to turn the rotor of a generator I66 of a Selsyn pitch indicating apparatus particularly illustrated and described in United States Patent No. 2,393,189, flled June 13, 1942, patented Jan. 1946, by Ri hmon for Remote indicating means.

The pump pressure manifold 98 is connected (Figs. 2, 3 and 4) through pipe I68 and plug I10 (Fig. 2) with port I I6 in tube I 00, while channel 68 leading to manifold 62 is conneotedwith port H4, and channel 10 leading to manifold 64 is connected with port I I8. With this arrangement, fluid under pressure from the pump is supplied through port H6 in tube I00 and port I22 in follow-up valve I02 to the annular space within the valve between lands I26 and I28 of control valve I04. Flow of fluid from this space to either manifold 62 or 64 is controlled by movement of control valve I04. When that valve is moved to the left as viewed in Figs. 2v and 4, fluid will flow from the space within valve I02 between lands I26 and I28 of valve I04 through port I20 in valve I02,

and port H4 in tube I00, and thence through channel 68 to manifold 62 to supply hydraulic fluid to one side of each pitch changing motor. At the same time, exhaust fluid from the opposite sides of the motors will flow from manifold 64 through channel 10, port I I8 and port I24 to the interior of valve I02 and thence through channels I59 in sleeve I to the interior of the propeller hub.

When valve I 04 is moved to the right as viewed in Figs. 2 and 4, fluid will be supplied from I10 through ports II6, I22, I24, H8 and channel 10 to manifold 64, while the exhaust fluid from the opposite sideof the motors will flow from manifold 62 through channels 68 and H4, through ports I20 and holes I12, into valve I04, and thus through the front end of sleeve I02 into the propeller hub, asdescribed above.

When valve I04 has been moved a certain distance corresponding to a speed change demand of the governor control apparatus. one ,side of each motor will be connected with the fluid from the pump pressure manifold 88' in the-manner described above and the opposite sides of the motors will be vented to the sump 96. The rotatable portions of the motors will thereupon start to rotate turning the propeller blades to change the propeller pitch. As the blades are rotated gear I2 is also rotated, and it rotates member I45 causing pin' I46 to track through cam slot I43 and thereby moving follow-up valve I02 in the same direction in which the control valve I04 was moved. When the blades have changed their pitch an amount corresponding to the movement of valve I04, sleeve I02 will have reached a position in which ports I and I24 are again centered relative to lands I25 and I28 of control valve I04 and movement of the motors will thereupon cease. When valve I02 is in above position relative to plunger I04, lands I26 and I28 have negative lap, i. e., they fail to entirely cover ports I20 and I24 but provide bleeder openings through the ports and surplus output of the pump can flow through control valve I02 to drain. Thus the'valves act to unload the pump when the pitch changing motors are not operating and also maintains an equal pressure on both sides of the pitch changing motors. As soon, however, as control valve I04 moves with respect to follow-up valve I02 negative lap will be eliminated and the output of the motor will be directed to one side or the other of the pitch changing motors, depending upon the direction of movement of valve I04, and the opposite sides of the motors will be connected with drain in the manner described above. The position of valve I04 may be adjusted relative to ring I52 by the adjustable screw thread connection I94 (Fig. 2) to obtain the proper position of this valve relative to follow-up valve I02.

High pressure and low pressure relief valves, generally indicated at I96 and I98, respectively, and particularly illustrated in Fig. 3 are included in the pitch changing hydraulic system to supplement the operation of control valve 66. The high pressure relief or blow-off valve I96 is provided to vent the pump outlet at a predetermined safe maximum pressure in the event the control valve 66 should, for some reason, fail to entirely dispose of the pump output. The low pressure control or exhaust pressure valve, interposed between the space within the propeller hub and the sump 96 is provided mainly to insure that the hub remains full of fluid for lubricating purposes. The space within the hub which hydraulically connects valves 66, I96, and I98 is diagrammatically indicated by the channel 200 in Fig. 3. The

three valves are symmetrically arranged in the hub as indicated in Fig. 1.

The high pressure relief valve I96 comprises a plunger 202 urged toward valve closing position by a compression spring 204. This plunger has at one end a reduced extension 205 which projects into a cylindrical chamber 208 in the end of the hollow valve bushing 206 to provide a stop. Chamber 208 is connected through port 209 and channels 2I0, hollow plug 2 and channel 2I2 with pressure manifold 98. The area of the end of plunger 202 in the space 208 is slightly greater than the area of the end incontact with the spring 204, as indicated by the slight Ill shoulder 201, and a bore 2 extends 'longitudi- 2I8 to the space within the propeller hub diagrammatically indicated as pipe 200 which space is connected with sump 96 through the low pressure relief valve I98 (Fig. 3).

The low pressure relief valve I98 (Fig. 3) comprises a plunger 220 slidably mounted in a bushing 222 and urged to valve closing position by a relatively light compression spring 224. Bushing 222 is secured in a sleeve 223 which is in turn secured in the propeller hub. Fluid from hub space 280, entering the end of the sleeve 223 acts on the end of the plunger 220 urging it to move against spring 224. When this fluid pressure is sufflcient to overcome the force of the spring the plunger uncovers port 226, which is connected with sump 96 through channel 228 and plug 230.

Guide members 232 and 234 connected to ring I52 and slidably supported in the hollow valve bushings 206 and 222, respectively,.(Fig. 3) assist in maintaing ring I52 (Figs. 2 and 3) in operative position, and prevent the ring from warping out of alignment with the periphery of annular member I54.

Guide 234 is drilled, as indicated at 235, to provide a channel for lubricant from the interior of the propeller hub. to the interior of. the'annular groove in ring I52. This fluid flows from the'hub interior through channel 225, port 22I and the hollow interior of bushing 222 through a bore extending longitudinally through rod 234 and communicating with the groove containing ring I52. The pressure in 200 exerts equal thrusts on ring I56 through rods 232, '234 and valve I04 because the diameters of, rods and valve are the same.

The pump cam supporting sleeve 92 (Fig. 2) is normally held against rotation by a gear train including spur gear 238 and worm gear 240 con nected to an electric motor 242, (Fig. 3), the pitch of the worm gear 240 being so arranged that the gear train is not reversible. In case, however, it is desired to operate the pump to provide fluid for the pitch changing mechanism when the propeller is not rotating, motor 242 may be energized to drive member 92 through the above gear train'to provide fluid under pressure to unfeather the propeller in flight or to change the pitch of the propeller when the power plant is not operating, as when the airplane is on the ground.

While one embodiment of the invention has been described and illustrated, it is to be understood that the invention is not limited to the particular embodiment so illustrated and described, but that such changes in the size, shape, and ararngement of the various parts may be resorted to as come within the scope of the subjoined claims.

Having now described the invention so that others skilled in the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows:

1. In a controllable pitch propeller having a hub enclosing a central space and provided with blade retaining sockets, blades mounted one in tion of a fluid connection connecting said motorand a source of motor fluid under pressure and j each socket, and 'at least one hydraulic motor for turning said blades in pitch changing: direc-- tions, a motor controlling 'valve iorming'a por- 9 hub space, means operatively connecting. said a portion of. a fluid connection connecting said motor and the space within said hub for controlling the flow of motor iluid to and fromsaid motor and; venting. the exhaust fluid from said motor into said hub space, said valve comprising,

sleeve with said motor to impart to said sleeve lengthwise movements proportional to the movements of said motor, and aplunger slidable in saidsleeve movable by a propeller pitch changing mechanism and provided with spaced lands cona sleeve having a central port connected with said source of motor fluid under pressure and end ports connected with the opposite sides of said] motor and with said hub space, means operatively connecting said sleeve with said motor to1imtrolling the connections of said end ports with said-center ports and said hub space, the means 7 connecting said sleeve with said motor comprism a fixed hollow member having a slot therein,

. .ahonow rotatable member surrounding at least a portion of said flxed member and having a spiral 'part to said sleeve lengthwise movements pro portional to the movements of said motor, a

plunger slidable in said 'sleeve movable by a:

"cam track therein of a shape diflerent from said slot, a pin extending transversely through said cam track and said slot and said sleeve, a gear I [train operated by said motor for rotating said propeller pitch changing mechanism and provided with spaced lands controlling the connections of said end ports with said center port and said hub space, said valve being disposed rotatable member, a blade synchronizing gear in said hub, and gear teeth on said blade synchronizing gear driving said rotatable member.

in a bore in said hub, and a detachable cover e a source of motor fluid under pressure and a portion of a fluid connection connecting said motor and the space within said hub for controlling the 4 flow of motor fluid to and from said motor and venting the exhaust fluid from said motor into said hub space said valve comprising, a sleeve having a central port connected with said source of motor fluid under pressure and end ports connected with-the opposite sides of said motor and connectable with said central port or with said hub space, means operatively connecting said sleeve with'said motor to impart to said sleeve lengthwise movements proportional to the move-.

ments of saidmotor, a plunger slidable in said sleeve movable by a propeller pitch changing mechanism and provided with spaced lands controlling the connections of said end ports with said center port and said hub space, the means operatively connecting said sleeve with said motor comprising a fixed hollow member having a slot therein, a hollow rotatable member surrounding at least a portion of said flxed member and having a spiral cam track therein of a shape different from saidslot, a pin extending transversely through said cam track said slot and said s1eeve,a gear train operated by said motor for rotating said rotatable membenf 3. In a controllable pitch propeller having a hub enclosing a central space and provided with blade source of motor fluid under pressure and a portion of a fluid connection connecting said motor and the space .within said hub for controlling the 'flow of motor fluid to and from said motor and venting the exhaust fluid from said motor into said hub space, said valve comprising, a sleeve havinga central portconnected with said source or motor fluid under pressure and end ports con- 4. In apropeller having pitch changing means,

blades mounted for pitch adjusting movement and a pitch-controlling follow-up valve in the propeller hub, means connecting said blades with one portion of said follow-up valve comprising, a sleeve'driven at a fixed ratio of the amount of movement of said blades, and a sleeve flxed with respect to said hub, one of said sleeves having a spiral cam slot therein, a pin connecting said position of said flxed sleeve with respect to said hubto adjust the relation between said valve portion and said blades.

5. In a propeller having pitch changing means, blades mounted'for pitch adjusting movement and a two-part,pitch-control1ing follow-up valve in the propeller hub, means connecting said blades with one part of said follow-up valve comprising, a sleeve rotatable at a fixed ratio of the amount of rotation of saidblades and a sleeve flx'ed with respect to said hub, said rotatable sleeve having a spiral cam slot therein, said fixed sleeve having an axially extending slot therein, a pin flxed with respect to said one valve part and passing through the slots in said sleeves, means including a screw-threaded joint connecting the other part of said follow-up valve witha control device, means preventing relative rotation of the two parts of said follow-up valve, means for adjusting the position of said flxed sleeve with respect to said hub to move said pin in said spiral cam slot and move said other valve part on said threaded connection to adjust the relation between said other valve part and said blades.

6. In a propeller having pitch changing means, blades mounted for pitch adjusting movement and a pitch-controlling follow-up valve in the propeller hub andplaced eccentrically with respect to the propeller shaft, means connecting said blades with one portion of said follow-up valve comprising, a sleeve mechanically connectedwith said blades to be driven at a multiple of the pitch changing speed of said blades, and a sleeve fixed with respect to said hub, one of said sleeves having a spiral cam slot therein, a pin connecting said valve portion and said sleeve and: passing through said cam slot.

'7. In a propeller having pitch changing means, blades mounted for pitch changing movement and a pitch-controlling follow-up valve in the propeller hub and placed eccentrically with respect to the pri'lpeller shaft, means connecting said blades withone portion of said follow-up valve comprising, a sleeve mechanically connected with said blades to be driven at a multiple of the 'pitch changing speed of said blades, and a sleeve fixed with respect to said hub, one of said sleeves having a spiral cam slot therein, a pin connecting said valve portion and said sleeve and passing through said cam slot, means for adjusting the position of said fixed sleeve with respect to said hub to adjust the relation between said valve and said blades.

8. In a controllable pitch propeller having a hub enclosing a central space and provided with blade retaining sockets, blades mounted one in each socket, and at least one hydraulic motor for turning said blades in pitch changing movements, a source of fluid pressure, a sump, a first fluid connection connecting said motor and said source, a second fluid connection connecting said motor and said space and a third fluid connection connecting said space and said sump, a motor hontrolling valve forming a portion of said first and second fluid connections for controlling the flow of fluid from said source to said motor and from said motor to said sump through said space, means forming a portion of said third connection for maintaining fluid in said space at a relatively low pressure.

9. In a controllable pitch propeller having a hub enclosing a central space containing movable blade mechanism, and provided with blade retaining sockets, blades mounted one in each socket, and at least one hydraulic motor for turning said blades in pitch changing movements, a source of fluid pressure, a sump, a first fluid connection connecting said motor and said source, a second fluid connection connecting said motor and said space and a third fluid connection, sepakate from said second connection, connecting said pace and said sump, a motor controlling valve forming a portion of said first and second fluid onnections for controlling the flow of fluid from aid source to said motor and from said motor( to said sump through said space.

10. (In a controllable pitch propeller having a hub enclosing a central space containing movable blade mechanism and provided with blade retaining sockets, blades mounted one in each socket, and at least one hydraulic motor for turning said blades in pitch changing movements, a source of fluid pressure, a sump, a first fluid connection connecting said motor and said source, a second fluid connection connecting said motor with one portion of said space and a third fluid connection, separate from said second connection, connecting another portion of said. space with said sump, a motor controlling valve forming a portion of said first and second fluid connections for controlling the flow of fluid from said source tosaid motor and from said motor to said sump through said space.

11. In a controllable pitch propeller having a hub enclosing a central space containing movable blade mechanism and provided with blade retaining sockets, blades mounted one in eachsocket, and at least one hydraulic motor for turning file of this patent:

UNITED STATES PATENTS Number Name Date 1,351,753 Haver Sept. 7, 1920 1,510,436 Engleson Sept. 30, 1924 1,957,183 Schmitthenner May 1, 1934 2,184,143 Hoover Dec. 19, 1939 2,205,625 Mader June 25, 1940 2,229,058 Dicks Jan. 21, 1941 2,280,713 Martin Apr. 21, 1942 2,280,714 Martin Apr. 21; 1942' 2,296,288 Martin et a1 Sept. 22, 1942 2,296,348 Hoover Sept. 22, 1942 2,307,102 Blanchard et al Jan. 5, 1943 FOREIGN PATENTS Number 1 Country Date 78,915 Switzerland Sept. 17, 1918 703,319 Germany Mar. 6, 1941 217,669 Switzerland Apr. 16, 1942 10 said blades in pitch changing moyements, a source of fluid pressure, a sump, a first fluid connection connecting said motor and said source,

a second fluid connection connecting said motor and said space and a third fluid connection, separate from said second connection, connecting said space and said sump, a pump continually operated by rotation'of said propeller and connected with said sump and said source for pumping fluid from said sump into said source, a motor controlling valve forming a portion of said first and second fluid connection for controlling the flow of fluid from said source to said motor and from said motor to said sump through said space.

12. In a controllable pitch propeller having a hub enclosing a central space containing movable blade mechanism and provided with'blade retaining sockets, blades mounted one in each socket, and at least one hydraulic motor for turning said blades in pitch, changing movements, a source of fluid pressure, a sump, a first fluid connection connecting said motor and said source, a second fluid connection connecting said motor and said space and a third fluid connection, separate from said second connection, connecting said space and said sump, a pump continually operated by rotation of said propeller and con-' nected with said sump and said source for pumping fluid from said pump into said source, a motor controlling valve forming a portion of said first and second fluid connection for controlling the flow of fluid from said source to said motor and from said motor to said sump through said space, said valve having lands and ports in which the lands are of less extent than the ports so that in central position the source is continuously connected with said sump through said space to continuously circulate said fluid through said space when the propeller is operating and the valve is in central position.

JOHN E. ANDERSON.

REFERENCES CITED The following references are of record in the

Images