US2174717A - Multiposition controllable pitch propeller - Google Patents

Description

Oct. 3, 1939. F. w. CALDWELL ET AL I 2,174,717

IULTIPOSITION CONTROLLA BLE PITCH PROPELLER Filed 1m 4'. 193a 4 Sheets-Sheet 1 dwell F. w. CALDWELL ETAL 2,174,717

IULT'IPOSITION CONTROLI ABLE PITCH PROPELLER 4 Sheets-Sheet 4 Filed Aug. 4, 1,936

IIIIIIIIIIHHH I 1 II III IHHIHII "Inn".

- INVENTOR. E'uanK Era/dwell Erie Mar-23in.

' ATTORNEY Patented Oct. 3, 1939 UNITED STATES PATENT OFFICE MULTIPO SITION OONTROLLABLE PITCH PROPELLER Delaware Application August 4, 1936, Serial No. 94,202

29 Claims.

This invention relates to improvements in multiposition controllable pitch propellers and more particularly to'propellers which may be'governor controlled and also adjusted to feathering position.

An object of the invention is the provision of a propeller which may be controlled either by hand or a governor through a predetermined working range, and may also be adjusted so that its blades are in a feathering position.

Another object is the provision of a propeller requiring, as a safety feature, special deliberate action to change its blade pitch from the normal working range, throughout which normal range its propulsive action is effective.

Another object is the provision of a propeller whose pitch may be changed from a position in which the blades are substantially parallel to the propeller shaft axis to a position in which the 20 blades are in reversed pitch.

Another object is the provision of a propeller in which the blades are normally turned in one direction by the action of centrifugal force, but may be turned in that same direction by means 25 of hydraulic pressure at a time when no centrifugal force is available.

. Other objects and advantages will be more particularly pointed out hereinafter, or will become apparent as the description proceeds.

30 In the accompanying drawings in which like reference numerals are used to designate similar parts throughout, there is illustrated a suita'ble'me'chanical embodiment for the purpose of disclosing the invention. The drawings, how- 5 ever, are for the purpose of illustration only and are not to be taken as limiting the invention, the scope of which is to be measured entirely by the scope of the appended claims.

In the drawings,

. Fig. 1 is a sectional view of a three-bladed pro- 50 Fig. 6 is a detail of the stationary cylindrical cam.-

Fig. 7 is a section taken along the lines 'I'-'! of Fig. 1, showing the spring connection between the blade and its operating gear.

. Fig. 8 shows a modification. of the propeller shaft structure to permit breathing through the propeller shaft.

Fig. 9 is a schematic view of the propeller and its control devices.

Referring to the drawings in detail, the nu- 5 merallll indicates the propeller shaft on which is mounted a spider 12 carrying blades 14, which blades are preferably of metal and are held in position by the hub barrel l6. Any metal suitable for a propeller blade will, as is well known, have a high modulus of elasticity compared with the modulus of non-metallic materials. This blade mounting is generally similar to the blade mounting shown in Patent No. 2,032,255 of Frank W. Caldwall, to which reference is made for a more complete description. The description herein will be confined, therefore, to features which differ from that disclosure.

The hub barrel I6 carries at its forward portion a housing H! which encases the propeller pitch changing mechanism. This pitch changing mechanism comprises generally, a piston 20 formed of concentric sleeves 2| and 23 joined at their forward ends by web 25. This piston 20 carries pins 22 on which are mounted a series of 25 ball bearings 24 and 26. The ball bearings 24 coact with a stationary cylindrical cam 28, and the ball bearings 26 coact with a movable cylindrical cam 30. The cam paths of these cams slope in opposite directions so that axial move- 30 ment of the piston 20 will cause rotary movement. of that piston and also increased rotary movement of the movable cam 30. Motion of the cam 30 is transmitted by means of gear teeth to the blades M to thereby change their pitch.

Fluid under pressure is led through the hollow shaft ID to the side of the piston 20 adjacent the propeller blades to change the pitch of said blades in one direction. In the embodiment shown, the pitch is increased in this manner. Under normal operating conditions, the blade pitch is changed in the opposite direction by the action of centrifugal force. The above described principle of pitch changing is disclosed generally in Patent No. 1,893,612 of Frank W. Caldwell, to which reference is made for more detailed description. It is obvious, however, that by a suitable arrangement of parts the principle of operation disclosed in Patents Nos. 2,032,254 and 2,032,255 of Frank W. Caldwell could be utilized.

The fluid, which may be engine lubricating oil or any other suitable fluid, is led through a passage 32 of plug 34, and passage 36 of plug 38, and through holes 40 onto one side of'the piston 20. The fluid, after passing through the holes "40',

may then flow around the pitch changing cams and in the space 42 between the inner and outer portions of the piston 20, but is prevented from passing the piston by the packing 44 secured to the piston 20, and the packing 46 secured to the tube 48, which in turn is secured to the engine shaft Ill. The tube 48 is part of an assembly comprising elements 48, 50, 52, 54, 56, and 60, which are all brazed or otherwise rigidly secured together into a single fluid tight unit assembly. This assembly is held in position by the nut 62 which forces this assembly against the plug 38 which in turn is held in position by the tube 64 and the pins 66 which pass through that tube.

The fluid after passing through holes 40 is also free to flow throughout the interior of hub barrel l6. The fluid is prevented from passing between the spider and engine shaft by packing 68, is prevented from passing between the hub barrel l6 and the housing l8 by packing 10, is prevented from passing between the hub barrel l6 and the blades 14 by packing I2, is prevented from passing between the hub barrel l6 and the spider l2 by packing l3, and is prevented from passing between the hub barrel sections by packing 14. Packings 16 and TI prevent the oil from escaping from the interior of engine shaft ID. The normally round packing 14 which may be of any suitable material, rubber and lead having been found satisfactory, is compressed within, and takes somewhat the shape of, the elongated mating grooves in the sections of hub barrel l6. Oil pressure wedges the packing tighter, and in the case of rubber may swell the packing.

It is both undesirable and dangerous to have the packing 12 rub upon the highly stressed portion of the propeller blade l4. In order, therefore, to prevent such action, and also to act as a cushion for the propeller bearing 15, a layer of hardened plastic material such as a Micarta" layer 19 which has a low modulus of elasticity is molded onto the surface of the blade end as indicated in Fig. 1. If desired, this Micarta may be finished in place after molding to obtain the desired shape and size. This Micarta serves as a bearing for the packing I2, preventing wear of the propeller blade. It also serves as a resilient backing for the bearing 15. The bearing 15 may comprise the usual loose rings having balls or rollers therebetween as shown and described in Patent Number 2,032,255, above referred to. .These rings will have a high modulus of elasticity, and may be of the form shown in Patent No. 2,101,149 in which the ring con tacts with the blade on a relatively small portion of the area of said ring or it may be of the form shown in Patent #2,032,255 in which the ring contact is throughout substantially its entire area.

From the above description it will be observed that when oil under pressure is introduced into the interior of hollow shaft 10, it will act to move the piston 20 to change the blade pitch and to lubricate all the working parts of the propeller and its pitch changing mechanism thus far described. When the interior of the hollow shaft I0 is connected with a drain and the pressure inside of the shaft thereby relieved, the action of centrifugal force on the blades l4 will act to reduce their pitch and will act through the cams 28 and 30 to return the piston 20 toward the position shown in Fig. 1 and also force oil out of the propeller shaft l0.

Referring to Fig. 6, it will be noted that the cam path 18 materially changes its slope at the point 80. Referring to Fig. 5, it will be noted that the cam path 82 materially changes its slope in a similar manner at point 84.

During the normal operation of the propeller, the pressure of the fluid that is introduced into the interior of the shaft I0 is limited to a predetermined amount, say, 200 lbs. per sq. in. This pressure acting on the piston 20 is insuflicient to force bearings 24 and 26 beyond the points and 84 because of the increased slope of the cams beyond these points. This change in slope of the cams, therefore, acts as a stop and determines the high pitch position of the propeller blades under normal operating conditions. This stop acts as a safety device by preventing the accidental positioning of the propeller blades in such a high pitch position that the engine propeller combination would be unable to develop an effective thrust.

The slope of the cam paths at 86 and 88 is such, however, that bearings 24 and 26 may be forced therealong by increasing the fluid pressure in the interior of the shaft I 0 to a predetermined amount, say, 300 lbs. per sq. in., this increased pressure acting on the piston 20 will then force the piston outwardly and turn the blades into a greatly increased pitch position. In the now preferred form, the increased pitch position selected is such that the faces of the blades are substantially parallel to the axis of the propeller shaft. In that position the propeller will no longer act as a windmill, so that, if the engine power is shut off, the propeller will remain stationary. One of the main advantages of placing the blades in this increased pitch, or feathered,

. position, is that the drag of the propeller is greatly reduced. In the event of engine failure in a multiengine ship, this means of reducing drag is particularly important.

In order to change the pitch of the propeller blades from feathering back to a lower pitch position, fluid under presure is permitted to pass from the side of the piston adjacent the propeller onto the forward side of the piston. The piston 29 is so constructed that the effective area on the forward side is greater than the eeffctive area adjacent the propeller blades. Because of this difference in area, equal presures on both sides of the piston will therefore tend to move the piston rearwardly toward the propeller blades. The above-mentioned difference in area is obtained by providing the sleeve 23 of the piston 20 with a projecting flange 90 which carries packing 92 which in turn slides upon the sleeve 52.

A valve 94 is inserted in one or more of the pins 22 and is held closed by a spring 96. This spring and valve are of such size that the valve will be held closed until the fluid pressure acting on the rear side of piston 20 reaches a predetermined amount, greater than the pressure required to turn the blades into feathering position, say, 400 lbs. per sq. in. This last-mentioned increased fluid pressure is sufficient to open valve 94 against the action of spring 96. The interior of the pin 22 below the piston 98, as seen in Fig. 1, is connected by passage I00 and holes I02 to the interior of sleeve 52 and tube 64. The tube 64 is in turn connected to a drain which would probably be the engine sump in the event engine lubricating oil were used for actuating the propeller pitch changing mechanism. The tight fit between sleeve I04 and the piston sleeve 23, and the tight fit between the pin 22 and the piston sleeve 23, prevent the leakage of oil under pressure acting on the rear of piston 20 into the drain passage 75 I00. When the valve 94 is open, the fluid under pressure may pass through conduit I06 from the rear side of the piston to the forward side thereof. The plunger 98 acts to prevent oil, after passing the valve 94, from entering the drain passage I00. If desired, the area of the plunger 98 may be made larger than the area of the seat of the valve 94 to maintain the valve in open position at a pressure lower than that required to open the valve. found preferable to have the valve seat and the plunger 98 of substantially the same area.

A valve, indicated generally at I08, acts to either retain oil under pressure in the space forward of the piston 20, or connect that space with a drain by means of holes I I and the. interior of sleeve 52. This valve is normally held open by the spring H2 and floating bushing II4. At the time that the blades have been placed in their desired feathered position by movement of the piston 20 to the right as seen in Fig. 1, the face I I6 of the flange 90 contacts with the face II8 of the valve body I20 and closes the valve I08 against its seat I22. Shortly after this valve is closed, positive stops I 24, carried by disc I25, coact with abutments I26 to positively limit the travel of the piston 20 in a manner which is described more in detail below. When fluid under pressure is introduced into the space to the right of piston 20, as seen in Fig. 1, this fluid acts upon the exposed area of valve I08 and maintains that valve in its closed position. The valve I08 may be opened either by a reduction of the pressure surrounding that valve to a value insuflicient to keep the valve closed against the tendency of spring II2 to open the valve, or by movement of the piston 20 to the left as seen in Fig. 1, suflicient to cause nut I28 to contact adjustable nut I30 and move the valve I08 to the left, as seen in Fig 1. Shortly after valve I08 is opened by movement of piston 20 to the left, positive stop I32 carried by disc I34, contacts abutment I26 on movable cam 30 to limit further movement of the piston in that direction. As indicated above, opening the valve I08 connects the surrounding space with a drain and acts to relieve the pressure in that area and permit travel of the piston to the right upon the closing of the valve 94 and introduction of fluid under pressure to the left hand side of the piston.

In the preferred form, the capacity of the pump supplying the fluid under pressure for changing the propeller from feathered position to a lower pitch position, and the size of the holes IIO, are so proportioned that although the pump may continue to operate, the pressure of the fluid acting on the piston 20 and plunger 98 is so reduced that the valve 94will close under the action of its spring 96. It would, however, of course be possible to so proportion the pump and the size of the holes H0, so that even with the valve I08 open, the pump could maintain suflicient pressure on the piston to hod the valve 94 open and thus hold the propeller in its low pitch position by fluid pressure. If the valve I08 is open when the propeller pitch is within its normal operating range, the propeller may then be operated in the normal manner first above described.

The discs I25 and I34, carrying stops I24 and I32 respectively, are adjustably secured against rotation in stationary cylindrical cam 28 by teeth I36. These discs I25 and I32 surround the portion I38 of the movable cylindrical cam 30 and hold the stops I24 and I32 in the path of the r abutments I26. From the above description it is In practice, however, it will probably be apparent that by suitably adjusting the discs I25 and I34, the abutments I26 may be caused to contact the stops I24 and I32 at any desired predetermined position, and thus determine the lim itinz nit-ch nositions of the propeller blades.

The now preferred method of operating the above described propeller is as follows: oil under pressure is supplied from an engine sump I40 (see Fig. 9), by a pump I42 which may be the pump which supplies lubricating oil to the engine, a portion of which is shown at I44. The oil under pressure is led to a governor I46 which may be of any suitable type, the particular one shown being similar to that shown and described in application, British Patent No. 470,282 to the Woodward Governor Company, accepted August 12, 1937 suitably altered, however, to accommodate the reversed direction of the action of centrifugal force and oil pressure on the propeller blades. Means I48 are provided on the governor for selecting the desired engine speed and also for positively setting the goverenor valve to connect the propeller actuating mechanism with the drain. A conduit I50 leads from the governor to an automatic valve I52, the outlet I54 of which connects with the interior of hollow propeller shaft I0. Action of the governor in admitting fluid to the interior of shaft I0, or connecting that space with the drain, will cause movements of the piston 20 and changes of pitch of the blades within the normal operating range of the propeller, the lower pitch of which may be determined by the stop I 32 and the upper limit of which is determined by the change of slope of the cam paths I8 and 62.

When it is desired to feather the propeller, fluid under increased pressure is provided by means of a pump I56, taking oil from any suitable place such as the engine sump or reserve tank I40. This pump is connected with inlet I58 of automatic valve I52. Upon operation of this pump the plunger I60 of valve I52 is lifted from its seat and closes the connection between the governor and the outlet I54, and connects the pump I56 with that outlet. As indicated above, this fluid under increased pressure forces the bearings 24 and 26 along the cam tracks 86 and 88 of increased slope and thereby moves the propeller blade to feathered position. Setting of the governor I46 will not prevent operation of the plunger I60 under the increased pressure of the pump I56. If the governor valve is in position to .connect conduit I50 with the drain, plunger I60 will, of course, be free to move. If, on the other hand, the governor valve is in a position to connect the conduit I50 with the pump I42, or other source of pressure, the usual relief valve on that pump or source of pressure, will act to relieve suflicient fluid to allow the plunger I60 to move under the increased pressure produced by the pump I56. The pump I56 may also supply fluid of sufficient pressure to'open the valve 04, thus admitting oil to both sides of piston 20 and thereby moving the propeller blades to a lower pitch position.

Fig. 7 shows the means conneecting the gear I62 with the propeller blade I4, this connection being made by means of spring packs I64 and bushing I66. These spring packs I64 are so arranged that during the entire range of propeller blade movement, they tend to force the propeller gear I62 into contact with the gear on the movable cam 30. The slots in the members I62 and I66 into which the spring packs are placed are machined so that thegear I62 is normally held eccentric to the sleeve I66. When the structure is assembled, the gear on movable cam 30 acts to move the gear I 62 relative to the bushing I66 and blade 14 to bring these elements substan' tially concentric and place these spring packs under load. This not only provides a flexible connection between the propeller and its driving gear, but also serves to pre-load the gear I62 and prevent any backlash between it and the gear on movable cam 30.

The structure shown in Fig. 8 is a modification of the propeller shaft shown in Fig. 10 to permit breathing of the engine through the interior of this shaft. In this structure, the sleeve I68 is open at one end to the interior of the engine crankcase and at the other end to the atmosphere, a screen I10 being provided at the atmospheric end. In this modification, the space between the tubes 52 and I68 leads to the drain. Oil under pressure is supplied through groove I12 cut in the forward bearing between the propeller shaft l0 and engine shaft I14.

Because of the similarity of the remaining part of the structure to that shown in Fig. 1, it is believed that its construction and operation will be understood from the description of Fig. 1 and the showing of Fig. 8.

While there has been illustrated and described a particular mechanical embodiment of what is now considered to be the preferred form of the invention, it is to be understood that the invention is not limited to the particular mechanical embodiment so illustrated and described, but that such changes in the size, shape, and arrangement of parts may be resorted to as come within the scope of the appended claims.

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

1. A controllable pitch propeller having in combination, a hub carrying movably mounted blades, a governor for controlling the pitch of said propeller below a predetermined high pitch limit, means independent of the governor for moving the blades to a pitch above the governor controlled high pitch limit, and means also independent of said governor for returning said blades to a pitch below the governor controlled high pitch limit.

2. In a controllable pitch propeller, in combination, blades movable in one direction to increase their pitch and movable in the other direction to decrease their pitch, fluid actuated means for moving said blades in both directions, said means including an element having different effective areas on different sides thereof, means for introducing fluid under pressure onto one side of said element to move the blade in one direction, and means for introducing fluid under an increased pressure onto both sides of said element for moving said blades in the other direction.

3. A controllable pitch propeller having in combination, a hub carrying movably mounted blades, a liquid pressure actuated device for moving said blades in one direction, said blades being turned inthe opposite direction by centrifugal force produced by rotation of said propeller when said liquid pressure is relieved, a source of fluid of predetermined pressure, means controlling the flow of said fluid from said source to said device for controlling the blade pitch between predetermined limits determined by limit stops, at least one of which stops is effective only when said pressure actuated device is subjected to a fluid pressure not materially greater than said predetermined pressure, a source of fluid having a pressure materially higher than said predetermined pressure, and means for introducing fluid under said last-named higher pressure to said liquid pressure actuated device to change the blade pitch beyond said one predetermined limit stop.

4. A propeller and pitch changing mechanism therefor comprising in combination, a hub carrying movably mounted blades, fluid operated means operatively connected with said blades, mechanism for introducing fluid under pressure to one side of said means for moving the blades in one direction through a normal working range, said blades being turned in the opposite direction by the action of centrifugal force when said fluid pressure is relieved, a governor for controlling the flow of fluid to and from said means, stops for limiting the extent of said normal range, a source of fluid pressure, means for introducing fluid from said source to said means for changing the pitch beyond said normal range, a valve actuated by said fluid from said source for disconnecting the governor controlled fluid from said means and for connecting said source with said means, stops for limiting the extent of pitch change beyond said normal range, and means for returning the blade pitch to a position within said normal range.

5. In a controllable pitch propeller, movably mounted blades, a piston operably connected with said blades and having different effective areas on its opposite sides, means for introducing fluid under pressure onto one side of said piston for moving said blades in one direction to change their pitch, a valve controlling a passage between the opposite sides of said piston, and operable by the fluid under pressure on one side of said piston when that pressure reaches a predetermined value to open the passage and introduce fluid from said one side onto the opposite side of said piston and move the piston in the opposite direction to change the blade pitch in the opposite direction.

6. In a fluid actuated device having different effective areas on different sides thereof, in combination, means for introducing fluid under pressure limited to a predetermined amount to one side of said device for moving said device in one direction, an exhaust conduit leading from the other side of said device, a valve operated by a predetermined difference in pressure on the two sides of said device, connecting said different sides, means for closing said exhaust conduit, and means for introducing fluid under a pressure greater than said predetermined amount to said one side to operate said valve to admit fluid under said last named pressure to the other side also to move said device in the opposite direction.

7. In a piston. and cylinder construction in which the piston is actuatable in both directions by fluid under pressure, means for applying fluid under pressure to both sides of said piston, means connecting the space at one side of said piston with a drain, a valve for closing said connecting means, means normally holding said valve open, means actuated by said piston for closing said valve when the piston has traveled a predetermined distance in one direction, and means actuated by said piston for opening said valve when the piston has traveled a predetermined distance in the other direction, said valve 7 being held closed during said last-named travel of said piston.

8. In a propeller, blades movable in one direction by the action of centrifugal force and in the other by hydraulic pressure, means for mov- -ing said blades, means including a governor for introducing fluid under a predetermined limited pressure to said blade moving means, stops for preventing movement of said blades by said limited pressure beyond a predetermined limit and means including a valve for disconnecting, said governor including means from said blade moving means and introducing fluid thereto under a pressure greater than said limited pressure for moving said blades beyond said predetermined limit.

9. In a controllable pitch propeller having blades mounted for pitch changing movements, a fluid actuated blade moving mechanism having opposite fluid receiving sides, means for supplying fluid at a predetermined pressure and means for supplying fluid at a pressure higher than said predetermined pressure, a pressure operated valve for directing application of fluid to said mechanism, a single conduit for introducing said fluid to both said mechanism and said valve, means for holding said valve closed when fluid is supplied to said valve and one side of said mechanism at said predetermined pressure to render said mechanism effective to move said blades in one direction, said valve being opened by fluid introduced through said conduit at said higher pressure and effective to direct said higher pressure fluid to the other side of said mechanism to render said mechanism effective to turn said blades in the opposite direction.

10. In a controllable pitch propeller having blades mounted for pitch changing movements, a fluid actuated blade moving mechanism having unequal opposed areas, manually controllable means for supplying hydraulic fluid at diflerent predetermined pressures, a single conduit for introducing said hydraulic fluid in one direction at any selected one of said different pressures to said mechanism, and pressure responsive means operative to block flow of said hydraulic fluid to one of said areas until a predetermined pressure of the fluid in said conduit is exceeded to render said mechanism operative to turn said blades in one direction only when subjected to one of said fluid pressures, said pressure responsive means adapted to be opened by a fluid pressure greater than said predetermined pressure to allow fluid to act on both sides of said mechanism to turn said blades in the opposite direction.

11. In a propeller having blades movable in one direction by the action of centrifugal force and in the other direction by hydraulic pressure, means for moving said blades, means for introducing fluid under a predetermined limited pressure to said blademoving means, stops for preventing movement of said blades by said limited pressure beyond a predetermined limit, and means for introducing fluid to said blade moving means under a pressure greater than said limited pressure for moving said blades beyond said predetermined limit.

12. In a propeller having blades movable by fluid pressures, means actuated by said fluid pressures for moving said blades, means for introducing fluid under a predetermined limited pressure to said blade moving means, stops effective when the blade moving means reaches a predetermined position to prevent movement of said blades by fluid at saidlimited pressure beyond said predetermined position, said stops constructed and arranged so that they are rendered inefiective by fluid introduced to said blade moving means at a pressure higher than said predetermined limited pressure, and means for introducing fluid to said blade moving means under a pressure higher than said limited pressure for moving said blades beyond said predetermined position.

13. In a propeller having movably mounted blades and mechanism for applying force to said blades to change the pitch of said propeller, in combination, stop means for positively limiting the range of pitch adjustment'of said propeller to a predetermined amount, and means rendered effective by movement of said mechanism to a predetermined point to resist further movement of said mechanism in the same direction by a force of predetermined value constituting an intermediate stop efiective only when the force exerted by said mechanism is below said predetermined value to limit the movements of said blades to less than said predetermined range, and means for increasing the force exerted bysaid mechanism to overcome the resistance of said second mentioned means and move said blades past said intermediate stop means.

14. In propeller pit' ch adjusting means, in combination, a pair of relatively movablecam members operative to change the propeller pitch in both directions, cam faces on said cams, cam followers travelling on said faces to move said cams, an abutment carried by one cam member, and a pair of adjustable abutments carried by the other cam member for limiting the relative movement of said cams in both directions by contact with the abutment on said one cam member.

15. In propeller blade pitch changing mechanism, in combination, a hub, a pair of substantially concentric cylindrical cams, one of said cams being fixed with respect to said hub and the other connected with said blades and movable with respect to said hub, one of said cams having a right hand cam path and the other having a left hand cam path, and a fluid actuated piston having cam followers traveling in said paths formoving said movable cam.

16. In a controllable pitch propeller, a plurality of blades, having a normal range of pitch ad justment and a feathering position, means including cams having a cam path for changing the pitch of the propeller blades operatively associated with said blades, the portion of thecam path used for changing the propeller blade pitch within the normal range having a predetermined slope and the portion of the cam path used for changing the pitch of the propeller blades between the normal range and the feathering position having a materially greater slope and acting as a stop for limiting the normal range.

17. In propeller pitch changing mechanism, in combination, an expansible chamber device including a piston, a stationary cylindrical cam, and a movable cylindrical cam arranged in a recess in said piston, and a pin connecting different parts of said piston on opposite sides of said recess and passing through the cam paths of both said cylindrical cams to impart rotational movementto one of said cylindrical cams with respect to the other upon reciprocatory movements of said piston.

18. In a controllable pitch propeller, a plurality of blades movable by fluid pressure and having a normal range of pitch adjustment and another range of pitch adjustment, mechanism actuated by fluid pressure for changing the pitch of the propeller blades, means for introducing fluid to said mechanism under a limited pressure to move said blades within said normal range, a cam operatively associated with said blades and having a cam path, the portion of the cam path used for changing the propeller blade pitch within the normal range having a predetermined slope, and the adjoining portion of the cam path used for changing the pitch of the propeller blade within said another range having a materially greater slope and acting as a stop for said normal range, and means for introducing fluid to said blade moving means under a pressure greater than said limited pressure for moving said blades beyond said stop into said another range.

19. In a controllable pitch propeller, a plurality of metal propeller blades, an inner hub member, means including a plurality of radial arms on said inner hub member for rotatably mounting said blades, an outer hub member surrounding said inner hub member and the base ends of said blades, means including anti-friction bearings within said outer hub member for retaining said blades in assembled relation on said arms, a hydraulic motor device having.a fluid pressure operated piston, means within-said outer hub member operatively connecting said blades with said hydraulic motor to turn said blades upon movement of said piston, means including said outer hub member providing a fluid space at one side of said piston to maintain said blade mounting means, said blade retaining means and said blade turning means immersed in hydraulic fluid, a fluid tight seal between said outer hub member and said inner hub member and between said outer hub member and each blade, and a layer of phenolic condensation product molded onto the portion of each blade within the respective fluid tight seal to avoid wearing or marring of said blade portions by said seals.

20. In a controllable pitch propeller, a plurality of propeller blades, an inner hub member adapted to be mounted on a drive shaft and having a seal to prevent leakage between said inner hub member and said shaft, means including a plurality of radial arms on said inner hub member for rotatably mounting said blades, an outer hub member surrounding said inner hub member and the base ends of said blades, means including anti-friction bearings within said outer hub member for retaining said blades in assembled relation on said arms, a hydraulic motor device having a fluid pressure operated piston, means providing a fluid space at each side of said piston, said means including said outer hub member and a housing connected thereto, means within said outer hub member and said housing but outside of said inner hub member operatively connecting said blades with said hydraulic motor to turn said blades upon movement of said piston, whereby said blade mounting means, said blade retaining means and said blade turning means will be immersed in hydraulic lubricating fluid.

21. Propeller pitch changing mechanism comprising, a propeller blade, intermeshing sets of gear teeth for turning said blade to change its pitch, and a resilient connection between said blade and one set of gear teeth for forcing said sets of gear teeth into intermeshed engagement to eliminate backlash and for cushioning the drive between said gear teeth and said blade.

22. Propeller pitch changing mechanism comprising, a propeller blade, a member having teeth thereon mounted on the propeller blade, spring packs located between said member and said blade and normally tending to urge the member to a position eccentric of said blade, and a second member having teeth meshing with the teeth on said first named member to urge said first named member toward a position concentric with said blade.

23. In combination with a propeller blade having a shank and mounted for movement about its longitudinal axis, mechanism including a thrust bearing and a packing surrounding said shank, and a layer of resilient material encasing said shank for cushioning the propeller thrust bearing and providing a wearing surface for said mechanism surrounding said blade shank.

.24. In combination with a propeller blade adapted to be mounted in a propeller hub andhaving a flanged base provided with a metal bearing receiving fillet, means comprising an antifriction thrust bearing having one race taking the load from the fillet for retaining said blade in said hub for rotation relative thereto, said fillet and said race being shaped to concentrate the transmitted load on a relatively small portion of the area of said race on the side of the race facing the fillet, and a load distributing layer of hardened plastic material molded on said fillet within said race.

25. In a controllable pitch propeller in combination, a hub, a propeller blade supported by saidhub adjacent one end only and driven through said hub, an anti-friction bearing having inner and outer races for retaining the blade in said hub and transmitting centrifugal and bending loads between said blade and said hub, the portion of said bearing adjacent said blade having a comparatively high modulus of elasticity, said blade having a shank of metal having a comparatively high modulus of elasticity, and having a portion adjacent said hub highly stressed by said centrifugal and bending loads, a thin layer of hardened plastic material, such as a synthetic resin, having a comparatively low modulus of elasticity located between the inner race of said bearing and said propeller blade to prevent galling caused by relative movement of said bearing and said blade and to prevent concentration of and reduce stress by distributing the said loads of said highly stressed blade shank.

26. In a controllable pitch propeller, in combination, a metal propeller blade having a flanged .hollow end provided with a curved surface portion; a hub including a. blade retaining barrel receiving said flanged blade end, and a sleeve adapted to be fastened to a propeller shaft having a projecting integral arm received in said hollow blade end; an anti-friction bearing comprising an inner and an outer race member and roller elements between said races adapted to be disposed between said blade end and said barrel with said inner race seated on the curved surface portion of said blade flange and said outer race secured in said barrel surrounding said blade, said bearing transmitting the centrifugal load and a portion of the bending load between said blade and said hub and said arm transmitting the remainder of said bending loads, whereby said blade is supported only at said flanged end and said curved surface portion is highly stressed by said transmitted centrifugal and bending loads, and a thin layer of synthetic resinous material molded to said curved surface portion and extending between said inner race and its seat for transmitting said centrifugal and bending loads from said curved surface portion to said inner race for the purpose of preventing galling caused by relative movements of said bearing and said blade portion, and to prevent concentration of stresses in said blade portion by distributing transmitted loads more uniformly over the entire area of the load transmitting surfaces of said blade and said inner race member.

2'7. In a propeller; blades movable in one direction by the action of a blade moving force and in the other by hydraulic pressure, means for moving said blades, means including a governor for introducing fluid under a predetermined limited pressure to said blade moving means, stops for preventing movement of said blades by said limited pressure beyond a predetermined limit, and means including a valve for disconnecting said governor including means from said blade moving means and introducing fluid thereto under a pressure greater than said limited pressure for inovting said blades beyond said predetermined 28. In a controllable pitch propeller having blades mounted for pitch changing movements, a fluid actuated blade moving mechanism having opposite fluid receiving sides, means for supplying fluid at a predetermined pressure and means for supplying fluid at a second pressure higher than said predetermined pressure and a third pressure higher than said second pressure, a pressure operated valve for directing application of fluid to said mechanism, a single conduit for introducing said fluid to both said mechanism and said-valve, means for holding said valve closed when fluid is supplied to said valve and one side of said mechanism at said predetermined pressure or said second pressure to render said mechanism blades mounted for pitch changing movements, a

fluid actuated blade moving" mechanism having opposite fluid receiving sides, means for supplying fluid at a predetermined pressure and means for supplying fluid at a second pressure higher than said predetermined pressure and a third pressure higher than said second pressure, a pres-' sure operated valve for directing application of fluid to said mechanism, a single conduit for introducing said fluid to both said mechanism and said valve, means for holding said valve closed when fluid is supplied to said valve and one side of said mechanism at said predetermined pressure or said second pressure to render said mechanism effective to move said blades in one direction, stops efiective when the blade moving means reaches a predetermined position to prevent movement of said blades by fluid at said limited pressure beyond said predetermined position, said stops constructed and arranged so that they are rendered ineffective by fluid introduced to said blade moving means at a second pressure higher .than said predetermined limited pressure, said valve being opened by fluid introduced through said conduit at said third pressure and effective to direct said fluid to the other side of said mechanism to render said mechanism effective to turn said blades in the opposite direction.

FRANK WVCALDWELL. ERLE MARTIN. JOHN ELIWER ANDERSON.

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