US2426007A - Variable pitch propeller arrangement - Google Patents

Description

Aug. 39, 1947.

A. G. FORSYTH VARIABLE PITCH PROPELLER ARRANGEIIENT Filed Nov. 14, 1942 7 Sheets-Sheet l Aug. 19, 1947. A. s. FORSYTH 2,426,007

VARIABLE 'PITCH PROPELLER ARRANGEIENT I Filed Nov. 14, 1942 7 Sheets-Sheet 2 azdlbalai Aug. 19, 1947. A. e. FORSY TH VARIABLE PITCH PROPELLER ARRANGBIENT' Filed Nov. 14, 1942 Ill/ l'l'l'l'l 7 Sheets-Sheet. 3

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' wmuansrrrca PROPELLER ARRANGE'IENT Filed Nov. 14', 1942 7 Shoots-Shoot 4 Aug. 19, 1947. A. e. FORSY TH' v2,426,007

VARIABLE PITCH PROPELLER ARRANGEMENT Filed Nov. '14, 1942 7 Sheets-Sheet 5 Aug. 19, 1947. A. e. FORSYTH 2,426,007

, VARIABLE PITCH PROPELLER ARRAHGEIEN'I' Filed Nov. 14, 1942 7 Sheets-Sheet s r h T Q N 1 h arc/"bale! Gru/rarn MW,

Aug. 19, 1947. A. s. FORSYTH 2,426,007

VARIABLE PITCH PROPELLER ARRANGEMENT Filed Nov. 14, 1942 7 Sheet s-Sheet 7 Patented Au 19, 1947' UNITED STATES PATENT orrlca VARIABLE PITCH PROPELLER ARRANGEMENT Archibald Graham Forsyth, Cheam, England, assignor to The Fairey Aviation Company "Limited, Hayes, England Application November 14, 1942, Serial No. 465,618 1'Claim. (01. 170-163) This invention relates to a variable pitch propeller system, and in particular to a, variable pitch propeller system employing two sets of propellers for contra-rotation on coaxial shafts.

In my copending application, Serial No. 449,123, filed June 30, 1942, an arrangement of the general type is described in which the pitch of the blades of the propellers of each set may be changed to effect conditions of fine pitch, coarse pitch, feathering and braking, the relative relationship of the pitch of the blades of both sets of propellers, however, remaining the same at all times. In the above-mentioned application, means are illustrated and described for efi'ecting the desired pitch at the will of the pilot as required v by flight conditions.

The present invention constitutes an improvement of such means, and primarily resides in providing special means to efiect a more rapid adjustment from one pitch condition to another as emergency flight and landing conditions may require.

Another object of the invention resides in the provision of booster means operable at the will of the pilot to assist the power means for effecting a pitch change from one condition to another. The invention contemplates booster means of various types and includes both electrical and hydraulic instrumentalities adapted to accomplish the desired result.

Still a further object resides in an improved control for such booster means as related to the pitch changing system as a whole.

In accordance with the invention, the blades of the two propellers are maintained in a. fixed relationship with respect to each other over the entire pitch changing range, the mechanism being so arranged that the pitch of the propellers may be the same or may differ to suit the requirements necessary to obtain maximum efficiency.

Further, in accordance with this modification,

position, and from coarse to feathering position. I

The invention effects pitch changing movement of the blades about their longitudinal axes through gearing arrangements such as described in my copending application, such gearing being driven by a motor which may be electric or hydraulic.

I tion.

booster motor to speed the pitch changing movement in either direction from reverse to flag posi- A further object resides in the provision of control means for actuating the booster means at the required periods.

These and other objects of this invention will become more apparent from a consideration of the following specification and claim when read in the light of the accompanying drawings, in which: v

Figure l isa side elevation, partly in section, showing one form of the invention;

Figure 2 is a cross-sectional view taken on line 22 of Figure 1; 1

Figure 3 is a view partly in elevation and partly in cross-section taken on the linev 3-3 of Figure 1; t

[Figure 4 shows a modification of the invention partly in cross-section and partly in elevation;

Figure 5 shows a still further modification in side elevation and partly in cross-section;

Figure 6 shows in section a preferred form of a hydraulic system adapted. to vary the propeller pitch;

Figure 7 is an end elevation on the line |'I of Figure 6;

Figure 8 is a cross-sectional view taken on the line 8-8 of Figure 6;

Figure 9 is a diagrammatic representation showing an electrical circuit arrangement used in carrying out this invention;

Figure 10 illustrates a modification of a hydraulic system adapted to vary the pitch of a propeller blade;

Figure 11 is a further modification of the arrangement shown in Figure 10;

Figure 12 illustrates a modification of the booster motor arrangement;

Figure 13 illustrates a modified type of clutch adapted to be used in this invention;

Figure 14 is a cross-sectional view taken on the line I4l4 of Figure 13.

In considering this specification and the accompanying drawings, attention is directed to my Patent No. 2,161,917 and my pending application, Serial No. 449,123, filed June 30, 1942.

Referring now more specifically to Figures 1, 2 and 3 of the drawings, the reference numerals 2 and 4 indicate two propellers mounted respectively on two coaxially disposed hollow drive shafts B and 8, each or which are adapted to be rotatively driven by internal combustion engines (not shown) with each engine having its own In particular the present invention employs a '55 controls. Obviously, with such an arrangement it'bGOOlIlGS possible to operate the engines at any desired \speeds relative to each other, or to stop one engine while permitting the other to operate.

In this embodiment of the invention, the roots of the propeller blades (in this case three on each shaft) are each mounted for rotary movement about its longitudinal axis so that the pitch of the blade can be adjusted over a range of 360. To accomplish this movement, the root of each propeller blade 2, 4, is rigidly secured to ring gear it, which is engaged by a worm gear l2, l2 rigidly secured on the shaft l4, l4. As these gears are turned in one direction or the other by means to be described, the worm gear l2, l2 will rotate the ring gears II) which, since the gears are rigidly mounted on the propeller blade roots, will rotate the blades about their respective longitudinal axes, thus changing the pitch of the blades.

In the present invention the propeller pitch changing means for'the blades 2 comprises a reversible electric motor it which is provided with a drive shaft l8 on which is rigidly secured coaxially therewith the gearwheel 20 which coacts with the gear 22 (coaxial with respect to the propeller drive shafts). As is clearly seen in Figure 1. t e gear 22 is provided with a laterally extend-. ing flange portion 24 having gear teeth out on the outer periphery thereof. A spider 26 carries the coaxially mounted gears 28 and 30, of which gear 28 is adapted to be engaged by the gear teeth formed on the flange 24 and to be rotated thereby. A ring gear 32 has gear teeth formed on its inner periphery which are also engaged by the gear 28 mounted on the spider 26. A gear 34 keyed to the frame 36 is adapted to mesh with the spider mounted gear 28. The gear 28 also meshes with a second ring gear 38 which is rigidly secured to the propeller hub. The ring gear 32 is provided with gear teeth cut on its exterior periphery which mesh with and rotate gear 40 under certain conditions to be discussed below. The gear 40 is rigidly mounted on the shaft l4, which, it will be recalled, has also fixedly secured thereon, the worm gear l2.

It is now seen that when the reversible electric motor 56 is energized-to rotate in one direction, the gear 20, driven by the shaft l8, will rotate the gear 22 which in turn transmits its rotation through the gear 28 to the ring gear 32. The rotation of gear 32 will turn gear 40 which, since it is mounted rigidly on shaft it, turns the worm gear l2. The worm gear 12 cooperates with the ring gear iii to rotate the propeller blade 2 with respect to its longitudinal axis thereby changing the pitch thereof.

The other end of the shaft i4 is provided with a second gear 42 fixedly mounted thereon. This gear, when rotated transmits power through a gearing system identical to that previously described in order to vary the pitch of propeller blade 4. The various elements found in the second gear train may be identified by-the primed reference numerals indicating similar elements to be found in the first system.

One of the objects of this invention is to provide means whereby the rate of change of pitch may be rapidly accomplished. This is achieved by selecting a high gear ratio with respect to gears 28 and 32. In addition thereto, it has been found advantageous to employ a booster motor 42 of approximately the same power as motor l6. Motor 42 is employed when it is desired to change the pitch from fine to breaking (and the reverse thereof), and its cooperation with the gearing system is readily understood.

The gear wheel 22 engages the freely rotating gear 44 rigidly mounted on one end of a shaft 40.

The other end of the shaft carries the female portion or clutch plate 48 also rigidly secured thereon. The male portion 50 of the clutch is telescopically mounted on and is keyed to the drive shaft 52 of the'electric motor 42. A pivoted link 54 is secured at one of its ends to the telescoping member 50. The other end of the link is secured to the shaft 56 which is operable by the energization of the electric solenoid'58. The solenoid 58 and the motor 42 are controlled through an electric circuit to be described.

In Figure 5. amodiflcation of the invention is illustrated. In this figurethe inner gearing system adapted to vary the'pitch of the propeller blade 2 is identical to the gearing systems described in connection with Figure 1, and identical reference numerals are employed to identify the same elements. However, in this modification, the gear wheel 42 engages the ring gear 50 which is provided with gear teeth on its outer periphery for this purpose. The inner periphery of the ring gear 60 is provided with gear teeth which are engaged by a gear 62 mounted coaxially with gear 64 on the spider 66. The gear 64 meshes with gear teeth formed on the inner periphery of the ring gear 68 and also cooperates with the gear 10 which is keyed to the shaft 8. As is seen in the drawing, the gear 62 also meshes with the gear 12 which is substantially U-shaped in cross section. This gear engages the gear 45 which when rotated, will turn the worm gear l2, thereby varying the pitch of the propeller blade 4.

In Figure 4, another embodiment of the invention is illustrated. In this modification the shaft l8 drives the gear 22. The gear 22 is engaged by .gear 28 mounted coaxially with gear 30 and is carried by the spider 26. The gear 28 engages teeth formed on the inner periphery of the ring gear 14 which is rigidly secured to the propeller hub. The inner ring gear 16 is provided with radially inwardly extending gear teeth which engage gear 30.

Gear 30 cooperates with gear I8 which is keyed to the frame 36. It will also be seen that the gear I6 cooperates with the gear 80 which is rigidly secured to the shaft 14. Hence, it is easily seen that energization of the motor [6 will turn gear 80 which rotates the propeller blade in the man- I ner described above.

The variable pitch gear mechanism is controlled through the equipment and electrical circuit diagrammatically shown in Figure 9. In considering this figure it will be seen that a portion thereof is quite similar to the electrical circuit shown and described in my copending application, Serial Number 449,123.

Included in the circuit shown is a battery 200 for supplying current to the electric motors I6 and 42, solenoid switches 202, 204, 206, and 208, manually operated featherin switch 2 I 0, a double switch 2I2, 2l2' operated by the governor 2l4 which is geared to a shaft 2l5 driven by the internal combustion engine, a manually operated switch 2 l6 for overriding the governor at the will of the operator, a braking switch M8 and a series of limit switches 220, 222, 224, 226, 22'! and 228.

The limit switches are controlled by a number of cam shaped disks 220', 222', 224', 226', 221' and 228' adjustably mounted on the shaft 230 which is connected with the motor l6 through reduction governor is indicated in dot and dash lines. The fine pitch switch 222 and the coarse pitch switch 224 are both located in the normal circuit. The

cams 222' and 224' are so positioned on the shaft 230 soas to permit the switches 222 and 224 to be held in their closed position during normal operation. In normal operation of this circuit the tension of the spring 230 is adjusted to regulate the governor 2I4 to suit the R. P. M. of the engine decided upon by the pilot for operation. The governor when operating thus actuates the pivoted switch lever 232 so that it will either close the fine pitch switch 2 I 2 or the coarse pitch switch 2I2'. In accordance with the particular switch actuated the electric motor ;I6 'will rotate the shaft 230-so as to tend to bringthe cams 222', 224' into contact with their respective switch arms. If the cams are rotated far enough one or the other of the cams 222', 224 will actuate either the fine pitch limit switch 222 or the coarse pitch limit switch 224, thus breaking the normal circuit and cutting off the motor.

The fine pitch limit switch 222 and the coarse pitch limit switch control the predetermined coarse and fine positions of the propeller blade pitch, For example, the fine pitch limit switch acts to prevent over pitching in a dive. In normal flight neither switch is actuated by their respective cams.

In this arrangement when the engine is stopped the governor weights 234 move in such a manner as to close the fine switch 2I2 (the coarse switch 2I2 can only be closed when the engine is operating). Thus the electric motor I6 is placed under operation and will rotate the cam shaft 230 until the cam 222' operates the switch 222 thereby breaking the motor circuit. This insures that the blades will always be left in fine pitch for a take oil.

Should it become necessary for any reason to over-ride" the. governor, the pilot may accomplish this by manually actuating the hand contr'ol switch 2I6 which is in the circuit indicated by clot and dash lines. Consequently, if this switch be actuated to cut out the governor, the electric motor I6 will be actuated to rotate -'the cam shaft 230 so as to tend to cause the cams 222' or 224 to operate their respective switches. The circuit to the motor is, of course, broken either by operating the hand control 2 I 6 or by the opening of either of the two switches 222, 224,

When it is desired to feather the propellers, it is necessary for the pilot to actuate the feathering switch 2l0 so that the normal circuit (full line) is broken and the feathering circuit indicated in dotted lines, is made. As is seen, during normal operation no current passes through this circuit.

Operation of the feathering switch to close the feathering circuit permits current to pass through the contacts of the feathering limit switch 226 and at the same time since the normal circuit is dead, the coarse pitch limit switch 224 will be dead so that actuation of this switch by the cam 224' will not operate to shut off the current to the motor I6. As the shaft 230' continues to re. tate, the cam 226' will operate the feathering limit pitch switch 226 thereby opening the feathering circuit, stopping the electric motor I6 and holding the propeller blades in feathered position.

When the feathering limit switch 226 is broken, the fine pitch limit switch 222 circuit is still alive, and due to the fact that the governor has moved the pivoted switch into fine position; the electric ill motor I 6 is reversed and automatically rotates the shaft 230 to bring the cams 222' and 224'- back into position to actuate their respective limit ,switches 22.2, 224.

It is also obvious that actuation of the hand control switch 2I6 in the hand control circuit' (broken line) may be used to bring the propeller blades back to normal position. It is necessary,

. ing switch2l0 is put into feathering position. 20

Moving the switch 2| 6 in a counter-clockwise direction from the position shown to the first set of terminals will cut out the governor and com.- plete the fine pitch circuit. Moving it clockwise to the first set of terminals will close the coarse pitch circuit. Continuing in the same direction to a position at right angles to the first position will effect an "off position in which the blades are locked. This switch obviously may be rotated as much as 360 in either direction. It will be apparent that usually this switch 2 I 6 will remain in a normal running position in which the governor is in actuation, but can be used, for example, on long cruises and the like, so that the pilot can set the pitch in the best possible position for the most economical operation.

As was stated above, one of the objects of this invention was to provide means for changing the pitch of the propeller blades rapidly from the fine pitcl'i position to breaking pitch position and reverse. To accomplish this feature of the invention, the booster motor 42 is brought into operation and simultaneously one or the other of the electric solenoids 266, 268 is energized to bring the clutch into engagement to add the power of the motor 42 to that of motor I6. r

The braking limit switch 2) during normal operation is dead since the normal circuit bridges it, but when it is desired to efiect the braking position after the aircraft is on th ground, it may be rendered live by braking switch 2I8 interconnected with the brake pedal or lever (not one side of the normally open switch240, the

other side of which is connected to the ground. The switch 240 is adapted to be closed by operation of a pin 242 when the latter is raised by the pivoted arm 232 controlled by the governor 2.

In the normal position of switch 2 I 8, the switch connects a pair of terminals, one of which 244 leads to the coarse" switch M2 and the other 246 to the fine switch 2I2. This latter terminal 246 is also connected in the hand control circuit by line 248 so that when'switch 2I8 is in normal position, the hand control switch 2I6 may still be actuated to override the governor.

In practice, the braking switch 2I8 is adapted to be operated by the foot brake pedal when the plane lands. As the pilot applies the brakes the switch 2I8 is turned from the position shown to its other position. This takes the current directly 7 to the braking limit switch 220, through the sole.

- 288 is energized simultaneously therewith and the armature thereof operates to close the motor switch 250 thereby energizing the motor i2 and also operates the linkage system to close-the clutch thereby adding the power of the motor 42 to that of the motor I6. Motors I6 and 42 con. tinue to operate until limit switches 228 and 228 are opened by the rotation of the cams 220 and Turning the hand switch 2!! to coarse position and releasing the brake pedal the switch 2I8 is moved'back to its normal position and establishes an electrical circuit through solenoids 202 and 206 which reverses the direction of the rotation of the motors, and maintains the clutch in engagement with the motor 42. The shaft 23o continues to rotate until the switch 221. operated by the cam 22'! is opened simultaneously with the opening of limit switch 224, thereby opening the circuits through all motors and sole- 1101118. The cams 221' and 228' normally hold the switches 221 and 228 in open position, allowing them to become active only during the-braking operation,

In off" position switch 2I8 completes the negative for the coarse pitch circuit (either governor or hand controlled) thereby making it-possible to go into reverse pitch when reverse pitch is required (when plane is on the ground and a foot pedal braking is applied to place switch 2I8 in .on position) even when the pilot controls are in coarse pitch position. Inner terminals 236 and 288 complete th ignition switch wires and complete the circuit through the governor actuated switch 240 to ground when switch 2 I8 is in on position. Switch 240 is normally open and can only be actuated to close the circuit when switch 2I8 is on. The switch 240 is designed to break only when going into a revers pitch position and only when a predetermined lower limit of R. P. M. is reached.

This arrangement constitutes a safety measure 7 since braking a reverse pitch position of the propeller cannot be effected until the aircraft is on the ground and the pilot has applied the foot pedal and the motor has slowed down to a predetermined R. RM.

Hence, it is seen that a rapid change from fine pitch to reverse pitch and the reverse is effected through the introduction of the power derived from motor 42.

In Figure 6 a hydraulic system adapted to vary the pitch of the propellers through the gearing arrangement described above is illustrated.

This embodiment employs a cylinder 82 which is provided with coaxial threaded apertures 84 in the respective ends thereof. A piston 86 is rigidly and coaxially mounted on the shaft 88 which is in turn mounted in the apertures 84 to permit reciprocal movement of the piston 86 in the cylinder 82. Threaded sealing rings 90 engage the threaded apertures and are adapted to hold packing 92 securely in place. A gear rack 94 is rigidly secured to the ends of the shaft 88 by means 01'' the supports 95. Adjacent each end of the cylinder 82 two openings 96 and- 98, respectively, are provided. One end of each of the pipes I and I02 is fixedly mounted therein and each end is packed (not shown) against leakage. A suitable reversible hydraulic pump I02 is connected to the other ends. Consequently, operation of the hydraulic pump I02 in one dil 8, rection will furnish fluid through one of the conduits I00, I02 and will provide a suction on the other; reversing the pump will reverse the function of the conduit pipes. Pump I02 may be It controlled in any well known manner such as manually or by a governor operating in response mhe rotational speed of the engine and pro- It is to be understood that fluid entering one 10 end of the cylinder 82 under pressure will force the piston 86 toward theopposite end and vice versa. In moving from one end of the cylinder to the other, the fluid pressure acting on the piston 86 causes a longitudinal movement of the gear rack 94. As is seen in Figures 6, 7 and 8,

the upper surface I04 01' the gear rack is substantially planar and cooperates with a similar surface on the bottom or base of the cylinder 82. These cooperating surfaces prevent any rotation of the rack about the shaft 88.

The' rack 94 engages the gear wheel 22 and as the fluid under pressure is admitted alternately to one or the other surfaces of the piston 86, the gear 22 is rotated first in one direction '26 and then the other which results in achange of the propeller blade pitch as explained above.

In the event a more rapid change of pitch is required, a booster pump and circuit is provided, the control thereof being positioned in the cockpit or is adapted to be operated by the brake pedal. The booster circuit comprises a hydraulic pump I06 connected to a source of fluid supply a (not shown) and is connected to the interior of the cylinder through conduits I08, I08. The

high pressure side of the conduit is, at the will of the operator, alternately connected with the interior of the cylinder at opposite ends thereof by adjusting valve II4. Whichever of conduits I08, I08'- is not connected to the high pressure side of pump I06 is connected to the fluid when it is in closed position. This circuit comprises the pipe I I0 and the spring tensioned valve device II2.

It .will be noted that the booster arrangement just described operates completely independently 01' the pitch varying arrangement which includes -conduits l00, I02. This has the advantage of not only permitting accelerated pitch changing movemerit of the blades when desired, but also provides a safety factor in that a defect or breakage in one of the hydraulic fluid supply systems will not leave the pilot without means for changing the propeller pitch. In systems wherein booster arrangements operate through one or more common parts, such as a valve, with the ordinary pitch control arrangement, a defect in the common part would disable both control systems.

Figure 10 illustrates a modification of the hydraulic system which may be employed in effecting the rapid change of pitch, from fine to braking 55 and the reverse thereof. This figure also shows a method for changing the pitch of the propeller blades through their normal phases of fine-pitch, coarse pitch and feathering.

In this construction, the cylinder 82', piston (not shown), gear rack 94, supports 95', threaded apertures 84' and threaded sealing rings 90' are identical to the correspondin elements shown in Figures 6, 7 and 8. This embodiment employs but two conduits 300 and 302, one end of each of the conduits communicating with the interior of the 9 cylinder 82' at a point adjacent each of its ends. The other ends of the conduits are connected with a valve device 384 which is controlled by the governor 386 connected to the internal combustion engine. I

A shaft 388 is mounted for reciprocal movement within the cylinder M8, the degree of movement being dependent upon the speed of the engine. Rigidly secured on the shaft 388 are the valve pistons 3|2,3i2'.

The intake port of the hydraulic pump 3l4 is connected to a source (container) of fluid supply 3l6 through conduit 3l8. The high pressure side of the pump 3 I4 is connected with a chamber 328 through pipe 322. The chamber in turn is connected with the interior of the valve 384 through the conduit 322.

The container 3I6 is also connected to the cylinder 3| 8 adjacent each end thereof by discharge conduits 324 and 326.

During normal operation of the internal combustion engine, the governor will reciprocate the shaft 388 and, of course, the valvepistons 312, 3l2', thereby connecting the conduits 388 and 382 with either the high pressure pipe 322 or with one of the discharge pipes 324 or 326. The change in pressure on one side or the other of the piston in the cylinder 82' will produce a movement of the gear rack 94 which is transmitted to the gear wheel 22 which rotates the propeller blades to effect a change of pitch. r

In the event it is desired to-move from normal running pitch to braking pitch, a booster pump 328 is provided. Pump 328 is energized by closing switch 338 which may be connected with the brake pedal. The low pressure side of the p mp 328 is connected by. pipe 332 to the fluid suppl and the high pressure side is connected with the chamber 328 through pipe 334. A one-way valve 336 is introduced in conduit 334 intermediate the supply through pipe 346, as shown when, how

sure on one or the other sides of the piston in I the cylinder-82' and will efiect a more rapid change in pitch in the manner described above.

When braking pitch is no longer required, the

switch 338' and valve 348 are returned to their original positions thereby cutting off the booster pump motor and connecting the low pressure side of pump 3 M with only the fluid supply.

Figure 12 illustrates a modification of the arrangement of the normal pitch changing motor 48 and booster motor 42. In this illustration the booster motor 42 is adapted to transmit its power (when required) directly to the shaft II when the motor 42 is energized and the clutch elements 48 and 58 are brought into engagement in the manner described. It will be seen in this figure'that the driving shafts of each motor are coaxial and oppositely disposed.

chamber 328 and the pump 328 to prevent the higher speed. This will, of course, change the pitch of the propeller blades very quickly. A pressure by-pass circuit comprising the valve 338 and the conduits 348, 342 is also provided, the function of which is well understood.

In Figure 11 a still further modification of th hydraulic system is illustrated. In this system, the gear 22, cylinder 82', gear rack 94', conduits 388' and 382', discharge pipes 324 and 326, pumps 314' and 328', valve device 384' and the governor 386' are identical'in construction to similar elements shown in Figure 10. In this embodiment, however, the high pressure side of the pump 3|4' is connected directly with the governor operated valve device 384' through conduit 344. The low pressure side of the pump is connected to the fluid supply through pipe 348, the three-way valve 348 and the pipe 358. The booster pump 328' is connected at its high pressure side, with the valve 348 by the pipe 352, and the low pressure side is connected with the fluid supply through conduit 358'. (A bypassing circuit is also provided for the booster pump 328 comprising the valve 338' and conduits 348', 342'.)

During normal operation only the pump 3l4' is employed to adjust the. pitch of the propeller blades. In this case the valve 348 is connected directly with the valve device 384', and the fluid Figure 13 illustrates a modification of the clutching mechanism for the booster motor, In this figure, the motor 42 is energized and simultaneously therewith the electro-magnets 488 mounted on the drive shaft 18 are also energized to cause the clutch plate 482 to engage the female clutch'portion 484 which is rigidly secured to the drive shaft l8. 7

Having described my invention in detail, it is to be understood that the invention is not to be limited to the specific examples described and illustrated herein, but is only limited by the scope of the following claim:

I claim:

In an airplane propeller pitch changing mechanism, a hydraulic cylinder; a piston in said cylinder; a rack and pinion arrangement drivably connecting said piston with the propeller blades; a first pitch control arrangement comprising a reversiblehydraulic pump connected to supply fluid under pressure selectively to either side of said piston; and a booster pitch control operable simultaneously with said first pitch control 'for causing accelerated pitch changing movement of of fluid to said cylinder by thepump of-said first pitch control arrangement. ARCI-IIBALD GRAHAM FORSYTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Date Number Name 2,236,841 Waseige Apr. 1, 1941 2,280,714 Martin Apr. 21, 1942 2,293,912 Mullen Aug. 25, 1942 2,246,745 Martin et a1 June 24, 1941 2,333,973 Beebe Nov. 9, 1943 (Other references on following page) Number 2,132,481 2,318,929

Name Date Number Country Date Kin Oct. 11;--1938 50,162 France Oct. 10, 1939 Hoover May 11, 1943 464,203 Great Britain Apr. '12, 1937 Schwarzhaupt et a1. Feb.-9, 1943 483,760 Great Britain Apr. 28, 1938 Algarsson Mar. 16, 1943 5, 463,737 Great Britain Apr. 6, 1937 Beebe an. 4, 1944 OTHER REFERENCES FOREIGN PAW The Bee-Hive, May 1938, pages 3 to 6inc1u- Country Date sive, published by the United Aircraft Corp. Great Britain Jan. 25, 1939 10 (CopyinDivision 9.)

Great Britain Feb. 6, 1940 v

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