US2664960A - Topping governor and reversing solenoid for variable pitch propellers - Google Patents

Description

M. E. LoNGFELLow ETAL 2,664,960

Jan. 5, 1954 TOPPING GOVERNOR AND REVERSING SOLENOID FOR VARIABLE PITCH PROPELLERS 3 Sheets-Sheet 1 Filed July 29, 1950 INV NToRs Melvin L angfe/nw. BYNEsanRRiclzmand AG E N T Jan 5, 1954 M. E. LoNGFELLow ETAL 2,664,960

TOPPING GOVERNOR AND REVERSING SOLENOID n FOR VARIABLE PITCH PROPELLERS l Flled July 29, 1950 3 Sheets-Sheet 2 ToPRoP'LLz/v CoNTroL .frana/vary P/.s v-o/v .55m/a CONTROLLI? /NPuT .Marr/Y INVENToRs AGENT Jan- 5, 1954 M, E. LoNGFELLow ETAL 2,664,960

TOPPING GOVERNOR AND REVERSING SOLENOID FOR VARIABLE FITCH PROPELLERS 3 Sheets-Sheet- 3 Filed July 29, 1950 M. .bm

lllllll AGENT Patented Jan. 5, 1954 TOPPING GOVERNOR AND REVERSING SOLENOID FOR VARIABLE PITCH PRO- PELLERS Melvin E. Longfellow, Manchester, and Nelson R. Richmond, Thompsonville, Conn., assgnorsto United Aircraft, Corporation, East Hartford, Conn., a corporation of Delaware Application July 29, 195o, serial No. 176,578

s claims. (o1. 17o-160.2)

This invention relates to improvements in aircraft propellers and more speciiically to variable pitch propellers having improved control means therefor.

It is an object of this invention to provide an improved pitch control and operating mechanism for variable pitch propellers.

A further object of this invention is to provide a variable pitch propeller control system comprising normal governing means and including an overspeed governing system which can be by-passed during operation of the propeller pitch reversing control mechanism.

Another object of this invention is to provide a topping or overspeed governing mechanism cooperating with a pitch reversing mechanism in a pitch control system of the type described herein. A f

These and other objects will become readily apparent from the following detail description of the accompanying drawings in which:

7Fig. 1 is a schematic illustration of a propeller and associated gear train for transmitting controlling movements from the control system to the hub carried pitch changing mechanism.

Fig. 2 is a schematic illustration of the propeller control system of thisinvention with the elements arranged as a continuity of Fig. 1.

Fig. 3 is an electrical diagram of the propeller control system.

Referring to Fig. l, a propeller is illustrated as being operatively connected by a driving element or gear it which may form a part of a turbine or reciprocating piston power plant and which also serves to drive a tachometer generator l2 which in turn transmits electrical energy to ran electronic governor schematically shown at`l4. rEhe electronic governor may be of the type shown in Patent No. 2,517,703 issued August 8, 1950. The electronic governor in turn both receives and transmits electrical signals to the propeller control system as will become apparent hereinafter. The electronic governor of the above-referred to patent would have its components connected in the present system as follows. Thus for kexample the generator in the patent is the lequivalent of the tachometer generator I2 whilerthe proportional solenoid respondsKL similar to that illustrated in Fig. 2 hereof. f rlherieedback potentiometer shown in the drawings may be connected in the with each of the blades having fluid operated vane motors 24 mounted within the shanks thereof. TheA vane motors 24 respond to high pressure iiuid to vary the pitch of the blades in a low pitch or high pitch direction, as indicated by the arrows, it being noted that the letters LP and HP are used in the drawings to indicate said same manner asvthe potentiometer H1 of Fig. 5

of the above-referred to patent. e

The propeller illustrated herein comprises a hub 2G which may havea plurality of radially eX- tending variable pitch blades 22 mounted therein pitch directions respectively.

The propeller hub 20 carries the entire pitch actuating mechanism internally thereof including an integral hydraulic reservoir, the actual construction of which is more clearly illustrated and described in copending application Serial No. 154,857, led April 8, 1950, by Arthur N. Allen, Jr.

A pressurized sump 3U is provided for supplying uid to a high pressure main pump 32 and a stand-by pump 34 by means of hydraulicr lines 36 and 38, respectively. The sump 38 is pressurized to some nominal value by means of a scavenge pump 40 which receives uid from an oil chamber (not illustrated) under atmospheric pressure. The sump `3l] is maintained at this predetermined normal pressure by means of a sump relief valve 42 which dumps relieved iuid back into the above-mentioned chamber which is under atmospheric pressure. High pressure uid from the pumps 32 and 34 is directed to a distributor valve generally indicated at 46 which controllably directs this high pressure fluid via the lines 48 or 5D to either side of the vane motors 24 for varying the pitch of the blades 22. Since the capacity of the main pump 32 is suflicient for normal pitch changing movements, the, output of the stand-by pump 34 is directed from the line 52 around the land 54 of the distributor valve 46 and then to the port 56 or the valve to a central drain passage 58 therein.

When the demand for pitch changing movements is high, as reflected by large movements of the distributor valve, the land 54 will close 01T the incoming iluid from the passage 52 so that the pressure in the passage 42 will immediately build up suiliciently to open the check valve teso that an additional volume of iiuid will be available forpitch changing movement to supplement the flow of high` lpressure iiuid coming from the main pump 32 via the line 82.

The central portion ofthe distributor valve 46 is actuated in reciprocating motion by means shaft 18 the valvec'entral portion/will be reposi-k tioned when the blade interconnecting gear 80 is rotated by the gear segments 82 (carried by the blade 22) during pitch changing movements of the blades.

A positr've'raitchet type pitchloc'k'l is provided. for automatically locking the blades against pitch changing movements in a low pitch direction in the event of failure oir-.hydraulic pressure in the system. A spring SZbiases @pitch lock piston 04 toward a lock position while fluid under pressure flowing via the line 95 forces the piston 94 toward an unlocked position. "Ihe'rluidunder pressure in the line 96 is fed via ja'passa'g'e which surrounds the follow-up shaft 'T8 'an'd normally communicates with the central drain chamber of the distributor valve Via a port 588, :the la-n'dfadjacent the port 98 normally permitting fluid-communication to the pitch `lock piston. "I'liedra'in pressure within the central chamber 58 of the distributor valve is 'maintained lat 'some' vpredeterminedfvalue `slightly `above Vthe pressure of vthe J30by means of ja pitch 'lockreliefvalve which is illustrated in the end ofthe distributor valve46.

'The pitch lock system shown herein 4is 'more 'fully described and 'claimed in ico-pending vapplication Serial No. 129,082, led November 23, 1949, by'Erle-Martin-and Thomas B. Rhines now U. S. Patent Serial No. 2,653,671, issued VSeptember 29, V1953.

The propeller parts described thus far are `contained withinfor form'a part of, the rotatable hub portion of the propeller assembly andthe'mechanism hereinafter described is carried in stationary housing 'held fixed relative to theassociated power plant. To this end, then, a pair of vintegral'gears -||0 and |2'are normally fixed'so that during Ipropeller rotation the gears I I4 -and `H6 which engage the gear ||0 will reivolve thereabout and in so doingfwill provide a rotational drive 'for the main pump 32 and the Stand-*by pump 84. The scavengepump40 contained I-wlthin the propeller 'hub will 4likewise lbe 'drivln'gly rotated through'its gear `||8"which also l'engz'iges-thenormally stationary gear ||0. A'seco'nd'pair of integral gears |20and |22 are, during -an'on-speed'propell'er condition, normally rotated atthe vsame speed asthepropellerby'meansof an 'epleyelic gear train generally' indicated vat A'|26 `which -train is driven -by a gear '|28 connected 'torro'tation ywith vthe propeller 'and `its drive "shaft The gear |20 '(which normally 'rotates'at `prop'elli'er speed) engagesa distributorivalve driving gear v|30 Awhich Ais xed to the distributor valvefdriving nut 10. `It'is th'enapparent'th'at Lduringan-onspeedcondition with the gears' |20 and |22 rotating ata speed'identical topropeller lrotation, thedistributor valve'drive gear |30 Will 'remain'stationary -so as `not to ldisturb-the setting of lthe distributor lvalve 46. l

The epicyclic gear train 26 comprises a shaft F40 on Which'all o'f'the gears thereon are mounted freely. The gears |42 and |44 are connected lftogether for simultaneous rotationy'as are `also forms the `planetary cage. A control gear |00 Aisflxed to a shaft |62-andis driven via the bevel `gears .|64 by "the'servo control output shaftl68. During 'anon speed conditionithen,"witlrthe servo Ycontrol output shaft |68 stationary, 'the -`control gear |60 will also remain stationary and likewise the planetary cage or gear |56 will also remain stationary. Under these conditions then, with the gear |28 rotating at propeller speed and 4since it engas 7the gear Mya driving train will 'bef-provided through the-sun gear |44, the planetary pinions |50 and |52, through the gears |48 uand |46 and finally to the gears |22 and |20.

This driving .connection just described in effect vtlien ,-providesiafsimple step-up, step-down gear ltrain which results in driving the gears |20 and bevel 4gears |64 will rotate the control gear |60 and the planetary cage A|56 so that the planetary pinions A|50 and 4152 -will revolve about their .respective sun gears |44 and |48 so as to vary the resultingvdriven speed vof the .gear |46 and the gears |22 and |20. This variation in speed of the gears |l20 and |22 then represents an increaseor'decrease, as the case may be, from the rotational speed of-.the propeller so that relative movement in either-direction is .obtained vbetween the lgear :L20 Vfand the distributor valve drive gear |30. As a'result, the distributor :valve `drive '-nut will .cause asubsequent reciprocating movement in the distributor lvalve :so as to vary the pitch of the propeller blades.

.A second .planetary gear cluster |80 has :also -provided as anfoperative connection r`between the propeller and the .servo vcontrol input `,shaft .|02 whosepurpose will be described hereinafter. The gear cluster |80 comprises a normally drivengear |04 which rengages the 'gear |28 gand, therefore, yis driven Ein timed relation to, and 'by the `rotation of, azpropeller. A sun gear |86 is .driven by 'the gear |8'4 and engages :a planetary pinion |88 whichin turn'meshes with the internal teeth of athe ring gear |90. :Since the ring gear meshes with the `normally'ifixed gear ||2 through .a re- 'versing gear |92,":it also will `be held stationary during-normal operation. "As a result, the :planetary pinion |88 will'revolve about .the'sun gear .|86 and .thereby through rits shaft '|.961the bevel gears |98 and the servo control input shaft .|82 will be rotated.

previously wzlesczribed, lthe normally station- Iary gears ||0 and? |.|.'2 yprovide for yoperation of 'the hub'carried .pumps when -the propeller -is rotating. Itis 'themapparent that some means is 'necessary to operate these pumps so that-high pressure fluid for propeller -pitch change is availablewhen the propeller is not rotating, as -for example, when it is desired to unfeather the -provpeller 'in ight -or on -the ground. To this end V'tation of the'normally rstationary gears 4H0 and VI|2 'in-one direction only, i. e., to prevent inadvertent motion-of the normally stationary gears ||0 and ||2 Aduring normal operation when the lreaction -of the pumps is imposed thereon.

Itisfthen-apparent'that during operation ofthe auxiliary motor the gears ||0 and '|12 will'be rotatedso as 'to provide drivingpower `for =thepropeller Vpumps While "at lthe lsame time providing driving power through vthe `reversing 4gear 92 to the planetary cluster |80 and the servo control input shaft |82. Hence, under these conditions with the propeller stopped the sun gear |86 of the gear cluster |88 will be held stationary due to the fact that its driving gear |84 and gear |28 are also stationary. With the ring gear |56 now rotating, the planetary pinion |88 will revolve about the sun gear 86 so as to rotate the bevel gears |68 and the input shaft |82. With the in put shaft now rotating in the same direction as it does when the propeller is rotating, the servo system to be described in connection with Fig. 2 then operates to produce the desirable controln ling movements in the output shaft |68 to eventually move the distributor v-alve as desired.

The particular gear train connections described herein are claimed in co-pending patent application Serial No. 159,772, filed May 3, 195|),by Nelson R. Richmond.

Referring to Fig. 2, the servo control input shaft |62 is shown as driving the gears 220 of a servo pump which provides high pressure oil to the servo controller system. The supply of fluid for this pump is omitted for convenience. The high pressure oil from the servo pump is supplied to a manifold 222 which in turn distributes the oil to a spring loaded relief valve 224, to a low pressure switch 226, to the high pitch side or chamber 228 of the servo rack and to the proportional solenoid valve 230 which acts as a metering device for the servo system. After the meo tered oil leaves the pilot valve 230 of the proportional solenoid, itis routed via a line 232 to a norm'ally closed chamber 234 of a reversing solenoid 236. The metered oil from the pilot valve 236 at the same time is routed through the passage 240 through a topping governor which is driven by the input shaft |82 and includes a valve 242 operated by the spring loaded fly weights 243. The metered oil normally passes through a topping governor valve 242 and ows via the line 244 to a chamber 246 of the reversing solenoid valve and to the low pitch side or chamber 248 of the servo rack.

A servo rack comprises a stationary piston 250 and a moveable cylinder 252 which carries the rack teeth 254. When the servo rack is actuated ink either direction it actuates the servo output shaft |68 through the gears 256.

Inasmuch las the output shaft |68 eventually transmits motion to the distributor valve in the propeller hub, a lock pitch unit is coupled to the output shaft to provide selective locking thereof against rotation. The pitch lock unit responds to selective electrical signals from the propeller control relay box or the lock pitch switch 226, the lock pitch switch providing automatic operation upon a failure of servo hydraulic pressure by means of electrical line 260.

The pitch lock unit comprises a pair of toothed disks 262 and 264 which are fixed to the output shaft |68. The teeth on the disk 262 are sloped in an opposite direction from those on disk 264 so that a locking engagement with either of the disks by the locking members 266 and 268 will prevent rotation of the output shaft |68 in one of two directions. In other words, the locking member 266 will prevent rotation of the output shaft |68 toward a high pitch direction but will ratchet away so as to permit free movement in 'a low pitch direction. The locking member 268 on the other hand by engagement with the disk 262 prevents rotation of the output shaft |68 in a low pitch direction only. Of course, simultaneous engagement of both the locking members 266 and 268 with the disks 264 and 262 would lock the out- Dutshaft |68 against movement in either direction.'- lThe locking elements 266 and 268 are biased in an engaging position by means of a pair of coil springs 210 and are held ina disengaged position by the solenoid coils 212 and 214. The solenoid coils are in turn energized by signals received from the propeller control relay box which comprises the various electrical control elements and switches for operation and propeller control.

The servo-unit lock system and associated mechanism is claimed in co-pending patent applicationSerial No. 159,736, filed May 3, 1950, by Melvin E. Longfellow, now U. S. Patent Serial No. 2,652,122, issued September 15, 1953.

In operation then (referring to the servo control systeml the output of the oil pressure pump 220 of the servo pump is maintained at a desirable pressure by means of the relief valve 224. This pressure always reacts on the servo rack tending to move it in a high pitch direction. This movement toward high pitch is resisted by the metered oil from the proportional solenoid pilot valve 230 which valve is adjusted in response to the signals received from the electronic governor. The electronic governor causes the pilot valve 230 to increase the metered oil flow to the servo rack and move the output shaft in the low pitch direction when the propeller R. P. M. is below the desired setting. As the propeller R. P. M. is higher than the governor setting, the pilot valve 230 shuts off the metered oil flow and opens the metered oil passage to drain which permits the servo rack and the connecting gear 256 to the output shaft |68 to move in the high pitch direction. The low pitch to high pitch area ratio of the stationary piston 250 of the servo rack may be in the order of two to one so that in the on speed condition the metered oil pressure is approximately one-half the magnitude of the servo pump output pressure.

The fly ball type topping governor may be set for some desired R. P. M. as for example for of maximum desirable propeller R. P. M. to provide a safety measure against sudden excessive propeller rotational speeds as might, for example, result in a high speed turbo-driven propeller arrangement. Thus, in the event that the normal governing system fails, the topping governor regulates the now of oil to the servo rack by means of its valve 242 to maintain constant propeller y R. P. M. at the topping governor overspeed setting. Since the topping governor controls the propeller at a relatively low rate of pitch change, Ia ball check valve 280 is provided in the reversing solenoid valve to permit by-passing of the topping governor in the event of a requirement for a high rate of increase pitch change is required such as would occur when feathering from an overspeed condition.

For reverse pitch operation both the reversing solenoid and the proportional solenoid are energized to permit direct high pressure servo oil iiow to the low pitch side of the servo rack and to isolate the topping governor from the system to prevent it from calling for a pitch change in the wrong sense if an overspeed occurs in reverse. The by-passing is accomplished by unseating the ball check 280 in the reverse solenoid 236. With the ball check unseated, high pressure oil, which in metered form is leaving the pilot valve 230 into the line 240, will be permitted to flow via the line 232 through the normally closed chamber 234 of the reversing solenoid valve 236 past the open ball check 280 and into the chamber 246 ofthe valve from whence it may ow directly'to the low pitch chamber 248 of the servo rack. Y

For feathering, the proportional solenoid is energized in the high pitch direction to allow a direct high pressure oil flow tothe high pitch side or chamber 228 to move it to the extreme high-pitch position. In other words, by energizing the proportional solenoid in-an extremehigh pitch direction causes it to no longer meteroil into the line 240 so that no pressure whatsoever is admitted to the low pitch side of the servo rack. A

Since the position of the servo controller output shaft is a direct indication of propeller blade angle, a pitch stop cam mechanism 290 is connected directly to the shaft |68 by means of gears 292. The cam mechanism consists of five adjustable cams to provide a normal high pitch limit, a normal low pitch limit, a reverse limit, a feather limit and a starting limit which would correspond to an approximate zero pitch blade angle. Each of the individual cam elements are arranged to selectively trip electrical limit switches 294 which in turn disable the desired portion of the electrical system con-tained in the propeller control relay box.. v

In order to sensitize'the operation of the electronic governor and its output signal to the propeller solenoid, a feedback potentiometer has its movable element connected to the shaft- 256 which carries the p-itch stop cam mechanism 220. Hence, the movements of the servo output shaft |68 will provide a simultaneous variationv of potential output of the potentiometer which output is fed back as a signal to the electronic governor to provide in effect an anticipator or follow-up signal.

Fig. 3 illustrates the various electrical units which represent the propeller control lrelay box and diagrammatically indicates the various electrical communications therein. Each Vof the previously mentioned electrically operated elements are also shown diagrammatically herein, as for example the auxiliary motor and lock pitch solenoids. For convenience, the specific electrical wire connections are not enumerated throughout. For convenience of description instead, the general operation of `each of these switches and the result produced on the operating electrical elements is generally described. As previously mentioned, one limit switch isV provided for each propeller stop position and these in addition to the other electrically responsive elements are diagrammatically indicated along vthe right hand side of Fig. 3. v

During normal governing operation the increase and decrease pitch solenoids are held energized through the normal lowv and normal high pitch limit switches. Then,lif for anyieason the governor servo system Fig.`2) moves toa lower pitch than ythe setting of the normal low pitch limit switch, the Yassociated Acam will trip this switch to open the circuit to the low pitch solenoid ofthe pitch lock and preventthe output shaft |68 of the servo unit from moving any furthertoward lowpitch. Following this, Yshould the governor servo system move again toward high pitch the output shaft |68 willratchet away from its locked position until the low pitch limit switch is returned to normal (as for example'by spring loading). The low pitch solenoid 212 of .the pitch loch unit will again be energized to`- disengage the lock. The normal high pitch limit switch will loci; the servo output shaft in-a similar manner by del-energizing the highpitch solenoidv 214'of the pitchv lock unit.

In the event vthat the feather switch is operated, a plurality of circuits are completed or closed. First, the holding coil 300 of the feathering switch is energized under the control of the closed feather limit switch. Second, the increase pitch relay is energized so that it opens the governor circuit and simultaneously applies battery current to the governor proportional solenoid with a polarity to causethe governor servo system to operate in a high pitch direction. Third, the high pitch solenoid 211| of the pitch lock unit is held energized (unlocked position) independently of the normal low pitch limit switch. Fourth, the relay 3|() is energized so that the switch 3|2 is closed to provide current to the auxiliary motor. Following this, the servo output shaft |68 actuates the distributor valve within the propeller hub to move the blades toward a feather position, keeping in mind that the position of the servo output shaft |68 is a direct indication of blade pitch position when the servo output shaft has moved to the feather position. The feathering cam will actuate the feather limit switch toward an open position to open the holding coil 352i of the feathering lswitch which will cause the switch to return to normal position. At the same time the high pitch solenoid 2"."4 of the pitch lock unit is de-energized so that its corresponding spring 219 (Fig. 2) will engage the lock preventing further movement of the servo output shaft toward a higher pitch, i. e., beyond feathering. As a precautionary safety measure, it is possible to override the cie-energizing operation of the feather limit switch by further manual operation of the feathering switch in a feathering direction.

To unfeather the propeller, the unfeathering switch is moved toward the UF position which energiaes the unfeather relay via the line 320; and since in moving tc the feathered position the normal high pitch limit switch had been moved to the dotted line position, the relay 3|!! (for the auxiliary motor) is energized also as follows. Battery current flows from the lock pitch switch via the line 324, through the high pitch limit switch (in dotted position), through line 326 and the line 328 adjacent the unfeather relay switch (which is now closed) and finally to line 330 and the relay 3| (l to energize the auxiliary motor. rihus it will be apparent that when the servo shaft returns to the -high pitch limit switch setting this switch will return to its normal (full line) position to de-energize the auxiliary mo- At the same time that current is owing from the lock pitch switch (Via line 324) as described above (for energizing the auxiliary motor), current will also flow through the normal low pitch limit switch via line 334 back through connection 336 and then via line 338 to energize the low pitch lock solenoid 212 toward an unlock position thus ernitting movement toward low pitch (unfea- At the same time since the propeller is not rotating, or is beginning to slowly rotate, the electronic governor will call for a reduced pitch thereby signalling the proportional solenoid accordingly.

It shouldbe noted that both a governor solel10id" and a proportional solenoid are illustrated 1n F1a 3 as being connected in parallel. Although both solenoids are required .to provide governing powerhaving high rate of response, the dual installation provides a safety feature in the event one solenoid becomes inoperative.

In order to obtain reverse pitch the reversing switches are closed. rI'wo reversing switches are shown with the switch adjacent the battery terminal serving as a safety switch operable to a closed position by engagement of .the aircraft landing gear with the ground in a manner wellknown in the art. With the switches closed, current then fiows from the battery to lines 35B, 352, 354 to energize the reversing relay. K At the same time the decrease pitch relay is also energized through lines 356, 358 while thereversing solenoid is energiz-ed via line 3dB.

It is apparent that the decrease pitch relay will open the circuit from the electronic governor and will apply battery current with proper polarity to the proportional solenoid via the contacts of the decrease pitch relay so as tok decrease pitch toward a reverse position.

The reversing relay energizes the low pitch lock solenoid (to permit movement toward low pitch) via the line Sill, the reverselimit switch, line 312, junction 335 and line 338. It Willbe noted thatthis circuit will beopened when the reverse limit switch is operated to an open position by its cam. The reversing relay when energized also simultaneously conditions the unreversing relay by energizing the latter via line 380. This connects the unreversing relay with the normal low limit switch which is held inthe dotted line position by its cam whentheservo output shaft moves to reversing position. Thus the unreversing relay will be held in this position by obtaining current from the lock pitch switch, the low pitch limit switch, line 382 and junction 384 even when the reversing relay is subsequently de-energized.

When the reverse limit switch is opened (when the propeller blades reach proper reverse position) the low pitch lock solenoid 212 is de-energized to lock the servo input shaft against movement toward low pitch.

In order to unreverse the reversing switch is returned to normal, as shown, and the reversing relay is de-energized. Although such de-energization breaks the flow of current to the line 380 of the unreversing relay, the latter is still energized by the contacts of the normal low limit switch (dotted line position) so that consequently the increase pitch relay is energized.

The increase pitch relay thereafter opens the circuit from the electronic governor and simultaneously directly energizes the governor and proportional solenoid to actuate the governor servo system toward high pitch. As the servo system moves past the normal low pitch position, the low limit switch is returned to normal thereby cie-energizing the unreversing relay which in turn de-energizes the increase pitch relay to return the pitch control to the electronic governor.

When starting a turbine power plant (turboprop installation) it is desirable to have the propeller blades in fiat pitch. Thus when the starting switch is operated the decrease pitch lrelay operates to decrease pitch, the starting relay ope-rates through the normal contacts of the starting switch, the relay 3! operates the auxiliary motor (to obtain pump pressure since the propeller is not rotating) and the low pitch lock is energized to an unlock position. The propeller servo system then moves toward low pitch until the start limit switch is opened by its respective cam. This de-energizes the starting relay and the auxiliary motor relay 3 I0 while the low pitch .lock is de-energ'ized into a ,lock position and the 10 blades are then in flat pitch. When the turbin power plant starts, the starting switch is returned to normal thereby yde-energizing the decrease pitch relay and returning control to the electronic governor.

A manual lock pitch switch is provided for manually de-energizing the high and low pitch lock solenoids 212 and 214 to lock the servo systern output shaft I 68 against movement in either direction. v

It is therefore apparent as a result of this invention that an improved propeller system has been provided having an overspeed system which willprevent sudden excessive'R. P. M. surges while being disabled when reversed pitch is being called for. Thus in any event the overspeed governorwill not be calling for an increase in pitch (toward positive from negative) when a. negative or reverse pitch is desired.

Although onlv one embodiment of this invention has been illustrated and described herein; it

is apparent that various changesandmodifications may be made in the construction and arrangement of the various parts without departing from the scope of this novel concept.'

What it is desired to obtain by'Lett'ers Patent l. In an aircraft propeller comprising variable pitch blades, power operated means forvarying the pitch of said blades in positive and negative pitch positions including a source of power therefor, controlling means operatively connected to said pitch varying means and said source' of .power for controlling said pitch varyingr means; speed responsive means for governing said controlling means including a servo motor operatively connected to. said controlling means, overspeed'gov'- erning means operable to preventpropeller speeds beyond a predetermined maximum duringp'ositive pitch positions of said blades. said overspeed governing-means including operative connections to said servofmotor, and mechanism for signalling said controlling means for a negative pitch position of said blades including-means for disabling said overspeed governing means, said mechanisrn comprising operative connections kto said speed responsive means and said servomotor. i

n 2. In an aircraft propeller comprising variable pitch blades, power operated means for varying the pitch of said'blades in positive and negative pitch positions including a source of power therefor. controlling means operatively connected to said pitch varying means and said source of power for controlling said pitch varying means, speed responsive means for governing said controlling means including a servomotor operatively connected to said controlling means. overspeed responsive governing means operable toy prevent propeller speeds beyond a predetermind maximum during positive pitch positions of said blades, said overspeed governing means including operative connections to said controlling means and said servomotor and manually controlled mechanism for signalling said control means for a negative pitch position of said blades including means forming a part of the operative connections of said overspeed governing means for isolating said overspeed governing means from said control means said manually controlled mechanism comprising operative connections to said speed responsive means and said servomotor. 3. In a propeller comprising variable pitch blades. means for varying the pitch of said blades in positive and negative pitch positions, means for controlling said pitch varying means including a source of power therefor, speed responsive means for governing said controlling means including a rst valve actuated thereby, said valve being operatively connected to said controlling means for actuating the latter, overspeed responsive governing means for maintaining the speed of said propeller below a predetermined maximum including a second valve in series with said rst valve and forming an operative connection from said first valve to said controlling means, and manually controlled blade reversing mechanism having operative connections to said valves for positioning said control means in a negative blade pitch position comprising means for disabling said overspeed responsive governing means and includingY an operative connection to said controlling means.

4. In a propeller comprising variable pitch blades, means for varying thepitch of said blades in positive and negative pitch positions, means for controlling said pitch varying means including a source of power and a servomotor, said controlling means being operatively connected to said pitch varying means, a speed responsive governor for governing said controlling means f including a rst valve actuated thereby, said valve being operatively connected to said servomotor, an overspeed responsive governor for maintaining the speed of said propeller below a predetermined maximum when said blades are in positive pitch positions including a second valve in series with said first valve and forming a bridging connection between said first valve and said servomotor, and pitch reversing means operatively connected to said servomotor and said valves including mechanism for lay-passing said overspeed responsive governing means, said reversing means comprising operative connections to said valves and said controlling means.

5. In a propeller according to claim 4 including pitch stop means for disabling said reversing means and said by-passing means when said blades reach a predetermined negative pitch position.

6. In a propeller comprising variable pitch blades, means for varying the pitch of said blades in positive and negative pitch positions, a source of power, means for controlling said pitch varying means including operative connections to said source and said pitch varying means, speed responsive means for governing said controlling means including a servo system therebetween,

said system comprising a servo source of power, 'a servomotor operatively connected to said controlling means, and a valve movable in response to said yspeed responsive means for controlling said motor and operatively connected to said servo source of power, an overspeed responsive governor including a valve movable thereby, said last mentioned valve having connections to said servomotor for limiting propeller rotational speed above a predetermined value, and manually operated means for signalling said first mentioned valve for a decrease pitch position including mechanism for disabling said overspeed governor means including operative connections to rst valve and overspeed governor means.

7. In a propeller comprising variable pitch blades, means for varying the pitch of said blades in positive and negative pitch positions, means for controlling said pitch varying means, speed responsive means for governing said controlling means comprising a first valve actuated thereby, a servomotor operatively connected to said rst valve and said controlling means for energizing said controlling means, a servo source of power controlled by said first valve, an overspeed responsive governor including a second valve operable thereby, said second valve including operative connections to said rst valve and said servomotor for limiting the maximum speed of rotation of the propeller.

8. In a propeller according to claim 7 including a third valve operatively connected to said second valve and said servomotor, and means for signalling said control means for a reverse pitch position including conduits connected to said third valve and providing for disabling said second valve.

MELVIN E. LONGFELLOW. NELSON R. RICHMOND.

References Cited in Vthe file of this patent UNITED STATES PATENTS

Images