US2516149A

US2516149A - Aircraft fuel system

Info

Publication number: US2516149A
Application number: US593917A
Authority: US
Inventors: Samiran David
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-05-15
Filing date: 1945-05-15
Publication date: 1950-07-25
Anticipated expiration: 1967-07-25

Description

July 25, 1950 D. SAMIRAN AIRCRAFT FUEL SYSTEM 2 Sheets-Sheet 1 INVENTOR.

Filed May 15, 1945 July 25, 1950 D. SAMIRAN 2,516,149

I AIRCRAFT FUEL SYSTEM Filed May 15, 1945 2 Sheets-Sheet 2 k9: JJE 5 31 m NO Another object of the invention is to so construct, arrange, and connect the drop tanks that, with a single setting of the selector cock, which connects the main pump to the main tank, the entire contents of the drop tanks will be transferred to the main tank a fuelisbeing used out of the main tank. y

Other objects and advantages will become evident as the invention is described in detail and reference is made to the drawing, wherein:

Fig. 1 is a schematic view of the complete system with its hydraulic and electricalconnections.

Fig. 2 is an axial section through the jaw clutch through which power is appliedtodrive theautp matic selector cock.

Figs. 3 and 4 are axial sections showing'the closed and open positions, respectively, of a pressure sensitive switch which shows when slam; from which fuel is being taken is empty.

Figs. 5 and 6 are transverse sections showing the closed and open positions, 'respectively,of a

manually openable switcl'i'forf deenergizing a solenoid which, when energized, maintains power connection to the tank selector cock.

Figs. 7 and 8 show open and closedpositlons,

" respectively, of the piston valve which prevents operation of some of the functions of the system except when the engine'is running.

Referring now totthe drawing, an aircraft engine l0 carries a main fuel' pump l2, the pump"' being operatively connected'to theengine to be driven thereby and adapted to supply fuel under pressure tothe carburetor 114,- or like fuel metering device. The engine pump is provided with the customary relief'valv'e whereby fuel is re-" 5 turned fromthedischarge' side of thepump back to the intake side whenj'the pressure at the discharge side exceedsaf preselected value, which, for illustrative purposes may, in the instant case, be taken as fiften pounds; It may preferably also'fig be provided with a small adjustable leakagepassage from the discharge side back to the intake. Such a leakage passage will return only a minute volume of fu'elfro'm the discharge side back to the intake side, but when the pump ispumping 45 air only, will return a volume of air equalto substantially the-entire-air pumping capacity'of the pump from the dischargeside ba'ckf to the intake side. The provision of the leakage opening therefore does not materially afiectfthe capacity of the 50 pump to raise the fuel pressure to the desired value, but insures that when the pump is pumping air no considerable air, pressure may buildup at the carburetor intake. "Theair eliminating feature of the engine pump isshown, described and 55 claimed in my depending application Serial No. 570,938, filed January 1, 194:5, nowl?atent'No. 2,431,345, issued Novemberf25', 1947.1,

A main tank [6 and 'an'auxiliarytank I 8 are carried within the aircraft as a permanent part 60 thereof. The main tank I6 is soj'arralnged that the reserve portion 11- of its" contents which extends from the bottom to the line l9. may not be drawn from the tank except} for emergency use, until after the other portion "2| above the line I9 65 and all fuel in the other tankshas been used. A belly tank 20 and wing tankszili and 24 are-carried externally on the underside of the fuselage and under the right and leftwingsrespectively. The external tanks 20, .22 and 24 may conveniently be 70 referred to as the droptanksl- 1 A fuel cock 26 has seven equally spaced stations to which the pointer 28 maybe turned, namely Off, B, L, Ri, A, M, and Re when proceeding.anti;-, clockwise. These indicia, with the exception of 75 4 on show the stations of inflow into the selector cock.

A single outflow pipe 30 emerges from the center of the selector cock, flowing first through a strainer 32, then through a pipe 33 to the suction side of the engine pump H. A pipe 34 connects the bottom of the belly tank 20 to the inflow station B, a branch 35 extending upward into the top of the tank 16. A manual valve 3| in the branch 35 is normally closed. A pipe 36 connects the bottomjof the left wing drop tank 2 2 to the inflow station L. A pipe 38 connects the bottom of the right wing drop tank 24 to the inflow station R1. A pipe 40 connects the bottom of the auxiliary tank l8 through an auxiliary pump 42, which is driven by an electric motor 44, to the inflow station A. An adjustable resistance 43 is employed to regulate the output pressure of the pump. A manual switch 45 is provided to disconnect the pump motor 44 from its current source. A pipe 46 connects the'bottom of the main tank I 6 through a pump 50 and branch pipe 48-, and the discharge side of the engine pump |2 through a pipe'53 and check valve 52, to the inflow passages M and Re. A rotatable member of the selector cock 26 is secured to the pointer 28 for rotation therewith and this member is provided with a channel for selectively or sequentially connecting the several inflow passages to the outflow pipe 30. The pump 50 is driven by an electric motor 54.'and is so arranged and connected in the system that it may act as a booster pump, drawing from the main body of fuel 2 I in tank "5 and delivering it to the suction side of the engine pump as an aid thereto, or it may operate as an emergency pump, drawing fuel from the reserve llland delivering, it to the discharge side of the engine pump when, for any reason, the engine pump fails to maintain a predetermined pressure at. the carburetor intake. Pump 50 is. provided with an inbuilt relief valve which is set to maintain the pressure at its discharge side somewhat below that of the engine pump. For illustrative purposes the discharge pressure of pump 50 may be taken at twelve pounds.

As a means for sensing when the engine pump has failed to maintain a predetermined pressure at the carburetor intake, there is provided a fuel pressure sensitive electric switch 56 which is connected by a pipe 58 to the discharge side of the engine pump l2 and to the intake of the carburetor I4. Switch 56 comprises a body in two parts, 60 and 6!, the interior being divided into two compartments, and 61, the lower compartments 65 being vented to the atmosphere at 63.

A spring-metal diaphragm 62 separates the

compartments

65 and 61, the diaphragm being slightly dished so that it will resist change in position from that shown in Fig. 3 to that shown in Fig. 4, or vice versa, with a resistance of approximately two pounds. The spring 64 is so proportioned that, in Fig. 3, it exerts an upward pressure of 11 and pounds, and in Fig, 4, an upward pressure of 14 and pounds. It follows that when the switch is closedas in Fig. l, with the

switchcontacts

66 and 68 in engagement, there is a resistance to downward movement of 11 and plus 2:13 and pounds. Switch 56 will accordingly open if a pressure of 13 and pounds is applied in the chamber 51. Conversely, when the switch is open as in Fig. 4, with the

switch contacts

66 and 68 separated, there is an upward pressure 01.

14 and A; pounds 2 pounds -l2 and pounds A drop in pressure in the chamber 51 to 12 pounds will accordingly allow the switch toclose. It will, of course, be understood that the pressures at which the switchtt changes from closed to open position-andviceversa, -are arbitrarily chosen for purposes" of illustration and that any quick make and break'pressure operated switch "having an appropriate overlap between opening and closing pressure, so as to .prevent hunting; willbe considered within the scope of the invention. Awarning signal light I is connected to the contact member 68' whereby the light comes .on coincidentally with a drop inpressure sufficient to close theswitch '56." i

, An electric motor '72 operates a vacuum pump ll 'such as is commonly employed in an aicraft, the pump having its suction side 16 'conn ected'to the various vacuum operated instruments usually iffiundonan aircraft and having'the pressure "side ([8 connected by pipes 80, 82 and .84 to thet'ops of the .

drop tanks

22 and 24. A check valvef86 is interposed betweenthe' discharge side I8 andthe ,pipeLBO and an air pressure regulator 88 is interposed between pipes 80 and 82.' A gauge 00gives .visible indication of the air pressure beinglmaintained. Pipes 92 and Mconnect the 'bottoms'of the

drop tanks

22 and 24 to the top of the drop tank 20, whereby, by maintaininga proper air pressure at the gauge 90, the fuel may be .forced outof-the drop-

tanks

22 and 24 into the drop tank 220,, and out of the drop tank .20 into the pipe 34 from which .it may be directed by way of station :13 of: the selector cock 26 directly to. the suction "side .of the engine pump I2, or, by opening the valve 3I;, through the main .tank I6, pump 50, :

pipes

148 and 53 to the discharge side of the en- .ginepump I2. I

Weighted floats Stand 98 operate conical valves I00 and I02 in tanks 22 .and 24,--\vhereby these :tanks empty uniformly and maintain a balanced loadomthewings, for, if one-tank empties faster thanzthe other, the greater height of the fioat in the duller tank increases its outflow passageway through the conical valve of the fuller tank and thereby maintains the balance. When the tanks ":22; and .24 have been emptied by air pressure as .zabovedescribed, the valves I00 and ;I 02 should .be

:closed except that there should either be a slight valve leakage in the closed position, or there should be separate leakage openings IOI and-I03 sothat airipressure coming into the tanks 22 and 24 :after they are empty may get through into the -tank'zu to pressurize the tank, 20 when it is desirableto discharge its fuel in that manner. Afloat I04 in the top. of the maintank 16 operates-a valve I03 .to .closed position toprevent fuel from'the-drop tanks entering the main tank I6by way of the pipe 34 faster thanit is being drawn from the bottom by the .pump 50.: v 3

float I08 operates an electric .switch 'I I0. "When the level of the fuel in the main .tankIS fallsbelow the line It, the switch I I0 closes,.and thereafter the pump 50 cannot any longer-act as a booster pump to deliver fuel from the maintank I6 byway of pipes 48 and -46, -through stationM of the Selector cock, and byway of pipes 30 :and133 to thesuction'side of the engine pump 12, :but can act 'asan emergency pump only to deliver themserve fuel I 1 by way of pipes 48 and 53 4'00 the: discharge side of the-engine pump I2, and that only .Whenthe pressure in the pressure sensitive switch 256 drops below "the predetermined value due to -a tank from which the engine pump is taking -fuel becoming empty. This is due to the fact that the electrical connection made by the switch -I-I-0 acts in conjunction withanothcr switch hereinafter described to prevent thvmotor' driven "selector m e .twol statigns one disc to the other.

selector cock --has-*stations,which is in the-instant 'embodiment is seven. A switch :I I8 is always-open as shown whenever the free enclof the operating arm I20 has dropped into one of the notches -I I6.

Four cams I22, I24, I26 and I28, also fasten the cam shaft I I2, are provided for closing the switches A, M, Re and C respectively, the oper- 'ating lugs =On-the cams 122, I24 and '-I'26-beih'g so positioned that the switches A, M and Re close only when selector cock pointer is set 'on A, M

or Re respectively, While the lug on the cam I28 is so made as to keep the switch marked 0' closed when the selector cock pointer is on either 2M or'Re orOff, and open on all other stations.

7 A disc I32a (see Figs. land 2) is fast' on the rear'end of the cam shaft II2. Disc I32aand a second disc I32 are joined together at the edges by a yoke 1-44; A tubular part 134 extends rearwa-rdly from the disc I32 and carries a toothed clutch part "37 at the free-end. A switch 136 is operable by a plunger I31 (see Figs. '5 and '6) "which lies between the discs Plunger "I3'I is slidable radially between the discs and-between the guide lugs I39 which also join A contact member 138 extends laterally from the plunger I3I w-hichis normally "held in contact with the contact member I40byaspring I42 as seen in Fig. '5. A small cam Iis fast on the forward end of a shaft I135 and-liesbetween the'discs I320. and I32. Cam I30 has a single V notch I43 (see Fig. 6) into which the -V end of the plunger I3I is held by the spring 142 when the switch is closed as-in .Fig. 5. Rotation of thecam I30 by the shaft ;.I in either direction will raise the plunger I31 and open the'switch I36 as seen in Fig. 6. The yoke I44 terminates in "a stop I45 (see Fig. 5) which prevents the plunger I3I 'ever rising high enough to get wholly out of the notch I43. 'It will ,be understood that the discs I320; and 132 with their connecting yoke 1'44 always rotate with theshafts I I2.and I35.

A .gear I4 6 has a prolonged tubular hub I48 with a flange I58. An electric motor I5I has an .inbuilt .highreduction gear box I'53'through which .a pinion I .is driven, the pinion being in constant meshwith thegear I46. .A spring I52reacts against .a stationary part I54 of the structure to movet-he flange 15d into .engagement with the stop I56. ,A .solenoid coil I50 receives electric current through the switch I36 and,v when ener- -gi-: zed, .moves the hub I48-the direction of the line to the motor I5'I, current will nevertheless be maintained-at the motor terminal through-the switches H8 and I as long as the pointer :28 A selector handle 7 I64 is fast on the outer end of the shaft I35. A grooved collar I66 fast on the shaft I35 is engaged by a stationary part I68 to allow rotation but prevent axial movement of the shaft. Inasmuch as the frictional resistance to rotation of g the selector cock 25 must be overcome by the handle I64 when manual operation of the selector cock is being efiected, it follows that, as soon as -a slight torque is manually applied to the handle I04, to turn thecam I30 the switch I36 opens as in Fig. 6, the coil I58 is thereby deenergized, the clutch I62 is disengaged by the spring I52 and the switch I65 is coincidentally opened, whereby the motor II need not be manually rotated through the high reduction gearing each time the selector cock is manually operated.

Since it is desirable that certain parts of the fuel system should not become operative except when the engine is running, there is provided a switch mechanism I which is responsive to the oil pressure of the engine lubricating system. Switch I10 comprises a contact bar I12 movable by a piston I14 into engagement with contacts I16 and I18, which are in turn separately movable into contact with the bar I12 by the manually operable handles I80and I02. The cylinder I84 within which the piston I14 is slidable is connected by a pipe I86 to the oiling system of the engine I0. A spring I88 urges the switch I10 to its open position. In order to provide a suitable overlap as between opening and closing of the switch I10 toprevent hunting, a detent ball I I9I is radially slidable in a pocket I93 in a boss I85 0f the cylinder I84 and is urged inward by aspring I95 into a notch I91 when the switch is open as in Fig. 7 and into a notch I99 when the switch is closed as in Fig. 8. The slopes of the notches I91 and I99, and the strength of the spring I95 are in such proportion that, when no pressure exists in the pipe I86, a force of 2 pounds will to left just before the ball I9I passes the point I81 and 3 pounds to move it from left to right, also just before it passes the point I81. The spring I88 is then so proportioned that it will 0 be required to move the piston I14 from right be offering a resistance to movement from right to left of 17 pounds just before the ball passes the point I81 and will be exerting a force of 19 pounds to move the piston from left to right also just before the ball passes the point I81. Obvi-,

.ously, it will take 17+2=l9 pounds oil pressure" to move the piston left until the point I81 passes the ball I9I to close the switch, and, when the pressure in the pipe drops to 16 pounds, the 19 pound force exerted by the spring I88 minus the 3 pounds resistance caused by the spring I95 will again open the switch. An oil pressure gauge I09shows when the pressure is being maintained at the desired value. A switch I90 is closable by the solenoid coil I92. A main switch I94 connects the battery I96 or other source of electric current to the system.

The operation of the system is substantially as follows:

Operation By closing the switch I94 current will be supplied,

,by way of the now closed fuel pressure responsive switch 55 to the relay coil I92 thereby closing the switch I through which an electric current is directed to the motor 50 which pumps to the discharge side of the engine pump I2 and to the carburetor I4 and the pressure responsive switch 56. v.Switch 56, however, remains closed because the relief valve of the pump 50 is set at twelve lbs. pressure while thirteen and one-half lbs. pressure is required to open the switch 56.

While this twelve lbs. pressure is being maintained, the engine may be started in the usual manner. When the engine starts, the engine pump cannot instantly obtain fuel because the selector cock is on the Off position. In a matter of several seconds, however, the engine oil pressure becomes high enough to close the oil pressure switch I10 whereupon electric current reaches the selector cock operating motor I5I and the solenoid coil I58 simultaneously, thereby engaging the clutch I62 and rotating the shaft Hz to turn the selector cock pointer 55 anticlockwise. When the pointerreaches the B position, the suctionside of the engine pump I2 is hydraulically connected to the bottom of the drop tank 20 and may therefore increase the pressure at the carburetor from twelve to fifteen lbs., which will open the fuel pressure sensitive switch 56 and thereby stop the selector cock motor I5I, disengage the clutch I62 and open the switch I90 to stop the motor 54 of the pump 50. Thereafter the fuel cock pointer 28 will remain at station B until the drop tank 20 has been pumped empty by the engine pump- I2. 'When the drop tank 20 is empty, air will be drawn therefrom by the engine pump I2 and discharged into the pipe 58 whereupon the pressure responsive switch 56 will close again and electric current will be directed simultaneously through the switch I90 to the motor 54 of the pump 50, through the selector cock motor I5! and through the solenoid coil I58 to engage the clutch I62 to move the fuel cock pointer 28 from station E to station L.

Between the time the selector cock leaves the station 13 and the time it reaches the station L, the suction side of the engine pump is disconnected from all fuel sources, and cannot therefore build up pressure to open the pressure sensitive switch 56, so that the pump 50 must continue to provide the twelve pounds pressure at the carburetor intake all the while the selector cock motor I5I is turning the pointer from station 13 to L. It is noted, however, that there is a possibility that the pressure at the pressure sensitive switch 56 might be built to fifteen lbs, and the switch opened while the pointer was intermediate the stations 13 and L and the selector cock motor thereby stopped short of its objective. Such a condition could develop if the relief valve in the motor pump 50 should stick slightly for several seconds only and build the carburetor pressure to fifteen instead of twelve pounds while the pointer 28 was moving and was intermediate two stations. In such an event, however, the time delay switch IIB would function to prevent stopping between stations, for it will be seen that, as soon as the pointer 28 moves several degrees away from any station, the time delay switch H8 is closed and does not open again until the pointer is within several degrees from the next station. It is further noted that while the selector cock motor I5I is started by current received through a closed pressure responsive switch 56 upon pres- 1 sure failure therein, it is kept operative until the next station is reached irrespective of whether the 9 pressure. is built up. andtheiswitch56 opened or not; because the time delay switchreceives current directly from the battery "andfdirects "it through the switch F65 to'the seiector cockmotor- I51? and to the solenoid coil IEB which closes the switch I65 as well as engages the-clutch l62'. Obviously then, when" the" pointerionceleaves a station it cannot stop short of" the nextstation. The cycle of operations which's'ln'f'ted'thesel'ector cock from B'to; L upon the drop: tank-Z'Wbecomi'ng empty repeated to shift "it from-l3 to Hi when the drop tank 22 'becomesempty; and is again repeated .to shift from-.Ritowhen the droptank 2'4 vbecomes empty. Themechanismwhereby'the three drop tanks 20,;2 2 and 24* arenow released and discarded is not shown.

It is noted that up tothispointidelhas been taken only from the-drop'tanksgandthattit came from the tanks directly to the intake side of the engine pump without theassistance of a booster pump. This procedure isouitesatisfactorysince flying during thisperiod 'is for the most'part at low altitude. However, "ii it becomes*necessary to go to a relatively higher altitudewhile the drop tanks have not yetbeen emptied, resort is had to pressurizin'g the dloptanks bythemotordriven Howeven'when' the drop tanks are Y 1|8reaches thesuction side of the engine pump at 1 aconsiderably increased pressure.

Coincident'a'lly with the makingof-" hydi'alflic connection from the auxiliary tank IB through the" booster pump 42" and stationfi- "of the selector cook '26; the cam I 22 closes the switch A- and provides current to'the boosten pump motor Mthroughout'the emptying ofthe auxiliary tank I'8. When the-auxiliary tank 1 8 is==empty"the same failure of" pressure at 'thepressure'responsive switch 56" moves the-selector cock pointer Z8 from, station A to stationM, whereby the cam I 22 opens the switch A and the cam: #14 closes: the switch M.

The closing of the'switch brings'current from the battery I96 to the motor il of'the pump 1 irrespective of whether the-pressure responsive switch 56,, the relay switch 1-95; 'orthe' oil pressure switch I10 are 'openor-closed, whereby the pump 50" will act" as a booster pump and draw fuel from the maintank li -and adeliver it to=the suction side of the: engine pump f2 until the level of the fuel drops" below the line H, whereupon. the float operated switch fl 0' will closeand light, the warning, signal '10.

, Current may now reach the selector cock operating motor 'l5l' for" rotating the sel'ectorcoc'k 26 through the float switch H0 and the fully closed oil pressure switch ITJJ; andwillrot'ate the selector cock anticlockwise; During movement between stations thelfi'ow ofliuel past thei'uel cook 26 to the suction side o'f'the enginepump of course. interrupted,. andthe-pressure responsive switch 56 closes; momentarily between each station. When the pointer passes Re-the suction side of the engine pump may; momen-' tarily get fuel from. the reserve ITandwiil therefore open the pressure responsive switclr56' which normally controls the selector cockpmotorjlt l.

gQBut this :timethe opening of 'the switch'ili'will 10 not stop the motor I51 "for it is now receiving current independently of the switch 56 through the reserve fioatlswitch H0;

Now inasmuch as, in the operation of the system above described, all other tanks were emptied before connection was made to the reserve supply Il, the selector. cock will continue to rotate round and round' until 7 the operator observes that the warning light continues to be lit. He then manuallyoperates the handles I- and- 182 of the oil pressureswitch 'l-lfllso as to withdraw the contact; members I16 and H8, whereupon no electrical connection will exist to the selector motor l5!" The operator may now manually place the selector. pointer 28 on station Re where upon current will flow from the batterythrough the cam operated switch Re to energize; the coil I92 and close the. switch l' whereupon current will flow to the motor 54 of pump 50 and fuel will be pumped from the reserve I Tito the suction side of the engine pump l2.

Inthe foregoing description of the operation of subject fuel systemit was assumed; that at. the start the pointer 28gwas at: the Off stationand that the entire system was permitted to func' tion automatically thereby emptying. theltanks in their normal anticlockwise-sequence. It may happen, however, that the pointer may have been inadvertently or intentionally placed at a different station, as for example on station A.

The carburetor may now be primed, iflnec'e'sisary, by means of the pump 50 as hereinbefore described When the engine is started, the fuel pressure sensitive switch 56 will stillbe' closed whereby, the selector cock motor will attempt to rotate the selector cock away iromthe A station, but before it can move it. as muchas'the, several station. A until this tank is empty.

The closing of the pressure, sensitive switch; 55

due to: this empty tank conditionwill. start. the

selector motor 15! which will move the, pointer '28 to station M, whereby it may take fuelfrom main tank- I G downtothe line l9 whereupon the "fioatswitch H0 isclosed and will therefore operate inconjunctionwith-the fully closed oil pressure operated switchtlll toxmaintain. connection tostthe-selector motor -l5l independently of the pressure sensitive switch 56.

The-selector cock will therefore rotate anticlockwise round and-rounduntil:the-pilot observes the continued operation of. the signal lll where- 1 upon: he may operate---the handle l 80 of the oil pressure switch H0 thereby withdrawing the eontact lz'l'fifrom the contact H2, and the pointer will stop; except that because of the cam switch C, it cannot stop 'on'station M,:Re or' Off, and because of the time delay switch H-8= itcannot step s between stations.

If the pilot vnow stops rotation of the selector with the pointer at station B, he-may useallrof the fuel in the three drop tankswithOutfurther changeofstation's after which the-warning light 10 will indicate to him that he should now shift to station-Re and? use thewreserve. supply 1 I11.

' If the pilot desires, he may operate the system by opening theoil pressure switch I10 so asto n11 then when the warning light indicates an empty tank, shift the selector cock manually to station M. The booster pump 50 will act as an emergency pump to pump to the discharge side of the engine pump and thereby maintain pressure at the carburetor until the shift has been made, whereupon the signal light 10 will go out and the pressure sensitive switch 56 will open.

Opening of the pressure sensitive switch 56, however, does not stop the motor 54 of the pump 50 for the reason that the motor 54 now receives current by way of the cam operated switch M. The pump 50 therefore now takes fuel from the main tank 16, pumps it through the pipe 45 through the selector cock 26, pipes 30 and 33 to the suction side ofthe engine pump l2 which in turn raises the pressure still further at the carburetor. Since the drop tanks are pressurized and the hand valve 3| is open, the entire remaining supply of fuel will pass from the drop tanks through the main tank and from themain tank to the suction side of the engine pump, the float valve I06 in the meantime preventing inflow into the tank 16 faster than it is being used therefrom.

Still another procedure in operating the system may be carried out as follows:

, By placingthe selector cock on station A, opening the hand valve 3! and the oil pressure responsive switch I10, the fuel in the auxiliary tank i8 will first be pumped to the suction side of the engine pump, the engine pump raising it to a slightly higher pressure at the carburetor. When tank I8 is empty, the pressure sensitive switch 56 will close, which will coincidentally close the switch I90 whereby current will be directed to the motor 54 of the pump 50.

Now the pump 50 cannot pump through pipe 46 because the selector cock is on station A, so

it pumps to the discharge side of the engine pump through pipe 53. Since the drop tanks are pressurized and the hand valve 3| is open, the

,entire fuel supply is used with the single setting on station A. llt is noted that with this method 'of operation the engine pump is used only while tion for each tank, adapted for connecting the respective tanks one at a time to the suction side of said pump, electric power means for rotating said selector cock from one station to the next, a pressure sensitive device at the discharge side of said pump adapted for directing an electric current to said electric power means for rotating said electric power means to rotate said selector cock away from any station when the pressure at said discharge side drops due to said station having said suction side connected to an empty tank, and a float operated switch means in one of said tanks adapted when the fuel in said tank falls below a predetermined level to direct an electric current to said electric power means to start said electric power means irrespective of said pressure sensitive device to rotate said selector cock.

2. In an aircraft fuel system a plurality of fuel tanks, a fuel pump, a selector cock having a station for each tank adapted for connecting the "respective tanks one at a time to the suction side of said pump, electric power means for rotating said selector cock from one station to the next, a r v a tank selector cock having a station for each pressure sensitive switch at the discharge side of said pump adapted for. directing an electric cur rent to said electric power means for rotating said electric power means to rotate said selector cock away from any station when the pressure at said discharge side drops due to said station having said suction sideconnected to an empty tank, and a float operated switch in one of said tanks adapted when the fuel in said tank falls to a predetermined level to direct an electric current to said electric power means to operate said electric power means irrespective of said pres sure sensitive device to rotate said selector cock.

3. In an aircraft fuel system a plurality of fuel tanks, a fuel pump; aselector cock having a station for each tank adapted for connecting the respective tanks one at a time to the suction side of said pump, power operated means for rotating said selector cock from one station to the next, a pressure sensitive device at the discharge side of said pump adapted for connecting a source of power to said poweroperated means for rotating said power operatedmeans to rotate said selector cock away from ,any station when the pressure at said discharge side drops clue to said station having said suction side connected to an empty tank, and a float operated means in one of said tanks adapted when the fuel in said tank falls to a predetermined level to apply said source of power to said poweroperated means to thereby start said power operated means, irrespective of said pressure sensitive device, to rotate said selector cock, a cam operated means rotatable in coincidence with said selector cock and having operating surfaces adapted-when operative to stop rotation of said selector cock at a predetermined series of. stations only, and a manual means for making said cam operated means effective." A I. 1

4. In an aircraft fuel system a plurality of fuel tanks, a fuel pump, a selector cock having a sta- I tion for each tank adapted for connecting the current to said electric power means for rotating said electric power means to rotate said selector cock away from-anystation when the pressure at said discharge side drops due to said station having said suction side connected to an empty tank, and a float operated electric switch in one of said tanks adapted when the fuel in said tank falls to a predetermined level to direct an electric current to said. electric power means to operate said electric powermeans, irrespective of said pressure sensitive device, to rotate said selector cock-electrically conductive means extending from said pressure sensitive electric switch andsaid floatoperated electric switch to said electric power means, a cam rotatable by said selector cock, said cam having operating surfaces corresponding to a selectedseries of stations on said selector cock, an electric switch actuated by said operating surfaces, and a manually operable switch means operative to open the direct circuit extending from the fuel pressure sensitive switch and the float operated electric switch to said electric power means, and operative tocpmplete a circuit trrough said cam operated switch in series, whereby said selector cock will stop only at thestations of said selected series.

5; In a fuel system having a plurality of tanks,

13 tank, a fuel pressure pump, anelectric motor for rotating said selector cock-from one station to the next, a pressure sensitive switch operative to close and to direct current to said motor when said selector cock has said pump connected to an empty tank, a delaying switch operative to open when said selector cock is turned to any station and to be closed when it is moving from any station to the next, a clutch for drivably connecting said selector cock to said. motor, a magnetically operable switch, electromagnetic means for coincidentally engaging said clutch and closing said switch and conductors forming a series circuit through said pressure sensitiveswitch and said delaying switch, or through said electromagnetic operable switch and said delaying switch when said pressure sensitive switch is open.

6. The structure defined in claim with a manual means for rotating said selector cook, a torque sensitive coupling the driving and driven parts of which are rotatably yieldable to the application of opposite torques thereto interposed between said manual means and said selector cock, a torque sensitive electric switch openable by the yielding of said coupling upon application of a torque to said manual means, and conducting lines extending to said electromagnetic means openable by said torque sensitive switch whereby manual operation of said selector cock disengages said electromagnetic means and thereby disengages said clutch.

7. In an aircraft fuel system, a plurality of fuel tanks, a fuel pump, a rotatable selector cock having a station for each tank adapted for connecting the respective tanks one at a time to the suction side of said pump, an electric motor for rotating said selector cock from one station to the next, a fuel pressure operated electric switch at the discharge side of said pump closable for conveying an electric current to said motor for rotating said selector cock away from any station when the pressure at the discharge side drops due to said station having said suction side connected to an empty tank, a float operated electric switch associated with one of said tanks closable for conveying an electric current to said motor independently of said fuel pressure sensitive switch for rotating said motor when the fuel in said tank falls below a predetermined level, an oil pressure operated electric switch, normally closed when said engine is in operation for directing current so said electric motor and a cam operated electric switch including an operating cam on said rotatable selector cock, said cam having switch closing lobes at a preselected part of its periphery, parallel electrical conductors extending from a current source through said fuel pressure operated electric switch and said float operated electric switch joined into a single conductor which extends through said oil pressure operated electric switch to said motor, a branch circuit extending from said oil pressure operated electric switch through said cam operated electric switch to said motor, and manually operable means associated with said oil pressure operated electric switch for opening the circuit through the said single conductor and completing a circuit through said cam operated switch.

8. In the old combination of a device including a shaft and actuating means for rotating said shaft manually or by power, an improvement in the actuating means which comprises a rotatable switch support fast on said shaft, an electric switch on said support, a switch spring for maintaining said switch in closed position, a power rotated member, a manually rotatable member, a cam on said manually rotatable member adjacent said switch, operative upon either a gain or a loss of rotative movement of the manual means with respect to the switch support to open said switch against the resistance of said switch spring, means to limit to part of a turn the degree of rotative movement of the cam with respect to the switch support, a clutch part on the manually rotatable member, a complementary clutch part on the power driven member, a clutch disengaging spring, and an electromagnetic device for engaging said clutch parts deenergized by the opening of said switch by operation of said manual means to allow said clutch disengaging spring to disengage said clutch parts for manual operation.

DAVDD SAMIRAN.

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

UNITED STATES PATENTS Number Name Date 1,398,315 Cawthra Nov. 29, 1921 1,407,374 Buckendale Feb. 21, 1922 1,419,553 Galloway June 13, 1922 1,681,487 Lee Aug. 21, 1928 1,764,936 Dean June 17, 1930 1,793,228 Hackethal Feb. 1'7, 1931 2,005,891 Elberty June 25, 1935 2,146,729 Gavin Feb. 14, 1939 2,314,899 Samiran Mar. 30, 1943 2,324,571 Fitz July 20, 1943 2,327,373 Samiran Aug. 24, 1943 2,327,980 Bryant Aug. 31, 1943 2,397,068 Wilson Mar. 19, 1946 FOREIGN PATENTS Number Country Date Great Britain Feb. 6, 1930