US2593910A - Variable pitch reversible propeller - Google Patents

Description

April 22, 1952 E. H. MORRIS EFAL 2,593,910

VARIABLE PITCH REVERSIBLE PROPELLER Filed Aug. 30, 1948 2 SHEETS-SHEET 1 Invento r s EDWARD H. MORRIS, ELLIS DANVERS & THOMAS E. GODDEN Attorneys April 22, 1952 E. H. MORRIS ETAL 2,593,910

VARIABLE PITCH REVERSIBLE PROPELLER Filed Aug. 30, 1948 2 SHEETS-SHEET 2 Fig.3.

Inventor s EDWARD H. MORRIS,

ELLIS DANVERS & THOMAS E. GODDEN Attorneys Patented Apr. 22, 1952 VARIABLE PITCH REVERSIBLE PROPELLER Edward Hollingworth Morris, Ashtead, EllisDanvers, Gloucester, and Thomas Edward Godden, Cheltenham, England, assignors to Rotol Lim ited, Gloucester, England, a British company Application August 30, 1948, Serial No. 46,874, In Great Britain September 2, 1947 Claims.

This invention concern variable-pitchpropellers of the kind in which the blades are capable of adjustment from a positive angle (to provide forward, thrust) to anegative angle (to provide backward thrust). Such propellers will be referred to as reversible pitch propellers.

Reversible pitch propeller are normally required to provide backwardthrustonly when the aeroplane is landing and the present invention has for its object to provide a system of control for propellers of the kindreferred to in which the backward thrust is obtainable only after the aeroplane has touched down.

According to the present invention a reversiblepitch propeller comprises a constant-speed unit for controlling the pitch of, the blades of the propeller, means to over-ride said unit and brin the blades to within the negative pitch-range and means for bringing said over-riding means into operation only whilst the aeroplane is on the ground.

According to one feature of thisinvention a reversible-pitch propeller comprises a constantspeedunit for controlling the pitch of the blades ofthe. propeller, electrical means to over-ride said unit and bring the blades to within the negative pitch-range and switch means, in the circuit of said electrical means, to control its operation, said switch being actuated to bring the electrical means into operation bythe weight of the aeroplane.

According to another feature of the invention a reversible-pitch propeller comprises a hydraulic pitchechange motor, a constant-speed unitto control, the blade movements in the positive and negative pitch ranges, means for over-riding the constant speed unit to move the blades from one pitch rangeto the other, an electrical control for said over-riding means and a switch for controlling the operation of said electrical control, said switch being actuated by the weight of the aeroplane.

Preierably said switch is actuated to bring the electrical over-riding control into operation by telescoping of the undercarriage of the aeroplane onlanding.

In order thatthe nature of the invention may be more clearly understood a practical application of it will now be described, by way of eX- ample, with reference to the accompanying drawings whereof:

Figure 1 is a side elevation of an aeroplane shown as it is coming into land,,the aeroplane ,incorporatingpropellers in accordance with this invention,

Figure 2 is a schematic representation of the propellers of the aeroplane of Figure 1,

Figure 3 is a circuit diagram of the control system for the propeller of Figure 2, and

Figure 4 is aschematic view of the engine-propeller assembly and of the main controls therefor.

In Figure-1 the aeroplane I00 has a pair of propellers 5 (one only of whichis seen in the drawings) which are driven, one each, by an engine carried within the nacelle NH. The. aeroplane carries a rectractable undercarriage I 0.2! comprising, in known manner two telescoping leg members I03, I04.

Each propeller 5 is hydraulically operated and is provided, in known manner, with a pitchchange motor 6 (see Figure 2) the ram 1 of which i connected with the individual propeller. blades 8 by means of a linkage 9.

Hydraulic fluid for the. operation of themotor 6 is provided by a pump I04 which supplies fluid to the valve I05 of a constant speed unit, generally indicated, at I06, and thence to the motor 6. The constant. speed. unit I06 isof known construction and comprises a fiy-weight governor I01 provided to adjust the valve I05, the flyweights being driven in usual manner from engine I0 I'through gearing I10.

There. is also associated with the propeller 5 a feathering pump I08, which isdriven by electric motor I40 and is adapted to provide fluid for the operation of, the motor 6 when blades 0 are to be moved to the feathered position or returnedfrom that position.

The engine in nacelle IOI is under the control of. the pilot, the power delivered by the engine being regulated in well known manner by throttle Ill, which is. adjustable by any suitable linkage, diagrammatically indicated at I12 (Figure 4), from lever I0 in the pilots cockpit. The lever I0 is also connected through a suitable linkage (indicated at H0 in Figure. 3) witha pinion 20I which engages a rack on a, sleeve III, the latter being axially adjusted with rotation of the pinionto vary, in .usual manner, the loading of spring I I2 to change the loading on the fiy-weight governor I01. It will be appreciated, therefore, that when the lever I0is adjusted theengine power is regulated. Simultaneously, the datum setting of the constant speed unit I06 is varied so that it accords with the operating conditions of the engine selected. by the pilot: the blades 8 are moved. in known manner as the datum setting of the constant speed. unit is. adjusted, so thattheir pitch corresponds to. the newly selected value. of, speed.

The lever I0 is also connected by meansof alinkage, diagrammatically indicated at II (Figure 3) with a switch, the arm of which is shown at I2.

The lever I is movable along a slot I3 from one end I4, corresponding to slow running of the engine, to the end I which corresponds to full power. The lever I0 may also pass through a gate I6 and into a slot I! and be thereafter moved towards the end I'll-which also corresponds to the full power of the engine. In passing through gate I6 from slot I3 to slot I! the lever I0 adjusts the switch I2 through linkage II so that the arm is set on the studs I9, 20. Similarly, when the lever is moved through the gate in the opposite direction the arm I2 is moved on to stud 2| for other movements of lever I0 the switch arm is not adjusted in any way.

Whilst lever I0 is in the slot I 3 the blades 8 are in the positive pitch-range so that the thrust is applied to propel the aeroplane forwardly. When the lever I0 is in the slot I! the blades 8 are set within the negative pitch-range and the propeller thrust is applied as a braking force to the aeroplane.

The pump I04 of the unit I06 draws oil from the lubricating system of the engine and, besides supplying the motor 6 through the valve I05 it passes oil to the valves diagrammatically indicated at 22, 23 and 24. Thus, valve 22 is supplied through channels I55, I56 and valves 23 and 24 through channels I55, I51 and I58. The valve 22 regulates the passage of the pressure fluid along channel I59 to a motor I I3 associated with a relief valve II 4 which is provided on the delivery side of pump I04 along channel I60. The valve 23 regulates the passage of fluid from pump I04 along channel I60 to a motor II5 associated with the constant speed unit so as to override it in a manner later described. The valve 24 regulates the passage of pressure fluid along channel I6I to a motor II6 which is provided to adjust a two-position valve III.

When motor I I5 is brought into operation the unit is overriden in its operation. Accordingly, for convenience, this motor will be referred to as the overriding motor, valve 23 as the overriding valve and a solenoid 25 which controls the operation of the valve 23 will be called the overriding solenoid. Valve III is only brought into operation when it is desired to move the blades from one pitch range to the other during reversing or unreversing of the blades 8. Accordingly, motor II6 will be referred to, for convenience, as the reversing motor, its valve 24 as the reversing valve and a solenoid 26 which is provided to adjust the valve as the reversing solenoid. The valve 22 regulates the passage of pressure fluid to relief valve II4 so as to increase the pressure at which it operates and accordingly the valve 22 and its actuating solenoid 21 will be referred to as the pressure-increasing valve and solenoid respectively.

The reversing valve 24 is normally spring urged to a position at which valve III is set so that pitch adjustments are performed (under the control of the constant speed unit) in the positivepitch range.

Carried by ram I of pitch-change motor 6 are a pair of shoulders 28 and 29 which are so arranged that, as ram I moves to the left (Figure 2) to bring the blades 0 from the positive pitchrange to the negative pitch-range, shoulder 28 engages abutment II8 when the blades have assumed a position hereinafter referred to as the fine-pitch position. The ram I is again stopped, when stop 29 engages stop II8, with the 4 blades at zero pitch. Stop H8 is removable to allow the ram to move to the left after the stop is engaged by shoulders 28, 29. Thus, the ram is brought into and adjusted in the negative pitch range.

The stop H8 is moved clear of shoulders 20, 29 in the following way:

When pressure fluid is delivered by pump I04 to motor 6 by pipe II9 to move the ram 1 to the left it also passes by duct I20 to valve I2I. The latter is urged by spring I 22 to the right (Figure 2). The normal fluid pressure on valve I2I is incapable of moving it against spring I22. When shoulder 28 or 29 engages stop H8 and ram I is brought to rest, the continued delivery by pump I04 raises the pressure in motor 6-and, thus on valve I2I. When the pressure reaches a predetermined value valve I2I is moved to the left due to the pressure in motor 6 acting thereon and duct I20 communicates with duct I23 and acts on piston I24. This piston is then moved to the right against spring I25 and shoulder I26 is moved from under stop I I8. The latter comprises a plurality of circumferentially spaced spring fingers I2I which tend to contract inwardly but are prevented from so doing by shoulder I26. When the shoulder is moved clear of abutment I I8 the fingers contract and carry the stop away from shoulders 28 or 29. When the ram is thus permitted to continue its travel to the left the resultant pressure fall resets valve I2I and piston I24 to the position shown in Figure 2. In this way after stop H3 is cleared from shoulder 28 it will be automatically re-set to engage shoulder 29.

The increased pressure required to remove abutment II8 will be reached as the blow-off pressure of relief valve II4 is made greater as later described. The arrangement of shoulders 28, 29 and stop II8 are well known and will not, therefore, be described in greater detail.

There is associated with the blades 8 a pitchfollowing mechanism, generally indicated at 30, and comprising a pin 3I carried by the root of a blade, a rod 32 and a plate 33 carried by the rod. The pin 3| and rod 32 are normally spaced apart (at I21) so that the mechanism has a lost-motion effect and it is arranged that slightly before the blades reach their fine-pitch setting the pin 3| will have been moved to engage rod 32 to move the plate 33 against a pair of contacts 34, 35. This could occur, for instance, at +10 pitch setting. The plate 33 is of conducting material and completes a circuit through the contacts 34, 35.

Similarly, with the continued movement of the blades 8 towards the negative-pitch range at about +5 the plate 33 engages contact 36 thereby completing a circuit through contacts 34 and 36: finally at about 5 the plate engages contact 3! thereby completing a circuit through the contacts 34, 31.

Generally, the function of the mechanism described is that when the lever I0 is moved from the slot I3 into the slot H the switch arm I2 is brought to engage contacts I6, 20. As a consequence the solenoids 25, 26 and 2! are energised in a selected manner thereby (i) to bring the ram 1 successively against the shoulders 28, 29, (ii) to enable the pressure fluid passing to the motor 6 to be increased so as to remove said stops automatically, (iii) to override the constant speed unit I06 so that the blades are moved from the positive pitch-range to the negative pitch-range and (iv) to reverse the flow of pressure fluid from valve I05 to motor 6 so that when the blades are in the negative pitch-mange the constant speed unit I05 will be effective suitably to adjust the blades in the required sense.

It is considered desirable that this sequence of operations just outlined be prevented from taking place until such time as the aeroplane has touched down since it is only during the landing run and for manoeuvring on the ground generally that the braking force is required. To this end, there is provided a switch 38 (see also Figure 1) which is closed when the undercarriage legs I03, I04 are telescoped, as occurs when the aeroplane touches down on landing. The switch 38 is in series with the aeroplane battery 39 and with the solenoids 25,, 26, 21 so that until the switch 38 has been closed as indicated no circuit may be completed from the battery 39 to any of the solenoids.

The sequence of operations performed under different flight conditions will now be described.

It will be assumed that the aeroplane is airborne and the sequence of operations which take place as the landing approach is made, as the machine touches down, as the braking effect is obtained by moving the blades to the negative pitch-range, as the unbraking operation is performed, as starting of the engine from rest takes place and, finally, as the aeroplane takes-off will then be described, in that order.

Whilst the machine is flying there is of course no load on the undercarriage and the switch 38 is open. As a consequence the entire circuit controlling the solenoids 25, 26 and 21 is dead. The propeller blades are within the positive pitchrange and are being adjusted automatically by the constant speed unit I06, the datum setting of which is varied by moving lever I0. The two shoulders 28 and 29 are in position to prevent movement of the ram I, firstly, beyond fine pitch and, secondly, beyond zero pitch into the negative-pitch range.

As the landing approach is made the pilot moves the power lever I0 from some position along the slot I3 to the slow-running end I4 thereof. As a consequence the datum settingof unit I 06 is adjusted and it is arranged that the power developed by the engine under these conditions is insufiicient to provide the power required to drive the propeller. .As a consequence, theapropeller windmills at the fine-pitch setting. i. .e., ram I is against shoulder 28, to provide the remaining portion of the power. This will havethe effect of producing drag thereby preventing the gliding speed of the aircraft from becoming excessive. If the pilot wishes to reduce this drag pleted from the battery 39, switch 30, lead I28,

switch 40 (which is normally closed) lead I29 to the solenoid 21 to energize the latter. The pressure-increasing valve 22 is opened to apply the pressure of pump I94 to motor II3 thereby loading relief valve II4 so that the pressure of fluid within the motor 6 may be increased sufliciently to withdraw stop IIB from the fine-pitch shoulder 28 against which the ram I has been brought during the landing approach (see above). As the propeller moves towards zero-pitch the plate 33 is "brought .into engagement with the .studs 34, 3 5 thereby completing a circuit from the battery, through switch 38, lead I28, lead 4| contacts 34; 35, lead I30 :and a solenoid 42 so that the switch is opened and the solenoid 21 is deenergised. This restores the normal pressure conditions in the motor 6 so that the :stop I I8 cannot be-withdrawn from shoulder 29. As a result the propeller is now free to constantspeed over :the rangeof pitch settings above the zero- .pitchzshoulder 29.

When the, pilot wishes to obtain a braking thrust he moves 'power lever I0 through thegate I5 and as a-consequence switch arm I2 is moved to engage studs I9 and 20. In so doing a pair of circuits are completed from the battery 39 one through lead I 3| to solenoid 2S and the other through lead I3 I Ito solenoid 43-.the circuits being in parallel. When solenoid 43 is energised, switches 44 and 45 are-closed and there is completed a circuit fromthe battery 39 through the studs I9, 20, lead I50, switch 44, lead I5I and switch 46 to the solenoid 25. At the same time a circuit is completed from the battery 39 through switch 45 to solenoid '27. As a consequence solenoids 25, 26 and 21 are now all energised.

When the machine touches down, the switch 38 may tend to open and close with bouncing of the undercarriageand to overcome this there is associated with the solenoid 43 a known form of .holding circuit (not shown) which is brought into use when the solenoid is energised to .ensure thatit is maintained in this state.

When solenoids 25, 2B and 21 are energised valves 23, 24 and 22, respectively, are opened thereby applying the pressure of pump I04 to motors I15, H6 and H3.

Operation of motor H3 loads relief valve I I4 to ensure that 'a pressure build-up will take place in motor 5 sufiicientto remove stop IIB from shoulder '29 so that the blades .8 may enter the negative-pitch range. Operation of motor II5 over-rides the unit I06 toensure that the pressure fluid is delivered by pump I04 continuously in one way and operation of motor IIB ensures that the pressureciiuid passes by duct [I I No carry theblades into the negative pitch range. When the .zero-pitchshoulder 29 isremoved and the blades placed within the negative pitchrange, plate 33 engages contact 31 at -5: contact 36 has previously been engaged but as this is in series with a switch 41, which has so far remained open, .it is not effective. When plate 33 engages contact 31 a circuit is completed from the battery 39 through leads I28, 4|, contacts 34,

31; lead I52 tosolenoid and switch 46 is opened whilst switch 41 is closed. There is associated with the solenoid '48 a known form of holding circuit 200which ensures that the solenoid'remains energised.

' When switch 46 is opened the overriding soleto provide that the propeller is operating within the negative pitch-mange andis bein automatically adjustedby unit I06 under the control of the lever 10. The latter is movable along slot I'I so as to vary the power of the engine. The le- (er I0 now controls to determine the braking force which is obtained.

When the aeroplane is brought to a standstill is desirable that the control system be re-set prior to the engine being stopped. To this end,

=7 the lever III is moved through the gate I6 so that it is in the slow-running position I4. As a result the switch arm I2 is moved to engage the stud 2I and the circuits to the solenoids 26, 21

switch M, lead I53, switch 2I,1ead ,l32 and solenoid 25. The overriding solenoid 25 is therefore energised and the valve 23 is set to bring motor II5 into operation to override unit IIB so'as to move the propeller blades into the positive pitchrange. The pressure fluid will now pass to motor 6 by duct I33 since valve III is not being adjusted to reverse the flow. As the blades are moved the zero-pitch shoulder 29 is moved towards its engaging position. At =+5 the plate 33 moves away from the contact 36 the circuit to solenoid 48 is broken, switch 41 is opened and solenoid is de-energized. The propeller is then within the positive pitch-range and i again returned to the control of the constant speed unit. The entire system is now ready for starting. The'engine may then be stopped.

When the engine is to be started, the lever I0 is placed at the slow-running position I4 and the engine started up. As the engine power increases the constant speed unit adjusts the blades 8 so that the pitch becomes coarser. At 10 the plate 33 moves away from the contacts 34, so that solenoid 42 becomes de-energised and consequently solenoid 21 i energised. The fluid pressure to motor 6 is therefore at its higher-than-normal value and holds the fine-pitch shoulder 28 in its inoperative position so that the propeller is free to constant speed above the zero-pitch shoulder 29, towards which it moves as the power is reduced.

From the starting position the lever I0 is moved along the slot I3 towards the full power position when it is desired to take-off. As a result the propeller speeds up and ram 1 moves to, and beyond, engagement of the fine-pitch shoulder 28 with stop H8: this stop, as has been indicated above, is held inoperative until the areoplane becomes airborne whereupon the load on the undercarriage is relieved and the switch 38 is opened. The entire electrical circuit thereupon becomes dead and the solenoid 21 is deenergised.

If desired the plate 33 and contacts 34-3I may be replaced by a pair of two-position switches which are operated by the rod 32 which engages a plate rotatable with the propeller. The switch arms are actuated by a bell-crank lever either directly or indirectly through the agency of a slider but which, in any case, is adjusted by a slipper with movements of the rotatable plate. The actuation of the switches -will be similar to that of the hub contacts described above.

We claim:

1. Thecombination with a variable-pitch, reversing,hydraulically-operated propeller for an aeroplane having an undercarriage and an engine to drive the propeller, of a constant-speed unit 8 to control the pitch adjustment of the blades of the propeller, a single control to adjust, over a range, both the power output of the engine and the speed setting of the constant speed unit in the positive and negative pitch ranges, means to over-ride the constant speed unit comprising a valve controlled motor operatively connected to the constant speed unit whereby the blades are moved from one pitch range to the other, electrical means operatively associated with said valve to control said over-riding means, said electrical means being actuated by the single control at its slow-running position of the engine and switch means operated by the aeroplane undercarriage to render said electrical control means inoperative, except when the undercarriage supports the aeroplane.

2. An engine-propeller assembly as claimed in claim 1 wherein the hydraulically-operated propeller includes a pitch-change motor and hydraulic connections between the constant-speed unit and the pitch-change motor and wherein the circuit of the electrical control means incorporates switches which are actuated by the blades of the propeller, said switches controlling hydraulic valve means which transpose the hydraulic connections between the constant-speed unit and a pitch-change motor of the propeller while the propeller blades are in the negativepitch range whereby said unit automatically adjusts the blades in the negative-pitch range.

3. An engine-propeller assembly as claimed in claim 2 in which a stop is provided normally to prevent movement of the blades to within the negative-pitch range, said stop being displaced to allow such movement by an increase in the hydraulic pressure in the pitch-change motor to a higher-than-normal value, means being provided to ensure that said higher pressure is built up when the speed-power control is suitably adjusted after the aeroplane has landed.

4. An engine propeller assembly as claimed in claim 3 in which the means for over-riding the constant-speed unit, for transposing the hydraulic connections between said unit and the pitch-change motor and for producing the higher-than-normal hydraulic pressure is each hydraulically controlled by the pressure fluid delivered by the pump supplying the pitch-change motor.

5. Anengine propeller assembly as claimed in claim 4 wherein there is provided a hydraulic motor to adjust each of said means, a valve to control the supply of pressure fluid from the pump to each said motor and a solenoid, forming part of said electrical control, for adjusting each valve.

EDWARD HOLLINGWORTH MORRIS.

ELLIS DANVERS. THOMAS EDWARD GODDEN.

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

UNITED STATES PATENTS Number Name Date 2,154,887 Baker Apr. 18, 1939 2,402,065 Martin June 11, 1946

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