US2425353A - Flexible, variable-diameter propeller - Google Patents

Description

Aug? 12, 1947 1 SPITZER, JR

FLEXIBLE, VARIABLE-DIAMETER PROPELLER Filed sept. 5, 1942 4 sheets-sheet 1 Allg 12 1947- L. sP'rrzER, JR

FLEXIBLE, 'VARIABLE-DIAMETER PROPELLER 4 Sheets-(Sheet 2 .Filed sepi, 5, 1942 INVENTOR m1I /v SP/zE/f JR.

, ATTORNEY i w llg- 12,1947- L. sPlTzER, JR

FLEXIBLE, VARIABLE-DIAMETER PROPELLER Eile-d sept. 5,' 1942 4 Sheets-Sheet 3l 4 w S k mm n NU m

VP T

Aug. 12, 1947.4 L, splTZER, JR 2,425,353

FLEXIBLE, 'VARIABLE-DIAMETER PROELLER I Filed' sept.. 5, 194g 4 sheetssneet 4 INVENTOR wim/v SP/ 725x?, JR, BY

ATTORNEY Patented ug. 1'2, 1.947

l UNITED STAT-'ES oFFIcn This invention relates in general to devices for' propelling airplanes and the like.

Ainn'gthe objects of the present invention itl is aimed to provide" propelling devices or'ai'rl planes and the like which can be driven at high velocities which may equal Aor even exceed the local Velocity of sound.

Withthis main object in mind, the present invention aims to provide an improved `propeller consisting of a plurality of flexible blades, with each blade held in the correct position relative to the air stream by aerodynamic and centrifugal forces.

It is still another object of the present invention to provide, in the interest of producing propelling devices for use at extremely high altitudes, blades, the lengths of which may be increased at Will to compensate forr the decreasing thrust and power at increasing altitudes.

It is still another `object of the present invention .to .provide a blade which will operate equally well'inlthe'subsonic and the supersonic ranges ofvelocity.

More specically, it is an object of theinvention'to provide an improved blade which will op'- erate bothin the subsonic and-supersonic ranges of velocitybwhich comprehends the use of a blade including .two strips of. flexible material' held in rigid'position relative to one another.

These and other features, capabilities and adl-`- Vantages of the invention will appear from the subjoined-detaildescription of specific embodiments thereof illustratedV in theacompanyirg Fig. 5 is a fragmental side elevation of the bladeV shown in Fig. 4, on a still largerl scale than that shown in Fig. 4.V l Fig.- 6 is-a fragmental transverse section ofv the blade shown inFig.4 5 on a still larger scale. K

Fig. 7 is a-fragmental transversesection onthe line 'l-l of Fig. 9 of a modification .disclosingv means-for protecting the blades againstinjurm Fig- 8 isa fragmentalplan View of thelembodl ment. shown in Figf?.

Fig.y 9is. a fragmental longitudinal section of the embodiment shown in Fig; 7.

Fig. 10"is a fragmental vieW oflthe bladeVv and"l protective medium shownin the embodimentof Fig'. 7 on la larger scale than that shown inFi 7j Before describing the present invention in dei' tail and in View of the radical departure thereof it might be well to review briey the problem in! volved.l The demandv for propeller's designedto operate! vat. high angular v velocityhasA led to gradual'increase of propeller tip speeds until these are now equal to or in some cases slightly 'greater than the local velocity of sound. The; greatlyincreased dragof normalairfoil sectionsl at lsupersonic velocities and the lack ofrigidity' inherent Vin-veryr blades, fhowever, makes fur-ther increase inthetipyelocities' impractical forpropellers of normal design.

The basicidea of the present improved blade resides in using such thin blades, With a thickness preferably 3%of the width, or less, that the liftdrag ratio and the loverall propeller efficiency .will' 'remainlarge` evenifthe propeller tipvelocityis far higher than the local velocity of sound.r The complete loss-oftorsional rigidity which this en tails is compensated for vlbyjthe useV of aerodynamic forces to maintain eachblade at Ithe cor-7 rectangle of attackl relative to the air` stream.v

This angle of attack `will remain roughly constant as-the airplane or the like varies either its speedY or its 'altitudes A constantf-angle'of; attackfyhasv as its result a decrease of propeller torque and-of power absorbed-with increasing altitude 'or withA decreasing speed' of the aircraft, theengine R.. P. M. remaining constant, but this result' can be offset'by increasingthe radiusof the propeller1 during flight. To this end, 'see Fig.-3, the blades I can be-extended lby the drum 5 to increase their length,'and consequently the propeller radius,-to-

the; required extent.

With'complete loss of torsional rigidi-ty characterizing such thinblades,"the twisting moment arising from centrifugal force becomes important,l and tends'to decrease the'iangleof attack, butjfthisl` difficulty may bef-overcome by the use of blades y whose length greatly exceeds theirwidth. Hence the blades I are 'not only ver-yvthincomparedto theirwid-th, butalso very long compared -to their-` A further important feature ofthe present Vin v vention resides, lsee, Fig. y4,' in splitting eachA blade into two parts, namely the two strips Zand 3, sep- `blade Vas a whole. `clination of 4 degrees of the rear strip 2 relative `Iniddle of the blade.

blade at an appropriate angle of attack when they velocity of air past the blade is either less than or greater than the velocity of sound. VIf the trailing strip 2 is inclined at about 4 degrees to the leading strip 3, the trailing strip 2 will act in the same way as the tail on a conventional airplane,

keeping the blade as a whole at a stable positive angle of attack. When the velocity of air past the blade is less than'that of sound, the equilibrium angle of attack will be limited to some vangle less than about 6 degrees by the turbulence produced at the sharp leading edge of the forward strip, which prevents the air load on the leading Y strip from increasing beyond a certain limiting lvalue, and which will therefore bring the center of pressure on the blade as a whole back to the` middle of the blade for a moderate angleof at- 4 Y tons per square inch, then with a tip velocity of 2000 feet per second, and a cross section of the base 6 ten times that at the tip "I, with the thickness of the blade increasing graduallyr from the tip 1 to the base 0, the resulting stress at the base would be about 32 tons per square inch, well below the fatigue limit of quenched and tempered nickel-chrome steel. It has also been found that if the tip velocity is reduced to 1400 feet per second,the cross section at the base need be only twice that at the tip to give a stress of 31 tons per square inch. With'this lower velocity, furthermore, the outermost 40% of the blade may foregoing the base S isrnerely indicated as inL creased in thickness as compared to the cross sectack. Since the center of support is some distance infront of the middle, as hereinafter described,V

the equilibrium angle of attack will not be excessive, for subsonic flow.

When the velocity of the air exceeds that of ished. With a blade made of two strips as hereinafter described, the movement of the'center of pressure of the resultant combination, as the air velocity changes from subsonic to supersonic, is a small fraction, roughly 7%, of the width of the With the aforementioned in to the leading strip 3, the average angle of attack for the two strips in supersonicoperation will be quite sufficient, about 3 degrees, to give high propeller power with high aerodynamic efficiency.

In the embodiment illustrated in Figs. 1 to 6, inclusive, the blade I, constituting a main part of the present'invention, is assumed, for the example illustrated, to be about 12 feet in length, about two inches wide at its widest length, and consisting of two strips, 2 and 3, integral with one another as shown, and each of about .6 inch in width, connected at intervals of 3 inches by reinforcing ribs 4, integral with the strips and having a cross section of about .02 inch by .10 inch. In Fig. 6 the relative proportions of the ribs 4 to the strips 2 and 3 are shown. It is assumed for the purpose of this-example that the greatest thickness of the forward strips 3 will be about .016 inch, while the greatest thickness of the trailing strips 2 will be about .007 inch, each strip tapering off to sharp edges both front and rear. The blade I with dimensions such as just set forth will Vhave its center of gravity lie roughly .28 inch forward ofthe The reinforcing members, or ribs, 4 will increase the total area of the blade Vby some 5%, the mass by at most 20%, and if the reinforcing members 4 are madeV of quenched `and tempered nickel-chrome steel like the rest ofthe blade, as hereinafter to be set forth, then the reinforcing members 4 will have suicient rigidity to keep the angular inclination of the willbe considerably increased in thickness. If the material of which the blade I were made is composed of quenched and tempered nickel-chrome steel, of whichV the fatigue strength is about 49 tion of the rest ofVv the blade with a view not to be limited'to any thickness less than twice the thickness of the blade proper.

In any case the total weight of the blade I will be not greater than one pound at the most, and for a propeller having 32 blades, as illustrated in Fig. 3', the total weight of all the blades should therefore be less than thirty pounds. The centrifugal force at the base of a single blade would Y be about one or two tons, if the blade is designed to operate with a .tip velocity of not more than 1400feet per second, while the total thrust would be about pounds at sea level, and less'at high altitudes. The thrust and torque would be transmitted to the base 0r root 6 of the blade and so on to the drum 5 and the shaft 8 by aslight forward inclination of the blade together with a slight lag. The embodiment afore described could apr ply atleast 4000 maximum horsepower at an airplane velocity of 300 miles per hour at seaglevel, and at least 1500V maximum Vhorsepower at the same velocity at 30,000 feet above s ea level.

From the foregoing it will be evident'that aY propeller made of blades I of this type would have numerous advantages. It would operate at or V'by increasing the total length of each blade, Y

since the increase of weight or reduction of propeller efficiencyv for supersonic operation produced by either change would -loe veryV small.

VaryingV the radius of the propeller would give very much moreY flexibility overa much Wider range than is given by the present variable pitch propellers, and has the additional advantage Qf higher, more uniform efficiency. Y The main feature of the invention, of course,

Vresides in the -discovery of a blade as heretofore described and illustrated in detail inA Figs. 3 to 6, inclusive. The part of the invention now to be described, while incidental to this type of blade,-

is, nevertheless, considered essential as lshowing one way of using a blade of ,this type in an airplane. f

In Figs. 1, 2 and 3 there is shown aidrive shaftV 8 which is fixed to the main shell or housing 9 by the splines I0. y connected to a suitable motor, not shown, Vwhich motor in` turn is mounted in the frame or body I I of the.r airplane in the usual wav.v zTo' this frame II there "is secured in the presentinstance `a rigid soft iron annular ring I2 spaced from the rear annular edge I3 of they shel1 9. The :shell 9, which is preferably about three feet in" diameter, has an innerfWalLor partition I4 through which the shaft extends. Tothispartition I4,

and yextending, rearwardly therefrom, there. is i 'Y This shaft 8 is mneianveiyY afiaasssw provided a cylindrical wall: I 5,`having'fatfit's rear; f ward end a partition 1I 5 @through which the fshaftl 8 also extends.

Adjacent to the annulus- I21`th`ere-1is rotatively; mounted yon theshaft 'B'the power wheel I1, the-v` hub I8 of which is positioned between the :par-

the cylindrical portion is provided wthth'e inclined gear teeth 24-to mesh withY the conical gears 25 and 26. front end ofthe cylindrical portion`20is' pro:- vided with a pluralityA of annular sets fof magnets 21, 28"and 29, positioned in'the present instance adjacent to a plurality of setsof armature windings 39,"3I and 32'on the annulusf33`xed on-tle` outer periphery of the rear end of the cylindrical partition I5.A The set ofV magnets 2| to 23,in elusive, when energizedfwill cooperate with'the annulus I2 to lock the power wheel I1 'inxed relationship to the frarneI I and againstrotatio'n with the shell 9. In turn, when the set of magnets 21, 28 and 29 and armature windings 30, 3'I

The. inner periphery "of i the tit'iorrxl 45.? The shaft X42 1 is j ournalld ation'eendf in the partitionw I 4 and' at. its other: endfinfthe l partition 46. When the power wheel. 'I 1 isneith'eriarrested nor "actuated' to rotate frinde'p'en'dent lof'Y thnffin ordervto anchor the train of gea-rsfjst described, including the power wheelI1," against?- displaoement; the `anchor or clutchnow t? be described is provided; Thisanchor'consis'tsfof av 101" oonioal goal-"26,v seeFi'g. 1, mounted ion the i shaft;a

48'1whic`h is journalled at oneend as'sho'wnilinthe shell '9 "and fat its other endisjournalled-'in'L the projectionf 52 'withl the vbushing 149i slida-blyi mountedfon the shaft 48,1 but 'rxedf'tol rotat'ef` 15a therewith by 'the spline 50:. Thetprojection" .521'

has *a* clutch disc* 53`fxed thereto to engagethe clutch disc 54fxed-'Fonfthe bushing49. These and the inner-face 'of the partition' I 5." The -bshr ing 49also Ahas a metal disc 5Iconstituting-anA armature disposed outside ofi the partitionl52l and adjacent-to the vmagnet 51 on the shaft-4855` 25E-.From the foregoing it will appear that whenl the and 32 are energized and theset of magnetsZI, i

22 and 23 is de-energized, then the kset of magnets 21, 28 and 29 will form a shunt-wound D. C. motor with the armature windings 30, 3I andY 32 to cause the power wheel I1 to rotate relative to the shell 9 in the direction of thearrow 34,

see Fig. 2, at a suflicient speed in turn to cause the drum- 5 through the train of gears now to be described to rotate at a faster rate'ofv speed than the rate of speed of the shel1'9. In other words,

'when the power wheell I1 is arrested'the drum 5 wheel I1 is caused to rotate'more rapidly *than* the'shell 9 by the motor formed by the magnets 21 to 29, inclusive, and the armature windings 30 to 32, inclusive, the drum I5 will be caused to rotate at a faster speed than thatof the shell 9 or segments 35 in turn to permit or 'cause the blades 'I to be extended or extruded from the shell 9 or the segments 3'5. The train of gears Vbetweerrthe power wheel I1 and the drum 5 consists essen` tially of the following: the teeth 24`meshing'" with the gear 25 vcause the-shaft 36'of the gearV 25 to be rotated, in turn to. cause the 'Worm 31 on the shaft 33 to rotate." The'worm 31vbeing in mesh with the worm wheel.38 on the shaft 39 will cause the small gear 40 fixed to the'shaft 39 to rotate and this gear 40; lbeing in mesh with the large gear 4I on the shaft 42,`wil1 cause the small gear 43 on the shaft v42 to be rotated. The small gear 43, in turn being in mesh with the large gear`44, rotatably mounted on 'th'eshaft 8, will cause the large gear 44 to' beV rotated relative to the shaft 8 either when thepowe'rwh'eel I1 is arrested relative to the shaft 8; or actuated at a different ultimateispeed than that of 'the shaft 8; The gear 44 as shown in Fig. lis integral with the drum 5;

The shaft 36 on which the-conical gear 251and` worm 31 are mounted'is journalled atoneend in the shell 9 and at its other end 'fin` thecollar or bushing 45 xed on theshaft 8, see-Fig-,. 2. The

shaft 39, see Fig. 1, is journalledfat oneend-inl the partition I6. andV intermediatef-,then-worm whee1-38-andgear Minis journal-ledfffinthefparf 755'andf1tempered .nickelchromersteelmrevertheless;. f

30flilar1y lock the pow-'er wheel I1againstrotation-v magnet 51 isde-energized the spring- 55-will bei` operative to cause Cthe clutch faces 53A and-54"to'V engage one another Vand lock the gearZIif-'agai'nstfv rotation relative to the shell 9i`and therebyisimrelative to the shell-9, in turn to anchor the train of Agears between the power -wheel 'I1 4andy drum-- 5 to rotate as a Vstationary mass with theashaft 8. On the other -hand,'as willv hereinafter bede- '357 scribed, whenever either themagnets 2|, 22iand 23` are `energized to anchorthe'power wheel` I1v to the annulus I2, or the magnets 21, 28iand'29 andv armature windings 38,* 3| and 32 areienergizedy to cause the powerV Wheel I1 to 'rotate"re1' 40 ativer tov the annulus 33," thef'magnet 51 will-*bev energized to attract the disc 56 'against'the'tem and 54 and permit the gear26to rotate relative Vt0 the shell 9; whereby inturnthe power wheel 45' I1 will be free to rotate relative "to the shell'Sf' As aforesaid, the Yembodiment of the invention illustrated in'Figs. 1 to 6,' inclusive,"is"equ.ipped with 32 blades. These are secured to the'outer `periphery of the drum" 5,' tangential thereto, so that should the drum 5Vbe rotated inthe direction opposite to that of` the arrow 58, theblades I may be caused to be wrapped around 'the drum 5 and upon one another.r As shown; the reinforcing strips 4 `will extend towardY thevv drum .55 when the blades I vare wrapped on the drum 5;

The shell 9, see Fig.'2, has 32 slots 59'dispos`ed between the partion 46 Vand theenlargement or radially extending partition 60,"see Fig; 1,` one slot for each blade I. These slotsV are wide enough' to enable the blades I freely to.. pass therethrough and also of sufficient depth to clear the reinforcing sectionsy 4. these openings 59 are formed-by the segments A35 which have an inner curved surface 6I to engage the free unobstructed Vfaces 62 of the blades r I as distinguished from the faces of the blades I on which the reinforcing sections 4 are mounted. The faces 6I of the segments 35are curved 70,so as to prevent anyuabrupt sharp corners en.-

of the highest fatigue strengthsuch fas quenched,

Furthermore,

on account Vof their extreme thinness, might bend" if they had to pass over sharp edges 'whenjleav. v ing the drum 5.

The electrical control for the magnets 23, inclusive, 21 to 29 inclusive, the armature windingsr38 to 32, inclusive, and maget 51,'will now be described. Preferably there is provided a block 80 that is attached to the frame havingtwo brushes 8| and 82 positioned to engage 1 the contact rings 83 and 84, respectively, mounted on the power wheel |1. present instance is connected, by the conductor 88 to the switch'l88, see Fig. 11, which in turn is connected'by the conductor 85 to a suitable` source of current, the negative side of which will be grounded by the conductor 81 as shown in Fig. 5. The brush 82 in turn is connectedby the conductor 89 to the switch |89 which in turn is connected by the conductor 85 to the suitable. l source of current aforesaid. The ring 83 in turn is connected by the conductor 9| to the magnets 2| to 23, inclusive, which in turn are grounded as indicated, to complete a circuit when the switch |88 is closed. The ring 84 in turn is connected by the conductor 86 to the magnets 21,V

28 and 29, inclusive, constituting the eld and to the armature windings 38, 3| and 32, inclusive, of a shunt wound D. C. motor which in turn lis grounded by the conductor 94 to complete a circuit when the switch |89 is closed. Y

The magnet 51 in turn is energized and only energized when either the switch |88-is closed to energize the magnets 2| to Y23, inclusive, or when the switch |89 is |closed to energize the magnets 21 to 29, inclusive, and the armature windings 30, 3| and 32,.inclusive. For this reason the conductor 96, passing through the shaft 8, as indicated in Fig. 1, is connected not only by the conductor 95 to the contact |95 of the'switch |89, fbut also by the .conductor 91 to the contact |91 of the switch |88. After passing through the shaft 8, as indicated, the conductor 96 is connected to one terminal of the magnet 51, the other terminal of the magnet 51 being connected to ground by the `conductor |03.

From the foregoing it will thus appear that when it is desired to retract the blades all or The brush 8| in the.

part of the way, it will only be necessary to close the switch |88 when it will engage the Contact A switch |88 and close the switch |89 in turn to energize the magnets 21, 28 and 29, the armature windings 38, 3| Vand 32, and the magnet 51 when the power wheel I1' again will be free to rotate independent of the shell 9, and the magnets 21,"

28 and 29A will cooperate with the armature wind# ings 3D, 3| and 32 to .cause the power wheel l1 to rotate in the direction of the arrow 34, see Fig. 2, at a suflicient speed in turn to cause the drum 5 through the associated train of gears to rotate at a faster rate of speed than the rate of i speed of the shell 9. On the other hand, when both the switches |88 and |89 are open, not only When the switch|88 is` On the other hand, when it is. desired to extrude the blades all or part of` the way it will only be necessary to open the will the magnets 2| to 23,'inclusive', and the magn nets 21 to 29,`inclusive, and the armature windings 30, 3| and 32 be'de-energized,` but the magnet 51 will also be de-energized to enable the spring ,55 again to cause kthe clutch Vdiscs 553'and 54 .toeng'age vone another and lock the power wheel |1 to rotate with the shell 9. When the -the blades'here bearing the reference character 63are similar in construction to the blades illustrated inthe embodiments shown in Figs. l`

toV 6, inclusive, Vand similarly connected to a drum 64 such as the drum 5. However., to protect the .blades from being bent by their reinforcing cross pieces65, such as the cross pieces 4 of Fig. 4, there is provided a protective strip -66 preferably com-V e -posed ofY rubber, one strip 66 foreach blade 65.

The strip 66 as shown in Fig. 7 is `connected to K the drum 64 directly under the blade 63, that is, between the blade 63 and the drum 64,'s0 that thel cross pieces 65 may embed themselves in the yield'abletextureof the strip 66 and thus protect the-blade from being bent by the cross pieces 65' when-the blade in the course of being wrapped on the drum 64 will have one portion of the blade foldedA on to another Y'portion thereof. embodiment the blades 63 when passing outside of Atheshell 461 will preferably engage a roller such as the roller 68 Yat the vend of a slot between the partitions 69 and 18. The smooth faces 1| of the blades 63; that is, the faces not obstructed by the cross pieces 65, engage the roller 68 as shown in Fig. 7.

These strips 66 areV connected at one of their ends as shown in Fig. 7 .to the drum 64, and at the other of their ends they are connected to.V

theA drum 1'2 .disposed adjacent to the drum 64, the vhub 13 of the drum 12 being mounted on the shaft 14 andin the lpresent instance extending radially inwardof Vthe drum 64 and engaging the side face of the gear 15.Y The hub 13 is rotatably mounted onv the shaft 14 but is connected by the coilspring 1,6 to the shaft 14, one end of the coil spring 16, see Fig. '7, Ybeing connected to the shaft 14, and the other end of the coil spring 16 beng connected in the inner periphery ofthe w drum .12. In order to guide the rubber strips 66 fromfthe drum 64 to the drum 1'2, they pass over the rollers 11 and 18, which are inclined relative to theaxis ofthe rollers 68 'at about 45 degrees. It is,.of course, obvious that there will loe one set of rollers 11 and 18 for each strip 66 and one strip 66 for each blade 63. In operation, it will appear thatwhen the blades 63 are retracted or wound upon the drum 64 they will Vadvance the strips 66 from Vthe drum 12 against the tension of the'spring 1 6, in which case the drum 64 will rotate in a counter-clockwise direction, see Fig. 7,

relativetolthe shaft 14, in which case the Spring 16 willbe at least vpartly woundup andk placed under tension. On the Vother hand, when the blades 63 are caused to extend or extrude Yfrom the shell 61, then during the extruding Aaction the drum 64 will rotatein a `clockwise direction relative to the shaft 14, permitting thedrum1'2 to rotate in the same clockwise direction under the tension of the spring16 to wrap the strips 66 on to the drum 12.

It is, of course, obvious, Ythat Withths blade the Vresultant increase'of propeller torque Vwith the distance re- In this vdecreasing altitude can readily-be oifsetiby reducing the radius of the-propeller during flight, thatis, ley-causing the iblades I of the first embodiment and blades 63 of the second embodi- 10 propeller, extending outward from a shaft or hu-b and having a length at least sixty times its average width and .having an average thickness not more than one-thirtieth times its average width ment, to be partially withdrawn. Since the del.5 consisting of vtwo strips of metal having a high sired lengthof propeller blade for a given altitude can readily be pre-determined, it will only be necessary for the pilot to cause the :blades to be withdrawn the degree necessary to correspond to the particular altitude attained.

Preferably, the blades I are secured to the drum 5 by wires passing through the minute openings 19, the number of openings 'I9 depending upon the length of `blade I provided and the fatiguestrength and forming two sections fixed in close proximity to one another,- one constitut- .ing the leading section and the other the trailing section, the leading section having -a greater y.10 thickness than the trailing section, the neutral thickness of the base 6. With a iblade I of the ,15 and having `a length at least siXtZ7 times its averdimensions here specified, where the base 6 doesv not exceed the thickness of the main part of the rblade-more than three times, then it may be `desirable to use a number of openings for the wires not to exceed 20 in number.

It is obvious that various changesand modifications may be made to the details of construction without departing from the generalspirit yof the invention as set forth in the appended Vofa propeller shaft, and a plurality of torsionally flexible blades extending outwardly from said age width and having an average thickness not `more than one-thirtieth times its average Width Y consisting of two strips of -metal having a high fatigue strength and forming two sections fixed inclose proximity to one another, one` constituting the leading section and the other the trailing section; the leading section 'having a greater thickness than the trailing section, the'front edge of the trailing section placed behind the rear edge of the leading section throughout the entire length ofthe blade, andthe neutral axis of the trailing section inclinedat an angle to the neutral axis of the leading section.

' 6. A blade for an airplane propeller extending propeller Shaft, each blade having an average ,30 Outward from a Shaft 0i hub and Consistiilg YOf thickness not more than one-thirtieth times -its average width to give an Ieflicient blade cross section at supersonic velocities -and having a length at least sixty times its average width to two strips of metal about twelve feet in length forming two parts each about one-half inch in y width, the leading edge of the trailing strip placed about three-fourths of an inch behind the trailmake the twisting moment due to centrifugallfg, ing edge of the leading strip,'the neutral axis of force less than the aerodynamic twisting forces for the desired range of propellerA pitchangles, composed of a metaly having a fatigue strength in excess of thirty-one tons persquare inch to the trailing section inclined at an angle between two degrees and `six degrees to the neutral axis of the leading section, each Sectionhaving .a

thickness lessthan .03 inch, composed of a mapermit efficient operation atpropeller tip veloci- 40 telifl With a fatigue Strength in EXCESS of'thirtyties up to and greater than the velocity of sound and at forward .propeller velocities up to and greater than the velocity of sound.

2. In an airplane propeller, the combination of one tons per square inch, and with means 'for connecting the twosections to one another'to effect the cross-sectional rigidity of theA blade without'interfering with its torsional flexibilitlr a propeller shaft, .and `a plurality-of torsionally,45 t0 Permit `ODBI'aJtOIi 0f the blade at Propeller tip flexible blades extendingoutwardly.from said" propeller shaft, each blade havingk an average thickness not more than .oneethirtieth .times its average wi-dth to givean efficient blade crossvelocities up to and greater than the velocity of sound and at forward propeller velocities up to and greater than the Velocity 0f sound.

'7. A torsionally flexible blade for an` airplane Section at supersonic velocities and havingkapgo" propeller extending outward from a shaft or Vhub length at least-sixty times its vaveragewidth to make the twisting moment `due to centrifugal force less than-thelaerodynamic twisting v.forces for the. desired range of propeller. pitch-.angles and consisting of two strips of metal having a high fatigue strength and forming two sections spaced from one another, one constituting rthe leading section, the other the trailing section,

composed of ,quenched and temperednickel-55 the ,OWF-al1 length 0f the blade being about chrome-steel,v and `formed toY enable aerodynamic*` forces to hold each segment of the blades length at the desired angleof attack to the .air flow, thus topermit eilicientioperation at propeller twelvevfeet, the two sections each about one-half y inch in width, thedleading edgeof the trailing section placed about three-fourths of an inch directlybehind the trailing edge of the leading tip velocities upto andincluding the velocity ofmo Section, and. in the Same. Piane as the leading sound, andf at-foriwardpropelleryelocities up to and greater than the velocity of sound.

w3. -*A'torsionally .flexible -lolade -for amairplane propeller, extending outward fromashaft or hub i section, the leading section being aboutpOl inch in thicknesathe trailing section being about y.007 inch in thickness, the neutral axis of the trailing strip finclined at an angle of about four degrees andhavinga ienginatleast sixtyi-.imes ,weaver-.65 .t0 the' neutral axis of the leadinstrip. and Yeage Width 4and shaving an average thickness not inforcing strips extendmg across and connecting .more .thanl one-,thirtieth times its 1averagewidth :consisting of .two strips lof-metal having. aA high fatigue strength. and vformed into: two sections the sections to one another at three inch intervals, said reinforcing strips being about .02 inch by .10 inch in cross-section with the smallest j fixed in-close proximity .to one another, onecm-I u70 dimension extending in the'direction of the blade sttutngthe leadingsectionf and the.. otherthe trailing i section, theffrontedge of `the ,trailing section placed behind .the rear edge of the Aleading section throughout the entire length` of ,the blade.

,lrlgth, .to effect'the cross-sectional rigidity of themed@ without interfering with its torsional ,'ilexibility, to hold eachsegment of the blades lengthat thepredetermined angle of attack to 1.4.-.:A torsionally;flexible` blade for an ,fairplane..75. the air flow, by means of aerodynamic forces, and

extension Ybeing Vand having a length at least sixty times its average width and having an average thickness not more than one-thirtieth times its average width consisting of two strips of metal having a high' fatigue strength and formed into two sections spaced from'one another, one constitutingV the leading section, the other the trailing section, andy reinforcing cro-ss pieces spaced at intervals along the blade for spacingthe sections fromone another to effect the cross-sectional rigidity of the blade without interfering with their torsional rigidityto permit eicient ope-ration ofthe blades Vat propeller tip velocities up to and Vgreater than` the velocity of sound and at forward propeller velocities greater than the velocity of sound', said reinforcing pieces having'their greatest dimen- 'sion in the Vdirection of the blade width, with `an extensioniperpendicular tothe face of the blade about seven to fourteen times the thickness of the blade, and with their shortest extension in the direction of the blade length, said shortest about the Vsame as the blade thickness." Y v' 9:]5n an airplane propeller, the of a propeller shaft, a pluralityT of fiexi'ble'blades extending outward from said propeller'shaft, the

blades each composed of two thin flexible metal Vstrips of high fatigue strength and formed into,

a leading section and a trailing section, fixed in Yclose/proximity to one another, the leading sectionl'being about twice as thick as the trailing section, the front edge of the trailing section placed directly behind'the trailing edge of the leadingsection, and in the same plane as the leadingsection'throughout the entire length of the blade, the distance between the sections being combination 4longdesc to said drum and slidably mounted on said guides, a power Wheel rotatably mounted on said shaft, a train of gears for drivingly connecting said power wheel to said drum, van anchor for anchoring said power wheel to said frame while said shaft rotates to enable said drum to be rotated in turn to withdraw said blades into said shell, and a second anchor for arresting said train of gears vrelative to saidV shell, whensaid power wheel is liberated to rotate with said shell, to enable said blades in retracted position to rotate with said shell. Y

12.'The combination of a frame, a driven shaft mounted in said frame, a shell fixed on said shaft, a drum rotatably mounted on said shaft, said she-ll havingv a plurality of Varcuate guides with spaces therebetween radially disposed to said drum, a plurality of exible blades connected to said drum and slidably mounted on .said guides, a power'wheel rotatably mounted on Ysaid shaft, Ya train of gears for drivingly connecting said power wheel to said drum, an electric Ino-` tivating means operatively connected between said shell and'power wheel to actuate said power Y, f .ormingpositiom and an anchor'ffor arresting about as great as the width of'one of the sections,

the neutral "axis ofthe trailing section inclined at an'angle between two degrees and six degrees to `the'neutral -Iaxisrof the leading section, and

means provided for connecting the two sections to oneV another to effect the cross-sectional rigidity of theiblade when operating at propellerV tip 'velocities' up to and greater than the'velocity ofY 'sound and at forward propeller velocities up to and greater than the velocity of sound.

'10; The combination of a frame, a driven shaftY mounted in said frame, a shell fixed on said shaft,

, aA drum rotatably mounted on said shaft, Ysaid shell having a plurality Yof arcuate guides with spacesY therebetween radially disposed to said drum, a plurality of flexible blades connected to said drum and slidably mounted on said guides, andmeans for operatively connecting said-shaft to said drum to Venable said drum to withdraw said blades out of extruding position relative to said shell,. or to extrude said blades to rotate with saidshell asa propeller, each of said blades being composed "of two sections, "one section consti-` tuting a leading section and the other a trailingV section, and means for connecting said sections to one another to maintain a predetermined angleY relative to one another.V

'11'.` The combination of a frame, a driven VshaftVV mounted' in'said frame, ashell fixed on said wheel at a greater speed than that of said shell to enable saiddrum to be rotated in turn to extrude said blades Yfrom said shell in propeller said train of gears relative to saidshell when said power wheel is liberatedY to enable said blades in extruded position to rotate with said shellin propeller-forming posi-tion. j Y

13. The combination of a frame, a driven shaft mounted in said frame, a shellxed on said shaft,

a drum rotatably mounted 'Yon said shaft, said shell having a pluralityof arcuate guides with spaces therebetween radially` disposed toy said drum, a plurality of flexible blades connected to said drum and slidably mounted on said guides,

a power wheel rotatably mounted on said shaft, `a train 'of gears for drivingly connecting ,said power wheel to said drum, an anchorjfor anchoring said power wheel to said framewhile Vsaid shaft rotates to enable said drum to be rotated in turn tojwithdraw said blades into said shell,V anelectric motivating means operatively connected between said shell and power lwheel whenA said anchor is interrupted to actuate said power wheel at a greater speed than that of said shell to enable said drum tobe rotated in turn to extrude said blades from said shell in propeller forming position, and a second anchor for arresting said train of gears'rela- Y tive to said shell both when said nrst anchor is truded position to rotate with said shell. 14. The combination of-a frame, a driven shaft mounted in said frame, a shell iixed on said shaft, a drum rotatably mounted on saidshaft,saidshell having a plurality of arcuate Vguides Vwith spaces therebetween radially disposed to vsaid Y drum, a plurality of flexible blades connected to said drum and slidably mounted on said guides,

a power wheel rotatably mounted on saidshaft,

a trainof gears for' drivingly connectlngsaid power wheelto said drumy an anchor for anchor-V ing said power vwheel tov said frame while Ysaid shaft rotates to enable said drum to be rotated Y in turn to Withdraw said blades into said shell, an Y electric motivating meansY operatively connected between said shell and power wheel whensaid anchor is interrupted to actuate said power wheel Y Vat a greater speed than that of said shell to en-i able said-drum 'tofbe rotated in turn to extrude lsaid blades from said shellin propeller forming I' position, a second anchor for arresting said train of gears relative to said shell both when said first anchor is interrupted and when said motivating means is at rest to enable said blades in retracted or extruded position to rotate with said shell, a control in said frame and means operatively connecting said rst anchor, second anchor and motivating means to said control, to be controlled thereby in turn to control the length of blades extended.

15. The combination of a frame, a driven shaft mounted in said frame, a shell fixed on said shaft, a drum rotatably mounted on said shaft, said shell having a plurality of arcuate guides with spaces therebetween radially disposed to said drum, a plurality of flexible blades connected to said drum and slidably mounted on said guides, and means for operatively connecting said shaft to said drum to enable said drum to withdraw said blades out of extruding position relative to said shell, or to extrude said blades to rotate with said shell as a propeller, each of said blades being composed of two sections, one section constituting a leading section and the other a trailing section, and means for connecting said sections to one another t maintain a predetermined angle relative to one another, a second drum rotatably mounted on said shaft, a plurality of protective strips, one strip for each of said blades extending from said second drum to said first drum with each protective strip connected to said second drum, partly to be wrapped around the same when said blades are extruded, and also connected to said first drum, one protective strip between each two successive blades to be wrappedy around said first drum when said blades are withdrawn to protect the blades from injury.

16. The combination of a frame, a driven shaft mounted in said frame, a shell fixed on said shaft, a drum rotatably mounted on said shaft, said shell having a plurality of rollers with spaces therebetween radially disposed to said drum, a plurality of flexible blades of quenched and tempered nickel-chrome steel not exceeding .02 inch in thickness connected to said drum and engaging said rollers, and means for operatively connecting said shaft to said drum to enable said drum to withdraw said blades out of extruding position relative to said shell or to extrude said blades to rotate with said shell as a propeller, each of said blades being composed of two sections, one section constituting a leading section and the other a trailing section, and cross pieces not exceeding .02 inch in thickness for connecting said sections to one another to maintain a predetermined angle relative to one another, a second drum rotatably mounted on said shaft, a plurality of ryieldably protective strips, one strip for each of said blades extending from said second drum to said first drum with each protective strip connected to said second drum partly to be wrapped around the same when said blades are extruded and also connected to said first drum, one protective strip between each two successive blades to be wrapped around said first drum when said blades are withdrawn to protect the blades from injury.

17. The combination of a frame, a driven shaft lnounted in said frame, a shell fixed on said shaft, a drum rotatably mounted on said shaft, said shell having a plurality of rollers with spaces therebetween radially disposed to said drum, a plurality of flexible blades of quenched and tempered nickel-chrome steel not exceeding .02 inch in thickness 'connected to said drum and engaging said rollers, and means for operatively connecting said shaft to said drum to enable said drum to Withdraw said blades out of extruding position relative to said shell or to extrude said blades to rotate with said shell as a propeller, each of said blades being composed of two sections, one section constituting a leading section and the other a trailing section, and cross pieces not exceeding .02 inch in thickness for connecting said sections to one another to maintain a predetermined angle relative to one another.

LYMAN SPITZER, JR.

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

UNITED STATES PATENTS Number Name Date 1,781,883 Reed Nov, 18, 1930 1,684,567 Wragg Sept. 18, 1928 1,491,972 Schiesari A'pr. 29, 1924 1,957,887 Hebbard May 8, 1934 2,163,482 Cameron June 20, 1939 2,145,413 Belfield Jan. 31, 1939 2,041,849 McCauley May 26, 1936 1,463,556 Reed July 31, 1923 1,831,366 Reed Nov. 10, 1931 1,145,388 Rochon July 6, 1915 2,172,334 Theodorsen et al. Sept. 5, 1939 2,226,978 Pescara Dec. 31, 1940 2,344,266 Reissner Mar. 14, 1944 FOREIGN PATENTS Number Country Date 527,443 Great Britain Oct. 9, 1940

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