Dec. 17, 17946, y RoToR BLADE Filed May 13,` 1942 l 2,412,908> ’ H. H. PLATT ET AL zîsheets-snee't 2 20 Z0 rz Laurezzce _Le dim/«5€ M, Patented been, 194e ' . `y UNIT-ED H . , > 2,412,903? Aly isheldftogethenb . ue nails‘and an. STATESï-zîî ‘1.121,41i`2îì9oa; n ï n t i s ' RMQREBLAQE ,LaurenceLetPage,.Ardrnore„;Ba., assignee; ‘ l " Application ilVIayl‘lS, ` " ` „cciaimsl‘ " Novem@ invention relates-to .airfoil blades vfor `‘use \ _ isjßjapplied. over `the `whole“ t f in aircraft liitingrotors and more particularly in . ‘y and fshrunl; onfbyf‘the applicati@l0f> a numben l l aircraft which arederiving actuated their either main by direct supportfrom power drive `rotors or,` _ of coats of “dope‘ß’` J„This typenf Jconstruction \ , by the action of relative airflowV over them,` other r has been `found in‘practice,tohayeseriousshort- > `wisc designated `generically as rotating-wlngvair- l. ~ Í. comme; @een .ne fabric @vering ‘dos not» anaccurateiairfoil reaction; `the fabric , craft, ,and in whichthe blades are attached to f ,_i maintain and plywood" coverings are so delicate thatgdarn- " the rotor hub by `pivots, permitting universalV „s age to them in lhandlingis of frequent occurrence; swinging of the blades.l ` It is well known that rotor blades presentdifiifl 1o- the covering t‘lnish is „not adequately resistant to"` cult and exacting problems in design, construe-»l ` ï abrasion` and is habiti'rally impairedj‘by thelaction y „ l of rainf_dxçofpsf,"` haihstones or small solid objects . tion requires anddurability. accurate and`Thus,.correct" enduring location performance `oifjïthe s c picked up `by the wind; the blade can be` made ,s chordwise centers of .pressure and ofgravity. l, fl‘fo `,.Ä„only it necessarilyexpensiife bywhandfiabricetlon in quantity ymethods"production. `willen make, ` i .this end,`the`airfoil section must‘be maintained 15,. ` One objëçtjof our.. present invention‘isgtcu` prof` to airfoil a high section degree andofthe conformance structural design with the must‘be»N basic „" ‘t vide a rotor blade .capable of quantity` production „at lowcost. `\ l capable of . accurate weight> control,` Q Í The blade` must be ¿capableV f withstanding` ' the very high centriiugalvforces developed'ildur ing the rotation and the outerfsurface must `be " Í ‘Another object ` I contour throughout its .working length, 2o,„ j accurate >Still another‘object is to provide aïrotorblade A . ` having aruggedîanda “ramon-resistantcateraar» ` Hiace."v` . ing capable aerodynamic of `withstandingfthe pressures developedby langeandliuctuat-ì ,tllëfliighÍ,` velocity of rotation, VtWin11trete and, , er objects, Y. t , view, as . t. s t Furthermore, to prevent .obiectionableL torsion es " appear'm‘ore fuuyrromî-the renewing detailed de and iiutter, the blade must be supported approxi- . scription, `appended_Q;¿claims and accompanyingA mately inthe center of pressure line andv theï ‘ drawing’sfour 'invention contemplates the use of chordwise location of the` center of gravityoi.each4 „ j‘ ‘a tubular "csparìior its main structural member; element ofc‘length of the lifting portionrnust be ` '¿ ‘ the prefabricationoi‘a ‘seamless¿envelopemolded,l orfothîerwise fabricated, of light, strong, resilient l ,c close to the center ofjpressure line as well.V l‘l‘o` this end, it is customary to include some’ fornir of` i, ‘ ' material,'ÃSÍI‘¿21T` as" reinforced plastiato a Acontour counterweight, usually non-structural, near the.; y ‘_ "having‘an exterlorairfoil cross-section; `the in-` leading edge of the blade due to` the fact that t _"sertion4 or lthe vl'tubulary spar througl'i` the hollow the centerof pressure of a suitable airfoil is` much 1 I interior je; the“ prerajbricated envelope; fand the nearer the leading than the trailing edge.`y ¿ _` „ ‘ *attachment of the ‘envelope to ‘the’ tubular _spar by suitable means" such as collars ‘and ribs, or Above "all, the `above requirements must be achieved while maintaining `_the total >weight` of "lugs, eldedßpinnedïor boltedtothe _spar and “screwed’ïtofthe envelope. ` ` ` ` ‘ the blade `Within the ’very narrow limits pre scribed, on the one hand by the general require-` \ Ourfjinvention‘ further contemplates the form ment for lightness in‘aircrait, and on‘the ‘other ï' Vfing of the envelope 0with a thicker wall inthe hand by the >maintenance of a‘ suitable angle of " equilibrium relative tothe rotor axis while‘inf ' Y the purposes *of'better'weight and strength dis-` nicht. tribution‘. ` Y c ‘ c ` “ ‘ " 1 ` Our'ïi'n've 'tion' alsoicontemplates ‘the use‘of an The type of construction which has hitherto,` .envelope‘ffornied with‘ione or more longitudinal ‘ffbullrheadstoïprovidëflocal stiffness‘without the Í been found most suitable ‘for approaching these " requirements is used as theismain one whereina structural tubular element.`steel "Tofth'is‘" spar " I45' vals, spar, by wood suitable ribs are means attached, such asatiianged spaced collars inter# ’i s, e e c tacheddirect'ly to lugssecured tothe spar.` l ` _ Ouriinvent'ion also includes other’novelieatures welded `or pinned to `the spar,` the saidtrilcs‘be-- 50 l .ci vconstructien'fwhich- will appearmore fwully from ` ` ` ‘ ing formed generally to the airioil section desired. 1 ‘l the following l‘det'zliilod description;` A formed Wood strip is applied atxthe trailing v ‘ edge, while the leading‘ends of the ribs supporti*> a counterweightrod of metal and a leading ledg For _purposes of " lustrating our l t vention, we ` have shown in the‘accojmpanyiiig drawings forms .frthereofiiiv " " ` ' usesince satisfactory t 2,412,908 l . ` Vand reliable results, although it is to be under stood that our invention is not limited to the pre cisearrangernent of the instrumentalities as here- ' in Referring vshown and to described. the drawings l n in'which like refer f ' ence'characters indicate like parts: ï n » Figure 1 representsa .plan'viewïof an aircraf y having rotor blades embodying our invention.¿ Figure Zrepresents a fragmentary, top eleva d d 4 d and then securely attached .to them by any suit~ able means such as cement and nailsjpr drive screws; the nails or screws preferably being coun tersunk so as to eliminate' surface irregularities. One method of finishing the tip, which has been ' found by us to be advantageous, in practice, `is 'illustrated in Figure 8. An extension piece 22 .of smaller diameterl is fitted into the end> of the tubular spar I5 and held in vplace by bolts 23, ` tional view of one of the rotor blades shown in 10 or by other suitable attachment means. The Figure 1, drawn to' a somewhat enlarged scale, extension 22 is tapered throughout its length and i ` parts being broken awayl better to reveal the ` construction thereof.L d s » Figure 3 represents ‘a cross-,sectional view » generally along the line 3_3 of Figure 2; may be extended into the. tip as shown, its end Figure 4 represents a fragmentary elevational being suitably reduced in dimension. view similar to that of Figure 2 but showing a modified form of- construction. Figure 5 represents a cross-sectional view _ along the line 5_5 of Figure 4. has, attached to it, ribs 244 similar to the main ribs I6 but of sizeand form modified to suit the desired tip contour. The counterweight rod 20 n . A ytip block 25, preferably of the same material ask the ribsfis preferably preformed to the de. signed aerodynamic contour and is integrally 20 formed, or fitted, with the inwardly extending ' Figures"6 and '7 represent cross-sectional views , similar to thatA of Figure 5 but showing alternative ’ forms of blade envelope' with different web ar-V trailing edge reinforcement' 26 of the tapered tip II; In attaching the tip block 25, the envel ope I8 is cut open `at the trailing edge and suit rangements from that voi' Figure 5. . ably" cut back over _the length >required forthe ' Figure 8 represents a top elevational view of the 25 tapering tip.V The end of the extension 22 is4 tip portion of the rotor blade shown in Figures l and 2, parts being broken away' better to reveal the construction'thereof._ ' ' preferablyl fitted into a. locating recess vin the» ' bloei; 25 to which it may be secured by a pin 2l,.- _ v ' ° and the envelope skin is then tightly pressed down Figure 9 represents across-.sectional view,'on over the tip skeleton and flnallyattached thereto an enlarged scale, along the lines-9. of Figure 1v 30 by means similar to the bonding of the envelope illustrating a.A detail of construction of the root I8 to the main ribs I6. _ The open trailing edges end portion of a rotor blade made according to are similarly pressed down onto and attached to the` trailing edge reinforcement piece 26.» The ' ' The rotor blade of the presentíinvention is of of the envelope skin are the/nl smoothed oil atype which >has been found'particularly well 35 .edges to form a true trailing edge and a ’smooth -surface suited for use in helicopters and autogiros. joint with the tip block~25. , n _ Inone embodiment shown in Figures 1, 2, 3 and Í We have found it prefer ble to mold the envel our invention.. ' ` " “ ‘ ‘ 8 we may provide' a rotor blade having uniform ' ope I3 with a thicker,` w ll >adjacent the leading » chord over most of its outboard portion I0, a edge than adjacent the trailing edge, as showny vtapered tip II and a non-lifting faired tube in .4_0 particularly’in Figure 3, in»v order’to withstand board portion I2. A fairing block I3 provides a theÍ higher pressures vand lthe greater >abrasive smooth transition from the outboard'portion l0 to action encountered near the'leading edge.. The> the inboard portion I2. A retaining collarIII is` wall thickness may, however, be'uniform,y or of formed on, or otherwise attached to the vinboar’cl any 'other thickness distribution, if desired, with end of the spar I5 for cooperation' with a suit out `departing `from our invention. InvFlg‘ures 4 and' 5, an alternative embodiment able ñtting (not shown) on the rotor hub 34. ï A central tubular spar- _I5 forms the structural ` , backbone of the blade and extends throughout lof ‘the present invention is illustrated. In r»this embodimentthe ribs I6 are omitted and the re most of its length. Within the outboard, work quisite stiffness is furnished by webs 28 and-29. ` ing portiony I0, the spar I5 is fitted with suitably 50 preferably molded integrally with an outer en ` spaced ribs I6, which are supported on the spar> velope 30. The attachment of the envelope 3l)> I5 by the flanged collars Il. The ribs I6 are to the sparV I5' may be `achieved bymeans of the preferably cut from suitably light sheet material - boltedfon lugs 3I to which the envelope 30 is de- ` such as wood or laminated plastic and are formed to fit 'accurately within» an outermost airfoil tachably secured by drive screws 32, the forward . web 28 acting as a location guide in assembly." envelope I8. 'The collars‘I'l may be attached to the ribs I6 by means of rivets I 9.o'r otherwise, -and The counterweight strip> 20 is attached as in the embodiment illustrated in Figures 2> and 3. to the spar`I5 by spot-welding, rshear-pins or v The tipmay be formed as hereinabove described, s --webs 28’and 29 being cut away to permit com 60 _ The airfoil envelope 'I8 is of molded seamlessy pression of the skin of the tip portion. f form and may be"prefabricated from any suit otherwise.- „ f v - . _ able resihent material such as fabric-reinforced < plastic.r Its exterior _form is molded to the pre determined airfoil contour selected for advan tageous performance of the aircraft, or to a form i which may readily` be deformed to such contour whenplaced over the rib and tube skeleton. A> counterweight rod 20, of suitably heavy materialL and of‘weight sufficientto provide the desired operative balance of the blade, is inserted in the envelope I8 adjacent the leading edge and secured Ain position by means of countersunk head screws 2i, or in any other suitable manner.'v The en n j y In Figures 6 and? there are` illustrated alter-A ’ native forms of prefabricated envelopes, that of Figures 6 having only one web and requiring auxiliary locatingmeans for assembling on the spar, andthat of Figure 7 having three Webs for ' greater rigidity if desired. ` . , In ,Figure 9 there is illustrated a form of fairing for the spar I5 over the inboard, inoperative por tion of the blade. 'I‘he fairing 33, of-light, non~ structural material, may ‘be attached to the spar by adhesive tape or otherwise. _‘ Y ` While we have shown the various features of velope I8 is slipped into' place over the ribs I6 75 >our invention in certain speciñc embodiments, we are aware that our invention may be embodied in ‘ d , ' 2,412,908 5 ' r other forms without departing from the spirit or ' extending from said spar and into the tapered tip essential attributes thereof. Thus, for example, of said envelope and having its outermost end while we have shown our invention as applied fastened to »said tip-block, and means for attach- , to a non-tapering, untwisted blade having its working airfoil applied only to the outboard por tion, our invention is equally applicable to blades ing’said envelope to said spar and to said tapered member at a plurality of spaced points. having full-length 'working surfaces, or having tapered plan form, or having tapered thickness, lrotor, a rotor blade comprising a prefabricated form-retaining generally seamless elongated en-> or having any desired twist, or having any com ‘ velope of molded plastic> or the like having an ex« bination of these characteristics. Furthermore, the speciiic methods of attachment of the various parts are susceptible of very Wide variation, both as to type and dimension, without departing from the scope of our invention. We therefore desire 2. In a rotating-wing aircraft having a lifting ternal airfoil contour and' having an outer 1on~ gitudinaliy tapered tip, a spar having its inner` end operatively attached to the hub of said rotor and having its outer end extending within said envelope along the untapered portion thereof, the present embodiments to be considered in all 15 the exposed portion of said spar being faired, a tapered coaxial member extending from said spar respects as illustrative and not restrictive, refer and into the tapered tip of said envelope and ence being had to the appended claims rather _having its outermost end fastened to said tip than to the foregoing description, to indicate the block, and means for attaching said envelope to scope of our invention. ` said spar and to said tapered member at a plu The invention having been hereinabove de-y scribed, what is hereby claimed as new and `de- sired to be protected by Letters Patent is: 1. In a rotating-wing aircraft having a lifting rotor, a rotor blade comprising a prefabricated form-retaining generally seamless elongated en velope of molded plastic having an external air foil contour and having an outer longitudinally tapered tip, said tip being reinforced at its trail l rality of spaced points. ‘ 3, In a rotating-wing aircraft having a. lifting rotor, a rotor blade comprising a generally seam- ` less form-retaining elongated envelope with ex ternal contour of airfoil section, said envelope `having a straight `leading edge and having its trailing edge swept forward at its outer end, a formed tip-’block closing the> outer end of said envelope, said tip-block having a portion ex ing edge and terminating in a formed tip-block, the wall of said envelope being thicker at the 30 tending along and reinforcingthe swept-forward portion of the trailing edge of said envelope, and leading edge than atV the trailing edge thereof, ' an inner supporting spar operatively connecting a spar having its inner end operatively attached , said envelope to the hub of the rotor. ` to the hub of said rotor and having its outer end extending within said envelope along the un HAVILAND H. PLATI‘. tapere'd portion thereof, the exposed portion of said spar being faired, a tapered coaxial member WYNN LAURENCE LE PAGE. '