US3105557A

US3105557A - Rotor blade

Info

Publication number: US3105557A
Application number: US47546A
Authority: US
Inventors: Wigal Voorhis Frederick
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-08-04
Filing date: 1960-08-04
Publication date: 1963-10-01
Anticipated expiration: 1980-10-01

Description

United States Patent O 3,105,557 ROTOR BLADE Voorhis Frederick Wigal, 600 Mobile Ave., Jackson, Tenn. Filed Aug. 4, 1960, Ser. No. 47,546 17 Claims. (Cl. 170-159) T-his invention yrelates to airfoil elements in general, and in particular to a rotor blade of the type used in lift and sustension of helicopters and the like aircraft, although it is not limited to such use.

The rotors in actual use may be characterized in four main classes, as follows:

(a) Laminated wood built around a metal spar.

(b) Small, wing-type ribs, spaced closely around a metal spar, and covered with fabric or aluminum sheet.

(c) Aluminum or fabric covering over shaped wood, cellular .plastic or honey-comb filler, built around a metal spar.

(d) Some arrangement of extruded aluminum sections which may or may not have :the spar as an integral part.

All of these types involve slow and laborious processes in the making, demand a high degree of craftsmanship, and entail high cost in the finished product.

It is therefore a principal object of the present invention to simplify the manufacture and reduce the cost of rotor blades. Another object is to achieve a proper airfoil section without the need for hand-finishing operations. A still further object is to provide a balanced blade without resort to protruding, external weight additions. Other objects include easy reproducibility of blades having proper balance and section, and the attainment of high strength and flexibility with low weight.

These and other objects are attained by the present invention, which may be briefly described as a blade built up along its length from la series of plastic units of airfoil section arranged in side-:by-side, relation, each unit consisting of an upper shell and a lower shell with stiftening, internal ribs, and secured on a plastic-lled, multitubular spar running the -length of the blade.

For a more detailed description of the invention, reference is made to the following specification, as illustrated in the drawing, in which:

FIGURE 1 is a top view of a rotor, foreshortened by removal of an intermeditae portion,

FIGURE 2 is an enlarged sectional view taken on the line 2 2 of FIGURE 1,

FIGURE 3 is an internal View of one of the halves of the airfoil shell, as seen along the line 3 3 of FIGURE 2, with the spar tubes removed,

FIGURE 4 is an enlarged, sectional view taken on the line 4 4 of FIGURE 1,

FIGURE 5 is an enlarged, sectional view taken on the line 5 5 of FIGURE 1,

FIGURE 6 is an enlarged, sectional view taken on the line 6 6 of FIGURE 1,

FIGURE 7 is an enlarged, sectional view taken on the line 7 7 of FIGURE 1,

FIGURE 8 is a sectional view taken on the line 8 8 of FIGURE 7, showing the spar element of FIGURE l without the surrounding, airfoil shell, and

FIGURE 9 is an axial section of a spar tube, showing an operation of filling the tube with plastic-impregnated reinforcing filaments.

Referring to the drawings by characters -of reference, there is shown a rotor blade built around a spar, indicated generally by the numeral 1, which constitutes the backbone of the blade, and as such chiey provides the mechanical strength of the system, as against bending ice stresses for instance. In one feature of novelty of the invention, later to be discussed, the spar is constituted by a series of tangentially united, tubular elements. In the embodiment shown, these are three in number, with a central tube 2, flanked on opposite sides by a pair of

outer tubes

3 and 4. The middle tube 2 should be centered on the pitch axis of the blade. This tube which is also preferably located at or near the point of maximum thickness of the airfoil is of a diameter to take full advantage of the available space within the airfoil, and consequently the

outer tubes

3, 4 are of a lesser diameter than tube 2 due to convergence of the vairfoil Walls or shells.

The airfoil shell, which is carried by the spar, as a covering mantle, is made up of a series of identical sections, each of which is indicated by the numeral 6 in FIGURE 1, land which is shown in detail in FIGURES 2 to 6. Thus, in FIGURE 2, it is seen that the airfoil is made up by a pair of identical, molded plastic shell halves having a skin 8 of airfoil contour, and a series of internal,

stiffening ribs

10 and 12. Defining the central plane of the complete airfoil, each'shell halfhas a forward flat region 14, a rearward flatregion 16 and two pairs of

transverse fbosses

18 and 19 lying on respective sides of the spar 1.

Ribs

10 and 12 have a generally similar profile throughout most of their lengths, but as seen in FIGURE 2, the ribs 12 have an extra, inward sweep in the neighborhood of the bosses to give added bracing thereto. The bosses 18 are also braced in the longitudinal direction of the rotor blade by ribs 20. In the region forward of the bosses 18, the

ribs

10 and 12 are provided with suitable, arcuate recesses 21 to snugly receive the

spar tubes

2, 3 and 4. As shown, the tubes are welded together, Ibut the system-may be fabricated in other ways, as by extruding in the form of a three-part tube, or by pressure deformation from a single, large tube. Preferably, the spar will consist of high strength aluminum or other light metal of suitable strength.

For quick, accurate and durable assembly, the airfoil units 6 are provided with integral dowelling elements alternately arranged so that the shell half may be used on either side of the airfoil. Thus, in FIGURE 3, the hat region of join, 14, has alternately occurring pins 22 and recesses 24. It will be seen that when a shell half is grought into mating relationship with another identical half, being thus turned through a angle, the pins of one will engage in the recesses of the other. Similarly, in the region of join, 16, at the trailing edge of the airfoil, alternately arranged holes 26 and pins 28 are provided.

With the shell halves accurately spotted by the mating pins and holes to produce the complete airfoil, the assembly of the unit is secured |by means of four screws 30 cooperating with axial bores in the

bosses

18, 19. As seen in FIGURES 1 and 2, the arrangement is such that two of the screws are applied from each side of the airfoil, and the screw heads on each side are diagonally disposed. Thus, each shell -unit (FIGURE 3) will have threaded bores in the lower left hand boss and in the upper right hand boss, the other two bosses having bores sufficient to .pass the screw shank. The outer side of the shell is provided with suitable countersinks for the screw heads. This arrangement of screws is not only consonant with the principle of using identical half-sections throughout, but also maintains proper. balance on both sides of the airfoil and throughout its length.

In order to provide la smooth, unbroken expanse of airfoil surface, the internal edges of the shell segments are arranged for overlapping engagement. As seen in FIG-

URES

3 and 4, the extreme leftward rib lll is located slightly inwardly of the edge of the shell to provide a marginal strip 32 wherein the thickness of the skin 8 is reduced by one-half. Correspondingly, the shell extends slightly beyond the extreme rightward rib to provide a marginal strip 34 which is rabbeted from the outer surface of the ainfoil to a depth of half the thickness of the shell whereby to overlap the marginal strip 32 of an adjacent section 6 to provide a neat joint. The lap joint may be secured by a suitable ycement or by yapplication of V-a solvent. The use of butt joints is also contemplated.

The outer Vend of the rotor blade may be closed by a suitable cap 36, of material similar to that of the shell segments, which can be fu-nther utilized .to hold the Iairfoil sections in place by welding or bolting, and/ or chemically bonding the cap to the spar, as well as to the outermost shell segment.

Any suitable means may be employed for attaching the blade to a rotor hub. For purposes of general illustration, the drawing shows a pair of aluminum sections 36 shaped to receive the spar I and clamped thereon by means of screws 38. This constitutes -a block providing suicient body for lany conventional coupling or attaching means.

In an important feature of the invention, the hollow tubes of the spar are loaded with ia filler to provide strength -with'out undue weight, and in a prefenred embodiment, resin-impregnated fiberglass hlaments are introduced into the tubes and cured in place. As seen in FIGURE 9, the loading of a tube is conveniently accomplished by drawing a looped skein of fibers 40, or roving as it is called, by means of a steel wire 42 engaged in the loop. The loading operation is facilitated by means of a funnel 44 received 'on the charging end of the tube. The fibers enter under high compression across the diametral direction land provide a closely packed mass which is subjected to cure, when in place.

As seen in FIGURES l and 8, the extent of loading of the fiberglass ller is different in the respective tubes. Only .tube 3, the one nearest the leading edge of the `airfoil needs to Ibe reinforced throughout its entire length. At the root end of the blade, near the rotor hub, where the greatest strength is needed, all of the tubes are reinforced, butin the middle tube 2, the lling stops considerably short of that in the forward tube, as at 48, and in the rearmost tube the terminus 50 of the filler is still closer to the rotor hub. Not only does this arrangement provide the required strength with minimum Weight, but also enables a fine :adjustment of rotor blade balance without the objectionable use of protruding auxiliary weights :as practiced in the prior art.

For the material of the airfoil shell sections it is preerred to use plastic Vof very tough but high impact material, such as polyamides, yacetal, or polycarbonates, and the Y impregnating material for thel glass fibers will preferably comprise a polyester or epoxy.

In the use of the invention for rotor blades, there is a distinct advantage in that a single form of mold cavity is adequate. This is so because rotor blades are commonly symmetrical, with the same curvature on the top as on the bottom, due to the need for maintaining the center of pressure at a given point during constant changes in the yangle of attack. However, even if a non-symmetrical Iblade is contemplated, only two mold forms will Abe required.

The advantages of the invention may be summarized as follows:

(l) The Vmolded plastic shells, establish, ab initio, the

proper curvature for the `airfoil section.

(12) The parts are molded to t correctly together, so that no hand finishing is required. This makes for simple 'and economical assembly.

(3) Since `all parts are molded in the same cavity they will all be very closely the same Weight, and there will be no balance problem in matched blades.

(4) impregnated, fiberglass reinforced spar gives high strength and exibility with low weight.

(5) In `a spar with separate, tubular sections,chordwise balance can be adjusted by the extent of filling in the respective tubes, thus obviating the use of external weights, which impair rotor eiciency.

While certain preferred embodiments have been shown and described, these are not intended as limiting since various changes, modifications and substitution of equivalents, for instance, will suggest themselves to those skilled in the art, in the light of this disclosure, and the invention should not, therefore be :deemed as limited except insofar as shall appear from the spirit and scope of the appended claims.

I claim:

il. An airfoil comprising a multi-tubular reinforcing spar having a central tube and `at least one tube on each side of said central tube of lesser diameter than said Central tube, ya ller of cured, resin-impregnated fiberglass in said tubes extending from `a common end of said tubes and terminating at progressively increasing distances in successive tubes, and a covering shell of symmetrical airfoil form enclosing said spar, said shell comprising identical sections of molded plastic arranged in side-by-side relation along the length of 4said spar, each said section comprising identical halves, each half comprising a wall of airfoil fOr-m, said wa-ll having ilat regions on the axis of symmetry of the complete airfoil, lat the leading edge,

at the trailing edge and at points intermediate the said edges, dowel means in the said at regions at said edges, said regions at said intermediate points lying on opposite sides of said spar and having threaded bores for fastening screws, ribs on the inner side of said wall extending 4from trailing edge to leading edge, and having recesses accommodating said spar, the respective, lateral edges of said wall being rabbeted from the front and rear, respectively, of said wall whereby to provide lap joints between adjacent halves along each side of said airfoil.

2. An airfoil .comprising .a multi-tubular reinforcing spar having a central tube and at least one tube on each side of said central tube of lesser diameter than said central tube, 'a filler of cured, resin-impregnated fiberglass in said tubes extending from a common end of said tubes and terminating 'at progressively increasing distances in successive tubes, and `a covering shell of symmetrical airfoil form enclosing said spar, said shell comprising identical sections of molded plastic arranged in side-by-side relation along the length of said spar, each said section comprising identical halves, each half lcomprising a wall of airfoil form, said wall having iiat regions on the axis of symmetry of .the complete airfoil at the leading edge, at the trailing edge, and at points intermediate the said edges, said regions at said intenmediate points lying on opposite sides of said spar and having threaded bores for fastening screws, ribs on the inner side of said wall extending from trailing edge to leading edge `and having recesses accommodating said spar, the respective, lateral edges of said wall being rabbeted from the front .and rear, respectively, of said wall whereby to provide lap joints `between adjacent halves along each side of said airfoil.

3. An airfoil comprising a multi-tubular reinforcing spar having a central tube and `at least one tube on each side of said central tube of lesser diameter than said central tube, a ller of cured, resin-impregnated fiberglass in said tubes extending from a common end of said tubes and terminating at progressively increasing distances in successive tubes, and a covering shell of symmetrical airfoil form enclosing said spar, said shell comprising identical sections o-f molded plastic arranged in side-rbyj side relation along the length of said spar, each said section comprising identical halves, secured together, each half comprising ya wall of airfoil form, `said lwall having at regions on the axis of symmetry of the complete air,- foil at the leading edge and at the trai-ling edge, and ribs extending between said edges and 'having recesses receiving said spar, the respective, lateral edges of said Wall being rabbeted from the front and rear, respectively, of

said wall `whereby to provide lap joints Ebetween adjacent halves along each side of said airfoil.

4. An airfoil comprising a multi-tubular reinforcing spar having a central tube and at least `one tube on each side of said central tube of lesser diameter than said central tube, a iiller of cured, resin-impregnated fiberglass in said tubes extending from a common end of said tubes and terminating at progressively increasing distances in successive tubes, and a covering shell of symmetrical airfoil form enclosing said spar, said shell comprising identical sections of molded plastic arranged in side-by-side relation along the length of said spar, each said section comprising identical halves secured together, each half comprising a wall of yairfoil form, ribs on the interior of said wall extending from the trailing edge to the leading edge and having recesses receiving said spar, the respective, lateral edges of said wall being rabbeted from the front and rear, respectively, of said wall whereby to provide lap joints between adjacent halves along each side of said airfoil.

5. An airfoil comprising a multi-tubular reinforcing spar having a central tube and at least one tube on at least one side of said central tube of lesser diameter than said central tube, a iller `of cured, resin-impregnated riberglass in said tubes extending from a common end of said tubes tand terminating at progressively increasing distances in successive tubes, and :a covering shell of symmetrical airfoil form enclosing Said spar, said shell cornprising identical sections of molded plastic `arranged in side-by-side relation along the length of said spar, with overlapping edges, each said section comprising identical halves secured together, each half comprising a wall of airfoil form, and ribs on the interior of said Wall extending from the trailing edges to the leading edge and having recesses receiving said spar.

6. An airfoil comprising a multi-tubular reinforcing spar having a cent-ral tube yand at least one tube on lat least one side of said central tube of lesser diameter than said central tube, a filler of cured, resin-impregnated fiberglass in said tubes extending from a common end of said tubes and terminating at progressively increasing distances in successive tubes, and a covering shell of symmetrical airfoil form enclosing said spar, said shell comprising identical sections of molded plastic arranged in side-by-side relation along the -length `of said spar, each said section comprising identical halves secured together, each half comprising a wall of lairfoil form, and ribs on the interior of said -wall extending from the trailing edge to the leading edge and having recesses receiving said spar.

7. An airfoil comprising a multi-tubular reinforcing spar having :a central tube and at least one tube on at least one side of said central tube of lesser diameter than said central tube, a filler of plastic material in said tubes extending from a common end of said tubes and terminating at progressively increasing distances in successive tubes, and a covering shell of symmetrical airfoil form enclosing said spar, said shell comprising identical sections lof molded plastic arranged in side-by-side relation along the length of said spar, each said section comprising identical halves secured together, each half comprising a wall of airfoil form, and ribs on the interior of said wall extending from the trailing edge to the leading edge.

8. An airfoil comprising a multi-tubular reinforcing spar having a central tube and at least one tube on at least one side of said central tube of lesser diameter than said central tube, a ller `of plastic material in said tubes extending from a common end of said tubes and terminating at progressively increasing distances in successive tubes, and a covering shell of symmetrical airfoil form enclosing said spar, said shell comprising identical sections arranged in side-'by-side relation along the length of said spar, each said section comprising identical halves secu-red together, each half comprising a wall of airfoil zform, and ribs on the interior of said wall transverse to said spar.

9. An airfoil comprising a reinforcing spar having a plurality of longitudinal passages, a iiller of plastic material in said passages extending Ifrom a common end of said passages .and terminating at progressively increasing distances in successive passages, and a covering shell of symmetrical Iairfoil form enclosing said spar, said shell comprising identical sections arranged in side-by-side relation along the length of said spar, each said section comprising identical halves secured together, each half comprising a wall of airfoil form, and ribs on the interior of said Wall transverse to said spar.

10. An airfoilcomprising a reinforcing spar having a plurality of longitudinal passages, a filler of plastic material in said passages, :extending from one end yof said spar `and terminating at progressively increasing distances in successive passages, and a covering shell of symmetrical airfoil form enclosing said spar, said shell comprising identical sections arranged in side-by-side relation along the length of said spar, each said section comprising identical halves secured together, each half comprising a wall of airfoil form.

11. An airfoil comprising a reinforcing spar having a plurality of longitudinal passages, a filler of plastic material in said passages, extending Ifrom one end of said spar land terminating at progressively increasing distances in successive passages, and :a covering shell of airfoil form enclosing said spar, said shell comprising identical sections arranged in side-by-side relation along the length of said spar, each said section comprising an upper and lower airfoil wall secured together.

12. An airfoil comprising a reinforcing spar having a plurality of longitudinal passages, a iiller of plastic m-aterial in varying amounts contained in the respective passages, and a covering shell of airfoil form enclosing said spar, said shell comprising identical sections arranged in side-by-side relation along the length of said spar, each said section comprising an upper and lower airfoil wall secured together.

13. An airfoil comprising a reinforcing spar having a plurality of longitudinal passages, -a iller of plastic material contained in said passages, and a covering shell `of airfoil form enclosing said spar, said shell comprising identical sections arranged in side-:by-side relation along the length of said spar, each said section comprising an upper and lower airfoil wall secured together.

14. An airfoil comprising a hollow, reinforcing spar, a plastic ller of cured, fiberglass roving contained in said spar, and a covering 4mantle of complete airfoil Kform enclosing said spar, said mantle constituting substantially the total structure of said airfoil, other than said spar, and comprising identical sections arranged in side-byside relation along the length of said spar, each said section comprising identical upper and lower airfoil shells secured together, .and extending from the leading edge to the trailing edge `of the airfoil.

15. An airfoil comprising ya hollow, reinforcing spar, a solid plastic iller contained in said spar, and a covering mantle of complete airfoil form enclosing said spar, said mantle constituting substantially the total structure of said airfoil, other than said spar, and comprising identical sections arranged in side-by-side relation along the length of said spar, each said section comprising identical upper and lower airfoil shells secured together, and extending from the leading edge to the trailin-g edge of the airfoil.

16. For use in an airfoil, a reinforcing spar comprising a series of tubular members tangentially attached together, and a filler of solid plastic material in said tubes and extending from one end Iof said spar to distances.

which increase progressively insuccessive spars.

17. For use in an airfoil, a reinforcing spar comprising a series of tubular members tangentially attached together, and a filler of solid plastic material extending from one end of said spar and terminating at distances which differ in at least two of said tubes.

References Cited in the le of this patent UNITED STATES PATENTS McCauley July 1, 1930 Bergen Nov. 6, 1945 Larsen May 21, 1946 Young OctA 14, 1952 Haines et a1. Aug. 11, 1953 Sterling Sept. 22, 1953 Stanley Nov. 17, 1953 Harness Oct. 1, 1957 Schliekelmann Mar. 25, 1958 Laskowitz Dec. 1, 1959 8 Marchetti Oct. 4, 1960 Stuart Apr. 25, 1961 Warnken Sept. 19, 1961 Hinds Apr. 3, 1962 FOREIGN PATENTS Germany Dec. 3, 1919 Germany July 20, 1940 Germany Jan. 29, 1941 Great Britain Apr. 16, 1952 Italy Apr. 22, 1955 Australia Feb. V6, 1956 Germany Aug. 7, 1958 Germany Apr. 28,1960

Claims

17. FOR USE IN AN AIRFOIL, A REINFORCING SPAR COMPRISING A SERIES OF TUBULAR MEMBERS TANGENTIALLY ATTACHED TOGETHER, AND A FILLER OF SOLID PLASTIC MATERIAL EXTENDING FROM ONE END OF SAID SPAR AND TERMINIATING AT DISTANCES WHICH DIFFER IN AT LEAST TWO OF SAID TUBES.