US2754918A

US2754918A - Weighted blade for rotary wing aircraft

Info

Publication number: US2754918A
Application number: US186021A
Authority: US
Inventors: Michael E Gluhareff
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1950-09-21
Filing date: 1950-09-21
Publication date: 1956-07-17
Anticipated expiration: 1973-07-17

Description

July 17, 1956 M. E. GLUHAREFF WEIGHTED BLADE FOR ROTARY WING AIRCRAFT Filed sept. 21, 195o -llllllllllllllll/II( INVENTOR MICHAEL E. GL UHAREFF ATTORNEY WEIGlJlTED BLADE FR ROTARY WING AIRCRAFT Michael E. Gluiiarei, Fairfield, Conn., assigner to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application September 21, 1959, Serial No. 186,021

9 Claims. (Cl. 17d-159) The invention relates to rotor blades for rotary wing aircraft and particularly to metal blades of the type in which an extruded spar forms the leading edge and main strength member of the blade and conforms to the airfoil contour of the blade throughout a substantial chordwise portion thereof.

lt is an object of this invention to provide a rotor blade of this type having improved chordwise balance.

A further object of the invention is to provide a rotor blade of this type having provision for adjusting the position of the bending wis of the blade to coincide with 25% chord line of the blade at which the gravity axis, the feathering axis and the aerodynamic center of the lade are located.

A further obiect of the invention is to provide an extruded spar for such a rotor blade having an internal construction such that the spar can be extruded with an integral thickened root end portion.

A still further object of the invention is the provision of a rotor blade of this type in which the airfoil contour of the blade aft of the spar is completed by a single sheet metal pocket along the outboard portion of the blade and a plurality or" divided sheet metal pockets inboard of the blade.

A yet further object is generally to improve the construction and performance of rotor blades for rotary wing aircraft.

These and other objects will be evident from the following detailed description of one form of the improved rotor blade shown in the accompanying drawings.

In these drawings:

Fig. l is a perspective view of a rotor blade embodying the invention with parts broken away to facilitate illustration.

Fig. 2 is a section through the blade taken on line 2--2 of Fig. l.

Fig. 3 is a section taken on line 3 3 of Fig. l.

Fig. 4 is a ysection taken through the outboard portion of the blade spar showing a modified construction.

Fig. 4a is a detail of the outboard end of the blade shown in Fig. 4.

Fig. 5 is a detailed perspective view showing the root end of the blade equipped for circulation of heated air for de-icing purposes.

Fig. 6 is an enlarged sectional detail of the root end of the blade of Fig. l.

As herein shown, the rotor blade consists essentially of an extruded metal spar 19 which extends from the root to the tip of the blade and comprises the main Ystrength member as Well as the leading edge portion of the blade. As will be evident from Figs. 1 and 2, the spar forms a substantial chordwise portion of the blade and conforms to the airfoil contour. The remainder of the chordwise extent of the blade is made up of V-shaped sheet metal pockets, or boxes, 12 and 13 the upper and lower forward edges 14 of which are adhesively secured to rabbets 16 formed along the upper and lower aft edges of the spar. As shown in Figs. 2 each of the pockets 12 nited States Patent Patented July 17, 1956 ice and 13 is virtually a separate metal box having ribs and end closure members 18, provided with stiffening dimples 20, which are also adhesively secured at the ends of the pockets by flanges 22 to the upper and lower surfaces of the pockets and by a tlange 24 to the flat aft wall of the spar.

All of the

pockets

12 and 13 are generally similar in construction except that the inboard pockets 13 are of short spanwise length and have spanwise gaps 26 therebetween which are sealed by suitable means (not shown) inside the pockets. The innermost of this series of pockets is secured to a special channel member carried by the trailing edge of the spar and has a special inboard end closure Z by which this inboard trailing edge pocket is faired into the spar. The outboard pocket 12 is similar to the series of inboard pockets 13 except for its length, this outboard pocket occupying `substantially 50% of the length of the blade and because of its one-piece construction, lending additional rigidity 'to the outboard portion of the blade in the plane of blade rotation for purposes hereinafter explained.

in accordance with this invention the extruded spar forms a single tube in cross section, being free from internal spanwise extended Webs formerly found necessary in spars of this type. Longitudinal internal ribs, or beads, 3i) are provided to strengthen the spar and one pair of these ribs 30 is provided adjacent the leading edge of the blade to provide a spade-shaped recess 32 which extends throughout the length of the spar. The inboard end of the hollow tubular spar may be connected to a source of heated air introduced through a duct 33. The heated air travels through the hollow spar and in the inboard region where there are no weight sections 56 will come directly in contact with the leading edge. Over the outboard portion the de-icing at the leading edge will take place due to conduction of the heat through the weight sections. However, the inboard portion of the blade is the most critical portion as it does not tend to throw the ice off due to centrifugal force. The outboard end of the spar and the outer end of the outermost pocket 12 are closed by a cap member 34 which has a passage 36 therein which communicates With the interior of the hollow spar and has an outlet 38.

Heretofore in rotor blade spars of this type it has been necessary to build up the root -section of the spar to make it strong enough to support the root fitting, which attaches the spar to the rotor hub, without developing excessive localized stresses at the root fastenings. This has usually been accomplished by bonding reinforcing plates to the upper and lower faces of the spar adiacent the root end, phenolic plates being interposed between the metal plates and the spar to eliminate fretting. Because of the tubular section of the spar of this invention, it is possible to extrude the spar from a single set of dies' without the necessity for rewelding the metal as it emerges from the dies as was required in previous spars having longitudinal reinforcing webs inside the spar. It is also possible because of the single tubular section of the present spar to form the root portion of the blade as an integral thickened section by the simple expedient of opening the dies near the end of the extruding process. The resulting section in which the upper and lower spar surfaces are thickened at du and 42. respectively, are shown most clearly in Figs. 3 and 6 and it will be noted from these figures that the stepped

plates

44 and 46 of the root iitting generally indicated at 43 receive this thickened root section of the spar closely therebetween.

The spaces between the spar and the

plates

44 and 46 are filled by phenolic spacers 49 to prevent chafing between the root tting and the spar. Also micarta spacers 50 are provided within the spar adjacent the root and tting to take the compression loads of the clamping bolts 52 of which there are two chordwise spaced rows (Fig. l). The spacers 50 are arranged in three spanwise rows two of which are in the lines ofbolts 52 and one of which lies between the bolts and is located by a pair of spaced ribs on the spar. These spacers 5) are provided with lightning holes 54 in a usual manner. As shown in Fig. l, the spacers through which the bolts 52 extend, terminate slightly outboard of the outboard end of the root fitting while the intermediate spacer Si) extends farther outboard into the vicinity of the second pocket 13.

One of the difficulties which has been encountered in metal rotor blades of this type has been the occurrence in llignt of control stick forces due to a deliection of the blades in the plane of rotation. This deilection results from bending moments set up in the spar by centrifugal forces acting on the blade.

For instance, it is known that the strength, or bending, axis of a structural member generally coincides with the center of gravity of the cross section of that member. Thus, if the strength member or spar of a blade also forms the leading edge of the blade, the bending axis of the spar (or the C. G. of the spar cross section) should coincide with the center of gravity of the full cross section blade which, it is known, should be located near or at the aerodynamic center of the airfoil section used. Otherwise, when the blade is subjected to centrifugal force during rotation, it will b deected by the moment of the weight of the non-structural parts of the blade around the bending axis of the spar or C. G. of spar cross section. Thus, if the chordwise C. G. of the blade is ahead of the bending axis of the spar, the blade will bend to the rear in the plane of rotation. Conversely, if the C. G. of the whole blade is to the rear of the bending axis of the spar, the blade will bend forwardly.

In blades where tubular spars are used, this problem is easily resolved inasmuch as the bending axis of the tube is along the center line of a circular section. Such a spar is usually designed to lie along the line center of gravity of the blade. Consequently, there is no moment of nonstructural parts tending to deflect the blade in the plane of rotation, that is if the blade is properly chordwise balanced at every section. However, in a blade where the spar also forms the leading edge, it can readily be seen that the bending axis of the spar will tend to lie some distance ahead of the center of gravity of the blade. This is particularly so in the case where the counterbalance for the non-structural portion of the blade is incorporated in the leading edge of the spar as part of the structural mass. The result is that blades of this type tend to be deected forwardly in the plane of rotation as the center of gravity of the whole blade lies at the 25% chord line which is behind the bending axis of the leading edge spar member.

To bring the bending axis of the blade spar back into coincidence with the 25% line, or aerodynamic center, it is possible to make the trailing edge member a continuous uninterrupted structure which would be able to resist the bending of the spar. However, this expedient would lead to a heavy stress concentration in the trailing edge of the blade which would tend to fatigue and crack the trailing edge with use. Furthermore, on quick starts of the rotor, as the blade was deflected to the rear in the plane of rotation due to its inertia, the trailing edge skin at the root of the blade would tend to buckle.

To eliminate these undesirable characteristics and still maintain a clear aerodynamic profile, the outermost pocket 12, which occupies a major outboard portion of the blade is formed as a single pocket so as to provide the best aerodynamic surface on the more sensitive outer portion of the blade, while the root portion is constructed with multiple short span pockets as has been the practice on previous blades. For example, this may be seen in my co-pending application Serial No. 142,988, issued December 9, 1952 as Patent No. 2,620,884. This large outer pocket, inasmuch as it is not tied in to the root of the blade, does not affect the bending axis of the spar over the inner portion where themajor blade bending occurs. Further, non-structural weight members 56, which are preferably made of a high density non-metallic material to prevent chang of the spar, or else metal weights c0at ed with a non-chafing material, are placed in the spadeshaped opening 32 formed by the curved inner wall surface, or bight, of the spar and the adjacent ribs 30 at the leading edge of the blade as required, to set up bending moments tending, under the action of centrifugal force, to bend the outer portion of the blade backward in the plane of rotation. These weight sections 56, several of which are shown in dotted lines of Figure l, extend from the tip toward the root portion of the blade as required to give the desired rearward bending moment to counter act the forward bending moment of the trailing edge members. These non-structural weight members 56 are held between the forward ribs 30 and the adjacent converging inner sidewalls, or bight, of the leading edge.

In Figure 2, the dotted line X represents the chordwise center of gravity location of the extruded spar member without the weight sections 56 therein, and would coincide with the bending axis of the spar member. This spar section is designed to have its bending axis as close as possible to the aerodynamic center of the airfoil section used. In the symmetrical section shown, for instance NACA 0012, the aerodynamic center occurs at the 25 chord. The dotted line Y represents the center of gravity of the extrusion with the trailing edge pocket 13 bonded to its trailing edge. As can be seen this combination brings the center of gravity of the blade section slightly aft of the 25% line where the optimum balance is desired. When the non-structural weight sections 56 are added, the center of gravity of the whole blade is brought to the 25 line which is indicated as Z. As has been previously pointed out, the outer pocket 12, although it might affect the bending axis location of the blade section in the outboard portion, has no effect on the inner portion of the blade where the major bending in the plane of rotation would occur, and consequently would not aiect the overall blade bending materially as the deflection of the blade tip is dependent almost completely on the bending of the root portion where the centrifugal bending moment is large as compared to the outer portion. Thus the bending axis of the whole blade remains substantially what it would be if the outer portion were made of segmented pockets as is the inboard portion. The blade is balanced around its 25% line to prevent deection under the action of centrifugal force in the plane of rotation and consequently to avoid the unwanted control stick loads due to bending of the blades in the plane of rotation.

In Fig. 4 a modified spar structure is shown. In this construction, internal spanwise ribs 30a are provided for locating a series of leading edge weight sections 56a which are inserted spanwise of the blade as in the previous construction but which are held between the ribs 30a and the converging inner sidewalls, or bight, of the leading edge of the spar so as to leave a leading edge chamber 56b through which heated gases may be circulated directly from a manifold 58 at the root end of the blade which is supplied by engine exhaust gases or other suitable heat ed gases from a pipe 60. Preferably the heated gases are directly circulated from pipe 60 and manifold 58 through a spanwise chamber 62 (Fig. 4) formed between the weight sections 56a and a channel member 64 which is positioned in the spar by a pair of upper and lower ribs 30. This channel may be formed of material which will increase the strength of the spar structurally. In this event, the weight sections 56a will have tapered holes 56e connecting passage 56b with chamber 62 so that the larger mass of air in chamber 62 will all be directed through these holes against the leading edge of the blade.

` As shown in Fig. 5, pipe 60 is connected through mani- 56h is connected by means of passage 36a to the outlet 38 and the rest of the hollow spar is sealed olf by plate 35 so that all the heated air will pass through passage 56b. Such an arrangement will have the advantage that the larger mass of air in passage 62 will not tend to cool near the tip of the blade and will provide the necessary heat to de-ice the leading edge.

It will be evident that as a result of this invention a metal rotor blade has been provided in which the chordwise bending axis of the blade can be adjusted so as to be coincident with the aerodynamic center and the chordwise center of gravity of the blade. It will further be evident that a rotor blade has been provided in which the root titting can be secured directly to the root portion of the blade without the necessity for further reinforcing the spar at this point. It will also be evident that an improved blade has been provided which is especially adapted for the incorporation of de-icing equipment.

Other rotor blade applications assigned to applicants assignee are application Serial No. 546,072 filed November l0, 1955 as a continuation-impart of application Serial No. 271,522 iled February 14, 1952, now abandoned; application Serial No. 154,620 filed April 7, 1950; and application Serial No. 312,590 led October l, 1952.

While a preferred embodiment of the invention has been shown and described herein, it will be evident that various changes in the construction and arrangement of the parts may be made without exceeding the scope of the invention.

I claim:

l. An all metal rotor blade comprising a one-piece hollow spar conforming to the airfoil contour of the blade from the leading edge throughout the chordwise extent of the part of the blade comprised by said spar including upper and lower walls which converge forwardly to form the leading edge bight of said spar, trailing edge pocket forming members connected to said spar along the trailing edge of the latter for completing the airfoil contour of the blade, said spar comprising a metal extrusion having integral spanwise weight locating abutment means on the inside surfaces of said upper and lower walls which extend along and are spaced aft of said leading edge bight, a plurality of weights free from structural connection to said spar arranged in spanwise abutting relation between and positioned by said abutment means and the bight of said spar in an end to end series extending from the outboard end of said spar in an inboard direction, and means for supporting said weights against movement in an outboard direction under the action of centrifugal force including means for supporting the most outboard weight of the series.

2. A blade for a rotary wing aircraft comprising a hollow spar the outer surface of which conforms to the airfoil contour of the blade chordwise from the leading edge thereof aft a distance greater than a quarter of the chord of the blade, said spar comprising the primary structural member of said blade, a plurality of trailing edge members attached to said spar to complete the airfoil contour of the blade, and weight means supported interiorly of said spar ahead of said quarter chord distance of said blade, said weight means being structurally separate of said spar.

3. A blade for a rotary wing aircraft comprising a hollow spar the outer surface of which conforms to the airfoil contour of the blade chordwise from the leading edge thereof aft a distance greater than a quarter of the chord of the blade, said spar comprising the primary structural member of said blade, said spar having upper and lower inner walls extending from the inner side of the leading edge, said spar having integral spanwise weight locating means on the inside surfaces of said upper and lower walls which are spaced aft of said leading edge, a plurality of trailing edge members connected to said spar to complete the airfoil contour of the blade, and a plurality of weights, said weights being mounted structurally separate of said spar by said locating means.

4. A blade for a rotary wing aircraft comprising a hollow spar the outer surface of which conforms to the airfoil contour of the blade chordwise from the leading edge thereof aft a distance greater than a quarter of the chord of the blade, said spar comprising the primary structural member of said blade, said spar having upper and lower inner walls extending from the inner side of the leading edge, said spar having integral spanwise weight locating means on the inside surfaces of said upper and lower walls which are spaced aft of said leading edge, a plurality of trailing edge members connected to said spar to complete the airfoil contour of the blade, and a plurality of weights, said weights having a slidable engagement with said locating means for moving said weights spanwise in said spar to locate them, said weights being mounted structurally separate of said spar by said locating means.

5. A rotor blade of the type having a tubular metal spar which forms the strength member of the blade and provides the airfoil contour of the blade throughout the chordwise extent of the spar and having segmented fairing means connected to the spar for completing the chordwise extent of the blade, said spar having internal spanwise guide means on its upper and lower walls, and balancing means mounted within said spar comprising one or more bars of substantial mass adapted to be inserted spanwise in said spar, the upper and lower surfaces of said balancing means coacting with said guide means for positioning said balancing means against chordwise movement in said spar.

6. A blade for a rotary wing aircraft comprising a hollow spar having a center of gravity and a longitudinally extending bending axis, said center of gravity being located substantially coincident with said bending axis, said spar having an outer surface which conforms to the airfoil contour of the blade chordwise from the leading edge thereof aft a distance greater than a quarter of the chord of the blade, said spar comprising the primary structural member of said blade, a plurality of trailing edge members connected to said spar to complete the airfoil contour of the blade, adjacent trailing edge members being spaced apart, said members adding weight tendf ing to move the center of gravity a distance rearwardly while not substantially moving the bending axis thereby offsetting the center of gravity from the bending axis, and balance weight means supported within said spar ahead of said quarter chord distance of said blade, said balance weight means adding weight tending to move the center of gravity a distance forwardly substantially equal to the distance that the members tend to move the center of gravity rearwardly while not substantially moving the bending axis thereby maintaining said center of gravity and longitudinally extending bending axis Substantially coincident.

7. A blade for a rotary wing aircraft comprising a hollow spar having a center of gravity and a longitudinally extending bending axis, said center of gravity being located substantially coincident with said bending axis, said spar having an outer surface which conforms to the airfoil contour of the blade chordwise from the leading edge thereof aft a distance greater than a quarter of the chord of the blade, said spar comprising the primary structural member of said blade, a plurality of trailing edge members connected to said spar to complete the airfoil contour of the blade, adjacent trailing edge members being spaced apart, said members adding weight tending to move the center of gravity of the combined spar and members a distance rearwardly while not substantially moving the bending axis of said spar thereby offsetting the center of gravity from the bending axis, and balance weight means supported within said spar ahead of said quarter chord distance of said blade, said balance weight means adding weight tending to move the center of gravity of said blade a distance forwardly substantially equal to the distance that the members tend to move the center of gravity rearwardly while not substantially moving the bending axis of said spar thereby maintaining said center of gravity of said blade and longitudinally extending bending axis of said spar substantially coincident.

8. A blade for a rotary wing aircraft comprising a hollow spar having a center of gravity and a longitudinally extending bending axis, said center of gravity being located substantially coincident with said bending axis, said spar having an outer surface which conforms to the airfoil contour of the blade chordwise from the leading edge thereof aft a distance greater than a quarter of the chord of the blade, said spar comprising the primary structural member of said blade, a plurality of trailing edge mem* bers connected to said spar to complete the airfoil contour of the blade, adjacent trailing edge members being spaced apart, and balance weight means supported within said spar ahead of said quarter chord distance of said blade, said balance weight means being structurally separate of said spar, said members adding weight tending to move the center of gravity of the blade a distance rearwardly while not substantially moving the bending axis of said spar, said balance weight means adding weight tending to move the center of gravity of the blade a distance forwardly substantially equal to the distance that the members tend to move the center of gravity rearwardly while not substantially moving the bending axis of said spar thereby maintaining said center of gravity of said blade and longitudinally extending bending axis of said spar substantially coincident,

9. A blade for a rotary wing aircraft comprising a hollow spar having a center of gravity and a longitudinally extending bending axis, said center of gravity being located substantially coincident with said bending axis, said spar having an outer surface which conforms to the airfoil contour of the blade chordwise from the leading edge thereof aft a distance greater than a quarter of the chord of the blade, said spar comprising the primary structural Cil member of said blade, a plurality of trailing edge members connected to said spar to complete the airfoil contour of the blade, adjacent trailing edge members being spaced apart, said spar having internal spanwise first guide means on its upper and lower walls, and balance weight means having second guide means which coacts with said first guide means, said coacting guide means supporting said balance weight means within said spar ahead of said quarter chord distance of said blade and structurally separate of said spar, said members adding weight tending to move the center of gravity of the blade a distance rearwardly while not substantially moving the bending axis of said spar, said balance weight means adding weight tending to move the center of gravity of the blade a distance forwardly substantially equal to the distance that the members tend to move the center of gravity rearwardly while not substantially moving the bending axis of said spar thereby maintaining said center of gravity of said blade and longitudinally extending bending axis of said spar substantially coincident.

References Cited in the tile of this patent UNITED STATES PATENTS 2,152,861 Bennett Apr. 4, 1939 2,230,393 Thomson Feb. 4, 1941 2,320,870 Johnson June 1, 1943 2,427,065 Nebesar Sept. 9, 1947 2,458,686 Davie, Jr Jan. 11, 1949 2,460,351 Hoffman et al Feb. 1, 1949 2,469,480 Sikorsky May 10, 1949 2,484,141 Alex Oct. 11, 1949 2,613,893 Young Oct. 14, 1952 FOREIGN PATENTS 206,843 Great Britain Feb. 9, 1925 278,874 Great Britain Oct. 20, 1927 432,555 Great Britain July 23, 1935 619,694 Great Britain Mar. 14, 1949