US3768923A

US3768923A - Variable length blade

Info

Publication number: US3768923A
Application number: US00859094A
Authority: US
Inventors: E Fradenburgh
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1969-09-18
Filing date: 1969-09-18
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30
Also published as: IT954097B; GB1332658A; DE2045637C3; FR2173631B1; CA940513A; FR2173631A1; DE2045637B2; DE2045637A1

Abstract

A variable length blade in telescopic form adapted to be used with comparable blades to form a variable diameter rotor or propeller and wherein the outer blade portion is caused to telescope with respect to the inner blade portion by jackscrew action and wherein the outer blade portion is connected to the jackscrew by a plurality of tension-torsion straps extending between the outer blade portion and a series of nuts on the jackscrew.

Description

United States Patent 1191 Fradenburgh 1 Oct. 30, 1973 [5 VARIABLE LENGTH BLADE 3,128,829 4 1964 Young 416/88 [75] Inventor: Evan Albern Fradenburgh, FOREIGN PATENTS OR APPLICATIONS Falffield, Con". 252,461 5/1926 Great Britain 416/87 [73] Assignee: United Aircraft Corporation, East H tf d Conn Primary ExaminerSamuel Feinberg Att0rneyVernon F. I-Iauschild [22] Filed: Sept. 18, 1969 Appl. No.: 859,094

US. Cl. 416/89 1 [51] Int. Cl B63h1/06.- [58] FieldofSearch ..4l6/147, 88, 87, 416/89; 74/424.8, 841,459

[56] References Cited UNITED STATES PATENTS 2,163,482 6/1939 Cameron ..416/ss 2,659,241 11/1953 1161mm ..74 /424 s [57] ABSTRACT A variable length blade in telescopic form adapted to be used with comparable blades to form a variable diameter rotor or propeller and wherein the outer blade portion is caused to telescope with respect to the inner blade portion by jackscrew action and wherein the outer blade portion is connected to the jackscrew by a plurality of tension-torsion straps extending between the outer blade portion and a series of nuts on the v jackscrew.

23 Claims, 17 Drawing Figures Patented 0a. 30, 1973' v 3,768,923

I 5 Sheets-Shoot 1 FIGJ I A 'IIIIIIIIIIIIIIII/ Patented Oct. 30, 1973 5 Shegts-Sheet 7:

Patented Oct. 30, 1913 3,768,923

Patnted 0a.. 30, 1973 5 Shoots-Shoot 5 FIGJB 1,

1 VARIABLE LENGTH BLADE CROSS-REFERENCE TO RELATED APPLICATIONS This application teaches a blade construction of the type generally disclosed in and usable with the system disclosed in copending application Ser. No. 759,287 filed Sept. 12, 1968, on Mechanism For Synchronously Varying The Diameter Of A Plurality Of Rotors And For Limiting The Diameters by Evan A. Fradenburgh.

BACKGROUND OF THE INVENTION 1. Field of Invention A This invention relates to variable length blades adapted to be used in variable diameter rotors or propellers of the aircraft type and which consists of a telescoping blade actuated by a jackscrew arrangement wherein the outer blade portion is connected to the jackscrew through a plurality of tension-torsion straps, which constitute a soft spring in connecting the outer blade portion to a plurality of nuts on the jackscrew so as to accomplish equal nut and nut thread loading under centrifugal load of the rotor in flight and so as to permit the blade to vary in pitch without causing the nuts to move on the jackscrew.

2. Description of the Prior Art In the variable diameter rotor art, blades of telescopic construction have been caused to vary in length and hence vary the diameter of the rotor by means of a jackscrew mechanism. One such construction is shown in Cameron U. S. Pat. Nos. 2,163,481 and 2,163,482 but this construction did not anticipate high centrifugal loading of the blading during the time of blade length variation in flight, nor did they anticipate the need to accommodate continual pitch change, such as modern helicopters experience due to cyclic pitch variation. In the Cameron construction a stiff tube connects a single nut on the jackscrew to the outer telescoping blade portion, and while such a construction was probably adequate at that time since Camerons rotor rotates at relatively low speeds and the blades are not subject to cyclic pitch variation, modern helicopters having high tip speeds and high stress levels require extensive design improvements in this area. To accommodate such design considerations utilizing the Cameron construction, an extremely long nut coacting with the jackscrew shaft would be needed and it would be impossible with such a long nut to achieve equal loaddistribution across the various threads of the nut since the elastic deformation which occurs in the parts being joined through the nut causes the end threads to be extremely heavily loaded while the intermediate threads are virtually load-free. Such loading, of course, causes excessive wear in the end threads and, in an extreme case, this loading of the end threads could cause failure of those threads, thereby throwing the load on the next adjacent threads to propagate progressive thread failure in rapid succession so that the nut would be free to slide off of the jackscrew, thereby releasing the outer blade portion.

If a short nut were to be considered for use, its threads and the jackscrew would have to be extremely large and heavy. Such size and weight requirements render usage prohibitive.

In addition, modern helicopters require almost continual cyclic pitch change of their blades, and the rigid tube of Cameron would therefore cause his single large nut to be continuously moving on the jackscrew shaft, thereby establishing an intolerable wear and heat generating situation, as well as undesirable radial in and out movements of the outer blade portions in an assymetrical rotor head pattern.

In the past, attempts have been made to achieve equal nut thread loading in a single nut construction of the type taught in Cameron by placing a lapping compound on the threads and loading the threads under a simulated centrifugal force and then letting the nut threads wear or lap themselves in to the point where each is equally loaded. This thread lap-in procedure is not successful because the heavy centrifugal loading placed on the threads during blade extension and retraction causes temperature buildup and resultant thermal deformation of the threads so that the carefully lapped-in and load equalizing thread clearances are lost due to this thermal deformation and the unequal thread loading situation reoccurs. In addition, this thread lapin solution produces thread load equalization only at the specific centrifugal load condition at which the lapping-in occurred.

Accordingly, since the centrifugal load on the blade varies in flight, a single thread load equalization condition is of no great assistance.

U. S. Pat. No. 3,128,829 shows a telescoping blade construction very similar to the aforementioned Cameron patents and it will be evident that it includes the same operational limitations.

SUMMARY OF INVENTION A primary object of the present invention is to provide a variable length blade utilizing a jackscrew and nut arrangement to produce telescopic motion between inner and outer blade portions and wherein the threads of the nut arrangement are equally loaded and blade diameter is unaffected by blade pitch variation.

In accordance with the present invention, a plurality of short nuts are placed on the jackscrew and individually connected to the outer blade portion by tensiontorsion straps. The use of a plurality of nuts introduces the requirement that the individual straps connecting the nuts to the blade tip distribute equal loading to each nut. In this invention such straps are of sufficient length and physical characteristics with respect to the nuts that they form a soft spring relative to the nut threads during blade centrifugal loading. The change in tension-torsion strap length by elastic stretching under tension loading caused by blade centrifugal loads is very large compared to possible changes in thread spacing. Accordingly, each nut will carry its proportional share of the total centrifugal load within a small percentage, and this equal nut thread load carrying capability will occur at all significant load levels.

In accordance with a further aspect of the present invention, due to the torsional mobility and flexibility of these elongated tension-torsion straps, the blade outer portion can change pitch, collectively or cyclically,

without imparting motion to the nuts on the jackscrew I shaft.

The invention provides structural redundancy by utilizing a plurality of thin tension-torsion straps between several nuts and the outer blade portion as opposed to a single connection between a single nut and the outer blade portion.

In accordance with a further aspect of the present invention, the nuts of the jackscrew-nut arrangement may be of the wing nut variety with the tension-torsion straps connected to opposite wings of each nut, and such nuts may be identical and staggered slightly to permit each tension-torsion strap to pass clear of all other straps, and these nuts may be pinned to prevent relative rotation therebetween, with the pin axis parallel to the screw axis so as to allow freedom of relative axial displacement required to insure equal nut loading. Since the jackscrew threads will elongate due to blade loading, and since the elongation will vary over the length of the jackscrew where the nuts are attached, freedom of axial displacement between the nuts is required and such pinning permits this axial displacement. i I

In accordance with a further aspect of the present invention, the nuts of the jackscrew arrangement can be of the same size and in alignment, with tension-torsion strap passing through a drilled passage in its own attachment nut and clearing through all other nuts on the blade tip side thereof, and wherein said tension-torsion straps are retained in said nuts and in a plate member at the blade tip by bolt head and nut engagement and other conventional means.

In accordance with still a further aspect of the present invention, both the nuts and the inner blade member are made of elongated cross-section so that the nuts have a limited degree of rotational freedom with respect to the inner blade member before bearing positively thereaginst in positive stop fashion.

In accordance with another aspect of this invention, positive stops are provided to limit the amount of telescoping motion of the outer blade member on the inner blade member.

In accordance with a further aspect of this invention, both the inner blade member and the outer blade member are mounted together for pitch change motion about the blade feathering axis.

In accordance with still a further aspect of this invention, bearing blocks are provided to support the outer blade member for telescoping action on the inner blade member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial showing, partially broken away, of a variable diameter rotor or propeller of a modern aircraft, such as a helicopter, illustrating my invention.

FIG. 2 is a top view, partially broken away, illustrating my invention used in a variable length rotor blade.

FIG. 3 is a showing through line 3-3 of FIG. 2.

FIG. 4 is a showing taken along line 4-4 of FIG. 2.

FIG. 5 is a showing taken along line 5-5 of FIG. 2.

FIGS. 5a and 5b are partial showings similar to FIG. 5 showing the nut member at the opposite ends of relative rotation travel with respect to the blade.

FIG. 6 is a partial showing,- partially broken away, of a variable length blade utilizing a preferredembodiment of my invention.

FIGS. 7 and 8 illustrate segmented nuts of the wing nut variety on a jackscrew and receiving tensiontorsion straps to illustrate another embodiment of my invention.

FIG. 9 is a schematic representation of a single, elongated nut on a jackscrew.

FIG. 10 is a graphic representation of thread loading on the nut of FIG. 9.

9 Wing nut. FIGS. 13 and 15 are a top view and an end view, respectively, and FIG. 14 is a section along line 14-14 of FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 we see the variable area blade in the environment of a variable diameter rotor 10, which may be used on a modern helicopter. Rotor 10 could also be a propeller for a fixed wing aircraft. Rotor 10 consists of a plurality of equally spaced blades 12 projecting from rotor hub 14 for rotation therewith about rotor axis of rotation 16.

Blades 12 are appropriately supported, for example by stack bearings (not shown), for pitch change motion about blade feathering axis 26 so that the blades may change pitch both collectively and cyclically. Blades 12 may be of the type more fully described in U. S. Pat. No. 2,163,482.

Swash plate assembly 30, which may be of the type more fully disclosed in U. S. Pat. No. 2,925,130, is sup ported from spherical bearing 32 and standpipe 34, which project from the housing of the transmission unit 24. Blade pitch controls 36, which are conventional and may be of the type fully disclosed in U. 5. Pat. No. 3,199,601, are utilized to cause the swash plate assembly 30 to translate along axis 16 and act through pivotal pitch change rod 38 and pitch change horn 40 to cause the pitch of blades 12 to vary collectively. Control 36 can also cause swash plate assembly 30 to tilt with respect to axis 16 and thereby cause the pitch of the blades to vary cyclically in conventional fashion. This cyclic pitch variation occurs throughout the rotation of blades 12.

Rotor 10 is supported from fuselage or wing 18 and is driven by engine 20 through reduction gear 22 and transmission 24. Engine 20 may be of the type shown in U. S. Pat. Nos. 2,711,631 and 2,747,367, and reduction gears 22 may be of the type shown in U. S. Pat. No. 2,91 1,851. While a rigid rotor is shown, the invention is equally applicable to an articulated rotor of the type shown in U. S. Pat. No. 2,925,130, so long as a universal joint (not shown) is placed in jackscrew shaft 66.

Engine 20 drives transmission input drive shaft 42, which carries bevel gear 44 at one end thereof. Bevel gear 44 coacts with and drives bevel gear 48, which is connected to and drives rotor drive shaft 51 to thereby cause rotor 10 to rotate about axis of rotation 16.

We shall now consider the mechanism which causes rotor 10 to change diameter. Stillviewing FIG. 1, we see that shafts 50 and 52 are positioned coaxially by appropriate support bearings (not shown), about axis 16 and each carries at one end thereof bevel gears 54 and 56, respectively, which form part of differential 58, which also includes pinion gears and 62 so that there is one such pinion gear for each blade 12 in rotor 10. These pinion gears 60 and 62 connect directly to jackscrew or jackscrew shaft 66 in each blade 12.

As engine 20 causes rotor 10 to rotate about axis 16, shafts 50 and 52 will rotate therewith. Each of the shafts 50 and 52 has a clutch or

brake member

70 and 72 connected thereto. Both of these brakes are pilot operated in conventional fashion, for example, through a solenoid mechanism. When brake 70 is applied, shaft 50 and bevel gear 54 are stopped and, as rotor drive shaft 51 and hub 14 continue to rotate, the pinions such as 60 and 62 will be caused to rotate and thereby rotate jackscrews 66. Nut assembly 100, which will be described in greater particularity hereinafter, threadably engages jackscrew shaft 66 and is free to move therealong feathering axis 26 within a chamber 102 defined between jackscrew 66 and inner blade portion or torque tube 104 of blade 12. Nut assembly 100 is connected to outer movable blade portion 106 through a plurality of tension-torsion strap members indicated in FIG. 1 generally as 110 so that translation of nut assembly 100 away from rotor hub 14 will permit centrifugal force to cause outer blade portion 106 to telescope outwardly with respect to inner blade portion 104, thereby increasing the diameter of rotor 10, and so that translation of nut assembly 100 inwardly will act through tension-torsion straps 110 to cause outer blade member 106 to telescopeinwardly toward hub 14 with respect to inner blade member 104, thereby reducing the diameter of rotor 10. Application of retraction brake 72 will cause blade 12 to retract and thereby reduce in length and rotor to decrease in diameter, while application of extension brake 70 will cause blade 12 to extend and thereby increase in length and rotor 10 to increase in diameter. It will be evident that the pitch and hand of the threads of jackscrew 66 and nut assembly 100 determines the rate of diameter change of rotor 10 and whether the diameter will increase or decrease.

Referring to FIGS. 2-5, we see a preferred embodiment of my variable length blade 12. Outer blade portion 106 is of airfoil cross-section and inner blade or torque tube portion 104 is of elongated cross-section, such as elliptical cross-section. Outer blade portion 106 consists of spar portion 108 and trailing edge portion 111. Blade tip cap 112 fits overthe outer end of outer blade portion 106 to provide a properly shaped aerodynamic tip therefor.

Spar bearing blocks

114 and 116 attach to spar 108 as shown in FIG. 3, by any convenient means such as screw members 120. Tu'be bearing blocks 122 and 124 attach to blade inner portion 104 by any convenientmeans such as bolt mechanisms 126 and 128 (See FIG. 4).

Spar bearing blocks

114 and 116 and tube bearing blocks 122 and 124 coact to guide outer blade portion 106 in its telescoping motion inwardly and outwardly with respect to inner blade portion 104. i

To cause outer blade portion 106 to translate with respect to inner blade portion 104, jackscrew 66 is caused to rotate in one direction or the other by the mechanism disclosed and described in connection with FIG. 1, and thereby cause nut assembly 100 to translate therealong and along feathering axis 26. Nut assembly or segmented nut 100 includes a plurality of individual nuts or nut segments 100a, 100b, 100C, l00c, and 100e as shown in FIG. 2. At least one tension-torsion strap extends from each opposite side of each of nuts 100a--l00e and connects to the tip portion of outer blade portion 106 in a fashion to be described in greater particularity hereinafter.

By viewing FIG. 2 it will be noted that during blade retraction, adjustable positive stop members 130 and 132 abut tube bearing blocks 122 and 124 in positive one of the primary load path members; that is, the jackscrew or straps.

As best shown in FIG. 5, nut assembly is of elongated shape along the blade chord axis 134 and is smaller in size than the inner wall of tube member 104, thereby permitting limited relative rotation of nut assembly 100 within innner tube or blade member 104 about axis 26. The elongated nut shape allows sufficient relative freedom between the nut and tube such that pitch change motions of the blade will not cause the nut to rotate on the jackscrew and to extend or retract the blade. If the nut were of the same shape and size as the inner wall of the tube, the cyclic pitch inputs would turn the nut and cause an undesirable and assymetric cyclic variation in blade length. Such cyclic relative oscillation between the nut and jackscrew would also result in an intolerable lubrication and wear problem. Since the spar bearing blocks 1 l4 and 116 provide rigidity to the tube 104, and since the nut assembly 100 and these blocks move radially inwardly and outwardly together, it is preferable to align the nut assembly 100 under the

bearing block

114 and 116 to provide extra tube stiffness as the nut surfaces bear against the inner wall of the tube during extension or retraction. Other than this slight limited relative motion of the nut and tube, the nut is restrained from further relative motion by its contact with the tube inner wall, such that jackscrew rotation will drive the nut axially to draw the outer blade portion inward or allow it to extend outward so shown in FIGS. 5a and 5b. The nut

external surfaces

109, 111, 113, and 115 are contoured to the contour of the inner surface 117 of the tube 104 so as to provide full surface contact when extension or retraction is to be made rather than line or point contact. Dependent upon the allowable stress consideration, the shape of the nut may be trapezoidal, triangular, or of other shape, so long as its sides make contact with the inner wall of the blade inner portion after a predetermined amount of relative motion has been completed. A preferred embodiment of my invention is shown in FIG. 6, wherein outer blade portion 106 is caused to telescopically move with respect to inner blade portion 104 along feathering axis 26, in a fashion now to be described. Individual nuts 100a-100e threadably engage jackscrew 66 and will be translated therealong in response to jackscrew rotation. Tension-torsion straps extend between nuts 100a-100e and the tip of outer blade portion 106 where theyengage plate member 140, which attaches to outer blade member by any convenient means such as

screws

142 and 144.

Tension-torsion straps 1 10 may be of any shape, such as a flat shape or may actually be circular in crosssection, and may be connected to nuts 100a-100e and outer blade member 106 in any preferred manner of fastening such as by threaded members, staking, snap rings, or the like. In the FIG. 6 construction the tension-torsion straps 110are of the wire or rod type and of circular cross-section and extend through drilled holes in nuts 100a-l00e and plate member 140. Two strapsattach to each nut and pass through aligned clearance holes provided as required in the adjacent nuts. As shown in FIG. 6

rods

110a and 110b, 110a and 110d, l10e and 110f, 100 and llOh, 110i and 110j, connect nuts 100a, 100b, 100c, 100d, and 1002, respectively, to plate 140 in blade outer portion 106. Each rod, such as 110a, passes through aligned apertures, such as 146, 158, 160, 162, and 164 in the nuts. The rods may have both heads, such as 150, at one end thereof, and nuts, such as 152, threadably engaging the opposite end thereof. It will be noted that the aligned holes for each strap clearance are offset from all other sets of aligned holes, thereby offsetting all straps.

In order to provide outer support for the jackscrew 66, bearing support 125 is installed at its outer radial end as shown in FIG. 4. Recesses screw fasteners 127 connect the bearing support to blade inner portion 104.

In operation, as nuts la-100e are caused to trans late on jackshaft 66, outer blade portion 106 moves in telescopic fashion with respect to inner blade portion 104 because each of nuts 100a-l00e is individually connected to the tip 112 of outer blade portion 106 through tension-torsion straps 110a-110j. These nuts and the threads therewithin will be substantially equally loaded due to blade centrifugal force during rotor operation. Tension-torsion straps 110a-110j constitute a soft spring with respect to nuts 100a-100e so that the straps will deform under centrifugal load and the nuts l00a-l00e will be loaded substantially equally. This result is achieved due to the extensive length of tensiontorsion straps 110a-110j as opposed to the height of nuts l00a-100e. We accordingly see that by the elongation of straps 1 due to tension loading by the blade centrifugal force, nut load equalization is accomplished. In addition, due to the length and torsional flexibility of straps 110, blade outer portion 106 can vary in pitch without imparting rotational motion to nuts l00al00e, since straps 110 will twist around feathering axis 26 during blade pitch change before friction forces on the nuts are overcome. As mentioned heretofore, it is necessary that the nut assembly be of sufficiently smaller size and selected shape to allow the blades to change pitch without contacting the nuts.

FIGS. 7 and 8 show another modification of my multi-nut unit 100, wherein

wing nuts

200, 202, 204, and

206 threadably engage jackscrew 66 and individual tension torsion straps 110k, 110l, 110m, and l10n extend from

wings

208, 210, 212, and 214 thereof. It will be understood that similar tension-torsion straps project from the corresponding wings (not shown) on the opposite side of wing nuts 200-206. It will be noted in the FIG. 7-8 construction that tension-torsion straps 110 are of flat stock and are retained in wings 208-241 by receipt of their bulbous ends in enlarged recesses in the wings. It will be further noted that the wings 208-241 of nuts 200-206 are slightly spaced angularly to avoid tension-torsion strap interference.

Pins

209, 211, and 213 extend between adjacent nuts 200-206 in a direction parallel to axis 26, so as to prevent relative rotation between the nuts while permitting simultaneous translation of all nuts along jackshaft 66 during rotor diameter varying operation and to allow relative axialv displacement between the nuts as required to insure equal nut loading. This axial freedom is provided so that non-uniform threads or screws which are due to manufacturing variations, elastic strains, or thermal expansion because of frictional heat during operation of the screw, will not cause one nut to pick up load at the expense of the other.

'justment means (that is, nut ends) may Referring to FIGS. 13-15 we see another method of attaching tension-torsion straps 110 to one of the segmented nuts 200. While one strap only is shown connected to one of the wings 208 of wing nut 200, it should be borne in mind that a strap is similarly attached to the opposite wing of nut 200 and to the wings of all of the other nuts, for example, as illustrated in FIGS. 7 and 8. It will be noted that in the FIG. l3l5 construction, tension-torsion strap 110 is of flat stock and is connected to wing 208 by bolt members, such as 300 and 302, which pass through holes in the end of strap 11 0 and are threadably received in threaded apertures, such as 304,'in wing 208. It will further be noted that ear 208 is contoured as best shown in FIG. 14 so that the straps from the various nuts may be closely spaced in the assembly and not required to be separated by the height of the head of

bolts

300 and 302. Close spacing is required because of the limited space available within the blade tube confines and the need for an angular degree of freedom between nuts and tube. The opposite end of strap 110 is connected to the tip of blade 12 in any convenient fashion.

The advantage to be gained by the multiple nut construction taught herein over the single elongated nut construction of the prior art, such as the Cameron patent, is made clear by viewing FIGS. 9 and 11 with their attendant thread load charts shown in FIGS. 10 and 12. FIG. 9 illustrates an elongated single nut member 220 on jackscrew 66 and by viewing FIG. 10, it will be noted that, due to elastic deformation of the nut and jackscrew, the end threads are heavily loaded, while the intermediate threads are virtually load-free. This uneven thread loading, of course, brings about uneven thread wear and, in the extreme case, could cause progressive thread failure as the outermost threads fail, followed by the next succeeding threads, until eventually and over a short period of time, all of the threads have failed causing the release of the two parts which were formerly joined thereby.

FIG. 11 schematically illustrates the multiple nut unit 100 of my invention, including small nut members 1 10a-l00d on jackscrew 66 with tension-torsion straps a-100h extending therefrom as shown. Now referring to FIG. 12 we see the virtually equal thread loading on all of the nuts in the FIG. 11 construction. This results from the relatively small number of threads in each nut.

Two factors influence nut loading and must be considered. The first involves the specific mechanical fits of the multiple straps at zero load.

All straps should exhibit. the same degree of slack from nut to blade tip attachment. lf inaccuracies in slack between the straps are kept small relative to the large strap elongation under load, the strain for all straps will be substantially the same Suitable slack adbe used if required. Y

The second consideration is the difference in strap length due to the difference in straps because of the unequal distances between the various axially spaced nuts and their common retention block at the blade tip. Because the strap overall length is large compared to the difference between the various straps, the difference in loading which the straps impose on each nut is relatively small and unimportant. If it is desired to avoid this difference in loading, the tip retention points for the various straps can be staggered to make all straps of the same length.

Tension-torsion straps 110 can be made out of any suitable material, such as steel in single or multiple strands, and could also be made of fiber glass, boron, or any of the exotic compositions of today. The nut segments of segmented nut 100 are preferably made of a good wear resistant material, such as beryllium copper, but other metals and composites could also suffice. jackscrew 66 is preferably made of steel or titanium.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person'skilled in the art.

I claim:

1. A variable length blade having a feathering axis and a blade tip end and including:

a. an inner blade portion,

b. an outer blade portion mounted for telescopic action with respect to said inner blade portion,

c. means to cause said outer and inner blade portions to telescope with respect to one another including:

1. a threaded jackshaftlocated within said inner blade portion and being fixed except for rotation with respect to said inner blade portions,

2. a plurality of nut members threadably engaging said jackshaft,

d. elongated tension-torsion straps connecting each of said nut members to said outer blade portion.

2. Apparatus according to claim 1 and including means to cause said jackscrew to rotate and hence vary the position of the outer blade portion with respect to the position of the inner blade portion to thereby vary blade length.

3. Apparatus according to claim 2 wherein said jackscrew rotating means constitutes means-to causesaid jackscrew to rotate in either direction.

4. Apparatus according to claim 1 wherein said tension-torsion straps connect to said blade outer portion at the blade tip end.

5. Apparatus according to claim 1 and wherein said jackshaft is concentric with respect to said inner and outer blade portions. 1

6. Apparatus according to claim 1 wherein said straps are of selected length and physical properties to distort under blade centrifugal loading sufficiently to substantially equally load each of said nuts.

7. Apparatus according to claim 1 wherein said blade portions are mounted for pitch change motion about said feathering axis and including means to cause said blade portions to change pitch about the blade feathering axis without causing motion of said nut members on said jackshaft.

8. A variable length blade including:

a. an inner blade portion,

b. an outer blade portion mounted for telescopic mow tion relative to the inner portion,

c. means to cause said outer and inner blade portions 'to telescope with respect to one another including:

1. a jackscrew internal to the blade mounted for rotation, I

2. a plurality of nut members engaging said jackscrew and adapted to contact the inner wall of the inner blade portion after a predetermined degree of relative angular movement,

3. a plurality of tension-torsion members individually connecting said nut members to the outer blade portion. 9. A variable length blade having a blade tip and in- 5 cluding:

a. an inner blade portion,

b. an outer blade portion supported from said inner blade portion for thereto, a

0. means tocause said outer blade portion to telescope with respect to said inner blade portion including: I

l. a jackscrew concentrically located within the interior of said inner blade portion and being mounted to be fixed with respect to said inner blade portion except for its own rotary motion,

2. a plurality of substantially equally sized nuts threadably engaging said jackscrew,

3. a plurality of elongated tension-torsion straps ex- I tending between and connected to each of said nuts and said outer blade portion.

10. Apparatus according to claim 9 wherein said blade portions are mounted for feathering action about the blade feathering axis and including means to cause said blade portions to move about said blade feathering axis to vary blade pitch without causing said nuts to rotate on said jackshaft. I

11. Apparatus according to claim 11 wherein said inner blade portion is hollow and of substantially elongated cross-section, and wherein said nuts are also shaped to be elongated in the same direction as the elongation of said inner blade portion so that during pitch change motion said blade portion can rotate a preselected angular amount relative to said nuts and, further, wherein as said jackscrew is caused to rotate to thereby cause said outer blade portion to telescope with respect to said inner blade portion, said nuts abut the inner wall of said inner blade portion to prevent rotation of said nuts. I

12. Apparatus according to claim 9 and wherein said nuts are of the wing-nut variety and are staggered with respect to one another on said jackshaft so that the wings of each of said nuts are out-of-alignment with the wings of the remainder of the nuts'arid so that said tension-torsion straps extend interference-free from the wings ofeach nut to the bi-ade outer portion.

13. Apparatus according to claim 9 wherein said nuts are pinned together to prevent relative rotation therebetween while permitting simultaneous translation of all nuts along said jackshaft and relative translatory motion between said nuts along said jackshaft.

14. Apparatus according to claim 9 and including positive stop means to limit the amount of rotation of said nuts within said inner blade portion.

15. Apparatus according to claim 9 wherein said inner blade portion is of elliptical shape and wherein said nuts are of elliptical shape and positioned within said inner blade position so that said inner blade portion is capable of limited relative rotation with respect to said nuts and wherein said nuts abut said inner blade portion to prevent rotation of said nuts with said jackshaft.

16. Apparatus according to claim 9 including means to limit the end travel of said outer blade portion with respect to said inner blade portion.

17. Apparatus according to claim 9 wherein said tension-torsion straps are flat members and wherein said telescoping motion with respect nuts are of the wing-nut variety and wherein one end of each tension-torsion strap connects to one of the wings of one of said nuts, and including bolt means connecting the end of the strap to the nut wing.

18. Apparatus according to claim 17 wherein the wings of each nut include an arcuate surface, and including bolt means connecting a strap end to the nut wing at a station on the wing away from the blade tip so that the strap engages and is supported by said wing arcuate surface.

19, Apparatus according to claim 9 wherein said nuts are identical in shape and positioned in alignment on said jackscrew and include a plurality of aligned holes through said nuts, and further wherein said tensiontorsion straps are wires with each strap extending through a series of aligned nut holes, and further including a plate member connected to the blade outer portion at the blade tip and including a plurality of holes therethrough in substantial alignment with the aligned holes of the nuts and wherein said straps pass through said holes of said plate member, and still further including means to connect each of said straps to said plate member and one of said nuts.

20. A variable diameter rotor including:

a. a plurality of equally spaced blades mounted for rotation about an axis of rotation,

b. each of said blades including:

1. an inner blade portion,

2. an outer blade portion mounted for telescoping motion with respect to said inner blade portion,

3. means to cause said outer blade portion to telescope with respect to said inner blade portion including:

A. a jackscrew member mounted for rotation within said inner blade member,

- B. a plurality of substantially equal sized nuts threadably engaging said jackscrew member,

C. a plurality of tension-torsion straps extending between and connected to each of said nuts and said outer blade portion.

21. Apparatus according to claim 20 wherein the number of threads on each of said nuts is small in comparison to the number of threads in said jackscrew.

22. Apparatus according to claim 21 wherein each of said nuts has an equal number of threads.

23. Apparatus according to claim 20 wherein said torsion straps are rod members having a fixed head at one end thereof and an adjustable head at the opposite end thereof and including:

a. a series of aligned drilled holes extending through said nuts,

b. a plate member attached to said outer blade portion at the blade tip and including drilled holes passing therethrough in alignment with said aligned drilled holes and wherein said straps extend through said aligned drilled holes of said nuts and said plate member and are retained therein by the coaction between said fixed and adjustable heads of the straps, said nuts and said plate member to thereby form a connection between the nuts and the blade outer portion through said straps.

3 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Io. 3,768,923 Dated October 30,1973

Inventor(s) Evan Albem Fradenburgh It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 11, line 1 Delete "11'' and insert --lO-- Signed and sealed this 2nd day of April 197L (SEAL) Attest:

EDWARD M.FLETCHER,JR. c. MARSHALL DANN Attesting Officer Commissioner of Paten'

Claims

1. A variable length blade having a feathering axis and a blade tip end and including: a. an inner blade portion, b. an outer blade portion mounted for telescopic action with respect to said inner blade portion, c. means to cause said outer and inner blade portions to telescope with respect to one another including: 1. a threaded jackshaft located within said inner blade portion and being fixed except for rotation with respect to said inner blade portions, 2. a plurality of nut members threadably engaging said jackshaft, d. elongated tension-torsion straps connecting each of said nut members to said outer blade portion.

2. a plurality of nut members threadably engaging said jackshaft, d. elongated tension-torsion straps connecting each of said nut members to said outer blade portion.

3. a plurality of tension-torsion members individually connecting said nut members to the outer blade portion.

3. means to cause said outer blade portion to telescope with respect to said inner blade portion including: A. a jackscrew member mounted for rotation within said inner blade member, B. a plurality of substantially equal sized nuts threadably engaging said jackscrew member, C. a plurality of tension-torsion straps extending between and connected to each of said nuts and said outer blade portion.

3. a plurality of elongated tension-torsion straps extending between and connected to each of said nuts and said outer blade portion.

3. Apparatus according to claim 2 wherein said jackscrew rotating means constitutes means to cause said jackscrew to rotate in either direction.

5. Apparatus according to claim 1 and wherein said jackshaft is concentric with respect to said inner and outer blade portions.

8. A variable length blade including: a. an inner blade portion, b. an outer blade portion mounted for telescopic motion relative to the inner portion, c. means to cause said outer and inner blade portions to telescope with respect to one another including:

9. A variable lengTh blade having a blade tip and including: a. an inner blade portion, b. an outer blade portion supported from said inner blade portion for telescoping motion with respect thereto, c. means to cause said outer blade portion to telescope with respect to said inner blade portion including:

10. Apparatus according to claim 9 wherein said blade portions are mounted for feathering action about the blade feathering axis and including means to cause said blade portions to move about said blade feathering axis to vary blade pitch without causing said nuts to rotate on said jackshaft.

11. Apparatus according to claim 11 wherein said inner blade portion is hollow and of substantially elongated cross-section, and wherein said nuts are also shaped to be elongated in the same direction as the elongation of said inner blade portion so that during pitch change motion said blade portion can rotate a preselected angular amount relative to said nuts and, further, wherein as said jackscrew is caused to rotate to thereby cause said outer blade portion to telescope with respect to said inner blade portion, said nuts abut the inner wall of said inner blade portion to prevent rotation of said nuts.

12. Apparatus according to claim 9 and wherein said nuts are of the wing-nut variety and are staggered with respect to one another on said jackshaft so that the wings of each of said nuts are out-of-alignment with the wings of the remainder of the nuts and so that said tension-torsion straps extend interference-free from the wings of each nut to the blade outer portion.

17. Apparatus according to claim 9 wherein said tension-torsion straps are flat members and wherein said nuts are of the wing-nut variety and wherein one end of each tension-torsion strap connects to one of the wings of one of said nuts, and including bolt means connecting the end of the strap to the nut wing.

19. Apparatus according to claim 9 wherein said nuts are identical in shape and positioned in alignment on said jackscrew and include a plurality of aligned holes through said nuts, and further wherein said tension-torsion straps are wires with each strap extending through a series of aligned nut holes, and further including a plate member connected to the blade outer portion at the blade tip and including a plurality of holes therethrough in substantIal alignment with the aligned holes of the nuts and wherein said straps pass through said holes of said plate member, and still further including means to connect each of said straps to said plate member and one of said nuts.

20. A variable diameter rotor including: a. a plurality of equally spaced blades mounted for rotation about an axis of rotation, b. each of said blades including:

23. Apparatus according to claim 20 wherein said torsion straps are rod members having a fixed head at one end thereof and an adjustable head at the opposite end thereof and including: a. a series of aligned drilled holes extending through said nuts, b. a plate member attached to said outer blade portion at the blade tip and including drilled holes passing therethrough in alignment with said aligned drilled holes and wherein said straps extend through said aligned drilled holes of said nuts and said plate member and are retained therein by the coaction between said fixed and adjustable heads of the straps, said nuts and said plate member to thereby form a connection between the nuts and the blade outer portion through said straps.