US2718267A - Blade cuff - Google Patents

Description

Sept. 20, 1955 WOOLF ET AL 2,718,267

BLADE CUFF Filed March 5, 1952 VENTOR5 DON R. W OLF LEE H. WURSTER.

BY LEO AVONDOyGlJ I H 7 yATTb NEY result in cuff failure.

United States Patent BLADE CUFF Don R. Woolf, Caldwell, and Lee H. Wurster, West Caldwell, and Leo Avondoglio, Verona, N. J., assignors to Curtiss-Wright Corporation, a corporation of Delaware Application March 5, 1952, Serial No. 274,886

12 Claims. Cl. 170-159 This invention relates to aircraft propellers and more particularly to improvements in cuffs or fairings adapted to be attached to the inner shank ends of propeller blades to enable improvement in the airfoil section of propeller blade shanks.

The majority of aircraft propeller blades, particularly those fabricated from metal and as applied to controllable pitch propellers, comprise a cylindrical root end which is secured in a propeller hub, and an outer blade portion of airfoil cross-section whose chord is much greater than its thickness. Between the root end and the blade portion there is a shank portion which gradually fairs these portions together in smooth curves to enable an effective and smooth transmission of stresses from the outer portion of the blade to the hub. This shank portion is normally tapered from the root towards the blade portion, in thickness, to blend the larger diameter root to the smaller thickness of the blade portion; it is inversely tapered to blend the relatively greater chordal dimension of the blade to the relatively smaller diameter of the root. This shank portion of the blade by its configuration is low in aerodynamic efficiency, and various arrangements have been disclosed in the prior art, in the form of attachments to the propeller blade, to give the shank portion of the blade improved airfoil characteristics to reduce its drag and to increase the propulsive effectiveness of this portion of the propeller blade. Propeller blade cuffs, as these devices are usually called, have frequently been made in the form of metallic sleeves of optimum airfoil form which embrace the shank ends of propeller blades and are firmly secured thereto Since metal propeller blades of any one model are subject to deviations in their contour in the shank portion, it becomes necessary in applying sheet metal cuffs to fit each cuff carefully to the individual blade and 'it has been most difficult to eliminate this hand fitting process and to obtain a standard cuff element which can be applied without the need for hand fitting.

These sheet metal cuffs have additional disadvantages from the standpoint of weight, cost, and possibilities of failure resulting from vibrative stress during propeller operation.

i to provide a cuff arrangement which will not be sensitive to vibrative stress in the propeller blade which may cuff arrangement which may be attached to and detached from a propeller blade without complicated processing procedures which have been required in some prior kinds of cuffs; A further object of the invention We further set out to provide a 2,718,257 i atented Sept. 2 9, 1955 is to provide a cuff arrangement which will minimize any increase in drag of the propeller blade by minimizing any increase in thickness of the propeller blade resulting from the cuff structure.

The objectives of this invention are attained in general terms by the forming of cuff elements from a porous, rubber-like material and by securing these cuff elements to a propeller blade by elastic sleeves or other clamping means so that the cuff elements are held in frictional engagement with the propeller blade surface, without utilizing adhesives or bonding processes which have the effect of making the cuff attachment to the blade permanent.

The invention may be more clearly appreciated by following the annexed detailed description in connection with the drawings in which similar reference characters denote similar parts and in which Fig. l is an elevation of a portion of a propeller and propeller blade incorporating the cuff of the invention; Fig. 2 is an approximate section on the line 22 of Fig. 1; Fig. 3 is a section on the line 3-3 of Fig. 1; Fig. 4 is a fragmentary sec tion-al view of an alternative arrangement of the invention; Fig. 5 is a section on the line 55 of Fig. 4; Fig. 6 is a section through an alternative form of blade and cuff; and Fig. 7 is a fragmentary section of the line 7-7 of Fig. 6.

Referring first to Figs. 1-3, a propeller hub 10 includes a blade socket 11 in which the root 12 of a blade 13 is rotatably mounted for pitch change by any appropriate bearing arrangement, well known in the art. The root portion 12 of the blade is preferably cylindrical in form to enable its rotatable fitting to the hub socket 11. The outer portion of the blade at 14 is of airfoil cross-section to enable effective operation of the propeller for propulsive purposes. it will be noted that the chord of the blade portion 14 has a greater dimension than the diameter of the root 12, and the thickness of the portion 14 is considerably less than the diameter of the root 12. Between the portions 12 and 14 is a shank portion 15 which blends the chordal dimension of the blade to the root diameter 12 is a converging taper, the shank portion 15 also blending the thickness of the airfoil portion 14 to the greater diameter of the root portion 12 in a. diverging taper. This shank portion has a gradually varying oval cross-section whose aerodynamic effectiveness is poor as compared with the airfoil portion 14 of the propeller blade.

In this present invention, we fit a leading edge cuff member 17 to the blade shank, and a trailing cuff member 19 to the blade shank, these members embracing parts of the shank and being separate at their edges from one another as noted at 21 and 23. At their innermost ends, the members 17 and 19 embrace almost half of the root portion of the blade. There is an area 25 where the blade shank forms a portion of the external surface of the assembly. Toward the outer portions of the shank 15 the edges 21 and 23 depart from one another leaving a relatively large surface area 25 of the blade shank as the outer surface of the assembly. These outer portions of the shank comprise relatively flat ovals which need only leading and trailing edge cuff additions to provide the required aerodynamic improvement.

In the form of the invention shown in Figs. 1-3, the cuff members 17 and 19 comprise molded blocks of a porous, rubber-like material, the outer surfaces of which are formed to yield an optimum airfoil profile to the blade shank. The inner surfaces 27 of the cuff members are molded to conform to exterior surfaces of the blade shank and when the members 17 and 19 are engaged with the blade shank, the frictional coefiicient between them is high so that displacement of the cuffs from the blade is prevented, provided that the cuff members are held in close engagement with the blade shank. Since there are manufacturing deviations in the profile and form of the blade shank, the cuff members 17 and 19 are formed from the rubber-like material by a procedure which will leave the cuff material, particularly on its inner surface, somewhat elastic so that, when placed against the blade shank, the member will closely engage this shank surface despite variations in the contour of the shank.

To hold the cuff members 17 and 19 on the propeller blade, a stocking or sleeve 29 embraces the members and blade shank and closely engages the exposed surface of both cuff members and shank. This sleeve 29 may comprise a fabric or cord reinforced rubber sheath which is stretchable. After the members 17 and 19 are assembled on the blade, the sleeve may be drawn over the assembly in a stretched condition so that when it is in final position the sleeve contracts and holds the members 17 and 19 firmly engaged with the shank. The sleeve may also constitute a wrapper arrangement the edges of which are secured together by a slide fastener or by other suitable securing means. Still another arrangement is to bind the members 17 and 19 on the blade shank by wrapping the assembly with an elastic tape, starting at the one end of the members and wrapping the tape in overlapping relation all the way to the other end of the members.

The materials used for the cuff members should have low density and yet possess the necessary strength and vibration resistance. They should likewise be resistent to temperature changes, absorption of moisture and the effects of gasoline, oil, aging, and exposure to sunlight and weather. Further, the material should resist permaent setting under compression. Suitable materials for the purpose include certain plastics such as poly-vinyl chloride or rubber (either natural, synthetic or artificial). Particularly, neoprene and Buna-N are effective and the sponging of the material, to make it porous and light,

may be accomplished by any of several known processes during the molding of the members.

The requirements for the cover sleeve or sheet 29 are much the same as those noted above but the cover sheet could also include sheet metal such as stainless steel or may comprise rubber or plastic reinforced with cord or other agents.

In the embodiment shown in Figs. 4 and 5, a clamp ring or collar 32 is secured around the cylindrical butt portion of the propeller blade, this clamp ring comprising two halves, as desired, as shown in Fig. 5. The ring is pro-' vided with two transverse pivots 34 and 36 at opposing portions, the pivots being located in the chord plane of the cuff assembly and in alignment with the leading and trailing edges thereof. The leading cuff member 17 contains a reinforcing element 38, part of which is engaged with the pivot 34. The trailing cuff member 19 contains a reinforcing element 40, part of which is engaged with the pivot 36. Preferably, the elements 38 and 40 are molded into and bonded to the respective members 17 and 19', and may be provided with perforations or protrusions 42 to increase the surface area of contact between the elements 38 and 40 and the material of the cuff members. The cuff members 17 and 19 are recessed at 43 to provide access for attachment to the pivots for assembly and disassembly. The pivots 34 and 36 are located close to the surface of the blade butt, and the centers of gravity of the members 17 and 19' are farther removed from the axis of the propeller blade than are the pivots 34 and 36. When the propeller is rotating and due to centrifugal force the members 17' and 19 will tend to swing about the pivots 34 and 36 against the propeller blade. Thus, the frictional engagement of the members against the propeller blade shank will be increased as a function of propeller speed to prevent displacement of the members with respect to the propeller blade. The clamp ring and its attachment to the cuff members 17' and 19 will also tend to minimize twisting of the cuff members on the propeller blade and will hold them firmly in their proper positions when the propeller is in non-operating as well as during all normal operating conditions of the propeller. The members 17 and 19, as in the arrangement of Figs. 1-3, are intended to be secured against the propeller blade by the sleeve 29 which embraces both cuff members and the propeller blade. The sleeve, as noted previously, may be of elastic, rubber or plastic material, suitably reinforced, or may comprise a metal sheath embracing the cuff members and the blade.

Figs. 6 and 7 show an alternative arrangement of the invention wherein the sleeve member 29' comprises a metallic sheath of stainless steel or one of the light alloys. The sheath 29' starts at the trailing edge of the cuff member 19 and extends forwardly and around the leading edge of the cuff member 17, returning on the other side of the blade to the trailing edge, the start and finish of the wrapping being indicated at 46 and 48. These trailing edge portions of the sheath may be secured to one another by any suitable means of attachment such as screws or other fastening, which, preferably, is readily removable. In the arrangement shown, the trailing edges 46 and 48 are provided with a plurality of inbent tabs 50 in alternating relationship so that the tabs inter-leave with one another. Each tab has a bent-over inner portion 52. When assembled in inter-leaving relation, the tabs 50 thus define a linear cavity 54 into which a lock pin 56 may be inserted from the root end of the cuff member 19. The lock pin may be suitably secured in position as by a cotter key or the like but is primarily held in position during propeller operation by the action of centrifugal force, the lock pin having a head 58 at its innermost end which will not pass through the cavity 54.

The locking arrangement including the elements 5058 are merely exemplary of one means of securing the sheath 29 to the cuff members and the propeller blade.

In the overall aspects of the invention, the porous rubher or plastic cuff members provide a simple, light and sturdy cuff assembly for a propeller blade, which overcomes many of the assembly and structural difficulties which have been encountered in the past with built up metallic cuff systems.

Though several embodiments illustrating the invention have been shown and described, it is to be understood .that the invention may be applied in various forms.

Changes may be made in the arrangements, without departing from the spirit of the invention. Reference should be had to the appended claims for definitions of the limits of the invention.

What is claimed is:

1. An aircraft propeller blade having a shank portion which tapers inwardly toward the blade root in chordwise dimension and which has a generally oval cross- 7 section outboard of the root, a slightly resilient porous rubber-like fairing having an outer streamlined surface and an inner surface conformed to the blade surface and assembled on the leading portion of the blade shank,

a separate porous rubber-like fairing having an outer streamlined surface and an inner surface conformed to the blade surface and assembled on the trailing portion of the blade shank the edges of said fairings being separated from one another and exposing the blade shank surface lying therebetween, and a stretchable elastic stocking sleeved over and embracing both fairings and the 1 blade shank to hold said fairings in assembled relation on the blade and forming the outer aerodynamic surface of the shank portion of the blade exposed between said fairings. I

2. An aircraft propeller blade having a shank portion which tapers inwardly toward the blade root in chordwise direction and which has a generally oval cross-sec- 1 tion outboard of the root, a slightly resilient porous rubber-like fairing having an outer streamlined surface and an inner surface conformed to the blade surface and as sembled on the leading portion of the blade shank, a separate porous rubber-like fairing having an outer streamlined surface and an inner surface conformed to the blade surface and assembled on the trailing portion of the blade shank, the edges of said fairings being separated from-one another and exposing the blade shank surface between said edges, and means embracing both fairings and the blade shank to hold said fairings in assembled relation on the blade comprising a wrapping of a plurality of runs of elastic tape, theruns of tape being in overlapping relation and forming the outer aerodynamic surface of the exposed shank portion of the blade, and of said fairings.

3. An aircraft propeller blade having a shank portion which tapers inwardly toward the blade root in chordwise dimension and which has a generally'oval crosssection outboard of the root, a slightly resilient porous rubber-like fairing having an outer streamlined surface and an inner surface conformed to the bladesurface and assembled on the leading portion of the blade shank a separate porous rubber-like fairing having an outer streamlined surface and an inner surface conformed to the blade surface and assembled on the trailing portion of the blade shank the edges of said fairings being separated from one another and exposing the blade shank surface lying therebetween, a metal collar clamped around the blade shank, and elements pivoted to said collar and imbedded in said fairings to assist in securing the fairings against outward displacement along the blade during operation.

4. A blade according to claim 3 wherein the pivots of said elements are disposed closer to the axis of the propeller blade than the centers of gravity of respective fairings.

5. An aircraft propeller blade having a shank portion which tapers inwardly toward the blade root in chordwise dimension and which has a generally oval crosssection outboard of the root, at slightly resilient porous rubber-like fairing having an outer streamlined surface and an inner surface conformed to the blade surface and assembled on the leading portion of the blade shank, a separate porous rubber-like fairing having an outer streamlined surface and an inner surface conformed to the blade surface and assembled on the trailing portion of the blade shank the edges of said fairings being separate from one another and exposing the blade shank surface lying therebetween, and elastic means embracing both fairings and the blade shank to hold said fairings in assembled relation on the blade.

6. An aircraft propeller blade having a shank of oval cross-section and which tapers inwardly toward the blade root in chord-wise dimension, a collar clamped around the blade root, the collar having transverse pivots crossing and disposed at the chordal plane of the blade, and two separate fairings each fitted at its edge to the blade shank and formed to extend the oval shank cross-section in a chord-wise direction to an airfoil cross-section, one of said fairings forming a leading edge portion for said shank and the other forming a trailing edge portion for said shank, the edges of said fairings being separated from one another and exposing the blade shank surface lying therebetween and each of said fairings being secured to one of said pivots.

7. An aircraft propeller blade having a shank of oval cross-section and which tapers inwardly toward the blade root in chord-wise dimension, a collar clamped around the blade root, the collar having transverse pivots crossing and disposed at the chordal plane of the blade, and two separate fairings each fitted at its edge to the blade shank and formed to extend the oval shank cross-section in a chord-wise direction to an airfoil cross-section, one of said fairings forming a leading edge portion for said shank and the other forming a trailing edge portion for said shank, the edges of said fairings being separated from one another and exposing the blade shank surface lying therebetween and each of said fairings being secured to one of said pivots, said pivots being disposed propeller operation.

8. An aircraft propeller blade having a shank (if-oval cross-section and which tapers inwardly toward the blade root in chord-wise dimension, a collar clamped around the blade root, the collar having transverse --pivots crossing and disposed at the chordal plane of the blade, two separate fairings each fitted at its edges to the 'blade'shank and formed to extend the oval shank cross-section in a chord-wisedirect'ion to an airfoil cross-section, one of said fairings forming a leading edge portion for said shank and the other forming a trailing edge portion for said shank, the edges of said fairings being separated from one another and exposing the blade shank surface lying therebetween each of said fairings being secured to one of said pivots, and elastic rneans wrapped around said fairings'and shank.

9. An aircraft propeller blade having a shank of oval cross-section and which tapers inwardly toward the blade root in chord-wise dimension, a collar clamped around the blade root, the collar having transverse pivots crossing and disposed; at the chordal plane of the blade, two separate fairings each fitted at its edges to the blade shank and formed to extend the oval shank cross-section in a chord-wise direction to an airfoil cross-section, one of said fairings forming a leading edge portion for said shank and the other forming a trailing edge portion for said shank, the edges of said fairings being separated from one another and exposing the blade shank surface lying therebetween and each of said fairings being secured to one of said pivots, said fairings comprising alightweight, porous, rubber-like material.

10. An aircraft propeller blade having a shank of oval cross-section and which tapers inwardly toward the blade root in chord-wise dimension, a collar clamped around the blade root, the collar having transverse pivots crossing and disposed at the chordal plane of the blade, two separate fairings each fitted at its edges to the blade shank and formed to extend the oval shank cross-section in a chord-wise'direction to an airfoil cross-section, one of said fairings forming a leading edge portion for said shank and the other forming a trailing edge portion for said shank, the edges of said fairings being separated from one another and exposing the blade shank surface lying therebetween and each of said fairings being secured to one of said pivots, said fairings comprising a. lightweight, porous, rubber-like material, the means of said securement of said fairings to said pivots comprising reinforcing metal members engaging said pivots and imbedded in said material.

11. In a metal propeller blade comprising shank portion tapering outwardly with lessening thickness to a blade portion and tapering outwardly with increased chord to the blade portion, said shank portion being generally oval in cross-section and blending into an airfoil crosssection at the blade portion, means to fair said shank to airfoil cross-section comprising a shank leading edge fairing and a shank trailing edge fairing fitted and secured to and around said shank portions, the margins of said fairings being separated from one another and exposing the surface of the blade shank portions lying between said fairing edges, said fairings having frictional engagement with the blade shank portion surface, said means comprising a wrapping of yieldable material embracing both fairings and said shank portion.

12. In a metal propeller blade comprising shank portion tapering outwardly with lessening thickness to a blade portion and tapering outwardly with increased chord to the blade portion, said shank portion being generally oval in cross-section and blending into an airfoil cross-section at the blade portion, means to fair said shank to airfoil cross-section comprising a shank leading edge fairing and a shank trailing edge fairing fitted and secured to and around said shank portions, the margins of said fairings being separated from oneanother and exposing the surface of the blade shank portions lying between said fairing edges, said fairings having frictional engagement with the blade shank portion surface, said means comprising a wrapping of yieldable material embracing both fairings and said shank portion said fairings comprising slightly flexible porous rubber-like material and said wrapping means comprising a plastic sheath.

References Cited in the file of this patent UNITED STATES PATENTS 1,324,014 Upson Dec. 2, 1919 Kemp Mar. 16, l Laddon Aug. 16, Woods July 14, .Martin Jan. 26,

Teeter Sept. 9, Dean Aug. 9,

' FOREIGN PATENTS Great Britain Ian. 1,

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