US2457815A

US2457815A - Propeller blade attachment

Info

Publication number: US2457815A
Application number: US547762A
Authority: US
Inventors: Marvin C Green
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-08-02
Filing date: 1944-08-02
Publication date: 1949-01-04
Anticipated expiration: 1966-01-04

Description

Jan. 4, 1949. I G EEN 2,457,815

PROPELLER BLADE ATTACHMENT Filed Aug. 2, 1944 an a FIG. 3

- IN VEN TOR.

Navel/ 1v 6 Gees/v Patented Jan. 4, 1949 2,457,815 a PROPELLER BLADE ATTACHMENT Marvin C. Green, Dayton, Ohio 5 H Application August 2, 1944, serial at; 847,762

11 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to means for attaching non-ferrous propeller baldes to hubs and constitutes an improvement over related subject matter disclosed in the copending application Serial No. 483,006, filed April 14, 1943, of C. R. Gaskell and M. C. Green now Patent 2,368,656 dated Feb. 6, 1945.

closed for attaching propeller blades to hubs, comprising a hub member and a plurality of symmetrically arranged screws disposed parallel to the axis of a propeller blade. having a shank adapted to be inserted by a force fit into a ferrule on the hub member. A compression plate is secured within the hub member, through which the screws pass, the screws having heads abutting the plate and threaded ends adapted to be screwed into the blade shank. This construction, theoretically, provides the blade with support against bending stress by virtue of the force fit between the blade shank and the ferrule, while radial stresses in the blade due to centrifugal force are resisted by tensile stresses in the screws which are transmitted to the compression plate by reason of the abutment of the screw heads thereon. As a matter of actual practice, however, it is desirable to protect the screws against contingencies wherein some bending stresses may be transmitted thereto which would cause certain screws to be stressed more than others and my present invention has for an object the provision of means for substantially equalizing tensile stresses among the several screws ofthe structure. Further, it has been found in practice that In the copending application, devices are dissubjected successively to the same tightening torque, rather wide deviations in tensile stress among the several screws occur, caused by differences in tensile reaction in the shank material as the shank is being drawn into the ferrule, this being especially true of wooden blades. Accordingly, it is another object of my invention to provide a propeller blade attaching structure as disclosed in the copending application with means for distributing and equalizing initial tensioning stresses among the several screws, and it is a further object to provide a simple, rugged and compact structure for accomplishing these ends.

In accordance with the objects of the invention, I provide propeller blade attachment means substantially as disclosed in the copending application but having additional structure comprising an elastic material, such as rubber, confined between a pair of compression plates and so disposed that compression stresses are transmitted thereto in reaction to the tensile stresses in the screws. Due to the comparative incompressibility of a confined elastic material, a reaction results similar to that of a liquid under pressure, in that the pressure is equally distributed throughout the material. In this manner, increasing or decreasing tensile stresses in one or more screws reacts on the elastic material correspondingly whereby such deviations are distributed substantially equally among the several screws by an arrangement disclosed in detail with reference to the appended drawings. in which:

Fig. 1 shows a longitudinal section of a preferred form of the device;

Fig 2 shows a modification thereof;

Fig. 3 illustrates a further modification; and

Fig. 4 shows a fragmentary perspective of a modification of certain elements of Fig. 3.

In Fig. 1, a propeller hub member A is shown having a threaded end I for engagement with a hub (not shown) and having a ferruled end 2 in which is force fitted the circular shank 3 of a propeller blade. Shank 3 has a chamfered end 4 engaging a beveled shoulder 5 at the base of the ferrule 2. Engagement of chamfered surfaces 4 and 5 tends to center shank 3 in axial alignment with-ferrule 2 and also tends to relieve longitudinal shear stresses in shank 3 due to the tensile loading thereof. Four screws 1, 8, 9, iii are shown as representative of a plurality of screws arranged in symmetrical configurations, e. g., screws 1 and Ill lie on a circle disposed about the axis of shank 3 and screws 8 and 9 lie on a smaller concentric circle. Screws 1 through. ID are in. threaded engagement with shank 3 and extend toward the hub through a compression plate ll. Plate H is disposed within hub Aand has a sloping shoulder i2 engaging sloping shoulder I: of the hub. The purpose of the sloping engagement of shoulders I! and I3 is to provide a force component against shoulder l2 tending to counteract buckling of plate ll upwardly at the center due to tensile stress in screws 1 through l0. Plate II has a recess l5 containing an elastic material [6, such as rubber, or the like, confined by means of a second compression plate l8 disposed contiguous thereto. The screws I through Ill pass through aligned perforations in elastic material It and the plate l8 and terminate in heads 20 through 23, respectively, abutting the exterior surface of the plate Hi. When tensile stresses are introducedinto the screws 1 through ill, the respective abutting heads 20 through 23 exert a force on plate 18 tending to compress elastic material l6 within the recess IS. The plate i3 has a smooth peripheral fit with recess l5 and is sufficiently thick to provide rigidity so that a tilting action thereof is obtainable in the event of the introduction of an unequal distribution of stresses among the screws. Consider, for example, that screw 1 has a tensile stress introduced therein greater than that of screw Hi. The increased stress will be trans-' mitted through screw head 20 and tend to draw plate l8 into the elastic material l6, thus causing a compressive stress in the material locally surrounding screw 1. Due to the comparative incompressibility of the confined elastic material, elastic fiow therein will take place forcing or squeezing displaced material toward screw III whereby the portion of plate 18 adjacent thereto will be forced outwardly, increasing the tensile stress in screw ID by virtue of the abutment of plate ill with screw head 23. The tilting action thus produced is, however, very minute so that no extrusion of the elastic material is at its peripheral engagement with recess i5 is experienced to any degrees affecting operation of the device. In this manner equalization of tensile stresses among the several screws is obtained as a matter of actual practice, and it has been found that for a propeller shank approximately four inches in diameter operative thicknesses of the elastic material l6 and plate l8 of about oneeighth of an inch each produces satisfactory results. In addition to the tilting action of plate iii a further effect has been observed in that plate I8 is subject under conditions of heavy stress to local flexing in areas underneath heavily stressed screw heads. When one or more screws receive increased tensile stress suificient to pull the locally surrounding area of plate l8 into the elastic material l6, elastic flow within the material takes place, causing a displacement of material against unstressed areas of plate l8 which distributes the increased tensile stress against the heads of the lesser strained screws. The fiexing action thus tends toward distribution of substantially equal stresses among the several screws. It will, of course, be understood that local fiexing of plate l3 should be within the elastic limit thereof, a consideration which is a matter of design and depends primarily upon the number of screws intended to be used and the stresses expected to be encountered as well as on the stress-strain characteristics of plate l8.

Referring to Fig. 2, a device similar to that disclosed in Fig. l is shown, the chief distinction residing in the coaction of the compression plate 25 and the hub member 26 with a sealing gasket 21 interposed therebetween, for the purpose of sealing wooden blade shanks against moisture changes. The compression plate 25 is provided with threads 28 for engagement in a propeller hub. I

The modification shown in Fig. 3 comprises two

hub members

30 and 3|, a shank 32 of a propeller plate being secured against bending stresses by a force fit within hub member 30. A compression plate 33 is secured within hub member 3| by a plurality of screws 35 and has a recess 36 wherein is confined an elastic material 3'l. A plurality of screws 40 through 44 pass individually through a corresponding plurality of compression plates 45 through 49, respectively, and have threaded engagement with shank 32 at one end and screw heads 5| through 55 in abutting engagement with plates 45 through 49, respectively, at their other ends. To simplify illustration of this structure, Fig. 3 shows individual compression plates 45 through 49, cooperating respectively with screws 40 through 44, but it will be understood by reference to Fig. 4 that the allocation of screws to compression plates is a matter of design. The area of the elastic material covered by individual compression plates is likewise a matter of desi n, as is the shape of such plates.

In Fig. 4, for example, five compression plates Ell through 64 are shown contiguous with elastic material 6-5 and provided with apertures 66 to accommodate 5 screws per plate. By confining an elastic material with a plurality of relatively reciprocal compression plates as shown in Figs. 3 and'4, the need for critical design of a single plate member such as the plate IS in the form shown in Fig. 1 is eliminated. Each individual plate may be considered as a separate piston exerting compressive stress against the local area of the elastic material with which it is contiguous. As heretofore described, since the elastic material acts as a liquid and transmits pressure stresses equally in all directions, it may be seen that if any stress tends to force one plate, as plate 45 of Fig. 3, into the elastic material 31, a distribution of stress will occur therein, acting outwardly against plates 46 through 49, thereby tending to equalize stresses among the several screws 40 through 44.

Although I have shown in the modifications herein disclosed, relatively simple configurations of screws for securing a propeller shank to a hub member, it will be understood that the configuration used in practice is a matter of design, and as a matter of actual practice it has been found that configurations more complicated than those disclosed herein operate satisfactorily in accordance with the principles set forth.

Having now described the invention and preferred form of embodiment thereof it is to be understood that the said invention is to be limited, not to the specific details herein set forth but only by the scope of the claims which follow.

I claim:

1. In a propeller mount, a propeller blade having a shank, a hub member having ferrule means receiving the shank of said propeller blade, and means for securing the propeller blade shank to said hub member comprising a plate member associated in fixed relation with said hub member and having a recess in one face thereof opposite the hub member ferrule means, compression plate means slidingly disposed in and completely covering said recess and capable of tilting action, an elastic material confined within and completely filling said recess between said compression plate means and the walls of said recess and adapted to flow in the manner of an incompressible liquid, and a plurality of tension members bearing on the compression plate means with a portion passing through the compression plate means, elastic material and plate member and secured to said propeller blade shank and operative to compressively stress said elastic material between said compression plate means and said plate member when said tension members are tensilely stressed.

2. In a mount for a propeller blade, a propeller blade having a shank, a hub means adapted to receive the shank of said propeller blade, means securing said propeller blade shank to said hub I means comprising, a transverse wall ai'iixedly as.- sociated within said hub means, a compression plate means in interiltting relation with said transverse wall on a side opposite the propeller shank receiving end of said hub means and capable of tilting action, said interfltting relation of said transverse wall and said compression plate means forming a completely enclosed chamber, a resilient material confined by and completely filling said chamber and adapted to flow in a manner of an incompressible liquid, and tension members secured to said propeller blade shank passing through said transverse wall, resilient material and compression plate means and bearing on the side of said compression plate means opposite said resilient material whereby the total tensile stress exerted on said propeller shank is compressively transmitted through said resilient material and is distributed between said tension members by elastic flow in said resilient material.

3. In a mount for a propeller blade, a propeller blade having a shank, a hub member having ferrule means receiving and radially securing the shank of said propeller blade, a transversely disposed wall in said hub member with a recess on a side thereof opposite said ferrule means, a compression member slidingly fitting in said recess to form a completely closed chamber, an elastic material completely filling said chamber and adapted to flow in the manner of an incompressible liquid within said chamber, tension members disposed to exert tensile stresses between said propeller shank and said compression member'and thereby compressively stressing said elastic material, said tension members extending axially parallel to said propeller shank and through, respectively, said compression plate, said elastic material and said transversely disposed wall, whereby elastic flow in said elastic material is operative to distribute changes in tensile stress in one or more of said tensile members substantially equally between substantially all of said tension members by reacting against said compression plate.

t. In a. mount for a propeller blade, a propeller blade having a shank, a hub member having ferrule means receiving the shank of said propeller blade, means for providing a recess within said hub member-comprising a transversely disposed plate retained therein forming a wall of said recess between the blade shank and said recess, an elastic material substantially confined within and completely filling said recess, compression means completely covering said elastic material on the side thereof opposite said wall to differentially stress said elastic material in compression at a plurality of areas thereon, tension members connected to said blade shank and disposed to exert tensile stress between said propeller shank and said compression means for compressively stressing said elastic material at said plurality of areas, whereby elastic displacement in said elastic ma terial is operative to distribute the total tensile stress between said tension members substantially equally therebetween.

5. In a propeller mount, a propeller blade having a shank, hub means, means for securing the shank of said propeller blade in said hub means comprising a transverse plate provided with a recessed face retained in said hub means with said recessed face opposite said blade shank, an elastic material adapted to flow in the manner of an incompressible liquid retained within and completely filling said recess, a compression plate local stresses contiguous with a surface of said elastic material and completely covering said recess to substantially confine said elastic material within said recess, a plurality of tension members associated. with said blade shank and adapted to individually exert tensile stress between the shank of said propeller blade and said compression plate for compressively stressing said elastic material, thereby distributing the total stress substantially equally among said plurality of tension members by elastic flow displacement within said elastic material.

6. In a propeller mount, a propeller blade having a shank, hub means, means for securing the shank of said propeller blade to said hub means comprising a transverse wall provided with an annular recess retained in said hub means with said annular recess opposite said shank, an elastic material substantially filling said recess and confined therein by a compression plate contiguous with a surface of said elastic material and adapted to be slightly tilted relative said transverse wall, a plurality of tension members for exerting stress between said propeller blade shank and said compression plate and operative to tilt said compression plate upon a condition of unequal stress among said tension members whereby elastic flow displacement in said elastic material is operative to equalize tensile stresses among said tension members.

'7. In a mount for attaching a propeller blade to a hub, a propeller blade having a shank, a hub member having means for securing the shank of said propeller blade therein comprising a removable' plate transversely disposed relative to the axis of saidshank in said hub means, a recess in the. face of said plate opposite said shank, an elastic material adapted to flow in the manner of an incompressible liquid completely filling said recess, a disk-like compression plate of a thick ness to allow local flexing under heavy local stress with heads abutting the opposite face of said compression plate so that tensile stresses in said tension members compressively stress said elastic material whereby unequal stresses among said tension members are operative by elastic flow displacement within said elastic material to differentially flex areas of said compression plate thereby increasing the tensile stress in thelesser stressed tension members for the purpose of distributing the total tensile stress between the shank of said propeller blade and said compression plate substantially equally among the plurality of tension members.

8. In a mount for attaching a propeller blade to a hub, a pr peller blade having a shank, a hub member having means for securing the shank of said propeller blade therein comprising a removable plate transversely disposed relative to the axis of said shank in said hub member, a recess in the face ofsaid plate opposite said shank, an elastic material having the elastic characteristics of an incompressible liquid completely filling said recess, a disk-like compression plate of a thickness to permit local flexing under heavy stress slidably disposed within and completely covering said recess to substantially confine said elastic material therein and contiguous therewith, a pl rality of elongated tension members extending through suitably aligned perforations in said canpresslon plate, said elastic material and said transversely disposed plate, respectively, and having ends adapted to be secured within said shank of said propeller blade, opposite ends of sad tension members being provided with heads abutting said compression plate so that tensile stresses in said tension members compressively stress said elastic material whereby unequal stresses among said tension members are operative by elastic flow displacement within said elastic material to diiferentially react on areas of said compression plate thereby increasing the tensile stress in the lesser stressed tension members for the purpose of distributing the total tensile stress between the shank of said propeller blade and said compression plate substantially equally among the plurality of tension members.

9. In a mount for a propeller blade, a propeller blade having a shank, a hub member comprising ferrule means for securing the shank of said propeller blade, a transverse wall within said hub membena recess within a face of said wall opposite said blade shank, an elastic material substantially filling said recess, a plurality of compression plates contiguous with the surface of said elastic material and substantially confining said elastic material within said recess and a plurality of tension members equally apportioned among said several compression plates and having abutting engagement with the external surfaces of their respective plates and having shank portions extending through suitably aligned perforations in said compression plates, said elastic material and said transverse wall, respectively, for threaded engagement with the shank of said propeller blade whereby unequal tensile stresses among said tension members is operative to differentially, compressively stress areas of said elastic material and cause elastic flow displacement therein reacting against said compression plates for the purpose of equalizing tensile stresses among the plurality of tension members.

10. In a propeller blade retention means of the character wherein the propeller blade shank is socketed in a hub member adapted to transmit loads on the blade to a propeller hub, and having tension screws secured in the blade shank parallel to the blade axis for transmitting tension loads from the blade shank to the hub member, the improvement which comprises providing a transverse wall member within said hub member arranged below the propeller blade shank and screws.

secured to the hub member, said wall member containing apertures for the passage of the tension screws therethrough, a cylindrical recess in said wall member on the side more removed from the propeller shank, a resilient rubber-like material adapted to flow in the manner of an incompressible liquid within and completely filling said recess, and compression plate means of a thickness to permit local flexing under heavy local stress completely covering said cylindrical recess engaged by said tension screws and in compressive contact with said resilient material, and plastic flow in the resilient rubber-like material providing for substantial equalization of the tension loads in the screws.

11. Improvement in non-ferrous propeller blade retention means comprising a hollow sleeve member adapted to be received in a propeller hub structure, a propeller blade having a cylindrical shank portion, said cylindrical shank portion on the propeller blade socketed within said sleeve, a plurality of radially extending tension screws within said sleeve member and threaded into said blade shank parallel with the shank axis, a transverse wall secured within said sleeve member radially inward thereof from the end of the blade shank, said wall member being apertured for free sliding passage of said screws therethrough, transverse abutment means positioned within said sleeve for movement with respect to said transverse wall, said screws' having load transmitting engagement with the abutment means, said wall and abutment means cooperating to define a chamber therebetween and a rubber-like material completely filling said chamber and resisting any change in volume thereof, thereby transmitting loads to the wall member and equalizing loads transmitted from the respective MARVIN C. GREEN.

REFERENCES CITED I The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,727,609 Kramer Sept. 10, 1929 2,051,205- Estabrook Aug, 18, 1936 2,254,821 Haw Sept. 2, 1931 2,270,583 Forton Jan. 20, 1942 2,339,549 Kubaugh Jan, 18, 1944 2,368,656 Gaskell Feb. 6, 1945 FOREIGN PATENTS Number Country Date 508,146 Great Britain June 27, 1939