US2344876A - Reinforced propeller - Google Patents

Description

March 21, 1944. Q E;` JAWS'ON 2,344,876

REINFORCED PROPELLER Filed April 6, 1942 A a) 20d ffm @g f@ 4f? ./m/W/"mwz larney.

Patented Mar. 21, 1944 UNITED REINFORCED PROPELLER Clarence B. Jamison, Beverly Hills, Calif., assignor of twenty per cent to Collins Mason, Beverly Hills, Calif.

Application April 6, 1942, Serial N0. 437,740

Claims. (Cl. Uli- 173) My invention has to do with propellers and, in its more particular aspects, it relates to nonmetallic blades for airplane propellers embodying novel means for strengthening the blade shanks and for retaining such blades in metal hubs.

While wood has many desirable qualities as material for airplane propellers, two major problems have prevented wood blades from being largely used in metal hubs such as are employed to enable the pitch angle of the blades to be adjusted or controlled. One of those shortcomings has been that the relative weakness, in essential respects, of Wood as compared with metal has rendered it necessary to employ blade shanks of such large diameter as to require inordinately large and heavy hubs to mount them. This problem is easy to understand when one considers the relatively weak tensile strength of Wood and contemplates the tremendous centrifugal forces of many tons as well as other stresses exerted on a propeller blade shank in operation. Another shortcoming has been the dilculty of positively and safely retaining the blade shanks in the hubthat is, to avoid throwing of the blades.

I have overcome those difliculties by incorporating in the blade shank a novel reinforcing element of relatively stronger material, such as metal, in such manner as to cause the tensile stresses normally applied to the weakest section of the blade shank to be transferred to and shared by the strongest section of the blade.

I am aware that attempts have been made heretofore to provide metal reinforcement for wood blades, but those attempts have been unsuccessful from a practical standpoint. One of the contributing reasons for the lack of success of those prior attempts has been due to the fact that the inherent nature of the two materials, wood and metal, rendered it impossible to obtain adequate bonding of the laminae. This has made it necessary to extend the metal reinforcing throughout the major part of the length of the blade and even then the tendency has been for the wood to pull away from the reinforcing.

It is among the objects of my invention to provide a non-metallic propeller blade such as Wood incorporating a novel reinforcing member and means of mounting it in the blade shank, which provides maximum strength for minimum crosssectional area and which is at the same time extremely economical of manufacture and light in Weight.

Another object is the provision of improved means for retaining a non-metallic blade in a metal hub.

Still further objects and corresponding advantages are inherent in my invention and how those as well as the foregoing objects are achieved will be made clear to those skilled in this art by the following detailed description of one of the preferred forms which my invention may take, for which purpose I shall refer to thev accompanying drawing, in which:

Fig. 1 is a longitudinal section taken on Vline I-I of Fig. 3; l

Fig. 2 is a longitudinal section on line 2--2of Fig. 3;

Fig. 3 is a cross-section taken on line 3- -3 of' Fig. 1; and

Fig. 4 is a cross-sectional view of the blade shank showing the relation of the laminae prior to being compressed together. 4

In the drawing, the numeral 5 designates a propeller hub consisting of two oppositely disposed halves providing a longitudinal bore' to receive the propeller shank assembly to be described, each half presenting at each end bosses provided with holes to receive bolts 6 for clamping the hub halves about the propeller 'shank assembly. r

The numeral l0 generally indicates a propeller blade having a shank portion ll, the blade tapering from the relatively smaller shank portion'to an adjacent airfoil portion I2 of relatively greater diameter. l

Shank portion ll tapers from its inner and outer endsto a reduced diameter central section l5 and is made up of Wood laminae lla, lib and l lc securely bonded together in superposed relation by a suitable bonding agent. While I show a shank made up of rive laminae, this number is by no means critical and any desired number of laminae may be used. Preferably, however, there should be an odd number so that there may be a central lamina for the purpose now tol be described.

As best shown in Figs. 1, v 2 and 3, the central shank lamina l la is relatively narrower than the outwardly adjacent laminae YI lb, is separated from the corresponding lamina I Id which extends into the airfoil portion of the blade, and terminates short of the inner end of the shank, so that a channel or recess is formed entirely around the central shank lamina ll a. Within this recess I place a metal insert generally designated 2li which is in the form of a somewhat rectangular frame having sides 20a extending longitudinallyof the shank, inner end 20h and outerv end 20c, which ends extend transversely vof the shank.- Sides 20a converge inwardly towards the center, conforming to the hour glass-shaped plan section of the shank.

As shown in Fig. 4, central laminae Ha, Hd are preferably made relatively thicker than the metal insert 2li-that is, they are relatively thicker before being compressed in the course of applying pressure to bond the glued laminae into a substantially integral mass-so that the metal insert will not prevent proper compressing of the central wood laminae Ila, lld. The centrai shank lamina may be considered as being comprised of the metal insert and the wood lamina Ha as a core, the latter fitting snugly into the frame-'like insert.

Shank II as thus composed is compressed within a split sleeve which in turn is threaded into a ferrule 32, the latter having annular flanges 32a, 32D tting corresponding recesses in the hub.

The diametrically opposite longitudinal splits 35 which divide sleeve 30 into two segments, are preferably circumferentially spaced from the insert 20 so that the outer tapered surface of the insert bears against the correspondingly shaped inner surface of the sleeve at points vremoved from .the splits.

The inner surface .31 of the outer end portion of the ferrule tapers to conform to the enclosed outer surface .33 of the blade Vadjacent the shank, so that relative rotation of the ferrule 'with respect `to the .sleeve `will cause the tapered inner surface 40 of the sleeve to compress the correspondingly tapered 4portion of the shank and insert, and will cause the tapered surface 3l `of the ferrule to-compress the portion 38 of the blade, thus venabling such adjustment as will at al1 times maintain .a tig-ht t regardless of :any shrinkage.

From the :foregoing description, it will be seen that `the relatively small area of the wood shank displaced by the metal insert 2i) so substantially increases thestrengthof the structure that wood blades vhaving Shanks Yof relatively small crosssection comparable with metal blades may be used, and at the same time the method of constructing the blade is so simple as to vprovide great economy in manufacture. Centrifugal forces tending to pull the shank 4longitudinally from the sleeve are taken directly by the metal insert and are thereby distributed evenly throughout the Wood :shank section by virtue of the core Ha being integrated by a firm bond with the remainder Aof the shank. inasmuch as the outer transverse portion 29e of the metal insert -is within the relatively larger and stronger section of the blade, the stresses are also taken by that larger and stronger blade portion.

I preferably provide the opposite faces `of the metal insert 20 with outwardly projecting barbs laminae llb when compressed together, thus further aiding the integration of the shank elements.

I nd it highly advantageous to taper the shank I l as well as the reinforcing member sides 20a from their outer ends towards the center, in conformance with the taper of the adjacent inner surface of the sleeve, because it permits a gradual reduction in the section of .the shank rather than .an abrupt reduction, which .latter would substantially increase the breaking moment at the point of reduced diameter.

While I have specifically referred to wood blades, it will be understood .of course that my invention also contemplates other non-metallic blades, such .as plastic blades and Iplastic-impregnated wood blades, and While I preferably employ aluminum as the metal of the insert 20, I may employ `other suitable metals.

The broad concept of my invention, as dened by the appended claims, of course may be carwhich become embedded in the adjacent ried out in structures varying from that herein specifically described, so that the details which I have hereinbefore employed to illustrate an adaptation of my invention are not be taken as limitative.

1. In a propeller, a hub having a radial socket, a blade having a laminated shank mounted in the socket, the centermost lamina of the shank comprising a relatively narrow center strip bonded to adjacent laminae and a reinforcing plate having a side portion extending along the side edge of the center strip and a portion eX- tending transversely of the shank between the center strip and the outer end of the blade, and means in the hub embracing the shank, said means engaging the side portion of .the reinforcing plate and constricting the outer laminae of the shank .against opposite faces of the reinforcing plate.

2. In a propeller, a hub having a radial socket, a Vblade having a laminated shank mounted in the socket yand tapering from its inner end to a reduced vdiameter medial portion, the centermost lamina of the shank comprising a relatively narrow center strip bonded to adjacent laminae and a reinforcing member having side portions extending along the opposite side edges of the center strip and converging towards the shank portion of reduced diameter, and means in the hub engaging the outer side edges of the reinforcing member and constricting the outer laminae of the shank against opposite faces of the .rein-forcing member.

3. The propeller of claim 2 wherein the reinforcing member includes a web extending transversely .of the shank between the center strip and the outer portion of the blade, said web being connected to the side portions of the reinforcing member.

4. In an airplane propeller of the class clescribed, a metal hub, a non-metallic blade having a shank, said shank tapering from its inner end to a reduced diameter portion, a longitudinally split sleeve embracing the shank and mounted in the hub, and a metallic reinforcing member having end portions extending transversely through the shank and side portions extending longitudinally along opposite sides of the shank, said sides being embedded in and conforming to the longitudinal sectional shape of the shank and bearing at their outer side edge portions against the inner surface of the sleeve.

5. In an airplane propeller of the class described, a metal hub, a non-metallic blade having a shank composed of superposed laminae the centermost of which is comprised of a center strip and a metal reinforcing member extending transversely through the shank and longitudinally thereof along opposite side edges of the center strip with its outer side edges flush with the adjacent outer side surface of the shank, said shank tapering from its inner end to a reduced diameter medial portion, and a longitudinally split sleeve mounted in the hub surrounding and embracing the shank, said center strip being bonded at its opposite side faces to the adjacent laminae whereby to prevent longitudinal movement of the reinforcing member with respect to the shank.

CLARENCE B. JAMISON.

Images