US2657754A - Hollow type aeronautical propeller - Google Patents

Description

Nov. 3, 1953 c. B. CONWELL HOLLOW TYPE AERONAUTICAL PROPELLER Filed April 29, 1952 IN VEN TOR. C/MZQL 15 5. CO/I/WH L illalllll|\\ ATTOE/Vfy Patented Nov. 3, 1953 UNITED STATES ATENT OFFICE HOLLOW TYPE AERONAUTICAL PROPELLER Application April 29, 1952, Serial No. 284,969

1 Claim.

This invention relates to an aeronautical propeller blade and, more specifically, to improvements in the construction at the inboard end of hollow type propeller blade.

It is the general object of the invention to provide a built-up hollow propeller blade construction having improved strength characteristics permitting the blade to Withstand great loads for extended periods of operation without damage or malfunction.

A more specific object is to provide in a hollow blade construction a shell which is particularly adapted to distribute the stresses at the shank or inboard end of the blade to thus avoid fatigue failure which is commonly manifested by cracking of the shell at the inboard end.

Other objects and advantages of the invention will become apparent to those skilled in the art from the following description of the annexed drawings which illustrate a preferred embodiment of the invention. I

In the drawing: I

Fig. lis a foreshortened elevational view of a propeller blade constructed in accordance with the present invention; and

Fig. 2 is an enlarged transverse sectional view of the blade taken as indicated by the line 2-2 of Fig. 1.

The present invention is particularly applicable to aeronautical propeller blades of the hollow type which comprise two main parts, namely, a core and a shell. In the drawing the core is designated generally by reference numeral and the numeral l2 refers to the shell.- A complete description of conventional blades of this general type may be found in the Martin Patent No. 2,522,955 and in the patent to Lampton No. 2,511,858. In describing the present invention, it will be unnecessary to include a detailed description of the conventional features of the blade,-but it should be understood that the core [0, in accordance with conventional practice, is formed from a cylindrical steel tube which is provided with a plurality of races I 4 in the shank end thereof, the races being utilized to retain the blade in a hub (not shown). The outboard end of the coretube is flattened to conform generally to airfoil configuration. The shell [2 is prefer.-

' ably formed from sheet steel into airfoil configuration and the open end thereof is placed over the flattened portion of the core tube and secured thereto as by brazing along. the opposed fiat faces of thetube. 'It will be apparent that the inboard or shank end of the shell will over hang the leading and trailing. edges of the core to define the open spaces 13 and I5, respectively,

therebetween;

It will be readily understood that the forces created in flight impose great loads upon the shell of the blade. These loads, which are ultimately borne by the core, tend to twist the shell about the core, tend to expand or contract the opposed sides of the shell, or cause other undesirable movements of the shell thus creating stresses therein. These shell stresses are more pronounced adjacent the core in what may be referred to as the transfer area, i. e., the area where the loads imposed on the shell are transferred to the core, the area being longitudinally of the core along the bonding area. In conventional core and shell blades, the stress concentration at the inboard end has been sufiicient in many instances to cause fatigue cracks to appear at the said inboard end of the shell. Of course, when fatigue cracks do appear, the blade must be scrapped as unsafe.

In accordance with the present invention, the blade shell is constructed and arranged to distribute the stresses in the transfer area at the shank end to avoid fatigue rupture. In the de-. velopment of the invention, it was discovered that if the inboard end of the shell was cut off at other than at right angles to the leading and trailing edges, the strength characteristics of the shell could be altered. It was determined that if the shells leading and trailing edges M5 and I8 were tapered on both sides of the shell as at 20 and 22 and if the tapered edges 20 and 22 were interconnected by an arcuate edge as at 24, the stresses would be so distributed in the transfer area as to materially increase the blades ability to withstand the imposed loads for extended periods of operation.

It was found that if the edges 26 and 22 each taper inwardly at an angle of approximately 20 to approximately 66 from the leading and trailing edges, the stresses at the transfer area adjacent the inboard end are distributed for optimum strength characteristics. In fact, the aforedescribed tapered edges have been found to improve the strength characteristics of the blade to an extent justifying removal of all exteriorly disposed stiffening and strengthening members such as collars and the like which have been incorporated in some prior blade constructions.

Furthermore, the extending taper provides agreater transfer area and the taper lends itself to the convenient assembly of a cult.

' I wise than indicated by the following claim.

I claimi An aeronautical comprising an elongated core constituting the propeller blade construction 3 strength member of the blade and having a shank and two opposed flattened surfaces extending outwardly therefrom, a sheet metal airfoilforming shell surrounding said core and having an open end through which the shank of the core projects, said core and said shell being bonded together'along the-:fiattened surfaces of saidcore with the leading and trailing edges of the shell overhanging the core in spaced relationship thereto, and a longitudinally extending projec-a tion on said shell extending along theshank 011 said core and bonded thereto along said flattened surfaces, said extending projyectiongbeing' defined:

by substantially straight edges; of: the. shell: ex tending from the leading and trailing edges thereof to the said core, said straightedg esu ex-- 4 tending at substantially the same angle to the longitudinal center line of the core and said angle being at least 20 and no more than 60, and said extending projection being further defined by arcuate edges interconnecting said straight edges at the opposed flattened surfaces of said core.

B". GJQNWELL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,465,007 Bragdon Mar. 22, 1949 25113858. Lampton June 29, 1950 ,6235% Kearns Dec. 3%, 1952

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