US2882974A

US2882974A - Propeller blade

Info

Publication number: US2882974A
Application number: US426181A
Authority: US
Inventors: Alfred L Boegehold
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1954-04-28
Filing date: 1954-04-28
Publication date: 1959-04-21
Anticipated expiration: 1976-04-21

Description

April 21, 1959 INVENTOR. Alfred L. 'Boegehold 6:11 M Wulm Attorney United States Patent PROPELLER BLADE Alfred L. Boegehold, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 28, 1954, Serial No. 426,181

4 Claims. (Cl. 170-159) This invention pertains to propeller blades, and particularly to hollow blades for aircraft propellers.

Heretofore hollow propeller blades comprising a forged section capable of sustaining substantially all of the load to which the blade may be subjected in operation and a sheet section brazed to the forged section so as to complete the airfoil, have been manufactured. A blade of this type is disclosed in the Blanchard Patent 2,205,132. In this type of blade, the bending stresses imposed on the two sections due to vibratory loading are unequal. More specifically, blade failure at the camber sheet joint can be caused by this unequal stress distribution. Accordingly, among my objects are the provision of a hollow propeller blade comprising a plurality of members so arranged so that the bending stresses imposed upon the joints therebetween are minimized; the further provision of a hollow propeller blade including a relatively rigid section and a plurality of relatively flexible sections; and the still further provision of a propeller blade having camber sheets with contoured edges that are welded to a thrust member.

The aforementioned and other objects are accomplished in the present invention by deforming the camber sheet sections so as to form rolled edges which are joined to the thrust member at a point of minimal stress. Specifically, the joint between the camber sections and the thrust member is located at, or proximate to, the neutral axis of the blade. By neutral axis of a propeller blade, I mean the axis about which the moment of inertia is a minimum.

The forged thrust member has an integral hollowcylindrical portion which constitutes the root of a propeller blade, an airfoil portion having marginal ribs which merge to form a tip portion, and one or more intermediate, longitudinally extending ribs, the airfoil portion constituting the thrust surface of the blade. The marginal ribs and the intermediate rib, or ribs, are formed with relieved sections arranged to receive the rolled edges of the flexible metal sheets which constitute the camber surface of the blade. The contoured edges of the camber sheet sections are then welded to the thrust member to complete the airfoil, the contoured edges forming fillets at the joints therebetween so as to materially reduce the concentration of stress at the joints. This is in accordance with the well known principle that stresses are concentrated at sharp, or abrupt, corners. Moreover, inasmuch as the joints between the'camber sheet sections and the thrust member are proximate the neutral axis of the blade, the bending stresses to which the joints therebetween are subjected to under vibratory loading are further minimized.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

Fig. 1 is a plan view of a propeller blade constructed according to this invention.

2,882,974 Patented Apr. 21, 1959 Figs. 2, 3 and 4 are enlarged sectional views taken along lines 22, 33 and 4-4, respectively, of Fig. 1.

As disclosed in Fig. 1, the propeller blade of this invention comprises two sections, a forged member 10, which constitutes the main support for the blade and which sustains the major portion of the load to which the blade is subjected in operation, and a camber sheet section 20 comprising a plurality of sheets 21, which overly portions of the section 10 and are connected thereto by means of a weld. The forged section 10 is preferably of steel and includes an integral hollow root portion 11 and an airfoil portion 12 of suitable aerodynamic shape, the exterior surface of which constitutes the thrust surface of the blade. The interior surface of the airfoil portion 12 is formed with a pair of upstanding

marginal ribs

13 and 14, which merge adjacent the upper end of the blade to form a tip edge 15. The airfoil portion 12 is also shown including an intermediate upstanding rib 16, which rib defines longitudinally extending cavities within the airfoil portion 12. It is to be understood that while only one intermediate rib is shown, any number of intermediate ribs may be employed to achieve the desired flatwise blade rigidity. Moreover, as shown in Fig. 1, one of the camber sheets 21 overlies portions of

ribs

14 and 16, while the other camber sheet overlies portions of the

upstanding ribs

13 and 16, the sheets being welded at the regions of con tact with the ribs, as will be more particularly set forth hereinafter.

With reference to Figs. 2 through 4, it may be seen that the thrust section 10 of the blade is formed with integral fillets at the juncture of the

upstanding ribs

13, 14 and 16 so as to reduce the concentration of stress at these points. The marginal rib 13 constitutes the leading edge of the blade, while the marginal rib 14 constitutes the trailing edge of the blade.

The camber section 20 comprises a plurality of relatively flexible sheets 21, which, as shown in Figs. 2 through 4, have contoured, or rolled,

edges

22 and 23, which present ends are arranged to abut and overly relieved portions of the upstanding ribs formed on the thrust section 10. By reason of the sheets 21 having rolled edges, fillets are formed by the camber sheet sections, which efiectively constitute a continuation of the integral fillets of the thrust member and thereby reduce the concentration of stress at the joint between the camber sheet sections and the thrust member. Thereafter, the camber sheet sections are welded to the thrust member, and the grooves formed between the juncture of the camber sheet sections and the thrust member are, likewise, filled with weld material, as designated by

numerals

24, 25, 26 and 27. Thereafter, the camber sheet surface is ground to form a smooth airfoil surface.

It should be noted that the joints between the camber sheet sections and the thrust member are disposed in the intermediate portion of the blade, so as to be proximate to the neutral axis of the blade. In this manner, the o1nts between the camber sheet sections and the thrust member are located in a region of lower bending stresses, which are imposed upon the blade due to vibratory loadmg. Furthermore, the contoured edges of the camber sheet sections result in materially less concentration of stress at these joints than in prior blade constructions by reason of the fact that the sharp corners therebetween have been eliminated. It is to be further noted that the camber sheet sections 21 flatten out adjacent the tip as well as the root portion of the blade so as to form the desired airfoil configuration.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A hollow metal propeller blade having thrust and camber surfaces, comprising, a first main strength-giving metal section forming the thrust surface of the blade, said section having a portion of airfoil configuration with continuous upstanding marginal and intermediate ribs on the interior surface thereof, said ribs terminating short of the end of the blade and forming a tip portion, and a plurality of sheet metal sections having inwardly curved edges, said sheet metal sections overlying portions of said ribs, said curved edges having ends abutting said portions of said ribs proximate to the neutral axis of the blade and being joined thereto so as to form the camber surface of said blade.

2. A hollow metal propeller blade having thrust and camber surfaces, comprising, a first main'strengthsgiving metal section forming the thrust surface of the blade, said section having a portion of airfoil configuration with continous upstanding marginal and intermediate ribs on the interior surface thereof, said ribs terminating short of the end of the blade and forming a tip portion, a plurality of sheet metal sections having contoured edge portions overlying portions of said ribs, said contoured edge portions having ends disposed in abutting relation with said portions of the ribs proximate to the neutral axis of the blade so as to form fillets whereby the concentration of bending stress imposed on said sheet metal sections is minimized, and means joining said sheet metal sections to said first section so as to form the camber surface of said blade.

3. A hollow blade for aircraft propellers having thrust and camber surfaces, comprising, a first metal section extending throughout the length of the blade and forming a blade root and the thrust surface of said blade, said first section having longitudinally extending upstanding intermediate and marginal ribs which define cavities, said ribs and said cavities terminating inwardly the end of the blade leaving a tip portion, and a plurality of sheet metal sections overlying portions of said ribs and cavities, said sheet metal sections having inwardly curved edges to form ends which abut said portions of the ribs in the medial portion of said blade so that the bending stresses to which the joints therebetween are subjected due to vibratory loading of the blade are minimized, and means joining said sheet metal sections to said first section so as to enclose said cavities and form the camber surface of said blade.

4. A hollow blade for aircraft propellers having thrust and camber surfaces, includi g, a first metal section forming the thrust surface of the blade, said section having continuous upstanding intermediate and marginal ribs with relieved portions, said ribs defining longitudinal cavities which terminate short of the end of the blade to form a tip portion, a plurality of sheet metal sections having inwardly curved edges to form ends which abut the relieved portions of said ribs proximate to the neutral axis of the blade, said sheet metal sections overlying said rib portions and constituting the camber surface of said blade, and means joining said sheet metal sections to said first section.

References Cited in the file of this patent UNITED STATES PATENTS 994,166 Kienast June 6, 1911 1,313,599 Ingells Aug. 19, 1919 1,992,338 Whitworth Feb. 26, 1935 2,006,339 Baumann July 2, 1935 2,124,549 Dicks July 26, 1938 2,433,433 McKee Dec. 30, 1947 2,782,862 Wright Feb. 26, 1957