US2293801A - Hollow metal propeller blade - Google Patents

Description

F. w. CALDWELL HOLLOW METAL PR()I"::1I..L I:,R BLADE Filed Oct. 1, 193a Aug. 25;, 1942.-

3 Sheets-Sheet 1 INVENTOR EBHKWCBIdme/I WM-4 4 M AT TORNEY Aug. 25, 3942.

F. w. CALDWELL HOLLOW METAL PROPELLER BLADE Filed Oct. 1, 1958 s Sheets-Sh eet 2 YNVENTOR ATTORNEY Aug. 25, 1942.

F. W. CALDWELL HOLLOW METAL TROPELLER' BLADE Filed Oct. 1, 1938 5 s heetsheet 3 INVENTOR- EEDKWfiHidWE/i BY f z ATTORNEY Patented a... 25,1942

UNlTED- STATES PATENT OFFICE v noLLow. m grates. be

Frank W. Caldwell, Hartford, Conn, easier to.

United Aircraft Corporation, East Hartfo. -onn., a corporation or lll eiaware hpcation ctor g 1. v "This invention reiates to improvements in hol= izim low metal propeller blades and n improved method for manufactm'ing the same, and has for anobiect the provisionoi a metal propeller blade having relatively thin metal walls .relnforced by internal struts .or web members.

A further-object resides in the provision of a hollow metal propeller blade having relatively thin walls and an aerodynamically efiicient air foil section which is not subject to rapid deterioration in use due toload and vibrational stresses.

- A still further object resides in the provision of an improved method for manufacturing a hollow metal propeller blade oi the character indi- 4 sated.

Gther objects and advantages willbe more particularly pointed out hereinafter or will becom apparent as the description proceeds.

.In the accompanying dra, inwhich like reference numerals refer to similar parts throughout,v there is illustrated a particular mechanical embodiment oi a propeller blade con-. structed according .to the invention as well as various stages in the process of manufacturing such a propeller-"blade. The drawings, however,"

are for the purposeoi illustration only and are not'to be taken as limlting'or restricting the scope of. the invention as set forth in'the accompanying claims. L y in the drawings,

mg l is a slde elevatlonal view oi a tubular propeller blade blanh at a preliminary stage in the manufacturing process.

Fig. 2 is a view similar to Fig. lbutEhowlng the same side of the tube blank provided .wlth a longitudinal slot for the reception of an internal reinforcing member.

Fig. 3 is a view similar to Fig. 2 showing the opposite side of the propeller blade provided with a slot for the reception of the internal Fig. 9 is asectional view on the aforementioned enlarged scale at station 5- -9 of Fig. 5.

Fig. 10 is a plan view or thacompleted proenlarged scale V the same enlarged ll, sass, Serial so. esters (or. lid-159) o I Y r peller blade alter the tubular portion, illustrated the reinforcing portion, illustrated in l igs. 5 to 9', inclusive. 5.

at station lflliof Fig. 10. Fig. 12 is a 'sectlonalview on the same enlarged scale at station 82-42 of Fig. 10.

Fig. 13 is a sectional view on the abovementioned enlarged scale at station l3-i3 of Fig. 10 and, a

scale at station lid-id of Fig. 10.

it has previously been proposedto form hollow metal propeller blades and especially hollow steel propeller blades from thin walled metal tubing,

and a large amount 01 experimental workhasbeen done with the object of developing a'successiui hollow, thin walled, metal propeller blade. and have been found subject to certain defects which it is among the objects of this invention to overcome. Where-such blades have been produced by deforming a metal tube 01 a substan- 7 h tially circular original cross section to an air-' foil section it has been found impossible to produce an eficient airfoil section because the leading and trailing edges of such a section require a curvature to which the tube walls cannot be bent without overstraining the metal. It has also been new? to produce the necessarily sharp leading and trailing edges, particularly the trailing edge, by welding the metal along this edge, but such a weld of the relatively thin tube walls has been found to be too weak to stand found that a thin walled tube, when reduced to an airfoil section, does not have sumcient rigidity and is subject, particularly in propeller blades 'oilarge size, to twist and flutter during opera-5 tion. It the wall of the tube blank ismade'sufficiently thick to resist the tendencies to bend,

twist and flutter during operation'there is no worthwhile gain in weight saving over a solid blade formed of a relatively light alloy metal such M '4:

=-- invention to produce a' very thin walled light weight propelIer'JbIade having an enlclent airfoil sectionand suflicient strength and rigidity to successfully resist the torcestendin'g blade during operation of the propeller.

In producing the improved propeller-blade a in Figs. 1 to d, inclusive, has been assembled with Fig. 11 is a sectional-view on an enlarged scale Fig. 14 is a sectional view on the same enlarged I Blades so constructed have been trled in service umin. It is among the obiectsof to produce bendingi twisting and fluttering oi the I eter substantially equal to the maximum width of the finished p'ro ller blade and formed of a high strength steel lloy. One end of the tube is then swedged down and the extreme end portion is upset to provide on the blank, generally indicated at l8, aQsubstantially circular shank portion .l2 of reduced diameter and .an annular flange H ioinedto the shank portion by a fillet l6 of relatively large radius for retaining the blade in its hub mounting. upsetting operation may be carried out as desired or according to some method well known to the art as this part of the process of producing hollow steel propeller blades has already been developed to a relatively high degree of efficiency. During the swedging and upsetting operation the remainder of the blank is not altered but is left as a substantially circular portion of a diameter substantially equal to the maximum width of the finished blade as indicated by the numeral l8 in Fig. 1. After theoriginal tube blank has been subjected to the swedging and upsetting operations to produce the blank illus trated in Fig. 1 having the shankportionl2, the flange I4 and the generally circular tubular por- 25 tion l8, the tubular portion I8 is machined to uniformly decrease the wall thickness from the shank outwardly and is then bifurcated by two longitudinal, substantially diametrically opposed, slots of irregular outline, as indicated at 28 inFig. 2 and 22 in Fig. 3. The form of the slots 28 and 22 will be more fully explained hereinafter. 1 g a In addition to the tube blank l there is pro- I vided a core member generally indicated by the numeral and particularly illustrated in Figs. 5 to 9, inclusive. This core 'member is preferably formedas a steel forging and has an outline which is the; same as the outline of the finished propeller blade and a thickness the same as the thickness of the hollow interior of the blade. The

. core includes a solid tip portion 28 and a plurality of tine like elements comprising a leading edge bead 28 integral with the tip portion, a trailing edge bead 38, and two spaced apart 1ongitudinal internal strut members 32 and 34, also integral with the tip portion 26.

are rabbetedr on both sides to provide shouldered depressions for the'edge portions of the i'urcations of the tubular blank l8 alongthe slots 28 and 22, and are machined to provide rounded 5 --bead portions extending beyond the sides of the tubular blank and feather edged flange portions along, their inner edges. 3 The internal strut members 32 and 34 are machined toa substantial Lsec'tion in which the end flange portions are taperedj outwardly to a feather edge. The spacing andshap of the members 28, 38, 32 and 84 change along the length of the propeller blade W to conform to the sectional contour of the blade at every station along its length, certain selected stations having been particularly illustrated in slots 2l and 22 come into contact with,the corresponding shoulders of the rabbeted portion of the leading edge and trailing edgetines 2.8 and II, the slots 2E and22 being so shaped that the edges of the opposite side of the blank conform to the contour of the correspondingshoulders when the blank is ppessed down to form with The leading ,edge and trailing edge tines or beads Hand 30 the core member 24 a blade member of the desired airfoil section. After" the furcations of the tubular blank have been pressed down into firm contact with the core member, to constitute 5 a cover therefor the cover member is welded to the core member by some suitable method such as electric resistance welding. According to onepreferred method of welding, strips of a suitable heat resisting material such as asbestos are The swedging, and 10 secured along each bead and strut member within the blade so aato overlap the-joint between the bead and strut members and the corresponding portions of the tubular blank, and an electric current is then passed through the structure until the contacting surfaces of the outer member and core member becomefused'together.

when the welding operation has been completed a blade is produced of the form and character particularly illustrated in Figs. 10 to '14, inclusive. The tip portion 28 and the leading and trailing edge beads 28 and 30 are integral portions of the core member and the weld joints between the cover member and the core member are located at some distance from the'leading and trailing edges. Furthermore, the thickness of the bead members between opposed-edges of strong weld construction at the indicated location. The leading edge and trailing edge beads b 28 and 30 are shaped to provide the necessarily the cover members is sufflcient to provide asharp ends at these edges so that the adjacent portions of the tube walis do not have to be sharply bent and. the internal struts 32 and 34 are located so as to maintain the opposed por- 35 tions of the tube wall in the 'exact shape and position desired and to provide internal bracing for the blade to render the blade sufliciently strong and rigid to resist the load and vibration forces imposed thereon during operation. As

40 is ,clearly' illustrated in Figs. 12 to 14, inclusive, the tubenwall is tapered from the shank to the tip endand the outer portion thereof is made extremelythin. It is therefore apparent that the above described construction will provide a propeller bladeof minimum weight consistent with the necessary strength and rigidity since the component parts are reduced to their minimum weight and reinforcement is provided only where J additional strength is required. The core ele- 60 ments are not? only shaped to provide the minimum weight consistent ,with the necessary degree of reinforcement but also to distribute and {equalize the blade stresses, particularly at the shank end of the blade. For accomplishing this beads 28 and 30 are shouldered and tapered at their shank ends, asis clea'riyillustrated in Fig. 5, g the internal strut 32 is terminated short of the ends of the other core elements and the shank end of the strut 34 is cut out as isclearly illustrated in Fig. 14 and tapered to avoid any abrupt change in thlstrr-ss transfer between the .cover member and the core member.

latter purpose the leading edge and trailing edge By bringing to a feather edge all portions of the core,

member which contact and are secured to the cover member, localized highly stressed'areas in the blade are avoided. Y

While a parti ular mechanical embodiment of a propeller bla e' constructed according to the invention and one practical method of menu-f facturing such a blade have been hereinabovedescribed and illustrated in the accompanying drawings for "the purpose of disclosing the mvention, it is to be understood that the drivention'is-not limited to the particular method and aeoseoi ponstruction so illustrated and described but that such changes in the size, shape and arrangement of the various parts of the propeller blade and such changes in the order and character of the various steps of the improved method may a be resorted to as come within the scope ofthe sub-joined claims.

Having now described the invention so that others skilled in the art may clearly understand the same, what is claimed and what it is desired to secure by Letters Patent is as follows:

1. A hollow metal propeller blade comprising, a multi-tined core member having a pair of outside tines constituting the leading and trailing edge portions of the-blade, and a bifurcated cover member having an integral shank portiom said cover member receiving the major portion of said I core member and welded thereto along contacting surfaces.

2. The arrangement as'set forth in claim in 2 which said core member and said cover member are both formed of the same material.-

3. The arrangement as set forth in claim 1 in which said core member and said cover member are both formed of high strength steel.

4. The arrangement as set forth in claim 1 in which all portions of said core member contacting said cover member are provided with feather edges to distribute the stresses transmitted between said cover member and said core member.

5. A hollow metal propeller blade comprising, a core member including a solid tip portion and a plurality of tines integral with said tip portion, and a bifurcated cover member having an integral continuous shank portion in which said core member is received in the bifurcated portion of said cover member and the outside tines of said core member-constitute the leading and trailing edges of said blade, said outside tines being rabbeted to receive the edge portions of the cover member furcations to provide a smooth external surface for said blade.

6. The arrangement as'set forth inclaim l in which the'wall thickness of said cover member decreases from said shank of said member.

'1. A hollow metal propeller blade comprising, a core member including a solid tipportion and a plurality of spaced longitudinal tine like portionsintegral wi portion to the tip end said tip portion, and a so portion having integral extensions forming the side portions of. the blade, and a tip portion having integral extensions-forming the leading and trailing edges thereof and reinforcing members for said blade, said portions being secured to gether substantially longitudinally of said blade.

9. A hollow propeller blade comprising, a shank portion having opposed longitudinal extensions forming substantially the entire side portions of the-blade, and a. tip portion having integral extensions forming the leading and trailing edges thereof and reinforcing members for said blade, said portions being secured together substantially longitudinally of said blade.

, 10. A hollow metal propeller blade comprising,

a multi-tined core member in whichthe outside tines constitute the leading and trailing edge portions of the blade and at least one intermediate tine. and a bifurcated cover member having an integral shank portion receiving the major portion of said core member and welded thereto along contacting surfaces.

11. a hollow metal propeller blade comprising, i

an integral multi tined'core member having a portion constituting the blade tip,'one tine collstituting one edge of said blade and at least one other tine constituting a reinforcing member. and

an integral bifurcated cover member having a portion constituting the blade shank, and portions constituting the blade faces. said cover member receiving the major portion ofsaid c'ore.

member with said face portions contacting said tines. said first-mentioned one tine separating- 1 said face portions at said one edge of saidblade.

said core welded together along contacting surfaces.

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