US2423700A - Propeller blade - Google Patents

Description

July 8,1947. G. w. HARDY PROPELLER BLADE Filed June 16, 1943 INVOR. GORDON W f/neov Patented July 8, .1947

PROPELLER BLADE Gordon w. Hardy, Cleveland heights, Ohio, assignor to The Marquette Metal Products Company, Cleveland, Ohio, a corporation of Ohio Application June 16, 194 3, Serlal No. 491,037

J 3 Claims.

This invention relates to a propeller blade particularly for aircraft and a new method of making such blade. I

One object of the invention is to provide a propeller blade which can be made without any great amount of hand work and have strength, flexibility and other desirable characteristics comparable to, if not excelling, the higher grades of laminated wooden propellers and all-metal propellers while at the same time being moisture and impact resistant and of light weight.

A further object is to provide an improved method of making metallically armored propeller blades.

A specific object is to provide a propeller blade having an adequately reinforced core including high strength plastic material and an armor sheath partially or wholly covering the same of sumcient tensile strength and impact resistance to prevent chipping and abrading of the propeller surface as by projectiles, particularly at low temperatures. I

A further object is to provide a metallically armored propeller in which the armor is completely bonded to the core, whereby adequately to resist all tendency to peeling off, whether by impact or temperature efiects or otherwise.

Another object is to provide an improved propeller blade made partially from plastic material with an improved reinforcing core formed substantially as an integral part of a shank piece or butt of the blade suitable for mounting in a metal hub provided with meansfor turning the blade about its longitudinal axis for pitch adjustment, feathering and the like.

Another object is to provide a de-icing means for propeller blades which means is operative efficiently to de-ice all the blade surfaces on which ice is likely to accumulate.

Further objects include the-provision of a propeller blade having adequate tensile, compressive,

twist resisting and impact resisting strength, not-' withstanding relatively light weight and resistance to the effects of temperature change and relative humidity or even immersion in water for long periods.

Further objects and features of the invention will become apparent from the following description and by reference to the accompanying drawing, in which Fig. 1 is a front view of one blade of a propeller and a more or less diagrammatic representation of a hub on which the blade may be mounted;

Fig. 2 is a sectional view showing, by way of example, a mold in which part of the core P013 tion of the blade can be formed, said view showing, in place in the mold, a metal shank or butt piece and inner reinforcing element rigid therewith;

Fig. 3 is a diagrammatic representation showing the manner of applying armoring metal to the completed core;

Fig. 4 is a relatively enlarged fragmentary cross sectional view showing particularly the relationship of the de-icing fluid tube and discharge nozzle jets therefor at one edge portion of the blade;

Fig. 5 is a greatly enlarged (e. g. magnified) typical section of the completed blade near its surface; and

Fig. 6 is a view similar to Fig. 5 showing a modification in a plastic portion of the blade core or body.

Several prior proposals for the use of inorganic plastics as materials for propeller blades have been made, and it has also been proposed to provide metal sheathing or armor for propeller blades made at least partially from plastics and for other non-metallic materials, as cores. Paper and fabric reinforced plastic cores of synthetic resin such as heretofore proposed require a great deal of labor to form them; and under the extremely high bending and twisting strains to which propellers for aircraft are subjected as well as impact forces, the laminations are apt to separate and the resinous material, being brittle,

is apt to fracture and become chipped or shattered. It has, in practice, usually been necessary to encase propellers made largely or wholly from organic plastics with a built-up partial or complete armor of metal or dope"-impregnated fabric in order to prevent contact of the plastic materials with moisture as well as in order to protect the plastic against being chipped or fractured by flying missles such as small stones and,

in case of fighting craft, flak. The difference in twisting and bending resistance or elasticity between the different materials heretofore used and the differential of expansion and contraction under heat between said different materials are common causes for short life on part of composite propeller blades including such plastic materials as heretofore used or proposed.

In the present arrangement I have sought to reduce all the differentials which commonly account for deterioration and partial or complete destruction of composite blades by using a plastic material for the core which has great toughness, hardness comparable to metal, practically no t den y to cold flow at moderately high temperatures or to fracture by impact or strain at sub-zero temperatures and which has little, if any, tendency to separate locally from the metallic armor or other metal portionsduring subjection to rapid temperature changes and extremely high bending and twisting strains. The unitary character of the blade is preservedin part by a metallic armor of composite nature, one component of which is selected for desirable bonding characteristics with the plastic as well as protection of the latter during application thereto and another component being selected principally with a view to greater surface strength and abrasion resistance. The above are only the salient features of the present method and propeller blade construction produced thereby. Others will be brought out later herein.

Referring further to the drawing. Fig. 1 shows a left hand portion of a blade in side elevation and a right hand portion in substantially central principal plane section along the major surface of a reinforcing sheet and central core piece supporting the sheet. The blade has a shank or butt portion l suitably formed, for example, generally cylindrically. and with flange projections as at 2 which, in the form shown, are buttress "thread effects for mounting the propeller in a suitable hub. A hub is diagrammatically indicated at 3 with a tubular extension 4 adapted to receive the pojections 2 and which may include provision for turning the entire blade about its longitudinal axis into high and low pitch, feathering and/or reverse positions. Reference is directed to my copending application, Serial No. 498,492 filed July 13, 1943, for a suitable hub construction providing for variable pitch as to the blades of which there may be any suitable number and arrangement and for one manner of supplying de-icing fluid to the blades. The ribs 2-on the butt portion I are, in actual practice, supported in split mounting sleeve members such as shown for example in my copending application Serial No. 476,398, filed February 19, 1943. For simplicity, the butt portion 1, as herein shown, is embraced by metal of the associated structure above described is secured between two hub extension 4 as though tunable for pitch adas at I in which event the reinforce will have cross passages as at 8 to enable injection of the plastic through the central bore and flow thereof outwardly-into a mold through such passages B in appropriate directions.

In addition to the reinforce 5, I preferably employ also a plate-like reinforce and plasticinterlocking element such as shown at Ill. The element I0 'is preferably in the form of a sheet metal blank 01 the general shape of the main face portions of the blade but somewhat smaller and having a fairly large number of passages ll therethrough. The passages are shown as comprising alternately oppositely necked or flanged openings through which the\plastic material at one side of the sheet In is adequately integrally bonded at intervals with the plastic on the other side of the sheet. The flanges present greater interlock or shoulder surfaces to the plastic than would plain punched-openings. The sheet ill may be anchored to the reinforce 5 and/or to the butt piece 2, a convenient manner of fastening the sheet comprising slotting the reinforce bar 5 longitudinally as at i2, slipping the sheet into the slot and then brazing'or welding the sheet to the reinforce at the lateral limits of the slot. The sheet material is cut away centrally of the reinforce bar as at l3 so as not to obstruct the inlet duct 1 for the plastic.

Assuming the composite shank and reinforcing appropriately heated mold members or dies-such as l5 and I6 which are separable substantially along a plane parallel to the principal plane of the blade when formed, the plastic may be injected into the main mold cavity H as through a nozzle I8 brought into sealing contact with an end wall of the butt piece I at the central hole I of the butt piece. Suitable mold heating and cooling means may include conduit passages formed in the mold as at 20 for receiving alternately steam and water or other heating and cooling media; and such passages are appropriately spaced, proportioned and positioned so that the heat is properly distributed as required to cause the plastic entirely to fill the cavity ll under pressure before any partial solidification takes place.

Appropriate vents may be provided for discharging excess plastic as at the tip-forming portion of the mold. The solidified plastic is indicated in Figs. 1, 4 and 5 at 22.

The method outlined above for incorporating the plastic with the central reinforce and butt piece structure is especially suited to the-plastic of a portion of the reinforce bar 5 are faced off as at 5a, as brought out by comparison of Figs. 1, 2 and 4.

In order to form a firm and permanent intermaterials cellulose acetate and cellulose acetate butyrate which are preferred largely because of their high tensile and flexural strength, impact resistance, hardness, lack of brittleness and small tendency to elongate or cold flow" under moderately high temperatures and to fracture under low temperatures. The above, of course, are only a few of the well known desirable characteristics I of the thermoplastic materials mentioned. Other 1 plastics having similar properties may be considalong, or the reinforce bar hay have any other surrounds the reinforce 5 and determines the shape of the blade is to be formed by injection ered'operative equivalents and within the scope of this patent. Thermosetting materials can, of

' course, beusedand the molding methods would vary asbest fits the particular plastic selected, whether thermosetting or thermoplastic,

molding as against transfer," "compression" or other molding methods any of which could be practiced instead, then the butt pieceand re- 1 A propeller blade form when ejected from the mold, such as shown in Fig. 2, is then encased preferably in a complete envelope of metal. In

order to avoid joints in covering a preformed blade body made of wood or the like with metal,

it has been proposed to treat such body with electrica-lly conductive substance sand'ithenv ap lyiithe metalgelectrolyticallyz '-':El'ec,trolytically zideposited metalr'ha's veryslittle tensile strength-:ar'idds. moreover, squite I.brittle;s;:but-1 athe ..principal-:disadvantage of its,.useaspropellerabladei ar'momor sheathinsxis that-it is:practically:impossiblejltoi secure ing-is suggestedgin Eig.-3 .-:wherein the spray noz-- zle forthe metal-,is'indicatediat 25 and the completed m'oldingflat 26:1? The molding is mainly supported as by.th el shanlripiece 2 for rotation as by automatically variable speed gearing mechanismzsu'ggested,f-diagrammaticaily only, at 21. Additional support is indicated at 28. Suitable means is also provided g-radually progressively and automatically,to change the zone of operation of the metal spray in respect to the blade surface either by shifting the blade or the nozzle continuously and "iria" direction parallel to the longitudinal axis of the blade at the required speed; as, determined,by the thickness of coating desired. Mechanisms for accomplishing such motions"; as referredtoabove are well known in the machine?tool-arts,,hence need no specific showingherelj; [-l

The. blade :jcore is spray coated locally, progressivelybyasuccessive steps, .on both sides at nearly the same time during turning of the blade at appropriate'varying speeds as different surface portions"'arei presented to the nozzle. Thereby the tendency for the blade to be warped (as would be -the ,asei if one side were completely coated andthefi the other side) is greatly reduced and a more-. u'riiform and smoother-coating can be obtained.

For the first coating which is applied directly onto the 'plastic and preferably by the use of a fairly-low melting point metal such as aluminum, the-nozzle is positioned much farther away from thernolding than in the case of the second coating'since, in the first operation, it is desirable to prevent scorching or melting of the core by the hot metal although sporadic softening of the plastic surfaces takes place and slight penetration necessary for firmbonding of the first coating of metal therewith; and, in the second operation, detrimental effects of heat are prevented by the insulative action of the underlying or first metal coating.

Incidentally, if the spray coating is done against the revolving and progressively relatively advanced molding (e. g. moving the spray gun for relative advancing) the application is in a more or less spiral path about the blade so that if there is any joint effect where one spraying operation overlaps metal deposited by the preceding operation, the joint" will extend around the blade in a direction at right angles to the longitudinal axis thereof rather than lengthwise of the blade at any point. Thus if the spraying operation starts at the tip the subsequent spray applications have a scale-like eflect, overlapping each other toward the tip for greatest resistance to becoming detached by centrifugal and abrasive forces during propeller operation.

The blade core is first given a complete and fairly light coating as of aluminum or other low melting point metal (see Fig. 5 at 29). The lower melting point metals have less tendency to scorch the plastic although some of the particles embed themselves in the surface of the plastic and enhance the bonding. The first coat 29 forms a. protective layer upon which higher melting point metal, for example, steel, can be spray coated as at 30 or possibly in some other manner, e. g. by electroplating in case the low melting point metal of the first coat is adapted to be coated electrolytically. The bond 3| between the first coating 29 and the plastic 22 may be enhanced by having the surface of the plastic somewhat rough. Roughness or "tooth effect can be secured either by a rough finish on the mold cavities or by sand blasting or etching of the plastic after molding (not illustrated.)

Another manner of enhancing the bond and, by the same means, reducing the density hence total weight of the plastic component is suggested in Fig. 6 wherein the plastic body 22a is shown as provided with innumerable small cavities 34, formed as by introduction and dispersion of gasforming materials into the plastic stock, some of which cavities break through to the surface as at 35 and thereby form tooth effects for mechanical bonding with the initial metal coating 29 in cases in which there is more thermal expansion differential than in the preferred selection of materials described above.

I have found that if the first coat is aluminum and the second coat steel, the composite armor is adequate to serve all the functions normally served by sheet metal armor such as already known in the propeller art, and it has the special advantages, namely full bonding over the entire coextensive surfaces; there are no joints, and the metal can be increased in thickness as at the leading edge of the blade, as suggested by Fig. 4,

or at any such other portions as may be found to be subjected to especially heavy duty.

Tube effects in propeller blades and cuffs for blades are already known, which tube effects are designed to distribute de-icing fluid to the blades during-rotation. So far as I know, however, it has not been considered desirable to provide for distribution of such fluid from inside the blade proper to the outlying surface portions of the blades. The theory has been that a limited disthe leading edge which tubehas nozzle apertures, for example, of graduated size (reduced size out- The de-icer fluid tube shown at 40 extends through an eccentric bore in the butt piece I for connection as by flexible tubing 41 with a supply line which, for example only, is shown centrally of the hub 3 diagrammatically at 42. The coupling and supply arrangement for the de-icer fluid tube from a pressure supply source is more completely shown and is claimed inmy co-pending application Serial No. 498,492 mentioned above.

The tube 40 leads from the butt piece I, to

2. A propeller blade comprising a central slotted metallic reinforcing bar tapering outwardly to a tip portion at one end, a perforated sheet metal reinforcing element mounted in the slot in said bar, extending longitudinally. of said bar and laterally of the blade, a molded core of organic plastic material surrounding said bar andv element and locked thereto by interlocking. en-

gagement with the perforations of said element and with the slot insaid bar, and a protective metallic armor bonded .directly to said plastic core. Y

' 3. A propeller blade comprising, a central slotted metallic reinforcing bar shaped at one end tov form a butt piece and tapering outwardly at the other end to form a tip portion, a perforated sheet metal reinforcing element mounted in the slot in said bar, extending longitudinally of said bar tributing alcohol or other de-icing fluid along.

the camber surface portions 'of the blade. The actual effect of discharging such de-icing fluid from the blade as by suitable pressure applied to the tube 40 is to volatilize the fluid in the zone of operation of the blades and the resulting mist of de-icer fluid accomplishes the de-icing regardless of the particular region of the blade from which the fluid is discharged and onto what surface the fluid tends to flow. Unless, however, the- 1. A propeller blade comprising a central hollow metallic reinforcing bar supported on a butt piece at one end and tapered outwardly to a tip portion at the opposite end, a perforated sheet metal reinforcing element mounted on said bar,

extending beyond said tip portion and laterally of the blade, a molded core of organic plastic material surrounding said bar and element and locked thereto by interlocking engagement with the perforations of said element and'withthe interior of said bar, and a protective metallic armor bonded directly to said plastic core.

and laterally of the blade, a molded core of organic plastic material surrounding said bar and element and locked thereto by interlocking engagement withthe perforations of said element and with the slot in said bar, and a protective metallic armor bonded directly tosaid plastic core.

GORDON W. HARDY.

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

UNITED STATES PATENTS Number v v Name Date 1,419,180 Thomson etal. June 13, 1922 11,843,886 Semmes Feb. 2, 1932 1,258,282 Welte .Mar. 5, 1918 2,063,019 Bardach et a1. Dec. 8, 1936 2,290,249 Piperoux July 21, 1942 2,217,979 Booharin Oct. 15, 1940 2,269,635 Mosehauer Jan. 13, 1942 1,384 308 DeGiers July 12,1921 1,846,256 Havill Feb. 23, 1932 2,266,129 Tegharty Dec. 16, 1941 1,308,527 Nilson July 1, 1919 1,860,655 Beebe Aug. 2, 1932 2,077,959 Smith Apr. 20, 1937 1,385,802 St. John July 26, 1921 FOREIGN PATENTS Number Country Date 674,727 Germany Apr. 21, 1939 760,098 France Feb. 16,1934 341,540 .Italy June30, 1936 Great Britain June 19, 1929

Images