US1864260A - Airplane propeller - Google Patents

Description

June 21, 1932. .1. SQUIRES AIRPLANE PROPELLER Filed Nov. 19, 1928 2 Slieets-Sheet l INVENTOR A TTORNEY June 21, I J, s S

AIRPLANE PROPELLER Filed Nov. 19, 1928 2 Sheets-Sheet 2 M v f wH/v SW55.

A TTORNEY Patented June 21, 1932 JOHN SQUIRES, OF DETROIT, MICHIGAN AIRPLANE PROI'ELLER Application filed November 19, 1928. Serial No. 320,240.

This invention relates to propellers and particularly to propellers employed in connection with aircraft, the principal object be-' ing the provision of a new and novel design that will be light but strong and which Wlll be efiicient in use.

Another object is to provide a propeller for aircraft and the like fabricated entirely from metal and employing stiffening members so positioned as to be acted upon by the centrifugal forces set up in the rotation of the propeller to aid in the stifi'ening effect thereof.

Another object is to provide a propeller of the class described designed to elimlnate the D non-efficient inner end portions of the conventional types of propeller blades and lead air which normally passes through such portions to a position to be acted upon by the more efficient portions of the blades.

- Another object is to provide a propeller of the class described in which the blades w1ll be substantially equally eflicient from their tips to their roots.

Another object is to provide a propeller of the class described having radially extending tubular members serving as a frame for the blades and suitably covered to complete the blades.

Another object is to provide simple and et'ri 3o cient means for assembling and carrying the frame structure of the blades.

Another object is to provide means for assembling the parts of my improved propeller in a manner which will offer the least wind 1:. resistance in its final form and will lend the greatest strength to the structure.

Another object is to provide a propeller of the class described including a relativelv large axial nose designed to eliminate the flow of u air through the center of the propeller and to direct it into contact with the blades positioned outwardly thereof and at a distance from the center of rotation of the propeller such as tobe effectively utilized by the rota- If tion of the propeller to produce a thrust.

A further object is to provide a propeller for aircraft in which surfaces of the blades are corrugated or otherwise pinned radially of the propeller.

The above being among the objects of the present invention, the same consists in certain features of construction and combinations of parts to be hereinafter described with reference to the accompanying drawings, and then claimed, having the above and other objects 65 1n view.

In the accompanying drawings which show a suitable embodiment of the present invention, and in which like numerals refer to like parts throughout the several different views,

Fig. 1 is a side view of one embodiment of mgvimproved propeller.

ig. 2 is a view similar to Fig. 1 with certain portions thereof broken away to illustrate the interior construction thereof.

Fig. 3 is an end view of the propeller taken as on the line 33 of Fig. 2, with the nose piece removed and certain parts thereof being broken away to better illustrate the construction.-

Fig. 4 is a sectional view taken through one of the blades as on the line 4-4 of Fig. 3.

Flg. 5 is a fragmentary sectional view taken as on the line 5-5 of Fig. 2, and showing the method of securing the blade covering. to the supporting tubes.

Fig. 6 is a side view of the hub member of the propeller.

Fig. 7 is a more or less diagrammatic fragmentary partially broken view showing a modified form of blade construction.

Fig. 8is a view, partly in section and partly in elevation, showing a modified form of propeller.

Fig. 9 is an elevation of one portion of the propeller hub shown in Fig. 8 with a portion of the blade supporting tubes extended therein.

Fig. 10 is a, view, partly in section and partly in elevation, of an end of a tube such as is used in the construction shown in Fig. 8.

Fig. 11 is an end view of said tube.

Fig. 12 is an elevation of one end of a pair of joined tubes such as are used in the construction shown in Fig. 8.

Fig. 13 is an end view of the tubes shown in Fig. 12.

Fig. 14 is a plan view of a portion of the propeller blade shown in Fig. 8, with parts broken awayto show a portion of the same in section.

It is known in connection with propellers for aircraft that it is impossible to attain a material effectiveness of that portion of the blades adjacent the hub because of structural limitations. These limitations usually result in. a thickening of the blade section adj acent the hub to afford an adequate strength at this point to resist centrifugal and other stresses. This thickening of the inner ends of the blades, of course, results in a deficiency of the propulsive effect of this portion of the blades.

The usual alternative form in metal propellers is to have the blade mounted upon or formed from an extension of a tubular shank. Because of these limitations it is obviously advisable not to attempt to utilize the central portion of the swept area but to design the propeller on the basis of maximum efficiency of that portion of the blade which does useful work.

In the usual design the structural arrangement of the blade results in power and propulsive losses because of rotational air friction of the inner ends of the blade and eddy currents set up thereby. I purpose, in the present invention, to provide a propeller in which no attempt is made to exert adjacent the hub of the propeller a propulsive effect on the air, and further in which the friction and eddies set up at the inner ends of the blades in conventional constructions are eliminated, and instead the air which would normally pass through the propeller adjacent the hub is directedwith minimum resistance to the blades at such a distance from the hub as to permit them to act on such air in an efiicient manner.

It is also well-known th. for many reasons including limitations of space and greater efliciency, it is desirable to employ propellers of relatively small diameters rotatable at relatively high speeds. Heretofore the use of such propellers has been limited to a great extent because of the structural limitations imposed thereon to Withstand the Whip and centrifugal forces to which they are subjected, and which have heretofore resulted in a propeller of excessive weight. By the employment of the present invention I am enabled to provide a propeller which is of extremely light construction and so designed as to resist a practically unlimited centrifugal force caused by high rotational speeds, and further designed to take advantage of the centrifugal forces acting thereon to stiffen the blades and thereby minimize distortion and whip of the blades.

Referring to the accompanying drawings I show a propeller comprising a hub member- 10 designed for direct connection to a propeller shaft. Secured to the hub 10 by any suitable means such as being threaded therein, welded or brazed, are two series of radially extending hollow sheet metal tubes 11 which form the frame Work for the blades. The tubes 11 may be cylindrical throughout their length but are preferably tapered from a maximum diameter at the hub 10 to a minimum at their outer ends as shown, for structural reasons.

As indicated in the drawings, I prefer to form pad-like projections 12 on the hub 10 in which the inner ends of the tubes 11 are secured in order to obtain maximum strength with minimum weight of the hub. The tubes 11 are arranged in a helical path about the axis of the hub 10 and preferably in a true helix for reasons hereinafter described. Surrounding the hub 10 and fitting around the respective tubes 11 is a drum-like structure 13 preferably formed from sheet metal and supported from the hub 10 by means of rela tively light spokes such as 14. The diameter of the drum 13 is preferably such as to eliminate that inner portion of each blade which would otherwise be inefficient for propulsive efforts were the blades extended to the hub and left free to act upon the air. The forward end of the drum 13 is closed by a nose 15 which blends into the adjacent end of the drum to form a projectile-like head designed to exert a minimumresistance on the air having a flow relative to it and shaped to direct the air flowing against it outwardly and rearwardly against the blades which extend radially from the drum so that such blades may etficiently utilize such air for exerting apropulsive effort. The tubes 11 which project out through the drum 13 decrease in length from the leading edge of each blade to the trailing edge thereof in accordance with the particular shape of blade employed and these portions of the tubes 11 are provided with a sheet metal covering 16 which completes the blade.

The covering 16 may be formed from one or more strips of sheet metal but where possible I deem it advisable that the covering for each blade be formed of a single strip of material bent midway of its width over the tube 11 at the leading edge and having the free edges thereof secured together at the trailing edge as best indicated in Fig. 4. The covering 16 is preferably secured to each of the tubes 11 by rivets such as 17 shown in enlarged View in Fig. 5, a sufficient number of such rivets being provided to eliminate any possibility of the covering being torn from the tubes because of the centrifugal forces acting thereon. Furthermore, I prefer to flange the inner end of the covering 16 where it joins the drum 13, as at 18, and to rivet such flange to the drum in order to further resist centrifugal forces, to aid in resisting twisting of the blades, and to stiffen the structure as a whole. To further aid in stiffening and strengthening the structure I prefer to depress the wall of the tubes inwardly, as illustrated in Fig. 5, around the openings for the rivets 7, and similarly depress the covering 16 at these points so as to form projections fitting in the depressions in the tubes and held therein by the rivets 17. It will be apparent that by thus rigidly securing the covering to the tubes, the covering itself acts as a stress transmitting member and because of its bein warped to a helical shape, acts to stiffen t e construction as awhole.

The blades themselves are preferably of aerofoil section as indicated in Fig. 4, and for this reason I refer to vary the diameters of the tubes 11 rom the leading edge of each blade to the trailing edge thereof so that this result may be effected, and the tubes 11 may even be flattened in certain instances, as indicated in Fig. 4 to effect this result.

With the construction thus far described it will be apparent that the air which would normally flow through the propeller adjacent the hub thereof in conventional constructions, and which air would be a hindrance rather than an aid in the propulsive elforts of the propeller, is in this construction caused to flow outwardly and rearwardly and pass through the propeller at such a distance from the axis of the hub as to permit the blades to efliciently react thereon. It will also be apparent that inasmuch as the tubes 11 extend radially from the hub, the centrifugal action acting on the tubes 11 tends to maintain them in their true radial position and this tendency acts to overcome any tendency of the blades to whip or otherwise distort in service. This utilization of the centrifugal force acting on the blade elements allows me to provide a propeller of maximum strength and stiffness with minimum weight, and the propeller may therefore be employed where high rotational speeds are necessary or desirable.

A screw propeller is most eflicient when the element which it moves and through which it moves travels as nearly as possible in a straight line and with a minimum of turbulence or eddy currents. It is obvious that the helical form of blade of such shape in respect to suction and pressure surfaces, as is best determined by experience, will be most eflicient when it functions equally well over all portions of its working surfaces. I therefore find it advisable to progressively increase the width of the blades from the tip tional speed of the tip of the blade, air will be drawn to the tip from the inner ends and thus lessen the useful effect of the latter. The use of the radially extending tubes 11 in a blade-of the construction described permits constructing such blades of any desirable width from the root to the tip, and with any and all portions of the blade surface area held to exact conformation by the action of the centrifugal force acting thereon within the limits of the ultimate tensional strength of the material from which the tubes are formed.

Although it is entirely possible and practical to secure the tubes 11 in the pads 12 by a threaded connection or by welding, brazing, or other means, I prefer to employ a construction permitting greater ease of assembly of its parts than is possible in the construction above described. The method I preferably use is indicated in Figs. 8 to 13 inclusive. In this construction the hub 10 is formed in as many separate parts as there are blades on the propeller; in the case shown, two. As indicated, the hub 10 is split axially from one end surface to the center of the adjacent end of the pads 12 and then is split centrally of the pads 12 in a helical path to the opposite end of the same, and then axially to the remaining end of the hub. The two halves of each of the pads 12 are provided with suitable recesses such as 25 in their matching faces which are aligned with each other in pairs when the halves are secured together, so as to form openings for the reception of the inner ends of the tubes 11, and the recesses 25 are enlarged at their inner ends as at 26, forming a shoulder 27 for the purpose presently described. The tubes 11 as indicated in Figs. 10 to 13 inclusive have their inner ends outwardly flared as at 28 to form a flange, and the flange 28 of each of the tubesis preferably provided with a stitlenin plate such as 29 closing such end, and pre erably welded or otherwise secured in place. The end 29 and the corresponding flange 28 of each tube is preferably rounded as indicated in Fig. 10 so as to merge with the inner surface of the hub 10 when in place. The tubes 11 thus formed are inserted in the recesses 25 of one half of the pad 12 and are positioned with the flange portions 28 received in the corresponding enlarged portion 26 of each recess and with the outersurface of the flange 28 hearing against the shoulder 27. The remaining portion of the hub with the complementary halves of the pads 12 are then positioned in place and bolts such as 30 extending through the openings such as 31 in the pads 12 are employed for drawing the hub portions to ether, clamping the tubes 11 between the ha ves of the pads 12, and securely locking them in place. A

With this construction it will be apparent that the operation of securing the tubes 11 in such centrifugal force.

I In some cases it may be desirable to so position two or more ofthe tubes 11 so that their inner ends are in contacting relationship for at least a part of their lengths.

' Such a case is illustrated in Figs. 9,12 and 13 which show the two leading tubes 11 for each blade contacting with each other at their inner ends. In this case the inner ends may be cut away as indicated at 32 in Fig. 12 and such cut away portions welded together as indicated. The tubes 11 in this case as in the previous case, are of course flanged as at 28 in the same manner as previously described and a stiffening plate such as 33 is preferably welded to cross their ends, the plate 33 in this case being a single plate such as indicated in Fig. 13 which accordingly serves to secure the two tubes together more securely.

It is of course not necessary that the covering 16 of the blades be smooth, but it is evident that it may be desirable in some cases to form the same of corrugated metal. In such cases I prefer to form the blades as indicated in Fig. 7 in which the covering 19 is corrugated as at 20 in a direction circumferential with respect to the axis of the propeller. The tubes 21 in this case may themselves be corrugated throughout their length as indicated in Fig. 7 so as to better cooperate with the covering 19 for securement thereto, or may be left smooth as in Fig. 8, as desired. By forming the corrugations 20 in a radial direction, the corrugations tend to prevent the centrifugal action of the blade on the airilfrom moving the air radially of the prope er.

Although the particular formation of the corrugations 20 shown in Fig. 7 are entirely suitable, in the construction shown in Figs. 8 and 14 the corrugations 34, which correspond to the corrugations 20 shown in Fig. 7, are more widely spaced lengthwise of the blade than in Fig. 20. This may be utilized as an aid in the o eration of applying the covering to the b ades in 061128.111 cases where it is found easier to form the covering in sections longitudinally of the blade than of a single piece. In such case, the sections may be secured together transversely of the blades by a simple lock joint such as indicated at 35 in Fig. 8 and which joints 35'serve to effect the desired corru ations, but I prefer to employ the joints in icated in Fig. 14 which are of the double type, as indicated at 36 and which eifects a more rigid structure to withstand the centrifugal forces to which such joints may be subjected to in service.

Although I have shown a propeller having a drum o certain proportions relative to the dlameter of the propeller, it will be obvious that the diameter ofthe drum may be varied within reasonable limits, although I prefer that it should be at least 25 per cent of the diameter of the propeller. Furthermore, the nose piece 15 and the drum 13 may be varied in construction to effect a. more or less projectile shaped nose, as best suits individual desires, and the particular shape of the blades may be varied as desired without departing from the broad aspects of the invention.

It will also be apparent that although I have shown a propeller with but two diametrically opposed blades, any desired number of blades may be used, and in case multiple blades are employed such blades may be staggered axially of the hub or arranged in any other manner desired.

Formal changes may be made in the specific embodiment of the present invention without departing from the spirit or substanceof the broad invention, the scope of which is commensurate with the appended claims.

What I claim is:

1. A pro eller having a blade formed with a tubular ramework and a covering for the framework, the tubes of the framework varying in diameter with respect to each other, to provide an airfoil section tapering from its leading edge to the trailin edge.

2. A propeller having a lade formed with a tubular framework and a covering for the framework, the tubes of the framework being of tapered construction and varying in crosssectional size with respect to each other, to provide an airfoil section tapering from its leading edge to the trailing edge.

3. A propeller having a blade formed with a tubular framework and a covering for the framework, the tubes of the framework varying from each other in cross sectional configuration, to provide an airfoil section tapering from its leading edge to the trailing edge.

4 A propeller having a blade formed with a tubular framework and a covering for the framework, the tubes of the framework being radially disposed and of varying cross sectional shape, the tube adjacent the trailing edge of the blade being flattened with respect to the tube adjacent the leading edge thereof, to provide an airfoil section tapering from its leading edge to the trailing edge.

5. A propeller having a blade formed with a tubular framework and a covering for the framework secured directly thereto, the tubes ofthe framework extending radially from the hub of the ropeller and so spaced relative to each ot er as to present a helical formation, said blade being progressively narrowed from its base to its tip.

6. A propeller havin a blade formed of a tubular framework inc uding three or more radially extending tubes,

of the tubes in the framework being positioned in other than a straight line to provide a cambered airfoil.

7. A propeller having a blade formed of a tubular framework including three or more radially extending tubes, and a covering for the framework, the bases of the tubes in the framework being positioned in other than a straight line and the blade being progressively narrowed from its base to its tip to provide a cambered airfoil.

8. A propeller having a hub portion, three or more tubes mounted on the hub in other than a straight line and extending radially from the hub and a covering for the tubes forming a blade surface.

9. In a propeller structure, a. hub member, radially extending blade frame members, said hub formed of separate axially divided portions with complemental faces, said faces being provided with matching recesses adapted to receive said frame members therein, and said frame members being provided with outwardly'extending flange portions cooperating with said hub to resist centrifugal forces acting on said members during rotation of said propeller, and a covering for said blade frame members.

10. A propeller comprising a hub split along a helical path, radial tubes mounted in said hub along said path forming tension members for the blades of said propeller, and a covering for said tubes.

11. A tension member for a propeller blade comprising a tubular member flanged at its inner end and braced to withstand centrifugal forces by the addition of a stiffening member secured to said flared end.

12. A propeller comprising a hub and blades, said blades comprising a plurality of tubes secured in said hub and projecting radially therefrom, said tubes varying in size from each other, and a covering for said tubes.

13. A propeller comprising a hub and blades, and blades comprising a plurality of tubes secured in said hub and projecting radially therefrom, said tubes varying in size and length from each other and a covering enclosing said tubes.

14. A propeller comprising a hub and blades, said blades comprising a plurality of in combination,

tubes secured in said hub and projectingradially therefrom, said tubes varying in size and cross-sectional configuration from each other, and a covering enc osing said tubes.

15. A propeller comprising a hub and blades, Sald blades comprising a plurality of tubes secured in said hub and projecting radially therefrom, said tubes successively varyingfrom each other in size from one edge of prising a hub, a propeller blade frame work, comprising tubular members radially arranged w1th respect to the hub and being spaced about the hub along helical lines, an airfoil covering ering being tapered from its leading to its trailm edge and being tapered from the root thereo outwardly to the tip in such manner that equal increments of area exertequal thrust, one of the tubular frame members being disposed in the leading edge of the airfoil cover and other frame members being tapered outwardly and the tips thereof being disposed in spaced relation with respect to each other in the trailing edge of the blade, the root of the blade covering being secured to a hood which encloses the hub and the inner ends of the tubular frame members.

JOHN SQUIRES.

for the framework, said cov-' said blade to the other thereof, and a covering for said tubes.

16. An aircraft propeller structure com-

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