US2400649A - Molded airfoil, especially for sustaining rotors - Google Patents

Description

y 19465 A. E. LARSEN 2,400,649

, MOLDED AIRFOIL ESPECIALLY FOR SUSTAINING ROTORS v F iledFeb. 27. 1942 2 Sheets-Sheet 1 M mm May 21, 1946. A. E. LARSEN MOLDED AIRFOIL ESPECIALLY FOR SUSTAINING ROTORS 2 Sheets-Sheet 2' Filed Feb. 27,. 1942 Patented May- 21, 1946 FFICEV MOLDED AIRFOIL, ESPECIALLY FOR SUSTAINING ROTORS Agnew E. Larsen, Jenkintown, Pa., assignor to Autoglro Company of America, Philadelphia, Pa., a corporation of Delaware Application February 27, 1942, Serial No. 432,544

2 Claims.

This invention relates to molded airfoils. While some of the broader aspects of the invention are applicable to airfoils generally, the invention is particularly concerned with rotative airfoils, and more especially with the blades of aircraft sustaining rotors. Sustaining rotor blades are customaril of considerable length and, therefore, give rise to special problems of struc ture and operationresulting, for instance, from the high centrifugal forces set up in operation.

One of the primary objects of the invention is the provision of a blade which may readily and economically be molded, rather than built up'of many pieces, ashas been customary in the practice of the'prior art. In general, according to the-preferred practice of the present invention, the blade is composed of two portions, one portion constituting a longitudinal strength structure having blade mounting means associated therewith, and the other constituting the molded material which is mounted on and secured to the strength structure and defines the airfoil contour of the blade.

Special features of construction of both of the major parts of the blade are provided for in accordance with the present invention, in order to meet a variety of different problems and requirements, all as will more fully appear hereinafter.

More specifically, it may be pointed out that the invention has in view making possible and practicable the molding of rotor blades from cellular, and preferably resilient, material of the general nature of expanded" or sponge rubber;

Many such materials, having varying degrees of the normal flexing and deformation of the blade which occurs in operation.

By the employment of molded cellular mate rial, lightweight construction is secured, and the total quantity of material used is kept at a minimum. How the foregoing and other objects and advantages are attained will appear more fully from the following description, referring to the accompanying drawings, in which- Figure 1 is a fragmentary perspective view of a blade constructed in accordance with this invention and more particularly illustrating the blade section:

Figure 2 is a plan view, on a reduced scale, of a part of the blade of Figure 1, the central portion and tip of the blade being broken away;

Figure 3 is a view similar to Figure 1 but illustrating a modified blade;

Figure 4 is a view similar to Figure 2 illustrat ing the construction of Figure 3;

Figure 5 is a fragmentary plan view of still another form of blade, with intermediate and tip portions broken away; I

Figure 6 is a fragmentary sectional view, on an enlarged scale, taken as indicated by the line 6-6 on Figure 5; I

Figure 7 is a view similar to Figure 1 but taken generally as indicated by the line on'Figure 6; and

Figure 8 is a detail view of one part employed in the form illustrated in Figures 5 to '7.

In connection with Figures 2, 4 and 5, it may be mentioned that the break in each of these views represents the omission of the major portion of the blade length since, in most instances, sustaining rotor blades have a length of the order of twelve to fifteen times the chord dimension,

The blade of Figures 1 and 2 comprises a longitudinal strength structure taking the form of a tubular metallic spar 9 extended preferably substantially throughout the entire length of the blade. At the inner end of the spar a fitting I0 is provided, having an apertured lug I I by means of which the blade may be pivotally connected to a rotative hub. Preferably, the blade mounting includes at least a flapping pivot providing freedom for movement of the blade transverse its mean rotative path of travel, and also a drag pivot (which may cooperate with lug ll) providing freedom for movement of the blade fore and aft within its general path of rotation. Since,

such pivots form no part of the present invention per se, only brief reference is made thereto.

The blade is preferably built up by initially forming upper and lower blade sections l2 and I3, adapted to interflt at mating surfaces lying generally in the mean plane of the blade. Each section is molded of cellular material and is provided with an elongated groove or recess adaptedto fit the spar 9. When assembled, the two sections preferably define .the complete airfoil contour of the blade, the sections being joined at the junction line I4 in the manner described more fully hereinafter,

It may be noted that Figure 2 illustrates the spar 9 as laid in the spar recess of the lower section l3 of the blade.

As will be observed from inspection of Figure l, the outer surface layer l5 of the molded cellucome very close to the spar 9. This is proofing dope or paint. Alternatively, be applied to the surface in a manner discussed spar, I prefer to employ.

exterior metal surface of two sections of the blade, or

Y highly advantageous from the In, this form of construction,

than interior portions of the blade, this denser layer being indicated by heavier stippling. Similarly, a denser layer l6 occurs'immediately adjacent to the spar 9, and in the preferred practice these dense layers l5 and I6 merge, or at least. each other, *above and below of advantage-in contributing to the strength of the cellular molded material.

A dense section II is also provided at the nose is of the blade, and another similar section I 8 at the trailing edge, these dense nose and trailing edge regions acting somewhat in the manner of nose and trailing edge stringers for stiffening and I reinforcing the blade. The nose region I the further object and advantage of mainta g the sectionalpenter of gravity of the blade well forward, which is of importance for aerodynamic reasons which need not be considered herein.

. or partial ribs spar are provided with flanges a projecting rearwardly therefrom 'a greater distance than in Figure 2, each of these flanges 20a desirably projecting part-way into a bulkhead 23 for reinforcement thereof.

Ports 25 in the bulkheads serve to interconnect carried by the the several cavities 24, and provision is made for has 15' venting these spaces, as through a vent 26, located adjacent the tip of the blade. Undesired buildup of pressure within the cavities 24 toward the .outboard end of the blade under the action of centrifugal force is thereby avoided.

,The blade structure of Figures 5 tot! inclusive is also built up on a longitudinal strength struc-- ture, taking the form of spar 21 of the general type shown in patent of Paul H. Stanley and Agnew E. Larsen, No.

- 2,272,439 granted February 10, 1942.

In accordance with the preferred practice, all 20 of the dense portions of the cellular molded material (I5, l6, l1 and iii) are provided by curing or heat treatment, such as vulcanizing,'this heat treatment process being effected in a manner to at least partially eliminate the voids in face layers and in the nose and trailing edge strips. In this way, not only the strength ofv the blade is enhanced but, in addition, a smooth exterior surface is provided. The surface may be finished by application of suitable weatherfabric may hereinafter in connection with the third form of blade disclosed.

With reference to the attachment of the mold- 'ed sections I2 and 13 to each other and to the brass .or copper plated. Similarly, the two sections oftlie blade may be directlyvulcanized to each other at their mating surfaces.

Bonding may also be achieved by the use of adhesives, either at the mating surfaces of the at the spar, or both.

In any event, the bonding of the molded matethe sur- 5 One of the primary differences between the blade here shown and those previously described is that the blade is molded in sections adapted to be arranged in a series lengthwise of the blade, each section defining the full cross sectional contour of the blade. Figure 6 illustrates portions of blade sections 28 and 30,and also the intermediate section 29 in full, and from examination of this bonding for this pur- With vulcanizable materials, the blade sec- I blade accordance with the description of Figures 1 to 4 rial to the spar throughout the length thereof is standpoint of transmitting the centrifugal loads from the molded material to the spar and from there through the root end mounting to the rotor hub.

Thebonding may also serve to secure the molded material to the spar in torsion.

If desired, collars l9, having flanges or-partial ribs2ll, may be secured to the spar at spaced intervals, as indicated in Figure 2, and fitted or ther enhance the keying of the blade proper to the spar,

view it will be seen that each section is provided with an aperture the several sections being serially threaded onto the spar. I p

A further characteristic of the blade of Figures 5 to 8 is the fact that outboard sections of the blade are of corresponding spar 21. As shown in Figure 5, the plan form-of the blade as a whole may also be taperedtoward the blade.

that each section of the be molded of material in the outboard end of It is contemplated here shown shall inclusive, althoughthese sections are desirably molded as units, rather than formed of upper and lower mating halves.

In building up the inboard end section is spar from the outer end 3| is threaded onto the spar tion so as to transmit force from the inboard molded section to the spar. This procedure followed for each successive section of the blade, working outwardly toward the tip. The rib 3| is provided with a flange 32 or other suitable means forwelding or other attaclnnent to the spar.

When all sections of the blade are assembled on the spar, junction strips 33, forinstance of rubberized fabric, may be. applied to join the first threaded onto the thereof, after which a rib and secured in posimating surfaces of adjacent sections and proembedded in the molded cellular material to fur- Many features of the arrangement of Figures 3 and 4 are similar to thosedescribed above. Here, however, the elliptical tube 2| and each of the blade sections l2a and He is provided with a series of recesses 22 .to the rear of the spar, the recesses being separated .by bulkheads 23. The recesses and bulkspar takes'the form of an 05 in combination with heads of each blade section are located so as to register when the two sections are brought together, thereby forming a series of cavities such as indicated at 24 in Figure 3, for lightening the trailing edge portion of the blade. 7

the collars I M.

vide a smooth exterior surface. Following this, a fabric covering 34 may be applied and doped in place.. In applying the fabric covering (which,

as before indicated, may also be used in the blades of Figures 1 to 4 inclusive) adhesive or dope may be relied upon for securing the fabric in place molded material. It maybe mentioned that this expedient may be employed as an alternative or the surface layer of increased density, in order to provide the desired strength-.- ening, reinforcement and surface.

While the ribs i l 'in the arrangement ofFigtires 5 to 8 may be the means relied upon for transmission of the centrifugal load from the an elliptical step-tapered adapted to receive the spar 21,

thickness,v somewhat to the taper steps of the blade of Figures 5 to a, the

the load of centrifugal if desired, heat may be applied so as to embed the fabric directly in the surface layer of the smoothness of the blade blade sections to the spar, even in this form the blade sections are also preferably bonded directly to the spar, as described above.

A ballast rod 35 may be threaded into apertures provided toward the nose of the blade sec- 1 tions for the purpose -of maintaining the cross sectional center of gravity well forward.

I claim: 1. An aircraft sustaining rotor blade comprising a main longitudinally-extending metallic spar; a plurality of retaining members fixedly located on said spar at intervals along its length; a plurality of blade body members of molded homogeneous material, said body members having cavities abaft the spar and bulkheads separating the cavities, and said body members further being preformed to receive the spar, to engage the retaining members within the bulkheads, and to matei'n abutting relationship; and an external covering of sheet material, said blade body members being mounted on said spar in abutting relationship and being secured by bonding as against ,relative movement of one member'with respect to another, and being secured asa ainst displacement lengthwise of the spar by said retaining elements, and being, further secured as against disruptive forces, by being bonded to said sheet material in the region of the joints between abutting body members, said retaining members serving also as stiffening members for the blade the cavities aforesaid.

as a whole. and for the bulkheads lyingbetween I 2. An aircraft sustaining rotor blade comprising preformed to receive the spar, to engage the retaining members within the bulkheads, and to mate in abutting relationship, and an external Q covering of sheet material, said blade body memhere being mounted on said spar in abutting relationship and being secured by bonding as against relative movement of one member with respect to another, and being secured as against displacement lengthwise of the spar by said retaining elements, and being further secured asagainst disruptive forces, by being bonded to said sheet materlal in the regionof the joints between abutting body members, said retaining members serving also as stiflening members for the blade as a whole, and for the bulkheadsdying between the I cavities aforesaid, in which structure means are provided for-venting adjacent cavities lengthwise of the blade and for venting the outermost" cavity to the atmosphere.

AGNEW E; LARSEN.

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