US2228524A - Variable pitch propeller - Google Patents

Description

Jan. 14, 1941. t s. T. LAMPTON 2,228,524 2 VARIABLE PITCH PROPELLER Filed Nov. 12,' 1937 2 Sheets-Sheet 1 r I 65672 L Z Z/fiEJIz Jan. 14, 1941. a, T, LAMPTON VARIABLE PITCH PROPELLER Filed Nov. 12, 1957 2 Sheets-Sheet 2 Patented Jan. 14, 1 941 UNITED STATES PATENT OFFICE VARIABLE PITCH PROPELLER Application November 12, 1937, Serial No. 174,136

6 Claims.

The invention relates to airplane propellers and more particularly to the type which embodies adjustable pitch-blades which are adapted to be fixedly secured in different pitch-settings.

One object of the invention is .to provide a propeller oi this type with a one-piece hub-body and improved means for fixedly securing the blades in the body.

Another object of the invention is to provide means for securing the blades in the hub, which comprises a shear-member which is disposed in the hub-bodyand is interposed between the blade and the retaining-nut for the blade.

Another object or the invention is to provide a propeller with a one-piece hub-body in which the blades are axially secured in such a manner asto eliminate unsymmetrical projections on the hub-bodyas well as those portions of the hub that are usually required in securing the blades in the body. The most important advantage of this is the possibility of utilizing preworked stock of regular section and thus reducing the cost of manufacture. Further, the reduction in hubsize results in a consequent saving in weight of the assembly.

Other objects of the invention will appear from the detail description.

The invention consists in the several novel features which are hereinaiter'setforth and are more particularly defined by claims at the conclusion hereof.

In the drawings:

Fig. 1 is a perspective of a propeller embodying the invention.

Fig. 2 is a transverse section through the body 9 of the hub on the longitudinal axis of the propeller-blades, with the blades and propeller-shaft shown in place. Fig. 3 is a similar section of the hub-body, the blades and propeller-shaft being omitted. Fig. 4 is a section on line 1-4 of Fig. 3. Fig. 5 is a longitudinal section of the propeller on the axis of the propeller-shalt. Fig. 6 is a perspective of the shear-ring interposed between the shank of the blade'and the thrust-nut. Fig. 7 is a detail-of the locking-device for the thrustnut.

The invention is exemplified as applied to a propeller-shaft a which is driven by a suitable engine and extends through a head which is mounted on the engine-casing, as well understood in the art. The propeller comprises a one-piece hub-body b and a pair of blades d mounted in the hub for pitch-variation. is preferably formed from rolled stock of suita- .ble material such as medium carbon steel, to avoid stantially free from integral projections.

The hub-body b the necessity of forging the blank into shape to form the body. The hub-body illustrated is machined from a blank consisting of a section of round, rolled stock so that its cylindrical periphery will be straight longitudinally and sub- This body I; is providedwith a bore b extending diametrically therethrough, for the propeller-shaft and the devices for locking the propeller on the shaft. The bore b of the hub is provided with 10 longitudinal splines b to interfit with splines a on the propeller-shaft a. The hub-body is secured against axial movement on the propellershaft. A rear-cone l3 abuts against a spacer M interposed between the head 0 and said cone. 15,

Cone l3 fits into a conoidal seat I) at the inner end of the transverse bore 1) of the hub-body. A split front cone l5 engages a conoidal seat I; in thehub-body. A thrust-nut I8 is threaded to shaft 0. and provided with an annular shoulder ll fitting into a groove in the split cone IS. The split or sectional cone l5'is adapted to .engage a snap-ring l8 fitting in a groove in the bore of the hub-body, for pulling the hub oil the shaft a.- Holes IS in the thrust-nut l6 provide means whereby a wrench or other tool may be applied to it for the purpose of rotating it on the screw-threads on the propeller-shaft. Tightening the nut lli'securely locks the hub on the propeller-shaft against axial movement by set-- ting up a tensile force in the shaft between the cone liand the cone l5.

The conoidal seat I) for the rear cone l3 which is formed in the hub-body is preferably formed entirely within the cylindrical outer contour of the hub-body. An important advantage of this resides in the fact that the boss usually provided may be eliminated and the stresses set up by the tightening of the hub-body against the rear-cone b are carried by the main portion of the hub 40 and not by a relatively thin boss. In practice,

it has been found that where bosses are used they have cracked from initial take-up of the nut. By eliminating bosses, the entire hub-body may be fabricated by machining rolled stock of medium carbon steel with a consequent elimination of expensive forging dies and the cost of forging and, in addition, the possibility of fractures resulting from excessive tightening of;.the

cones, is overcome.

By forming the hub-body symmetrical or cylindrical from end to end and confining the retaming-devices for the blades in sockets in the ends of the body, the outside thereof is kept free from projections. This makes it possible to effeet a saving in cost of fabrication because the machine-work necessary is entirely within the body.

A hole 2| and a pair of adjacent holes 22 at each side of the propeller-shaft and outwardly of the bore 12', extend longitudinally through the hub-body and between the stock of the hub-body between the seats d for the blades. This lightens substantially the hub-body without materially interrupting the lines of stress-flow existing in the hub when in operation.

Each propeller-blade d is provided with an integral annular shoulder or enlargement d at the inner end of its shank and a conoidal face it at its inner end which fits against, and seats on, a conoidal seat b formed in the hub-body. A curved annular face or fillet d is formed between the outer periphery of the annular shoulder (1 and the portion of the shank disposed radially outward thereof to form an angular circumferential seat for the shear-member f. This shear-member consists of a split-ring formed of two semicircular'sections f. The sections 1' of ring I have a circular cross-sectional portion F and an upstanding rib or integral flange .P. The radius of the cross-section of the portions P of ring 1 corresponds with the fillet or radius of face d on the shank of the propeller-blade. This ring serves as a shear-element between the retaining-nut g for the blade.

Nut 9 is formed of a single piece and is provided, for retaining each blade in the hub, with buttress-threads on its outer periphery for engaging an internal screw-thread around a socket b. The inner periphery of nut g is such that the annular shoulder at, which is integral with the blade, can pass therethrough to permit the onepiece nut to he slipped onto the shank of the blade from its inner end and over said shoulder. Sockets 9' are provided in the outer face of nut g to receive a spanner-Wrench for the purpose of rotating the nut to tighten or remove it. The nut g is formed with an annular seat 9 which is curved in cross-section on a radius which corresponds substantially to the radius of the crosssection of the circular portions F of the sections 1' of ring I. As a result, approximately of inner area of the sections J" will fit onto the fillet or annular shoulder d on the blade, and about 90 at the diametrically opposite portion of section 1' will fit on, and be engaged by, the seat g on nut g. The nut y, when rotated to move it inwardly in the socket b in the hub, will engage the sectional-ring f and force it against the annular shoulder 11 on the blade, which will force the conical inner face 11 of the blade (1 against the seat b in the hub-body. In assembling the propeller, the nut g is first slipped over the annular shoulder d on the blade and then the sections 1* of ring I are interposed between the nut and the shoulder and placed together to form the ring I.

When the blade is held loosely in the body of the hub by means of the nut g and split-ring I, it can be rotated on its longitudinal axis to vary the working pitch of the blade. The portion of the ring I which engages the retaining-nut is lubricated prior to assembly, while the portion contacting with the curved shoulder or abutment d on the blade is maintained in a dry condition. When the blade has been turned to the desired pitch-angle and is held in its assigned position.

' the nut 9 will be tightened with asubstantial initial load. Since the friction is less -on the lubricated surface than on the dry contacting surfaces between the split-ring j and the blade, the blade-position will not be altered during the tightening of the nut. Due to the fact that the pre-load is applied at approximately 45 to the longitudinal axis of the blade because of the angular contact between the torus-shaped sectional ring I and the angular face d on the blade, and between the nut and the ring, the radial components of the pre-load force develop a hoop or expansion stress in the retaining-nut g. This callses the nut to expand and take up any existing clearance between the buttress on the nut and the hub-body, which is of importance in overcoming galling due to vibration or shaking of the blade by reason of any such clearance. The nut 9 acts to impose on .the hub-body the outward thrust of the blade. The forces impressed on. a propeller-assembly are proportionate to the square of the propeller speed and, therefore, the

' frictional resistance due to initial loading to prevent displacement or vibration of the blade, re-

mains effective at any speed of the propeller. The frictional resistance preventing the rotation of the blade d occurring at the angularly opposed curved faces of the torus j and between the shoulder d of the blade and g of the nut is pro-- portional to the normal forces and the co-eflicient of friction, a constant. Since the normal forces to which the mating surfaces are subjected are proportional to the square of the speed of the propeller, theresistive force to rotation of the blade is similarly proportional to the square of the speed and compensates for the increased ro tative moment of the blade as the speed is increased. v

The ring I is usually machined as a single piece and subsequently split diametrically at f. The ring is suitably hardened or otherwise heat-treated to present a proper bearing-surface to the angular surfaces on the blade and the retainingnut. The flange f on ring I serves as means for holding the stock in a chuck while it is being machined and also serves as a guide for positioning the ring, which is circular in cross-section, symmetrically on the curved annular shoulder a A resultant advantage of this construction is that a split retaining-nut for clamping the blade into the hub and a nut on the outside of the hub-body are avoided. A split retaining-nut with an external screw-thread presents difficulty in aligning the sections which are avoided by the one-piece retaining-ring of the invention.

Nut 9 is locked against rotation during the operation of the propeller by plates 30 which are provided with teeth to interfit with an annularseries of gear-teeth 3| integrally formed on, and at the ends of, the sockets b in the hub-body. A pair of screws 32 are adapted to secure each plate 30 on the outer face of nut a and locked to the hub-body. Plural pairs of holes 33 are formed on the nut 9 so the plates may be accurately set to lock the nut in the hub in any position to which it may be rotatably adjusted.

The invention exemplifies a propeller-hub embodying a one-piece hub-body which is symmetrical from end to end so it may be fabricatedfrom a section of rolled metal stock or steel and without the use of expensive forging dies. It also exemplifies means for axially securing a blade in a one-piece hub by means of a nut inside of the hub-body and a sectional shear-member between the blade and the nut which facilitates the as' sembly of the blade of the propeller. It also exemplifies securing-means for the blade which includes a one-piece nut and means whereby the 50 surfaces between the shoulder and the element,

initial loading and the centrifugal-force, during operation, will exert expansion-stresses on the nut to take up any existing clearance between the threads on the nut and the hub-body to overcome any vibration or. shaking of the blade in the body. It also exemplifies a simple and efficient construction for propellers with adjustable pitch-blades which can be economically produced. The invention is not to be understood as restricted to the details set forth, since these may be modified within the scope of the appended claims, without departing from the spirit and scope of the invention.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent i. In an adjustable pitch aircraft propeller, the combination of a one-piece hub-body, a blade rotatable in the hub for pitch-variation and provided with an integral projecting shoulder. in the hub, a one-piece retaining nut for the blade, screw-threaded to the body, and a split torus interposed and jammed between the shoulder of the blade and the nut, the shoulder on the blade having means for exerting radial. expansion stresses on the torus, and the torus having means for radial expansion of the nut.

2. In an adjustable pitch aircraft propeller, the combination of a one-piece hub-body having a socket with an internal screw-thread, a blade rotatable in the hub for pitch-variation and provided with an integral projectingshoulder in the hub, a one-piece retaining-nut for the blade provided with an external screw-thread for engaging the screw-thread in the hub and having an opening of greater diameter than the shoulder,

and a split torus interposed and jammed between the shoulder of the blade and the nut, the shoulder on the blade having means for exerting radial expansion stresses on the torus, and the torus having means for radial expansion of the nut.

3. In an aircraft propeller, the combination with a hub body, and a blade rotatably adjustable in the body for pitch variation, provided with an integral projecting shoulder inside the body, of means for maintaining the blade in fixed pitch settings comprising a retaining member around the blade and secured in the outer end of the body and a shear element between the shoulder! on the blade and the retaining member, the engaging and between the element and the retaining memher, being shaped and opposed to jam the shear element between the retaining member and the shoulder with a substantial component or the jamming forces exerted in adirection normal to the longitudinal axis of the blade for increasing the restraint of the blade-against rotative forces when the blade is in operation.

4. In an adjustable pitch aircraft propeller, the combination with a hub body, and a blade rotatably adjustable in the body for pitch variation, provided with an integral projecting shoulder inside the body, of means for maintaining the blade in fixed pitch settings comprising a retaining nut around the blade and secured in the outer end of the body and a shear ring between the shoulder on the blade and the nut, the engaging surface between the shoulder and the ring, and between the element and the nut, being shaped and opposed to jam the ring between the retaining member and the shoulder with a substantial component of the jamming forces exerted in a direction normal to the longitudinal axis of the blade for increasing the restraint of the blade against rotative forces when the blade is in operation.

5. In an adjustable pitch aircraft propeller, the combination with a hub body, and a blade rotatably adjustable in the body for pitch variation, provided with an integral projecting shoulder inside the body, of means for maintaining the blade in fixed pitch settings comprising a retaining memher around the blade and secured in the outer end of the body and a shear element between the shoulder on the blade and the retaining member, the engaging surface between the shoulden and the element, and between the element and the retaining member, being opposedly inclined relatively'to the axis of the blade to jam the shear element between the retaining member and the shoulder for increasing the restraint of the blade against rotative forces when the blade is in operation.

6. In an adjustable pitch aircraft propeller, the combination of a shaft, a plurality of blades, a one-piece hub-body having its-outside substantially symmetrical from end to end and provided with seats for the inner ends or the blades, recesses around the blades at its outer ends, and a transverse bore for the shaft, and means, comprising nuts in said recesses and threaded'to the body, for retaining the blades in fixed position in the body, the body being provided with holes extending longitudinally therethrough between the seats outwardly of the bore, and of sumcient area to substantially reduce the weight of the body.

GLEN T. LAMPTON.

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