US3117716A

US3117716A - Ducted rotor

Info

Publication number: US3117716A
Application number: US272141A
Authority: US
Inventors: Rodney K Wernicke
Original assignee: Bell Aerospace Corp
Current assignee: Bell Aerospace Corp
Priority date: 1963-04-10
Filing date: 1963-04-10
Publication date: 1964-01-14
Anticipated expiration: 1981-01-14

Description

1964 R. K. WERNICKE 3,117,716

DUCTED ROTOR Filed April 10, 1963 INVENTOR. RODNEY K- WEP/V/CK! AT TOPN E Y5 v United States Patent 3,117,716 DUCTED ROTOR Rodney K. Wernicke, Hurst, Tern, assignor to Bell Aerospace Corporation, Wheatfield, N.Y. Filed Apr. 10, 1963, Ser. No. 272,141 7 Claims. ((31. 230-120) This invention relates to ducted propellers, fans, or the like; and more particularly to means for improving the efiiciency of operation thereof.

Whereas it is well known that for maximum efficiency a ducted propeller or fan or the like must operate with minimum blade tip clearance relative to its shroud, due to inequalities of manufacture and typical hazards of usage it has heretofore been requisite to provide an undesirably large gap between the blade tip path and the wall of the enclosing duct in order to insure against accidental collision and/or undesirable frictional contact therebetween.

It is an object of the present invention to provide an improved form of blade for propellers or fans or other rotor arrangements when used in ducted systems, whereby the blade may operate with safety substantially closer to the duct Wall, compared to prior ducted rotor arrangements.

Another object is to provide an improved device as aforesaid an improved rotor blade tip construction whereby the blade tip path automatically adjusts relative to the duct wall to provide minimum clearance therebetween. Another object is to provide an improved blade construction including a floating blade tip shoe which automatically moves into close-fitting relation with the enveloping duct, while at the same time rictional contacts therebetween are precluded.

Other objects and advantages of the invention will appear from the specification hereinafter and in the accompanying drawings, wherein:

FIG. 1 is a fragmentary plan view of a rotor blade and an associated duct or cowling, embodying the features of the present invention;

FIG. 2 is a fragmentary front edge view of the device in FIG. 1;

FIG. 3 is an enlarged scale plan view corresponding to a portion of FIG. 1, but showing a modified arrangement of the invention;

FIG. 4 is a fragmentary front edge view of the device of FIG. 3; and

FIG. 5 is an end view of the rotor blade tip arrangement of FIGS. 3, 4.

FIGS. 1-2 illustrate an embodiment of the invention in connection with a ducted rotor system including a cylindrical duct Within which is rotating a rotor blade designated generally at 12 and arranged to be driven as by means of a rotor shaft 14. The direction of rotation of the blade 12 is indicated by the arrow in FIG. 1. In accord with the present invention the blade tip and portion is hollowed as indicated at 16 to receive in telescopic fitting relation therein a shoe 18 which is generally profiled at its end face to complement the curvature of the cowling 10. In one form of the invention however, as shown in FIGS. l2, the end face 20 of the shoe 18 is curved adjacent its leading edge on a sharper radius than the curve of the cowling 10, so that the leading end portion of the shoe is disposed further away from the cowling 10 than are the main body portions of the shoe. Thus, as the blade swings inside the cowling 10 a quantity of air will be entrapped by the funnel-shaped opening formed between the leading end of the shoe 18 and the cowling 10, and is compressed into the form of an air film upon which the shoe rides as the blade rotates, instead of sliding against the cowling 10.

It will of course be understood that centrifugal forces,

"ice

due to rotation of the blade, will automatically bias the shoe 18 outwardly toward the cowling; but, as explained hereinabove, the film of air entrapped between the shoe and the cowling will preclude any actual contact therebetween. As shown in FIG. 2, the end face of the shoe 18 at the leading edge thereof may be concave-shaped, as indicated at 22; to enhance the entrapment of air between the shoe and the cowling wall for the purpose explained hereinabove.

FIGS. 35 illustrate a modified form of blade shoe arrangement wherein a tension spring as indicated at 25 is provided to assist the film of entrapped air to maintain the shoe in minutely spaced relation from the cowl surface, against the action of centrifugal forces imposed upon the shoe as the blade rotates. In addition, the spring acts to retract the shoe into the blade when the blade is not rotating. FIGS. 3-5 also illustrate other arrangements for mounting the shoe on the blade and for creating the desired air cushion bet een the cowling wall and the blade shoe. Thus, in this case the shoe is illustrated to be of open end form, and mounted and guided to float relative to the main blade structure by means of

pins

28, 30 slidably fitting telescopically in openings formed in the blade structure.

In lieu of forming the leading edge of the blade shoe in funnel-like manner to entrap air as shown in FIGS. 3-5, a ram air inlet opening 26 may be provided in the leading edge of the blade to extend inwardly therefrom and then into communication with a spanwise directed channel 32. The opening for the mounting pin 28 and the air inlet channel 32 may be coincident; for example, the mounting pin 28 may be hollowed to convey the ram air, or a totally separate opening may be employed as preferred. in any case the ram air is thus directed to flow into the interior of the shoe 13 by reason of the air ram and/or centrifugal pumping action, to form a cushion of compressed air between the shoe and the duct wall 14), thereby permitting the overall blade tip structure to follow a path of minimum clearance with the shroud as explained hereinabove.

The blade tip extension or shoe member is preferably formed of some lightweight material such as Teflon or some other suitable plastic material having a low coefficient of friction, because during periods when the propeller is not running at full speed there may be temporary surface contacts between the shoe and the shroud.

It will of course be appreciated that whereas only a few forms of the invention have been illustrated and described in detail by way of example herein, various changes may be made therein without departing from the spirit of the invention or the scope of the following claims.

I claim:

1. A ducted fan assembly comprising, in combination,

a cylindrical shroud,

a fan blade rotatably mounted concentrically within said shroud and having an end portion terminating closely adjacent to but spaced from the inner surface of said shroud,

said end portion of the blade having a recess therein opening toward said inner surface of the shroud,

a shoe device slidably received in said recess for movement beyond said end portion of the blade toward contact with the inner surface of said shrorud under the influence o-f centrifugal force effected by rotation of said blade,

means for rotating said blade in a predetermined direction,

said shoe having an arcuate outer end face of substantially the same radius of curvature as the inner surface of said shroud,

and means for forming a cushion of air bet-ween said shoe and said inner surface of the shroud to maintain 6 said shoe out of contact with such inner surface of the shroud,

said means comprising a leading edge outer end face of said shoe which is of lesser radius of curvature than said inner surface of the shroud.

2. A ducted fan assembly comprising, in combination,

a cylindrical shroud,

a shoe device slidably received in said recess for movement beyond said end portion of the blade toward contact with the inner surface of said shroud under the influence of centrifugal force effected by rotation of said blade,

means for rotating said blade,

means for forming a cushion of air between said shoe and said inner surface of the shroud to maintain said shoe out of contact with such inner surface of the shroud,

and means for mounting said shoe within said blade and resiliently resisting outward movement of said shoe.

3. The assembly as defined in claim 2, wherein said shoe is hollow and provided with an opening at said outer end face thereof,

said means for forming a cushion of air comprising duct means extending from the leading edge of said blade into the hollow interior of said shoe.

4. The assembly as defined in claim 3, wherein said duct means includes a guide pin carried by said shoe and extending radially inwardly therefrom into telescoping relation with said blade.

5. A ducted fan assembly comprising, in combination,

a cylindrical shroud,

means for rotating said blade,

said shoe having an arcuate outer end face of substantially the same radius of curvature as the inner surface of said shroud and being recessed inwardly from said outer end face to provide a pocket opposed to said inner face of the shroud,

and duct means extending from the leading edge of said blade to said pocket to build up a cushion of superatmospheric air therein to maintain said shoe out of contact with the inner surface of said shroud.

6. The assembly as defined in claim 5 wherein said duct means includes a hollow guide pin projecting radially inwardly from said shoe and telescopically, slidably received in said blade.

7. A-ducted fan assembly comprising, in combination,

a cylindrical shroud,

means for rotating said blade so as to urge said shoe radially outwardly toward said inner surface of said shroud,

and said shoe including means cooperative with said inner surface of said shroud for building up and maintaining a cushioning film of air between said shoe and such inner surface of the shroud.

References Cited in the file of this patent UNITED STATES PATENTS 625,182 Mason May 16, 1899 2,776,107 Willi Jan. 1, 1957 2,814,512 Quinn et al Nov. 26, 1957 2,857,150 Sharp Oct. 21, 1958 FOREIGN PATENTS 389,793 Germany Feb. 7, 1924 446,821 France Oct. 11, 1912

Claims

1. A DUCTED FAN ASSEMBLY COMPRISING, IN COMBINATION, A CYLINDRICAL SHROUD, A FAN BLADE ROTABLY MOUNTED CONCENTRICALLY WITHIN SAID SHROUD AND HAVING AN END PORTION TERMINATING CLOSELY ADJACENT TO BUT SPACED FROM THE INNER SURFACE OF SAID SHROUD, SAID END PORTION OF THE BLADE HAVING A RECESS THEREIN OPENING TOWARD SAID INNER SURFACE OF THE SHROUD, A SHOE DEVICE SLIDABLY RECEIVED IN SAID RECESS FOR MOVEMENT BEYOND SAID END PORTION OF THE BLADE TOWARD CONTACT WITH THE INNER SURFACE OF SAID SHROUD UNDER THE INFLUENCE OF CENTRIFUGAL FORCE EFFECTED BY ROTATION OF SAID BLADE, MEANS FOR ROTATING SAID BLADE IN A PREDETERMINED DIRECTION, SAID SHOE HAVING AN ARCUATE OUTER END FACE OF SUBSTANTIALLY THE SAME RADIUS OF CURVATURE AS THE INNER SUREFACE OF SAID SHROUD, AND MEANS FOR FORMING A CUSHION OF AIR BETWEEN SAID SHOE AND SAID INNER SURFACE OF THE SHROUD TO MAINTAIN SAID SHOE OUT OF CONTACT WITH SUCH INNER SURFACE OF THE SHROUD, SAID MEANS COMPRISING A LEADING EDGE OUTER END FACE OF SAID SHOE WHICH IS OF LESSER RADIUS OF CURVATURE THAN SAID INNER SURFACE OF THE SHROUD.