US2917255A - Self-regulating rotochute - Google Patents

Description

w. H. A. BOYD 2,917,255

2 Sheets-Sheet 1 WILLIAM H. .4. 50m

INVENTOR SELF-REGULATING ROTOCHUTE Dec. 15, 1959 Mfg Filed Aug. 1, 1958 Dec. 15, 1959 w. H. A. BOYD 2,917,255

SELF-REGULATING ROTOCHUTE Filed Aug. 1, 1958 2 Sheets-Sheet 2 INVENTOR 22 WILLIAM H. A. Bow

United States Patent 2,917,255 *SELF-REGULATING ROTOCHUTE' William Hunter A. Boyd, Kensington, Md., assignorto the United States of America as represented by the Secretary of the Army Application August 1, 1958, Serial No. 752,676

3 Claims. (Cl. 244-138) (Granted under Title 35, US. Code (1952), sec. 266) cause rotochutes fall almost vertically from the point, of

air drop, thereby making possible accurate aiming of the object to be dropped.

Rotochutes incorporatea plurality of blades .which are I W which is tobe supported in descent is fastened to adapted to rotate and provide lift as the rotochute falls 1 through the air,.-thus slowing the rate of descent. It is of considerable importance that the blades reach a high rotational speed as soon as possible afterthe rotochute is dropped so that an immediate lift can be created by the blades. a high initial speed of descent which is hard to reduce.

It is also important that the blades not be permitted to reach excessively high rotational speeds during the drop which would damage or break-up the 'rotochute because of the severe centrifugal forces developed. i 4

Prior art rotochutesordinarily incorporate a high blade pitch to produce a relatively high initial blade rotational speed. To prevent thisrelatively high pitch from, producing excessiveblade rotational speeds, gover- This will prevent the rotochute from attaining r y nor-type devices responsive to the centrifugal forces produced by the bladeshave been used to keep the blade rotational speeds at asafe value. These devices add undesirable weight to the rotochute and greatly increase the cost andcomplexity of the resulting rotochute.

Accordingly, it is a principal object of this invention to provide an improved rotochute which is cheap, simple, and easyto manufacture. v

.. It is a further object to providean improved rotochute for producing a large initial torqueso as to rapidly bring the blades up to speed. As the blades speed up, the centrifugal forces produced by blade rotation act on the flexible strip reducing blade pitch. By suitable design of the flexible strip, therefore, the blades may be prevented from reaching an excessive speed. 7

The specific nature of the invention, as well objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

Figure 1 shows a side elevation of the rotochute in accordance with this invention.

cylindrical tube 11in any convenient manner. A generally cylindrical collar 12 is coaxially and rotatably connected to tube 11 and may be locked vto tube 11 by set screws. 27. Ball or roller bearings (not.shown), seated in grooves in collar 12 and tube 11,v may be used topermit rotationofcollar 12.when set screws 27 are removed.

.Tube 11 can thereby remain substantially stationary when the collar 12 is rotated if so desired. The collar 12 has flange member. 38a and 38b forming cutout portions 12a and 1211, respectively. These cutout portions are adapted to pivotably receive blocks 16. having blades 13 and 18a aflixed thereto. While two blades 18, 18a are shown in Figure 1, .it is evident that any number of blades can :be used.. All blades are preferably of the same size and shape, and are preferably symmetrical. to collar 12. Since all blades are constructed the same, reference in this descriptionwill be made only to .oneblade 18 and its connection to collar 12 at cutout portion 12a. Q

The block. 16, to which the blade 18 is affixed by screws 17, extends into the cutout portion 12a. of collar .12. The.block. 16 has a bore 16a therethrough which is coaxial. withjbores 13 and 14 in flange members 38b. ,Pin 15 passesthrough the bores 13, 14.,and 16a so as to pivotably connectfthe block 16to the collar,12.. Pin 15 is perpendicular to: the axis of rotation or, collar 12 and permits .block 16 to pivot at the endsof'collar 12. This permits the blades 18 and 18a to beifo'lded down against the tube 11 during storage anditransportation.

The blade 18 comprises two membres, an inflexible relatively long inner blade member 19. and a flexible relatively short outer blade member or impeller 22. Block 16 is provided with an inclined flat surface 16b which is at a small. positive angle with respect to theaxis of rotation of the collar 12. This angle is the angle of attack and is referred to by the lette'r A in Figure 2. Since inner blade 19 is afiixed to block 16 at one end by screws 17', the inclination of surface 16b determines the pitch of inner blade 19 relative to its axis of rotation.

' 3 Thus when the rotochute is dropped from a height, it

as other ordinarily will turn in the direction from its leading edge 21 to .its trailing edge 21a-as a result of the positive angle of attack of inner blade 19.

At the outermost end of inner blade 19 is outer blade or impeller 22. Outer blade 22 is fixedly connected to the end of inner blade 19 by rivets'2llor other suitable means. vOuter blade 22 is-flexibleand is made of considerably thinner material than inner blade 19. Thus, while inner blade 19 is. substantially inflexible, outer blade 22 is relatively flexible. Inner blade 19.and outer blade 22 can be composed of'any suitable material, such as copper beryllium, aluminum or plastic.

As shown in Figure 4, impeller 22 is bent along line 23 to form a first part 26 and a second part 25. First part 26 is substantially coplanar with inner blade 19 while second part 25 is bent at a substantial angle with respect to the planes of blade 19 and first part 26, thereby forming a negative angle of attack. Line 23, which defines the line of bend, extends from the leading surface 24 of outer blade 22 at a substantial angle to the longitudinal axis of the inner blade 19 and outer blade 22, and across the surface of blade '22 to the trailing edge 24. It is important that the line of bend be at a'substantial angle to the longitudinal axis or the inner blade 19 and the outer blade 22 so that centrifugal forces-produced by blade rotation will act to reduce the angle of bend. The action of these centrifugal forces on the flexible impeller will be described later.

The operation of the rotochute 10 may be deserib'ed as follows. Initially blades '18 and 18a are folded down so that their longitudinal axes'are substantially parallel to the longitudinal axis of tube 11. 'The blades 18 and 18a are held locked in this position by any suitable means (not shown) until the rotochute T is dropped. 'Air striking outer blade 22 causes outer blade 22 to open the blades 18 and 18a to theposition shown in Figure l'immediately after the rotochute is dropped. As explained previously, it is'ini'portant that the blades 18 and 18a reach a high initial speed as soon as possible so that an immediate lift can reproduced to slow the descent o'f'wei'ght W. Outer blade 22 accomplishes this by adapting the bend of the impeller to provide a'high initial pitch, thereby developing a large starting torque to turn the blade 18. Thepitch of the impeller 22 which drives the blade 18 must therefore necessarily be opposite to the pitch of the inner blade member 19 which provides. lift. Also, it is evident that the initial driving pitch of the impeller 22 must be considerably greater than that of the inner blade '1'9to provide the desired operation.

While it is important that the blades 18 and 18a be driven at a high speed as soon as possible to create lift, it is also important that the blades 18 and 18a not reach aspeed where excessive centrifugal forces would be developed, as would be the case if the high pitch of the outer blade 22 remained constant; This problem is overcome by means of the flexible impeller 22. Centrifugal forces acting on the bent second part 25 of the impeller 22 reduce the angle of bend, thereby decreasing thedriving pitch. It can be seen, therefore, that the blades 18 and 18d will thus rapidly be driven to a high predetermined speed and will maintain this predeterminedspeed because of the speed-regulating'action of the flexible impeller 22. It will be understood that this predetermined blade speed and the resulting rate of descent is determined by the pitch'of the rigid inner blade 19, the initial pitch of the impeller 22,'the bend angle and flexibility of the impeller 22 and the load W carried.

When the rotochute 10 is dropped, air resistance acting against blades 18 and 18a may cause these blades to pivot around pin through an angle which is greater than ninety degrees. Thereafter, centrifugal forces developed by rotation of blades 18 and 18a will restore the blades to substantially the horizontal plane, as shown in Figure 1.

In one embodiment of a rotochute in accordance with this invention, the blade 18 is composed of aluminum. Inner blade 19 is 16 inches long, 4 /2 inches wide, /2 inch thick and has a'positive angle of attack A, of four'degrees. Outer blade 22 is Sinches long, 3 inches wide, inch thick and has a negative angle of attack B of 25 degrees.

The angle formed between line 23 and edge 24 is 45 de y gre'es. The outside diameter of the cylindrical portion of collar 12 is 3 inches. When a rotochute having four opposed, equi-spaced blades designed as above, was dropped from an elevation of approximately 3,000 feet, the blades rapidly attained a constant speed of 700 revolutions per minute and supported a load of 40 pounds in descent at the rate of 55 feet per second.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

I claim as my invention:

1. An improved rotochute having self-regulating blade speed characteristics comprising: means to which objects to be dropped can be attached, a plurality of blades connected to said means for rotation about a common axis, each rotatable blade comprisin'g'an inner blade member and an outer blade member, said inner blade member being substantially inflexible and connected at its innermost end to said means, said inner blade member having a pitch so that sa-id inner blade member develops forces of lift when driven in a predetermined direction around said means, said outer blade member afiixed to the outermost end of said inner blade member, said outer blade member being flexible relative to said inner blade memher and having a pitch opposite to, and substantially larger than that of said inner blade member, the size and pitch of said outer blade member being such that said outer blade member develops a torque which drives said inner blade member in said predetermined direction when said rotochute is falling through air, each outer blade member being flexible enough to reduce its pitch in response to centrifugal forces produced by the rotation of said blades, the reduced pitch decreasing the driving torque on said blades, thereby self-regulating the speed of said blades.

2. An improved rotochute having self-regulating blade speed characteristics comprising: means to which the object to be air-dropped can be attached; a generally cylindrical collar connected to said means, the longitudinal axis of said collar being the axis of rotation of said rotochute, a plurality of blocks pivotally connectedto the outermost extremities of said collar, said blocks having surfaces inclined transversely to the axis of rotation of said collar, each of said blocks pivoting about an axis perpendicular to said axis'o'f rotation, a plurality of blade members, each of said blade members comprising a substantially inflexible 'inner blade member and a flexible outer blade member, the inner blade members connected at their innermost ends to said inclined surfaces, the angle of inclination of the inclined surfaces of said blocks determining the pitch of said inner blade members, said inner blade members developing forces of lift when driven in a predetermined direction around said axis of rotation, eachof the flexible outer blade'members aflixed to the outermost end of each inner blade member, said outer blade members having a pitch opposite'to that of said inner blade members, said outer blade members being of such a size and pitch as to drive said inner blade members in said predetermined direction when said "r'ot'o'chut'e is falling through air, each outer blade member 'being flexible enough to reduce its pitch in response to centrifugal forces produced by therotation of said blades, the reduced pitch decreasing the driving torque on said I blades, thereby self regulating the speed of said blades.

3. The invention as defined by claim 2, wherein a first part of each outer blade member nearest said inner blade member is coplanar therewith, and a second part of said outer blade member is bent with respect to said first part, the line of bend being at a substantial angle to thelongitudin-al axis of said first part of each outer blade member.

ReferencesCited in the file of this patent UNITED STATES PATENTS 2,706,097 Johnson Apr. 12, D55

FOREIGN PATENTS 146,516 Great Britain July 14, 1921 432,124 Great Britain July 8, 1935

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