US 3374973 A
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March 26, 1968 D. T. LOKERSON DRAG DEVICE Filed April 6, 1966 INVENTOR DA l/ID 7'. L O/(EPSOIV ATTORNEY}.
United States PatentOfiice 3,374,973 DRAG DEVICE David T. Lokerson, Silver Spring, Md., assignor to th United States of America as represented by the Secretary of the Army Filed Apr. 6, 1966, Ser. No. 540,774
9 Claims. (Cl.,244--138) This invention relates to a drag. device, and more particularly to an aerodynamic decelerator banner .array used to produce aybraking effect on airborne vehicles and falling bodies.
In the testing and operational evaluation of rockets and other missiles containing recorded flight data it is necessary to locate the rocket or missile after impact in order to recover the data, as well as costly instruments and components. Where large test ranges are employed, a relatively small missile is almost impossible to locate, particularlyif radar or optical tracking cannot be utilized. Furthermore, the missile maybury itself into the earth upon impact leaving little or no evidence of its location. A number of methods of recovery have been employed in the past with varying degrees of success.
One method :of recovery involves the use of a radio beacon carried with the rocket or missile and ejected automatically prior to impact. The radio beacon then trans- -mitsradio signals to mark the location of the rocket or missile for subsequent recovery by search teams. A problem attendant "to this method of recovery is the protection of the mechanical and electronic components of the radio beacon from the impact .shock when the beacon strikes the ground. Various impact dampeningdevices may be employed on the beacon itself, but it is also desirable to utilize a preliminary decelerating effect while the beacon is still airborne. Various drag devices such as parachutes,
:drag .fins, trailing balloons and streamers are well known in this art, but each of these devices has limitations which are undesirable in this application, particularly where the beacon may experience tumbling after ejection. In addition to decelerating the beacon to a velocity within the capabilities of the mechanical impact dampening mecha- .nism employed, thebeacon must be oriented properly to strike the grou nd in such fashion that the impact dampening devices on the beacon will work properly.
Accordingly, it is an object of this invention to provide a drag device which will be both effective as an aerodynamic decelerator means and as a means for orientinga falling body in a predetermined position to assure proper impact with the ground.
Another object of theinvention is to provide a drag device which will be effective in decelerating falling i bodies regardless of whether or not the descent is smooth or accompanied by tumbling of the body.
A further object of the invention is the provision of a drag devicein which the maximum allowable drag is effected with a minimum area of exposed material.
A still further object of-t he invention is the provision of a drag device which reduces or eliminates the high snatch forces attendant conventional drag devices such as parachutes.
Still another object of the invention is the provision of a drag device requiring no special release or motive mechanisms.
These objects and features are realized in an array of polyurethane banners mounted in pairs on cross-arms which are attached to a nylon tow rope. Each banner is proportioned to give maximum effectiveness for the exposed area of material.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment Patented Mar. 26, 1968 of the invention, as illustrated in the accompanying drawings in which:
FIG. 1 is a perspective view of a falling beacon with a trailing banner array constructed in accordance with the principles of the present invention; and
FIG. 2 is a plan view of a portion of the banner array.- v
The invention will be understood more readily by referring to the drawing in which FIG. 1 shows a radio beacon 1 having a drag device 3 in the form of a banner array attached thereto by means of a nylon tow rope 5. The array is made up of spaced pairs of banner elements such as shown at 7, 7' and 9, 9'. The banners 7, 7' and 9,9 are fastened to banner support members 11 and 13, respectively,-which are spaced along tow rope 5 and disposed perpendicularly thereto. Each of the banner support members 11 and 13 has a tapered hole in the central portion thereof through which passes the nylon tow rope 5. In order to prevent the banners from sliding down and bunching together along the tow rope protuberant portions 17 and 19 are provided, for example, by stitching through the nylon rope with additional thread to form an enlarged portion which will-not pass through the tapered holes in the banner supports. The banner supports then are secured firmly in place by wedging over the protuberances 17 and 19.
The banner, members 7, 7' and 9, 9' are secured to the banner support members 11 and 13 by folding a portion of each banner thereover and securing by gluing, stitching, heat (sealing, or other suitable method. The banner elements may be formed of any desired material, but it has been found that many materials break or tear because of the fluttering effect produced in flight. A polyurethane elastomer sold commercially by the Sieberling Rubber Company of Newcomerstown, Ohio as No. URSOT has been found to be ideally suited for this application and has never broken or torn in wind tunnel or actual flight tests.
In designing a drag device for a radio beacon capsule having an overall length of approximately 8 inches and a diameter of approximately 3 inches with a weight of about 2 pounds, it was found that a banner array of 20 polyurethane-banner members attached to a .inch Woven nylon tow rope produced a tested drag force at 1,000 feet per second velocity of pounds. The .total banner array is approximately 3 feet in length, and each individual banner is /8 inch wide by 3 inches longv by 0.01 inch thick. The drag effectiveness of this banner array is estimated to be 50% of that of the same total flat plate area if .the fiat plate is headed directly ,into the wind.
A necessary property of the material used for the banner element is that of a restoring force. In wind tunnel testsfabrics with no restoring force to hold them in a flat plane stalled repeatedly with the flag or banner curved acrossthe direction of, the wind, and drag dropped to a low value. Materials having the requisite restoring force, however, never stopped fluttering. The aerodynamicdrag produced by the device of this invention appears to be caused primarily by energy transfer resulting from banner flutter and attendant air turbulence.
The drag of a fluttering banner was evaluated and reported on by R. S. Fairthorne in an article entitled Drag of Flags, Aeronautical Research Committee Reports and Memoranda No. 1345, London, 1931. Fairthorne found the drag coefiicient K to be E. E K 0.39( 1.25x +0.012
where b=the length of the flag in the direction perpendicular to the flow of air c=tl1e length of the flag in the direction of the flow of air v Thus rewritten,
Then the drag force:
where A=bc=area banner V=velocity This indicates that the drag force decreases slowly as the length c is increased. These equations were derived from the study of large flags of small mass per unit of flag area. Fairthornes work indicates that large drag coeflicients are possible, and in wind tunnel tests it was observed that when the banner length exceeded a certain length L which is dependent on the mass per unit area of flag material W, drag stopped increasing significantly and the banner fluttered only over the critical length measured from the trailing end. In air and atmospheric pressure for materials having a mass per unit area W of 0.01 to 0.25 pounds per square foot, the critical length in inches was approximately L =1.5 +5 SW. The drag coefficient was found to be:
K=O.5 when 03L and and the 0.05, by surface friction. Tests also showed that when K 0.05 when C 2 L the flag tends to twist and prevent fluttering, so that K becomes very small. The drag force is then, F= /zKpbcV The wind velocity needed to support fluttering depends on the materials stifiness. All materials fluttered when tested in wind velocities less than 50 fps. The flags appear to cause the same drag in very turbulent air as they do in smooth air. The flags in the beacon drag system are spaced one directly behind another connected to the beacon by a nylon rope, yet the entire drag system exhibits a drag coeflicient of 0.5.
From the foregoing description it will be appreciated that the device of the present invention provides a large aerodynamic drag per unit of the packing volume of the device, a factor which is critical because of limited space in airborne devices. The banner array can compete with parachute devices in this respect. The banner array is virtually foul proof and eliminates the high snatch forces attendant to parachutes and other conventional drag devices. The elongated flexible tow member facilitates release of the banner array and no special release or motive devices, such as would 'be required in parachutes, ballons and folding fin devices are required.
While the invention has been shown and described with particular reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.
What is claimed is: 1. A banner drag device comprising a rope like elongated flexible tow member, a plurality of longitudinally spaced banner support members mounted on said tow member, and a plurality of banner members mounted on said support members, each banner supported by a single support member to form an array of banners. 2. The combination according to claim 1 wherein the length of said banner members is determined by the formula L 1.5 +5 5 W where W is the mass per unit area of the banner material in pounds per square foot and L is'expressed in inches. 3. The combination according to claim 2 wherein said banner members are made of a polyurethane elastomer. 4. The combination according to claim 3 wherein said flexible tow member is a nylon rope. 5. A banner drag device for decelerating airborne objects comprising an elongated flexible tow member a plurality of longitudinally spaced banner support members mounted on said tow member, and a plurality of banner members mounted in pairs on said support members to form a tandem array of banners. 6. The combination according to claim 5 wherein the length of said banner members is determined by the formula L =l.5+55 W where W is the mass per unit area of the banner material in pounds per square foot and L is expressed in inches. x 7. The combination according to claim 6 wherein W falls within the range of values between 0.01 and 0.25 pound per square foot. 8. The combination according to claim 7 wherein said banner members are made of a polyurethane elastomer. 9. The combination according to claim 8 wherein each banner member is approximately A; 'inch wide, 3
inches long and 0.01 inch thick.
References Cited UNITED STATES PATENTS 3,250,500 5 /1966 Hall 244-153 FOREIGN PATENTS 476,371 5/ 1929 Germany.
MILTON BUCHLER, Primary Examiner.
R. A. DORNON, Assistant Examiner;