Aerodynamic site marker balloon

Aug. 6, 1968

J. A. MacpADDEN ETAL

3,395,877

AERODYNAMIC SITE MARKER BALLOON

Filed Sept. 26, 1966

Sheets-Sheet 1

<img file="US3395877A_D0001.tif" />

FIE 1

<img file="US3395877A_D0002.tif" />

Aug. 6, 1968

J. A. MacFADDEN ETAL

3,395,877 aerodynamic site marker balloon

Filed Sept. 26, 1966

Sheets-Sheet 2

<img file="US3395877A_D0003.tif" />

United States Patent Office

3,395,877

Patented Aug. 6, 1968

3,395,877

AERODYNAMIC SITE MARKER BALLOON John A. MacFadden and Raymond J. Buresch, Northfield, Minn., assignors to G. T. Schjeldahl Company, Northfield, Minn., a corporation of Minnesota

Filed Sept. 26, 1966, Ser. No. 582,059

Claims. (Cl. 244—33)

ABSTRACT OF THE DISCLOSURE

A lighter than air inflatable structure comprising an aerodynamically shaped envelope having a nose portion, a tail portion and a body portion disposed intermediately thereof, the envelope having stabilizer means secured to the tail portion and comprising an air inflatable duct having an axis disposed and spaced in generally parallel relationship to the axis of the envelope, the duct having a forwardly disposed intake and a rearwardly disposed restricted discharge opening, the envelope being provided with tether line means for tethering the envelope to an anchor point.

The present invention relates generally to a site marker balloon, and more particularly to an inflatable, lighter than air, aerodynamically stable site marker balloon. Balloons of this type may be utilized in tethered relationship above surrounding ground clutter, obstacles, and the like, in order to mark a site which will be visibly ascertainable from remote areas such as, for example, from rescue aircraft, or from distant or remote observation points or may lift, support or carry a radio antenna, a transmitter or receiver aloft.

Frequently, in difficulty traversable terrain, such as in rough or mountainous areas, jungles, or the like, it may become desirable to mark a site from one ground area which will be capable of being spotted or located from remote areas or sites, or to raise an antenna or a transmitter to a suitable altitude. In these instances, when gusty or strong winds are available aloft, site markers, unless arranged in an aerodynamically stable configuration, may be difficult to fly at altitudes significantly above the surrounding terrain. In other words, if the aerodynamics of the balloon are such that it presents too great resistance to the ambient air, the device may be unable to achieve any significant altitude and will be driven or held down against the surrounding terrain or surrounding vegetation such as trees or the like. Thus, in order to successfully deploy such a balloon which is to be employed as a site marker, it must be aerodynamically stable and present a reasonably small profile to the wind, consistent with its being of a sufficient size so as to be located either visually or by reflective signals or the like.

In the past, site marker or antenna supporting balloons have peen proposed which employ a structure which is essentially spherical in form. These devices fail when the ambient atomsphere is either windy, gusty, or otherwise difficult for flying tethered devices. The apparatus of the present invention alleviates these problems by providing an aerodynamically shaped structure which is provided with a tether line, and which is also provided with directional stabilizing devices for controlling the balloon while it is in flight.

_ Therefore, it is an object of the present invention to provide an improved aerodynamically stable site marker balloon which is capable of being tethered under adverse flight conditions.

It is a further object of the present invention to provide an improved aerodynamically stable site marker balloon which is easily fabricated, readily inflatable, and ready for flight without requiring any unusual preparations.

It is yet a further object of the present invention to provide an improved aerodynamically stable site marker balloon which is provided with stabilizer means to enable the balloon to be flown under adverse weather conditions in a tethered condition.

Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims, and accompanying drawings wherein:

FIGURE 1 is a pictorial view showing the site marker balloon of FIGURES 2 and 3 in actual tethered operation;

FIGURE 2 is an elevational view of an aerodynamically· stable site marker balloon fabricated in accordance with the present invention, and showing the ram-filled air scoop disposed at the tail portion thereof;

FIGURE 3 is a vertical sectional view taken along the line and in the direction of arrows 3—3 of FIGURE 2;

FIGURE 4 is a view similar to FIGURE 2 of a modified form of ram-filled air scoop disposed adjacent the tail portion thereof;

FIGURE 5 is a view similar to FIGURE 2 showing a still further modified stabilizer design; and

FIGURE 6 is a view similar to FIGURE 2 showing a still further modified ram-filled air scoop of pillowed form.

In accordance with the preferred modification of the present invention, and with particular attention being directed to FIGURES 2 and 3 of the drawings, the site marker balloon generally designated 10 includes an envelope structure 11 having a nose portion 12, a tail portion 13 and an intermediate body section 14. Secured to the tail portion 13 of the envelope 11 is the stabilizer scoop 15, this stabilizer scoop being secured to the envelope structure 11 along the bond lines 16 and 17. It will be observed that the stabilizer 15 has an axis which is generally parallel to the axis of the envelope 11, and it will be further observed that the stabilizer has a forwardly disposed intake area 18 along with a rearwardly disposed discharge opening 19. The cross-sectional area of the intake opening will be observed to be substantially greater than the cross-sectional area of the discharge opening. This is to permit the ram air to inflate the stabilizer element 15 and maintain it in inflated condition during tethered flight. The aerodynamically stable site marker balloon 11 is provided with tether lines shown at 20, 21 and 22, these tether lines joining at a common apex 23 such as a ring or the like, and this common apex point being in turn joined to the main vertical tether line 24. In some instances, the tether line may comprise a portion of an airborne electronic or electrical system, such as a conductive lead or the like.

As indicated in FIGURE 2, the duct 15 if generally tapered in its configuration along the axis extending from the intake opening to the discharge opening. This generally tapered configuration will, of course, provide for stability in flight, and will also provide for a general maintaining of the inflated condition of this ram air-filled duct.

With attention being directed to FIGURE 3, it will be seen that the balloon device is fabricated from a pair of gore elements 27 and 28, these gores being joined along their common edge surfaces as at 29 and 30. If a material such as polyethylene is utilized, heat sealing techiques may be employed, however, when a difficult heat sealable or non-heat sealable material is being employed, such as polyethylene terephthalate, an alternate bonding technique should reasonably be employed, this being by way of an adhesive such as a thermally activated adhesive, or a conventional solvent adhesive system which may be applied to the surface to be joined, and thereafter cured and dried. It will be appreciated that the bonding tech3,395,877 ³ .

niques which may be employed with the various suitable materials are numerous, and those skilled in the art will be aware of those appropriate techniques.

The technique of bonding the scoop device to the gores such as at 16 and 17 is likewise similar to the techniques used at the juncture of the individual gores as at 29 and 30. Again, those skilled in the art will readily employ suitable techniques of bonding or fusing without encountering unusual problems.

The tether lines 20, 21 and 22 are bonded to the surface of the individual gores by conventional techniques. For example, the tethering element 31 may be bonded to the surface of one of the gores, and this tethering element 31 may be provided with a line retaining loop such as at 32 for holding the tether line 21. Similar line retaining means are available for the tether lines 20 and 22. The envelope 11 is provided with an inflation duct as shown at 34. This duct may be of the conventional type which will permit the inflatant gas to be introduced into the envelope readily and will thereafter retain the envelope in sub- 20 stantially closed form to provide retention for the inflatant gas. As is conventional, helium or hydrogen will normally be employed as the inflatant in these site marker balloons. Suitable hydrogen or helium containing cartridges, or suitable hydrogen generating schemes may be employed 25 to provide the inflatant for the system. These inflatant means are available commercially and as such do not form a part of this invention.

Turning now to the various modifications, such as are shown in FIGURES 4-6, and with particular reference 30 to FIGURE 4, the envelope structure 11 is provided with a somewhat modified form of stabilizer assembly including a plurality of superimposed ducts 41, 42 and 43, each of these ducts being arranged to be inflated by ram air, and each having a generally parallel axis, one to another. 35 Their configurations are generally similar to those of the stabilizer 15 shown in FIGURE 2. As indicated in connection with the device of FIGURE 2 the axis of each of the ducts is again generally parallel to the axis of the envelope structure 11. The ducts are bonded by heat seal- ⁴⁰ing techniques, as previously indicated, the duct 41 being secured to the body of the envelope 11 in the same manner as the device of FIGURE 2, the ducts 42 and 43 being bonded to the generally arcuate segments of the next inwardly disposed duct, as indicated.

Turning now to the structure shown in FIGURE 5, the ^4oenvelope 11 is provided with a circumferential stabilizer device 45 which again is ram-air filled, and which has a generally frusto-conical configuration. The stabilizer 45 is provided with an inlet opening having an area which exceeds that area at the discharge opening or end thereof. ⁵⁰This annular area may be readily calculated.

Turning now to the structure shown in FIGURE 6, the envelope 11 has a modified form of stabilizer 50 at the tail portion thereof, this stabilizer including a generally conically shaped element 51 which is bonded or otherwise secured to the surface of the envelope 11 along seam lines such as at 52 and 53. Preferably, these bond lines run generally parallel to the axis of the envelope 11, and are preferably equally radially spaced.

In one typical embodiment, an uninflated structure having a length of 105 inches and a width of 38 inches was fabricated. The forward portion of the envelope was in the form of a hemisphere, the rearward portion having a taper ratio of 1:4 from the maximum diameter portion to the tail. This provides an assembly having a fineness ratio ^bof 4:1 for the envelope structure. In connection with the stabilizing elements or ducts, these have a preferred ratio of area between the inlet and outlet portions of between 2 and 3 to 1, and preferably have a ratio of about 2.25:1. γθ This provides a maximum degree of stabilizing affect together with a minimum introduction of drag to the system. The length of the duct, in connection with the apparatus of FIGURE 2, for example is 26 inches on the 105 inch long envelope; the linear dimension of the lead portion 75 of that duct is 27 inches with an area ratio of 2.25:1 between the inlet opening and discharge opening. If superimposed ducts are used, each succeeding duct will have a similar configuration, and the next adjacent duct will have a length of about 13 inches with a lineal length of 18 inches on the intake side. Any additional ducts will be preferably in a similar ratio to that ratio shown hereinabove.

While a fineness ratio of 4:1 has been suggested and ₁₀ utilized advantageously, it will be appreciated that a fineness ratio ranging from between about 3:1 and 5:1 may be useful without severely detracting from the aerodynamic stability of the balloon structure.

It will be appreciated by those skilled in the art that 15 the specific examples provided herein are for purposes of illustration only, and are not to be otherwise construed as a limitation upon the coverage to which this invention is otherwise entitled.