US2730316A - Load-retarding canopy structure - Google Patents

Description

Jan. 10, 1956 L. P. FRIEDER ET AL LOAD-RETARDING CANOPY STRUCTURE 2 Sheets-Sheet 1 Filed June 25, 1951 P. FR' DER WFILTER s, FINKEN m M H m LEONFIRD .LBY

1956 L. P. FRIEDER ET AL 2,730,316

LOAD-RETARDING CANOPY STRUCTURE Filed June 25, 1951 2 Sheets-Sheet 2 L Y INVENTORS LEON'HRD P. FRIEDER BY \NFILTER s. FINKEN Maw HTTORNEY 2,730,316 Patented Jan. 10, 1956 LOAD-RETING CANOPY STRUCTURE Leonard P. Frieder, Great Neck, and Walter S. Finlcen, Brooklyn, N. Y., said Finken assignor to Frieder Application June 25, 1951, Serial No. 233,444-

2 Claims. (Cl. 244-145) This invention relates to parachutes and the like, and is more particularly directed to the provision of improved canopy structure having superior characteristics of retarding force, strength and stability, especially for a fabric canopy assembly of a given size and weight. Further and more specific objects are to provide parachute canopies of novel design and arrangement wherein a high buoyancy or other retarding effect is produced, yet with remarkable stability against oscillation or like undesirable effects and where localized strains of the fabric are substantially avoided; and to produce such canopies wherein for a given diameter, i. e. horizontal dimension, the full advantages of the best of previously produced structures re realized yet with an improved arrangement requiring substantially less fabric and therefore occupying a smaller space when in folded or packed condition, and likewise having substantially less weight, it being understood that minimization of weight and space are extremely important factors for parachute apparatus that is to be carried aloft in an airplane or like vessel or projectile.

A specific object is to provide improved apparatus, e. g. parachute canopy structures of flexible textile fabric, arranged with a multiplicity of shroud lines extending from the hem or mouth region of the canopy to a load, such devices being designed for release at an elevated position and very often at a high speed, the improved characteristics herein below described being designed to afford greater resistance to opening shock, better stability in subsequent free or other flight (while exerting the loadsupporting or retarding force) and greater effective load capacity, especially with respect to the size and weight of the canopy. Further and more specific objects will be explained or will become apparent in the course of the following disclosure of the invention and of its novel principles, as well as its significant features of departure or distinction from prior parachute canopy structures and the like. I

Probably the most widely used type of parachute, at least until very recent years, has involved a so-called flat canopy, e. g. a fabric piece or more commonly a plurality of fabric pieces arranged to lie normally (when not infiated) in a flat plane, the assembly usually having a circular edge to which shroud lines are connected, for convergence to the point of load attachment. When such a parachute blooms in use, the downward pull of the shroud lines and the upward or inward force of air cups the fabric assembly into a shallow, more or less parabolic shape, familiarly characteristic of parachutes. More recently, use has been made of canopies preformed to have a hemispherical contour, for example as described in the prior U. S. Patent No. 2,412,392, granted December 10, 1946, on the application of Walter S. Finken. In such canopies, the several fabric portions which are joined by seams to constitute the finished assembly, are so cut that the canopy, before inflation, assumes a substantially hemispherical shape, reference'to its being preformed thus signifying that if properly supported (but without inflation) the canopy will occupy the described special configuration even when there is essentially no tension in the fabric at any place. Hemispherical canopies have been found specially advantageous, particularly in having much greater stability than the older flat-type parachutes, and likewise in exhibiting improved strength, especially against the sudden shock of opening at high speeds. While the flat type of canopy might be theoretically capable of exerting large retarding force, e. g. a force, in lowering loads, which is akin to and therefore may be conveniently described as a force of buoyancy, the large and unequal stresses in a developed flat canopy, pulling it into the described, shallow cup-shape, have tended to prevent realization of any substantial advantage for such canopies in respect to retarding force. Indeed the customary, theoretical treatment of a flat canopy is to rely chiefly on the so-called velocity head of air entering the mouth of the canopy and moving upward against the fabric; and in order to avoid undue strain on the fabric, a crown or polar opening is usually provided to relieve a considerable part of the velocity head and to promote at least some measure of stability. As indicated, hemispherical parachutes have achieved much better stability in flight, as well as other material improvements, and for many purposes provide a thoroughly satisfactory parachute, affording reliable operation and the realization of satisfactory load-supporting or retarding effect in a fully controlled manner.

It has now been found, however, that the essential advantages of a hemispherical canopy may be well realized in a parachute structure having a novel, preformed shape in accordance with the present invention, while at the same time the improved canopy, for a given diameter or for a given load-carrying or supporting capacity, contains a smaller total surface and is therefore lighter in weight. The improved structure, moreover, affords an optimum realization of the load-supporting strength of the canopy fabric, e. g. both against initial shock and in working condition during flight. More specifically, the improved canopy is preformed to a substantially oblate, curved configuration, a particularly important arrangement being one wherein the canopy has a lower part constituted by a zone or frustum of a hemisphere, surrounded by a polar segment (essentially an upper half) of an oblate spheroid, e. g. a sphercid defined by revolution of an ellipse about its minor axis. Described in other words, a preferred canopy structure of the present invention consists essentially of a multiplicity of fabric pieces (usually textile fabric, although other sheet materials may sometimes be used) so cut and assembled as to provide a preformed cup-like shape of the character just described, for example wherein the mouth or hem line of the canopy (which may be herein identified as the equator of the canopy, in distinction from the equator of any solid figure embodied in the canopy) is constituted by the lower edge of a zone of a sphere, which at its upper edge joins continuously and smoothly with the lower edge of a spheroidal segment that covers the uppermost part and crown of the canopy. Preferably, in most cases, the spherical zone constitutes a zone of a hemisphere wherein the lower edge is an equator of the sphere, the upper edge of the zone being determined by swinging a spherical radius upward to an angle of say 20 to 40 (preferably about 30), the spherical portion thus being essentially a frusturn of a hemisphere. The upper part of the canopy then most advantageously consists of a polar section of an oblate ellipsoid (formed by revolving an ellipse about its minor, vertical axis), such polar section being essentially a zone of one base, the base being preferably cut by a plane which intersects the generating ellipse at'points where the radius of curvature forms the same angle with the horizontal as does the spherical radius at the above described, upper limit of its swing. In other words, the preferred configuration is such that the spheroid and the hemisphere frustum have their respective lower and upper edges meeting tangentially, i. e. so that they have a common tangent at each point of their common, adjoining edges, it being understood that the base of the spheroidal zone is congruent with the upper base of the hemispherical frustum.

It has specifically been found, that when inflated, the entire area of a surface which is preformed to the described shape, provides a smooth, uniformly stressed contour which is inherently and essentially devoid of localized or unequal strains. Indeed, in the preferred embodiments, the fabric stress, i. e. along the surface of the fabric, is believed to be substantially uniform throughout the entire canopy, and at least throughout the upper half or so of the structure. As a result, the canopy may withstand shock or pneumatic pressures up to the full tensile strength of the constituent fabric. Under full strain, either of initial shock or of subsequent load-supporting action, the canopy lies in essentially its preformed hemispherical-spheroidal shape, and there is essentially no high concentration of forces at localized areas or regions, such as tend, for example, in flat-type parachutes, to limit the safe total load or total shock which the canopy may withstand. The load is distributed in a desirably uniform manner, permitting the assembly to withstand or support an essentially maximum value of total load.

At the same time, the structure exhibits a reaction or effect of buoyancy which is substantially greater than can be achieved with a hemispherical canopy of equivalent diameter, i. e. a hemispherical canopy having the same mouth or hem opening. While in large measure (as explained above) attention has heretofore been focused on the effects of velocity head entering the open bottom of a flat-type canopy, and while special arrangements related to such velocity head have been used or attempted (e. g. the customary crown opening of a flat canopy, and likewise special structures such as the so-called ribbon canopies designed to provide a turbine blade effect), we have found that the present, improved canopy provides a greatly enhanced and extremely useful realization of the reaction force that may be defined as barometric buoyancy. For example, in the case of a hemispherical canopy having a closed crown, and particularly havinga crown section of smaller porosity than lower parts of the device (as described and claimed in the copending application of Leonard P. Frieder and Walter S. Finken, Serial No. 122,962, filed October 22, 1949), a well defined region of low barometric pressure exists above the crown when the canopy is expanded and being drawn downward, or otherwise in the direction of its mouth, under load. The pressure difference, thus essentially a difference of static or barometric pressure between inner and outer surfaces of the crown region, affords a substantial measure of the buoyancy of the canopy; indeed, as just indicated, this pressure drop from a somewhat super-atmospheric pressure internally of the crown to a zone or cap of lowerthan-atmospheric pressure above the crown is enhanced both in vertical depth and lateral extent by the provision, in hemispherical canopies, of a crown section having relatively low porosity. In the present spheroidal-hemispherical structures, the low pressure region above the crown is found to be even more greatly enlarged, i. e. extending to a considerably further height above the crown, and having an outward boundary which more nearly equals the width of the equatorial zone of the canopy. In consequence, for a given size of canopy, the buoyancy effect is very significantly larger in the present apparatus.

Indeed, research has indicated that maximum buoyancy of this barometric or static type is achieved by a flat or plane member or crown region. While it might therefore seem that the older, flat-type canopies would be characterized byhigh realization of. such buoyancy effect, they cannot, of course, be maintained in a fiat condition in use. Even though their crown or upper portion is somewhat flattened or curved (when inflated) and may superficially resemble the upper spheroidal part of our improved canopy, such configuration of the older structures is achieved by distortion and non-uniform straining of the fabric body, e. g. to an extentsuch that the tensile strength of the fabric ordinarily limits, in a very serious manner, the extent to which high buoyancy may be there utilized in practice. Furthermore, in the actual structure of flat canopies, the effect is largely vitiated by the crown vent, necessitated for avoidance of oscillation or even worse instability of the parachute. In contrast, the present canopy, which preferably has a completely closed crown (indeed a completely closed surface, except for certain preferred porosity characteristics, as explained below) affords a maximum effect of buoyancy, which can be fully realized because the fabric is uniformly stressed and a much larger load, distributed over the canopy, can be withstood.

At the same time, the present canopy, especially by reason of its lower, hemispherical contour, is characterized by an inherently high stability and an effective control of forces that would otherwise tend to cause spilling of air, oscillation or the like. That is to say, the preformed spherical contour of the zone at the lower part of the structure is found to function in a manner similar to that of the hemispherical canopies, specifically in providing a cone or bow wave of high pressure which projects downwardly or ahead of the canopy opening. Whereas flat-type canopies are often in a condition of unstable equilibrium in that upon anysidewise rocking, air is spilled first from one edge and then the other so as to promote continuance of such oscillation, hemispherical canopies are generally characterized by absence of such spilling or siphoning of air adjacent the mouth, and indeed by the exhibition of forces positively tending to restore the canopy to a position of true flight, e. g. with the axis vertically or otherwise aligned with the direction of drag. It has been found that such stabilizing effects are occasioned chiefly by the shape and structure of the lower part of the. hemispherical canopy, and in consequence the present parachutes are similarly characterized by high, inherent stability. This function of the equatorial region of the spherically-shaped zone is promoted by shroud line suspension means arranged to draw the hem edge somewhat inward, namely in an incurving manner which aids in defining and limiting the. downwardly and centrally sloping wall, so to speak, of the protruding high pressure cone that appears to be present in the use of the present parachutes, just as in the case of well-constructed hemispherical canopies.

The structure and principles of the present canopies may be more fully understood in the light of the accompanying drawings, wherein:

Fig. l is a somewhat diagrammatic perspective view of an embodiment of the. present parachutes, shown in expanded form, as for support of a load;

Fig. 2 is a diagram showing the preformed canopy of Fig. 1 in vertical section, with certain geometric relationships;

Fig. 3 is a schematic view showing one way of laying out suitable goresof which thecanopy of Figs. 1 and 2 may be constructed;

Fig 4 is a planviewof the crown or polar section of the device of Fig. 1;

Fig. 5 is a plan view showing the fabric pieces, in juxtaposed but non-assembled state, employed for the crown section of Fig. 4;

Fig. 6 is a greatly enlarged, fragmentary perspective view showing a suitable structure for the hem of the canopy;

Fig. 7 is a similarly enlarged, fragmentary elevational view showing the. hemregion; and shroud line connections of the canopy in use;

Fig. 8 is a further diagrammatic view, partly in perspective and with a portion of the canopy broken away, to illustrate certain pressure and flow effects believed to exist in the vicinity of the canopy; and

Fig. 9 is a diagrammatic illustration of another embodiment of an improved canopy structure.

Referring to Fig. 1 of the drawings, a parachute embodying the invention comprises a canopy generally designated 10 and made of suitable fabric, e. g. woven textile of nylon, silk, cotton or other material appropriate for such devices. Specifically, the canopy is constructed of a plurality of gores 12 extending from the hem 13 at the mouth or hem edge 14 of the canopy, to the edge 15 of a crown or cap region designated 16, the gores being sccured together, by appropriate seams along their upright edges in a circumferential array around the canopy. Secured in uniformly spaced and distributed arrangement around the circumference of the hem (in a manner more particularly described below) a plurality of shroud lines 18 extend downward to an apex connection at 19, for support of a load diagrammatically illustrated at 20. It may be noted in passing, that parachutes of the sort herein described may be used for a wide variety of purposes, e. g. to support various inanimate loads, such as cargo to be dropped, functioning equipment such as radio or other signaling apparatus, and the like; or the parachute may be of the personnel type, i. e. to support a person descending from aircraft. Other uses include the support of projectiles or unmanned craft which are to be returned to earth after a predetermined flight, and to afford drag or retarding effect in situations of so-called infinite load, e. g. for braking or slowing a fast-moving airplane. It will be understood that in accordance with conventional requirements of parachutes, the size of the canopy, nature and weight of its fabric, arrangement of shroud lines, and other structural characteristics will depend on the spe cific nature and circumstances of use in each case.

As indicated above, the gores 12 are so cut that the canpoy 10 has a preformed configuration such that throughout a region A, having an altitude, say, approximately equal to two-thirds of the total altitude of the canopy from the equator 14 to the apex of the crown 16, is a zone of a sphere, preferably a frustum of a hemisphere having its lower base (at 14) constituted by the base of the hemisphere. The shape of the gores 12 (and the cooperating crown cap 16) is such that the preformed configuration at the upper part B of the canopy is a segment of an oblate spheroid, e. g. essentially the upper half of such figure, arranged as to constitute a surface continuing smoothly from the upper edge 22 of the hemispherical frustum A.

In use of the canopy, e. g. when it is inflated and actually in service to support or retard a load as shown in Fig. 1, the arrangement and effect of the shroud lines 18 s preferably such that the lower edge 14 is drawn slightly inward, e. g. providing a configuration of the canopy surface at 23 which curves somewhat inward from the true spherical surface indicated by dotted lines 24, this incurving portion 23 extending through the hem region and usually somewhat above the latter, although occupying a total space, along the vertical or meridional dimension of the canopy which is a small fraction of the distance A. This incurving arrangement at the lower edge has been found to promote the stability of the canopy and to afford a better control of the high pressure area which projects below the mouth 14, as explained hereinabove.

in Fig. 2, the solid line 10 represents the preformed shape of the canopy, e. g. as seen in vertical section, the incurving portions 23 being here shown in dotted lines. The pole of the canopy is indicated at C and the center of the equatorial plane, i. e. the mouth of the canopy. at D, the line EDP thus representing a diameter of the base or opening of the structure. The distance A, representing the hemispherical frustum, extends from the points E and F to points G and H, at appropriate distances above the base line EDF. As will be noted, the curves EG and PH are circular arcs described by the radius R, from the center D. Above the points G, H the curve GCH defining the upper surface of the canopy is a segment of an ellipse, e. g. approximately the upper half of an ellipse arranged with its minor axis in the vertical direction, along the polar axis CD of the canopy. Since elliptical curve GCH is preferably arranged so that a tangent, as 25 to the circular radius R at H, is also tangent to the elliptical curve at the same point, such point H (and likewise the point G) is then, in strict theory, slightly elevated above the precise horizontal extremity of the major axis 26 of the ellipse. Since the ellipse is preferably a very fiat one (for example having a ratio of major to minor axes equaling 2 to l, or very preferably 3 to l or more) the major axis 26 of the ellipse is displaced only a slight distance below the horizontal line 22a (GKH) and the upper part of the canopy may thus be considered as substantially the upper half of a spheroid defined by revolution of the elliptical curve about the polar axis CD. In fact, in constructing the canopy, it is found that no appreciable fabric strain or distortion, or other departure from the intended results (i. e. beyond an inconsequential stretching of the fabric to a tangent relation at points G and H), is incurred by cutting the gores or other pieces to contours geometrically determined by assuming that the upper part GCH is in fact a complete half spheroid; and such configuration of the canopy is therefore assumed to be employed, for practical convenience and brevity of terminology, in much of the disclosure herein.

Considering the dotted line 27, which indicates the upward continuation of the circular lines EG and FH, and thus the contour of a complete hemisphere of which the frustum A is a part, it will now very clearly be seen that the upper region of the canopy GCH is essentially much flatter than a hemispherical shape.

While other specific proportions and arrangements may be employed in many cases (there being some advantage even to a canopy which is wholly or simply the upper half of an oblate spheroid), special advantage is believed to be achieved, and indeed unusually effective realization of the improved results noted above, where the altitude of the hemispherical frustum A is such that the angle GDE lies between, say 20 and 40, or more preferably from 25 to 35. in the specific arrangement shown, the angle GDE is selected as 30, representing a contour for the complete canopy which has been found to be peculiarly significant in attainment of all of the improved results described above. The altitude CK of the spheroidal segment B may correspondingly vary, in relation to other dimensions of the canopy. Preferably, it may be from one-third to two-thirds of the altitude DK of the hemispherical frustum, unusually satisfactory results being obtained (e. g. in a device wherein the angle GDE is about 30) when CK is approximately equal to one-half the frustum altitude DK. The proportions now given for the various parts essentially determine the complete shape of the canopy (including the curved surface B), an alternative specific mode of defining the surface B being by virtue of its minor and major axes. The major axis is essentially the distance GH, while the minor axis CL (taken as identical with CK) equals a fraction of the distance or amount by which the hemispherical radius R exceeds the altitude DK of the hemispherical frustum A, such fraction being one-half, where the spherical altitude of G and H is 30 as given above. Constructed to have these relationships, the canopy appropriately comprises the flattened, upper surface, GCH, which extends smoothly and continuously from the upper edge of the hemispherical frustum A, the spheroidal segment B then being preformed to the shape into which a fiat parachute canopy (having an ultimately equal, opening radius KG) occupies when distorted by load-supporting, operating strain.

As explained above, the canopy is preformed to the prescribed shape, i. e. so that if it were suspended upside down, it would naturally lie (without appreciable pressure on its surfaces) in the desired configuration, providing the mouth opening l4'is stretched to its intended, full circle". While it will now be apparent, especially in the light of recognized principles of geometry, that gores or other fabric pieces to be assembled for constitution of'the described canopy shape may be cut in a variety of ways, Fig. 3 illustrates in a general and diagrammatic manner, one mode of so fashioning the gores 12. Each of these gores is conveniently of the general shape of the frustum of a spherical triangle, but resting on a rectilinear base 30. Theupright or meridional sides 31, 31 of the gores are conveniently defined by two or more successive curves, each a continuation of the preceding one, and the effective shape of each gore being thus readily determined in accordance with geometrical principles so as to afiford the desired, inherent surface contour for the ultimate assembly of gores sewn edge to edge. Advantageously, each side 31 may be defined by circular arcs of long radius, the portion A (for the hemispherical frustum) being an are ON of a circle having its center at M on the base line 30 (extended), and the upper portion NP being an arc of a circle of longer radius, having its center Q on the line NM extended (so that the two arcs are tangent, i. e. have a common tangent, at N). While the gores might conceivably be fully triangular in shape, e. g'. each extending to an apex S, each is preferably formed with an upper part removed, as indicated at PS, to provide a separate cap or crown structure 16 as indicated above. It will be understood that the number and width of the gores 31 will depend on the mouth diameter, or rather the equatorial circumference, of the canopy, and on the width of textile fabric available. Where a crown structure of the type of Fig. 4 is used, the number of gores is preferably four, or more usually a multiple of four, so that the crown seams may advantageously be a continuation of seams between gores.

Fig. 4 shows the assembled and shaped crown 16 in plan view. While in some cases the crown (having a radius not more, and preferably considerably less than the altitude CK of the spheroidal segment) may be constructed of a single piece of fabric, it is preferable to embody in this part of the canopy, even the relatively small shaping or preforming appropriate to the central part of the flattened curve GCH. While such result may also be obtained with other proportions and configurations of fabric pieces, a preferred structure avoids having any seam or seams extend to or across the pole. Thus the arrangement shown in Fig. 4 embodies a central, outwardly flaring piece 34 and two cooperating segments 35, 36. As shown in Fig. 5, these pieces 34' to 36, when laid out flat, depart slightly from fitting together at' their adjacent edges, but when fitted and sewed by appropriate seams they assume the plan appearance of Fig. 4 with a preformed, slightly convex shape as required for the crown region of the canopy. It will be understood that in the case of all of the several pieces utilized for construction of. the fabric canopy, appropriate principles of parachute manufacture are preferably embodied or followed, the several gores and other members being made of fabric cut on the bias and each being arranged so as to represent a bias relationship to the immediately adjoining. pieces of the assembled canopy. Furthermore, each of the pieces shown in Figs. 3 and 5 will be understood as originally cut with sufficiently excess material along the edges (i. e beyond the outlines shown) to provide the desired seams and the desired hem along the lower edge 30.

By way of specific example and with the understanding that the invention is adapted to a very wide variety of sizes and kinds of parachutes, one very effective parachute canopy embodying the inventionhad an equatorial diameter (EF, in Fig. 2). of 24.25 feet, and was composed of identicalgoresof textile fabric correspondmg.. to the gores::12..in Fig. 3. The crown section, madeas nr'Figs: 4 and s,- hada radiusor Qinches' sniin 5 Fig. 3); ,The'totarauitude- ST or each gore pattern was about "zl tincnes -(les's the crown radius of 9.in'ches), and the altitude WT of the portion corresponding to the hemispherical frustum was approximately 76.2 inches, the distance WN (or WN) being about 19.8 inches, and the base width 00' being 45.7 inches. The radius MN was 949.8 inches and the radius QP 1114.3 inches, it being understood that these and all other dimensions represent the theoretical center lines of the seams and the hem, the usual seam or hem allowances being added as explained above.

While other hem arrangements and likewise other shroud line attaching structures may be employed, Figs. 6 and 7 show a satisfactory construction, embodying certain basic features which are describedand claimed in U. S. Patent No. 2,365,184, granted December 19, 194-4, on the application of Leonard P. Frieder and Walter S. Finlren', the presentely illustrated structures embodyingsome improved features which are described and claimed in the above cited application Serial No. 122,962. Specifically the fabric of the gores 12 is folded back on itself a plurality of times at the hem 13, to constitute a channel or tubular structure 38, the folds being preferably sufficient in number and so arranged that there are three layers of fabric on each face of the central channel 38 as shown. A hem cord 40 extends circumferentially around the canopy, in floating relation within the hem channel 33. Preferably, a supplemental tape 41 is disposed beneath'an'd around the cord 49, providing additional bearing and reinforcing structure for the latter. Appropriate openings 42 are provided at spaced intervals along the hem 13, to permit attachment of shroud lines 1S,there being corresponding openings 43 in the tape 41, so that the cord 49 is accessible at each such locality. The upper end of the shroud line 18 is appropriately connected to the cord at the corresponding opening, for example by provision of a simplelo'op 44 in the shroud line, surrounding the cord. While in some cases a complet'ely floating cord 40 may be employed, the cord may be bartaclted' (by appropriate stitching) at localities 45, 46, close to each opening 42, so as to prevent longitudinal motion of the cord in the hem sleeve. in consequence when the canopy expands, the cord 40 is drawn down to a limited or controlled extent, as shown in Fig. 7, with consequent gathering of the canopy material at regions immediately above and adjacent the opening 42. In this fashion, the desired incurving of the lowermost edge of the canopy is achieved, while preventing excessive withdrawal of the hem c'ord such as might result' in an excessive contraction of the canopy hem line. As stated, Fig. 7 illustrates the operating condition of a portion of the canopy edge, i. e. when the canopy is inflated and acting to support a load, the gathered or rufilcdpart of the fabric being indicated at 47.

In use, the canopy is found to achieve the several advantageous results described above, specifically in the provision of greater buoyancy and thus greater retarding force'for a structure of given size and weight, while at the same time promoting maximum utilization of the shock and load-resisting capacity of the fabric, and affording excellent stability of the device from the time it first opens. Fig. 8 illustrates certain pressure and flow relationships which as indicated above, are at present believed'to' characterize the improved parachute devices. Thus here, the external arrows 50 represent certain major directions of air flow around the canopy, while the cone-shaped downwardly projecting region 52 represents the area of high pressure which is believed to exist, in such configuration, as the canopy moves downward under the force of the load. Above the canopy, and bounded by an upper line 53, there is a space 54 where low barometric pressure is believed to be established, e. g. a region'o'f low'pressure which is almost coextensive in diameter with theca'nopy'md which has a very substantial altitude above'a-Iarge'part of'the' upper canopy surface. The line 55 represents the upper boundary of a hemispherical surface having the same hem opening 14, the region between the line 55 and the line 53 indicating the low pressure area customarily achieved for a hemispherical canopy. By virtue of the much greater depth of the total low pressure area 54, and having in mind that the pressure decreases progressively from the upper line 53 downward, it will be seen that a much more effective lifting or buoyant force is achieved (be tween the high or atmospheric pressure within the canopy the low pressure above the upper surface) by the present structure than even in the case of the hemispherical device.

At the same time, the entire fabric of the canopy 10 is uniformly stressed, so that the load is thoroughly distributed and there are no localized regions of high stress where the fabric reaches the breaking point before other portions are similarly effected. Thus in contrast to the flat type of parachute, the present arrange ment provides a much greater, safe load-carrying capacity, i. c. with respect to a fabric of given weight and strength.

As explained above, the hemispherical shape of the lower part of the canopy cooperates effectively in providing the controlled high pressure cone 52 or how wave, and thus in affording the high stability which characterizes hemispherical canopies and which is generally impossible to achieve (i. e. an avoidance of oscillation or the like) in flat-type parachutes. As a result of all of these factors, the illustrated device provides a stable, highly effective parachute, which has exceptional resistance to opening shocks (that can be very high at the higher aircraft and launching speeds now in use or contemplated) and which can be made of relatively light fabric, with consequent saving of weight and packing space, in great contrast to all types of parachutes heretofore manufactured.

in presently preferred embodiments of the improved parachute structure, the canopy may advantageously have zones or regions of different porosity, with consequent beneficial effect on the opening characteristics and stability of the device. For example referring to Fig. 8, the lowermost zone of the canopy, indicated at 56 and bounded by the hem edge 14 and a circular boundary 52-, may have a relatively low porosity, while a somewhat higher porosity is provided for an intermediate region, preferably the entire region 58 between the circle '7 and the line 22 that divides the hemispherical and spheroidal portions. The crown portion, indeed preferably the entire spheroidal part B, is of low porosity. Such structure has been found to achieve superior results, both in affording rapid and complete inflation of the canopy when it is first released under load, and stability and permanence of inflation during subsequent flight. According to present understanding, the low porosity hem region 56, which may have an extent measured along the meridional curve of the canopy ranging from a few to 5% or of the entire length of such curve from hem line M to the apex C, permits maximum expanding force to be exerted by the pressure of enclosed or incoming air, so as to bring the hem region promptly to its full, desired opening upon initial release of the parachute. The low porosity crown region, which occupies at least a very substantial part and preferably all of the spheroidal zone B, promotes the formation of the desired low pressure area 54 over the upper part of the parachute, it being particularly important that the cap region in be of low porosity and preferably be of mnltiplepiy construction, e. g. with each of the segments to 36 comprising two layers of fabric fastened only at their edges. The double crown structure, in fact, promotes attainment of the desired pressure conditions, especially upon initial opening, by breaking the pressure drop into successive steps, so to speak. At the same time, the higher porosity region 58 is understood to permit substantially greater passage of air (than the other regions) as indicated by the dotted arrows 64), the accompanying dynamic or 1 elocity head cooperating to achieve and maintain inflation at this locality. As will be appreciated, the lower zone 56 of relatively small porosity (preferably less than the crown zone 5) not only facilitates opening and maintenance of the developed shape of the canopy, but prevents spilling or other outflow of air, particularly when this region or its lower part is inwardly curved in use as indicated at 23 in Fig. 1. By the corresponding restraint against downward and outward air flow, the forward high pressure cushion 52 is better maintained and the stability of the apparatus enhanced.

it will be appreciated that to accomplish differing porosity zones, the component gores 12 can each be made in a plurality of pieces (as indicated by the dotted lines 57 and 22 in Fig. 8), the specific nature and porosity characteristics of the fabric at various regions being dependent in any given case on the requirements and circumstances of use of the canopy, as will now be readily understood.

It may be noted that the present structure, in its preferred forms, is materially different in effect from socalled skirted types of flat canopies, i. e. canopies having an originally fiat rather than preformed shape, but accompanied by a depending skirt of cylindrical or inwardly or outwardly tapering form. Such structures have been found to fall short of the extent of stability which characterizes the present device, and furthermore are subject to highly localized stresses in the expanded and distorted condition of the fiat upper section, e. g. as explained hereinabove. By way of summary, the presently preferred canopies consist of the upper half of an oblate spheroid, or a major part of such upper half, surmounting a hemispherical frustum having an upper base congruent with the base of the ellipsoidal zone and with the zones so defined that the spheroidal and spherical surfaces are tangent or continuous, i. e. at a common tangent, at the circle of connection. The minor axis, or at least the altitude of the spheroidal zone is advantageously less than the altitude of the hemispherical frustum, being preferably not more than about /2 of the altitude of such frusturn; moreover, the altitude of the frustum is conveniently substantially less than one-half the major axis (e. g. the radius of the spheroid-on the line 22a of Fig. 2) of the spheroid. As indicated, the major and minor axes of the spheroid, and more specifically the altitude CK, are proportionately dimensioned to provide a spheroidal surface wherein the load of the complete assembly is translated into substantially uniform pressure load throughout the fabric of the zone B. it will be understood that for optimum strength and optimum control for pressure conditions, the cap section not only prevents gore seams from crossing the pole 6 but is also such that there is no seam of the cap section which itself crosses the pole.

While it is at present preferred to use a Zone A which is a frustum of a hemisphere and which has its lower edge lying in a great circle of the originating sphere, other intermediate zones of a hemisphere may be employed for the region A, including such zones, i. e. bounded by planes remote from the poles of the generating sphere, as extend across the spherical equator. Special results of extreme stability are attainable with apparatus of the last-mentioned character, although for most presently contemplated conditions of service, the illustrated structure (Fig. 1) is not only satisfactory but preferable, at least from the standpoint of eficiency. Fig. 9 shows a relatively extreme case of the modification just mentioned, e. g. wherein the lower boundary 22b of the spheroidal crown section B is joined to the major-width portion of the hemispherical frustum A, the later then curving inwardly to a hem edge 14b of somewhat reduced diameter. Since the line 22b is in this case a great circle of the spherical portion A, e. g. as described by the radius 62, the line of juncture G'J will intersect the canopy surface at a point of equal tangency for the two curves when the upper portion B is a truly complete, upper half of a spheroid. The lower edge or mouth opening 14b then has a smaller diameter than the circle 22b, for still greater enhancement of the 7 high pressure area 5212. That is to say, special structures of the sort shown in Fig. 9 may be of advantage in special or unusual cases, e. g. in situations wherein even more rapidly complete opening characteristics are desired, without essential sacrifice of stability. It will be seen that while we now prefer the structures wherein the hem edge 14 or 1412 is at least as large as the circle at the base of the spheroidal portion (22b in Fig. 9) and very preferably as large as appears at 14 in Fig. 1, the arrangement shown in Fig. 9 is useful under some circumstances. It will be appreciated that in Fig. 9 as in the forms first described, the altitude KD' of the lower hemispherically-shaped zone A may be not more, and preferably less than the minor radius (here SD) of the hemispherical frustum, such altitude corresponding to an angle GDS' which lies, say, between 20 and 40, and is preferably equal to about 30.

In all arrangements of the invention, the spheroidal portion has an altitude which is smaller than the horizontal radius at the lower edge of the portion, preferably much smaller, e. g. such that the described altitude-radius ratio, or the minor to major axis ratio of the spheroid, is not more than about 1 to 3. In all forms, the shroud lines 18 or 18' should be appropriately long (to avoid undue contractive force or streaming tendency by the reaction of the load on the canopy in the course of opening) the length of the shroud lines being thus equal at least to the major diameter of the spherical zone, and being preferably at least two or three times that diameter. The present canopy is, as will now be understood, designed to have as little tendency toward streaming or streamlining as possible, experience now indicating that the likelihood of the canopy streaming (failing to open) when released increases somewhat as the shape of the upper part of the canopy approaches a spherical contour, the tendency being critically substantial in canopies where the overall shape is more cone-like than a hemisphere, i. e. toward the shape of a steep vertical cone.

Canopies of the character herein described are also adapted for useful load-retarding effect in other fluid media, e. g. for use as sea anchors.

It is 'to be understood that the invention is not limited to the specific embodiments herein shown and described but maybe carried out in other ways without departure from its spirit.

' We claim: 7

1. An aircraft spin-retarding parachute canopy formed of sheet material and extending from a closed crown to a mouth opening adapted to be secured by shroud lines to a load, said canopy having, when unstressed, a contour consisting-essentially of an intermediate zone of a sphere having an altitudesubstantially equal to one-half the'radius-ofits base and an upper, oblate, inverted cupshaped zone tangentially joining the upper periphery of said intermediate zone and having an altitude substantially equal to one-half the altitude of said intermediate zone,

said' contour having a substantial and continuous curvature of all points along its intersection with any horizontal or vertical intersecting plane, said canopy material being substantially uniform throughout any horizontal cross-section through the canopy, whereby the canopy is cordless and ventless and stress due to said load is distributed uniformly throughout the canopy when the canopy is inflated.

2. An aircraft spin-retarding parachute canopy as defined in claim 1, composed of a plurality of radially extending gores of flexible sheet material having arcuate inner edges and straight outer edges and radially extending edges defined by tangentially connecting arcs of different radii, the'arc at the outer end of the gore having the smaller radius, said gores being attached to each other along their radial edges, the outer periphery of the assembled gores defining said mouth opening, said gores being somewhat shorter radially than a radius of said canopy, and a closed crown having a circular periphery and attached along its periphery to the inner edges of the gores.

References Cited in the file of this patent UNITED STATES PATENTS 2,342,384 Volf Feb. 22, 1944 2,358,582 Little Sept. 19, 1944 2,501,670 Fogal Mar. 28, 1950 FOREIGN PATENTS 149,418 Great Britain Aug. 10, 1920 271,488 Great Britain July 14, 1927 678,946 France Jan. 2, 1930

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