US1981600A - Uninflammable balloon - Google Patents

Description

NOV. 20, 1934. J LETOURNEUR 1,981,600

UN I N FLAME-(TABLE BALLOON Filed Aug. 26, 1931 2 Sheets-Shet 1 ii? way Nov. 20, 193.4. J. LETOURNEUR MABLE BALLOON UNINFLAM 2 Sheets-Sheet 2 Filed Aug. 26, 1951 1 Wm n5 2 J Patented Nov. 29, 1934 UNITED STATES UNINFLAMIiIABLE BALLOON Jean Letourneur, Versailles, France Application August 26, 1931, Serial No. 559,467 In France September 19, 1930 8 Claims.

The main danger occurring in the use of balloons lies in the inflammability of the gas used for their inflation. Amongst the gases employed for that purpose helium alone is uninflammable, but the scarcity of the known sources of this gas and the difficulties presented by its extraction are such that the present production of helium is quite insufficient to meet the requirements of aerostation. It is therefore necessary usually to resort to other gases, such as hydrogen, notwithstanding the danger attending their use.

Such danger however may be considerably reduced and done away with in practice by using two envelopes: one which is the gas envelope properly so-called which contains a light but inflammable gas, and another which entirely surrounds the first, whilst the space included between the two envelopes is inflated with a gas which causes no reaction with the oxygen of the air and with the light inflating gas. Hereinafter said gas is designated under the name of inert gas. If said gas is lighter than air it naturally imparts to the complex its ascensional power. In this case therefore helium can be employed with. much advantage and, failing the same, use may be made of nitrogen or any other inert gas or mixture of gases, but in this case the question of lightness is only secondary and the main property to be sought is that it should be inert in the sense above given to this term. If it is then supposed that a balloon constructed in the abovementioned manner is pierced by a burning object, as, for instance, an incendiary projectile, it is easy to understand that the ignition of the balloon will be avoided. As a matter of fact, the gas escaping into the atmosphere through the inlet and outlet holes of the outer envelope cannot become inflamed because it is inert. Likewise, the light gas which escapes through the inlet and outlet holes through the inner envelope is also incapable of catching fire, because it escapes into an atmosphere of inert gas with which there is no reaction. It is of course necessary that the thickness of the protective layer of inert gas should be suiflcient. Such thickness must be determined by previous experiments according to the nature and the size of the burning object or the projectile, the contact of which with the balloon is dangerous, the nature of the inflating gas, the nature of the inert gas, the use for which the balloon is intended, theclimate of the regions where the balloon is intended to be used, etc. Hereafter in the specification the term thickness limit of the protective layer will be applied to the smallest layers producing the protection desired.

But, in application, this fundamental device is difficult to realize correctly. In fact, it is necessary that at each instant during the ascension, and at each point of the balloon, the thickness of the layer of inert gas should be at least equal to the thickness limit. Now, owing to the rising and falling motions of the balloon and the changes in the outer temperature, the volume of the gases, light and inert, undergo important variations, and the envelopes which hold them experience considerable modifications in their forms, which it is generally diflicult to control, so as always to comply with the essential condition of the aforesaid minimum thickness.

The object of this invention is to produce bal-' icons with a double envelope in which the thickness of the protective layer of inert gas always remains automatically at least equal to the thickness limit so as to provide these balloons with a practically absolute protection against fire, meaning such risks as it is desired to guard against. It is applicable to captive, free and dirigible balloons. It consists substantially in providing the 30 inner envelope and the outer envelope with extensible contrivances judiciously chosen and in arranging these two envelopes relatively to each other in such manner that under all circumstances during the ascension, the space between the two envelopes is always at least equal to the thickness limit.

In particular the two envelopes are homothetic for a given condition of their inflation. In particular also, the extensible contrivances are arranged in such manner that the two envelopes remain homothetic in a constant ratio, during the, variations of volume allowed by the free play of their elastic connections. In particular, again, the extensible contrivance of the outer envelope consists wholly or partly of the extensible contrivance of the inner envelope, vand vice versa. Finally, if the thickness limit is of a small absolute value, it may be suflicient to adopt an approximate method whereby the two envelopes are no longer strictly, but only approximately homothetic during their variations of shape without the protection required being thereby diminished.

The construction of extensible envelopes for balloons is founded, as is well known, on the following principle :--The envelope consists of panels of impermeable material assembled according to the methods in use for this kind of construction, but its outer surface is deformed by the use of elastic connections. When such an envelope is 119 inflated. the elastic connections begin to stretch, the material assumes a shape and undergoes a superficial tension'which equilibrates the tension of the elastic connections. The gas is therefore slightly compressed and consequently the shape of the envelope is regular and always the same for an identical inflation. Fi'irthermore, if the introduction of gas into the balloon continued, the" elastic connections become lengthened, the volume of the keel increases and the shape of the outer surface is altered. The same phenomenon occurs when the balloon rises in altitude and the surrounding pressure decreases. Inversely, when the balloon descends and the surrounding pres-- sure increases, the volume of the envelope, due to the play of elastic connections, diminishes, whilst remaining all the same under pressure. Inall these motions, the mass of gas contained in the envelope is constant. The total ascensional power of the balloon is therefore kept constant, whilst losses of gas in the ascensional movement are avoided. If furthermore the elastic connections are arranged in such manner that the centre of gravity of the volume of the keel remains the same during all the movements of extension and contraction of said connections, it is known that great facility of equilibration results therefrom, which makes it possible to give a considerable stability to the balloon.

forces ofaction andconsequently the exact shape of the surface, which means that the shape varies with the volume, but is perfectly definite at each instant.

Hence, if a balloon is constructed with a double .envelope consisting of two extensible envelopes,

inasmuch as, at every instant during the ascension, it is the same cause (surrounding pressure and. temperature) which influences these two keels to produce their volume and therefore their external shape, it will be possible to construct these two envelopes and to assign to them respeotive positions which are such that at every instant and at all points their distance apart is at least equal to the thickness limit.

Generally speaking, it will be found an advan tags to choose for the two envelopes homothetic shapes in a ratio which is such that for the smallest volume it is necessary to provide during the ascension (in principle at the moment of leaving the ground), the minimum space apart of the two envelopes is at least equal to the thickness limit. If furthermore the two extensible systems are such that the two envelopes become deformed, whilst remaining homothetic and in the same ratio, the distance apart will vary in function of the volume. It will therefore be capable of only increasing during the ascension and hence it will always be at least equal to the thickness limit. This condition of constant homothetic state of the two envelopes will be greatly assisted by to which the protection under this patent will naturally have to be extended, as well as to apparatus in which the same process is used and to their detached elements. It will be easily understood with the aid of the following and the accompanying drawings which are of course given by way of non-limiting examples only.

Fig. 1 shows a transverse section of a balloon constructed according to the system claimed.

Fig. 1 shows a detail View of part of Fig. 1 on an enlarged scale.

Fig. 2 shows a longitudinal section of Fig. 1.

Figs. 3 and 4 illustrate a transverse section and longitudinal section of another balloon which constitutes another example of construction.

A is the inner envelope which is filled with light gas; it belongs to the trilobe type. Its transverse section consists of an equilateral triangle with apices 1,2 and 3 and three equal arcs connected with said apices (1, 6, 2)--(2, 4, 3) and (3, 5, 1). According to Fig. 2 the different sections perpendicular to the axis 10-11 are at each point similar to that in Fig. 1. The apices 1, 2 and 3 rest on curves (10,1, 11)(10,2, 11) and (10, 3, 11) judiciously chosen, so as to give to the inflated keel a suitable shape. The envelope A is therefore formed byv a volume having the general shape of a triangular prism with curved edges, and three lobes resting on the three faces of said prismatic surface. The surface of the lobes is formed by panels of impermeable material assembled in accordance with the usual methods for this kind of construction. The sides of the triangle are formed on the contrary by elastic connections such for instance as sandows, that is multi-stranded shock-absorber elastic, 7, 8 and 9 on the whole or part of their length. The length of these elastics, when at rest,.before fixing and their distance apart, are regulated in such manner that they impart to the keel a suitable pressure to use the balloon.

Around said envelope is arranged another envelope B which has a circular section. It carries on each side and symmetrically with reference to the vertical plane containing the axis two expansible double pleats, each formed by a hollow fold and having elastics in four planes, such as 12, 13, 14 and 15 attached to the keel according to meridian lines of the surface. Said elastics are not shown in Fig. 2, but only near the points,- the starting point of the meridian lines on which they rest. The space between the envelopes A and B is filled with inert gas and the connection between these two envelopes is formed by a number of elastic connections arranged according to the planes of symmetry of the lobes, such as 16, 17 and 18. These connections are calculated in such manner as to be moderately stretched when the balloon is inflated up to the volume which corresponds to zero altitude. Furthermore, the distance apart between the two envelopes is determined in such manner that for the same degree of inflation,-it is, at each point, at least equal to the thickness limit. The envelope B further carries the usual accessories, planes, elevators, gondolas, suspension means etc., not shown in the drawings.

When the balloon rises, the surrounding pressure diminishes and the volume of the two keels increases by the deformation of their outer surface. It is easy to perceive that in the case of the envelope B the hollow folds open and the section remains circular, but with a constantly increasing radius. In regard to the keel A, the sides of theequilateral triangle increase in length and the points such as 1, 2 and 3 move away from the axis, whilst the points situated on the plane s section is of the quadrilobe type.

of symmetry of the lobes such as 4, and 6, remain approximately invariable. The volume of the keel increases because its section approximates a circular section, but its outer overall space does not appreciably change. The minimum distance apart existing in the plane of symmetry of the lobes is therefore increasing. The maximum distance which existed on the outside of the re-entrant angle, is reduced, but it can never be reduced below the thickness limit, inasmuch as the section of the keel A can never attain the circular. When returning to the ground, the reverse phenomenon takes place; the two keels are reduced in volume, but the distance apart can never fall below the thickness limit, inasmuch as for the zero altitude such distance apart is already at least equal to the thickness limit. Automatic protection is therefore assured.

A is the envelope with light gas; its transverse It is formed by a square, having apices 21, 22, 23 and 24 and four circular arcs (21, 25, 22)--(22, 26, 23) 23, 2'7, 24)--(24, 28, 21). According to Fig. 4 the different sections perpendicular to the axis 29,

are at each point similar to that shown in 3. The apices 21, 22, 23 and 24 rest on curves (29, 21, 30)-(29, 22, 30)-(29, 23, 30) (29, 24, 30) judiciously chosen so as to give to the balloon a suitable acre-dynamic shape. The envelope A is therefore formed by a volume having the general 7 whole or part of their length. The length of said give to the envelope. is provided another envelop-e B, the surface of connections, when at rest, and their distance apart are regulated in such manner that the tensions they produce on each element of len th should correspond to the pressure it is desired to Around said first envelope which is homothetic of the first relatively to the centre 0 of the figure at the maximum cross section. The transverse sections of said second envelope are therefore similar to those of the keel A. The different elements are numbered on the drawings by adding 20 to the figure which indicates the corresponding elements of envelope A. The apices of the squares of the transverse sections 41, 42, 43 and 44 therefore rest on the curves (49, 41, )(49, 42, 50)(49, 43, 50) and (49, 44, 50), which in Fig. 4 are homothetic of the corresponding curves of the keel A. In tie keel B there are no elastics forming the sides of the square section of the prism with a quadrangular base.

The connection between the two envelopes is ensured by elastic connections such as 21, 41, 22, 42, 23, 43 and 24, 44 situated in the symmetrical diagonal plane of the transverse section and preferably attached to the fixation point of the sandow elastics of the keel A. These connections are not shown in Fig. 4.

The smallest distance between the envelopes is obviously in the section of the maximum cross section, at the nearest points of the homothetic centre, that is to say in the re-entrant angles corresponding to the apices of the squares. The ratio of the homothetic position is to be calculated so that in the case of the smallest volume it may i be possible to obtain for the balloon when rising the minimum distance apart or a distance at least equal to the thickness limit.

The envelope B also carries the usual accessories, planes, elevators, gondolas, suspending means, etc., not shown in the drawings. Nevertheless, it is an advantage, in certain cases, to fix the suspending means to the inner envelope, and allow them to pass through the envelope B through apertures, so as to reduce the resistance of the balloon in the wind.

When the balloon rises the surrounding pressure diminishes. Due to the play of the elastic connection, the two surfaces become deformed, whilst increasing in volume. The volume of the lreel A increases in invers ratio proportional to the variation in pressure. The same applies to the keel B and therefore also to the volume included between the two envelopes and corresponding to the volume B-A. If furthermore the elastic connections are judiciously chosen and if in particular they are lengthened proportionally to the loads they carry, it is obvious that the two surfaces will remain constantly homothetic and in a constant ratio. But in this increase of volume, all the elastic connections become lengthened and the surface moves, so to speak, away from the axis and particularly to the re-entrant angles. The minimum distance apart between the two envelopes therefore also goes on increas in". In the longitudinal direction there can be no appreciable displacement of the two keels relatively to each other, because if such a displacement tool: place, all the elastic connections provided between the two envelopes would give components parallel to the axis which would at once bring the twoenvelopes back to their respective positions.

To' sum up, if a value at least equal to the thickness limit has been given to the smallest interspace between the two envelopes, in the furrows, at the height of the maximum cross section, for the smallest volume, that may be reasonably considered under the conditions of the ascension, it is certain that, in all the variations of volume which take place during the ascension, the distance apart at all points will always be at least equal to the thickness limit, and consequently protection will be assured.

In a number of cases of application, the thickness limit need not be considerable. On the other hand the total variation of volume of the heels, which depends on the conditions under which the balloon is used, is also in most cases rather small. Under these circumstances, the variation in the length of the elastic connections between the two envelopes, such as 21, 4l'22, 42 etc., is very small. It is therefore possible, in a number of cases, to replace said elastic connections by non-elastic connect-ions as, for instance, strips of material cut out or assembled together like 49, 41, 50, 30,

21, 29, 49. In the variations of volume in the keel, due to the play of the connections of the elastic contrivanoe of the keel A, the two surfaces no longer remain strictly homothetic, but only appreciably so.

etween the two surfaces in the region of the furrows 21, 41 remains appreciably constant, but as this distance apart is, owing to its construction, at least equal to the thickness limit, the protection is again assured.

It remains quite clear that if an incendiary projectile passes through the balloon, the balloon will not catch fire, but the two envelopes will be pierced. There will be an escape of gas and therefore a fall of pressure, but so long as the elastic In particular, the distance apart connections remain stretched, the homothetic form of the two envelopes will be appreciably maintained. All the pilot will have to do is to stop rising before the damage to the envelope may have any serious result upon landing. All the same, however, the main danger, namely fire, will have been avoided.

In the case where the incendiary projectile may touch the balloon tangenitally and pass through the outer envelope only, the intermediate space between the two envelopes will become defiated through the inlet and outlet apertures, but the inner envelope, due to the play of the elastic connections like 21, 22 will retain its form and pressure and the material of the outer envelope Will become folded. It will then be for the pilot to decide whether he is to continue or not the ascension with an unprotected balloon, but here again fire with its serious dangers will have been avoided.

It remains clearly understood that the probability of occurrences of this description as well as the time eventually necessary for landing, is to be taken into account in determining the thickness limit. Likewise and due to the fact that the materials for balloons are not absolutely impermeable, the relative porosity of said materials may be taken into account to determine the thickness limit. ihis porosity may also be taken into account when the balloon is inflated or refilled before the ascension. If it is feared that owing to the much higher ratio of the surface to the volume, the loss of inert gas should be greater than the loss of light gas, it is easy not to exactly fill up the envelope A and, for instance, to put the envelope B only under pressure. Under these circumstances, the tension of the elastic connec- 'tions of the contrivance of the envelope A like 21,

22 will be transmitted entirely through the intermedium of connections either elastic or not, such as 21, 41 in the envelope B. As and when the loss due to the porosity of the material of the envelope B occurs, the envelope A will progressively become stretched, whilst absorbing a portion of the tension of the elastic connections like 21, 22 Without the envelope B becoming deformed. It will be sufficient to determinaat the moment of the refilling of the balloon before the ascension and whilst taking into account the relative porosity of the envelope A and B and the probable duration of the ascension, up to what point the normal inflation with inert gas must be exceeded, so that at the moment of landing, the envelope B may still be under pressure.

It is self-evident that the examples above given are only given for the purpose of clearly explaining the object of this invention and to show the diversity of its possible applications, but they limit in no way the arrangements which can be realized by this invention. I I

What I claim and desire to secure by Letters Patent of the United States of America is:-

1. In an elongated non-inflammable balloon, the combination of an outer expansible envelope, an inner expansible envelope inclosed within said outer envelope, an inflammable lifting gas filling said inner envelope, an inert gas filling the space between said inner and outer envelopes, a plurality of extensible elastic tensile connections attached to each of said envelopes for taking up the variations in volume of each of said inner and.

outer envelopes, and tensile means for maintaining the relative positions of the two envelopes, the expansibility of both outer and inner envelopes ensuring under all atmospheric conditions a protective jacket of inert gas equal to or greater than a predetermined minimum safe thickness.

2. A balloon as claimed in claim 1, in which the inner and outer envelopes have a common axis and a common centre of figure at the maximum cross section.

3. A balloon as claimed in claim 1, in which the inner outer envelopes have a common as well as a common centre of figure, and in which the envelopes are homothetic relatively to the said centre.

4. A balloon as claimed in claim 1, in which the two envelopes have extensible'elastic tensile connections comprising multi-strand'ed elastic cords, for the purpose set forth.

5. A balloon as claimed in claim 1, in which.

the inner envelope in cross section has a plurality oi re-entrant angles, and in which the said re-entrant angles are interconnected by elastic deformable means, for the purpose set forth.

6. A balloon as claimed in claim 1, in which the inner envelope has in cross section a plurality of ice-entrant angles which are interconnected by elastic deformable means, whilst the outer envelope is attached to the inner envelope by elastic means. i I

'7. A balloon as claimed in claim 1, in which the outer envelope is formed with two double pleats extending from end to end and having elastic connections between portions of the pleats and the envelope arranged in a plurality of planes, for the purpose set forth.

8. A balloon as claimed in. claim 1, in which the two envelopes and their deformable means are such that the envelopes remain homothetic and in constant ratio during the variations of volume allowed by the elastic connections in the envelopes.

JEAN LETOURNEUR.

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