US2591044A

US2591044A - Fuel tank construction

Info

Publication number: US2591044A
Authority: US
Inventors: Warren C Bomhardt; Earl H Sorg
Original assignee: Glenn L Martin Co
Current assignee: Glenn L Martin Co
Priority date: 1945-10-26
Filing date: 1945-10-26
Publication date: 1952-04-01
Anticipated expiration: 1969-04-01

Description

April 1952 w. c. BOMHARDT EI'AL. 2,591,044

FUEL TANK CONSTRUCTION Filed 001:. 26, 1945 VII/M 1N VEN TOR. WAR/PEN 6. BOMHAl-POT EARL H. 50/?6 A TTOR/VEY Patented Apr. 1, 1952 FUEL TANK CONSTRUCTION Warren 0. Bomhardt, Baltimore, and Earl H. Sorg, Hyde, Md., assignors to The Glen L. Martin Company, Middle River, Md., a corporation of Maryland Application October 26, 1945, Serial No. 624,756

4 Claims.

This invention relates to an integral tank structure for the storage of liquids and more particularly relates to a structure for rendering the seams of integral tanks fluid-tight for hydrocarbon liquids, yet remains sufficiently flexible so that the liquid will not seep through the seams upon repeated deflection of the structure.

The efficient storage of liquid fuel and oil, particularly in aircraft, presents somewhat of a problem. It is most desirable to utilize space in aircraft that is not particularly useful for other purposes for the storage of fuel and lubricating oil. The space in the wings between the front and rear spars and adjacent ribs is usually employed for the storage of fuel and oil. In seaplanes the portion of the hull under the floor is fitted and used for storage purposes. Due to the fact that the construction of the hull and the wings of airplanes are light weight riveted aluminum structures, it has been difficult to fabricate an integral tank and depend upon sealing the riveted joints adequately to hold fuel. Many attempts have been made to coat seams with fillers and sealing compounds and to place caulking strips in the riveting joints. Special sealing and treatment of the rivets has also been resorted to with only temporary success. The problem of storing hydrocarbon liquids in aircraft was successfully solved by use of the Mareng cell, described in the Gray and Zivi Patent 2,102,590, issued December 21, 1937. This patent relied upon a bag or cell placed in the cavity to be used for the storage of fuel, the dimensions of which were substantially equal to the cavity so that the cell acted as a containing structure, while the cavity walls bore the fluid pressure load of the liquid in the bag or cell. This construction solved the problem of storing fuel in cavities in aircraft that has been universally adopted for this purpose. While the cell wall is thin, it has a certain volumetric capacity and therefore takes up some of the space that might be used for the storage of fuel as well as adds to the dead-load weight of the airplane. The structural deflection of the aircraft in flight could not cause leakage or seepage of the fuel.

While the above solution has been quite satisfactory, it is still desirable to store fuel in integral tanks if some method or means can be devised to seal the seams of the tanks against leakage when the seams are stressed by the deflection of the structure.

It is an object of this invention to provide a material to be used as a caulking strip in the seams of integral tanks, which material has a predetermined degree of swelling when in contact with hydrocarbon liquid so that the material on the inner edge of the seam near the hydrocarbon liquid will be caused to swell a controlled amount to keep the space in the riveted joint fluid-tight at all times.

Further and other objects will become apparent from the description of the accompanying drawings which form a part of this disclosure and in which like numerals refer to like parts.

In the drawings:

Figure 1 is a fragmentary view of a portion of a seaplane hull embodying the invention.

Figure 2 is a section taken on the line 2--2 of Figure 1.

The side walls of a seaplane hull in Figure 1 are shown at 3 with the bottom walls 4 sloping down to the keel 5 from the chines 6. A space in the bottom of the seaplane hull underneath the floor I is usually utilized for the storage of fuel and oil. This space may be divided by partitions such as 8 into compartments. The usual construction of such a hull involves riveted joints which have in the past been as carefully sealed and caulked as possible but still were not sufficiently tight when the structure was stressed so that they could be used for the storage of fuel without covering the lon eron 9 and ribs ID to permit the insertion of a Mareng cell. In order to make the cavities in a seaplane hull formed as described above, suitable for the storage of fuel, it is merely necessary to incorporate in each riveted joint as shown in Figure 2 sealing strips such as I I or I2 made in accordance with this invention. The single riveted joint l3 will be rendered fluid-tight by reason of the strips ll placed between rib l0 and side wall 3. At a double riveted lap joint such as [4, it will be necessary to employ in addition to sealing strip H, a second sealing strip 12.

It is usual in attaching the skin on the frame of a seaplane to place the skin on the frame during the process of drilling the rivet holes. After all of the holes are drilled and prior to riveting, sealing strips II and 12 are put in place and a hot instrument run through the rivet holes will puncture the sealing strip used. It is possible but not as practical to drill the skin and ribs with the sealing strip in place.

The advantage of the particular tape employed in this invention is derived from its composition. A vinyl resin compound is employed for the purpose that eXhibits flexibility and swelling characteristics in fuel, particularly in the aromatic blended fuels. The swelling characteristic is of a controlled degree so that that portion of the tape in contact with the fuel swells to make the joint fluid-tight. If, after continuous flexing, the seam permits the seepage of fuel further than the initial swelled portion of the tape, further swelling of the tape will take place as the fuel seeps along the seam to render the seam fluid-tight. There are many materials that exhibit a swelling characteristic when immersed in such hydrocarbon liquids but the degree of swelling is usually uncontrolled. Either excessive swelling will take place or swelling not great enough to produce the desired results for the purpose of this invention. Most of the materials that do swell when in contact with these hydrocarbon liquids become soft and weak or hard and brittle which renders them unsatisfactory for repeated exthat would render them suitable for the purpose of practicing this invention. Synthetic resin elastomeric materials swell to various degrees in aromatic blended fuels but the softeners incorporated in their compounds are either extracted by the action of the fuels rendering them hard and brittle or the resins do not exhibit the desired swelling characteristics. The gasket material employed in this invention is obtained by milling a composition of 70% of a material known as VYNW and 30% of material known as Paraplex G-25 and then molding or extruding the stock into the desired gage and shape. The material known as VYNW is a copolymer of 93- .95% vinyl chloride and 7-5% vinyl acetate. The material known as Paraplex G-25 is a poly ester of glycol sebacate.

If it is desired touse this material as a coating for fabrics, it can be made up in a solution consisting of il VYNW, 4.9% Paraplex G-25, 32.6% cyclohexanone and 51% methyl ethyl ketone. This solution may be applied as a coating to a fabric such as thin cotton flannel until a total thickness of approximately .045" to .050" is obtained after-the evaporation. Such fabric can be readily coated with this material by the customary calendering process. This formulation can also be extruded or cast into a film of any desirable thickness and used as outlined above. When the solvent evaporates from the above solution, the resulting'material-will be approximately 70% VYNW and 30% ParaplexG-ZS.

The sealing material made in the manner described above has a very low coldflow characteristic, that is, that when distorted by the pressure involved in the riveting operation of the Joint it tends to remain intact and resist the pressure and maintain its shape rather than ooze out of the crevices and cracks under pressure. The material can be made into a strip having smooth surfaces that form a good seal with the sheel metal being riveted.

The swelling characteristic of the -material used as a seal in the joint of a structure is the most important feature. The composition of matter described above when extruded or cast into a thin strip or film, when immersed in ordinary aromatic aviation fuel which is a 40% aromatic fluid with 60% 100 octane gasoline; will exhibit the swelling characteristic of up to about 36%, When the material is in the seam of a riveted joint only the'edge in contact with the fuel will swell and as the seam opens up and fuel seeps in, the material will swell to stop the seepage of fuel into the seam. When the fuel is removed from the scam, the tape resumes its normal volume.

It will be rare in use that the material will be required to swell to its full amount of 36% but it will always be some lesser amount. When the composition is made up with cyclohexanone and methyl ethyl ketone as solvents and used as a coating on flannel or fabric, the swelling is held In other words, the swelling is In some to about 15%. restrained by the reinforcing fabric.

. installations the reinforced coated tape may be desirable Where only limited degrees of swelling will be required, but for maximum sealing, the cast or extruded form of tape within the reinforced fabric is most desirable.

' It is to be understood that certain changes,

alterations, modifications and substitutions can be made'without departing from the spirit and scope of the appended claims.

We claim as our invention:

1. A tank for the storage of hydrocarbon liquidshaving its structural members secured together by a plurality of rivets, a sealing strip inserted in each joint between said members, said rivets extending through said members and said sealing strip, said strip comprising a composition of substantially 70% of copolymer of about 06% vinyl chloride and 4% vinyl acetate and of a poly ester of glycol sebacate.

2. A tank for the storage of hydrocarbon liquids having its structural members secured together by a plurality of rivets, a sealing strip inserted in each joint between said members, said rivets extending through said members and said sealing strip, said strip comprising a composition of vinyl chloride and vinyl acetate, with a poly ester of glycol sebacate which exhibits a swelling characteristic of about 36% when immersed in aromatic fuel.

3. A tank forthe storage of hydrocarbon liq- .uids having its structural members secured together by a plurality of rivets, a sealing strip inserted in each joint between said members, said rivets extending through said members and said sealing strip, said strip comprising a strip of fabric impregnated with a composition of substantially of a copolymer of about 96% vinyl chloride and 4% vinyl acetate, and 30% of a poly ester of glycol sebacate.

4. 'A tank for the storage of hydrocarbon liquids having its structural members secured together by a plurality of rivets, a sealing strip inserted in each joint between said members, said rivets extending through said members and said sealing strip, said strip comprising a strip of fabric impregnated with a composition of vinyl chloride and vinyl acetate, with a poly ester of glycol sebacate which exhibits a swelling characteristic. of about 36% when immersed in aromatic fuel.

WARREN C. BOMHARDT. EARL H. SORG.

REFERENCES CITED -The following references are of record in the file of this'patent:

UNITED STATES PATENTS Number Name Date 2,140,672 Gray et a1. Dec. 20, 1938 FOREIGN PATENTS Number Country Date 523,247 Great Britain July 10, 1940 OTHER REFERENCES Fligor et al.,'Resinous Plasticizers from Sebacic Acid, Ind. and Chem. Eng. 37 (5), pp. 504-508, May 1945.

Chem. and Eng. News, Dec. 10, 1944, page 2115.

The Resinous Reporter, February 1944, page 8.

The Resinous Reporter, July 1944, pages 6-8.

Claims

1. A TANK FOR THE STORAGE OF HYDROCARBON LIQUIDS HAVING ITS STRUCTURAL MEMBERS SECURED TOGETHER BY A PLURALITY OF RIVETS, A SEALING STRIP INSERTED IN EACH JOINT BETWEEN SAID MEMBERS, SAID RIVETS EXTENDING THROUGH SAID MEMBERS AND SAID SEALING STRIP, SAID STRIP COMPRISING A COMPOSI96% OF VINYL CHLORIDE AND 4% VINYL ACETATE AND 30% OF A POLY ESTER OF GLYCOL SEBACATE.