The end of the plug which is inserted into the case is slightly beveled to facilitate easy assembly. This plug is forced into and glued to that end of the case having the smaller outside diameter and also is secured by means of two tacks at opposite sides. After the plug is glued in place holes are punched through the walls of the case, registering with the holes drilled through the plug so that the electric wires may pass down the outer side of the case thus connecting with the ignition at the far end.
The white-light composition consists of -
This mixture is dampened and made slightly adhesive by adding a shellac binder. The composition is mixed in quantities of 77 pounds of barium nitrate, 13 pounds of aluminum, and 5 pounds of sulphur. Barium nitrate which has been thoroughly pulverized is mixed with the other two ingredients, the same method of hand mixing being used as previously described. The mixture is screened twice through a 30-mesh sieve. After screening the mass is dampened with a binder, as described above, and is again rubbed through the 12-mesh sieve. Variations from the above formula are adopted by different manufacturers. It would appear that one of the important points in connection with the composition is that when loaded in the case it should be driven home with a sufficient pressure, or that the composition should be of such ingredients as to prevent the shrinking of the composition during the setting of the binder. Such shrinking would produce a space of lesser resistance close to the inner walls of the case, permitting the gases during combustion to work their way in between the charge and the walls of the case to blow out the contents before functioning. As it is desirable to get an illumination of 22,000 candlepower, burning for 1 minute, the compression of the charge is an important factor.
The red-light composition consists of -
Sulphur (flour) ..................
This mixture is made up in batches consisting of 24 pounds of strontium nitrate, 6 pounds of aluminum, and 6 pounds of sulphur. It is mixed by hand in a fiber tub and passed three times through a 16-mesh sieve. Great care should be taken to see that the mixture is homogeneous, it being desirable to mix by hand after sifting. This mixture is then dampened with a binder consisting of two ounces of shellac in a quart of alcohol. About a pint of this solution is used for a batch. The mixing of the composition and the thoroughness with which it is packed in the case, as previously mentioned in connection with the white composition, influence the proper burning and candlepower of the light. Manufacturers claim that the alcohol contained in the binder shows a marked influence upon the candle-power. It is, however, not unlikely that the variation in the alcoholic content causes the difference in the mass of the composition.
The composition is best loaded into the case by means of an air press. The press is constructed with two plungers and a movable platform having two metal shelves supporting the cases. This is not unlike the type of press used for loading rockets. The metal shelves are operated by an eccentric lever, receiving the paper cases in such a manner that they can be securely clamped. After the cases are clamped in position on the shelves they are filled with the loading composition and subjected to a 60-pound pressure. Three successive charges are rammed home in this manner. The compressed composition fills the case to within 5/16 inch of the top. The first-fire composition is then put in, occupying about 1/8 of an inch, which gives clearance for the igniter.
The first-fire composition is a simple black-powder quick-fire mixture consisting of -
This mixture is slightly dampened with the shellac-alcohol solution previously mentioned.
The composition is mixed in batches consisting of 12 pounds of saltpeter, 8 pounds of sulphur, and 2 pounds of charcoal. These dry ingredients after being mixed by hand are passed through a 16-mesh sieve, again thoroughly mixed, and the screening is repeated. The composition is then dampened with a pint of the solution of shellac and alcohol. The first-fire composition is loaded on top of the illuminating composition while the cases containing the illuminating composition are still in the press, the composition being rammed home by means of the plungers used in compressing the light composition. A stratum of from 1/16 to 1/8 of an inch of this composition is thus formed on top of the light composition.
The igniter for the wing-tip flare is an article made by the Du Pont de Nemours Co., Wilmington, Del., called the Du Pont flash igniter. The composition of this igniter is shown in figure 197. This igniter consists of a small squib or tubular case, filled with gunpowder, used as a firing charge. The tubular case is of paper, 1/4 inch in diameter by 3/4 inch long, and has attached to its ends two insulated electric wires, approximately 2 feet in length. When a current is passed through these electric wires or leaders, the charge of gunpowder loaded into the squib is exploded, which in its turn ignites the prime that fires the illuminating composition.
Fig. 196. - Igniter and leaders.
The electric wires or leaders are carried along the outside surface of the case and are threaded through the 2 3/32-inch holes in the wooden plug, issuing out of the plug through the central orifice. These wires are drawn toward, and fixed snugly against, the side of the case.
Figure 196 shows the igniter and connecting leaders; the squib or small tube is shown beside the igniter.
Figure 197 is a longitudinal cross section of the flare in which the igniter and connecting wires are clearly shown. These igniters or squibs are tested by means of a galvanometer three times: first, before they are put into place; second, after they have been installed in the light case; and finally after the light case is completely assembled. These squibs are tested by means of a light current sufficient to give a reading on the galvanometer, but not to an intensity that might cause ignition of the charge.
The cover for the top end of the light case consists of a strawboard washer, punched from No. 20 strawboard 1 7/8 inches in diameter. This washer has a 3/4-inch-diameter hole in the center, and is held in place by means of the cloth inside the drumhead.
Fig. 197. - Cross section of flare.
This inside drumhead is made of muslin and measures 3 inches square. It is pasted on the cardboard cover at the top end of the flare, over the igniter, and is drawn about the sides and securely attached to the case by means of paste.
This consists of a piece of Kraft paper 3 inches square, cut from sheets 24 by 36 inches, of 30-pound stock. This drumhead is pasted over the muslin drumhead and drawn down about the end, being attached firmly to the case.
A muslin wrapper 4 1/2 inches wide by 8 inches long is pasted around the case, having one of its edges flush with the igniter end of the case and extending beyond the other end of the case. That portion of the inside wrapper which extends beyond the edge of the case is now pasted down over the wooden plug.
The outside wrapper is made of 20-pound Kraft paper cut in pieces 4 3/4 by 7 inches long. This paper is pasted around the outside of the flare, having its edge flush with the top end at which the igniter is placed and overlapping the other end where it is pasted down firmly on the wood plug.
This seal is for the purpose of holding firmly the electric wires which pass through the base plug and project beyond. Melted sulphur is poured into this hole and fills the small cavity in the base plug.
After the completed flare is dried it is dipped in a black paint, made from lampblack and shellac dissolved in alcohol.
The name label is printed on white paper for the white flare and on red paper for the red flare. It is 1 1/2 inches wide and 5 1/4 inches long. This label is pasted around the flare at the base-plug end.
Fix This End In Holder
Red - One Minute This flare must be tested by galvanometer before attaching to plane.
October, 1918. Manufacturer.
The packing container consists of the ordinary mailing tube of strawboard, measuring 2 1/2 inches in diameter and 12 inches long, with metal bottom and metal screw cap. This container holds two of the flares.
In packing the flares in the container three packing wads are used. These are of felt, 2 1/2 inches in diameter, one at the bottom of the container, one between the two flares and the other on top just below the screw cap. Care is exercised in packing to insure proper disposition of the wires.
A band of 30-pound Kraft paper, 12 inches long and 1 1/2 inches wide, is pasted around the top of the container to cover the joint between the screw cap and the body.
The drumhead is made of Kraft paper 6 inches square. This is pasted over the top of the container cover, drawn down over the sides and firmly attached.
Another label is pasted on the side of the container designating the character of the article.
After the container is thoroughly dry it is dipped in melted paraffin.
Wooden boxes with tin lining are used for packing cases, the flares being tightly sealed by soldering the lining forming the inner tin container. 100 flares are packed in each box.
Plate 16. WING TIP FLARE FLOW SHEET.
Plats 17. WING TIP FLARE MATERIAL CHART.