Rocket Heads.
Heads for small rockets may be made of two or three rounds of paper rolled dry, and secured on the inner and outer edges with paste. After sticking it on the case, which it may be made to fit, as in fig. 36, pinch the top in like a choke, only tight, and tie it round with twine or flax. For coloured rocket heads, 6⁄8 and upwards, the head may be enlarged by fixing a collar round the top of the case. To make the collar for a 6⁄8, roll a case on a 9⁄8 former, and when dry cut it into short lengths in the lathe, as recommended for pill-boxes; if unprovided with a lathe, saw it with a fine-toothed saw. The advantage of the enlarged head is, that it brings the stars nearer to the rocket, and prevents it from being top-heavy. Another way is to make the heads tapering, and the tops conical, as in fig. 39. One part is rolled on fig. 34, the other on fig. 35; or, a cone may be made of a circular piece of paper, without a former. Cut the circle, along the radius, to the centre; bend it into a cone; secure the edge with sealing-wax, and paste paper over it to overlap the rim: snip the edge with the scissors; paste it inside, and secure it to the other part. But the quickest way of all is to make a long paper bag, which may be made to fit to the greatest nicety. For this purpose take a tape-measure; or lay down, on the edge of a strip of writing paper, 7 or 8 inches long, and 1 inch broad, 6 inches, divided into eighths, transferred from a foot-rule. Suppose the 6⁄8 rocket has a collar, which, on being measured by the paper just alluded to, is found to be 42⁄8 inches round; add to this 3⁄8 for lapping over, making 45⁄8 inches. Cut a piece of imperial brown 45⁄8 broad, and as long as the case, 6 inches. Make this into a paper bag, 21⁄8 inches broad. Be careful that the corners are perfect; a strip of double-crown may be pasted over them. When dry, pinch the mouth open till cylindrical, and merely allow the stars to drop in without forcing them; this will keep the top edge of a wedge shape, fig. 37, and answer the purpose of a cone. If the paper is thin, the bag must be made of two thicknesses; the paper will, then, require to be 9 inches by 6; 43⁄8 of this will have to be kept dry, and the other 45⁄8 pasted.
A head, made in this way, if required to hold gold rains, or serpents, can instantly be reduced to a cylindrical shape, by pushing the rocket-case right up it, to the top; this will cause the corners to stick out, like two horns; press them down, and secure them with sealing-wax. Attach a cone, if desired.
Heads made like figs. 38 and 39 may be of three thicknesses of paper, pasted all over.
Fig. 39 shows the manner of tying on the sticks. No variation must be made in their lengths, and it is not advisable to alter their size. To adapt it to the wood, however, a slight alteration might be permitted. For instance, instead of 3⁄8 square, it might be 21⁄2/8 by 31⁄2/8, a slight increase one way, compensated by a slight diminution the other. It must, however, on no account, be so increased and diminished, as to approach the shape of a lath, as such stick would vibrate, and cause the rocket to quiver. When the heads are a paper bag of the shape of fig. 37, the stick must be tied on, as indicated by the dotted lines.
If the stick is suited to the rocket, it will, when suspended on the finger almost against the mouth, as at f, fig. 40, lie, not quite horizontal, but slightly sloping downward. The wood should be dry pine, free from knots. The sticks are generally cut with a carpenter's cutting-gauge. If the learner has a lathe he will find a 6-inch circular saw convenient for cutting them.
For amateurs, a 6⁄8 rocket is a good size; large enough, and small enough. If 5⁄8 and 4⁄8 are made, two hollow drifts will be sufficient; for 3⁄8, one hollow drift. Very small rockets, 2⁄8, are made for children; they are rammed solid, and a hole is pushed up them with a bradawl.
Rockets in former times, before the present days of competition, were charged in moulds. These were of gun-metal, bored truly cylindrical, furnished with hinges, to open and admit the case; they were then screwed up, and might be charged as hard as possible. Names were given them according to the bore of the mould, that is, the external diameter of the cases; a 4⁄8 was termed an ounce rocket; a 5⁄8, a two ounce; a 6⁄8 a quarter pound; a 71⁄2/8 a half pound; a 9⁄8, a pound; a 12⁄8, a two pound.
These names were determined by the weight of a leaden ball of the same diameter as the bore. Now a sphere of lead, 71⁄2 inches diameter = 90 lbs., or 1440 ounces; consequently one of 15 inches = 720 lbs., similar solids being to each other as the cubes of their like dimensions: the latter sphere being twice the diameter from top to bottom; twice the diameter from left to right; and twice the diameter from front to back; 2 × 2 × 2 = 8.
The external diameter of the rocket being 71⁄2 inches, the internal would be 5 inches, and this would be a 90-pounder: hence, for an inch rocket, we have the proportion,