I.
The Howell torpedo is, in dimensions and general appearance, very similar to the Whitehead. Like the Whitehead it carries a war-head containing the explosive charge of gun-cotton, which is rendered operative automatically, during the run, and is exploded by contact with the target.
The Howell shows no trace of itself during its run, but at the end of its course when its buoyancy brings it to the surface, it is readily sighted by the smoke from the calcium-phosphide, a charge of which is placed, for practice runs, in a pocket on top of the torpedo.
The motive power of the Howell is the energy stored up in a fly-wheel, which is spun up to 10,000 revolutions per minute by a steam motor. This wheel weighs about 128 lbs.
The torpedo is distinguished for its great directive power derived from the gyroscopic properties of the fly-wheel.
The shell of the torpedo is made of a hard rolled metal composed of 80 parts of copper, 20 parts zinc, and a trace of lead. The model of 1894 is about 11 feet long and 14.2 inches in diameter. The shell is 1/16 in. thick. The total weight of the torpedo, including the gun-cotton charge of 100 lbs., is something over 518 lbs. The positive buoyancy of the torpedo is 10 lbs.
The torpedo is divided into three sections, (1) the head; (2) the cylinder; (3) the after section. These sections are joined together by water-tight joints.
1. THE HEAD.
Practice.—Contains water instead of gun-cotton. A central tube passes through the water tank and carries balance weights to give longitudinal trim.
War.—Contains gun-cotton and the detonator.
The primer of the gun-cotton is contained in a central pocket. The percussion detonator is located in the forward end of the primer case.
The nose contains the firing pin and its mechanism. The firing pin is rendered operative by the action of a small four-bladed propeller on a safety nut.
The nut travels on a thread chased on a pin. Upon entering the water, the safety nut being revolved by the propeller, travels out on the pin until it brings up on the guard on the end of the pin, where it continues to revolve freely.
The construction of the firing mechanism is such that the pin is now operative and upon contact with the target a safety pin is sheared, and the force of the blow, which compresses and trips the firing-spring, causes the firing-pin to strike and explode the detonator.
2. THE CYLINDER.
Contains the fly-wheel and its gearing, and pockets for depth register and charge of phosphide of calcium.
3. THE AFTER SECTION.
Contains immersion regulator, impulse movement, immobilizer, and two sections of the shafts. The rear, or tail section, carries the stuffing boxes of the shafts, tiller, and immobilizer rods. The shaft stuffing boxes serve also as thrust-bearings. The rear end of this section is called the tail cone and contains the pitch mechanism and carries the tail frame, fin, rudders, and propellers.
II.
The Howell torpedo has twin-screws driven by the fly-wheel whose axis is at right angles to the longitudinal axis of the torpedo. The propellers have adjustable blades, the pitch of which, by means of the pitch mechanism, is made to constantly change during a run, increasing' as the speed of the fly-wheel decreases. The ratio of the propeller revolutions to wheel revolutions is as 4 to 5.
There are two rudders. The horizontal rudder steers the torpedo up or down. The vertical rudder is for the purpose of keeping the torpedo on an even keel, and insures its rectilinear direction in a horizontal plane. "By virtue of the gyroscopic force of the fly-wheel an exterior force acting on the torpedo and having a tendency to direct it from its horizontal course will simply cause the torpedo to roll, and the motion that is then given to the V.R. will cause the torpedo to roll back in the opposite direction, and will eventually bring it to an even keel.
This curious property of the torpedo may be readily exhibited in the shop by spinning up the fly-wheel, and then striking the torpedo a sharp blow on the nose. Instead of moving laterally as might be expected, the torpedo will simply roll over.
The propeller shafts are parallel and are geared with the flywheel. The rudders have tiller-rods which extend into the after section, where they are connected with the "impulse movement.''
III.—The Immersion Regulator and Impulse Movement.
In the port side of the torpedo, in the after section, is fitted a flat piston. This piston is held in its outward position by the tension of the immersion spring. The tension varies with the depth at which it is desired to run the torpedo, and is set by hand, access to the immersion spring being had on the starboard side.
The principal feature of the immersion regulator is the "angle guide." This device is shown in Figure 1. S.S. are two very light flat springs. The angle guide is mounted on the piston rod in such a manner that when the piston rod moves in or out, the angle guide will be tipped one way or the other. It is connected with the H. R. pendulum by an adjustable lever.
The H.R. pendulum swings on a knife edge fixed in the bracket at the top of the torpedo. The V.R. pendulum is located on the port side of the torpedo.
It is by the swing of the H.R. pendulum when the torpedo is diving or ascending, and by the motion of the piston when the torpedo is above or below the set depth, that the position of the angle guide is determined, which thereupon transmits, by means of the impulsive movement, the proper throw to the H.R.
Movement of the piston will tip the angle guide, so also will movement of the H.R. pendulum, and the latter dominates the force exerted by the piston, as will be seen later on.
The mechanism of the impulse movements consists of two racks TT (see Fig. 2) sliding in a frame with reciprocal motion simultaneously approaching each other and receding. The motion is derived from two eccentrics which themselves take motion through gearings from worms on both shafts. These impulses are very rapid, usually 4 ½ per second; the number depending, of course, upon the speed of the shaft, and are continuous as long as the shaft revolves.
These movements or impulses act upon the rudder in this way: The tiller rods have attached to them the little arms or "pallets," PP (Fig. 2). These pallets are pivoted at the center. On one end is a pin upon which rest the light springs of the "angle guide."
When the angle guide is tipped by the motion of either the piston or H. R. pendulum, or both, acting together or against each other, the pallet will also be tipped and the toe of the pallet coming in the path of the rapidly moving impulse rack will engage the teeth on the rack, and thus the tiller rod be pushed either forward or to the rear, transmitting motion to the horizontal or diving rudder. In a similar way the V.R. pendulum actuates an adjustable V.R. angle guide, to control the V.R. pallet in reference to the upper impulse racks.
It is clear that as long as the torpedo is moving at set depth with its horizontal axis in the plane of the horizon, the pallets also will be in the same plane, and the impulse racks will travel to and fro without coming into contact with them. There will be no move of either piston or pendulum.
Suppose, however, the torpedo is above the set depth. The pressure on piston being less than spring tension, the piston will be set out, the angle guide will tip and engage the forward end of the pallet with the impulse rack, and produce a certain amount of down rudder, causing the torpedo to dive. The pendulum then swings forward, and in doing so tips the angle guide in the opposite direction, which engages the after end of the pallet in the impulse rack, causing up rudder, thus checking the dive. The pendulum's influence being thus greater than that of the piston, this result is obtained, otherwise the torpedo would continue to dive.
If the torpedo is below set depth and approaching it, the reverse action takes place.
IV. The "immobilizer" is a rod which has longitudinal motion given by the pitch frame. It holds the pendulum forward or back as desired (when the torpedo is launched) a short interval of time, about two or three seconds perhaps. It will be seen that by holding the H.R. pendulum forward, the angle guide will tip the after end of the pallet to engage the impulse rack, thus producing up rudder. In this way the torpedo's dive is checked. The H.R. pendulum is automatically released at the set time.
V. The torpedo is ejected from the tube (above water) by a 5 to 6-oz. charge of black powder, this being sufficient to throw the torpedo clear of the ship's side.
VI. The fly wheel is spun up by means of a small steam motor which is readily disconnected from the torpedo. The energy in the wheel at 10,000 revolutions per minute is equal to 500,000 ft. pounds, and it requires 30 horse power for one minute to store it, but it requires only ¼ H.P. to keep the wheel at 10,000 after it has been spun up.
The range of the torpedo is 800 yards; its speed over 400 yards 26 knots. This is the maximum yet attained with the torpedo of 14.2 inches diameter.