OPERATION OF FLASH STEAM POWER PLANTS FOR MODEL BOATS
THE flash steam method of propelling model power boats of the racing
type produces a far greater speed than would otherwise be possible.
Flash steam plants are far more complicated than ordinary
steam-propelled power plants, and for this reason the author devotes a
chapter to their description.
A considerable equipment of tools and not a little mechanical ingenuity
are required to produce and assemble a workable flash steam plant.
However, such plants have gained great popularity in the past few years,
and all of the hydroplane racing craft are propelled with such outfits.
These power plants are capable of delivering such a tremendous power
that speeds as high as thirty-five miles an hour have been reached by
boats measuring 40 inches long.
The illustration, Fig. 128, shows a flash steam plant and its various
parts. Each part and its function will be described in this Chapter in
detail. The gasolene tank _A_ is used to hold the fuel, which is fed to
the gasolene burner _C_. The gasolene burner operates on the principle
of the ordinary gasolene torch. First the tank is filled about
three-quarters full with gasolene. An air-pressure is then produced in
the tank with a bicycle pump. The pipe leading from the gasolene-tank at
the top is coiled around the burner, and the free end of it is bent and
provided with a nipple, so that the gasolene vapor will be blown through
the center of the helix of the coil formed by the pipe bent around the
burner. This is quite clearly shown in the drawing.
[Illustration: FIG. 128]
The cylinder is merely a piece of stovepipe iron bent to shape and
provided with several air-holes at the burner end. To start the burner,
the vaporizing coils must first be heated in an auxiliary flame. The
flame of an ordinary blow-torch is suitable for this purpose. After
the coils have become sufficiently hot the valve at the top of the
gasolene-tank is opened, and this causes a stream of gasolene vapor to
issue at the nipple. This produces a hot flame at the center of the
vaporizing coils, and in this way the coils are kept hot. The purpose of
heating these coils is further to vaporize the gasolene as it passes
through them on the way to the burner. Once started, the action of the
burner is entirely automatic. The vaporizing coils are made of Shelby
steel tubing with an internal diameter of 1/8 inch.
It will be seen that the flame from the gasolene-torch is blown through
the center of the boiler coils _B_. Thus, any water passing through
these boiler coils is instantly converted into steam. In other words,
the water "flashes" into steam. The heat of the blow-torch is so great
that most of the boiler coils are maintained at red heat even while the
water is passing through them.
Notice the water-tank _G_. A little scoop, formed by a pipe of small
diameter, protrudes through the bottom of the boat, so that the forward
motion of the boat will cause water to rise in the tank _G_. An
overflow is also provided, so that, should the water not be sucked out
of the tank quickly enough, it will not flood the boat. The overflow
pipe hangs off the side of the boat.
The water pump _E_ sucks water from the tank, and pumps it through the
check-valve _K_ (this valve permits water to pass in one direction only)
into the boiler coils. The boiler coils, being red-hot, cause the water
to flash into steam the instant it reaches them. By the time the steam
has reached the opposite end of the boiler coils, it is no longer steam,
but a hot, dry gas at a terrific pressure. From the boiler coils the
steam passes into the steam-chest of the engine, and thence into the
cylinder, where it expands, delivering its energy to the piston.
It will be seen that the water-pump _E_ is geared to the engine. Owing
to this, it is necessary to start the water circulating through the
boiler coils by the hand pump _F_. This hand pump forces water through
the boiler coils just as the power pump does. After the hand pump is
started the engine is turned over a few times until it starts. The
valve _H_ is then closed, which cuts the starting pump _F_ entirely out
of the system, because when the engine starts it also drives the water
pump _E_, and therefore the action becomes entirely automatic.
The relief-cock _L_ is placed in the system to be used if the engine
stalls. By opening the relief-cock the pressure in the complete system
is immediately relieved. At all other times the relief-cock is closed.
A second pump, _I_, is also included in the system. This, like the
water-pump, is geared to the engine and driven by it. It is the duty of
this pump to convey oil from the lubricating tank _M_ into the steam
feed-pipe just before it enters the steam-chest. In this way the live
superheated steam carries a certain amount of lubricating oil with it in
the cylinder.
Owing to the high temperature of the superheated steam, it is impossible
to use brass cylinders on the steam-engines employed with flash steam
systems. Steel seems to be the only cheap metal that is capable of
withstanding the attack of flash steam. Brass is out of the question,
since its surface will pit badly after it is in use a short time.
The boiler of a flash steam plant is covered with sheet iron so as to
prevent drafts of air from deflecting the flame from the center of the
boiler coils. The cover is provided with ventilators, so that the burner
will not be smothered. If enough oxygen does not enter the interior of
the boiler coils, poor combustion will result, and the gasolene flame
will not develop its maximum heat. Upon referring again to the diagram,
it will be seen that the exhaust steam pipe from the engine discharges
into the stack of the boiler covering. This discharge greatly
facilitates the circulation of air through the boiler coils.
After a flash steam plant has been started it will work automatically,
providing all the parts are in good running order. Flash steam plants,
however, are difficult to get in the proper adjustment, and once
adjusted they are easily disturbed by minor causes. Owing to the fact
that every square inch of surface in the flash coils is heating surface,
the amount of water supplied to the boiler must be exactly what is
needed. The heat must also be regulated so that the temperature of the
steam will just meet the engine's needs. Many times an increase in heat
causes the steam to reach such a temperature that it will burn up the
lubricating oil before it reaches the cylinder of the engine. This is
liable to cause trouble, because sticking is apt to occur.
Model power boats with speeds as high as thirty-five miles an hour have
been made in America. Such high-speed boats must be assembled with
infinite care, owing to the fact that the mechanism they carry is more
or less erratic in its action, and unless it is well made results cannot
be expected.
[Illustration: FIG. 129]
There are probably few sports more interesting than that of model
power-boat racing. The Central Park Model Yacht Club of New York city is
one of the most progressive clubs in America, and its members not only
have a sail-boat division, but they also have a power-boat division. The
members of the power-boat section have races regularly once a week, and
the most lively competition is shown. It is indeed amusing to watch
these little high-speed boats dash across the pond, their bows high in
the air and their little engines snorting frantically. Owing to the
difficulty of keeping these small racing boats in a straight line, they
are tied to a wire or heavy cord and allowed to race around a pole
anchored in the center of the pond, as illustrated in Fig. 129. The top
of the pole should be provided with a ball-bearing arranged so that the
cord to which the boat is fastened will not wind around the post. In
this way the boats are caused to travel in a circle, and as the cord to
which they are fastened represents the radius of the circle, the
circumference can readily be found by multiplying the radius by 2,
which will give the diameter. The diameter is then multiplied by 3.1416
to obtain the circumference. If the boats were permitted to travel wild
they would run into the bank, a fatal procedure when they are running at
high speed.
Speed boat hulls are usually of the hydroplane or sea-sled type. This
type of hull is extremely easy to make. Such a hull is shown in Fig.
130. It will be seen that it has an aluminum bottom. The propeller and
propeller strut will be noticed in this illustration.
[Illustration: FIG. 130]
[Illustration: FIG. 131]
[Illustration: FIG. 132]
The drawing for the particular hull shown in Fig. 130 is given in Fig.
131. First the two side pieces are cut out to the shape shown. In this
particular instance the over-all length of the sides is 39-1/3 inches.
This is called a meter boat, and is built with this length to conform
with the English racing rules. Next a bow piece is cut out, and this is
produced from solid wood. Only two materials are used in the
construction of this hull, aluminum and mahogany. Square mahogany strips
are cut out and fastened inside of the side pieces by means of shellac
and 3/8-inch brass brads. The bottom of the hull is made of 22-gage
sheet aluminum. This is fastened to the square mahogany strips, since
the sides of the boat are entirely too thin for this purpose. The method
of fastening the strips of aluminum will be made evident by referring to
Fig. 132. The aluminum bottom does not run completely over the bow
piece, but merely overlaps it sufficiently to be fastened by brass
brads, as illustrated in Fig. 135. The single step in the bottom of the
boat is fastened by a mahogany strip, through which the stern-tube runs
and the water-scoop. The back of the boat is made up of mahogany. A
small aluminum hood is bent to shape, and this is fastened to the bow of
the boat and prevents the boat from shipping water.
In building a hull of this nature the mechanic should exercise care to
see that it is in perfect balance, and that the sides are finished and
varnished as smoothly as possible. This will cut down both air and water
resistance. The position of the propeller strut and stern-tube will be
seen by referring to the drawing of the hull in Fig. 131.
The propeller of a high-speed boat is of a high pitch and generally of
the two-blade type. It should be at least 3 inches in diameter and with
a pitch of about 10 inches. By this it is meant that the propeller
theoretically should advance 10 inches through the water for one
revolution. The rudder is generally fastened in one position, in case
the boat is not used on a string and pole. It will be found advisable,
however, always to run the boat in this way, and in such cases the
rudder can be entirely dispensed with.
[Illustration: FIG. 133]
The boiler of a flash steam plant is extremely simple. Such a boiler is
shown in Fig. 133. It consists merely of a coil of copper or Shelby
steel tubing with an internal diameter of 1/4 inch. The boiler coils
should be wound around a circular form of wood about 2-3/4 inches in
diameter. In the case of copper it will not be found very difficult to
do this, providing the copper is heated before being wound on the wooden
form. If the copper is heated it is advisable to wind the wood with a
layer of sheet asbestos before the copper tube is wound on. It is almost
necessary to do this winding with a lathe, but if the mechanic does not
have access to such a tool he may have to find other means of doing it,
or possibly he can take it to a local machine shop and have the work
done for a few cents. The boiler coil should be wound about 9 inches
long.
A casing of Russian sheet iron is made to slip over the boiler, leaving
sufficient space between. Ventilating holes or slots are cut in the
cover to permit of a free circulation of air. The boiler covering is
also provided with a funnel through which the exhaust gases from the
blow-lamp pass.
[Illustration: FIG. 134]
[Illustration: FIG. 135]
The blow-lamp used operates on the same principle as the ordinary
blow-torch. The details of such a lamp are given in Fig. 134, and a
finished torch is shown in Fig. 135. Instead of making the valves
necessary for the blow-torch, it is advisable to purchase them, for they
are very difficult to make accurately. The valve at the back of the
torch regulates the gasolene supply that passes through the nipple. The
hole in the nipple should be about twenty thousandths of an inch. Owing
to the fact that the copper coil wound about the burner is short, the
tube can be filled with molten resin before it is bent. In this way the
tube will not kink or lose its shape while being wound. After it is
wound it is placed in the fire and the molten resin forced out with a
bicycle-pump. Such a blow-torch produces a tremendous heat and throws a
hot flame far up into the boiler coils.