Draft (airflow)

“ For the ship navigating the waters of Smith Sound a light draft is far better than a heavier one, permitting her to hug the shore in order to get round barriers, or, when crowded by heavy ice, to retreat close to the shore and let it ground outside the ship. Another distinct advantage of light draft in a ship is the greater ease with which she will rise under the heavy pressure of ice-floes. The greater her draft, the harder it is for her to rise and avoid the grip of the ice. ”

“ This branch-flue we run into the smoke-pipe or draft-flue G, and in order to open and close it at will, we have arranged within it a damper or valve I, which has its rod, by which it is turned, extended to the outside of the casing of the stove. By opening the damper a direct draft is obtained, and the fire can be kindled very speedily, and the draft does not have to pass up through the body of coal in the reservoir, as in our other patented stove. When the damper is closed, the highly ignited gases pass down the descending flues J J, as in our former patent. ”

“ The subject of forced draft is of great importance, and, as a corollary of high-speed development, is being studied with keen interest. There are wide differences of opinion not only as to the proper systems, but even as to the value of the principle. ”

“ Under the above assumptions, whenever a stack is working at its maximum capacity at any altitude, the entire draft is utilized in overcoming the various resistances, each of which is proportional to the square of the velocity of the gases. Since boiler areas are fixed, all velocities may be related to a common velocity, say, that within the stack, and all resistances may, therefore, be expressed as proportional to the square of the chimney velocity. ”

“ Compressed air is as good to run an engine with as steam, for both of them have tremendous powers of expansion. As soon as the air is released from the supply tank—which keeps it compressed in a space that is many times smaller than it would take up when it is free—and has passed into the cylinders of the engine, it begins to expand, or to spread out in every direction, exactly as steam does. ”

“ A gas-containing envelope, made of a light, strong, varnished fabric, is kept taut by the pressure of the gas within; the car, constructed of wood or metal tubing, is suspended by ropes from the envelope, and contains engine and crew, with a two-bladed propeller revolving astern. Such a machine, in its control, had an elevating-plane and rudder, upon the same principle as those of the aeroplane. One of the difficulties to be overcome was the expansion and contraction of gas in the envelope owing to differences in altitude and temperature. ”

“ Flying thousands of feet above the ground Man had found that the thinning atmosphere was too rare and each flyer was consequently supplied with its own oxygen tank containing enough of the precious gas to sustain the pilot for one hundred hours. An open valve in the side of the globe allowed enough of the poor grade of air to flow from the outside to the tank and thence into the globe reviving the air sufficiently to the proper proportions needed for the driver. ”

“ But directly it has to face the wind, and fight its way against it as an airship must do, then it has to be made of sufficient strength and rigidity to withstand the wind’s power, or it will be blown to pieces. To make so large a thing as an airship withstand a rough wind, it must be built of very strong and rigid materials. To do this means to add to the weight of the machine. To lift the increased weight, a larger machine which can hold more gas is needed. The larger the machine the more surface it offers to the wind, and the stronger therefore must be its construction. ”

“ So the airship could be made either heavier or lighter than air, and losses of weight through the consumption of fuel, the casting of bombs and so forth, could also be compensated by admitting air to sections of the general gas-bag. ”

“ The absence of the knowledge how to obtain a really gas-proof envelope is, no doubt, one of the greatest difficulties of airship construction. As has already been pointed out, the gas-holding quality of gold-beaters’ skin is remarkable. ”

“ When we are too far below to use this device, we run on air already compressed in reserve [43] tanks. We can carry enough for five hours of running without renewing it. In case the pressure is not high enough, we expand it,—heating it by electric radiators.”
“And your fresh air?”
“Still compressed air,” laughed the inventor. “We drive out the old foul atmosphere through specially devised valves, the fresh air taking the place of it.”
“Then the only time you have to utilize the gas is in starting your engine?” asked Ned. ”

“ Air stored under pressure in a reservoir can be used expansively, in an ordinary steam engine returning an equivalent amount of work that was required to compress it—less the friction.
The admission of the air being through a single tube, it creates a constant flow of air in one direction only, thus filling the cylinder at each stroke with air at atmospheric pressure. This movement gives a momentum to the air which causes it to fill the cylinder to its fullest extent at each stroke. ”

“ Imagine a balloon all ready to be inflated, that is, ready to be filled with gas. The bag or “envelope” hangs limp and lifeless. Together with the basket, ropes, etc., which are attached to it, it probably weighs several hundred pounds, yet because its volume is so small it displaces very little air. Now we commence to inflate the balloon. As the gas rushes in, the envelope commences to swell; it grows larger and larger, displacing a greater volume of air every moment. When fully inflated it displaces a volume of air much greater in weight than itself. ”

“ Invert a cold, dry tumbler over a burning jet, and you will always observe moisture gathering on its surface. Another pretty experiment may be performed with H by inserting the stem of a common clay pipe in a piece of rubber tubing, slip the other end of the tubing over the gas jet, prepare some strong soap suds, and with a little care you can blow beautiful soap bubbles with your pipe, which, by a skillful movement may be detached, and they will rise in the air like miniature balloons; by placing a burning match under them they will explode. ”

“ An automatic venting of a gas ballonet of just sufficient size to compensate for the weight of the dropped shell would answer in a balloon: a similar automatic change in propeller speed and angle of planes would suffice with the aeroplane. There is no doubt but that air craft may be made efficient agents of destruction on a colossal scale. ”

“ As the balloon or airship ascends the density of the air decreases as the height is increased. As an illustration of this the barometer falls, as everyone knows, the higher it is taken, and it is accurate to say that up to an elevation of 10,000 feet it falls one inch for every 1,000 feet rise. It follows that as the pressure of the air decreases, the volume of the gas contained expands at a corresponding rate. It has been shown that a balloon filled with 1,000 feet of hydrogen has a lift of 70 lb. ”

“ The steam breath gradually grows and is exhaled with more vigor. Presently he belches up a barrel or so of water which falls back into his throat. Then in a minute come two or three such little spasms, when up lifts a rounded column two or three feet in diameter, rising higher and higher in exact perpendicularity 150 feet high. The jet breaks more or less as it rises into pointed sprays, which, when there is no wind blowing, fall with almost precise regularity about the up going column. ”

“ Air-bags are placed inside the cavity of the gas-bag, usually one near each end of the airship, and these are inflated by pumping air into them under pressure. In this way an outward pressure of as much as 7 lbs. to the square foot may be produced, equivalent to the resistance of air at a speed (either of the wind, or of the airship, or of both combined) of 48 miles per hour. It is evident, however, that the pressure upon the front end of an airship making headway against a strong wind will be much greater than the pressure at the rear end, or even than that amidships. ”

“ The airship is, therefore, nothing else than a dirigible balloon, for the engines and other weights connected with the structure are supported in the air by an envelope or balloon, or a series of such chambers, according to design, filled with hydrogen or gas of some other nature. ”

“ A swift, boisterous wind shakes the wings of the plane which slopes to the right and to the left according to the movements of the pilot. At times the entire machine vibrates 156 and we feel ourselves so closely bound in its flight that often we believe its wings are attached to our very shoulders. As I look back at the oil guides I see the sparks from the exhaust tube escaping rapidly like a swarm of fireflies swept by the wind. The tube of the silencer which is fastened onto the motor, although the exhaust remains at present completely open, is red and incandescent. ”

“ All one has to do is to insert in the balloon model a little tube to furnish a jet of the room's atmosphere from an air pump and light it with the electric spark. Similarly, should a pin-prick have made ever so slight a vent in my air-ship balloon, the interior pressure would have sent out into the atmosphere a long thin stream of hydrogen that might have ignited had there been any flame near enough to do it. ”

“ It requires some form of support such as a tripod, or in tunnel work it can be braced against the roof or sides. Some data on steam and air drills are given in Table 56. The effect of the length of the transmission pipe, temperature of the outside air, pressure at the boiler or compressor, etc., will have a marked effect on the amount of steam or air to be delivered to the drill. Compressed air is affected more than steam by these outside factors, but it has an advantage in that as it loses in pressure it increases in volume so that the loss of power is not so marked. ”

“ Moreover, the direct longitudinal compression due to the rigging is applied to a point considerably above the axis of the ship. In a large non-rigid many of these difficulties can be overcome by distributing the weight into separate cars along the envelope itself.
We have seen that as an airship rises the gas contained in the envelope expands. If the envelope were hermetically sealed, the higher the ship rose the greater would become the internal pressure, until the envelope finally burst. To avoid this difficulty in a balloon, a valve is provided through which the gas can escape. ”

“ By the escape of steam from the arms the fans were caused to revolve with immense energy, so much so that the model rose to an immense altitude and flew across two fields before it alighted. The motive power employed was obtained from the combustion of charcoal, nitre and gypsum, as used in the original fire annihilator; the products of combustion mixing with water in the boiler and forming gas-charged steam, which was delivered at high [114] pressure from the extremities of the eight arms. ”

“ These German airships were held together by rib-like skeletons of steel and aluminium and a stout inelastic canvas outer-skin, within which was an impervious rubber gas-bag, cut up by transverse dissepiments into from fifty to a hundred compartments. These were all absolutely gas tight and filled with hydrogen, and the entire aerostat was kept at any level by means of a long internal balloonette of oiled and toughened silk canvas, into which air could be forced and from which it could be pumped. ”

“ To decrease the velocity, when large volumes of air are required, the air passages are made larger, and the mine is divided into sections and the air current subdivided into a corresponding number of independent circuits. This splitting of the air not only lessens the cost of ventilating, but greatly increases its efficiency by permitting the circulation of much larger volumes, and has the added advantage that the effect of an explosion or other accident vitiating the air current is often confined to a single division of the mine, and affects but a small part of the working force. ”

“ There is also a shut-off valve, hand operated, which can be set to provide a flow of oxygen to one man, to two men, or to none at all. Then there is a regulating valve operated by an aneroid barometer which adjusts the oxygen flow to the altitude, the flow increasing as the machine goes higher. Finally in the pilot's view there is a flow indicator consisting of a small fan wheel which tells the aviator that the oxygen is actually flowing. ”

“ According to this plan, although both names stand for an aerial vessel88 capable of travelling in the sky by its own motion, an airship is a machine supported in the air by reason of its buoyancy, while a flying machine is kept aloft only by virtue of its onward movement.
In other words, part of the construction of an airship consists of a bag or balloon, filled with gas or hot air, which causes the whole to rise and maintain its position in the air. ”

“ I was obliged to do it in my air-ship balloon, whose cylindrical form must be preserved at all cost. For me there must be no transformations as from apple to pear. Interior pressure only could guarantee me this. The valves to which I refer have since my first experiments been of all kinds—some very ingeniously interacting, others of extreme simplicity. But their object in each case has always been the same: to hold the gas tight in the balloon up to a certain pressure and then let only enough out to relieve dangerous interior pressure. ”

“ The first of these objections is met by making the trap a half S one, so that the fluids fall down one limb with sufficient force to wash out the bottom of the trap thoroughly with each discharge, and the second by the fresh-air inlet, which relieves the pressure that otherwise might force the traps.
15. The fresh-air inlet affords free entrance for air, and, as the main lines of pipe are open above the roof, the difference in length of the pipes will give rise to a constant current of fresh air through them, in one direction or the other. ”