THE WHYS AND WHEREFORES OF AIRSHIPS
By Clifford Albion Tinker
Formerly of the Bureau of Aeronautics, Navy Department Airships: How are they navigated, how are they landed, how are they anchored, how many men in. their crew, are they safe, and what good are they anyway? These questions are timely, pertinent, and frequently asked; their answers are not difficult, nor do they involve technical jargon incomprehensible to the non-scientific. Aeronautics, like all human activities, is ninety per cent common sense; highly mysterious and obscure theories have little to do with practical aviation.
Navigating an airship, while a common-sense proposition involving good sound navigational principles, depends, however, on a knowledge of factors not present in surface-ship navigation. The air as a navigating medium has certain characteristics common to the ocean, but in addition, it offers meteorological handicaps which go far beyond any difficulties that ocean traffic has to contend with. The navigator of an airship is the busiest little navigator that one could imagine. He is one nerve-center cooperating with other nerve-centers which go to make up the officers and crew of an airship.
Machinery is never quite fool-proof and the human element must always be reckoned with. Automatic machinery, up to a certain point, can be relied upon; after that, thinking man with trained intelligence completes the cycle. An airship's crew, while not necessarily supermen, must be trained and skilled, and resourceful beyond mere machine operators or balloonists; a mental "dud" has no place on such craft;.
To navigate an airship under way, one is concerned with problems involving three dimensions. Like a surface ship, she has to be steered horizontally to cover the shortest course possible from port to port. In addition, however, she must be navigated at varying heights above the land or sea to enable her to take advantage of changing atmospheric conditions or to pass over high mountains, fog, local storms, or other impediments. There is complexity here which Calls for skill.
Vertical rudders control an airship in steering on a horizontal course in exactly the same way that one steers a surface vessel; but in height steering, problems are involved which do not interest the surface craft navigator. The airship is enabled to ascend on an even keel by discharging ballast, and to descend by discharging gas. She can be kept on a level course or inclined up or down by her elevator planes, and so may climb or descend by using the thrust of the air on the top or bottom of her hull. When a height is reached, however, where the dynamic lift imparted by the motors and the air thrust just balances the reduction of gas lift due to the gain of altitude, the ship ceases to ascend, the action of her elevator planes becomes neutral, she must discharge ballast to climb farther. Likewise, by use of the elevator planes, she can be forced downwards until the thrust equals the gain of lift when gas must be discharged if lower altitude is the object.
Large rigid airships require two steersmen, one who operates the rudder wheel and holds the ship on the designated compass course, while the other keeps the ship at the proper altitude by operating the elevator planes and by regulating the discharge of gas and ballast.
Surface-craft navigators are supplied with fairly complete data for all their calculations, and ocean navigation is really a matter of well-understood routine. On the charts the speed of the ship and the directions of the various ocean currents, both of which are constant, are pricked off. Even dead reckoning methods by the patent log come within close enough limits for all practical purposes in the open sea, while the accurate standardization of propellers plus astronomical observations, which are nearly always obtainable, place surface navigation as one of the simple arts. This is not quite so in the case of the airship. Her course and distance made good are the result of her own speed and the speed and direction of the air currents in which she is carried along. Sometimes these air currents are of tremendous velocity.
One can readily see how the airship navigator cannot plot a course by dead reckoning unless he knows the speed and exact direction of the air movement. When an airship is flying over the land, if visibility permits, oftentimes the navigator can determine the air drift by taking observations on fixed points on the surface, and can thus adjust his compass course to enable the ship to maintain the necessary true course. Airship navigators over the North Sea during the World War, when at comparatively low altitudes, figured out their air drift by noting the direction of the waves, a fairly accurate method.
When an airship is caught in a fog or thick haze, a dense storm, or even heavy cloud formations, either over the land or the sea, astronomical observations are impossible, the computation of air drift is out of the question, and in such a case an airship may be driven many miles off her course. Such a contingency, however, is minimized by the use of directional radio apparatus on the airship used in conjunction with ground stations just the same as the radio compass stations along the coast give ships at sea their position and lead them along by continued bearings to port and safety.
Rather a formidable list of navigational instruments is required on an airship. In addition to the magnetic steering compass, there is supplied a prismatic compass which is used in taking bearings of known points on the surface of the earth to determine the ship's position, and a drift indicator, which shows the amount of leeway that the airship is making. Other instruments are: an inclinometer, which shows whether or not the ship is in a horizontal position; an aneroid barometer, for measuring approximate heights of the ship; a statoscope, which indicates the air pressure, whether it be increasing or decreasing, which tells the navigator whether the ship is falling or rising; and a barograph, which is a recording barometer, the ink line which it traces on a chart being used in calculating the rate of ascent.
The foregoing instruments are all used by the directional and height steersmen, while the navigator himself, in addition to the steersmen's instruments is supplied with a standard chronometer, giving Greenwich time; and a "trip clock" which is always set at zero at the beginning of the flight, thus furnishing a "time-elapsed" record. The air pressure due to the velocity of the ship, and which has a constant relation to the speed, is measured by a Pitot tube and indicator, while a propeller speed indicator mounted in the air stream is calibrated to give revolutions in terms of air speed. This speed indicator works on practically the same principles as the patent log used by surface mariners.
In the thermometer line the navigator is well supplied. Wet and dry thermometers give the temperature and humidity of the atmosphere, and a thermo-couple gas thermometer operating an indicator gives the temperature of the gas in the gas bags. The readings from these three thermometers applied together serve to calculate the lifting power of the airship under changing atmospheric conditions.
Airships, when not cruising, are either housed in sheds, moored to the ground, anchored over the water, or swinging from mooring masts. The method of landing, mooring, and getting underway, depends upon which one of the above situations confronts the crew.
By all odds, the easiest and most economical means of mooring an airship is the mooring mast. The most expensive and difficult problem of handling an airship is on the ground in connection with hangars and airdromes. Unless the hangar and airdrome are used as a terminal and for repair and up-keep purposes, the expense is enormous; but, inasmuch as terminal hangars are combined with manufacture, overhaul, up-keep and repair, a large force of mechanics and ground men is always available for handling the aircraft, thus reducing the immediate cost of operation. From 300 to 400 men are necessary to handle a large airship on the ground and to "walk" her in and out of a hangar. On the other hand, ten men can handle the biggest airship when making fast or uncoupling from a mooring mast.
The difficulty of handling airships on the ground is due to the possibility of sudden changes of wind, making it a problem to land and enter or leave a shed without damage. The method employed in housing an airship on the ground consists of bringing the ship up to the shed stern first, with the bow to windward of the doors, if a cross wind is blowing. The ship is then "walked" into the hangar by men having hold of her guy ropes, the bow being allowed to drift toward the center line as the stern of the ship is pushed into the building. If the wind is blowing directly in and out of the hangar, it is not necessary to hold the bow to windward, the ship being walked straight in.
The handicap of shifting and variable winds is overcome, to an extent, by the use of wind shields built on either side of the hangar entrance, and, in some instances, the doors are so arranged that they act as wind shields. The mechanical handling of airships in and out of hangars has not been developed to any great extent, although in England and Germany, trolleys running on rails in and out of the sheds have been used, a method which simplifies the operation of housing and reduces the personnel required.
Mooring over the land, aside from the use of mooring masts, is accomplished by wire cables, usually three in number, which are passed through bollards or posts, sunk into the ground at the apices of an equilateral triangle, the cables being then spliced into a mooring swivel at the point of mooring. The mooring swivel is attached to a floating ring on the ground, which moves about to accommodate the pitching and tug of the ship. When airships are moored in this manner, ballasting and gassing, to counteract super-heating and sudden changes in the weather, have to be arranged for on the ground and carried up to the ship by means of a pilot balloon.
When mooring over the sea, an airship drops a sea anchor, or "drogue," formed of a large canvas bucket which fills itself with from two to four tons of water, exerting a drag on the ship's movements and keeping her bow to the wind. The "drogue" is then picked up by surface craft and the airship towed where required or allowed to ride from a mooring rope made fast to the surface ship.
The mooring mast has increased the possibility of commercial use of airships tremendously and reduced the expense of operation materially. The mast consists of a latticed steel structure from 150 to 225 feet high, preferably not less than one-quarter the length of the airship to be moored, and having at the top a swivel arrangement which allows free movement of the airship as she surges and swings in the wind. An elevator is installed in the mast for the accommodation of passengers, freight, and express matter, the passengers walking across a platform from the swivel structure into the ship, thence down the runway to the cabins. Pipes for the supply of gas, fuel, and water ballast extend up the mast and are coupled to the intake pipes and valves on the ship.
In England, mooring masts have been tested out for long periods, proving to be safe for ships even in winds up to ninety miles an hour, and ships have been moored and unmoored in winds up to fifty miles an hour without difficulty.
Mooring an airship to a mooring mast is simplicity itself. As the airship, en route to the airport, radios in her time of arrival, preparations at the mast are quickly made. A mooring cable of steel leads from a steam or electric winch at the base of the mast, up the center, through the revolving circular cone and down to the ground again, and is then led out about 600 feet from the mast in the direction of the approaching ship. Two men stand by the end of the cable to make it fast to the ship's cable, one man stands by the winch, and two at the top of the mast to manipulate the anchoring gear.
The ship approaches at an altitude of about 500 feet and reels out her mooring cable in a loop, and when over the end of the cable on the ground, lets go the outboard end of the mooring cable. The two cables are joined and the ship, on signal from the men standing by, rises to an altitude of about 1,200 feet, discharging ballast until she is about two tons light and trimmed down by the stern. The cable is then reeled in at a signal from the ship to haul down.
When she is within about 500 feet of the top of the mast, two other cables about 600 feet long, leading from her mooring stands, are let down. These cables are secured to surging cables, led from the ground into the forward hatch of the ship, and a steady tension is kept on all cables until a cone on the ship's bow slips into an inverted cone on the mast. A cable from a small winch is then hitched on the mooring cable and the gear pulled down until taken up on the mooring collars at the head of the mast. This securely moors the ship. The surging and holding-down cables are then disconnected and hauled into the ship.
To release the ship, a pendant is let down through the revolving cylinder and tension put on it by means of a hand reel until the locking springs on the cones are free of pressure and can be pulled out. All the engines are started and the after-motor is thrown in gear and speeded up to offset the air speed. With engines backing at the moment when all is ready for letting go, the cone springs are pulled out and the ship rises.
An airship moored to a mast has to be kept trimmed down by the stem at all times when landing, riding at the mast, or getting away. Otherwise, the wind, hitting the nose of the ship, throws the stem up and the ship surges about very badly.
The duties of the crew of an airship in maintaining the ship in commission, in overhauling and repairing the ship and its motors, and "preparing ship for flight" involve duties which might be called "stunts"—they are so entirely different from the procedure on any other kind of craft in existence. Even Jupiter, Neptune, and the gods of the four winds would pop their eyes out at the turning of levers, the sounding of gongs, the shinning along trusses, and wandering around among gas bags, fuel tanks, ballast tanks, and cabins which the crew are obliged to do every day while the airship is inflated.
The first thing in the daily routine is taking the "lift and trim." This is nothing less than calculating the total lift of the airship by summing up the amount of ballast; meaning water, gasoline, oil and other necessaries on board the ship, and noting the result on a special chart. By doing this a daily lift record of the ship is kept, and from this record may be noted how much the lift varies from day to day, for if one day's lift is less than that of the foregoing, and no gas has been valved, it is plainly apparent that a loss has occurred, and immediately the gas bags are inspected for leaks.
By recording the location of ballast on board, the "trim," which means the tendency for lightness or heaviness in one end of the ship or the other, can be noted and compensated for if necessary. It is highly desirable to keep weights distributed evenly along the length of the ship, otherwise undue stresses may spring the hull structure.
Lift and trim being taken, the crew is sent to the cleaning stations throughout the ship. Not only is the ship itself cleaned and thoroughly polished, but the engineers overhaul and condition the engines and cars, the riggers inspect the controls, gas bags, valves, the outer covering, the fin surfaces, and do any necessary upkeep work to maintain the ship in a top-notch condition.
The framework of an airship, being of duralumin, is extremely light, and in climbing around on the girders of the hull structure there is more or less breakage of small braces and wires, making it necessary for almost constant hull inspection and repair work to be going on. Then again the outer cover fabric may get torn and blown loose at the joints, and when this happens repairs must be made immediately. Otherwise, the small holes would develop into big rents and result in the stripping of large sections of the envelope. The gas bags being very thin and light require a deal of attention. Chafage results in leaks and the consequent loss of gas, lowering its purity and reducing its lift.
Leak detectors are used for inspecting the gas bags. These detectors are applied to the outside of the goldbeater skin covering and register any traces of gas going through them. The leak detector being only twelve inches in diameter, and the surface of the balloonets or bags being tremendous, this leak inspection is a tedious process. Balloonets found to be unusually porous, causing rapid gas leaking and loss of purity, are at once replaced. The bags which are taken out are air inflated, inspected, and repaired where possible. When station equipment is inadequate for this work the bags are sent to the factory for repair. Every week each bag is tested for gas purity which serves as a check on the general condition of the gas tightness of each balloonet, and the ship as a whole.
Other routine work which claims the attention of the crew consists of checking the tension of various wires, correcting any discrepancies, tautening the outer cover, cleaning and reseating water ballast discharge valves, and general inspection of all the controls to see if they are functioning properly. These general inspections are carried out weekly, or oftener if an airship is in constant use.
Preparing an airship for flight is a very active operation. A great many things are going on at one and the same time. The first thing to know is how large a crew is going to be carried, how much freight and the number of passengers, the nature of the flight, and its probable duration. With these factors known, calculations are made which give the amount of gas needed for the necessary additional lift, how much ballast must be carried, and how much fuel will be consumed. The officer-in-charge gives the requirements to the chief engineer, who superintends the taking on board of the fuel and the gas and other mechanical supplies.
The gas is admitted to the ship through a central gassing hose which leads off to each balloonet, the gas coming in directly from the storage holders through large mains sunk in the hangar floor or from the mains in a mooring mast. Four or five men are stationed along the keel inside the ship when gassing is going on to check the amount going to each bag and tie them off when the desired percentage of fill is reached. One man stands by the valve in the gas main and turns off and on as ordered, while the gassing coxswain, on duty in the ship, keeps track of how much gas is going into the ship, which bags it goes into, a list of the bags filled and tied off, and other gassing details.
As the gas enters the ship the lift increases, and this is overcome by putting water ballast aboard, superintended by a detail of four to six men. This is accurate work, for it must be remembered that large rigid airships are six hundred or more feet long, and too much water in one end or the other results in an upsetting movement which brings the overbalanced end down on the hangar floor, or in dangerous proximity to the ground if at a mast, and exerts an excessive lift on the other, a condition which may result in damage to the framework.
While the water ballast is being taken in the fuel supply comes aboard directed by the engineer's force, the fuel being distributed in tanks along the ship so that her "trim" may be maintained. Water ballast and fuel must not be taken on board at a faster rate than the incoming gas, so that the buoyancy of the ship may not be materially changed but kept approximately the same at all times.
After the ship is gassed, fueled, and ballasted, very careful lift and trim charts are worked out showing the amount and location of all fuel and ballast. These charts are posted in the pilot house and are constantly referred to by the operating officer on all flights. Finally, the engineers inspect and turn over all motors, and the ship is ready for flight.
When the crew goes on board a sufficient amount of ballast has to be immediately discharged to compensate for their weight. When passengers and freight come aboard more ballast has to be discharged. It will thus be seen that the airship's crew is kept very busy just prior to a voyage.
If starting from a hanger, an additional thousand pounds of ballast is discharged to increase the buoyancy and thus facilitate the ship's handling and give it positive lift for leaving the ground.
An airship flight is carried out, as far as possible, along the lines of any seagoing operation. All orders are given and all watches stood and relieved just the same as on a surface ship. During flight, in addition to the two helmsmen, there is on duty in the control car, the captain of the ship or the first lieutenant, the senior navigating officer, an assistant navigating officer, and one other watch-standing officer, who relieves the captain or first lieutenant when requested; otherwise, he makes frequent tours of inspection along the keel to -see that the gas bags are in proper position, the valves functioning, and the riggers on duty at their stations. The watch is relieved every four hours, a procedure carried out on all ships. In the radio cabin, generally in the control car, there is a radio operator always on watch.
Every two hours the gasoline supply is checked, the amount remaining computed, and its location posted on the chart in the control car. The engineer officer inspects the various power units, checking their operation at frequent intervals, and he also keeps an eye on the gasoline supply along the keel. If it is not necessary to utilize all the power units at one time, the engineer officer advises the officer having the deck the units that are to be used and those in reserve or being overhauled.
Another touch which reminds one of surface ships is the way orders are transmitted from the control car to the power units. An engine telegraph is used, designed, of course, for airships. When it is desired to "conn" the ship, orders are given to the steersman in accordance with Navy practice. Orders to the height steersman are given in a similar manner, although they are varied to suit the circumstances.
The crew of a three-million-cubic-foot airship, for commercial purposes, numbers about twenty men. Military and naval craft, however, carrying bombs, machine guns, and aerial cannon, would employ a larger crew, including ordnance and gunnery officers and men.
Quarters for passengers in the newest airships are gorgeously decorated, luxuriously upholstered, and more comfortable than any train or steamship could possibly be, and this, plus the stability of the airship, furnishes a method of travel unsurpassed by any other known means. In the British passenger airship R-36, are accommodations for fifty passengers on a scale rivaling that of the highest class hotels.
In the Paris Daily News the R-s6 was described as a flying palace, in which travelers are lulled to sleep in the sky. The ship is 672 feet long, has a lifting power of sixty-three tons, a maximum speed of sixty-five miles an hour, and a cruising range of 4,000 miles.
To quote from the Daily News: "Entering the passenger car one is struck by the delicate construction—slender aluminum pillars and semi-transparent walls of 'doped' cotton, stretched tightly over a marvelous framework. The dining-room, with its linen-covered and silver-laden tables, its rugs and soft curtains, is reminiscent of a cozy city cafe. The sleeping quarters are a marvel of ingenuity. There are two rows of cabins, each accommodating two passengers on light hammock-slung beds, the finest sleeping-car accommodation available. During the day the beds are folded up, and the apartment is transformed into a magnificent drawing-room with delicate light-blue curtains and deep, comfortable lounge chairs."
Are airships safe? Indeed they are. Millions of miles have been flown in airships, and hundreds of thousands of passengers carried without the loss of a life. Vulnerability in war must not be confused with peace-time operation of airships. A comparatively large number of German rigid airships were lost by gunfire during the war. In fact, they might be considered to be particularly vulnerable in battle, but so were concrete and steel forts, battleships, and battle cruisers.
Fire is popularly regarded as the chief danger to airship operation, but while the fire hazard exists, very few ships, except in battle, have been so destroyed in operation. Of course, open fires are prohibited, and smoking is not allowed, the cooking and heating being done by electricity. This is because the lifting gas, hydrogen, is by itself inflammable and gasoline fumes, also inflammable, are sometimes present inside the envelope.
American rigid airships, however, will not be exposed to these dangers. The buoyant medium will be helium, of which this country contains practically all of the world's supply. An engine is now being tested in one of the great manufacturing plants of this country which will do away with gasoline as a fuel, and with the fire hazard removed there can be no safer method of travel than by airship.
In answer to the question—"What good are airships?"—one need only say that they furnish the quickest, cleanest, most comfortable long-distance method of transportation known to man. No dust or cinders, no jerking and rattling, no seasickness or slatting about on a stormy sea. Comfort, cleanliness, and luxury, at a medium cost, make air transport an enjoyable and inexpensive experience.
There has been formed in the United States a great air transport corporation which will establish, within a year, several airship lines across the country, employing ships of enormous size, of great speed, and large carrying capacity. This will provide a supplementary means of transport in addition to our transcontinental railroads which will place the United States in the foremost position in aeronautical development in the world.