During the summer of 1916, German submarine activities made it very, clear that the pre-war methods of coping with such craft were astonishingly ineffective. It did not then appear that the United States would become involved in the war, but the possibility began to be discussed, and special attention was naturally paid to the technical problem presented by anti-submarine warfare. Due to the strict secrecy, shrouding the anti-submarine operations of the Allies, only very vague accounts of the weapons used were available. It did appear, however, that it was necessary, as in the receipt for rabbit pie, first to catch your submarine. This seemed to be a problem of intensive patrol of coastal waters and the approaches to maritime ports. We knew of the conversion of trawlers, yachts and miscellaneous small craft for this purpose and, of course, were aware of the British contracts placed in the United States for motor boats and flying boats.
In addition to such craft, rather fragmentary accounts began to appear in the press, or were brought back by returning travelers, which indicated that the British were experimenting with small airships or dirigibles for coastal patrol work. This intelligence was not at all definite and entirely non-technical.
The possible need for dirigibles by our own navy happened to be under consideration at that time. The department, in May, 1915, had contracted for one dirigible with a firm which had got hold of a German engineer, a German mechanic and an Austrian dirigible pilot, supposed to be experts. This first dirigible designed and built under the supervision of the imported talent was a great disappointment, for when it was completed, two years later, April, 1917, it was so much over weight that it could barely lift itself off the ground. It was entirely without military value and was further worthless as a training ship, an account of its complicated and unreliable power plant installation. It did, however actually fly and since the firm had built the ship in good faith and at a cost greatly in excess of the contract price, it was formally accepted and designated A-1. After a few short flights it was put back in its shed, deflated, and eventually broken up.
This experience was naturally most discouraging, especially as little or nothing was learned which would serve to insure a satisfactory design if another attempt were made. The prospects for developing airships for the navy were very poor. Aside from the concern which built the A-1, the Connecticut Aircraft Company, there were in the country no firms with any experience in modern airship construction.
However, intimations of the success obtained abroad with dirigibles could not be ignored, and as the failure to provide dirigibles if called for by the Department would rest with the Bureau of Construction and Repair, it was necessary to anticipate such a call and to learn the new art. For this there was no teacher.
In any branch of engineering, when one passes beyond the limits of practical experience, one must depend on theory; and where an adequate theory has not been developed one must deduce a convenient one. The theory of free ballooning was well established and the literature of the art extends back a hundred years, but the theory of airship design is not at all complete, as the bulk of the work before the war had been done by the French and German armies and was naturally kept secret. However, we had the manuscript of Prof. Marchi's lectures at the University of Paris on airships and balloons, Basenach's book "Prall Luftschiffe," Haas und Dietzius on "Stofifdehnungen und Formänderungen der Hiille von Prall Luftschiiife," Eberhardt on "Theorie und Berechnung von Motorluftschiflfen," and a few papers in the technical press or presented before scientific societies. When all of the available literature was assembled it made an imposing pile, but a careful threshing revealed very little that was definite enough to be useful. The theory was, however, sufficiently complete in a general way except for a void with regard to the stability and control in flight. For knowledge of practice and details of construction, we were a little better off though wholly without experience. An investigation of dirigible construction in England, France and Germany had been made in 1913 and a good deal of information obtained, in spite of the normal European military restrictions. However, such information applied to dirigibles of 1913 and we were well aware that we were in 1916, and it was evident that the British had developed an entirely new type.
In order to be prepared for the future, various theoretical and experimental studies were undertaken by the bureau in the summer of 1916. A need for training officers in operating airships was felt by the office of the chief of naval operations, which in October, 1916, asked the bureau to prepare studies for a training airship to carry six men and to have an endurance of 4 hours at 40 miles per hour. Some work was done on this problem, but was abandoned on receipt of later requirements from that office for an airship to be used both for training and coast patrol. These later requirements were received on December 13, 1916, and specified a maximum speed of 45 miles, endurance of 12 hours at 35 miles, a crew of 3 men, with radio for 150 miles, and provision for alighting on the surface of the sea and for towing from a vessel.
These military requirements were carefully compared with information available as to foreign construction and with an independent analysis of the coast patrol problem.
From British accounts a small airship was useful. We knew they used a 75- or 80-horsepower motor, but did not know the speed, endurance or load. It was clear, however, that for patrol work the endurance should be enough to permit daylight patrols of 10 or 12 hours duration. At night, a patrol airship would be relatively useless and hence such an endurance seemed great enough.
The speed must be sufficient to enable the airship to get back to her base against a head wind. As our ships would operate off the Atlantic coast and as the prevailing winds are westerly, it was necessary to provide a safe margin of speed. It was believed that a wind of 30 miles per hour was the limit for handling the dirigible in and out of her shed and, therefore, she would not operate on days with greater wind. This would permit operating in all fair weather. To provide for a margin to get home, an excess speed of 15 miles was considered reasonable, giving an air speed or speed in still air of 45 miles.
The size of the ship determines the total displacement or lift. The English experience seemed to point to the smallest size consistent with other qualities and in our ignorance and inexperience it seemed very desirable to attempt the smallest size of ship that promised to be useful. It also had to be remembered that there were no qualified pilots available and our first pilots would have to teach themselves to fly. A small ship appeared especially desirable for training.
The only engines in the country with any claim to reliability were at this time the Curtiss 8-cylinder 100-horsepower, and the Hall-Scott 4-cylinder 100-horsepower aeroplane engines. These engines were of the high revolution type not especially suitable for airship work, but there were no others. Twin engines would give greater reliability than one, but would require a larger ship. A decision was made to try to use but one engine in order to keep down the size of the ship.
Having fixed the above characteristics, it remained to fix the load to be carried; fuel and oil for ten or twelve hours, three men (the crew), radio, a blower to keep up pressure of air in ballonets, an allowance for ballast and bombs, and a margin for unforeseen equipment and contingencies.
The necessary lift required an envelope of about 77,000 cubic feet, which with ordinarily good hydrogen gas gives a total lift or buoyancy of 5275 pounds.
The envelope was then designed to give this lift and made of a shape which should be easy to drive. Experiments were conducted at the wind tunnel at the Washington Navy Yard to determine the resistance of this shape in order that the speed could be computed. It appeared possible to obtain the desired speed of 45 miles, but without any margin to spare.
We had heard that the British dirigibles were fast, but aside from them there was no record of a dirigible of such small size ever having been driven at a speed so high as 45 miles. Unless the fin and rudder surfaces were correctly proportioned, there would be difficulty in steering the ship at high speed. A research in the wind tunnel was, therefore, undertaken with a model of the ship fitted with fins and rudders of various sizes and arrangements. From these experiments fins and rudders were designed which appeared to be on the safe side and to guarantee stability in flight. (These surfaces were found on the trials to be satisfactory and, subsequently, it was possible to reduce them in area when our pilots became more expert.)
The car to carry the engine, fuel tanks, pilots and other weights was designed after aeroplane practice, and presented no difficulties, except balance. The fuel tanks might be in flight full or nearly empty and to avoid disturbing the trim of the ship the tanks must be under the center of buoyancy of the envelope. The weight of fins and rudders tends to make the ship trim by the stern and to balance this, the fixed weights, engine, men, radio, blower, etc., should be placed forward of the center of buoyancy a sufficient distance. To provide for proper balance the car was designed to have the tanks in the rear end under the center of buoyancy of the envelope and the engine forward with the men and other weights between. This gave a long car resembling the fuselage of an aeroplane and distributed the weights correctly.
The next problem was the suspension of this car from the gas bag, or envelope, in such a manner as not to deform the bag or put undue tension on any part of its fabric. The envelope was merely a fabric gas bag held taut by internal gas pressure and the greatest delicacy and skill were required in suspending the car. The calculations involved in the design of the suspension had to be devised from general engineering principles, but were not very satisfactory on account of the indeterminate nature of the distribution of load between various suspension members. It was desired to use the lightest fabric for the envelope that could be considered safe and to this the suspension was to be attached so that the envelope would be held fair and stiff with no more than one inch of water pressure inside. The calculation made was an application of the naval architect's usual method for calculating the longitudinal strength of ships and appears to be justified by the results.
To verify the calculated strength of the envelope fabric and the internal pressure necessary to preserve a fair form under the influence of the suspension loads and the forces expected on fins and rudders, a water-model experiment was made. This form of test was described by Haas and Dietzius, who give credit to Crocco, and proved to be extremely useful. So complete a method of verification by model experiment with the actual materials to be used, is, I believe, unique in practical engineering work.
The water-model tests were made with a 1/30th size model envelope made of the fabric which it was proposed to use, filled with water and suspended in an inverted position by cords arranged as proposed for the actual suspension. The model was, therefore, geometrically similar as to form and suspension to the full sized ship and the theory of the method shows that when tested 1/30th size the stresses and deformations of the envelope are identical with what is to be expected for the ship. Tests were made at different pressures and at different trims to make sure that when climbing or diving nothing abnormal would happen.
From the water-model tests it was clear that a gas pressure inside the envelope of about one inch of water was often but not always necessary. To maintain this pressure, regardless of changes of barometric pressure with altitude, changes of temperature, or loss of gas by leakage, ballonets or air bags were built inside the envelope which could be inflated by a wind pipe connecting with a scoop placed in the rear of the propeller under the bottom of the car. This means of pressure maintenance was, of course, useless if the engine were dead, and to provide for this emergency a blower was inserted in the air line. This blower was an ordinary multi-vane ventilating blower driven by a 2-horsepower motorcycle engine.
The ballonet capacity was fixed at 25 per cent of the total volume of the envelope. Such a capacity was enough to compensate for the change in pressure incident to a change of 7500 feet in altitude on a normal day. There were two ballonets provided, one in each end of the ship, so that they could, by manipulation of suitable valves, be used as trimming tanks. This system had been used on French and German dirigibles.
The required speed of 45 miles meant that at high speed the nose of the ship would tend to cave' in, due to external pressure unless the interior gas pressure were about 2 inches of water. As it was not desired to carry so high a pressure, the nose was stiffened by battens of ash. This feature had been seen on English dirigibles.
The characteristics of the design were as follows:
Length: 160 ft.
Diameter: 31.5 ft.
Height: 50 ft.
Power of main engine: 100 H. P.
Power of blower engine: 2 H. P.
Maximum speed: 45 miles per hour
Cruising speed: 35 miles per hour
Endurance at 45 miles: 10 hours
Endurance at 35 miles: 16 hours
Gasoline capacity :100 gals.
Ballonet Volume: 19,250 cu. ft.
Envelope Volume: 77 ,000 cu. ft.
Gross lift at .068 lbs. per cu. Ft: 5,275 lbs.
Weight empty: 3,256 lbs.
Instruments, etc.: 100
Blower outfit: 100
Radio outfit: 250
Lighting set: 15
Two men: 320
Fuel and oil: 633
Ballast: 290
Margin: 311
Useful Load, 38 per cent or: 2,019 lbs.
By January 6, 1917, the designs and calculations were sufficiently well advanced to indicate that an airship could be built which would materially exceed the military requirements specified by the chief of naval operations in his letter of December 13, 1916, and preliminary plans and specifications were submitted to the Secretary of the Navy. The type was approved by the general board January 26, 1917 and by the secretary January 27, 1917. At that time it was the intention to build one or two airships as an experiment, but relations with Germany were rapidly becoming strained and on February 17, 1917 the Secretary of the Navy authorized the construction of 16 airships of the type proposed.
In its letter to the Department, the bureau stated that the construction of such a ship was within the capacity of the industrial facilities of the country, but authorization of the construction of 16 of them came as a thunderbolt. To get delivery of such a quantity in any reasonable time seemed at first glance entirely impossible, when it was realized that the work would have to be done by firms entirely unfamiliar with the work and without allowance of time for experiment and research. It was clearly impossible to allow time enough to build an experimental ship to the bureau's design and, after correcting any defects, to proceed with the construction of the other units. This would have been the normal peace time procedure, but six months time was not available and a start had to be made at once.
The chief constructor, therefore, decided to go ahead with the construction regardless of the unproved nature of the design and on February 6, 1917, sent copies of the plans and specifications to five firms which had offered their facilities to the department for war work and which he considered to be in a position to help. Representatives of these five firms met with the chief constructor on February 12 to discuss ways and means for getting the 16 ships built quickly.
The five firms requested to undertake the work were the Curtiss Aeroplane & Motor Corporation of Buffalo, the Connecticut Aircraft Company, and the three great rubber manufacturers. Goodyear, Goodrich and U.S. Rubber. The conference resembled a patriotic meeting rather than a gathering of prospective government contractors, but in spite of a very great desire to help the Navy it was immediately apparent that no one of them was in a position to handle the work. In the first place they were without experience in airship building with the exception of the one unsuccessful attempt of the Connecticut Aircraft Company. None of the rubber companies had ever made fabric of the hydrogen resisting quality and strength required, and it would be necessary not only to develop new processes but to put in new machinery and special equipment to manufacture it. Supplies of the special fine cotton cloth needed would have to be obtained and the market for it was in an abnormal condition.
None of the firms represented had any building large enough to erect an airship, and though the navy was planning to put up eight airship sheds at coastal stations, the date of completion of such sheds was indefinite and probably too remote to render such sheds available for the first few ships turned out. It was of utmost importance that one ship should be rushed to completion in order to prove the design before the others were too far advanced.
It was agreed at the conference that the manufacturers should form a committee which committee should arrange that each concern would bid for such proportion of the work as appeared to be within its capacity, that the raw materials, information, and experience of all would be pooled both before and during manufacture, and that each would bid a flat price with a guarantee and bond. The present form of cost-plus contract or "Navy Order" was then unknown, and the bid price arrived at was purely an estimate based to a large extent on information from abroad which the bureau made available to the committee. The price agreed upon was about $40,000 per airship with a guarantee to produce a practical ship making more than 35 miles per hour and a guarantee to replace any defective parts for three months. As things worked out, most of the contractors lost money, for the work was done as a rush job and no expense was spared.
The Goodyear Company as the most experienced, having built free balloons for a number of years, was in the best position to go ahead. R.H. Upson and R.A.D. Preston, aeronautical engineers of the Goodyear Company's staff, had had several years experience in designing, making and practical handling of free balloons. They could be relied upon to cope with the present problem. Goodyear agreed to put up at its own expense a complete erection and testing establishment consisting of a field near Akron, O., with a large capacity hydrogen generating plant and an airship shed 200 feet by 100 feet by 100 feet, together with the barracks for the necessary field organization. This decision was reached March 20, 1917, ground was broken for the hangar and hydrogen plant April 1, 1917, and the first balloon (a free balloon) was inflated in the hangar June 1, 1917.
The Goodrich Company to make up for its lack of experience in making up airship envelopes cabled for M. Juillot, the well-known engineer of the Lebaudy firm in Paris, whom they had been in correspondence with. M. Juillot sailed immediately and later when the United States had declared war on Germany the Department was able to arrange for the release from the French Army of two of M. Juillot's assistants, M. Bourguigon and M. Gautier. These men, together with Mme. Bourguigon who was a skilled fabric worker, were of the greatest assistance in introducing the practical refinements in manufacture about which information was so much needed.
The United States Rubber Company decided not to attempt to build complete airships, but undertook to supply fabric for the Connecticut Aircraft Company.
On March 14, 1917, contracts were awarded as follows: Goodyear nine airships, Goodrich two airships, Curtiss three airships, and Connecticut two airships. The Curtiss Company undertook to supply cars, power plants and fins to Goodyear and Goodrich and later turned over its contract for three complete ships to Goodrich, supplying the same parts for them. Connecticut sub-contracted for its cars and fins with the Pigeon Frazer Company of Boston and got its power plant from the Hall-Scott Motor Company of San Francisco.
At first great difficulty was had by all concerns in making gastight fabric in accordance with the very rigid specifications. These had been based on French practice in requiring a diffusion of only nine liters per square meter for 24 hours (at 15°C and 760 mm.).
The chemical organization necessary to make this rather delicate and elaborate test on a piece cut from each roll of fabric naturally did not exist in the bureau. There were in all about 112,000 yards of fabric to be tested or 2260 rolls. An organization of such magnitude could hardly be improvised effectively, but a way out of the difficulty was found by utilizing existing facilities. The three rubber companies making fabric were required to put in hydrogen diffusion measuring apparatus of a uniform type and to make the tests themselves following a standardized procedure. The bureau contracted with the Pittsburgh Testing Laboratory, Inc., to supply chemists to supervise the tests in the contractors' laboratories and to represent the bureau. Finally, as a final check and control on the work, the U.S. Bureau of Standards was asked to put in similar equipment in its chemical laboratory, in order that entirely independent tests and researches on rubberized fabrics might be carried out. In this way most valuable advice and assistance were rendered by the bureau of standards.
When samples of fabric which could pass the specification test were finally turned out, exposure tests were started at the Bureau of Standards, Washington Navy Yard, and at Pensacola Air Station, in order to eliminate those whose life would be short. It was very soon discovered that some apparently very excellent fabric from one contractor perished quickly in strong sunlight but this was not discovered in time to prevent some of such fabric being used in his first few ships. This is, of course, one of the difficulties of rapid production; there is no time for cautious investigation. However, with the discovery of this phenomenon which seemed to be a matter of oxidization of the rubber compound, the remedy for it was also found and the envelopes made of the early fabric were all replaced by the contractor. During the building of the ships, the fabric was constantly improved and it is safe to say that this improvement was of the order of 500 per cent. This intensive research eventually produced the fabric now used which is found by comparative tests to be superior to the best developed during the war in England, France or Italy.
For some of this improvement, credit must be given to information received from England after the United States declared war. The English methods were of the greatest assistance. with them as a guide, the American manufacturers were able to adopt their own peculiarly American shop practices to work out a fabric which finally equaled the, best foreign product.
The Goodyear Company completed the first airship in May, 1917, before their shed at Akron was completed. The Goodrich Company had in the 'meantime found an abandoned shed at the "White City," Chicago, put it in order and arranged for a large supply of hydrogen in flasks. In order to get a trial of a type ship for the benefit of all contractors, it was arranged to ship the first Goodyear ship to Chicago. The ship was assembled, inflated and given a short flight by Mr. R. H. Upson, of the Goodyear Company. He was so favorably impressed with the results that on the second time up, the weather being favorable, he considered there was less danger in trying to fly home to Akron than in attempting a return to the little field at Chicago which was seriously restricted by buildings and telegraph wires. Accordingly, he headed for Akron at midnight and at noon of the next day, Decoration Day, 1917, landed in a meadow 10 miles from Akron. Had the oil supply held out he could have landed on the Goodyear field, but the motor seized at the last minute.
The flight is remarkable in several particulars. In the first place, it was one of the longest dirigible flights on record up to that time. In the second place, it was a maiden flight of a new airship designed from theoretical and experimental data .by a designer of no experience and built in two months by a firm without previous airship experience. In the third place, the flight is astonishing because Mr. Upson was not then an airship pilot and, by our present standards, could not have been expected to handle the ship until he had gone through several weeks' instruction at the hands of an experienced pilot. However, he was an experienced balloonist and as an engineer had a thorough appreciation of how the airship was designed to function.
This flight was very encouraging for the production program, as it proved that the design was all right and permitted the contractors to go ahead with confidence. From then on the ships were delivered with regularity and by the end of the year were operating at the various naval air stations.
The following table gives the dates of delivery of these ships:
No. |
Mfg. |
Date |
---|---|---|
B-1 |
Goodyear |
July 19, ’17 |
B-5 |
Goodyear |
Aug. 11, ’17 |
B-13 |
Goodrich |
Sept. 11, ’17 |
B-3 |
Goodyear |
Oct. 22, ’17 |
B-4 |
Goodyear |
Dec. 4, ’17 |
B-15 |
Connecticut |
Dec. 14, ’17 |
B-14 |
Goodrich |
Jan. 11, ’18 |
B-2 |
Goodyear |
Jan. 22, ’18 |
B-9 |
Goodyear |
Jan. 31, ’18 |
B-8 |
Goodyear |
Feb. 25, ’18 |
B-7 |
Goodyear |
Feb. 27, ’18 |
B-6 |
Goodyear |
March 3, ’18 |
B-10 |
Goodrich |
April 15, ’18 |
B-16 |
Connecticut |
April 15, ’18 |
B-11 |
Goodrich |
May 8, ’18 |
B-12 |
Goodrich |
June 6, ’18 |
As the airships came along improvements and changes based on experience were incorporated. Suggestions for improvements in details of design came first from the contractors and later, as more navy pilots became trained, a few useful suggestions came from the service. The Goodyear Company proposed many refinements in design which they introduced as a result of the experience of their test pilots, Mr. Upson and Mr. Preston. The enterprise of that firm in providing a flying field at Akron near their works placed them in a position to experiment in the air.
The improvements of most interest were those which led to an increase in speed. The first ships had a speed of about 40 miles per hour. It was found that one of the vertical fins could safely be left off thus cutting down the resistance of one fin and its supporting wires. Later the car was suspended closer to the envelope, shortening the suspension and saving resistance. Still later the suspension itself was simplified and knots and loops cleaned up. A somewhat longer and easier form of envelope gave greater lift and probably less, or at least no more, resistance. The air pipes to the ballonets were placed inside the envelope to save resistance. Improved propellers were developed also. The air scoop finally became only a short sheet metal tube hinged to the envelope proper which could be let down into the slip stream of the propeller or pulled up out of the way, greatly decreasing the resistance and weight of the ship by eliminating the scoop under the car, the blower and air line to the bag.
As a result, the speed was progressingly raised from 40 miles to 48 miles with the same engine. The designed maximum speed was 45 miles per hour, but the contractors were required to guarantee 35 only.
A gratifying feature of the construction was the weight. If the ships had run over the designed weight their usefulness would have been seriously compromised. Fortunately, all ships, including the first of the series, showed a useful lift in excess of the designed load. In some cases it appeared that the structural weights would run over, but in those cases the buoyancy also ran somewhat in excess of the designed figures, leaving a good margin for the useful load.
An automatic gas valve of entirely original design was developed by John R. Gammeter of the Goodrich Company for these airships. This valve has proved to be so reliable, so gastight and positive in its operation that it has since been used as standard equipment on the department's later airships and kite balloons.
The ships in service have more than fulfilled all expectations. Designed to cruise for 16 hours, a record on patrol of 40 hours has been made with one of them at Key West. Aside from the short life of the fabric on the first ships, which was replaced, the ships have stood up well, and seven are still in use. One Goodrich ship was in continuous service with its original envelope for 15 months. Another ship, made by Goodyear, kept one inflation of gas for nine months and during this time was in the air 743 hours.
More remarkable still, though flown by all sorts of inexperienced people not a life has been lost as a result of accident. There have been plenty of accidents, in fact, nearly every sort of operating mishap has taken place, but by a combination of good luck, good design, and good construction, the men have been saved.
One ship broke down at sea off Cape May and fell into the water, but remained afloat until the crew could be taken off by a passing schooner. The car was provided with pneumatic floats. Another ship broke down at sea off Long Island but remained in the air for three days and eventually made a safe landing at Halifax, saving both ship and crew. The valves were tight and the ship could operate as a free balloon.
On a dark night at Akron, an airship collided with a kite balloon which had been left up on the end of a 1000-foot wire. The envelope was torn and the gas released causing the ship to fall. The engine being forward struck the ground first and the crew were piled up on top of it. One of the men was badly hurt.
In the first few months at Akron before anyone had become a really qualified pilot, ships often got into difficulties. One pilot got his ship trimmed over 60 degrees by the head, but the suspension held. Probably a dozen times, ships have become involved with trees. At one time, there was an apparent affinity for chestnut trees. In no case was any serious damage done except to the envelope. As the pilots became experienced the roosting in trees stopped entirely.
A few gasoline fires have been experienced in the air, but the hydrogen in the envelope never caught fire. The car is suspended well below the envelope, and gas valves are out of the way. In all of these cases- the crew put out the fire in time to avert disaster.
One ship at Pensacola had a gasoline fire when on the ground ready to start. The crew jumped out and the handling gang instead of putting out the blaze let go the handling lines. The ship floated away and after a long time the fire reached the hydrogen and she exploded. It is unlikely that such a fire, starting when in the air, would have got any great headway, as the crew would not have been tempted to jump.
Jumping from a dirigible is, of course, always possible, with a parachute, and parachutes are supplied as regular equipment, but now only seldom carried. There has been no case of a crew having to abandon ship via the parachutes, though men have jumped in parachutes for practice. The first man in the United States to jump from an airship going at lull speed was Ensign R. Emerson of the Bureau of Construction and Repair, who was responsible for the type of parachute supplied and wanted to make sure of it. The experiment was successful.
The navy's first attempt to design, build and operate airships has been fraught with difficulties, but has been on the whole very successful. This is to some extent due to the modest size selected for the first attempt, but mainly to the energy and enthusiasm of the people concerned, both in and out of the service. The "B" class airships, as these 16 were called, were used at home for training and coast patrol. In France our air forces operated French ships and in England, English ships. But though the B ships had no direct war service, they contributed their mite by training our pilots so that they could go abroad and take over immediately the operation of the foreign types. About 170 pilots were so trained in the United States on B ships before the armistice. In addition, B ships were used on coast patrol and flew over 13,600 hours or about 400,000 miles.
The B class airships are in no way an improvement over contemporary English airships of the same type and are in some respects less handy and simple, though of greater carrying capacity and endurance. The only noteworthy features are the conditions of their design, manufacture and initial operation. The ships were put into production from plans without waiting for the perfection of an experimental ship.
A long time afterwards, I had the pleasure of talking shop with a British airship designer who had little to say that was complimentary regarding this design. His attitude in general was that we had showed nothing new and, in his opinion, could have improved the design in many features. When I told him that the first ship completed was put through final acceptance trials within four months of placing the contract by a firm without previous experience and by a free balloon pilot without airship training, he was astonished and agreed heartily that the conservative policy adopted had saved months of experimenting. He considered that to put a series of airships into production based wholly on paper designs required either courage or ignorance, or both, and that our successful outcome constituted a "world's record." I had to tell him that a great deal of the design which appeared to him as normal practice required on our part extensive theoretical and experimental research. We had no practical experience to go on, and even such a vital matter as the necessary factors of safety had to be arrived at by a largely theoretical investigation of the possible stresses in operation. Logically enough, we arrived at what is substantially French and British practice which in their case is based on experience with airships built in the past.
After the completion of the B class ships, there was an almost complete stop to airship work in the United States and an improved single engine type which was designed in the winter of 1917-18 was not built. The reason for this was a discouraging report from abroad as to the effectiveness of airships on anti-submarine patrols. But the conclusion drawn from airship operations abroad in the bad winter weather proved to be premature. As the good weather of the spring of 1918 permitted English and French airships to operate more freely, it became apparent that we should proceed immediately with a larger and faster type. Using this time all of the practical experience gained at home with B class ships and detailed information from abroad with regard to British, French and Italian airships, the bureau undertook to take a step in advance and to design a ship of maximum performance. Full use was made of all available sources of information. In the initial stages of the design the data regarding the performance of British airships, obtained from the British Admiralty through Lieut. Commander P.L. Teed, R.N.V.R., who was attached to the office of the British Naval Attaché at Washington—was especially helpful.
Experience showed the advantages of high speed to cope with winds, great endurance to follow convoys long distances, and a duplicated power plant to lessen chances of complete breakdown at sea. The C class was designed with these ends in view.
To obtain high speed, a new form of envelope and a car of very low resistance were developed from wind-tunnel experiments. The speed was to be obtained by a combination of high power with the utmost refinement in design to keep down resistance. Twin engines were used giving a total of 250 B.H.P. The actual speed on trial was 60 miles per hour, making probably the fastest airship of its size ever built.
During the intensive research to improve the B class envelope fabric, it was determined that deterioration was largely caused by the combined action of heat and the actinic rays of sunlight. Attempts were made to meet the trouble by filtering out the actinic rays through coloring first the exterior of the fabric, and later the rubber gas film between the plies of cloth. Proper coloring materials were hard to get, and it was usually found that the deterioration resulting from the heat absorbed by the fabric was nearly as rapid as before. About the time the C class design was begun, information from abroad showed that the British airships were suffering from the same troubles and that the most successful protection for the fabric was a coating of aluminum powder, the object of this coating being to stop all the light from going below the surface of the envelope and to reflect and radiate quickly nearly all the heat. The C class envelopes were made of fabric coated with bright aluminum. This fabric has been found by comparative exposure tests superior to the best developed during the war in England, France and Italy.
The principal dimensions and characteristics of the C-5, as weighed off before her start for Newfoundland, were as follows:
Length: 192’ 0”
Diameter: 41’ 9”
Volume: 182,000 cu. Ft.
Purity:98.6%
Temperature: 65° F.
Barometer: 30
Total Lift: 12,700 lbs.
Weight empty: 7,940 lbs.
Weight Carried:
Crew (6) men: 1015 lbs.
Fuel: 3250 “
Oil: 120 “
Navigating equipment: 25 “
Radio: 250 “
Food: 15 “
Water for drinking: 85 “
Ballast: 0 “
Useful load: 4,760 lbs.
Endurance at 45 m. p. h., 47 hrs., or 2150 miles.
Endurance at 55 m. p. h., 28 hrs., or 1540 miles.
During 1918, contracts were placed with Goodyear and Goodrich for 30 airships, the cars to be supplied from the Burgess Company, Marblehead, Mass. After the armistice, contracts were reduced to 15 ships.
C-1, the first ship, was completed in September 1918, and on its maiden trip October 22, 1918, flew 400 miles from Akron to Washington in 8¾ hours. It flew over the Navy Department building and landed at Anacostia to permit an inspection by officers of the department. It then preceded to Rockaway, Long Island. Later in the year, the C-1 was ordered to Key West and flew down the coast stopping at intermediate air stations.
The C-5 on May 14, 1919, flew from Montauk to Newfoundland with six men in 25 hours, 50 minutes, a distance of 1022 nautical miles on chart without stop. This flight will remain for a long time as a notable achievement. The distance actually flown (not being in a straight line) was about 1200 nautical miles or very nearly the distance from Newfoundland to the Azores.
The C-5 was unfortunately lost at Newfoundland in a gale while moored out in a field and was, therefore, unable to attempt the Trans-Atlantic Flight which was within her designed endurance.
The navy's first airships, the B class, were thoroughly practical ships and while not remarkable for performance, are interesting as the solution of a design and production problem. The navy's second lot of airships, the C class, were, in performance, an enormous advance over the B class and placed us at once abreast of the times. These ships are generally admitted to be, for their type, equal to or superior to anything abroad.