NC Navy Curtiss
The NC flying boats which were used on the trans-Atlantic flight marked the culmination of the war development of aircraft in the Navy. Being designed for war service, the boats were not at all freak machines put together to perform the single feat of a record-breaking flight, but are roomy and comfortable craft, designed and built in accordance with standard navy practice.
In 1910, when aviation competitions were just beginning, one of the most distinwished of early aircraft constructors declared himself satisfied that it would never be possible to exceed a span of 100 feet with the type of airplane then known, yet the first crossing of the Atlantic by air was made in less than a decade with an airplane which exceeded by 25 per uent the limiting dimensions thus boldly laid down. The increase in size was due in part to improvements in efficiency from an aerodynamic standpoint, but much more important factors have been the use of new structural arrangements and the giving of more careful attention to the efficient distribution of weight.
In August, 1917, Rear-Admiral D. W. Taylor, Chief Constructor of the Navy, initiated the project of building the largest flying boats in the world, to be of novel construction. Admiral Taylor had in mind the development of a seaplane of the maximum size, radius of action, and weight-carrying ability, for use in putting down the submarine menace. Had the German submarines gained the upper hand in 1918, the war would still be going on, and these great flying-boats would be produced in quantity and flown across the Atlantic to the centres of submarine activity.
This project was conceived with a view to getting antisubmarine planes into the war zone independent of shipping. The plan was to produce these great flying boats in quantity and to fly them across the Atlantic to the center of submarine activity. The armistice came before this plan could be carried out, but the trans-Atlantic flight which was undertaken in May, 1919, was strictly in line with the original purpose of the design and really in the nature of a service trial.
Early in September, 1917, Rear-Admiral D. W. Taylor called Naval Constructor Hunsaker and Commander G.C. Westervelt into his office, and gave them instructions to begin the design of a seaplane that could cross the Atlantic under its own power. The longest nonstop flight that had then been made was only about 1,200 miles, and that had been accomplished under ideal conditions, in the immediate neighborhood of a flying field where any ordinary mishap would have resulted merely in an enforced landing. The shortest route across the Atlantic required one hop under very difficult conditions of at least 1,330 miles. The Chief Constructor of the United States Navy wanted an aicraft that would bridge that gap, and, if possible, the full 1,933 miles from Newfoundland to Ireland.
The project was undertaken in the late summer of 1917, when the largest flying boat in existence was an early model of the H-16 equipped with twin Rolls-Royce engines. This ship had a cruising radius of 500 miles. The Navy was looking for a plane that could carry a heavy load of depth bombs across the ocean if necessary - one that could proceed to the hunting ground at daybreak, stay aloft all day, and return to its base at dark.
The success attained from previous attempts which had been made to produce flying boats larger than two-motored ones had hardly justified the effort. The production of some of the Curtiss boats of large size, were the only ones consistently devoted to developments in this direction. Those efforts, had not been productive of great success. From this fact, it is quite certain, had resulted, in considerable measure, the lack of confidence felt in these larger flying craft. This lack of success was due to the fact that though designs grew larger practically the same type of construction was maintained. This resulted in an increase in weight out of proportion to the increase in engine powers. Engine powers had not increased sufficiently, and engine weights per horsepower had not decreased rapidly enough, to meet this weight increase, and the result was flying boats over-weighted, under-powered, and of small cruising radii. With large sizes in aircraft there go inevitably all of the disadvantages of this size. Manufacturing facilities must be great, and buildings enormous.
The naval designers consulted with Mr. Glenn H. Curtiss, who, within a few days, submitted preliminary designs for two biplanes, both essentially alike in principle. One suggestion was for a five-motored boat of roughly 1,700 horsepower, the other for a three-motored boat of roughly 1,000 horsepower. Both were biplanes, and were similar in general except for the differences in size made possible by the differences in power. The boats for which these outline plans were submitted differed from the conventional type of flying boat in that the hulls were considerably shorter, and the tails, instead of being supported on these hulls, were supported on booms carried from the hull and from the wings. The smaller, three-motored design, was decided upon.
In working out the design for this machine with the engineering force of the Curtiss Corporation, the Navy, for the first time in the history of airplane construction, used the strictly scientific method. All airplanes of new model in that day and time were built by the empiric method. The builder roughly sketched his design, built a plane accordingly, and then, if the machine failed to perform as it was expected to, made changes in the construction, and kept on making changes until the model was either a success or definitely a failure. The project was far too great and too costly for the Navy to trust to any such slipshod plan. The design for the plane was worked out scientifically with as much care as would be put into the design of a bridge or a battleship. All pressures, weights, stresses, resistances, and so on, were exactly calculated in advance. The original calculations showed that a boat, weighing under 25,000 pounds, as projected, and driven by the power specified, taking into consideration the other factors to be worked into the design, would not have the speed at first estimated, and therefore would not have a radius of flight that could carry it from Newfoundland to Ireland. Thus, before a dollar was spent for materials, the Navy definitely abandoned a transatlantic seaplane as impracticable at that time, and took up the design of a plane of slightly smaller weight (22,000 pounds) which should have a flight radius sufficient to take it from America to the Azores. And this was the seaplane finally constructed.
The resulting flying boats were designated NC, the N for Navy and the C for Curtiss, because they were the joint production of the Navy and the Curtiss Engineering Corporation. The designers of the NC were Mr. G. H. Curtiss and Mr. W. L. Gilmore, of the Curtiss Co., and Commanders Westervelt, Richardson, and Hunsaker, of the Navy.
The term flying-boat is used for the NC type because it is actually a stout seaworthy boat, that ploughs through rough water up to a speed of 60 miles per hour, and then takes to the air and flies at a speed of over 90 miles per hour. This seaplane is neither a hydroplane nor a flying boat. It may be considered a compromise between these two types. The three engines are arranged as tractors in separate nacelles placed between the wings, and the pilot and assistant pilot are located in a cockpit just abaft the center motor. One gunner's cockpit is located on top of the center plane, while another is placed in the bow. The tail is of the biplane type and supported by hollow spars in an inverted pyramidal form of structure resting on the stern post of the hull. The pilot and observer have an entirely satisfactory view for general maneuvering and for landing and get-away. It was contemplated that additional gunners would be placed in the after portion of the hull with guns mounted on brackets so that they could cover the arc of fire from the beam to the stern and downward; also that this seaplane would carry a number of bombs, together with a non-recoil gun of large calibre at the bow.
The design and the construction of the NC-1, with its triple motors, huge size and other distinctive features, was carried out by the Navy in co-operation with the Curtiss Engineering Corp. It is not specifically a flying boat nor is it of the pontoon variety of seaplane, but combines the most valuable advantages of both, its size and purpose being considered. While it is entirely new and original in type, the NC-1 incorporates proven essentials in aircraft construction, and even before it was tested was regarded in naval circles as a pre-insured success rather than as an experiment.
This was the first American tri-motored seaplane, being propelled by 3 Liberty motors that develop a maximum of 1200 hp., giving it a cruising speed of 80 m.p.h. The flying weight of the machine is 22,000 Ib., while the weight of the seaplane itself, unloaded and without a crew, is 13,000 Ib. An idea of the size of the big seaplane is shown by the fact that the wing spread is 126 ft., the breadth of wing 12 ft., and the gap between wings 12 ft.
The hull of the NC was 45 feet long by 10 feet beam. The bottom was a doubleplank V with a single step somewhat similar in form to the standard Navy pontoon for smallest seaplanes. Five bulkheads divided the hull into six water-tight compartments with water-tight doors and a wing passage for access. The forward compartment has a cockpit for the lookout and navigator. In the next compartment are seated side by side the principal pilot or aviator and his assistant. Next comes a compartment for the members of the crew off watch to rest or sleep. After this there are two compartments containing the gasoline-tanks (where a mechanician is in attendance) and finally a space for the radio man and his apparatus. The minimum crew consists of five men, but normally a relief crew could be carried in addition.
The bare hull, as completed by the builder and ready for the installation of equipment, weighed only 2,800 pounds, yet the displacement was 28,000 pounds, this giving a ratio of 0.1 pound of boat per pound of displacement. This lightness of construction was attained by a careful selection and distribution of materials. The keel was of Sitka spruce, while the bottom planking was of Spanish cedar. Longitudinal strength was given by two girders of ash braced with steel wire. To guarantee water-tightness and yet keep the planking thin there was a layer of muslin set in marine glue between the two plies of planking.
The wings carried a load of 11.7 pounds per square foot in the air, but the structural weight was only 1.2 pounds per square foot. The total wing area was 2,380 square feet. The main wing spars were hollow spruce boxes. Each rib was a truss designed like a bridge consisting of continuous cap strips of spruce, corresponding to the upper and lower cords of a bridge truss, tied together by an internal web system of vertical or diagonal pieces of spruce. The ribs were 12 feet long but only weighed 26 ounces each. An interesting detail of the wing construction was the hinged leading edge which enclosed the control cables to the ailerons. This eliminated the air resistance of these cables, while at the same time they were accessible for inspection by merely swinging up the leading edge on its hinges.
The tail surfaces of the NC were made up as a biplane which resembled in general appearance and size the usual airplane. The NC tail was in fact twice as large as the ordinary complete single-seater fighting airplane. The tail was over 500 square feet in area, and the structure was supported by three hollow spruce booms braced by steel cable in such a way as to remain clear of all breaking seas and to permit a machine gun to be fired straight aft from the stern compartment without interference. This method of support was a radical change from former American and foreign practice, but resulted in several advantages besides an important saving in weight.
The great outstanding accomplishment of the aeronautical endeavour of the United States, during the World War, was the Liberty engine. Starting almost from a standing start, this engine was developed in something less than a year into the leading aviation engine of its type of the entire world. The four Liberty engines which drove the boat were mounted between the wings. At 400 horsepower per engine, the maximum power was 1,600 horsepower, or, with the full load of 28,000 pounds, 17.5 pounds carried per horsepower. One engine was mounted with a tractor propeller on each side of the center line, and on the center line the two remaining engines were mounted in tandem, or one behind the other. The front engine had a tractor propeller and the rear engine a pusher propeller. This arrangement was novel and had the advantage of concentrating weights near the center of the boat so that it could be maneuvered more easily in the air.
The first of the four NC flying boats which were constructed was completed and flown on October 4, 1918, or approximately one year from the commencement of the design. This huge biplane measuree 126 feet across the wings, while the hull of the boat was more than 50 feet long. In this test, although the craft was somewhat tail heavy, its operation as a whole was very satisfactory, and indicated that the work of the designers had been a success. It was found necessary to make slight changes in the position of the horizontal stabilizer to neutralize this tail-heavy condition, but otherwise no radical changes were required in the design or construction.
All records for carrying a large number of passengers in any type of airplane were broken Wednesday, 27 November 1918, at the Naval Air Station, Rockaway, when the Navy's newest type of seaplane, the giant NC-1, the largest seaplane in the world, made a flight with 50 men on board. Most of the men were accommodated in the large boat body. Separately, the NC-1 made the trip from Rockaway to Washington, about 350 miles, in 5 hours and 20 minutes. The flight from Washington to Hampton Roads, 150 miles, was covered in 2 hours and 15 minutes, and the trip from Hampton Roads to New York, 300 miles, took 4 hours and 20 minutes.
The NC-1 was propelled by three Liberty motors, and on one of its first public flights carried fifty-one passengers, afterward making a successful flight to Rockaway Beach, Long Island, from Langley Field on Hampton Roads, an airline distance of approximately 300 miles, in 4 hours and 20 minutes. It left the water weighing, with its load, 22,000 pounds as projected, but was able to fly at a slower speed than the design had indicated. Its maximum speed, eighty miles an hour, was greater than that calculated in the design. It was concluded that to accomplish an " all-the-way-across" flight would require the maintenance of the size as originally decided upon, and the addition of one more engine. The Navy tried the experiment of installing a fourth Liberty engine in the plane, and with this added power it flew successfully when weighing, with its load, 28,000 pounds. Four engines were thereupon definitely adopted for the plane.
So successful were the experiments with this first great flying-boat that several others of the same type were immediately constructed, a fourth Liberty motor being added to the later models. The second NC boat, the NC-2, was completed in March, 1919, and the NC-3 and NC-4 were completed in April, 1919.
The NC flying boat weighed when fully loaded 28,000 pounds, and when empty, but including radiator water and fixed instruments and equipment, 15,874 pounds. The useful load available for crew, supplies, and fuel was, therefore, 12,126 pounds, or over 43 per cent. The NC was capable of an endurance flight of 1,400 miles, carrying a crew of five men (900 pounds); radio and radiotelephone, 220 pounds; food and water, signal lights, spare parts, and miscellaneous equipment, 524 pounds; oil, 750 pounds; and gasoline, 9,650 pounds. The radio outfit was of sufficient power to communicate with ships 200 miles away. The radiotelephone could be used to talk to other planes in a formation or within a distance of 25 miles.
Six NC boats, the NC-5 through NC-10, were built at the Naval Aircraft Factory to Curtiss specifications. The first Navy order was in 1918; no NC was delivered prior to 1919, too late to see war service.
A squadron of six left Philadelphia in November 1919, they made a seven months' cruise to the Caribbean Sea and the West Indies, and returned to Philadelphia in June 1920, after covering a distance of no less than 12,731 miles under their own power, without serious mishap or loss of life. The squadron was accompanied on its voyage by the minelayer Shawmut, as a mother ship, and the minesweeper Sandpiper as a repair and fuel ship. As a rule the Sandpiper preceded the squadron from port to port, with the Shawmut bringing up the rear, keeping a vigilant lookout for machines which might have met with accident. Both ships acted, therefore, as a movable base, though the facilities they possessed were necessarily restricted. It was not found necessary, however, to dock the flying boats, and repairs of a nature which required the boats to be lifted from the water were few and far between, the crews themselves carrying out minor repairs en route.
As each flying boat carried its own anchor and cable, the machines came to anchor at the various ports of call in the same way as ordinary surface vessels. Landings were frequently made in the open sea with the wind blowing at a velocity of 40 knots, and on more than one occasion the boats rode safely and undamaged through an 80-knot gale. The weather encountered shortly after the cruise began was such as to impose a severe test on the airworthiness and nautical qualities of the squadron, and the behaviour of the machines is held to have demonstrated that flying boats of this type are capable of carrying on active operations over periods of time hitherto considered out of the question.
The last NC boat was lost on 22 January 1921 and stricken from the inventory in March 1921.
|
NEWSLETTER
|
| Join the GlobalSecurity.org mailing list |
|
|
|
