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U. S. NAVAL INSTITUTE, ANNAPOLIS, MD.

DESIGN AND CONSTRUCTION OF THE NC

FLYING BOATS

By COMMANDER G. C. WESTERVELT, C. C., U. S. Navy

In June, 1917, two months after the entry of the United States into the World War, no definite air policy or program had been adopted by this country. This condition was due to the lack of any conclusive information regarding the work of the Allied Governments along these lines, and to varied and contradictory recommendations which had been received from the War Departments and the Admiralties of Great Britain and France as to the types of planes which should be adopted by this country. To remedy this condition an informal joint Army and Navy Board was appointed to proceed to Europe and to make a study of air matters among the principal governments engaged in the war against Germany, and to recommend the steps to be taken by our government in building up its own air services and in carrying out a definite air policy.

The personnel of this committee was Major R. C. Bolling, Captain V. C. Clark, Captain E. S. Gorrell, Captain Howard Marmon and Captain Hughes representing the army, and Lieutenant W. G. Child and the writer representing the navy. In accordance with instructions to the committee, they proceeded to Europe, arriving in London the latter part of June. At this time, the naval activities of the U. S. Government were directed mainly against the submarines. The center of naval activities was the American Embassy in London, and by this time the naval officers had become keenly aware of the grave menace of the German submarines. At the embassy all discussions centered around this subject, and it was evident that fuller methods of combating the submarine must be provided and provided very

quickly. Accordingly, we began a particular and detailed study of the types of aircraft for use against the submarine menace. This study was carried on in England, in France, and in Italy, and, as a result of this study, it was concluded that the quickest way for the navy to obtain results in the air would be with kite balloons, for observation purposes, anchored to a destroyer or some other type of patrol vessel, and with seaplanes of the flying boat type, as differentiated from the hydroaeroplane, for patrol purposes and for the bombing of submarines.

At this time, the largest flying boat in use for patrol work was the H-12, a craft equipped with two Rolls-Royce motors, with a lifting capacity of approximately 9000 lbs., and a cruising radius of slightly over 500 miles. This type of boat had proved successful in patrol work, except for its limited cruising radius. Because of the fact that the regions in which submarines were active were often a considerable distance from the naval air bases, the entire time available for patrol was often used in flying to and from a base. It was very desirable that larger craft should be provided, craft which could not only carry a heavy load of bombs, but which also had sufficient radius of flight for the trip from the naval bases to the patrol regions and return.

The writer returned to this country on September 1, 1917, and on September 2 reported the results of the investigations to Rear Admiral D. W. Taylor, the Chief of the Bureau of Construction and Repair. Admiral Taylor had been much interested in the work of the larger flying boats, and his parting injunction to the writer before his departure for Europe was to examine carefully the work being done along the line of flying craft much larger even than any then in use. When the report with its recommendations had been presented to Admiral Taylor, he immediately went far beyond any recommendations which had been made, and ordered the design of a flying boat able to fly itself, if possible, across the ocean. This would mean the capacity to proceed before daylight from a seaplane base to the patrol area, to spend the day in patrol work or in convoy, and to return to its base after dark. In addition to this, it must be able to carry several bombs of a size sufficient to increase very materially over the possibilities of that day the danger zone in the bombing of submarines.

All the information made available regarding the design and construction of flying boats of great size indicated the enormous

difficulty of such a project. The trend of opinion of the European air ministries was against such large sizes, and, as far as the methods of construction and the motor powers available at that time were concerned, the limit of size had been practically reached. On the presentation of these facts to Admiral Taylor, and the pointing out to him of the possibility of failure of such a project, he declined absolutely to be interested in this phase of the problem, and in his characteristic manner closed the discussion he was having with Naval Constructor Hunsaker, head of the Construction and Repair Aeronautical Section, and the writer, with instructions to "get busy and produce results."

This was the inception of the design of the NC type of flying boats. After a conference between Naval Constructor Hunsaker and the writer, it was decided to call upon Mr. Glenn Curtiss, at that time the American most experienced in the design and construction of seaplanes, for his suggestions as to the type of seaplane which might best fulfil the requirements. In obedience to a request from Admiral Taylor, Mr. Curtiss came to Washington, and, in a conference between the naval officers above referred to and himself, it was decided to give consideration to the possibilities of a seaplane capable of sustained flight from Newfoundland to Ireland, if possible, or at least capable of flight from Newfoundland to the Azores. Certain definite conclusions reached by the bureau regarding the probable type of such a seaplane were given Mr. Curtiss for his examination.

Within a few days after this conference, Mr. Curtiss returned to Washington with preliminary plans for two types of flying boats, embodying in their general characteristics the conclusions of the bureau-one a five motor 1700 horsepower machine, and the other a three motor 1000 horsepower machine. Both were biplanes, similar in design, and differing only in size, the size being dependent upon the available horsepower. The hulls of these machines differed greatly from the conventional design. They were much shorter than the conventional boat hull, were shaped more like the pontoon of a seaplane, and with the intention that the tail surfaces instead of being supported by the hull would be carried by a system of outriggers in part from the upper wing beams, and in part from the stern of the hull. These suggestions covered rough sketches only of the proposed machines, together with certain estimates based on extensive experience as to weights

and sizes. Admiral Taylor was in favor of the larger boat. The writer, however, due to his experience in airplane construction, his familiarity with the limitations in manufacturing facilities, and because of the small experience of our designers, and of uncertainties regarding the availability of suitable engines, argued in favor of the smaller craft. The final decision was to not attempt the construction of the larger size of 1700 horsepower but to stick to a smaller one of approximately 1000 horsepower.

In taking up the design of such a seaplane, it was very evident that radical changes in the method of design must be followed. With the methods of design at the time almost generally employed, the limits of size had been practically reached. The largest machine at that time in use was the Handley-Page night bomber. In the design of this airplane new and advanced methods had been employed, and to its study much consideration was given. This machine had a total lifting capacity of 11,000 lbs. and was equipped with two 275-horsepower Rolls-Royce motors. The dead weight was approximately 6600 lbs., and the allowable weight for oil, gasoline, cooling water, crew and miscellaneous supplies, which grouped together are called by the name of "useful load," was 4400 lbs. This made the value of the useful load 40 per cent of the gross load, which was the maximum percentage which had been obtained in any large machine. Naval Constructor Hunsaker in estimates which had been made of various planes of an average lifting capacity of 2500 lbs. had found that the percentage useful load was from 30 to 32 per cent. The proposed design for the 1000-horsepower flying boat called for a total load of approximately 25,000 lbs. In comparing this machine with the HandleyPage night bomber, it was apparent that the design of the HandleyPage would have to be improved upon and the percentage of the useful load made at least as high if this design was to be considered successful. One possibility of improvement of the design was in the use of the Liberty motor which was at that time undergoing its first tests, and which gave promise of being lighter for its power that any other motor then in use.

It has been found in the design and construction of large airplanes and seaplanes that the unescapable dead weights, such as engines, propellers, radiators, gasoline and oil tanks, crew, etc. which must be allowed for, require, in a completed plane which will carry them successfully, a total weight of, roughly, from three to

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