N.S.1 North Sea
In 1916 the first ship of the North Sea type was flown. Sixteen of these ships were built. A ship larger again than the Coastal was found to be required for extended cruising in the North Sea and for work with the Fleet, and the N.S. ship was designed. This class was intended to work with the fleet and had an endurance of some 24 hours at 50 knots. The N.S. 1, or North Sea type, in use at the end of the war, had an endurance, on occasion, of from two to three days. The North Sea type was designed to act as a scout with the fleet, or to carry out patrols of 20 hours. Its envelope has a cubic capacity of 360,000 feet, and the normal crew is 10 men, but the car will carry 20. Since the signing of the armistice, one of these vessels has made a record voyage for a non-rigid airship of 61 hours 21 minutes, and is understood to have been surpassed on two occasions only by Zeppelins. This class are 262 feet in length, main diameter 55 feet, and they are fitted with two 275 h. p. Eagle or two 260 h. p. Fiat engines.
It was owing to the incapacity-apparent or real- of the British military or naval designers to produce a satisfactory rigid airship that the 'N.S.' airship was evolved. The first of this type was produced in 1916, and on her trials she was voted an unqualified success, in consequence of which the building of several more was pushed on. The envelope, was made on the Astra-Torres principle of three lobes, giving a trefoil section. The ship carried four fins, to three of which the elevator and rudder flaps were attached.
She marks a distinct departure from the earlier classes; her machinery is in a unit quite separate from the main car, which latter only carries the crew and navigating party. The characteristic of these ships, more particularly the N.S. class, was that the petrol tanks and all other weights possible were carried direct on the envelope. In the N.S. class the car was separate from the power unit and the weight distributed over the length of the ship. This gave important advantages over all earlier non-rigids where the loads had been concentrated in the car. The gasoline carried by this ship amounted, under certain circumstances, to about three tons, and the distribution of this load constituted a very interesting problem. In the first ship it was carried in a number of tanks attached to either side of the top lobe at a convenient distance above the top ridges.
Access to tanks was obtained through the gun tube, which passes up through the centre of the ship, and then down a ladder way to a walking way along the top ridges. It was not, however, considered desirable that a man should have to be sent on top of the ship every time it was desired to turn on an additional gasoline tank, and arrangements were made to lead wires from the power unit round the surface of the envelope to each individual tank. This method operated satisfactorily, but difficulty was experienced with the hose conveying the gasoline from the tanks to the car. The weight involved in the whole installation was also considerable. An alternative scheme was therefore designed and installed in the next ship. This provided large 90-gal. gasoline tanks drawn up through the under surface of the envelope and suspended from the two top ridges by independent internal rigging generally similar to the main rigging.
It is an interesting point that in the first few ships these tanks were made totally of fabric lined with a special gasoline-resisting dope. Experiments on these tanks had been proceeding for a considerable time, and one tank had contained gasoline for over twelve months without serious loss of fuel or any apparent damage to the dope. It was found, however, after these tanks had been in use in several ships that an alteration in the constituents in the gasoline had included something which gradually softened the dope and caused cracking and leakage. As it was probable that further alterations in the gasoline might be made as the war proceeded, it was decided to be desirable to substitute aluminum tanks for these fabric ones, and metal tanks were, therefore, substituted in all later ships.
The long covered-in car was built up of a light steel tubular framework 25 feet in length. The forward portion was covered with duralumin sheeting, an aluminium alloy which, unlike aluminium itself, is not affected by the action of sea air and water, and the remainder with fabric laced to the framework. Windows and port-holes were provided to give light to the crew, and the controls and navigating instruments were placed forward, with the sleeping accommodation aft. The engines were mounted in a power unit structure, separate from the car and connected by wooden gangways supported by wire cables. A complete electrical installation of two dynamos and batteries for lights, signalling lamps, wireless, telephones, etc., was carried, and the motive power consisted of either two 250 horse-power Rolls-Royce engines or two 240 horse-power Fiat engines. The principal dimensions of this type are length 262 feet, horizontal diameter 56 feet 9 inches, vertical diameter 69 feet 3 inches. The gross lift is 24,300 lbs. and the disposable lift without crew, petrol, oil, and ballast 8,500 lbs. The normal crew carried for patrol work was ten officers and men. This type holds the record of 101 hours continuous flight on patrol duty.
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