To the envelope of the N.S. is rigged a long covered-in car. The framework of this is built up of light steel tubes, the rectangular transverse frames of which are connected by longitudinal tubes, the whole structure being braced by diagonal wires. The car, which tapers towards the stern, has a length of 85 feet, with a height of 6 feet. The forward portion is covered with duralumin sheeting, and the remainder with fabric laced to the framework. Windows and portholes afford the crew both light and space to see all that is required. In the forward portion of the car are disposed all the controls and navigating instruments, together with engine-telegraphs and voice pipes. Aft is the wireless telegraphy cabin and sleeping accommodation for the crew.
A complete electrical installation is carried of two dynamos and batteries for lights, signalling lamps, telephones, etc. The engines are mounted in a power unit structure separate from the car and reached by a wooden gangway supported by wire cables. This structure consists of two V-shaped frameworks connected by a central frame and by an under-structure to which floats are attached. The mechanics' compartment is built upon the central frame, and the engine controls are operated from this cabin.
In the original power units two 250 horse-power Rolls Royce engines were fitted, driving propellers on independent shafts through an elaborate system of transmission. This proved to be a great source of weakness, as continual trouble was experienced with this method, and a fracture sooner or later occurred at the universal joint nearest to the propeller. When the modified form of ship was built the whole system of transmission was changed, and the propellers were fitted directly on to the engine crankshafts.
At a later date 240 horse-power Fiat engines were installed, and the engineers' cabin was modified and an auxiliary blower was fitted to supply air to the ballonets for use if the engines are not running.
In the N.S. ship as modified the car has been raised to the same level as the engineers' cabin, and all excrescences on the envelope were placed inside. This, added to the improvement effected by the abolition of the transmission shafts, increased the reliability and speed of the ship, and also caused a reduction in weight.
The leading dimensions of the ship are as follows: length, 262 feet; width, 56 feet 9 inches; height, 69 feet 3 inches. The gross lift is 24,300 lb.; the disposable lift, without crew, petrol, oil, and ballast, 8,500 lb. The normal crew carried when on patrol is ten, which includes officers.
As in the case of the Coastal, a gun is mounted on the top of the envelope, which is approached by a similar climbing shaft, and guns and bombs are carried on the car.
These ships have become notorious for breaking all flying records for non-rigid airships. Even the first ship of the class, despite the unsatisfactory power units, so long ago as in the summer of 1917 completed a flight of 49 hours 22 minutes, which at the time was the record flight of any British airship. Since that date numerous flights of quite unprecedented duration have been achieved, one of 61 1/2 hours being particularly noteworthy, and those of upwards of 30 hours have become quite commonplace.
Since the Armistice one of these ships completed the unparalleled total of 101 hours, which at that date was the world's record flight, and afforded considerable evidence as to the utility of the non-rigid type for overseas patrol, and even opens up the possibility of employing ships of similar or slightly greater dimensions for commercial purposes.
N.S. 6 appeared several times over London in the summer months of 1918, and one could not help being struck by the ease with which she was steered and her power to remain almost stationary over such a small area as Trafalgar Square for a quite considerable period.