British Airships, Past, Present, and Future

by George Whale

RIGID AIRSHIP No. 9

Rigid Airship No. 1 having met with such a calamitous end, the authorities became rather dubious as to the wisdom of continuing such costly experiments. Most unfortunately, as the future showed and as was the opinion of many at the time, rigid construction in the following year 1912 was ordered to be discontinued. This decision coincided with the disbanding of the Naval Air Service, and for a time rigid airships in this country were consigned to the limbo of forgetfulness. After the Naval Air Service had been reconstituted, the success which attended the Zeppelin airships in Germany could no longer be overlooked, and it was decided to make another attempt to build a rigid airship in conformity with existing Zeppelin construction. The first proposals were put forward in 1913, and, finally, after eleven months delay, the contract was signed. This airship, it has been seen, was designated No. 9.

No. 9 experienced numerous vicissitudes, during the process of design and later when construction was in progress. The contract having been signed in March, 1914, work on the ship was suspended in the following February, and was not recommenced until July of the same year. From that date onwards construction was carried forward; but so many alterations were made that it was fully eighteen months before the ship was completed and finally accepted by the Admiralty.

The ship as designed was intended "to be generally in conformity with existing Zeppelin construction," with the following main requirements stipulated for in the specification:

1. She was to attain a speed of at least 45 miles per hour at the full power of the engines.

2. A minimum disposable lift of five tons was to be available for movable weights.

3. She was to be capable of rising to a height of 2,000 feet during flight.

The design of this ship was prepared by Messrs. Vickers, Ltd., and as it was considered likely that owing to inexperience the ship would probably be roughly handled and that heavy landings might be made, it was considered that the keel structure and also the cars should be made very strong in case of accidents occurring. This, while materially increasing the strength of the ship, added to its weight, and coupled with the fact that modifications were made in the design, rendered the lift somewhat disappointing. The hull structure was of the "Zahm" shape as in No. 1, a considerable portion being parallel sided, while in transverse section it formed a 17-sided polygon. In length it was 526 feet with a maximum diameter of 53 feet. The hull framework was composed of triangular duralumin girders, both in the longitudinal and transverse frames, while the bracing was carried out by means of high tensile steel wires and duralumin tubes. Attached to the hull was a V-shaped keel composed of tubes with suitable wire bracings, and in it a greater part of the strength of the structure lay. It was designed to withstand the vertical forces and bending moments which resulted from the lift given by the gasbags and the weights of the car and the cabin. The keel also provided the walking way from end to end of the ship, and amidships was widened out to form a cabin and wireless compartment.

The wiring of the transverse frames was radial and performed similar functions to the spokes of a bicycle wheel. These wires could be tightened up at the centre at a steel ring through which they were threaded and secured by nuts.

In addition to the radial wires were the lift wires, which were led to the two points on the transverse frames which were attached to the keel; on the inflation of the gasbags, the bags themselves pressed upon the longitudinal girders on the top of the ship, which pressure was transferred to the transverse frames and thence by means of the several lift wires to the keel. In this way all the stresses set up by the gas were brought finally to the keel in which we have already said lay the main strength of the ship.

The hull was divided by the transverse frames into seventeen compartments each containing a single gasbag. The bags were composed of rubber-proofed fabric lined with gold-beater's skin to reduce permeability, and when completely full gave a total volume of 890,000 cubic feet. Two types of valve were fitted to each bag, one the Parseval type of valve with the pressure cone as fitted in No. 1, the other automatic but also controlled by hand.

To distribute the pressure evenly throughout the upper longitudinal frames, and also to prevent the gasbags bulging between the girders, nets were fitted throughout the whole structure of the hull.

The whole exterior of the ship was fitted with an outer cover, to protect the gasbags and hull framework from weather and to render the outer surface of the ship symmetrical and reduce "skin friction" and resistance to the air to a minimum. To enable this cover to be easily removed it was made in two sections, a port and starboard side for each gasbag. The covers were laced to the hull framework and the connections were covered over with sealing strips to render the whole weathertight.

The system of fins for stabilizing purposes on No. 9 were two--vertical and horizontal. The vertical fin was composed of two parts, one above and the other below the centre line of the ship.

They were constructed of a framework of duralumin girders, covered over with fabric. The fins were attached on one edge to the hull structure and wire braced from the other edge to various positions on the hull. The horizontal fins were of similar design and attached in a like manner to the hull. Triplane rudders and biplane elevators of the box type were fitted in accordance with the German practice of the time. Auxiliary biplane rudders were fitted originally abaft the after car, but during the first two trial flights they proved so very unsatisfactory that it was decided to remove them.

Two cars or gondolas were provided to act as navigating compartments and a housing for the engines, and in design were calculated to offer the least amount of head resistance to the wind. The cars were composed of duralumin girders, which formed a flooring, a main girder running the full length of the car with a series of transverse girders spaced in accordance with the main loads. From each of these transverse girders vertical standards with a connecting piece on top were taken and the whole exterior was covered with duralumin plating. The cars were suspended in the following manner. Two steel tubes fitting into a junction piece at each end were bolted to brackets at the floor level at each end of the transverse girders. They met at an apex above the roof level and were connected to the tubing of the keel. In addition, to distribute the weight and prevent the cars from rocking, steel wire suspensions were led to certain fixed points in the hull.

Each car was divided into two parts by a bulkhead, the forward portion being the control compartment in which were disposed all instruments, valve and ballast controls, and all the steering and elevating arrangements. Engine-room telegraphs, voice pipes and telephones were fitted up for communication from one part of the ship to the other. The keel could be reached by a ladder from each car, thus providing with the climbing shaft through the hull access to all parts of the ship.

The original engine equipment of No. 9 was composed of four Wolseley-Maybach engines of 180 horse-power each, two being installed in the forward car and two in the after car. As the ship was deficient in lift after the initial flight trials had been carried out, it was decided to remove the two engines from the after car and replace them with a single engine of 250 horse-power; secondly, to remove the swivelling propeller gear from the after car and substitute one directly-driven propeller astern of the car. This as anticipated reduced the weight very considerably and in no way lessened the speed of the ship.

The forward engines drove two four-bladed swivelling propellers through gear boxes and transmission shafts, the whole system being somewhat complicated, and was opposed to the Zeppelin practice at the time which employed fixed propellers.

The after engine drove a large two-bladed propeller direct off the main shaft.

The petrol and water ballast were carried in tanks situated in the keel and the oil was carried in tanks beneath the floors of the cars.

The wireless cabin was situated as before mentioned in a cabin in the keel of the ship, and the plant comprised a main transmitter, an auxiliary transmitter and receiver and the necessary aerial for radiating and receiving.

No. 9 was inflated in the closing days of 1916, and the disposal lift was found to be 2.1 tons under the specification conditions, namely, barometer 29.5 inches and temperature 55 degrees Fahrenheit. The contract requirements had been dropped to 3.1 tons, which showed that the ship was short by one ton of the lift demanded. The flight trials were, however, carried out, which showed that the ship had a speed of about 42 1/2 miles per hour.

The alterations previously mentioned were afterwards made, the bags of the ship were changed and another lift and trim trial was held in March, 1917, when it was found that these had had the satisfactory result of increasing the disposable lift to 3.8 tons or .7 ton above the contract requirements, and with the bags 100 per cent full gave a total disposable lift of 5.1 tons.

Additional trials were then carried out, which showed that the speed of the ship had not been impaired.

For reference purposes the performances of the ship are tabulated below.

Speed:
Full 45 miles per hour
Normal = 2/3 38 " " "
Cruising = 1/3 32 " " "
Endurance:
Full 18 hours = 800 miles
Normal 26 " = 1,000 "
Cruising 50 " = 1,600 "

No. 9 having finished her trials was accepted by the Admiralty in Mar. 1917, and left Barrow, where she had been built, for a patrol station.

In many ways she was an excellent ship, for it must be remembered that when completed she was some years out-of-date judged by Zeppelin standards. Apart from the patrol and convoy work which she accomplished, she proved simply invaluable for the training of officers and men selected to be the crews of future rigid airships. Many of these received their initial training in her, and there were few officers or men in the airship service who were not filled with regret when orders were issued that she was to be broken up. The general feeling was that she should have been preserved as a lasting exhibition of the infancy of the airship service, but unfortunately rigid airships occupy so much space that there is no museum in the country which could have accommodated her. So she passed, and, except for minor trophies, remains merely a recollection.