British Airships, Past, Present, and Future

by George Whale

The urgent need for a non-rigid airship to carry out anti-submarine patrol having been satisfied for the time with the production of the S.S. B.E. 2C type, the airship designers of the Royal Naval Air Service turned their attention to the production of an airship which would have greater lift and speed than the S.S. type, and, consequently, an augmented radius of action, together with a higher degree of reliability. As the name "Coastal" or "Coast Patrol" implies, this ship was intended to carry out extended sea patrols.

To obtain these main requirements the capacity of the envelope for this type was fixed at 170,000 cubic feet, as compared with the 60,000 cubic feet and, later, the 70,000 cubic feet envelopes adopted for the S.S. ships. Greater speed was aimed at by fitting two engines of 150 horse-power each, and it was hoped that the chances of loss owing to engine failure would be considerably minimized.

The Astra-Torres type of envelope, with its system of internal rigging, was selected for this class of airship; in the original ship the envelope used was that manufactured by the French Astra-Torres Company, and to which it had been intended to rig a small enclosed car. The ship in question was to be known as No. 10. This plan was, however, departed from, and the car was subsequently rigged to the envelope of the Eta, and a special car was designed and constructed for the original Coastal. Coastal airship No. 1 was commissioned towards the end of 1915 and was retained solely for experimental and training purposes. Approximately thirty of these airships were constructed during the year 1916, and were allocated to the various stations for patrol duties.

The work carried out by these ships during the two and a half years in which they were in commission, is worthy of the highest commendation. Before the advent of later and more reliable ships, the bulk of anti-submarine patrol on the east coast and south-west coast of England was maintained by the Coastal. On the east coast, with the prevailing westerly and south-westerly winds, these airships had many long and arduous voyages on their return from patrol, and in the bitterness of winter their difficulties were increased ten-fold. To the whole-hearted efforts of Coastal pilots and crews is due, to a great extent, the recognition which somewhat tardily was granted to the Airship Service.

The envelope of the Coastal airship has been shown to be of 170,000 cubic feet capacity. It is trilobe in section to employ the Astra-Torres system of internal and external rigging. The great feature of this principle is that it enables the car to be slung much closer to the envelope than would be possible with the tangential system on an envelope of this size. As a natural consequence there is far less head resistance, owing to the much shorter rigging, between the envelope and the car.

The shape of the envelope is not all that could have been desired, for it is by no means a true streamline, but has the same cross section for the greater part of its length, which tapers at either end to a point which is slightly more accentuated aft. Owing to the shape, these ships, in the early days until experience had been gained, were extremely difficult to handle, both on the landing ground and also in the air. They were extremely unstable both in a vertical and horizontal plane, and were slow in answering to their rudders and elevators.

The envelope is composed of rubber-proofed fabric doped to hold the gas and resist the effects of weather. Four ballonets are situated in the envelope, two in each of the lower lobes, air being conveyed to them by means of a fabric air duct, which is parallel to the longitudinal centre line of the envelope, with transverse ducts connecting each pair of ballonets. In earlier types of the Coastal, the air scoop supplying air to the air duct was fitted in the slip stream of the forward engine, but later this was fitted aft of the after engine.

Six valves in all are used, four air valves, one fitted to each ballonet, and two gas valves. These are situated well aft, one to each of the lower lobes, and are fitted on either side of the rudder plane. A top valve is dispensed with because in practice when an Astra-Torres envelope loses shape, the tendency is for the tail to be pulled upwards by the rigging, with the result that the two gas valves always remain operative.

Crabpots and non-return valves are employed in a similar manner to S.S. airships.

The Astra-Torres system of internal rigging must now be described in some detail. The envelope is made up of three longitudinal lobes, one above and two below, which when viewed end on gives it a trefoil appearance. The internal rigging is attached to the ridges formed on either side of the upper lobe, where it meets the two side lobes. From here it forms a V, when viewed cross sectionally, converging at he ridge formed by the two lobes on the underside of the envelope which is known as the lower ridge.