nd 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 mad