the war progressed, and the designs of the raiding Zeppelins
improve, so did the design and performance of the British Coastal
defence airships. The SS Class ships had proved
not only a deterrant and protection for submarines, but they
could also engage the enemy threat as well. A larger ship was
therefore required with a bigger bomb load, and longer airborne
duration. The Coastal Class was born..
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.
Using a French Astra Torres
ungainly looking tri-lobed envelope and based on the French design,
a new larger scoting ship was required to have a longer duration
and heavier bomb load.Design and advancement on the envelope also
progressed with an unusual Tri-lobe design. This was
seen as a stronger, more aerodynamic. Again, the use of existing
technology was used to keep the costs down and production speeds
up with demand. The gondola was based on two tail-less Avro shorterned
aeroplane fuselages connected end to end, and carried 2 engines
in tandem. This produced a four of five seater car. The prototype
was delivered in early 1916 with other copies to follow.
The Tri-lobe envelope was 196 feet long and a capacity of 170,000
cft. The ridges in the envelope was connected to fabric curtains
inserted to help maintain the shape. Four ballonets were also
fitted, two in each of the lower lobes, and a single scoop consisting
of a single sheet of aluminium tuble of oval cross section reached
down towards the forward propellor. Later versions of the ship
had the scoop at the rear propellor. Single skids replaced the
normal undercarriage and also protected the propellers. The rigging
was also the same type as seen in an existing Astra Torres ship.
The Coastals were fitted with
a larger bomb load, a wireless, and 2 machine guns, one of which
was on top of the envelope. This was accessed by a tube and rope
ladder from the gondola. Sometimes commented as the "ugliest"
dirigibles ever made, these ships sometimes were erretic and unstable
in flight. The responsiveness in the controls was sluggish and
often caused the crew to be airsick. However one of the main advances
in airship technology was the very high rate of climb which the
coastals managed to provide.
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
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
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.
To the whole length of the
top ridges are attached the internal rigging girdles and also
the lacing girdles to which are secured the top and side curtains.
These curtains are composed of ordinary unproofed fabric and their
object is to make the envelope keep its trilobe shape. They do
not, however, divide the ship into separate gas compartments.
The rigging girdle consists of a number of fabric scallops through
which run strands of Italian hemp. These strands, of which there
are a large number, are led towards the bottom ridge, where they
are drawn together and secured to a rigging sector. To these sectors
the main external rigging cables are attached. The diagram shows
better than any description this rigging system.
Ten main suspensions are incorporated
in the Coastal envelope, of which three take the handling guys,
the remaining seven support the weight of the car.
The horizontal fins with the
elevator flaps, and the vertical fin with the rudder flap, are
fixed to the ridges of the envelope.
The car was evolved in the
first instance by cutting away the tail portion of two Avro seaplane
fuselages and joining the forward portions end on, the resulting
car, therefore, had engines at either end with seating accommodation
for four. The landing chassis were altered, single skids being
substituted for the wider landing chassis employed in the seaplane.
The car consists of four longerons with struts vertical and cross,
and stiffened with vertical and cross bracing wires. The sides
are covered with fabric and the flooring and fairing on the top
of the car are composed of three-ply wood. In the later cars five
seats were provided to enable a second officer to be carried.
The engines are mounted on
bearers at each end of the car, and the petrol and oil tanks were
originally placed adjoining the engines in the car. At a later
date various methods of carrying the petrol tanks were adopted,
in some cases they were slung from the envelope and in others
mounted on bearers above the engines.
Wireless telegraphy is fitted
as is the case with all airships. In the Coastal a gun is mounted
on the top of the envelope, which is reached by a climbing shaft
passing through the envelope, another mounting being provided
on the car itself.
Bombs are also carried on
frames attached to the car. Sunbeam engines originally supplied
the motive power, but at a later date a 220 horse-power Renault
was fitted aft and a 100 horse-power, Berliet forward. With the
greater engine power the ship's capabilities were considerably
Exceedingly long flights were
achieved by this type of ship, and those exceeding ten hours are
far too numerous to mention. The moot noteworthy of all gave a
total of 24 1/4 hours, which, at the time, had only once been
surpassed by any British airship.
Towards the end of 1917, these
ships, having been in commission for over two years, were in many
cases in need of a complete refit. Several were put in order,
but it was decided that this policy should not be continued, and
that as each ship was no longer fit for flying it should be replaced
by the more modern Coastal known as the C Star.
The record of one of these
ships so deleted is surely worthy of special mention. She was
in commission for 2 years 75 days, and averaged for each day of
this period 3 hours 6 minutes flying. During this time she covered
upwards of 66,000 miles. From this it will be seen that she did
not pass her life by any means in idleness.
The Coastal airship played
no small part in the defeat of the submarine, but its task was
onerous and the enemy and the elements unfortunately exacted a
heavy toll. A German wireless message received in this country
testified to the valiant manner in which one of these ships met
2 Classes of Coastal
were desgined, the standard Coastal and the C* (C
Star) Class. The most successful ship in this class was the C9
which flew from Mullion in Cornwall. The ship had a service flying
life of 2,500 hours 11 minutes, some 68,201 miles. The longest
single flight recorded by a Coastal ship was 24 hours 15 minutes
by C24 on 9th 10th July 1917. Production of this class of ship
ceased in 1916.
Only 2 were destroyed through
enemy action in the entire war. In total 45 Coastal
Class ships were built, however 12 were totally destroyed in some
manner and only 4 survived to the Armistice.