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..
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
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.
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.
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.
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
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.
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.
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.
and non-return valves are employed in a similar manner to S.S.
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.
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
main suspensions are incorporated in the Coastal envelope, of
which three take the handling guys, the remaining seven support
the weight of the car.
horizontal fins with the elevator flaps, and the vertical fin
with the rudder flap, are fixed to the ridges of the envelope.
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.
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.
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.
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 increased.
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.
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.
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.
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 with destruction.
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.
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.