NAVAL AIRSHIPS.--THE RIGIDS--RIGID AIRSHIP No. 1
The responsibility for the development the Rigid airship having been
allotted to the Navy, with this object in view, in the years 1908 and
1909 a design was prepared by Messrs. Vickers Ltd., in conjunction with
certain naval officers, for a purely experimental airship which should
be as cheap as possible. The ship was to be known as Naval Airship No.
1, and though popularly called the Mayfly, this title was in no way
official. In design the following main objects were aimed at:
1. The airship was to be capable of carrying out the duties of an
aerial scout.
2. She was to be able to maintain a speed of 40 knots for
twenty-four hours, if possible.
3. She was to be so designed that mooring to a mast on the water
was to be feasible, to enable her to be independent of her
shed except for docking purposes, as in the case with surface
vessels.
4. She was to be fitted with wireless telegraphy.
5. Arrangements were to be made for the accommodation of the crew
in reasonable comfort.
6. She was to be capable of ascending to a height of not less
than 1,500 feet.
These conditions rendered it necessary that the airship should be of
greater dimensions than any built at the time, together with larger
horse-power, etc.
These stipulations having been settled by the Admiralty, the Admiralty
officials, in conjunction with Messrs. Vickers Ltd., determined the
size, shape, and materials for the airship required. The length of the
ship was fixed at approximately 500 feet, with a diameter of 48 feet.
Various shapes were considered, and the one adopted was that
recommended by an American professor named Zahm. In this shape, a
great proportion of the longitudinal huff framework is parallel sided
with curved bow and stern portions, the radius of these curved portions
being, in the case of the bow, twice the diameter of the hull, and in
the case of the stern nine times the same diameter. Experiments proved
that the resistance of a ship of this shape was only two-fifths of the
resistance of a ship of the same dimensions, having the 1 1/2 calibre
bow and stern of the Zeppelin airships at that time constructed.
A considerable difference of opinion existed as to the material to be
chosen for the construction of the hull. Bamboo, wood, aluminium, or
one of its alloys, were all considered. The first was rejected as
unreliable. The second would have been much stronger than aluminium,
and was urged by Messrs. Vickers. The Admiralty, however, considered
that there was a certainty of better alloys being produced, and as the
ship was regarded as an experiment and its value would be largely
negatived if later ships were constructed of a totally different
material, aluminium or an alloy was selected. The various alloys then
in existence showed little advantage over the pure metal, so pure
aluminium was specified and ordered. This metal was expected to have a
strength of ten tons per square inch, but that which arrived was found
to be very unreliable, and many sections had, on test, only half the
strength required. The aluminium wire intended for the mesh wiring of
the framework was also found to be extremely brittle. A section of the
framework was, however, erected, and also one of wood, as a test for
providing comparisons. In the tests, the wooden sections proved,
beyond all comparison, the better, but the Admiralty persisted in their
decision to adopt the metal.
Towards the end of 1909 a new aluminium alloy was discovered, known as
duralumin. Tests were made which proved that this new metal possessed
a strength of twenty-five tons per square inch, which was over twice as
strong as the nominal strength of aluminium, and in practice was really
five times stronger. The specific gravity of the new metal varied from
2.75 to 2.86, as opposed to the 2.56 of aluminium. As the weights were
not much different it was possible to double the strength of the ship
and save one ton in weight. Duralumin was therefore at once adopted.
The hull structure was composed of twelve longitudinal duralumin
girders which ran fore and aft the length of the ship and followed the
external shape. The girders were secured to a steel nose-piece at the
bow and a pointed stern-piece aft. These girders, built of duralumin
sections, were additionally braced wherever the greatest weights
occurred. To support these girders in a thwartship direction a series
of transverse frames were placed at 12 feet 6 inches centres throughout
the length of the ship, and formed, when viewed cross-sectionally, a
universal polygon of twelve sides. For bracing purposes mesh wiring
stiffened each bay longitudinally, so formed by the junction of the
running girder and the transverse frames, while the transverse frames
between the gasbags were stiffened with radial wiring which formed
structure similar to a wheel with its spokes. The frames where the
gondolas occurred were strengthened to take the addition weight, while
the longitudinals were also stiffened at the bow and stern.
Communication was provided between the gondolas by means of an external
keel which was suspended from extra keel longitudinals. In this design
the keel was provided for accommodation purposes only, and in no way
increased the structural stability of the ship as in No. 9 and later
ships. This keel, triangular in section, widened out amidships to form
a space for a cabin and the wireless compartment. The fins and
rudders, which were adopted, were based entirely on submarine
experience, and the Zeppelin method was ignored. The fins were fitted
at the stern of the ship only, and comprised port and starboard
horizontal fins, which followed approximately the shape of the hull,
and an upper and lower vertical fin. Attached to these fins were box
rudders and elevators, instead of the balanced rudders first proposed.
Auxiliary rudders were also fitted in case of a breakdown of the main
steering gear abaft the after gondola. Elevators and rudders were
controlled from the forward gondola and the auxiliary rudders from the
after gondola.
The gasbags were seventeen in number and were twelve-sided in section,
giving approximately a volume of 663,000 cubic feet when completely
full. Continental fabric, as in use on the Zeppelin airships, was
adopted, although the original intention was to use gold-beater's skin,
but this was abandoned owing to shortage of material. These bags were
fitted with the Parseval type of valve, which is situated at the top,
contrary to the current Zeppelin practice, which had automatic valves
at the bottom of the bags, and hand-operated valves on the top of a few
bags for control purposes. Nets were laced to the framework to prevent
the bags bulging through the girders.
The whole exterior of the hull was fitted with an outer cover; Zeppelin
at this time used a plain light rubber-proofed fabric, but this was not
considered suitable for a ship which was required to be moored in the
open, as in wet weather the material would get saturated and
water-logged. Various experiments were carried out with cotton, silk
and ramie, and, as a result, silk treated with Ioco was finally
selected. This cover was laced with cords to the girder work, and
cover-strips rendered the whole impervious to wet. Fire-proofed fabric
was fitted in wake of the gondolas for safety from the heat of the
engines.
Two gondolas, each comprising a control compartment and engine-room,
were suspended from the main framework of the hull. They were shaped to
afford the least resistance possible to the air, and were made of
Honduras mahogany, three-ply where the ballast tanks occurred, and
two-ply elsewhere. The plies were sewn together with copper wire. The
gondolas were designed to have sufficient strength to withstand the
strain of alighting on the water. They were suspended from the hull by
wooden struts streamline in shape, and fitted with internal steel-wire
ropes; additional wire suspensions were also fitted to distribute the
load over a greater length of the ship. The engines were carried in
the gondolas on four hollow wooden struts, also fitted internally with
wire. The wires were intended to support the gondolas in the event of
the struts being broken in making a heavy landing.
Two engines were mounted, one in each gondola, the type used being the
8-cylinder vertical water-cooled Wolseley developing a horse-power of
160. The forward engine drove two wing propellers through the medium
of bevel gearing, while the after engine drove a single large propeller
aft through 4 gear box to reduce the propeller revolutions to half that
of the engine. The estimated speed of the ship was calculated to be 42
miles per hour, petrol was carried in tanks, fitted in the keel, and
the water ballast tanks were placed close to the keel and connected
together by means of a pipe.
No. 1 was completed in May, 1911. She had been built at Barrow in a
shed erected on the edge of Cavendish Dock. Arrangements were made
that she should be towed out of the shed to test her efficiency at a
mooring post which had been prepared in the middle of the dock. She
was launched on May 22nd in a flat calm and was warped out of the shed
and hauled to the post where she was secured without incident. The
ship rode at the mooring post in a steady wind, which at one time
increased to 36 miles per hour, until the afternoon of May 25th, and
sustained no damage whatever. Various engine trials were carried out,
but no attempt was made to fly, as owing to various reasons the ship
was short of lift. Valuable information was, however, gained in
handling the ship, and much was learnt of her behaviour at the mast.
More trouble was experienced in getting her back into the shed, but she
was eventually housed without sustaining any damage of importance.
Owing to the lack of disposable lift, the bags were deflated and
various modifications were carried out to lighten the ship, of which
the principal were the removal of the keel and cabin entirely, and the
removal of the water-trimming services. Other minor alterations were
made which gave the ship, on completion, a disposable lift of 3.21
tons. The transverse frames between the gasbags were strengthened,
and a number of broken wires were replaced.
On September 22nd the ship was again completed, and on the 24th she was
again to be taken out and tested at the mooring post. Unfortunately,
while being hauled across the dock, the framework of the ship
collapsed, and she was got back into the shed the same day.
Examination showed that it was hopeless to attempt to reconstruct her,
and she was broken up at a later date. The failure of this ship was a
most regrettable incident, and increased the prejudice against the
rigid airship to such an extent that for some time the Navy refused to
entertain any idea of attempting a second experiment.
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.
RIGID AIRSHIP No. 23 CLASS
After the decision had been made in 1915 that work on No. 9 should be
restarted, the Admiralty determined that a programme of rigid airships
should be embarked upon, and design was commenced.
Several ships of the same class were, ordered, and the type was to be
known as the 23 class. Progress on these ships, although slow, was
more rapid than had been the case with No. 9, and by the end of 1917
three were completed and a fourth was rapidly approaching that state.
The specification, always ambitious, laid down the following main
stipulations.
(1) The ship is to attain a speed of at least 55 miles per hour
for the main power of the engines.
(2) A minimum of 8 tons is to be available for disposable weights
when full.
(3) The ship must be capable of rising at an average rate of not
less than 1,000 feet per minute, through a height of 3,000
feet starting from nearly sea level.
As will be seen later this class of ship, although marking a certain
advance on No. 9 both as regards workmanship and design, proved on the
whole somewhat disappointing, and it became more evident every day that
we had allowed the Germans to obtain such a start in the race of
airship construction as we could ill afford to concede.
We may here state that all of the ships of this class which had been
ordered were not completed, the later numbers being modified into what
was known as the 23 X class; four in all of the 23 class were built, of
which two--Nos. 23 and 26--were built by Messrs. Vickers, Ltd., at
Barrow, No. 24 by Messrs. Wm. Beardmore and Co., at Glasgow, and No. 25
by Messrs. Armstrong, Whitworth and Co., at Selby, Yorkshire.
In many respects the closest similarity of design exists between No. 9
and No. 23, especially in the hull, but it will be of interest to
mention the salient differences between the two ships.
The length of the hull, which in No. 9 was 520 feet, was increased in
No. 23 to 535 feet, and the number of gasbags from seventeen to
eighteen. This gave a total volume of 997,500 cubic feet compared with
890,000 cubic feet in No. 9, with a disposable lift under specification
conditions of 5.7 tons as opposed to 3.8 tons.
The longitudinal shape of No. 23 is a modified form of "Zahm" shape,
the radius of the bow portion being twice the diameter of the parallel
portion, while the stern radius is three times the same diameter.
In design the hull framework is almost a repetition of No. 9,
particularly in the parallel portion, the same longitudinal and
transverse frames dividing the hull into compartments, with tubes
completely encircling the section between each main transverse frame.
The system of wiring the hull is precisely the same in both the ships,
and nets are employed in the same way.
The triangular section of keel is adhered to, but its functions in No.
23 are somewhat different. In No. 9 it was intended to be sufficiently
strong to support all the main vertical bending moments and shearing
forces, but in No. 23 it was primarily intended to support the
distributed weights of water ballast, petrol tanks, etc., between the
main transverse frames. Unlike No. 9, the keel is attached to the main
transverse frames only. The cabin and wireless cabin are disposed in
the keel in the same manner, and it also furnishes a walking way for
the total length of the ship.
The stabilizing fins, both vertical and horizontal, are similar to
those attached to No. 9, but the system of rudders and elevators is
totally different. In place of the box rudders and elevators in No. 9,
single balanced rudders and elevators are attached to the fins; they
have their bearing on the outboard side on the external girders of the
fins, which are extended for the purpose. The elevators and rudders
are composed of a duralumin framework, stiffened by a kingpost on
either side with bracing wires.
The bags, eighteen in number, are made of rubber-proofed fabric lined
with gold-beater's skin. It is interesting to note that the number of
skins used for the bags of a ship of this class is approximately
350,000. The system of valves is entirely different from that in No.
9. The Parseval type of valve with the pressure cone at the bottom of
the bag is omitted, and in the place of the two top valves in the
former ship are a side valve of the Zeppelin type entirely automatic
and a top valve entirely hand controlled. The side valve is set to
blow off at a pressure of from 3 to 5 millimetres. The outer cover was
fitted in the same manner as in No. 9. Two cars or gondolas, one
forward, the other aft, each carry one engine provided with swivelling
propellers and gears. They are enclosed with sides and a fireproof
roof, and are divided into two compartments, one the navigating
compartment, the other the engine room. The cars are in all respects
very similar to those of No. 9, and are suspended from the hull in a
similar manner. The remaining two engines are carried in a small
streamline car situated amidships, which has just sufficient room in it
for the mechanics to attend to them. Originally this car was open at
the top, but it was found that the engineers suffered from exposure,
and it was afterwards roofed in.
The engine arrangements in this ship were totally different to those of
No. 9, four 250 horse-power Rolls Royce engines being installed in the
following order. Single engines are fitted in both the forward and
after cars, each driving two swivelling four-bladed propellers. In the
centre car two similar engines are placed transversely, which drive
single fixed propellers mounted on steel tube outriggers through
suitable gearing.
The engines are the standard 12 cylinder V-type Rolls Royce which will
develop over 300 brake horse-power at full throttle opening.
The engine is water cooled, and in the case of those in the forward and
after cars the original system consisted of an internal radiator
supplied by an auxiliary water tank carried in the keel. It was found
on the flight trials that the cooling was insufficient, and external
radiators were fitted, the internal radiator and fan being removed. In
the case of the centre car no alteration was necessary, as external
radiators were fitted in the first instance.
The engines are supported by two steel tubes held by four brackets
bolted to the crank case, these being carried by twelve duralumin tubes
bolted to the bearers and transverse frames of the car respectively.
The drive from the engine is transmitted through a universal joint to a
short longitudinal shaft, running on ball bearings. This shaft gears
into two transverse shafts, which drive the propellers through the
medium of a gear box to the propeller shafts, making five shafts in all.
The engines in the centre car being placed transversely the
transmission is more direct, the engines driving the propellers through
two gear wheels only. The propeller gear box is supported by steel
tube outriggers attached by brackets to the framework of the car. The
petrol is carried in a series of tanks situated beneath the keel
walking way, and are interconnected so that any tank either forward or
aft can supply any engine, by this means affording assistance for the
trimming of the ship.
Four-bladed propellers are used throughout the ship.
Water ballast is carried in fabric bags also situated beneath the keel
walking way, and a certain amount is also carried beneath the floor of
the car.
Engine-room telegraphs, swivelling propeller telegraphs, speaking tubes
and telephones, with a lighting set for the illumination of the cars
and keel, were all fitted in accordance with the practice standard in
all rigid airships.
The lift and trim trials taken before the initial flight trials showed
that the ship possessed a disposable lift under standard conditions of
5.7 tons. The original disposable lift demanded by the specification
was 3 tons but this was reduced by 2 tons owing to the machinery
weights being 2 tons in excess of the estimate. Since then these
weights had been increased by another half-ton, making a total of 2 1/2
tons over the original estimate. It was evident that with so small a
margin of lift these ships would never be of real use, and it was
decided to remove various weights to increase the lift and to
substitute a wing car of a similar type to those manufactured for the R
33 class for the heavy after car at present in use.
R 23 carried out her trials without the alteration to the car, which
was effected at a later date, and the same procedure was adopted with R
24 and R 25. In the case of R 26, however, she had not reached the
same stage of completion as the other two ships, and the alterations
proposed for them were embodied in her during construction. The
gasbags were of lighter composition, all cabin furniture was omitted
and the wing car was fitted in place of the original after car. This
wing car is of streamline shape with a rounded bow and tapered stern.
The lower portion is plated with duralumin sheets and the upper part is
covered with canvas attached to light wooden battens to give the
necessary shape. This effected a very considerable reduction in
weight. The original 250 horse-power Rolls Royce engine was installed,
now driving a single large two-bladed propeller astern. A test having
been taken, it was found that the disposable lift under standard
conditions was 6.28 tons. It was therefore decided that all the ships
of the class should be modified to this design when circumstances
permitted. Speed trials were carried out under various conditions of
running, when it was found that the ship possessed a speed of 54 1/4
miles per hour with the engines running full out.
To summarize the performances of these ships as we did in the case of
No. 9, we find:
Speed:
Full 54 miles per hour
Normal =2/3 48 " " "
Cruising =1/3 33 " " "
Endurance:
Full 18 hours = 1,000 miles
Normal 26 " = 1,250 "
Cruising 50 " = 1,900 "
The production of the rigid airship during the war was always
surrounded with a cloak of impenetrable mystery. Few people, except
those employed on their construction or who happened to live in the
immediate vicinity of where they were built, even knew of their
existence, and such ignorance prevailed concerning airships of every
description that the man in the street hailed a small non-rigid as "the
British Zeppelin" or admired the appearance of R 23 as "the Silver
Queen." The authorities no doubt knew their own business in fostering
this ignorance, although for many reasons it was unfortunate that
public interest was not stimulated to a greater degree. In the summer
months of 1918, however, they relented to a certain extent, and R 23
and one of her sister ships were permitted to make several flights over
London to the intense delight of thousands of its inhabitants, and a
certain amount of descriptive matter appeared in the Press.
From that time onwards these large airships have completely captured
the popular imagination, and many absurd rumours and exaggerations have
been circulated regarding their capabilities. It has been gravely
stated that these airships could accomplish the circuit of the globe
and perform other feats of the imagination. It must be confessed that
their merits do not warrant these extravagant assertions. The fact
remains, however, that R 23 and her sister ship R 26 have each carried
out patrols of upwards of 40 hours duration and that, similarly to No.
9, they have proved of the greatest value for training airship crews
and providing experience and data for the building programme of the
future. At the present time highly interesting experiments are being
carried out with them to determine the most efficient system of mooring
in the open, which will be discussed at some length in the chapter
dealing with the airship of the future.
RIGID AIRSHIP 23 X CLASS
During the early days of building the airships of the 23 class, further
information was obtained relating to rigid airship construction in
Germany, which caused our designers to modify their views. It was
considered a wrong policy to continue the production of a fleet of
ships the design of which was becoming obsolete, and accordingly within
ten months of placing the order for this class a decision was reached
that the last four ships were to be altered to a modified design known
as the 23 X class. As was the case with the ships of the preceding
class when nearing completion, they were realized to be out of date,
and special efforts being required to complete the ships of the 33
class and to release building space for additional larger ships, the
construction of the second pair was abandoned.
The main modification in design was the abolition of the external keel,
and in this the later Zeppelin principles were adopted. This secured a
very considerable reduction in structural weight with a corresponding
large expansion of the effective capabilities of the ship.
It has been seen that the purpose of the keel in No. 9 was to provide a
structure sufficiently strong to support all the main vertical bending
moments and shearing forces, and that in No. 23 this principle was
somewhat different, in that the keel in this ship was primarily
intended to support the distributed weights of petrol, water, ballast,
etc., between the transverse frames.
In this later design, namely, the 23 X class, it was considered that
the weights could be concentrated and suspended from the radial wiring
of the transverse frames and that the keel, incorporated in the design
of the former ships, could be dispensed with.
For all practical purposes, apart from the absence of the keel, the 23
X class of airship may be regarded as a slightly varied model of the 23
class. The main dimensions are nearly the same, and the general
arrangement of the ship is but little changed. The loss of space owing
to the introduction of the internal corridor is compensated by a
modification of the shape of the bow, which was redesigned with a
deeper curve. The hull structure was also strengthened by utilizing a
stronger type of girder wherever the greatest weights occur. In these
strengthened transverse frames the girders, while still remaining of
the triangular section, familiar in the other ships, are placed the
opposite way round, that is, with the apex pointing outwards.
The walking way is situated at the base of the hull passing through the
gas chambers, which are specially shaped for the purpose. The corridor
is formed of a light construction of hollow wooden struts and duralumin
arches covered with netting.
In all other leading features the design of the 23 class is adhered to;
the gasbags are the same, except for the alteration due to the internal
corridor, and the system of valves and the various controls are all
highly similar.
The arrangement of gondolas and the fitting of engines in all ways
corresponds to the original arrangement of R 23, with the exception
that they were suspended closer to the hull owing to the absence of the
external keel. The substitution of the wing car of the 33 class for
the original after gondola, carried out in the modifications undergone
by the ships of the 23 class, was not adopted in these ships, as the
wireless compartment installed in the keel in the former was fitted in
the after gondola in the latter.
The disposable lift of these ships under standard conditions is 7 1/2
tons, which shows considerable improvement on the ships of the former
classes.
Summarizing as before, the performances appear as under--
Speed:
Full 56 1/2 miles per hour
Normal 53 " " "
Cruising 45 " " "
Endurance:
Normal 19 hours = 1,015 miles
Cruising 23 1/2 " = 1,050 "
The two ships of this class, which were commissioned, must be regarded
within certain limits as most satisfactory, and are the most successful
of those that appeared and were employed during the war. Escort of
convoys and extended anti-submarine patrols were carried out, and
certain valuable experiments will be attempted now that peace has
arrived.
In spite of the grave misgivings of many critics, the structure without
the keel has proved amply strong, and no mishap attended this radical
departure on the part of the designers.
RIGID AIRSHIP No. 31 CLASS
The airship known as R 81 was a complete deviation from any rigid
airship previously built in this country. In this case the experiment
was tried of constructing it in wood in accordance with the practice
adopted by the Schutte-Lanz Company in Germany.
It must be frankly acknowledged that this experiment resulted in
failure. The ship when completed showed great improvement both in
shape, speed and lifting capacity over any airship commissioned in this
country, and as a whole the workmanship exhibited in her construction
was exquisite. Unfortunately, under the conditions to which it was
subjected, the hull structure did not prove durable, and to those
conditions the failure is attributed. Under different circumstances it
may be hoped that the second ship, when completed, will prove more
fortunate.
In length R 31 was 615 feet, with a diameter of 66 feet, and the
capacity was 1 1/2 million cubic feet.
In shape the hull was similar to the later types of Zeppelin, having a
rounded bow and a long, tapering stern. The longitudinal and transverse
frames were composed of girders built up of three-ply wood, the whole
structure being braced in the usual manner with wire bracings. It had
been found in practice with rigid airships that, if for any reason one
gasbag becomes much less inflated than those adjacent to it, there is
considerable pressure having the effect of forcing the radial wires of
the transverse frames towards the empty bag. The tension resulting in
these wires may produce very serious compressive strain in the members
of the transverse frames, and to counteract this action an axial wire
is led along the axis of the ship and secured to the centre point of
the radial wiring. This method, now current practice in rigid airship
construction, was introduced for the first time in this ship.
As will be seen from the photograph, the control and navigating
compartment of the ship is contained in the hull, the cars in each case
being merely small engine rooms. These small cars were beautifully
made of wood of a shape to afford the least resistance to the air, and
in number were five, each housing a single 250 horse-power Rolls Royce
engine driving a single fixed propeller. Here we see another decided
departure from our previous methods of rigid airship construction, in
that for the first time swivelling propellers were abandoned. R 31
when completed carried out her trials, and it was evident that she was
much faster than previous ships. The trials were on the whole
satisfactory and, except for a few minor accidents to the hull
framework and fins, nothing untoward occurred.
At a later date the whole ship was through fortuitous circumstances
exposed to certain disadvantageous conditions which rendered her
incapable of further use.
R 33 CLASS
September 24th, 1916, is one of the most important days in the history
of rigid airship design in this country; on this date the German
Zeppelin airship L 33 was damaged by gunfire over London, and being hit
in the after gasbags attempted to return to Germany. Owing to lack of
buoyancy she was forced to land at Little Wigborough, in Essex, where
the crew, having set fire to the ship, gave themselves up. Although
practically the entire fabric of the ship was destroyed, the hull
structure most fortunately remained to all intents and purposes intact,
and was of inestimable value to the design staff of the Admiralty, who
measured up the whole ship and made working drawings of every part
available.
During this year other German rigid airships had been brought down,
namely L 15, which was destroyed at the mouth of the Thames in April,
but which was of an old type, and from which little useful information
was obtained; and also the Army airship L.Z. 85, which was destroyed at
Salonica in the month of May. A Schutte-Lanz airship was also brought
down at Cuffley, on September 2nd, and afforded certain valuable
details.
All these ships were, however, becoming out of date; but L 33 was of
the latest design, familiarly called the super-Zeppelin, and had only
been completed about six weeks before she encountered disaster.
In view of the fact that the rigid airships building in this country at
this date, with the exception of the wooden Schutte-Lanz ships were all
based on pre-war designs of Zeppelin airships, it can be readily
understood that this latest capture revolutionized all previous ideas,
and to a greater extent than might be imagined, owing to the immense
advance, both in design and construction, which had taken place in
Germany since 1914.
All possible information having been obtained, both from the wreck of
the airship itself and from interrogation of the captured crew,
approval was obtained, in November of the same year, for two ships of
the L 33 design to be built; and in January, 1917, this number was
increased to five.
It was intended originally that these ships should be an exact
facsimile of L 33; but owing to the length of time occupied in
construction later information was obtained before they were completed,
both from ships of a more modern design, which were subsequently
brought down, and also from other sources. Acting on this information,
various improvements were embodied in R 33 and R 34, which were in a
more advanced state; but in the case of the three other ships the size
was increased, and the ships, when completed, will bear resemblance to
a later type altogether.
As a comment on the slowness of construction before mentioned, the fact
that while we in this country were building two ships on two slips,
Germany had constructed no fewer than thirty on four slips, certainly
affords considerable food for reflection.
The two airships of this class having only just reached a state of
completion, a detailed description cannot be given without making
public much information which must necessarily remain secret for the
present. Various descriptions have, however, been given in the daily
and weekly Press, but it is not intended in the present edition of this
book to attempt to elaborate on anything which has not been already
revealed through these channels.
It is regrettable that so much that would be of the utmost interest has
to be omitted; but the particulars which follow will at any rate give
sonic idea of the magnitude of the ship and show that it marks a
decided departure from previous experiments and a great advance on any
airship before constructed in Great Britain.
It is also a matter for regret that these two ships were not completed
before the termination of hostilities, as their capabilities would
appear to be sufficient to warrant the expectations which have been
based on their practical utility as scouting agents for the Grand Fleet.
In all its main features the hull structure of R 33 and R 34 follows
the design of the wrecked German Zeppelin airship L 33. The hull
follows more nearly a true streamline shape than in the previous ships
constructed of duralumin, in which a great proportion of the total
length was parallel-sided. The Germans adopted this new shape from the
Schutte-Lanz design and have not departed from this practice. This
consists of a short parallel body with a long rounded bow and a long
tapering stem culminating in a point. The overall length of the ship
is 643 feet with a diameter of 79 feet and an extreme height of 92 feet.
The type of girders in this class has been much altered from those in
previous ships. The hull is fitted with an internal triangular keel
throughout practically the entire length. This forms the main corridor
of the ship, and is fitted with a footway down the centre for its
entire length. It contains water ballast and petrol tanks, bomb
stowage and crew accommodation and the various control wires, petrol
pipes and electric leads are carried along the lower part.
Throughout this internal corridor runs a bridge girder, from which the
petrol and water ballast tanks are supported. These tanks are so
arranged that they can be dropped clear of the ship.
Amidships is the cabin space with sufficient room for a crew of
twenty-five. Hammocks can be slung from the bridge girder before
mentioned.
In accordance with the latest Zeppelin practice, monoplane rudders and
elevators are fitted to the horizontal and vertical fins.
The ship is supported in the air by nineteen gasbags which give a total
capacity of approximately two million cubic feet of gas. The gross lift
works out at approximately 59 1/2 tons, of which the total fixed weight
is 33 tons, giving a disposable lift of 26 1/2 tons.
The arrangement of cars is as follows: At the forward end the control
car is slung, which contains all navigating instruments and the various
controls. Adjoining this is the wireless cabin, which is also fitted
for wireless telephony. Immediately aft of this is the forward power
car containing one engine, which gives the appearance that the whole is
one large car.
Amidships are two wing cars each containing a single engine. These are
small and just accommodate the engine with sufficient room for
mechanics to attend to them. Further aft is another larger car which
contains an auxiliary control position and two engines.
It will thus be seen that five engines are installed in the ship; these
are all of the same type and horse-power, namely, 250 horse-power
Sunbeam. R 33 was constructed by Messrs. Armstrong Whitworth Ltd.,
while her sister ship R 34 was built by Messrs. Beardmore on the Clyde.
In the spring of 1918, R 33 and R 34 carried out several flight trials,
and though various difficulties were encountered both with the engines
and also with the elevator and rudder controls, it was evident that,
with these defects remedied, each of these ships would prove to be
singularly reliable.
On one of these trials made by R 34, exceedingly bad weather was
encountered, and the airship passed through several blinding
snowstorms; nevertheless the proposed flight of some seventeen hours
was completed, and though at times progress was practically nil owing
to the extreme force of the wind, the station was reached in safety and
the ship landed without any contretemps. This trial run having been
accomplished in weather such as would never have been chosen in the
earlier days of rigid trial flights, those connected with the airship
felt that their confidence in the vessel's capabilities was by no means
exaggerated.
The lift of the ship warranted a greater supply of petrol being carried
than there was accommodation for, and the engines by now had been
"tuned up" to a high standard of efficiency. Accordingly it was
considered that the ship possessed the necessary qualifications for a
transatlantic flight. It was, moreover, the opinion of the leading
officers of the airship service that such an enterprise would be of
inestimable value to the airship itself, as demonstrating its utility
in the future for commercial purposes.
Efforts were made to obtain permission for the flight to be attempted,
and although at first the naval authorities were disinclined to risk
such a valuable ship on what appeared to be an adventure of doubtful
outcome, eventually all opposition was overcome and it was agreed that
for the purposes of this voyage the ship was to be taken over by the
Air Ministry from the Admiralty.
Work was started immediately to fit out the ship for a journey of this
description. Extra petrol tanks were disposed in the hull structure to
enable a greater supply of fuel to be carried, a new and improved type
of outer cover was fitted, and by May 29th, R 34 was completed to the
satisfaction of the Admiralty and was accepted. On the evening of the
same day she left for her station, East Fortune, on the Firth of Forth.
This short passage from the Clyde to the Forth was not devoid of
incident, as soon after leaving the ground a low-lying fog enveloped
the whole country and it was found impossible to land with any degree
of safety. It having been resolved not to land until the fog lifted,
the airship cruised about the north-east coast of England and even came
as far south as York. Returning to Scotland, she found the fog had
cleared, and was landed safely, having been in the air for 21 hours.
The original intention was that the Atlantic flight should be made at
the beginning of June, but the apparent unwillingness of the Germans to
sign the Peace Treaty caused the Admiralty to retain the ship for a
time and commission her on a war footing. During this period she went
for an extended cruise over Denmark, along the north coast of Germany
and over the Baltic. This flight was accomplished in 56 hours, during
which extremely bad weather conditions were experienced at times. On
its conclusion captain and crew of the ship expressed their opinion
that the crossing of the Atlantic was with ordinary luck a moral
certainty. Peace having been signed, the ship was overhauled once more
and made ready for the flight, and the day selected some three weeks
before was July 2nd.
A selected party of air-service ratings, together with two officers,
were sent over to America to make all the necessary arrangements, and
the American authorities afforded every conceivable facility to render
the flight successful.
As there is no shed in America capable of housing a big rigid, there
was no alternative but to moor her out in the open, replenish supplies
of gas and fuel and make the return journey as quickly as possible.
On July 2nd, at 2.38 a.m. (British summer time), R 34 left the ground
at East Fortune, carrying a total number of 30 persons. The route
followed was a somewhat northerly one, the north coast of Ireland being
skirted and a more or less direct course was kept to Newfoundland.
From thence the south-east coast of Nova Scotia was followed and the
mainland was picked up near Cape Cod.
From Cape Cod the airship proceeded to Mineola, the landing place on
Long Island. All went well until Newfoundland was reached. Over this
island fog was encountered, and later electrical storms became a
disturbing element when over Nova Scotia and the Bay of Fundy. The
course had to be altered to avoid these storms, and owing to this the
petrol began to run short. No anxiety was occasioned until on
Saturday, July 5th, a wireless signal was sent at 3.59 p.m. asking for
assistance, and destroyers were dispatched immediately to the scene.
Later messages were received indicating that the position was very
acute, as head winds were being encountered and petrol was running
short. The airship, however, struggled on, and though at one time the
possibility of landing at Montauk, at the northern end of Long Island,
was considered, she managed after a night of considerable anxiety to
reach Mineola and land there in safety on July 6th at 9.55 a.m.
(British summer time). The total duration of the outward voyage was
108 hours 12 minutes, and during this time some 3,136 sea miles were
covered. R 34 remained at Mineola until midnight of July 9th according
to American time. During the four days in which she was moored out
variable weather was experienced, and in a gale of wind the mooring
point was torn out, but fortunately, another trail rope was dropped and
made fast, and the airship did not break away.
It was intended that the return should be delayed until daylight, in
order that spectators in New York should obtain a good view of the
airship, but an approaching storm was reported and the preparations
were advanced for her immediate departure. During the last half-hour
great difficulty was experienced in holding the ship while gassing was
completed.
At 5.57 a.m. (British summer time) R 34 set out on her return voyage,
steering for New York, to fly over the city before heading out into the
Atlantic. She was picked up by the searchlights and was distinctly
visible to an enormous concourse of spectators. During the early part
of the flight a strong following wind was of great assistance, and for
a short period an air speed of 83 miles per hour was attained. On the
morning of July 11th the foremost of the two engines in the after car
broke down and was found to be beyond repair. The remainder of the
voyage was accomplished without further incident. On July 12th at
noon, a signal was sent telling R 34 to proceed to the airship station
at Pulham in Norfolk as the weather was unfavourable for landing in
Scotland. On the same day at 8.25 p.m., land was first sighted and the
coast line was crossed near Clifden, county Galway, at 9 p.m. On the
following morning, July 13th, at 7.57 a.m. (British summer time), the
long voyage was completed and R 34 was safely housed in the shed,
having been in the air 75 hours 3 minutes.
Thus a most remarkable undertaking was brought to a successful
conclusion. The weather experienced was by no means abnormally good.
This was not an opportunity waited for for weeks and then hurriedly
snatched, but on the preordained date the flight was commenced. The
airship enthusiast had always declared that the crossing of the
Atlantic presented no insuperable difficulty, and when the moment
arrived the sceptics found that he was correct. We may therefore assume
that this flight is a very important landmark in the history of aerial
transport, and has demonstrated that the airship is to be the medium
for long-distance travel. We may rest assured that such flights,
although creating universal wonder to-day, will of a surety be accepted
as everyday occurrences before the world is many years older.