With the Imperial Airship
Scheme underway in 1926, the plans for other airship bases was
planned for expansion. Masts were constructed at Montreal, Ismalia
in North Egypt and Karachi in India. The mast head for South Africa
had been constructed and a shed was also constructed in Karachi.
The following guidelines were laid out for setting up masts and
bases at further destinations, these included Mobassa, Capetown,
Perth, Melbourne and Wellington.
Text taken directly from Air
Ministry document "Approach Towards A System of Imperial
Air Communications" Memorandum by the Secretary State
for Air laid before the Imperial Conference 1926, together with
the REPORT of the Imperial Air Communications Special Sub-Committee
THE SITING
AND LAY-OUT OF AN AIRSHIP BASE.
Selection of Site
Whilst the linking up of commercial centres is the main object
of high speed airship transport, there are certain operational
factors which have to be borne in mind in selecting the precise
site for an airship base and settling the type of base to be erected.
A commercial airship will normally fly at a height above the ground
of about 2,500-3,500 feet. While there is no difficulty in flying
higher than this, evrery 1,000 feet of height means a loss of
about one-thirtieth of the total lift, and consequently diminishes
the airship's carrying capacity.
It follows from this that
a site for an airship base should be selected as nearly as possible
at sea level, since if an airship base is situated, say, 2,000
feet above sea level, the airship on leaving would halve less
useful lift for freight. For the same reason the base should,
if possible, not be sited so as to necessitate flying over mountain
ranges at the outset or in the early part of the journey, since
the ascent can only be made by reducing the load of the airship
which is uneconomic from the operating point of view.
On the other hand when an
airship has been flying for some time and has thus used up a certain
weight of fuel, an increase of height can be gained without the
same loss of useful load. Due regard should also be paid to weather
conditions, especially in choosing a site for a shed base with
docking facilities, where an airship may have to be man-handled
into the shed. They are not of so great consequence for an inter-
mediate base with mooring mast only, as the airship would always
be flown from the mast and not handled on the ground.
At the same time local meteorological
conditions might affect regularity of service; thus a locality
in which thunderstorms are prevalent would generally be unsuitable.
It was on account of climatic conditions that the shed base for
India was sited at Karachi, leaving the question of bases at Bombay
and Calcutta to be dealt with later. In the immediate vicinity
of a base there should be no obstruction such as hills, high buildings,
etc., and any high masts for wireless telegraphy or meteorological
purposes should be located as far as possible from the mast and
shed, 'so as not to be a source of danger to an airship landing
or leaving.
Local communications
Should be good to permit of passengers and freight being dealt
with expeditiously. A main railway line should be in the vicinity.
Feeder services by aeroplane should also be kept in view. .
Area for
Shed and Mooring Mast Base
A minimum area of about 600 acres is necessary, but a larger area
(up to 1,000 acres) is preferable in order to provide for future
extensions, in particular additional mooring masts.
Area for
Mooring Mast Base
A clear space of about 800 yards square (about 130 acres) will
suffice for a base with one mast provided there are no buildings
of a greater height than 40 feet within 300 yards of the aerodrome.
As the space required for landing operations at the mast is only
about 100 acres, it is possible to use the remainder for grazing
or other purposes. All electric cables in the vicinity of a base
should be laid underground.
Drainage and Foundations
The land should be well drained and not subject to floods. In
order to avoid expensive foundations the soil should be suitable
for loads of not less than 2 tons per square foot.
Water Supply
There should be a plentiful
supply of fresh water for ballast and general purposes. Salt water
will not serve. owing to its corrosive action on aluminium alloys.
The total amount of water required when abase is fully functioning
is one of the questiot:ls on which the experimental flights will
throw light. As an approximate estimate, the following figures
may be given :-
For ballast for each airship at the mast 50,000 gallons per day.
For general purposes. .20,000 per dayI
For hydrogen, assuming a production of 1,000,000 cubic feet per
week, by water gas process 20,000 per day or by electrolytic process..3-5,000
per day
Average weekly total, say 700,000 gallons. If a temporary hydrogen
plant (silicol) is erected, an additional 200,000 gallons per
week would be required. To meet any emergency a 100,000 gallon
reservoir will be necessary) at most sites.
Shed
The dimensions laid down for the shed in course of erection at
Karachi are:-
Length 850 feet.
Width 180 feet.
Height 170 feet.
The shed is constructed to stand a wind pressure :--- (a) 35 lbs.
per square foot horizontally on roof. (b) 30 lbs. per square foot
horizontally on sides or ends. (c) 30 lbs. per square foot horizontally
on main sliding doors with doors open or shut. A shed of the above
dimensions will probably meet future requirements for the next
10-15 years, but in any case as sufficient height has been allowed
to meet further developments in the design of airships, the question
of extension is not a serious matter. Good ventilation is necessary
to allow easy escape of hydrogen, and a!l electric fittings should
be gas tight to prevent explosions. As contracts for such buildings
are of considerable magnitude, the design and execution should
be supervised by an Engineer of repute, and only Contractors experienced
in this work or used to erecting similar large engineering structures
should be invited to tender.
Mooring Mast
The existing type of mast consists of a steel structure
200 feet high, fitted with a receiving arm at the top to which
the airship is anchored. The structure is built to withstand the
pull of the airship up to 30 tons in any direction, in addition
to a wind force on the structure of 30 lbs. per square foot. A
lift is provided to convey passengers up and down the mast. Mains
for hydrogen, water and fuel run up the mast for the replenishment
of the ship, and are joined to similar mains in the ship by flexible
connections. The mast should be sited in such a position that
an airship arriving or departing does not have to fly over the
shed or other high buildings) and in any case these should be
at least 800 to 1,000 yards away.
Anchor Points
Twenty-four snatch block anchor points should be provided to take
the sideguys when the. airship is landing to the mast. These should
be spaced in a circle round the mast at a radius of 750 feet from
it, and should be designed to take a maximum pull of 25 tons in
any direction. They should be placed flush with the ground to
avoid obstruction.
Hydrogen
Plant
The type of hydrogen plant to be provided will vary according
to locality and requirements. There are a number of processes
used in connection with hydrogen production, but only three of
these have been used to any extent. in this country in making
hydrogen for aeronautical purposes, viz., iron contact or water
gas process, electrolytic process, silicol process. The latter
would not normally be used at permanent bases on account of its
high cost of production, but is useful as a temporary arrangement
when a large output of gas is required intermittently at low capital
cost. An outputof 1,000,000 cubic feet per 24 hours can be obtained
from a plant costing £20,000 to £25,000. Plants of the iron contact
and electrolytic types cost about £80,000 including cost of storage
holders of 1,000,000 cubic feet capacity (about £30,000), which
are necessary on account of slow rate of production. These figures
are for plants capable of producing about 1,000,000 cubic feet
per week, which is the amount of gas which should be available
at anyone time, on a route operated by airships of 5,000,000 cubic
feet capacity. In both the iron contact and electrolytic processes
work has to be continuous, and shifts are necessary. The selection
of one or the other will depend largely on whether cheap coke
or cheap electricity is available.
Power and Light
If local current is not available, a power plant of 100 kilowatts
will probably be required, preferably two 50 kilowatt sets. and
two 10 kilowatt sets for light loads such as lighting, and wireless
sets, for use when the larger plant is not running. An additional
100 kilowatt set might. be needed for a permanent station in regular
operation.
Fuel Storage
A minimum supply of 10,000 gallons of fuel should be available
for refuelling airships
Personnel
For the experimental flights of R.100 and R.101 it is estimated
that the ground staff at the shed base at Karachi will be about
150, of whom 100 will probably be natives; at the mooring mast
base at Ismailia the total may be 100, of whom about 70 may be
natives. These figures will be checked and possibly revised as
the result of the experimental flights.
Meteorological and Wireless Telegraphy Arrangements
A local meteorological section is necessary at each airship base
to deal with local conditions and to receive reports from other
stations, and transmit them to airships in flight. 'roo much importance
cannot be placed on this organisation, as not only is it an aid
to safe navigation, but it will also enable an airship to take
the most favourable route, and thus facilitate the economical
running of an airship line. The main function of Wireless Telegraphy
at an airship base will be the transmission of the meteorological
data, and the carrying out of direction finding work, as an aid
to the usual navigation methods. A local Wireless Telegrapliy
set should also be available to ;-elay messages through the nearest
high-power station. The receiving station and meteorological office
should be housed as far as possible in the same building or in
the immediate vicinity of each other .
Capital Cost of Bases
It is very difficult to give a figure for the costo! bases when
a regular service is in operation, as so much will depend on .the
scale and type of accommodation provided for dealing with passengers,
mails and freight. The cost of erection will also vary in different
dominions and localities. The following figures, which are based
on the cost of the works carried out for the Air Ministry for
the purpose of the experi- mental flights, may serve as a guide
to the scale of expenditure involved. Permanent stations on a
regularly operated route would probably cost £80,000-£100,000
more to build and equip.
