The viability of using airships for the transport of natural gas, and the initial design of such a system, the airship and its associated subsystems together with a continuing economic analysis of the project were investigated. Investigations, on a funded basis, were also carried out into the application of the airship for A.S.W. and A.E.W. uses, and a further investigation into the transport of mineral concentrates for an Australasian mining concern was completed

Wood, J. E. R.

English

NASA Technical Reports Server

+J
504676- 1 +i
+y
THE AEROSPACE DEVELOPMENTS CONCEPT
John E.R. Wood *
i
ABSTRACT: For the last three years, Aerospace Developments have been +_:
under contract to Shell International Gas. Their brief has been to assess _'
the viability of using airships for the transport of natural gas, and to com-
plete the initial design of such a system, the airship and its associated sub-
systems together with a continuing economic analysis of the project. Invest-
lgations, on a funded basis, have also been carried out into the application of
the airship for A. S.W. and A.E.W. uses, and a further investigation Into
the transport of mineral concentrates for an Australasian mining concern has
recently been completed.
'L
_++r_ INTHODUC 'lION
L
!_i The present day method of transportation for Natural Gas has several major disadvantages.
It is a high cost operation, which demands considerable investment both in surface vessels
_ and In fixed ground plant. Briefly, the system in use at present is as follows:
1. The gas is piped from the well (or wells) to a central liquefaction plant. This is
++ usually located at, or near, the coast.
2. From the liquefaction plant theogas is piped aboard liquid Natural Gas (L. N. G. )
carriers. It Is stored at - 161-C throughout the voy,'_e.
": 3. On arrival at the home port th_ gas is stored in a liquefied state, and is then
* Director. Aer,_space Developments, Londo., England
i:
k
_; £K'i_ING PAi3_BLANK NUi tli_
+' '_51
f
9 . •t
1976007927-351
https://ntrs.nasa.gov/search.jsp?R=19760007958 2020-03-20T01:37:17+00:00Z
re-gasified and passed into gaseous pipe storage for subsequent distribution to consumers.
Both the tankers and the liquefaction plant are enormously expensive. A large L. N. G.
_-, carrier costs, at present day prices, in excess of $100 million, and a large liquefaction plant
:" with its associated tankers, demands an investment approaching $2 billion. Much of this
" investment has to be concentrated In ground plant located in areas of high political instability
(Algeria, Libya, etc.). These assets may be sequestered by the p_rent countries at any ,
f time, and without any notice. The liquefaction plant consumes approximately 26% of the
_ energy it produces in the liquefaction process and the scale of investment required means
: that a very large market mtst be assured before any deliveries can he contemplated. Sinai; :
wonder then that the need for a cheaper, less politically susceptible, more flexible system , ,.:
has been recognised for a long time. *:
THE AIRSHIP AS A GAS CARRIER ¢
.,
Because the gas methane (the prime constituent of Natural Gas) is lighter than air, with a
=. lifting force of approximately 45 Ibs/1000 cubic feet, there is an Gbvious attraction In using .:
a Lighter Than Air craft for tr,'msporting the material, since the payload will also provide
the ascensional force (at least on the outward voyage). Even if the gas is assumed to con-
tain Its maximum possible concentration of contaminants (sulphur, CO2 etc.) It is still no _
heavier than air. The main problem centred ar(,und the fact that, because the volume of the
gas is increased in the ratio of 645:1 over its liquefied state when it is expanded to atmos-
pheric pressure and ambient temperature, and because hoop stress considerations demand
that the gas be carried under these conditions in order to carry a sensible amount of gas,
the craft has to be a very large one Indeed.
b
CHOICE OF TYPE OF CRAFT
An initial examination of the economic considerations, together with the knowledge that,
within the bounds of technical competence {and certain construction costs) ""he Bigger the
Better" at least from the point of view of ultimate costs/cubic feet, led to the requirement
for a craft approaching 100, 000,000 cubic feet, which, in dimensional terms, is very large
indeed'
For craft even approaching this size there appears to be only one answer, the Supported
Monoeoque type of construction. Supported because at some point In the journey the gas
will have to be removed from the craft, and therefore gas pressure will not be available to
stabilize the outer skin, and Monocoque because this :s the only type of construction that is
sufficiently amenable to the present day demands of quality control and rapid assembly
whilst retaining adequate margins of strength. The "Zeppelin" type of construction Is often
still held to be the best type of construction, and the reasons for this advocacy :tre very
difficult to ascertain. A fairly rudimentary armlysis of cr_tft of this type will shuw that this
system of construction was inadequate to meet the demands on strength grounds alone for
the sort of annual utillsatlons that mus___..tbe achieved in order to make the system profit-rifle.
Even when used for the sort of craft that were constructed forty years ago, the rigid girder
construction was not safe enough, by modern stan&trds, and wa_ ,lemandlng In terms of
in-flight maintenance, and yet many people are still ad_ee;ttlng the use of such construction
, methods for craft far larger than those of old, and they arc Intending to use these craft la
- applications far more demanding them any that have been required in the ires *. There is :t
great deal of evidence to suggest that even such staunch advocates of conventional airship
practise ;is Charles Burgess were convinced of the need for a "stressed skin" type '_tructurc.
llad the Initial design for such an airship resulted in a much smaller size of cr:fft, then it
is imsslble that a different appro:tch might have been adopted {probably an intern'dly
352
1976007927-352
s'
supporteo "BI,IMP") but for a craft of the size required, we are confident that the type of
construction system adopted represents :m optimum.
TIIE CRAFT ITSELF (Figure 1)
,
. As may Le seen from the illustration, the era/t represents a fairly conventional approach
to airship aerodynamics. It has a length/diameter ratio of 6:1 w :ch represents a reason-
, able compromise between controllability and cost of materials (it Is lntereJtlng to note that
, recent economic analyses show that, as far as material costs are concert_ed, there are ..
advantages in reducing the length diameter ratio to as little as 2:1. These analyses do not ,. .:
take accotmt however of the control and mooring difficultie_ associated with craft of this , _,
type. ).
The craft itself Is approximately 1,800 feet In length with a maximum diameter of ._00 feet. t
This entails conshterable difficulties as records a constructlot_ facility, anti the methcxls
used to overcome thin problem are described later in this report.
The use of a considerable degree of cylindric midship section Is a sensible nne, there is
little, If any, advantage In resistance terms In adopting a fully streamlined form, :rod
the advantages in terms of jigging and construction costs militate heavily in fa:'our of the
type of design which has been adopted.
TIlE BASIC SYSTEM OF CONSTRUCTION (Fi,oxtre 2)
The pri mary unit of construction Is the "tmltary panel" which Is 20 feet in length by lo feet
in height. Since there Is a very definite need to conserve weight, and beeau:_e the primary
1_$,, m_xle of failure Is In compressive buckling of the top skin, it was (!celded to (Icvelo I) a
' _i material which combined the best of both worhls. It was decided to utilise a "s:mdwich"
: form of eo_tructlon, using stainless steel cute," ,'mclInner skins, which arc :tdecluate for
;" the tensile lo,'tds that will be It,posed, together with :t Keflar fibre inner core, the lint'pose
: of which in to increase the"l' value of the matrix. The result is :tmaterial which ombines
x
_ light weight with excel)tior, al strength albeit :it a f:dr',y high unit cost. "l_e decision to use
a poly'tmltle fibre rather than a metal such as aluminium as the infill for the matrix was
,, based on two major considerations.
_-:o 1. The need to obviate, as much as possible, the rl: 3f corroshm due to tht, ingres..'
_" of water under the outer skin.
, 2. The necessity to avoid the possibility of electrox_le action between the lnilll :rod the
,_ outer skins.
_' In order to minimize the weight of the lnfill, a aoneycomb type of structure has been used
_- for stabl!izlng the outer and inner skins.
The basle method of the :tss_,nlbly is outlined in l-'lgnre 2. Storage is I_|'m,'id,'d for tile steel. _
the honeytomb and the elmxy type "ldhesD,'e (refrlgel'ated). The honeyt'onl_ I_:thei_ :Ire _"
pre-i)rofilcd to a.q :recur:de curv:tture, anti the p:l.nels ;ire tht, n })4)lltit'd t(} the outer :m.I illl'lt'l'
skin by :m :tutt_.'alve pr_'ess, the comph,te_l panel then Illoves it) :l final fildshing |_:t_,'lt'_lt,_t,
profiling etc. ) before being passed to a coatpleted materi:tls stockyard. 'l'tais sv.qttqll
enables the httest metht_ls of qu:dlty control (ultrasonics. r:tdiation, bavk:;c'_tte, t.tc. ) t_,
be emldoYed to ensure continuously high standartls qff nl-lterJal Integrity. _t_'_ll'll _lqe t'lfflSitlel's
t lnillio/I .,,;qltA',ll't, feet ,_I"that ore :drshlp :done of this _ize _'111require :q_proxim:ttely l _,
:, J5J
1976007927-353
Ihoneycoml) and 3 million square feet of skin material, the necessity for proper quality copt-
• v'c_lx_illI_ ;)plv)r_,nt.
A comprehensive stress :m.'tlysls, based on "finite element techniques" developed by
Professor Arg3a'ls, has been c:trrled out on the craft, together with :m :tn:tlysis of likely
gust loads th:tt will be iml)osed on the craft during4 in service operations. "rod the results
[n(lic:ttc than :tn overall safety facto:" approaching :g is likely to I)c achieved. (This :malysi,_
: / t:tkes account of the maximum :xeroJyn.'tmic loads likely to b.- encountere(I.) These s:ffety
f:tctors :u'e consl(ler:tL_ / in excess of thoqe retluire(i for current civil :tircr;tf,* :tpplications. ,,
:rod at r well for futui e development.
POWERING RE(_UIREMENTS FOR AII{SIIIPS
As part of the current progr:xmme, a comprehensive ex:_min'ttlon of the powering require- r
--'"" ment h.ls been e,trried out. "['his progr:tmn_e, carried out uncler the supervision of
Professor Young of Queen M:).ry College. has entailed :t (let:tiled eval,_.ttion of the bound:try
.. layer conditions (,bt:tlnlng around an airship of the size contempl::'ed. Tiiere is _tn obvious
• r
adv'mtage In using :l power pl:mt that has alrmtdy been developed, even though the lower
speed of advance of the airship when compared to eonw.,nttonM aircraft m:ly reduce the
efficiency of the unit. It Is desirab!e to keep the number of power units to :t minimum, in
order to recluce the rumt)er and eomplexlt/of associated sub systems, :rod to ease prohlems
concerned with cockpit control.
A summary of the powering requirements Is given below.
' tlull Volume 50 million cubic feet
: Speed (re. I,. a. ) S. tl. P.
40. 9r!.
70. 4, 558.
100. I?. 2,t6.
140. 33, 305.
Hull Volume 100 million cubic feet
Sl_ed (m. p. h. ) S. II.P__..__.
tO. 1, ,t33.
70. 6, 906.
100. 19, 265.
140. 5O, 230.
It e'.m l_, re.t(llly :q)prcci-ite(! that the powering dlsbeneflt from incre:ised speed is far l:trger
th:m th:tt lmi,osed l)y increasing size. Sine=, the economic crui,4e speed f,)I" the cr:tft lies
_a the r:inge 90 = 100 kts. ') is I)OSslble to use existing po_er Ill:rots for tht, sm:dh, r cr:d.
In the i)rototvl)e |)rogr:tmme t_o l)rotcous .'ngiaes. driving Ilovercr_lft lyl)e (l. e, l:ti'gc
|)l:t(Ic :ire:t) i)rol ) sets _.lll t)e adequ:tte. The I)roteou:_. which will he of the re:trine )yl)_,.
h:ts :tccumuktte(I over 500. I)o00l)er:ttive hours, has :t high mc:m time I)t,tween ()_(.rh:tuls,
:trill is :tlrc-idy av:ttl'il:le sb:ift(,(I to :t II. II. Y, tyll( ` IIovt, rcr:dt lir()l)(.,iii)r. 1,'or tilt, l:li'gcr
J54
t
I
1976007927-354
ifllllli .,
t
/ ships it is possible to utilize a multiple (4 or 6) proteous arrangement, but it is rather more
_,'/ likely that an exhaust turbine, co._nected to a high by-pass fan unit such as the RB-211 would
' -J represent a more sensible approach. In the gas carrying application the craft would use a
certain amount of gas to fuel the engines, and this further reduces the maintenance require-
ments.
It is nc,t intended to install these engines in any type of vectoring moun_ing, this is usually
a much more expensive exercise than most people imagine, and often entails major redesign
of the p_wer plant itself. As may be seen from the first illustration, the engine units are
"poddedP, this is not an attempt to improve propellor efficiency, but rather an effort to
reduce blade tip noise. In the prototype craft it will be possible to mount the engines above i
the wing section, and to use the wing to further improve the noise attenuation characteris .....
tics of the craft.
¢
Because of the thickness of the fin root, It is possible to provide access to the engine pods
in flLght. It Is unlikely, hc_ever, that licensing authorities would look kindly on anything +
other than emergency repairs being carried out whilst the craft Is in flight, All electronic
and mechanical interfaces have been _esigned to be as modular as possible, and any major
servicing would be carried out on a replacement basis.
Attention has also been focussed on the decision to place the engines on the tail surfaces.
,_t is pointed out (correctly) that this entails an increase in the loading on the tail surfaces.
The weight penalty, at least for a gas-turbine engine is, however, small and the control
surfaces have to be designed to absorb high aerodynamic forces anyway. In addition,
placing the engines at the tail has the following major advantages:
1, The engines are installed well clear of the boundary layer, thus there Is little
boundary layer lnterraction, with consequent power savings.
2. When fully pitchable propellers are fitted, the transverse separation of the
engines enables a high turning moment to be applied, even at very slow
airspeeds, this is particularly useful when approaching or leaving the mast.
, 3. Because the power units are situated at the told height of the elevators,
rather than on the underJIde of the hull (common practice on many ea_'ly
airships) there is far less chance of the engine being driven through the
hull and into the methane gas in the event of a grounding.
THE BUILDING FACILITY FOR THE CRAFT
One of the major cost areas in the development of this craft, will undoubtedly be the pro-
vision of a suitable facility within which the airship may be built. There are those who
advocate building the airship in the open, using everything from a roofed over clay pit to
a lake, or who suggest that by using turntables etc. a large airship may be constructed
without any protecti _,z from the elements. This we have always regarded as fanciful.
Although the prototype craft are sized to fit inside the facilities still in existence in the
U.K., the full scale ships will require a shed some 2, 000 feet in length by 400 feet high.
Comparative studies of conventional and inflatable structures, which have been commis-
ioned both in the U. S. A. and the U.K. have resulted in the decision to use an air stabilized
structure, in which the prime loads are taken by a supporting steelwork and cable system,
with inflation being used to stabilize the building against gust loads. A ground plan,
show[ng the existing sheds at Cardington, England, together with the new "super she_'
355
i
1976007927-355
j E
_ superimposed upon them, is shown in Figure 3. The total cost of such a facility is est-
imated to be approximately $40 million at present day prices.
:_ GASSING AND DE-GASSING THE SHIP :_
_ The ship will almost certainly be gassed through a fairly conventional "Stub" type tubular '_
mast. The gas, fed in through a central connection, is led to individual compartments by .:_
four "Box Keels" at 90° to each other within the ship. A "Top Hat" membrane system
r iS used to keep air and gas separate within the craft. At the discharge terminal the gas is !i
forced back through the box keels by purging the ship with a carrier gaaOn the other side of _
the membrane, the gas is passed to ground storage for future distribution. Various systems i
for returning the craft to th_ gas field have been under consideration, and the version ....
shown uses an internal helium annulus to provide sufficieut buoyancy to lift the craft in the
_" "light ship" condition, the excess buoyancy being counteracted by ballast being taken aboard.
/_.,D- ¢
THE PROTOTYPE PROGRAMME
Itisregardedas beingimpossibletoconstructa fullsizecraftwithouta comprehensive
• prototype programme. In addition to a large number of static rigs, a series of craft
_" ranging from 2 million - 30 million cubic feet are intended to be built before work on the
100 million cubic feet ship can commence. These craft will be built using the same
techniques and panel sizes !ntended for the fleet size ships, in order to opf.imize the
assembly techniques and to provide feedback operational information. Because of this, ::
these craft will not be as efficient in terms of their payload/total lift ratio as vessels built
q by alternative means, nevertheless, these craft still have enough lift to provide a useful
j payload and illustration 4 shows the 8 million cubic feet ship in an anti submarine role. _
_, CONCLUSION
The _ork being carried out for Shell is part of an on going process. All being well it Is
hoped to complete the construction of a prototype craft by the beginning of 1979, and for
a full size craft to be operational by 1984. This exercise is by no means a low key area
of financial activity, precise costs are classified by SheD, and Indeed are as yet not }
finalized in many areas. But a unit cost of $60 million/ship may confidently be expected. _
It has been the purpose of this necessarily brief paper to emphasize the fact that at h: . • ', !.I
one major industrial company has seen fit to initiate, and to continue to support, on a _ ,
significant financial scale, a thorough investigation into the possibility of utilising Lighter i ;
Than Air craft on a major scale. It would perhaps be pertinmt to add that due to obvious
considerations of commercial confidentiality much of the information given has necessarily :_
been of a superficial nature. Should more detailed information on the project be required, ;
it is respectfully suggested that initial approaches should be made to Shell International _
Gas themselves. _
356
1976007927-356
I,I,I,LW
fir r
q o -7
...... ;.....-I._., ....i__..
f.'P-d,--i: Jr__L:A, _-___.L_&_J-__=.__"__ ,- :_-
\ I i ' I I I I I ', _ i K . _._1-
Figure 1
FINISHED PANELS OUT
i
: I FINAL PROFILING SAY
I
*
I '£
[ PANEL |ONDING lAY
ii :'
I----I --- I _.-- |
IASI MATIRIALS
l_ ml)
Figure 2 _-
?
i
I*
RF_gOI)UCI_ILI_YOF Tli_357
OI_IGII,I._I-,I'A.GB18INDOI_ _.,,
1976007927-357
1976007927-358


The aerospace developments concept

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server