A design study is described for a large low-cost rigid airship intended primarily for the movement of large indivisible loads (cargo) between industrial sites. A survey of the ship and its overall performance is followed by accounts of the operational procedures for the above function and for an alternative application to unit module transfer between fixed terminals. A final section indicates the estimated costs of construction and operation. Safety factors are also considered. Lifting devices such as winches, hoists are shown and described, and airship configurations are also shown

Mowforth, E.

English

NASA Technical Reports Server

N76-15050 i
THEAII_LOAT HL PI_OJECT
Edwin Mowforth *
I_
ABSTRACT: This paper describes a design study for • l•rge low-cost r
rig/d alrshlp intended primarily for the movement of l•rge indivisible ]o•ds
between unprepared sites. A survey of the ship and its overall performance
is followed by •ccounts of the operational procedures for the •bove function
and for an alternative application to unit module transfer between fixed
terminals. A final section indicates the estimated costs of construction
and operation.
' i
.1
Objectives '_
: The Alrfloat HL (Heavy Lift) project was initiated late in 1970 •s s design study for an
• irship to carry l•rge indivisible Io•ds over moderate dl0tances - typically, 400 tonne
over 2 000 km - between unprepared and possibly congested industrial sttes. The
associ•ted requ/rement of minimum cost has dlctsted • 'low technology' design policy t_
mak/ng the greatest practicable use of currently accessible mater/als, installations,
techniques and experience in order to bypass, wherever possible, expensive involvement )
in research and development programmes. The outcome is • vehicle lacking
sophistication and falling somewhat short of optimum technical efficiency, but offering' _
the facilities of rapid man_scture and of immediate commercial effectiveness even If
only one ship is built.
.................. i
• Design Director. Al:'float Transport Limited. and Lecturer in Mechanical
: Engineering, University"of Surrey. _
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1976007927-404
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1 ._._.......... ._.,/ ,_ ,] ,.-- - .... _ i I IIIllllII I ,
'. GeneralDescription
, Hull - The hull is seen from Fig I to be of conventional form, 400 m long and 85 m in ,_
diameter; it comprises a light alloy framework covered by a tcxtilc skin and dlvldcd
.. internally by radially-braced transverse frames Into 27 cells, each containing a
reinforced Mylar c_sbag to give a total helium capacity of 1 342 000 m3.
• i_. 400rn
_" IHOISTAXIS
,_ "__ TAll.CONE EJECTION
i
" GAS/DuALFUELSYSTeM:FuEL _/ FUEL BLIMPVERSION MP DOCKING
Propulsion - The ship carries I0 Rolls-Royce Marine Proteus dual fuel gas turbines,
each driving a 6.4 m dlame',er Hawker Siddeley propeller. 2 units are mounted at nose
and tall and can be vectored for lateral thrust, while 6 of the 8 disposed along tI_ lower
flanks can vector the propellers for vertical thrust. The shlp normally cruises at 145 km/h
using 4 engines when alone or 5 when towing a fuel blimp.
Control - To achieve the necessary l_osltlon control In hovering flight there are 8 radially
disposed fully-floatlng fins f-t either end ol the hull, bydraullcalIy 0owered through
independent pump and motor sets driven electrically by duplicated gas tu1-hlne generator
sets In the nose. Hovering and normal cruise control are aut3matlc, gusting being
sensed by the _orwartl probes and compensated by control operation under the dir,,ction of
a master contcol unit.
Fuel - The ship may operate on aviation kerosine, on natural gas or on dual fuel, a
eombinat/on ofhath.
I
1
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1976007927-405
Kerosine operation uses 2 fixed 20-tonne tanks, topped up in flight from 10-tonne transfer
tanks picked up and carried with the payload or ballast. The cruising weight loss of 4
tonne/h Js met by routin_ journeys over free water surfaces from which water may be
raised at intervals of up to 1 000 km through suspended pumps and hoses with the ship
trimmed in hovering flight by vertical thrust. Between stops the discrepancy is met by
dynamic lift, and the interval may occasionally be extended by the use of a rain water
f_
collection system. __
On natural gas operation the HL airship tows a blimp, !35 m long, which carries 59 000 m 3 .
of fuel gas; this offers an effective stage length of about 1 200 Ion. The blimp has its own _'
._ prouulsion unit and control system and can fly independently under radio control, _o that _ -
refuelling may be effected by detaching the empty blimp and docking a full one with the HL _ ' "
-_ ship flying, at 60 km/h. While the blimp is detached the HL ship runs on a bridging :_
supply of 5 000 m 3 of fuel gas housed in a taflcone which may be ejected in case of fire; _
a further reserve of kerosine extends the operating period in an emergency. ,_
Natural gas .From European sources is lighter than air, so that the blimp becomes
heavier as fuel is consumed. In the above system the blimp carries water ballast which
is progressively discharged to balance the lift loss; in the alternative dual fuel system _
this _atel is replaced by kerosine which is pumped forward and consumed at the
necessary rate to maintain trim. The Proteus engines of the HL ship may all run on !
eithergas or kerosine,and thenecessarydualfuelratioismaintainedby alt_.rnating
between different combinations of gas and off burning units. "[_e effective stage length
_ using the 135 m blimp is then 2 000 kin.
LoadingSystem- Loads arepickedup inhoveringflightby attachmenttoa frame ....
J
suspendedfrom a swivellinghoistmotmted inthehull. The hoistisdrivenelectrically,
beh_ powered by two gas turbinegeneratorsets;itcan be rotatedtoaligntheframe
: with the load axis regardless of wind direction, and has a compensation system for pitch
and roll of the hull during load transfer. The use of the system in Open Site and in
Module Operation will be described in a later section.
_ Accommodation - The controldeck and crew accommodation are intwo offsetnacelles
i. adjacenttothehoist.A cruisingcrew of3 isenvisaged,witha nominalloadexchange
"_ handling crew of 4. In 24-hour operation on extended circuits 3 full crews and 3 cabin%
_ staff may be carried, totalling 24. A transfer lift between the nacelles permits the
exchangeofpersonneland smallstoreswiththegroundwhilehovering.
_ Performance
_ l,nderISA conditionsand assuming 5% aircontaminationoftheliftin_helium,thegross
disposableliftvaluescorrespondingtopressureheightsof500, I 0d0 and 1 500 m become
respectively 520, 460 and 400 t.,Jnnc for the oil-burning version, reduced by 8 tonne for
_ the and dual fuel versions with tailcone With a 10-tom_e reserve ofgas gas storage.
kerosineand 20% excessrangeallowance,therange-payloadrelationshipsare indicated
inFig 2 forcruiseat145 km/h closetothepressureheight,using4 engineson the
fi kerosineversionand 5 on theblimp-towingtypes.
Inallcasesthepayloadcorrespondingtoa givenpressureheightwillfallby aboutI0
O
_ tonne for every 3 K rise in atmospheric temperature, and vice versa.
,_, The nose engine is not suitable for axial propulsion, but flight is possible on any
symmetricalcombinationo[theremaining9 units;on 9 enginesateconomicalcruise
,_ (3 000 hp) the airspeed in ISA conditions becomes 205 km/h for the kerosine ship and 190 _,
1976007927-406
' ; FRESSURE I I i ,:
_, _ H EIGH T; I-- GAS I'-"DUAL FUEL
' 500 '_,
•; 400
r ,
} I GROSS . ;,
PAYLOAD , ..
, TONNE "_'-_ ,_
, _?
_ 300
<
i
I- ' ' 4 ENGINE CRUISE ON KEROSINE
_._- 200 /
_ / 5 ENGINE CRUISE ON GAS/DUAL FUEL ;
t, L
-_ '° i
_ 100
<, O 1000 2 000 3 000 '
' EFFECTIVE STAGE LENGTH KM
Fig. 2. IPERFORMANCE OF AIRFLOAT HL AIRSHIP ( SA)!
when towinga blimp;thecorresponding'idling'speedson one engineonlyare 75 and 70
km/h. Allquotedspeedsrefertoaxialflightand may fallby 2or 3 km/h when thehull
axisispitchedfordynamic lift.
Open Site Operation
For the movement of large indivisible loads between industrial sites the hoist frame is
coupled as in Fig 3 to a load frame which h_s ballast frames suspended froth electric
winches at its ends. Latches on the load frame bottom booms correspond with pickups on
simple sub-frames which have been built onto the load prior to its proposed transportation
date.
!
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1976007927-407
i,
iy
LOAD FRAIvlE/_LI_'H[ _ IF "I''-'" _ ,-
BALLAST'_' rx_' ' 'ul_) iLL _11 TRANSFERI.IFT _
y
HOIST i
FRAME.fl"_E_t_-,_L OAD
: _' _BALLAST PACK 1:
"-K
,, Fig.& _ /_LOAD
;,! OPEN SITE LOAD _ _:,
:_:_, EXCHANGE ',::' SYSTEM (::$"
!-_' AIRFLOAT HL AIRSHIP
s,,
-'. To pick up a load, the airship arrives ' in ballast', i.e. with packs of 15-tonne water ,
:, containers suspended from the ballast frames, and takes up a controlled hovering position
% 15 to 50 m above the load according to local conditions. As the load frame is being _
_:' lowered by the main hoist it is aligned with the load and the ballast packs are let down \
r_
_:_ relative to the load frame so that they will touch g_o,.md first with about 1 m clearance
between latches and pickups, as in Stage A of Fig 4. The ballast packs are manoeuvred
into position and grounded by downthrust of the vectored propellers while the ballast
winches on the load frame draw it down onto the sub frames; the latches are then
_"i' engaged to attach the load (Stage B). Upthrust is now applied and the ballast winches
_!! reversed, allowing the load to rise from the ground; in this position (Stage C) the load
._ security and c.g. may be checked before finally detaching an appropriate number of
- ballast units so that the airship may rise bodily with the load (Stage D), which is then
_ hoisted up and secured in Lhe flight position. After departure of the airship the ballast
_,;_ containers are emptied and taken away by ground service vehicles, which also have the
_ 409 Ri,_RODUCI_,It,IT'/ UI" lltl_; :
ORIGINkI_ PAGE IS POOR ,
1976007927-408
• t
: task of providing containers and setting up ii
_ , A: _-_DOWNT}_UST ballast packs at delivery sites for exchange ;
r--" LOC_TIONI V | with incoming loads; the delivery sequence _
: ___L_ _ is then the reverse of the pickup process ib------ outlinedabove. The oil-burning version of
_" _ . J the HL ship uses further ground vehicles to i
_ _ supply fuel in 10-tonne fibreglass transfer
. _, _. tanks which are incorporated into the ballast
_ _T T'_ packs in place of ballast containers; the gas
iJ II versions detach and dock fuel blimps in
flight wherever these may be conveniently ' _"
B: M'r _'_ flown into the operating circuit.
ATTAC'HME v The weight of the load frame and attachments, _
"_° estimated to be 30 tonne, must be deducted
. from the gross payloads of Fig 2 to obtain
"" the permissible weight of the payload and
its sub frames.
- Module. Operation
_ T Operation between fixed bases permits the
L . _ _ use of p_rmanent transfcrinstallations
_ throughwhich loadedmodules of similar
weightmay be rapidlyexchangedwithout
.: theinvolvementofexternalballastsystems.
"q_ Fig 5 indicates the components of the module
system; there is now no intermediate load
_ frame, the hoist frame engaging the upper
_ booms ofliftingbeams runningacrossthe
:' D: I _# module. The permissible weight of the
CLEARANCE [ U loadedmodule thenbecomes thegrosspay-
load plotted in Fig 2.
A standard module has been designed, 60 m
long, 25 m wide and 10 m deep, which with
different internal arrangements can
accommodate for example 250 cars and
1 000 passengers; or 3 000 foot passengers;
or 15 loaded vehicles averaging 24 tonn,.
_H HrL ap:ece. _maiiermoduie_ m_y be post.ulatcdfor balk grain and fluids, perishables and
.] containers, though there are few applicationsFig. 4 OPEN SITE LOAD 1 in he latter cate ories where the airshipEXCHANGE SEQUENCE may be expected to show a decisive
commercial advantage over existing systems.
Different module exchange mechanisms are under consideration; the one in Fig 5 uses
_wo transfer pools separated by a causeway which carries a ballast block, equivalent in
weight to a loaded module, on a frame of adjustable height. The incoming module is
lowered into its pool and held down by vectored thrust while tracking bollards move it
_nto the exchange position, the airship following in response to control signals from a
4tO
1976007927-409
_ M OOULE
IN
,, L IGHT {
F .i
POSIT ION
_ ,
: i I"
! J I_M_LAST
. HOIST FRA_ -----i,// _
; TRANSFER
c
-i
Fig. 5.[FIXED BASE MODULE EXCHANGE
ISYSTI'M OF AIRFLOAT HLAIRSHIP
position gyro in the load frame. In the exchange position gle module is coupled to the
ballastblock,whichmoves verticallytoholdthemodule levelwhilethehoistframe is
trackedacrossthemodule and ontotheblock. At thisstagetheballastblockmay, inan
emergency or for some other reason, be lifted out in place of a module; in the normal
transfer sequence, however, the block is now dlscomlected from the incoming module, i
co'..Tled to the outgoing one, and again used tocontrol the level of the latter while the
hoist frame is moved onto its suspension beams. Finally the module is disconnected, _"
moved out into the centre of its pool, and lifted clear.
Maintenance and Construction
The sizeoftheHL airshiprecludesaccommodation Ina hangarof reasonablecost,and _'_
it must therefore live permanently in the open. For ma}ntenance the airship is clamped
r "y
; l
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1976007927-410
,/ !
_!, to a base turntable through its load frame and through additional stays to the engine
_ mountings; the turntable is rotated through a control unit responding to signals from wind
: sensors surrounding the base, so that wind loads on the hull are kept within acceptable
c limits.
,_' i Construction must be carried out on the same turntable. The hull comprises an assembly
,_ l of prefabricated units, each composed of two or three gas cells complete with shell
/ , structure, covering and gasbags; the latter are partially filled to reduce handling weightand to check for leaks and valve function. The units incorporating the hoist are first set
4, I
_, up on the turntable, and further units are then added at either end so that the structure
; cantilevers towards nose and tail and can be turned to suit wind conditions. The hull .
units are lifted into place by hoists travelling along a temporary dorsal girder mounted __
_ along the top of the hull .....
S etT
:_ The most critical operating conditions arise during load transfer, and this phase has '
: therefore received more attention than any other in the design of the HL system. The Open
., Site sequence allows the airship to lift either the load or the ballast clear of the site at
"_ . any moment during the exchange period; an equivalent facility is offered by the ballast
block in the module system, though here a critical condition arises while the hoist frame
-" is tracking between lifting stations and the system is therefore being further examined.
._ The failure during load exchange of any one engine will modify the control envelope, but
will not require immediate withdrawal from the sequence except in severe turbulence.
_,_ Flying control and computer systems are duplicated against electrical or mechanical
laP'.Ire.
""'; In moving flight the principal danger, particularly when n,noeuvreing close to the ground,
is that of structural damage and gasbag rupture due to collision with ground obstacles or
_; light aircraft; larger commercial and military aircraft will tend to operate at higher
_' altitudes and under stricter traffic control. The shell structure is di ffuse and highly
redundant, and may be expected to absorb appreciable damage in most areas without
significant immediate loss of airworthiness; gasbag rupture, however, requires more
attention. Each gasbag in the IlL airship is divided internally by an annular membrane
into two compartments, so that rupture of the outer skin cannot release more than hal the
gas content. In addition, 62 tonne of emergency water ballast carried in tanks at nose and
tail permit balancing both of lift loss and of pitching trim loss arising from the collapse
of any one gasbag or of any two half-bags.
The fire hazards inherent in gaseous fuels are met by the controlled separation techniques
which have already been indicated. A burning fuel blimp may be towed on an extended
cable until it burns out or can be released over a 'safe' area. Similarly, if the airship's
tailcone becomes ignited the fuel blimp may be cast off and the tailcone 'trailed' on a
cable until it can be safely jettisoned, running meanwhile on the kerosine reserve while
the fuel blimp follows under its own power. The blimp is then reattached for continued
flight.
Costs
Estimation of the cspltal cost of the HL airship is based upon the assumption that no
initial facilities exist; the final figure, referred to current U.K. averages, therefore
l includes the cost of the construction site, of the accommodation, materials and personnel
i
; l
I
E
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1976007927-411
for design, research, construction and crew training, and of one base turntable. A large ,_
item in the cost is a flight simulator system, to be used initially for control system
development and later for crew training; the nature of the project renders simulator
: training more appropriate than flight training in a small airship, and no specific ;_
allowance has been made for the construction of a small vessel within the HL programme, i
Some use may, however, be made of any small airship which becomes available, such as
.one of the Goodyear or WDL blimps, or the larger Airfloat GP airship which forms the t i
, basis of a parallel project.
Exact costing is inhibited by unstable economic conditions; a comprehensive costing _.
exercise was, however, carried out by Airfloat in 1972,, and subsequent application of a
sui!able spectrum of inflation factors and known cost increases has led to a current
estimate of about £9 000 000 ($23 000 000) for one basic airship, using kerosine alone. , #..
There are then additional items for airship and mission variants; 3 fuel blimps and a :' .J
refuelling base for the gas burning versions, ground service vehicles and facilities for
open site work, 3 modules and 2 exchange terminals for module operation, leading to the
following approximate capital costs:
Open Site Operation Module Operation
Oil-burning HL airship £10 000 000 £11 000 000
($25 000 000) ($28 000 000)
Gas-burningHL airships £12 000 000 £13 000 000
,_ ($30 000 000) ($33 000 000) .:
These costs refer to one airship; subsequer, t ships and their associated facilities would be
_ expected to cost about £3 000 000 ($7 000 000) less than the above totalq.
_ The annual operating cost is found not to differ greatly between Open Site and Module
systems, therunningcostofthegroundservicesfortheformer balancingthatofthe
,: module terminalsforthelatter;thereare, however, significantdifferencesbetweenthe
running costs of alternative fuel versions, and at current U.K. fuel prices the annual
• operating cost for a 46-week working year in a 15-year depreciation period becomes about
i £5 200 000 ($13 000 000) on kerosineb £4 000 000 ($10 900 000) on dual fuel and _"
£3 300 000 ($8 000 000) on natural gas alone. These figures refer to a single airship
i recovering the whole of its capital cost.
On Open Site work the annual capacity of one HL airship is about 450 000 000 tonne-km on
kerosine and 470 000 000 tonne-km on dual fuel or gas; the corresponding figures for
module operation with a n.odule of 100 tonne tare weight are respectively :_50 000 000 and
370 000 000 tonne-km. The unit capacity rates are then found to be:
Kerosine Dual Fuel Gas
Open Site Operation:
pence/capacity tonne-km 1.2 0.9 0.7
cents/capacity U. S, ton-mile 4.1 3.1 2.5
Module Operation:
pence/capacity tonne-km 1, 5 1.1 0.9
cents/capacity U.S. ton-mile 5.4 3.9 3.2
41.1
t
1976007927-412
• _ It should be emphasised that these are capacity rates estimated for construction in the U.K.
and operation in Europe; their relationship with true r_tes will depend upon the area of
operation and upon the load factors which can be achieved in the selected traffic category.
,4
¢
r
\
1976007927-413


The Airfloat HL project

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