ADVANCES IN STEAM AEROSTATION
Thomas J. Goodey, The Flying Kettle Project, 86 Whitestile Road, Brentford, Middlesex, England TW8 9NL
+44 7729 478 238
www.flyingkettle.com
thomas@flyingkettle.com
ABSTRACT
HISTORICAL SUMMARY
Over the last two hundred years the use of steam as
LTA lift gas has been repeatedly suggested, both for
free balloons and for powered airships, but until April
this year no attempt has succeeded. Previous proposals
have been put forward by Cayley1, Liwentaal2,3,
Erdmann4, Papst5, Alcock6, Young7, Giraud8, and
Domen9. The main advantages of steam are that it is
extremely cheap and is easy to provide in the field, and
that it provides quite good lifting power. Steam's
outstanding disadvantage is that it continually loses
heat and condenses, although the high latent heat of
water means that the steam in an envelope constitutes a
very large heat reservoir. The square/cube effect is
prominent with a steam LTA craft: the disadvantages
are proportional to envelope area, while the advantages
are proportional to envelope volume. A steam balloon
can be operated in the "dribble" or in the "reboiling"
flight modes. A large ground boiler is required for
initial filling, and insulation can be provided upon the
envelope. A summary of the results of our small-scale
experiments is presented, along with the parameters of
our large ground steam generator. We have
successfully inflated a medium-scale steam balloon of
volume 320m3: this was a world first. It now appears
that, with further development, the steam balloon can
be a serious challenger to the hot air balloon. The
prospects for steam-lifted airships – perhaps even
powered by steam – also appear bright.
Sir George Cayley first proposed the use of steam or a
steam-air mixture for providing aerostatic lift. In 1815
he wrote1, referring to hot-air airships:
Liwentaal with
his Yarrow boiler
"...by using steam in lieu of heated air for inflating the
balloon, or at least a great mixture of it with the heated
air…… Several inconveniences arise upon the
introduction of steam into balloons, the chief of which
are the necessity of doubling the structure, so as to
suspend the steam balloon within one of heated air or
gas, and of the materials being incapable of absorbing
water.....
Cayley had already visualized several of the prominent
obstacles to the use of steam.
In 1901-2 Alexander Liwentaal2, an undeservedly
obscure aeronautical pioneer, actually built a full-scale
steam balloon of 1345 m3. He constructed a very
sophisticated lightweight Yarrow-type boiler, intended
to be carried on board, and possibly based upon the
boiler of Hiram Maxim's steam aircraft with which he
had been associated. There is no extant account of his
efforts to inflate this balloon, but they were
presumably unsuccessful. Liwentaal subsequently
wrote several letters3 to Count Zeppelin soliciting
support for further steam balloon trials and
developments, and suggested a demonstration in front
of the German Kaiser.
Steam balloon, boiler, and basket ready for inflation attempt
(with unidentified man)
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Liwentaal
carrying his boiler
A few years later, Dr. Hugo Erdmann proposed4 the
use of superheated steam as lift gas in a balloon or
rigid airship in German Patent 214,019 (1908). He
suggested eiderdown as an insulating material. This
patent application may well have been parasitic upon
Liwentaal's work and inspired by Zeppelin, who was
known for his tough patenting attitude.
The concept appears to have become dormant until
Hermann Papst became active5 in the sixties. He
obtained a number of patents relating to steam lift gas,
including US Patents 3,456,903, 3,897,032, and
4,032,085. None of his ideas was outstandingly
practical, and no applications resulted.
As for the use of steam as lift gas for a free balloon,
the first modern suggestion seems to be due to W.
Newman Alcock in a ballooning newsletter
"Wingfoot" in 19616. And a couple of similar notes by
David Young7 appeared in "Aerostat" in 1973/4. A
very detailed and clear-sighted steam balloon proposal
was set forth by Andre Giraud8 in French Patent
2,684,952 (1991). I don't know if Giraud made any
steps toward practical implementation. He was actually
the French Minister of Defense under Mitterand, so
political tasks may have taken precedence. He died not
long afterward. I believe that, if Giraud had lived, we
would have a steam balloon in the air today.
Further, there is an ingenious type of low-tech balloon
pioneered by the French and called a "bulle d'orage",
made of cheap black polythene, which is filled on the
ground with warm air saturated with water vapor to a
proportion of the order of 40 gm/m3. Thus this is not a
steam balloon as such, but the concept is related. The
bulle d'orage carries no fuel or burner. When such a
balloon is released and rises, the adiabatic cooling of
the warm wet air lift gas due to pressure reduction with
increasing altitude is largely compensated by release of
latent heat due to progressive condensation of the
water vapor, and in fact the resultant lift gas cooling
rate as the balloon rises is less than the rate at which
the external atmospheric temperature drops with the
altitude, so that the value of lift is maintained and even
increases as the balloon rises. The solar heating effect
is also important. A bulle d'orage is capable of
attaining great heights. The premier apostle of the
bulle d'orage is M. Jean-Paul Domen9. His European
Patent 524,872 goes into great detail about various
parameters of operation. In 1996 he built a large bulle
d'orage which lifted a load of 270 kg to a height of 12
kilometers, the advantage of course being the
extremely low cost. He also made a brief manned
flight..... flying hanging from a bag made from black
plastic garbage bag material and package shipping tape
may not be to everybody's taste!
THEORETICAL CONSIDERATIONS
GENERAL PERFORMANCE COMPARISONS — As
compared to the highest-lift gases - hydrogen and
helium - the advantages of using steam as lift gas are
that it is relatively safe and is so cheap that it may be
vented without cost concerns. However its lift is not as
good. Moreover for indefinitely continued flight the
condensing water needs to be continually re-boiled,
and the weight of the boiler and fuel required are
substantial. So, for craft of similar volume, the payload
and performance of a steam LTA craft must be much
lower than those of a helium or hydrogen craft. But
this may not be true when craft of similar cost (rather
than volume) are considered, because the material for
the envelope of a steam craft is expected to be much
cheaper than helium-tight material, and of course the
steam itself is extremely cheap. As compared to hot air,
the merit of steam is that its lift is more than twice as
great, so that for the same lift the envelope area is
approximately halved. (This does not necessarily mean
that the rate of heat loss is half, however; the situation
is more complicated than that.)
INITIAL FILLING — To produce the same amount of
lift, about six times as much energy is required for
boiling water to produce steam lift gas, as for heating
air to produce hot-air lift gas. Therefore it is inevitable
that, for the initial filling of a steam balloon or steam
airship on the ground before takeoff, a large and heavy
ground-based boiler of very high steaming capacity is
required. This important point was first realized by
Andre Giraud; Liwentaal doesn't seem to have
appreciated it, and his attempt to use his flight boiler
also for initial inflation may have been one cause of his
lack of success. This fact constitutes a substantial
barrier to practical implementation of a steam balloon
or airship; you need to make a heavy and expensive
ground steam generator before starting aerial trials.
(Since the steam will be required in a field situation, it
is not really practicable to use available steam from a
factory or laundry, although perhaps geothermal steam
could be employed.)
THE OUTSTANDING ADVANTAGES OF LARGE
SIZE — The lift of a steam balloon or airship is
proportional to the cube of its characteristic linear
dimension, while both the rate of total heat loss and the
envelope weight are proportional to the square.
Moreover, the incremental cost of the steam lift gas
(whose volume varies as the cube) is utterly
insignificant. This means that it is very advantageous
for a steam balloon or steam airship to be large - as
large as possible within the limitations of the
equipment.
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MODES OF FLIGHT
With a steam balloon there are two possible modes of
flight: the simple "dribble mode", and the more
sophisticated "reboiling mode".
THE DRIBBLE MODE — Here, the balloon is filled
with steam using the ground boiler and is then released,
slightly lighter than neutrally buoyant, carrying the
pilot and passengers and a large quantity of ballast
water. There is no onboard boiler or fuel. As the steam
in the balloon progressively condenses due to heat loss
through the envelope, the resulting condensate water is
drained from the bottom of the balloon and is ejected
into the atmosphere, and simultaneously the pilot
discharges ballast water so as to compensate for the
progressive loss of lift. Thus the duration of the flight
is limited by the amount of ballast which can be
carried at takeoff; when the ballast gets low, the pilot
must land. This type of flying will have a charm all of
its own, because it will be utterly silent, and the
altitude control will be superb. Although the "dribble"
flight mode may seem crude – rather like the old
smoke balloons – I think it has excellent possibilities.
An important basic figure is the rate of loss of lift from
a steam balloon as the steam condenses into water, in
this "dribble" flight mode. If one kilo of steam in an
envelope condenses into water, the loss of volume is
1.70 m3, so that the gross loss of lift in the ISA is
2.09 kgf. If the resulting one kilo of condensed water is
retained on board, this 2.09 kgf constitutes the net lift
loss. However if the condensed water is discharged,
the net loss of lift becomes 1.09 kgf. Therefore, for lift
loss to be compensated by ballast discharge to
maintain level flight, 1.09 kg of ballast must be
discharged for every 1 kilo of condensate released. It is
interesting that these two figures are nearly equal.
THE REBOILING MODE — Here, the balloon is filled
with steam using the ground boiler and is then released
for flight, carrying the pilot and passengers, an
onboard burner/boiler unit, a quantity of fuel, and
perhaps some ballast. As the steam condenses due to
heat loss, the resulting condensate is drained from the
bottom of the envelope and is reboiled by the onboard
burner/boiler unit into steam, which is fed back into
the envelope. Thus the duration of the flight is only
limited by the amount of fuel which can be lifted at
takeoff. Since one kilo of hydrocarbon fuel can be
burnt to boil more than 15 kilos of water, it is evident
that much longer flights can be made in this reboiling
flight mode than in the dribble mode, even allowing
for the weight of the onboard burner/boiler unit.
Altitude regulation is performed by varying the rate of
burner operation and accordingly the reboiling rate.
CURRENT DEVELOPMENTS
For some time it has been my personal hobby to
promote the idea and the practice of using steam as
LTA lift gas. It is a simple low-tech idea which has
never been successfully tried.
In terms of actual implementation, the use of steam lift
gas in a balloon must surely come first in the logical
development of the subject, before any airship
application. If one can't get steam lift gas to work well
in a balloon, it is not likely to work in an airship!
Moreover, from the cost point of view, to develop and
fly a balloon filled with steam is a project which can
be tackled by an individual on a hobby basis, whereas
to develop a steam airship promises to be a much more
expensive proposition, one scarcely within the reach of
a private individual.
MY EXPERIMENTS — Previous theoretical proposals
to use steam as lift gas have been vulnerable to the
criticism of being rather deficient in concrete data.
Particularly, the Papst patents and the Alcock article
suggest many concepts which are ingenious in theory,
but the numerical values given are extremely
speculative and perhaps rather optimistic, particularly
with regard to the all-important question of insulation
performance. Therefore I have undertaken several sets
of experiments in order to derive the numerical
parameters which are necessary for planning steam
flight seriously. Although this is by no means high
technology - it's strictly kitchen/garage work - to the
best of my knowledge this research is original. The
goals of this experimental program were:
(1) Steam filling the envelope of an LTA craft
obviously will progressively condense into water and
trickle downwards to the bottom of the envelope. The
question is: how much parasitic weight is entailed? In
other words, at any moment, what weight of water (per
square meter) is thus trickling down? This weight is of
course a dead load upon the craft, and it cannot be
eliminated, although the Giraud patent8 suggests means
for minimizing it.
(2) With a "naked" steam balloon, at what rate does the
steam condense? That is, how many kilograms of H2O
per square meter of the envelope per hour condense
from steam to water due to heat loss through the
envelope? No attempt seems ever to have been made
to quantify this rate of naked envelope steam
condensation; published figures for the loss of heat
from steam pipes etc. cannot reliably be applied to the
cooling of a very large bag of steam in the outdoors,
because of variations with scale in the complex
processes of convective cooling. It is quite
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extraordinary that the steam airship and steam balloon
concepts have been repeatedly proposed and discussed,
for nearly two hundred years, without any effort being
made to determine the value of this fundamental
parameter experimentally.
(3) How much can this condensation rate be reduced
by fitting various types of insulation over the
envelope? It is evident that in practice the steam
balloon and steam airship concept really stands or falls
upon the question of whether an insulation jacket can
actually be manufactured, sufficiently effective in
insulating performance to reduce the rate of
condensation to an acceptable value, while still
sufficiently light to allow the craft to fly. The normal
methods for testing insulation materials are not very
applicable for determining effectiveness in this special
context. Published parameters such as "R-values"
cannot be relied upon; rather, insulating performance
must be evaluated during actual application for
insulating the envelope of a steam balloon.
SMALL-SCALE
EXPERIMENTS — I first
constructed a miniature test
envelope of the classic
ball-and-cone balloon shape
made from twelve gores, of
total area 3.5 m2, using a
black siliconized nylon
balloon fabric. I managed to
inflate this envelope with
steam from a small boiler
system, and to keep it filled
for several hours. This was
the first time, as far as I know,
that a flexible bag had ever
been completely inflated with
steam, at least for more than a
transient period. The steam
condensation rate for this
small uninsulated black
envelope was
1.43 kg/m2.hour. I was also
able to measure the amount of water trickling down
inside the envelope at any one time: it was about
80 gm/m2. I then insulated this envelope with an inner
layer of simple bubble wrap and an outer layer of
reflective aluminized polyester film (Mylar). The
condensation rate with this quite unsophisticated
insulation system was 450 gm/m2.hour.
MID-SCALE EXPERIMENTS — I built a larger test
envelope, approximately spherical, from the same
material, of area about 9 m2, and glued reflective
Mylar over substantially its entire outer surface. Thus
this test envelope was silver
on the outside and black on
the inside. When it was
inflated with steam, using no
insulation jacket, the
condensation rate was
935 gm/m2.hour. Thumping
hard on this large envelope,
inflated with steam and tight
as a drum, vividly reinforced
one's awareness of steam as a
real substance.
Then I manufactured an
insulating jacket from a
sophisticated fluffy insulation
material known as Primaloft
PL1, nominal density
133 gm/m2. (This material is
used in high-quality sleeping
bags and outdoor gear.) When
this jacket was fitted over the
above envelope inflated with
steam, the condensation rate
was 275 gm/m2.hour. I
extrapolate that, with a somewhat thicker Primaloft
PL1 insulating jacket, quilted in a more sophisticated
way and weighing 250 gm/m2, the rate of steam
condensation could be reduced to about 200 grams per
square meter per hour. Making the jacket still thicker
and heavier would probably become less and less
effective.
Finally, I made a new envelope from a cheap but
relatively heavy woven polypropylene tape fabric
(similar to that used for tarpaulins), covered with
reflective Mylar
film on one side
and with a thin raw
aluminum foil on
the other. Buildings
in New Zealand,
Australia, and
south-east Asia are
often insulated with
an inexpensive
fabric of this type.
The raw aluminum was of course on the outside and
the Mylar on the inside. Without any insulation jacket,
the condensation rate proved to be 640 gm/m2.hour.
This was quite different from the rate for the above
envelope which had a black interior. Opinions may
differ as to whether the improvement (i.e. the reduction
in heat loss) was due to the color of the interior, or was
because the exterior was covered with raw aluminum
rather than with reflective Mylar. Although the Mylar
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looks like a mirror at visible wavelengths, its
emissivity for radiating heat in the infrared band may
be completely different. The raw aluminum was quite
vulnerable to damage during handling.
THE GROUND STEAM GENERATOR — A
high-capacity mobile Giraud-type steam generator is
essential for the initial ground filling of a steam
balloon or steam airship, so I tackled the ambitious
task of building one. The entire design was dictated by
the requirement to keep the total mass less than 3.5
tons, so that it could be towed on the road legally.
In summary, I consider that 200 gm/m2.hour is the
lower practical limit for the condensation value for a
steam balloon, with any reasonable form of insulation.
Piling on more and more insulation will only run into
the phenomenon of diminishing returns.
I constructed a fire-tube type boiler incorporating more
than 700 kg of 22 mm copper pipe, wall thickness
0.1 mm. The heat exchange area is a whopping 90 m2.
With sufficient firing, this should have a maximum
steam production capacity of around 3 tons per hour.
(The burner currently used provides a much lower
firing rate, because we are not yet ready to use the full
steam production capacity.) I employed this
apparently primitive design because a water-tube
boiler with steel tubes of similar heat exchange area
would have been at least twice as heavy; steel tube of
0.1 mm wall thickness cannot be bent into coils.
And I built a firebox insulated with a sophisticated
high-temperature rock wool material, and mounted the
boiler on it. As an experiment I tried loading up this
unit with 250 kg of coal, and I started the fire off with
5 liters of diesel oil, which perhaps was a mistake….
The firemen were quite amused!
The white cloud in the right hand picture below was
steam, and the initial column of black smoke (maybe
the fault of the diesel) had pretty well died away, so
basically the unit was working well. There are,
however, obvious disadvantages to coal.... it is hard to
get perfect control of the combustion process...
I have not yet done any experiments on insulating this
last envelope; work is ongoing.
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Obviously coal-firing was impractical, so the next
stage was to get the unit mobile and to convert it for oil
firing. At present, fitted with an oil burner powered by
a small gasoline engine, this ground steam generator is
working smoothly on gasoil (i.e. diesel or heating oil),
and produces large amounts of steam on demand.
THE STEAM DISTRIBUTION SYSTEM — The next
task was to build a steam distribution system to convey
the steam to the balloon, since parts of the ground
steam generator are at temperatures of several hundred
degrees, and obviously the balloon must be kept well
away from them. In order to stop it becoming
waterlogged, this system needs to have quite
sophisticated means for draining condensate. Also a
large-scale steam control valve was required. The
pictures show the solution I have reached.
THE FIRST TRIAL ENVELOPE – With the help of the
Alom Group of Sarawak, Malaysia, we built a trial
envelope from a polypropylene fabric, like the one
described above but this time laminated with reflective
Mylar film on both its sides, and weighing about
175 gm/m2. The envelope volume was about 320 m3.
We sealed the seams with common household silicon
sealant.
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FIRST EVER STEAM BALLOON INFLATION
We performed a successful tethered inflation of this
envelope on 17 April 2003: the first inflation of a
full-scale steam balloon in history. The arrangements
for getting the steam into the envelope, and for
controlling the envelope while it is being inflated, do
actually require some further elaboration. As can be
FUTURE POSSIBILITIES
THE NEXT LARGE ENVELOPE — The above first
small envelope goes against the principle that a steam
balloon should be as large as possible. Since the
potential of this ground steam generator is about 3 tons
per hour of steam, which is a lot, we should aim at a
steam balloon of great capacity.
ENVELOPE DIMENSIONS — My plan for a full-sized
steam balloon is to utilize the time-tested ball-and-net
gas balloon constructional formula. Thus the envelope
should be nearly spherical, and I plan its approximate
parameters as being: diameter 23 m, area 1,660 m2,
and volume 6,370 m3. When filled with steam this
envelope should provide gross lift of about 4,000 kgf.
At full blast, the steam generator should take two to
three hours to fill this balloon. Envelope weight with
net (without any insulation) will be about 350 kg and
parasitic water about 150 kg, so the envelope net lift
will be about 3,500 kgf.
This envelope offers the following flight possibilities.
Uninsulated "dribble" flight
According to my experiments, without any further
insulation, this envelope, if white inside and covered
on the outside with a reflective "Mylar" type material,
may be subject to a condensation rate of about
700 gm/m2.hour, i.e. about 1,160 kg/hour in total. For a
"dribble" flight, allowing a few hundred kilos for
seen from the left-hand picture, it was a bit of a
struggle to control the envelope while it was partially
inflated. and as it transited from lying down to
standing up. When completely full the envelope stood
nicely and tugged upwards strongly, even though quite
a quantity of air had gotten into the envelope along
with the steam. For the first time ever, the lifting
power of steam was manifested to the naked eye!
basket, pilot, several passengers, and ballast water
tankage, it will therefore be possible to carry 3,100 kg
of ballast water, which will be easily enough for two
hours flight. This will be a pretty decent performance,
considering that the only cost for a flight will be that of
about 600 kg of gasoil fuel for the ground fill.
Double envelope – "dribble" flight
If this envelope were to be doubled, i.e. if another
similar envelope were mounted over its outside with an
intermediate air gap, which is not a simple
construction to implement, the envelope weight would
be roughly doubled, and the heat loss would be
expected to be reduced to below half, so that about
four hours "dribble" flight duration could be
anticipated.
Insulated envelope – "dribble" flight
If a Primaloft insulating jacket as described above of
weight 250 gm/m2 and thus of total weight 400 kg,
were fitted over the first (single layer) envelope, the
net lift would be reduced to about 3,100 kgf, so only
about 2,700 kg of ballast water could be carried. But
the condensation would now be only about
200 gm/m2.hour, i.e. about 330 kg/hour in total.
"Dribble" flight duration would now be about 8 hours,
which is extraordinary, considering that no flight boiler
is being used.
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The problem with this type of insulating jacket would
be, not its weight, but its bulk. The volume might be
30 m3 or more. This would present something of a
problem upon retrieval. Personally, I am not convinced
of the practicability of a bulky insulation jacket of this
type upon a balloon, which needs to be retrieved after
every flight. The case with an airship is quite different;
a relatively thick insulation jacket is very practicable.
Possibilities for the "reboiling" flight mode
Allowing 200 kilos for an onboard burner/boiler
system (which is ample with a sophisticated unit), and
supposing a high boiler efficiency of 80% so that the
combustion of 1 kilo of onboard gasoil fuel reboils
about 15 kg of water, the following approximate
figures for "reboiling" flight performance are easily
derived:
UNINSULATED SINGLE ENVELOPE
Fuel load
Fuel consumption
Flight duration
2,900 kg
80 kg/hour
36 hours
DOUBLE ENVELOPE
Fuel load
Fuel consumption
Flight duration
2,500 kg
40 kg/hour
60 hours
INSULATED ENVELOPE
Fuel load
Fuel consumption
Flight duration
2,100 kg
21 kg/hour
100 hours
These flight durations are greater than could ever
realistically be required, except in long-distance
balloon racing. It should be noted that the solar heating
effects which torment a conventional gas balloon as it
goes under clouds and comes out again do not affect
the actual lift of a steam balloon operating in the
reboiling mode at all, but only cause its rate of fuel
consumption to vary.
We see that, as an alternative possibility, a large
number of passengers could be carried for an all-day
flight.
These performance extrapolations are not particularly
speculative; they are solidly supported by our
experiments, as far as they go. At the very least, they
show that the steam ballooning concept is well worth
pursuing further.
POSSIBLE AIRSHIP DEVELOPMENTS
Any possible actual development of a steam airship is
a long way off, but the general outlines of what might
be possible are emerging. Within limits, the picture is
encouraging.
First, the obvious disadvantages of using steam lift gas
in an airship are relatively low lift, and the necessity
for reboiling the condensate water. The advantages are
cheapness, and the ability to deflate the airship after
each flight, thus obviating the need for a hangar or
mast. A rigid airframe would sacrifice this second
great advantage of steam lift gas while preserving all
its disadvantages, and so I think that the idea of a rigid
steam airship is a non-starter.
The problem of the bulk associated with an insulating
jacket, which might give trouble with a steam balloon,
does not apply to a non-rigid steam airship, because
airships virtually always return to base after a mission.
So we can assume that a steam airship would be fitted
with something like the Primaloft insulating jacket
detailed above weighing about 250 gm/m2, and that the
rate of steam condensation would be about
200 gm/m2.hour.
In order to minimize condensation the volume of the
envelope relative to its area ought to be maximized.
The ideal is a sphere, but this is not a very practical
shape for an airship. A lenticular configuration could
be interesting. At least a steam airship could not be of
the conventional Hindenburg-type shape with fineness
ratio about 4:1; there would be too much area to lose
heat. Therefore a high-speed steam airship is
impracticable. The compromise might be a dumpy
shape like a puffer fish, presumably pitch-stabilized by
pendulum action. Or a lenticular….
For discussion let us consider an airship of volume
similar to our large balloon envelope, i.e. 6,370 m3,
and with area now about 2,400m2 since it is no longer
spherical, made from the same fabric as above and
fitted with a Primaloft insulating jacket. (It is probable
that ballonets could be dispensed with, because the
volume of the steam lift gas can easily be varied by
changing the boiler operating rate.) The total envelope
and insulation weight is now about 1,060 kg, and the
parasitic water will be about 200 kg, so that the net
envelope lift will be about 2,800 kgf and the steam
condensation rate will be about 500 kg/hour. It will
take about 30 kg/hour of fuel to reboil this condensate,
so fuel for a ten hour mission will weigh about 300 kg,
and the burner/boiler should not weigh more than
200 kg. We are therefore left with about 2,300 kg
available for the empennage, gondola, engines, engine
fuel, pilot and flight gear, and payload. This seems
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American Institute of Aeronautics and Astronautics
quite adequate for an airship adapted for advertising or
camera platform missions. And the price will certainly
be right! In capital and operating cost, such a steam
airship would more closely resemble a hot-air airship
than a helium airship.
STEAM PROPULSION FOR A STEAM AIRSHIP
Such an airship filled with steam lift gas could of
course be powered by a conventional gasoline or diesel
aeronautical engine, but the intriguing possibility
arises of using a steam engine. The spent exhaust
steam from the engine would naturally be discharged
into the envelope to replenish the lift gas. Since a
steam airship must in any case carry a boiler for
reboiling the condensate water, and since the envelope
itself would function as the condenser for the steam
engine, only the actual steam engine itself would be
required in addition. A steam reciprocating engine can
be quite lightweight and is very reliable, and its high
torque and low rpm characteristics are very suitable for
airship application. Moreover, maneuvering thrusters
could be driven by steam vane motors, which are very
light indeed, so they could be mounted at any
convenient point on the envelope. However such vane
motors could not be used as the main airship engines,
because their thermodynamic efficiency is poor.
An idea of what is possible can be gathered from the
details of the first and only flight of a steam powered
airplane, performed by Besler in 1933 - a little-known
episode in aviation history. The Besler brothers
participated in bringing the Doble steam car to its very
high pinnacle of development, and then they turned
their attention to steam power for aircraft. Their trials
were successful: the airplane was eerily quiet and
could land in a very short distance with engine reverse
thrust – but the concept was not adopted commercially.
The Besler Corporation worked on an improved
version of this steam aircraft power plant in 1958, and
the system produced is now on exhibit in the
Smithsonian Institution. Salient points from the test
data were (in Imperial units):
Engine and auxiliaries, weight
Boiler/burner and auxiliaries, weight
Power output (max at 2000 rpm)
Specific fuel consumption (cruise)
Steam production (max)
160 lbs
170 lbs
160 hp
0.8 lb/hp.hour
2100 lb/hour
The weights could be considerably reduced with
modern practice and materials. The specific fuel
consumption is not as good as that of an internal
combustion engine, but for the steam airship
application this is irrelevant, since the vented steam is
required in any case for lift purposes. The above
figures prove conclusively that a boiler/burner unit can
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American Institute of Aeronautics and Astronautics
be built sufficiently light to be used in a steam balloon
or airship, and that a steam engine system weighing
about an hundred kilos, fed by such a boiler, can
provide more than a hundred horsepower. The entire
plan appears quite viable, although rather outré .
ground handling of a Steam Airship will, in this
restricted operational context, more than compensate
for its deficiencies.
—o0o—
THE STEAM AIRSHIP MISSION
Obviously the non-rigid steam airship does not have
the potential to displace the helium airship in every
application. However I think that it will have its niche.
Specifically, I think that a steam airship will be able to
satisfy the demands that hot-air airships try to satisfy
but fail. Consider the following mission requirement:
During reasonably fine weather, to fly over a
major sporting event and maintain station for
a few hours, displaying advertising or
carrying a news camera.
A hot-air airship is not able to meet this requirement.
Theoretically it might be capable, but in practice the
wind is usually too strong - because a hot-air airship is
defeated by even a light wind. At present a helium
airship is the only possibility for this mission, and they
are extremely expensive to operate, fundamentally
because they must be kept inflated indefinitely.
I believe that, with development, a steam airship will
be able, in average good weather, reliably to:
Arrive from base, deflated and packed in a
single vehicle, at an unprepared launch site in
a park within a few kilometers of the target
area;
Be inflated with steam from a ground boiler
carried upon or towed with the same vehicle,
by a small ground crew;
References:
(1) Sir George Cayley - letter dated 24 December 1815
in the "Philosophical Magazine".
(2) Jean-Claude Cailliez – "Alexander Liwentaal, a
European aeronautical pioneer from Geneva",
pub. SECAVIA, Geneva (ISBN 2-8293-0260-5).
(3) Letters exchanged between Alexander Liwentaal
and Count Zeppelin, in the Zeppelin Archives at the
Zeppelin Museum at Friedrichshafen.
(4) Hugo Erdmann - German Patent 214,019 (1908).
(5) Hermann Papst - US Patents 3,456,903 (1969),
3,897,032 (1975), and 4,032,185 (1977).
(6) W. Newman Alcock - article in "Wingfoot" (1961).
(7) David Young, articles in "Aerostat", 1973/74.
(8) Andre Giraud - French Patent 2,684,952 (1991).
(9) Jean-Paul Domen - European Patent 524,872 (1993).
------
Fly to the target area and hold station over it
for several hours;
Return to the launch site and be deflated and
returned to base.
And I believe that the cost may be perhaps twice that
of a hot-air airship, but much less than that of a helium
airship. And I think that the up-wind performance of a
steam airship will be sufficiently reasonable for this
mission to be possible on, perhaps, 80% of days.
In fact for a limited mission such as the one specified
above, the full capabilities of a helium airship - such as
long-term endurance, high airspeed, and poor-weather
flight capability - are not actually needed. The steam
airship will have the most important qualities
necessary for advertising and camera platform work:
hover capability in moderate winds, and large size.
And I think that the low cost and the convenience in
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American Institute of Aeronautics and Astronautics