STEAM LTA - PAST, PRESENT, AND FUTURE
Thomas J. Goodey
The Flying Kettle Project
86 Whitestile Road
Brentford, Middlesex
England TW8 9NL
07759-656-559
www.flyingkettle.com
flyhigh@flyingkettle.com
ABSTRACT
Steam as LTA lift gas: its advantages and disadvantages. A ground boiler is required for
initial filling. Possibility of mounting insulation upon the envelope. The double envelope
concept. Advantages of size; the square/cube law. The "dribble" and "reboiling" flight modes
for a steam balloon. Review of previous proposals: Cayley - Erdmann - Papst - Alcock Giraud - Domen. Our experiments, and the condensation rates established. Our Giraud-type
ground steam generator. Future plans: a large "dribble" balloon, and a "reboiling" balloon
carrying a flight boiler. Airship possibilities. Combination with a steam engine for
propulsion. Vane motors for maneuvering. The Besler steam aircraft engine. The steam
airship mission: limited but effective.
THE CONCEPT OF USING STEAM AS LIFT GAS
The idea of using steam (H2O in its vapor phase) as LTA lift gas - either for a balloon or an
airship - has been suggested many times. These suggestions all appear to have remained
merely theoretical, although several were quite detailed. It appears that no full-scale trials, or
even experiments, have ever been performed. Yet the idea of using steam as lift gas is
attractive, although there are some obvious difficulties.
In the past, hydrogen, helium, methane, ammonia, and hot air have been used as lift gas.
Hydrogen offers the best lifting performance of 11.19 N/m3 in the ISA (International
Standard Atmosphere), but its high flammability makes hydrogen politically unacceptable
nowadays. Helium provides 10.36 N/m3 lift and is completely safe, but it is very costly and
is difficult to transport and supply. Methane provides only 5.39 N/m3 lift and has no
particular merit because it offers no safety advantages over hydrogen. Ammonia provides
4.97 N/m3 lift, is fairly cheap, and is non-explosive and quite easy to transport and supply,
but it is corrosive, toxic and malodorous, and has not found favor in practice.
Hot air must be kept hot by burning fuel, and buoyancy control can be performed by varying
the fuel burning rate. Hot air is very cheap and easy to supply, and is completely safe, but it
provides rather poor lift. In practice the temperature of the air in a hot-air balloon envelope
Steam LTA - Past, Present, and Future
Page 1
varies between 100ºC and 120ºC, and thus the lift provided is between 2.7 N/m3 and
3.2 N/m3.
Steam as lift gas, either for an airship or a balloon, will have the following characteristics.
First, to remain gaseous at sea level pressure, steam must of course be maintained at a
minimum temperature of 373ºK, i.e. 100ºC. Because the molecular weight of H2O is 18
while the average molecular weight of air is about 29, and taking temperature into account,
the lift provided in the ISA by steam lift gas is 6.26 N/m3. This is about 60% of the lift of
helium and more than twice the lift of hot air. Steam is non-corrosive, non-poisonous, very
cheap indeed, and odor-free. It cannot ignite and can be easily produced anywhere.
GAS
M.W.
Temp.
(°C)
Density
Lift (N/m3)
Ease of
Buoyancy
(kg/m3)
in ISA
provision
control
H2
2
15°
0.084
11.19
bad
fair
fair
no
He
4
15°
0.169
10.36
good
very
high
very
bad
no
CH4
16
15°
0.676
5.39
bad
low
fair
no
NH3
17
15°
0.718
4.97
fair
low
fair
no
hot air
29
(avg)
110°
(avg)
0.921
(avg)
2.98
(avg)
good
very
low
good
yes
steam
18
100°
0.587
6.26
good
very
low
good
yes
(H2O)
Safety
Cost
As compared to the highest-lift gases - hydrogen and helium - the advantages of using steam
would appear to be that it is safe, and also that steam is so cheap that it may be vented
without cost concerns. However its lift is not as good. Moreover steam will continually
condense upon the inside of an envelope into water droplets which will trickle downward to
the lowest point of the envelope. For indefinitely continued flight this condensate needs to be
continually re-boiled, and the weight of the boiler required, and of its fuel, can be expected
to be substantial. So, for craft of similar volume, the payload and performance of a steam
LTA craft will 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 may well be much cheaper, 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
Steam LTA - Past, Present, and Future
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for the same lift the envelope area is approximately halved. (This does not necessarily mean
that the rate of heat loss is half, however, although it is less; the situation is more
complicated than that.)
To produce the same amount of lift, about seven 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 water boiling capacity will be
required. This important point was first realized by Andre Giraud. It presents a substantial
barrier to practical implementation of a steam balloon or airship.
INSULATING THE ENVELOPE
Heat insulation is not conventionally provided upon hot air balloon or hot air airship
envelopes, because the areas are so great, and the lift provided by hot air is so weak, that
even very light insulation would be a losing proposition except in the case of an extremely
large craft (square-cube law). But with a steam balloon or steam airship envelope whose area
is halved as compared with that of a hot air
craft of similar lift, it becomes practicable to
provide an insulation layer, and this will
confer a dramatic reduction in heat loss.
Nevertheless the areas involved are very
large, and only very light insulating systems
can be considered. Various expedients are
possible. Making the envelope from a
material which has low heat emissivity
(Mylar or metal foil) on the outside is very
effective. The idea of a double envelope has
been suggested, for example by Alcock (as
shown), but the best means for stabilizing
the outer jacket in position and keeping it
inflated is by no means obvious.
THE 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 cost of the steam lift gas (whose volume varies as the cube) will
not be significant as compared to other costs. This means that it is very advantageous for a
steam balloon or steam airship to be large - as large as possible within limitations of plant.
MODES OF FLIGHT
With a steam balloon (but not an airship), there are two possible modes of flight: the "dribble
mode" and the more sophisticated "reboiling mode".
Steam LTA - Past, Present, and Future
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In the "dribble mode", 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. However, no onboard boiler or fuel is carried. As the steam
progressively condenses due to heat loss, the resulting condensate is drained from the bottom
of the balloon and ejected into the atmosphere, and simultaneously the pilot discharges
ballast water so as to compensate for the lift lost. Thus the duration of the flight is limited by
the amount of ballast which can be carried at takeoff; when the remaining 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 degree of vertical control will probably be the greatest in all
aeronautical history.
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 the gross loss of buoyancy in the ISA
is 2.09 kg. If the resulting one kilo of condensed water is retained on board, this 2.09 kg
constitutes the net lift loss. However if the condensed water is discharged, the net loss of
buoyancy becomes 1.09 kg. Therefore, for buoyancy loss to be compensated by ballast
discharge to maintain level flight, 1.09 kg of ballast must be discharged for every kilo of
condensate discharged. It is interesting that these two figures are nearly equal....
In the "reboiling mode", the balloon is filled with steam using the ground boiler and is then
released, slightly lighter than neutrally buoyant, carrying the pilot and passengers, an
onboard boiler/burner 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
balloon and is reboiled by the onboard unit into steam, which is supplied back into the
envelope. Thus the duration of the flight is only limited by the amount of fuel which can be
carried at takeoff. Since the burning of one kilo of hydrocarbon fuel can 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
apparatus. The larger the balloon, the lesser proportion of its load will the boiler/burner unit
constitute.
STEAM LIFT GAS IN HISTORY
I have conducted a fairly comprehensive review of the literature on this rather arcane subject
of steam aviation. We can be on pretty safe ground in believing that the earliest suggestion
of steam as LTA lift gas was by that under-appreciated genius Sir George Cayley. In 1815 he
wrote, referring to hot-air airships:
"...by using steam in lieu of heated air for inflating the balloon, or at least a great
mixture of it with the heated air. The power of steam is greater than air at the
usual temperature in Montgolfier balloons in the ratio of 18 to 11, although the
first inflation will cost more fuel in the ratio of 2.6 to 1. The resistance to a
steam-balloon will be only as 1 to 1.38, when compared with one of the same
power inflated by heated air; and hence a considerable saving of power would be
the result of adopting it. But several inconveniences arise upon the introduction of
steam into balloons, the chief of which are the necessity of doubling the structure,
Steam LTA - Past, Present, and Future
Page 4
so as to suspend the steam balloon within one of heated air or gas, and of the
materials being incapable of absorbing water.....
Cayley's acumen summed up in a nutshell several of the obstacles to the use of steam as lift
gas. His suggestion clearly relates to a powered airship. Presumably he was contemplating
the use of a steam engine for propulsion, since absolutely no alternative (other than muscle
power) was conceivable at the time; even electric motors hadn't yet been invented, let alone
the dreaded infernal combustion engine!
Moving up to the 20th century, in German Patent 214,019 (1908) Dr. Hugo Erdmann
proposed the use of superheated steam as lift gas in a balloon or rigid airship. He suggested
eiderdown as an insulating material. (In my opinion the idea of superheating the steam lift
gas is not practical.)
The pre-eminent postwar apostle of steam lift gas for airships was Hermann Papst. He
patented several concepts relating to the subject in Germany, other European countries, and
the USA. In US Patent 3,456,903 Papst proposed a double walled envelope for a steam
airship; he believed that such a double walled air-inflated structure would be extremely
effective for insulation. His US Patent 3,897,032 relates to a method of adding heated water
vapor to lift gas. And his US Patent 4,032,085 relates to a steam airship with pressurized
front and rear compartments.
As for the complementary idea of using steam as lift gas for a free balloon, this is outlined in
the Erdmann patent, but the first modern and detailed suggestion seems to be due to W.
Newman Alcock in a long-defunct ballooning newsletter "Wingfoot" in 1961. He went into
the concept at some length. And a couple of notes by David Young appeared in Aerostat in
1973/4. However, the most detailed proposal I have so far found in patent literature is French
Patent 2,684,952 to Andre Giraud (1991). It describes the use of a ground boiler for initial
filling of the envelope, among other concepts - he seems to have been the first to appreciate
that important concept. I don't know if Giraud ever got anywhere with practical
implementation ... he was actually the French Minister of Defence under Mitterand during
the Cohabitation, so he may have been rather busy with more mundane tasks. Unfortunately
he is no longer with us.
Further, there is an ingenious type of low-tech balloon made of black plastic pioneered by
the French and called a "bulle d'orage", which is filled on the ground with warm air
saturated with water vapor to a proportion of the order of 40 gm/m3. The balloon carries no
fuel or burner. When the balloon is released, the adiabatic cooling of the warm wet air lift
gas due to pressure drop during the ascent is largely compensated by latent heat released by
condensation of the water vapor in the lift gas, and in fact the resultant cooling rate as the
balloon rises is less than the rate by which the external atmospheric temperature drops, so
that the value of the lift is maintained. With a modest payload a bulle d'orage is capable of
attaining very high altitude. There is too little water vapor for any substantial contribution to
the lift. The great apostle of the bulle d'orage is M. Jean-Paul Domen. His European Patent
524,872 describes a sophisticated type. In 1996 he built a large bulle d'orage which lifted a
load of 270 kg to a height of 12 kilometers. He has even performed a brief manned flight,
sort of a hop..... flying hanging from a bag made from black plastic garbage bag material
taped together may not be everybody's cup of tea!
Steam LTA - Past, Present, and Future
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OUR CURRENT DEVELOPMENTS
For some time I have made it a personal avocation to promote the idea and the practice of
using steam as lift gas. It is one of the few simple low-tech ideas which has never been tried,
although it is not quite obvious why.
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.
So I make no apology for the fact that my concrete efforts so far have focused upon the
development of a steam balloon, and I shall now presume to describe these ballooning
efforts in the context of an Airship Convention.
MY EXPERIMENTS
Previous theoretical proposals to use steam as LTA 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 ingenious concepts, but the numerical values given are
extremely speculative and perhaps 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 steadily condense into water
and trickle downwards to the low point of the envelope. The first question is: how much
parasitic weight is entailed? In other words, at any moment, what mass 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 patent suggests means for minimizing it).
(2) At what rate does the steam condense? That is, for a "naked" steam balloon or airship
envelope without any insulation jacket, full of steam, how many kilograms of H2O per
square meter of the envelope per hour are condensed 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 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
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 condensation rate experimentally.
(3) How much is this condensation rate reduced by fitting various types of insulation over
Steam LTA - Past, Present, and Future
Page 6
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 their
effectiveness in this special context. Published parameters such as "R-values" cannot be
relied upon, and the performance of various insulation materials must be evaluated during
actual application for insulating the envelope of a steam balloon.
(By the way, it is not necessary to perform any experiments to determine or verify the lifting
power of steam - 6.26 newtons per cubic meter. That is a simple matter of basic physics.)
OUR SMALL-SCALE EXPERIMENTS
We 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.
We 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. The steam condensation rate for
this small uninsulated black envelope was 1.43 kg/m2.hour. We
were also able to measure the amount of water trickling down
inside the envelope at any one time: it was about 80 g/m2.
We then insulated this envelope with an
inner layer of simple bubble wrap and an
outer layer of reflective aluminized
polyester film (Mylar):
The steam condensation rate with this
quite unsophisticated insulation system
was 450 g/m2.hour.
OUR MID-SCALE EXPERIMENTS
We built a larger test envelope, approximately spherical, from the same material, area about
9 m2. And we glued Mylar over substantially its entire outer surface:
Steam LTA - Past, Present, and Future
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When we inflated this envelope with steam, using no insulation
jacket, we found a condensation rate of 935 g/m2.hour.
Thumping hard on this large envelope, inflated with steam and
tight as a drum, vividly reinforced our awareness of steam as a real
substance.
Then we manufactured an insulating jacket from a sophisticated
fluffy insulation material known as Primaloft PL1, nominal weight
133 g/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 g/m2.hour
We believe that it can confidently be extrapolated that, with a
somewhat thicker Primaloft PL1 insulating jacket, quilted in a
more sophisticated way and weighing 250 gm/m2 in total, 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 start to run into the
phenomenon of diminishing returns; we consider that
200 gm/m2.hour is the lower limit value in practice that can be
obtained for condensation, with any practical form of
insulation.
OUR GROUND STEAM GENERATOR
A high-capacity Giraud-type mobile steam generator is essential for the initial ground filling
of a steam balloon or steam airship, so we have tackled the ambitious task of building one.
The entire design has been dictated by the requirement to keep the total mass less than 3.5
tons, including trailer, this being the maximum legal weight which can be towed in the UK.
We constructed a fire-tube type boiler incorporating more than 700 kg of 22 mm copper pipe,
Steam LTA - Past, Present, and Future
Page 8
0.1 mm in wall thickness. The heat exchange area is a whopping 90 m2. This should have a
steam production capacity of around 3 tons per hour maximum, granted sufficient firing of
course. We used this apparently primitive design because a water-tube boiler with steel tubes
of comparable heat exchange area would have been at least twice as heavy.
And we built a firebox and mounted our boiler on it. As an experiment we tried firing this
unit with 250 kg of coal, starting it off with 5 liters of diesel oil (which perhaps was a
mistake). The firemen were quite amused!
Steam LTA - Past, Present, and Future
Page 9
The white cloud in this last picture was steam, and the smoke (perhaps the fault of the diesel)
had pretty well died away, so basically the unit was working well. There are, however,
obvious disadvantages to coal.... the control of combustion leaves something to be desired....
We realized that coal-firing was not practical, so the next stage has been to get the unit
mobile and to convert it for oil firing. These pictures show the system ready for installation
of the oil burner unit and testing:
Now, fitted with an oil burner unit powered by a
small gasoline engine, our ground steam generator
is working smoothly on gasoil (heating oil),
producing large amounts of steam on demand.
OUR FUTURE PLANS
Next we must build a steam distribution system to convey the steam to the balloon, since
various 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.
Then we will be ready to perform a test inflation, and to start actual steam ballooning.
Steam LTA - Past, Present, and Future
Page 10
THE FIRST SMALL TRIAL ENVELOPE - "DRIBBLE" FLIGHT
We already possess a small envelope, made from a siliconized nylon balloon fabric similar
to the fabric used in our experiments, and built according to a conventional hot-air balloon
structure. It is not laminated with reflective Mylar, so it is not optimal for a steam balloon,
but it will serve for a first test of the "dribble" flight mode. The area is 400 m2 and the
volume is about 600 m3, so the lift will be about 380 kg. And we have built a water ballast
dispensing system.
The weight schedule on takeoff will be roughly:
Envelope weight ................................. 45 kg
Parasitic water ....................................... 35 kg
Load frame, seat, ballast system ........... 20 kg
Pilot ....................................................... 80 kg
Water ballast ......................................... 200 kg
The condensation rate may be about 10 kg/minute at a maximum, according to our
experiments, so the water ballast may be expected to last about 20 minutes. Flight duration
should therefore be about 15 minutes before the pilot must come in to land. Even such a
modest flight should be quite entertaining - completely silent and superbly controllable although it will really just be a proof-of-concept.
OUR NEXT LARGE ENVELOPE
The small envelope described above goes against the principle that a steam balloon should
be as large as possible. Since we will be able to manufacture about 3 tons per hour of steam
with our ground generator, which is a lot, we should aim at a steam balloon of great capacity.
We intend to make our next envelope from a cheap, tough and relatively heavy woven
polypropylene tape fabric, similar to that used for common plastic tarpaulins. Such material
is unsuitable for hot-air balloons because it is too heavy, but steam offers ample lift. We
have located a source for a fabric of this type, laminated with Mylar film on one side and
with thin aluminum foil on the other. The aluminum foil has very low heat emissivity and is
Steam LTA - Past, Present, and Future
Page 11
ideal as the outside of the envelope, while the Mylar on the inside will be an excellent steam
and water barrier. The material is quite inexpensive. It weighs about 175 gm/m2.
ENVELOPE DIMENSIONS
The plan is to make a nearly spherical envelope, diameter 23 m, area 1,660 m2, and volume
6,370 m3, which when filled with steam will provide gross lift of about 4,060 kg. At full
blast, our steam generator should take two to three hours to fill this balloon. Envelope weight
will be about 310 kg and parasitic water about 150 kg, so the envelope net lift will be about
3,600 kg.
This envelope offers the following flight possibilities.
UNINSULATED "DRIBBLE" FLIGHT
According to our experiments, without any further insulation, this Mylarized envelope may
be subject to a condensation rate of about 975 gm/m2.hour, i.e. about 1,620 kg/hour in total.
For a "dribble" flight, allowing a few hundred kilos for basket, pilot, several passengers, and
ballast water tankage, it will therefore be possible to carry enough ballast water for two
hours flight (3,240 kg). This will be a pretty impressive 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 is doubled, i.e. another similar envelope is mounted over its outside with an
intermediate air gap, which is not a simple construction to implement, the envelope weight
will be roughly doubled, and the heat loss is expected to be less than 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 were fitted over this
envelope, the net lift would be reduced to about 3,200 kg, so only about 2,800 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.
The problem with this type of insulating jacket would be, not so much 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.
"REBOILING" FLIGHT MODE POSSIBILITIES
Allowing 200 kilos for an onboard burner/boiler system (which is shown by the Besler boiler
data cited later to be ample), and supposing a high boiler efficiency of 80% so that the
Steam LTA - Past, Present, and Future
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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 .......................... 3,000 kg
Fuel consumption ............ 120 kg/hour
Flight duration ................. 24 hours
DOUBLE ENVELOPE
Fuel load .......................... 2,500 kg
Fuel consumption ............ 50 kg/hour
Flight duration ................. 50 hours
INSULATED ENVELOPE
Fuel load .......................... 2,000 kg
Fuel consumption ............ 20 kg/hour
Flight duration ................. 100 hours
These flight durations are greater than could ever realistically be required, except in
long-distance balloon racing. This shows that, as one possibility, a large number of
passengers could be carried for an all-day flight. These performance extrapolations are
somewhat speculative, but they are supported by our experiments as far as they go, and at
least they show that the steam ballooning concept is well worth pursuing.
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 reheating. 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.
In order to minimize condensation the volume of the envelope ought to be maximized
relative to its area. The ideal is a sphere, but of course this is not a practical shape for an
Steam LTA - Past, Present, and Future
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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.
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. The above polypropylene
fabric is not strong enough to withstand very high internal pressure, but we are not talking
about a high-speed airship. (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 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 kg and the steam condensation rate will be
about 600 kg/hour. It will take about 40 kg/hour of fuel to reboil this condensate, so fuel for
a ten hour mission will weigh about 400 kg, and the burner/boiler should not weigh more
than 150 kg. We are therefore left with about 2,200 kg available for the empennage, gondola,
engines, engine fuel, pilot and flight gear, and payload. This seems 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 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 conventional
gasoline or diesel aeronautical engines, 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, and since the envelope itself would function as the condenser for
the steam engine, only the actual steam engine itself would be additionally required. A steam
reciprocating engine can be quite lightweight, and its reliability and high torque / low rpm
characteristics are very suitable for airship application. Moreover, maneuvering thrusters
could be driven by steam vane motors, which are very light indeed. However vane motors
could not be used as 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 aeroplane by Besler in 1933 - a little-known episode in aviation history. The
Besler brothers had participated in bringing the Doble steam car to its very high pinnacle of
development, before they successfully turned their attention to steam power for aircraft.
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The Besler Corporation worked on an improved version of this steam aircraft power plant in
1958, and the system they produced is now on exhibit in the Smithsonian Institution. Salient
points from the test data were (in Imperial units):
Engine and auxiliaries, weight .......................... 160 lbs
Boiler/burner and auxiliaries, weight ................ 170 lbs
Power output (max at 2000 rpm) ...................... 160 hp
Specific fuel consumption (cruise) ................... 0.8 lb/hp.hour
Steam production (max).................................... 2100 lb/hour
These 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 steam is required in any case for lift
purposes. The above figures prove conclusively that a boiler/burner unit can 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 outré .
CONCLUSION - 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.
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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 more-or-less
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;
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 ground handling of a Steam Airship will,
in this restricted operational context, more than compensate for its deficiencies.
—o0o—
References:
Cayley - letter dated 24 December 1815 in the "Philosophical Magazine".
Erdmann - German Patent 214,019 (1908).
Papst - US Patents 3,456,903 (1969), 3,897,032 (1975), and 4,032,185 (1977).
Giraud - French Patent 2,684,952 (1991).
Domen - European Patent 524,872 (1993).
Alcock - article in "Wingfoot" (1961).
David Sarlin - article in Steam Power Club News (April 1981)
Besler Corporation - Final Report on Aircraft Steam Powerplant #1843.00 (1958)
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