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Author Topic: Is a steam powered airship physically impossible?  (Read 15271 times)
Tower
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« on: March 02, 2012, 04:05:07 am »

Someone mentioned in another thread that they though a steam powered airship would be impossible due to thermodynamics'.

And this got me thinking, is this true and how would you determine if it is or not?

My plan is fairly simple, determine the lifting capacity of a large zeppelin, say the Hindenburg, determine the combined horsepower of its engines, determine the weight and horsepower of some steam engines and then add it all up and see what I get.

But before I start researching I was going to ask if there is a different way I should go about this or if someone else has already done it already?

No doubt even if it is possible it would be very inefficient  but now I want to know if its even remotely possible or if physics makes it impossible for a airship to ever lift a steam engine powerful enough to propel it.
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Mr. Boltneck
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« Reply #1 on: March 02, 2012, 05:37:38 am »

Given that there was a steam-powered airplane, which is a much tougher weight:power problem than one should face with an airship, my best guess (and it is only that) is that a steam-powered airship would be possible, especially with modern materials. Not necessarily practical, but possible.
If I had to build an airship with a non-IC, all-mechanical powerplant, I suspect that a Stirling motor, using either catalytic heating or a modern flameless combustor, might be a good way to go, seeing as it is safer, efficient, and doesn't need a boiler or condenser system. As a plus, the cold air of higher altitudes would actually add efficiency, by increasing the temperature difference between the hot and cold sides.
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« Reply #2 on: March 02, 2012, 07:19:59 am »

Someone mentioned in another thread that they though a steam powered airship would be impossible due to thermodynamics'.


That'd be me, I think. The actual thrust of the post was to illustrate how factual History and Science are not precisely paramount in the Steampunk genre, but its an interesting problem nonetheless.

At the risk of being labeled a crotchety old curmudgeon...
A Stirling engine's an interesting idea, but what kind of fuels does it use? How is it actuated? I'd think you would need some kind of force or energy source to get it started. Wouldnt including that source add weight? Have there been any full-sized locomotives powered by Stirling engines?



Given that there was a steam-powered airplane



That makes want to grab my banjo... Wink
« Last Edit: March 02, 2012, 07:29:17 am by MWBailey » Logged

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robotmastern
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« Reply #3 on: March 02, 2012, 07:49:43 am »

im not sure of a locomotive but there is a hybrid concept car with one proposed by dean kamen inventor of the segway and founder of FIRST robotics
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Narsil
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« Reply #4 on: March 02, 2012, 09:20:49 am »

It's certainly not impossible to have a steam powered airship but the fundamental characteristics of steam engines aren't that well suited to any kind of aircraft and you lose a lot of the advantages that they have in other applications.

There is a lot of confusion about Sterling engines, In small packages, say portable generators they can achieve efficiency comparable to IC engines, although that tends to drop off their size and power increases. Their big advantage is that they can produce useful work from relatively small differences in temperature and can work from pretty much any heat source. This makes them potentially useful for using 'low grade' energy which is difficult to utilise any other way.

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elShoggotho
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« Reply #5 on: March 02, 2012, 09:23:31 am »

Think of a steam powered airship like a 19th century steam powered factory. You get one huge main engine with a central shaft. Power is distributed to the outlying propellers via belts. Clever mechanics (read: gears) to have the outlying secondary shafts counter rotational. No idea if that would solve the main problem, but it would put the engine to the center of gravity.
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« Reply #6 on: March 02, 2012, 09:25:53 am »

This has actually been hashed over a few times already. As I recall, the consensus is that it is possible in principle, but would be horribly impractical even if one could overcome the technical hurdles, which are of Himalayan scale.
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« Reply #7 on: March 02, 2012, 10:09:26 am »

It's certainly possible. After all since bouancy is independent of flight speed, you could have a 20 ton steam engine onboard that gives you the speed of a bicycle. Better to use other methods.
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« Reply #8 on: March 02, 2012, 11:24:17 am »

Flash boiler and turbine - not actually that bad power to weight. The Bristol Tramp never flew, but it did manage to cram two 1500hp turbines for a total of 3000hp into a takeoff weight of less than nine tons. Indeed one of the major problems with the Tramp was too much power!

For comparison, the LZ-127 Graf Zeppelin had five engines giving a total of 2750hp.

Edit: While there were problems getting a good enough boiler for the Tramp, it is by no means impossible.
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« Reply #9 on: March 02, 2012, 01:14:59 pm »

Just because something is steam driven does not make it Steampunk. Creating a steam-powered airship is not the same as making a working Steampunk airship - one is an engineering puzzle, the other is a fantasy (using the term in nothing but a positive manner).

There is no way to make a Steampunk airship in real life, because we do not live in a world which allows lighter-than-air privateers to haunt the trade routes, or to explore the ruins of the Antarctic civilizations, or be part of Her Majesty's Aerial Defence Forces. Sorry, but Steampunk is much more than what a thing is, it is mostly what we do with that thing.
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« Reply #10 on: March 02, 2012, 01:30:23 pm »

Returning to the turbine idea, the LZ-127 Graf Zeppelin had about fifteen tonnes of payload capacity. While I can't easily get the figures for the weight of the diesel propulsion system, it was possible to fit a steam power-plant of slightly greater power than the LZ-127's into a max takeoff weight of eight and half tonnes (five and a half empty weight) so yes, it would be possible to make a steam airship, very possible.

It wouldn't be coal fired with men in boilersuits shoveling the fuel in manually, nor would it have pistons cranks and flywheels. It would not automatically be steampunk, but it certainly could be.
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Matthias Gladstone
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« Reply #11 on: March 02, 2012, 03:12:23 pm »

It's not only possible, , but it's already been done; arguably the first powered flight was by a steam powered airship in 1852:

It wasn't fast enough to stem the head winds it ecnountered though, so it was only really useable on calm days - as others have said, it's not that practical a solution.
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elShoggotho
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« Reply #12 on: March 02, 2012, 06:26:08 pm »

Just because something is steam driven does not make it Steampunk. Creating a steam-powered airship is not the same as making a working Steampunk airship - one is an engineering puzzle, the other is a fantasy (using the term in nothing but a positive manner).

There is no way to make a Steampunk airship in real life, because we do not live in a world which allows lighter-than-air privateers to haunt the trade routes, or to explore the ruins of the Antarctic civilizations, or be part of Her Majesty's Aerial Defence Forces. Sorry, but Steampunk is much more than what a thing is, it is mostly what we do with that thing.
That's not the question, Sir. If you want to keep it a fantasy at all costs, that's your choice. Now step aside while we do SCIENCE!
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Atterton
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« Reply #13 on: March 02, 2012, 07:19:59 pm »

I'd imagine a problem with steam engines might also be the change in mass. Admittedly a diesel engine will also use up fuel, which makes the airship lighter. However if you have large water tanks and re-condensation systems aboard an airship, for use in a steam engine, it might give problems with balance or similar.
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« Reply #14 on: March 02, 2012, 07:36:36 pm »

I think that one of the key things about SP, at least for me, is that it is about doing very sophisticated things with essentially simple technology refined to a high level.

Using exotic and unexplained technology can work if it's there for a really good narrative reason, but it does need to be kept carefully circumscribed or you are in danger of drifting away from what gives SP it's special character.

I think that they way steam fits in to this is that it's that blend of fundamentally simple tech, (ie it's just about possible to build a steam engine in a shed) with very sophisticated execution. Similarly airships are such an iconic theme for SP because they are a way to get practical powered flight without having to resort to very modern materials and manufacturing processes. There probably could have been practical airships on a commercial scale in the 19th century if somebody had really wanted to do it. Again, to me SP is much more about tweaking the circumstances to bring about a different route of technological and social evolution than just transplanting radical new technologies or shoehorning in basically modern concepts.

The good thing about using Victorian type tech is that it's perfectly possible for a non-specialist to grasp the underlying concepts with a realistic amount of application and research and from there there is a lot of scope to apply creativity and imagination. A lot of the stuff is there already, it's often a case of finding new applications for it with the benefit of hindsight.

From this perspective a  steam powered airship actually fits into this very well since it's just about possible but also a big challenge so it takes a bit of thought and research, however this means that whatever you come up with is likely to be original and interesting. This could almost be seen as the opposite to sticking gears on a laptop.

The other really interesting thing is that this also opens up even more strands to investigate and interesting questions to answer...

Who would be motivated to design a commercial airship in 1850 and why ?
What would the social, economic, political and cultural implications ?
What circumstances would need to exist for it to succeed ?
What new technologies and industries might be created as a result ?

I think it's these sorts of inquiries which are at the real heart of SP and the great thing is that anybody can ask these questions, they aren't trivial by any means but the starting points are accessible to anyone with an inquiring mind and tehse sorts of puzzles are often the best way to learn new things.
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oldskoolpunk
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« Reply #15 on: March 02, 2012, 08:35:08 pm »

There was supposedly a successful steam powered aircraft in the 1930s. There's a
film
. The claimed power plant was conventional - an oil burner, flash boiler, reciprocating engine, and condenser. It should have worked.

I'm a bit suspicious of the film. There's lots of coverage of the plane on the ground and taxiing. The film of the takeoff then cuts off during the takeoff run, just before the plane should be lifting off.  Then we briefly see a vague, distant plane for a few seconds. Then we see a landing of a distant plane. Then we see the steam plane taxiing up to the camera. No shot both shows what's clearly the steam plane in flight. Other than this demo, it's not clear that it ever flew again. My guess is that the thing had weight problems and could barely fly, if it could fly at all.

A steam powered airship might have some advantages.  Modern airships, like the Zeppelin NT and the
Lockheed P791
have multiple steerable props. This provides much better stability and control than the early airships achieved. The P791 is especially impressive, landing on a runway and taxiing to the hangar under its own power. With one boiler and multiple reversible steam engines, that level of control might be achieved with steam.

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Tower
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« Reply #16 on: March 04, 2012, 06:14:24 am »

So far I've figured out that the Hindenburg (my example airship since its the easiest to find data on) had a total of 4,800 hp between four engines and the dry weight of those engines was about 17,000 lbs. (combined)

So far I've had a hard time finding specs for steam engines that include both weight and horsepower but most locomotives  seem to weigh around 250,000 lbs and have 4-6 thousand horsepower. And of course, a large amount of that weight  would not be the engine itself but wheels and carriage components that you would not need for a airship.  I found some modern V twin steam engines that produce 20 HP and weigh only 150lbs each. If you used 240 of them (somehow) you would have 4,800 HP at a weight of only 36,000 lbs. (excluding boiler of course.)

The gross lifting capacity of the Hindenburg envelope was 476,000 lbs so it seems feasible so far,

As to the problem the the weight of a condenser I've found some speculation on the net that the gasbag itself could be used as a condenser because of its sealed nature and enormous surface area.
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« Reply #17 on: March 04, 2012, 06:33:20 am »

Very slightly off topic in a way but it might help answer the question of why one would want a steam-powered airship...

I had a dream several months ago in which we dealt with the zombie apocalypse by living, several of us, aboard a very large steam-powered airship.

It was slow and wallowed and couldn't go much faster than a horse could trot, but-- and this is the key bit-- it was secure from zombies and only needed wood and water to fuel it.

Water we hauled up from lakes in buckets, and when we needed more wood we'd send down several men with axes on ropes. The ropes were attached to harnesses and not removed; if a threat presented itself we simply lifted them back up to safety.

We travelled for months this way (no idea what we did for food though) and eventually made it to Vancouver Island, where the zombies couldn't reach. Had problems keeping non-crew off the ship once we got there, though.

But it strikes me that something that could travel vast distances (even if slowly) and refuel off the land would be very useful in the case of some kind of disaster, or for exploration.
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« Reply #18 on: March 04, 2012, 08:57:33 am »

In terms of real world history small marine steam engines like the ones found in small motor launches would probably be a good place to start. Since they're generally fairly compact and easy to maintain. They were around for quite a while too and so reached quite a high level of development.

One complication in specifying and comparing steam engines with other types is that they are often specified in terms of boiler horsepower which is a completely different unit to mechanical horsepower used when referring to IC engines and electric motors and it's not always clear which unit is being used.

The best bet is to specify everything in kW and other SI units to eliminate any ambiguity. 


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Tower
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« Reply #19 on: March 04, 2012, 09:19:41 am »

Quote
But it strikes me that something that could travel vast distances (even if slowly) and refuel off the land would be very useful in the case of some kind of disaster, or for exploration.

Sustainability is the most fundamental appeal of steam power. Its a machine that can live off the land.


Quote
The best bet is to specify everything in kW and other SI units to eliminate any ambiguity. 

Your right of course but during the age of steam few engines where measured that way so its hard to find data in SI. I can convert but that does nothing the help the problem if the original data is in BHP (which it often is)
« Last Edit: March 04, 2012, 09:36:02 am by Tower » Logged
Matthias Gladstone
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« Reply #20 on: March 04, 2012, 11:11:59 am »

I think another minor problem is that of the gearbox - reciprocating engines have quite a low rpm, so you'd need to gear up to power an airscrew. The weights listed for steam trains etc don't include that gearbox, and it'd need to be quite hefty to deal with that power, so it may be worth finding the weight of a comparable marine gearbox as well.
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SPBrewer
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« Reply #21 on: March 04, 2012, 11:42:57 am »

   Are we talking about an Airship constructed today?  Or, and airship constructed in Victorian days?
I seems that many are thinking of steel engines and boilers from locomotives.
   I would imagine if constructed today, the engines and boilers would be made of Titanium.  Heat from the boilers could be routed to the bags for hot air lift.  The cold outside air would help in condensing the water exhausted from the engine(s), so that it is recycled.
Just kicking around some ideas.

Also, Wikipedia seems to support the 1933 flight of the Besler airplane.
And, it lists:

1852: Henri Giffard flies a 3 horsepower (2 kW) steam-powered dirigible over Paris; it was the first powered aircraft.

See:
http://en.wikipedia.org/wiki/Steam_aircraft

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« Reply #22 on: March 04, 2012, 11:53:01 am »

The gearing issue is mitigated by the fact that propellers or steam piston engines don't need variable ratio transmission, which is where most of the weight and complexity of an automotive gearbox comes from.

The proper drive ratio could very likely be designed into the transmission without much extra weight or complexity.

In fact there's no fundamental reason why steam engines should have to run at low rpm, it's just that a lot of the applications they were designed for required a low speed high torque power source. Bear in mind that the Stanley steam cars were direct drive and one held the land speed record for several years in the 1900s. Nor do propellers necessarily require very high rpm, in fact if anything you would want to gear an IC engine down to use with an aircraft propeller.  The limiting factor of the speed and diameter of a thrust propeller is usually the onset of shock-waves as the tips approach the speed of sound, the rotational speed at which this occurs obviously depends directly on the diameter of the propeller.
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Matthias Gladstone
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« Reply #23 on: March 04, 2012, 12:24:12 pm »

That's true, you do have the advantage of size. I guess it depends on the level of "authenticity" you're trying to achieve - I definately think you'd be wanting to increase rpm for most reciprocating Victorian engines (which from memory operate  from around ~30 to ~120 rpm, depending on era, ship and application), but reducing it for most turbines (~3000-6000 rpm).  But I agree, with modern materials, you could tailor the engine to the correct rpm, or change the propeller pitch and diameter to match, although perhaps at the expense of efficiency.

As an aside:
For Graf Zeppelin:
Cruising speed = 75 mph
RPM (it's not stated whether it's engine or prop; assume direct drive) = 1508

« Last Edit: March 04, 2012, 12:38:57 pm by Matthias Gladstone » Logged
Tower
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« Reply #24 on: March 04, 2012, 12:45:12 pm »

It shouldn't be hard to gear a steam engine to run propellers. Most IC aircraft engines use no gearing at all and the propeller is mounted directly to the driveshaft.

One problem would be with steam transmission. Assuming you have one central boiler and several steam engines you would have fairly long pipes carrying steam out to your nacelles. Remembering that steam engines are in truth HEAT engines and that is a lot potentially lost power do to radiative cooling of both the engine and the steam lines. You would need both to be wrapped insulation.


Here is another interesting idea. Are we sure that a propeller is the best way to use steam power for propulsion in the air? What about venting the steam directly through nozzles? In theory you should have better efficiency this way...of course you would use up water at a prodigious rate. Maybe you could condense it out of the air somehow.
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