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Author Topic: Is a steam powered airship physically impossible?  (Read 15267 times)
Matthias Gladstone
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« Reply #25 on: March 04, 2012, 12:56:52 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.


That's exactly the point; steam engines aren't ICEs. In my opinion, to use an engine roughly of victorian design, you'd have to use a gearbox as the rpm values are too high or low for direct drive. I don't think it's fatal problem, but the gearbox would mean additional weight. You could still run the propeller using direct drive, by playing around with the pitch and diameter, but I think you'd suffer fairly harsh penalties in terms of efficiency.
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Dr. Madd
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« Reply #26 on: March 04, 2012, 01:34:01 pm »

Given modern materials, better gearage, I'd say a resounding yes.
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« Reply #27 on: March 04, 2012, 02:01:58 pm »

Actually larger diameter propellers are, in principal, more efficient than smaller diameter ones, especially bearing in mind that high speeds aren't really the objective with airships.

The Stanley steam engine operated at about 450rpm at 30mph and gearing this up by a factor of two or three could be accomplished by the drive train that you would need anyway with insignificant additional weight. Also high rpm engines don't necessarily require exotic materials, most IC engines are constructed almost entirely from cast iron and steel. You would want better manufacturing tolerances then were the norm in the mid 19th century but that's not that difficult to do if you have the incentive, in fact machining tolerances made quantum leaps almost overnight at several points to keep pace with innovations in firearms design.  

There is also the fact that the relatively flat torque curve of a steam engine means that the complexity of variable pitch propellers can be dispensed with without sacrificing efficiency.

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Matthias Gladstone
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« Reply #28 on: March 04, 2012, 02:41:20 pm »

That's not really the point I was making, which was that if you took a contemporary victorian engine you'd need to gear it, and that gearbox would incur a weight penalty (however small). With marine propellers (and I assume it's the same for aircraft), it's usually a case of balancing torque, rpm, thrust, pitch and advance ratio until an optimum is found.
However, I found an empirical formula relating rpm, shaft power and diameter (again for a marine prop):

D = (632.7*SHP^0.2)/RPM^0.6

Although the various coefficients are unlikely to hold true when transitioning from a marine to aircaft prop, and I don't know for what efficiency or pitch such a propeller would run at, I think it proves you right in that controlling diameter could be used instead of controlling rpm and diameter for an airship prop.
« Last Edit: March 04, 2012, 02:43:01 pm by Matthias Gladstone » Logged
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« Reply #29 on: March 04, 2012, 02:44:26 pm »

Depends what you mean by Victorian engine - the Steam Turbine was invented in 1884 and steam turbines like to run fast - 3000rpm plus is common.
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Matthias Gladstone
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« Reply #30 on: March 04, 2012, 02:55:17 pm »

I already mentioned steam turbines and associated rpm's.
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« Reply #31 on: March 04, 2012, 03:02:57 pm »

I already mentioned steam turbines and associated rpm's.

So you did  Wink.

The reduction required for a steam turbine, then - assuming a target of 1500rpm - would be between 2-1 and 4-1. A fairly sensible arrangement would have the turbines mounted crossways roughly on the centreline, with a simple gearbox at the tip of the propeller spar - this would only need to be a couple of bevel gears.

I'm not saying that a steam turbine based system would be better than a diesel system, just that it is possible. I don't think marine engines are necessarily a good comparison - just look at the differences between a marine internal combustion engine and an aviation one.
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Matthias Gladstone
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« Reply #32 on: March 04, 2012, 03:09:07 pm »

True, but they seem a good place to start as there aren't many aviation steam engines available for comparison - i'd argue that if you were starting from scratch in the late 19th, you'd start with a marine engine, as they're self contained systems.
Also, it depends on the IC engine - gas turbines used in marine applications often are modified versions of aircraft engines, and the smaller diesels are similar in design. Of course, the large two stroke low and medium speed engines have much less in common!
-Matt
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« Reply #33 on: March 04, 2012, 03:37:56 pm »

The major issue, however, is not so much the specific design of the steam engine as the boiler and all the associated gubbins needed to achieve reasonable efficiency.

While anything is probably possible I think there is certainly a point where the underlying qualities which make steam power relevant to steampunk are far over the horizon.

I think there is a strong argument that a 1940s IC engine is a lot closer to the ethos of SP than a fully automated computer controlled steam turbine.

Of course stretching the technology with the benefit of hindsight is very much a part of the whole point of the exercise so we don't need to limit ourselves to things which actually existed in the 19th century but rather ask ourselves how credible it is that they could have existed.

I suspect that the practicality of a steam airship depends a lot on how big you can make the airship. Another important factor in this is how far the advantages in self sufficiency make up for any potential disadvantages in weight and performance compared to other solutions.

When considering self sufficiency water is perhaps the biggest issue, while it is possible to use any old lake or river water in a simple  steam engine there is a price to pay in terms of increased maintenance and problems with things like super heating and condensers which are a big part of achieving good efficiency.
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« Reply #34 on: March 04, 2012, 10:14:32 pm »


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.


Run the hot steam lines thru the envelope of the airship.  The heat leaked out will keep the envelope hot and producing lift.  Wink
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Matthias Gladstone
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« Reply #35 on: March 04, 2012, 10:40:23 pm »

Or perhaps a steam-electric drive?
You could even take this one step further and have a tesla tower broadcasting the power to the vessel. Or have it on a long cable like a giant bumper car.
« Last Edit: March 04, 2012, 10:42:33 pm by Matthias Gladstone » Logged
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« Reply #36 on: March 04, 2012, 10:51:59 pm »


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.


Run the hot steam lines thru the envelope of the airship.  The heat leaked out will keep the envelope hot and producing lift.  Wink


Alternatively, use driveshafts to transfer power from the main body to propeller nacelles.
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« Reply #37 on: March 05, 2012, 02:56:53 am »

I like the steam electric idea. You would only need one transmission and your engine could run at one constant speed.

Hmmm, you would need some batteries or a large capacitor bank though...
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« Reply #38 on: March 05, 2012, 07:00:28 am »

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.

Actually, the vast bulk of a locomotive's weight is the boiler and the water it contains, without which a steam engine is nothing but ballast. On the other hand, railway locos use fire-tube boilers because of their much greater reserve steam capacity for hills and so forth; a dirigible should be able to do with a much more compact water-tube (ie. "flash") boiler.

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)

I believe railway steam locos were generally rated by drawbar HP, which isn't the same as BHP but should be close enough for Government work.

I like the steam electric idea. You would only need one transmission and your engine could run at one constant speed.

Hmmm, you would need some batteries or a large capacitor bank though...

I like this idea too. You could run the generator from a steam turbine, which would be smaller, lighter and more efficient than a reciprocating steam engine. You wouldn't need batteries (neither locomotives nor diesel-electric ships use them); you would just need the switch gear to control the speeds of the motors.
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« Reply #39 on: March 05, 2012, 07:17:48 am »

I like the steam electric idea. You would only need one transmission and your engine could run at one constant speed.

Hmmm, you would need some batteries or a large capacitor bank though...

I like this idea too. You could run the generator from a steam turbine, which would be smaller, lighter and more efficient than a reciprocating steam engine. You wouldn't need batteries (neither locomotives nor diesel-electric ships use them); you would just need the switch gear to control the speeds of the motors.

Go Electric and skip the Steam, like they did on the Caspartine.  Just capture some lightning every now and then.  Smiley
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« Reply #40 on: May 06, 2012, 06:08:37 pm »

I've been doing Internet research into this topic and the consensus of those most credible sources seems to be that such a feat is a challenge, but doable.

The thermodynamics claim that this impossible is flatly false. However all of those doing work in building airships have preferred hot air ships to steam for good reasons. I'll try to put together a list of links to what I've found so far, but the issue is simple: why add weight to an airship in the form of water?

Likewise using the Hindenburg as a basis for load bearing estimations is also flawed in that steam does not have the same static lifting capacity of hydrogen or helium and the only reason steam would be chosen over these is because they are too expensive as steam has only 2/3rd the lifting capacity of H or He.

So then what is left? The question of why actual airship manufacturers today still do not choose steam over other means? The answer I believe is that hot air is cheaper, easier and there are other methods of powered control than a bulky engine.

That said, if a light weight, low powered steam prop could be built then the 2x boost in lifting power might make steam an attractive option.  So far all my attempts to finding a successful method of circumvent the weight of a boiler and gearbox have yet to be fruitful.

However impossible is definitely not the question, practical ... Ergo a fundamental of sp tech is at the heart of the question.

Given this I'm tempted to split the difference and offer another alternative. What about a much smaller, lighter stem device that generates power and as a byproduct of its exhaust offers a boost to strictly hot air by venting exhaust into the envelope. The small amount of electricity produced could be used for a low/1 speed direction prop motor. Maneuverability would be abysmal, but at least weight wouldn't cripple take off and the designers can work within the known limits and design factors of already successful vehicles of familiar technology.
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« Reply #41 on: May 06, 2012, 06:17:32 pm »

I believe the original question was about using steam for propulsion, not as the lifting gas.
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« Reply #42 on: May 08, 2012, 10:14:18 pm »




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.


Ohh I wish I had dreams like that. Sad

Sounds like a pump and hose system would work quite well for refilling the water tanks. Just do a low pass over a lake and suck up as much as you need.
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« Reply #43 on: May 09, 2012, 04:14:12 am »

I believe the original question was about using steam for propulsion, not as the lifting gas.

Using Steam for propulsion only is then a much easier task since the designer must only concern themselves with an engine capable of producing adequate heat for the hot air lift and adequate thrust to overcome the baloons suspended inertia and weather conditions to allow directional control of the baloon. That being the case thruster designs could be quite modern indeed and provide significantly greater thrust with some tweaking than otherwise might be expected from a propeller or motor driven system alone. Why worry about gearboxes and weighty transmissions. Surely there is a screw or turbine system that can maximize a small amout of power over a long wind up period to generate a potent thrust.

I'd be more worried about noise cancellation then. LOL
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Matthias Gladstone
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« Reply #44 on: May 09, 2012, 11:36:12 am »

I believe the original question was about using steam for propulsion, not as the lifting gas.

Using Steam for propulsion only is then a much easier task since the designer must only concern themselves with an engine capable of producing adequate heat for the hot air lift and adequate thrust to overcome the baloons suspended inertia and weather conditions to allow directional control of the baloon. That being the case thruster designs could be quite modern indeed and provide significantly greater thrust with some tweaking than otherwise might be expected from a propeller or motor driven system alone. Why worry about gearboxes and weighty transmissions. Surely there is a screw or turbine system that can maximize a small amout of power over a long wind up period to generate a potent thrust.

I'd be more worried about noise cancellation then. LOL

I think the point is that a gas buoyant at standard temperature and pressure (i.e helium or hydrogen) provides the lift, while thrust is provided by a steam engine - the general question is as to whether a steam engine can have a power to weight ratio high enough to make a possible, then practical, airship. Also, the problem with any sort of body moving through a fluid isn't so much accelerating it in the first place as overcoming the resistance force from pressure, viscous resistance etc while in flight.
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« Reply #45 on: May 12, 2012, 02:05:15 am »

Here is a link to some actual math done on the steampunk empire by a friend of mine.  Check the math if you will but he's figured out how you could actually make something that would work.  Of course it would be nothing like the monster airships in the fantasy realm but it would lift 2 adults and a full payload.  Steering and wind conditions would of course matter greatly!

http://www.thesteampunkempire.com/group/l-e-a-d/forum/topics/medium-sized-airship
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« Reply #46 on: July 20, 2017, 05:52:17 pm »

One was actually built and flown as early as 1852! It wasn't very practical though.

https://en.wikipedia.org/wiki/Giffard_dirigible
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« Reply #47 on: July 21, 2017, 06:31:09 am »

One was actually built and flown as early as 1852! It wasn't very practical though.

https://en.wikipedia.org/wiki/Giffard_dirigible


The Giffard dirigible. 3HP steam engine. 250 pound engine, 100 pound boiler. 350 pounds for the power output of a small lawnmower engine.

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« Reply #48 on: July 21, 2017, 04:00:00 pm »

The Gifford ship flew, but it couldn't cope with headwinds.
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« Reply #49 on: July 29, 2017, 11:28:50 pm »

Solar Moth - Solar Thermal Rocket (Atomic Rockets)

If you had a stratospheric airship, you could use such a system with water, and potentially reach hypersonic velocities. Granted, it would be a huge airship, and the acceleration wouldn't be what you normally expect from rockets - perhaps 1 m/s^2 at most. On the other hand, it would run on sunlight and water, so it may end up being cheap to operate.

Add in some ablative heat shields and parachute packs for people who are expected to jump out when you reach enemy territory. Her Majesty's Espatiers have landed and have the situation well in hand.
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