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I'm looking for an answer concerning a steam powered airship. The steam is generated via coal burning. The ship is propelled by an X amount of steam engine propellers (think Besler steam plane). The craft would have to have a coal reserve and an X amount of water tanks which would make for a good amount of weight. Would the ship be able to get off the ground, and if so, would it be able to fly at a useful speed?

The picture below is a pretty good representation of the type of craft I had in mind. However, take into account that the one in the photo has no visible propellers or coal and water reserves. enter image description here

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    $\begingroup$ Does this need to be on Earth? A denser atmosphere would help a lot... $\endgroup$ – Matej Lieskovsky Jan 11 '17 at 1:22
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    $\begingroup$ Are you willing to give up steam to retain coal powered aspect? It seems that coal powered or sawdust powered turbines might be possible... Gas turbines have much higher power-to-weight (PWR) than steam engines, dust powered ones will lose some PWR but not so much as to become impossible. Also, gas/dust turbine will use air as working fluid, eliminating need for weighty water tanks (in case of steam locomotives water weights much more than coal). So... how about blimp with coal powered turbofan engines? That might actually be possible. $\endgroup$ – M i ech Jan 11 '17 at 1:30
  • $\begingroup$ This is not on earth but rather a fantasy world. However, I do not want to deviate the planet makeup to drastically, it is identical to earth in terms of weather and atmosphere. $\endgroup$ – Ezra P. Jan 11 '17 at 1:30
  • $\begingroup$ I did mention the use of gear powered propellers to provide thrust. I probably should have put that here instead of as an answer, rookie mistake. $\endgroup$ – Ezra P. Jan 11 '17 at 1:31
  • $\begingroup$ It is funny that the ship depicted has a fin on the bottom. $\endgroup$ – Willk Jan 11 '17 at 15:13

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You could theoretically make a steam-powered airship, but it wouldn't be worth the hassle. Moreover, by the time that we had the technology to make the airship frame itself we already had very good diesel engines.

  • The efficiency of a plain old non-compound Watt-type reciprocating steam engine is about 2.5%. For an airship you want a condensing engine, because you absolutely want to minimise water loss. Water is heavy.

  • Stephenson's Rocket locomotive of 1829 weighed 4300 kg (complete with water in the boiler). You need at least two engines, unless you plan to have some fantastically complicated transmission chains. Let's say that with a little better engineering you can reduce the weight to 3 tons per engine.

  • The first commercially sort-of successful airship, the Zeppelin LZ10, was 140 meters long, had 17800 cubic meters of hydrogen and could carry 13 crew and 20 passengers; it was powered by 3 engines of 100 kW each, with a maximum speed of 77 km/h.

  • Say that your airship will use 2 light-Rocket style engines, souped up to give 100 kW each, and you want to have enough fuel for 5 hours; suppose that you burn some kind of coke or anthracite giving 30 MJ/kg. The two engines will weigh 6 tons, and you need to carry about 5 tons of fuel. You need 12 tons of lift only for the engines, water and fuel!

  • 12 tons of lift require 12000 cubic meters of hydrogen. The ship structure will also require lifting, plus any passengers. Overall, your ship needs to be much bigger than LZ10; say, 180 meters long, 34000 cubic meters of hydrogen.

And from here comes the fundamental problem: what material are you going to use for the ship structure? The airship cannot be a blimp, because if needs to lift those heavy engines, water and coal: it needs a rigid structure. The structure cannot be made of iron — too heavy. Cannot be made of wood — too weak. You need aluminum. But if you have aluminum, why are you playing around with steam engines?

The second big problem of using inefficient steam engines in an airship is the loss of weight. Every ton of coal you take on board at take off and burn requires that you vent 1000 cubic meters of hydrogen in order to remain in equilibrium with the displaced air — airships are aerostats. When you land, you need to refill the gas cells, otherwise you won't be able to take off again.

The third problem is the nature of steam engines, which burn their fuel in the open, which is a big huge enormous hazard for a hydrogen-filled airship. (Cannot be filled with helium, for reason of the need to vent lifting gas to compensate for the stupendous loss of weight given by burning coal with a very low energetic efficiency.) Real life zeppelins used diesel engines, because they don't need sparks...

P.S. The picture in the question is fundamentally wrong, in that the gondola is way too big. Look for example at LZ120 (better pictures at airships.net) for a clear view of the relationship between the body filled with lifting gas and the gondola.

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  • $\begingroup$ The picture is obviously not a truly accurate representation but rather just starting point. I am aware that gondolas on real world airships are much much smaller, but that doesn't make for a good story. What I am getting at is how to portray a fictional airship as accurately as possible while still maintaining the fantastic idea of a flying boat. I suppose creative license will have to do. $\endgroup$ – Ezra P. Jan 11 '17 at 1:56
  • $\begingroup$ Why do you need two engines? Are you implying that you need two propellers? $\endgroup$ – kingledion Jan 13 '17 at 0:46
  • $\begingroup$ @kingledion: You need at least two propellers, which must be able to turn at different speeds. Real airships had four, six or more. Airships are very large, and you need multiple propellers to control their heading/position/attitude. $\endgroup$ – AlexP Jan 13 '17 at 2:40
  • $\begingroup$ @AlexP FFG-7 Frigates manage with a single shaft and a large rudder. Sailing ships made due without any propellers. A giant airship is half sailboat anyway with its enormous surface area to mass ratio. I still don't understand the need for multiple propellers. $\endgroup$ – kingledion Jan 13 '17 at 4:50
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    $\begingroup$ @ZioByte, it's very necessary. You can't recover the carbon dioxide produced by burning coal. Balancing the weight loss from burning fuel was a constant struggle for airships. The Graf Zeppelin did it by burning "blau gas", a neutrally-buoyant hydrocarbon mixture (about a third of the ship's envelope was used to store fuel). The Hindenburg used diesel fuel and had condensers on the exhaust pipes to recover the water vapor in the exhaust, and a system of gutters that would let it turn rain into ballast. Other airships had other systems, or just accepted the gas loss. $\endgroup$ – Mark Jan 12 at 22:12
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Since we have Steam engines, you might sidestep the problem with the complimentary technology of Stirling Engines. Rev Stirling developed the engine because of the safety issues of contemporary steam engines (especially boiler explosions and steam leaks), and inadvertently also developed perhaps the most efficient heat engine possible (Stirling Engines can operate at close to the Carnot Limit).

enter image description here

Simple Stirling Engine. Plans here

A Stirling engined airship would not have a boiler, water, condensers or much of the other paraphernalia associated with steam engines, making the airship much lighter and also making trim changes due to the consumption of fuel and water much easier (no water is being used and the amount of coal fuel needed can also be reduced). While contemporary Stirling engines had low power to weight ratios compared to steam engines, modern Stirling engines can have comparatively high power to weight ratios. If there is a strong demand for this type of engine in your world, it can be easily assumed the engineering community would have worked hard to discover ways to make Stirling engines lighter and have higher power outputs.

The only real issue would be to develop some sort of "firebox" or combustion chamber which can provide heat to the engine without endangering the rest of the ship.

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If you had a fantasy steampunk world where the air pressure is comparable to what it is on the planet Venus (90 atmospheres) but breathable like Earth then such a vehicle might be possible. However you'd have to ignore all of the other negative effects that such high pressure would cause. Or maybe a thicker atmosphere combined with lighter gravity. The only other approach would be some steampunk fantasy material like Cavorite (H.G. Wells First men in the Moon) or Liftwood (RPG game Space 1889). Otherwise such a vehicle is not possible. Too little attention to weight reduction and not enough gas volume. Oh by the way the Besler aeroplane used a coil-tube flash boiler that burned oil producing steam at 1130 psi and 430° C. It could NOT run on coal.

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  • $\begingroup$ Also check Windforge. It was a game with a lot of potential, a pity the dev's abandoned it. $\endgroup$ – Renan Mar 28 '18 at 14:03
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Given you've front ended the tags with magic I'm going to go that road; you build a closed cycle steam engine using material reinforcement spells so it's basically made of foil, a locomotive engine we based on the Flying Scotsman built this way weighed about 20 kilograms (we made ours using a couple of other permanent spells; a heater that kept the "combustion" chamber white hot and a cooling spell that kept the condenser ice rimed, to make it into a perpetual motion device). You use further material reinforcements to built vacuum cells instead of using lifting gas and armourplate the shit out of the whole thing because you've got to overcome all that excess buoyancy somehow. Speed is limited only by story.

Depending how far you want to go you can use any configuration and materials you like really because "a wizard did it" so you can mess with the standard densities etc... or you can create materials that don't exist that make the whole exercise realistic; have a look at The Edge Chronicles by Paul Stewart and Chris Riddell, Wiki here, where lighter-than-air wood and stone both feature as methods to facilitate skyship building.

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  • $\begingroup$ This was part of what I was thinking. A stirling engine. $\endgroup$ – Jammin4CO Aug 14 '17 at 17:26
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    $\begingroup$ @Jammin4CO Yup a Stirling Engine is a thermal engine, just like a steam engine, except it uses air as a working fluid instead of steam. In fact the Stirling engine has been described as the idea of a thermal engine made manifest, since it's the simplest of all thermal engines. $\endgroup$ – Ash Aug 14 '17 at 17:40
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Ridiculous, huh? Check out Wikipedia Henri Giffard. I don't disagree, but the problem is the exhaust, imho. Your pictures seem to neglect the enormous problem of smoke, soot, embers, and sparks. Take a look at any photo of a steam powered coal fueled locomotive to "get real" here. Some reason the steam couldn't run a turbine with very small (negligible) losses? Even a very 'clean' combustion machine - like modern internal combustion engines, can 'back-fire' and start fires. But, seems to me that coal power isn't out of the question, with proper exhaust (and exhaust pre-processing).

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  • $\begingroup$ I really didn't think of the exhaust at all, good point. What I've learned from the answers so far is that a coal/steam powered airship would have to look much different than the one I have in mind (which is mostly wooden). $\endgroup$ – Ezra P. Jan 11 '17 at 1:15
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One alternative to steam could be the use of gears via manual labor. For example, 16th century galley ships relied on rowing as a primary means of propulsion. They achieved this via men (often hundreds) rowing large oars below deck. What if, instead of oars, the men cranked gears. The gears would in turn power propellers that would propel it forward.

This would solve the problem of burning coal on a wooden craft and would eliminate soot, steam and smoke.

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    $\begingroup$ Humans are horrible as engines. A well-nourished well-trained male human weighs 80 kg and can sustain maybe 100W of mechanical output over a few hours. You need 8 such humans for one measly horse-power -- 1 ton of humans gives you 1.25 kW (1.7 HP). Steam engines are inefficient as hell and have an abysmal weigt-to-power ratio but they are still hundreds of times better than humans. $\endgroup$ – AlexP Jan 11 '17 at 1:59
  • $\begingroup$ AlexP, duh. I don't envision a bunch of dudes peddling their feet and spinning a propeller. Think of a 10 speed bicycle. You crank that maybe up to the highest setting and it's tough to pedal, but once you get going on smooth and level ground, you pick up a lot of speed but only have to put in minimal effort to maintain it. $\endgroup$ – Ezra P. Jan 11 '17 at 2:15
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    $\begingroup$ You need to spin the propeller continuously if you want your airship to move continuously, just as the rowers needed to row continuously to propel the galley. Moreover, air resistance increases in proportion with the cross-sectional area (which is huge in the case of an airship) and the square of the speed. To get an idea of how bad humans are as engines, consider the tiny original Mini, which used a 25 kW engine for a top speed of 116 km/h. To produce 25 kW continuosly for several hours you would need 250 humans, weighing 20 tons. $\endgroup$ – AlexP Jan 11 '17 at 2:26
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Lets do some math

To create 1 kilowatt hour of energy, it takes about 95 Liters of water in a steam turbine. Now these things are about 1 ton each let's say.

Now a typical jet engine (can be used on an air ship) uses about 5 megawatts of energy. 1 Megawatt is 1000 kilowatts. So for this jet engine to power your airship you will need 5,000 kilowatts of energy. Now multiply that by 95.

You would need 475,000 liters of water for a 1 hour flight. This is carrying about 220 tons.

1 liter of water is 2.20 pounds.

You will carry about 1,045,000 pounds of water. Which is about 500 tons. This is a lot more than what your airship can carry.. This is excluding the amount of coal you will be carrying. You will also need multiple steam engines to process enough water into steam. If this airship does fly, it will be quite slow.... An attack on this airship would be way too easy by the other nations.

PS. Please correct me on any mistake in MATHS

EDIT

As Li Zhi has said these steam engines arn't always 100% efficient, actually they usually are not.

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  • $\begingroup$ Thanks for your answer. So a different power would be advisable. I always thought that steam engines on a large flying craft was ridiculous, which is why I asked this question. Do you have any alternative recommendations, or would scrapping airships as a story theme be a better idea? $\endgroup$ – Ezra P. Jan 11 '17 at 0:57
  • $\begingroup$ Airships as a story theme are a fine idea, just thinking of a proper way to power them is difficult. Now you could make the airship resemble a blimp to create the lift off the ground using helium/hydrogen/hot air. Then theres the problem in steering, however here you may be able to incorporate a steam powered turbine that will take a lot less water because most of the lifting is done by the air in the blimp. $\endgroup$ – abc1234 Jan 11 '17 at 1:04
  • $\begingroup$ Out of curiosity, where does the OP mention a steam turbine? or was that edited out? $\endgroup$ – WhatRoughBeast Jan 11 '17 at 1:33
  • $\begingroup$ Well she said steam powered airship, so a steam turbines would be a plausible comparison $\endgroup$ – abc1234 Jan 11 '17 at 1:42
  • $\begingroup$ I don’t follow your logic that since a single modern jet engine is 5 MW then an airship needs that much. How much power did real airships like the Hindenburg use? $\endgroup$ – JDługosz Jan 11 '17 at 7:30
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According to Wikipedia Henri Giffard flew a steam powered airship in 1852.

The Giffard dirigible or Giffard airship was an airship built in France in 1852 by Henri Giffard, the first powered and steerable (French: dirigeable - "directable") airship to fly. The craft featured an elongated hydrogen-filled envelope that tapered to a point at each end. From this was suspended a long beam with a triangular, sail-like rudder at its aft end, and beneath the beam a platform for the pilot and steam engine. Due to the highly flammable nature of the lift gas, special precautions were taken to minimise the potential for the envelope to be ignited by the engine beneath it. The engine's exhaust was diverted downwards to a long pipe projecting below the platform, and the area surrounding the boiler's stoke hole was surrounded by wire gauze. On 24 September 1852, Giffard flew the airship from the hippodrome at Place de l'Etoile to Élancourt, covering the 27 km (17 mi) in around 3 hours, demonstrating maneuvering along the way. The engine, however, was not sufficiently powerful to allow Giffard to fly against the wind to make a return journey.

https://en.wikipedia.org/wiki/Giffard_dirigible1

Obviously more advanced steam engines could have been used in later dirigibles if more efficient internal combustion engines had not become available.

Would steam turbines have had a better power/eight ratio?

Would using oil or kerosene as fuel for a steam engine have been more efficient?

How far could steam engines for airships be developed? Could they have competed with airplanes as well as airships with internal combustion engines did?

How could they avoid being replaced by airplanes?

If anyone has good answers to those questions you might be able to have reasonably plausible sort of steam powerered airships.

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  • $\begingroup$ Your answer seems to be half of a question itself. Are you sure you dont want to ask a new question instead..? $\endgroup$ – dot_Sp0T Jun 3 '17 at 7:33
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When looking a your picture, and thinking about history, all you would need is the technology to store compressed hydrogen. Use it both to replenish the envelope for elevation changes and also to burn for fuel, perhaps in a stirling engine like @Thucydides suggested. You would use the cold compressed hydrogen on one side and the burning hydrogen on the other.

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It would all depend of the level of technology your world has and how wedded you are to the idea of lifting a wooden ship complete with a hole in the side and useless bowsprit along with all the other heavy junk a sea ship needs to weigh it down so winds don't make it capsize. If so I'd consider making it out of Martian liftwood (Space 1889) with a varnish of H. G. Welles Cavorite (First Men In The Moon). Weight vs Buoyancy is the primary issue. However lets assume that your civilization has advanced material science but just never got around to developing internal combustion engines (piston or jet) or lightweight electric motors and fuel cells. The reasons I'll leave up to you. In that case it is definitely possible. Consider the Magesterium airship seen in the movie The Golden Compass. Discard the fantasy 'anbaric' thrusters and the oversized tail fin and you have a basic dirigible/blimp with one important addition. The gas bag filled with lift gas (helium or hydrogen) has a secondary chamber surrounding the front end. See the picture. enter image description here I would suggest that a secondary liftgas fills this chamber. One that can be adjusted in buoyancy, isn't flammable, and doesn't need the heavy complication of high pressure cylinders and compressors. That liftgas would be steam. Steam has over twice the lifting power of hot air and you will have plenty of it in the engine exhaust. Modern day polyester mylar, teflon and a new recent flexible aerogel would make a lightweight and durable laminate balloon material with good thermal retention properties. As steam condensed it would drain down to a reservoir for return to the boiler. This will eliminate the need for a separate condenser further lightening your airship. A closed steam cycle would also reduce the amount of heavy water you would have to carry. If you have access to lightweight low voltage high amperage DC generators you could carry a small one to make fresh hydrogen from your water supply in an emergency. A win-win design. Since you are insisting on coal as a fuel I would suggest a fluidized bed combuster with bed of a lightweight refractory sand, possibly alumina. Over it would be a flash boiler similar to that used in the 1910 White Steam Car. The steam engine would be a smaller simpler version of the radial steam turbine used in the 1894 Turbinia steamship. Of course everything would be constructed of lightweight polymers, and aluminum and magnesium alloys. Heavier metals would be used only where absolutely necessary and kept to a minimum. Aerogel would be used for insulation where possible. If you designed it properly I think you could get a pretty respectable performance out of a vehicle like that.

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