Why did passenger airships (zeppelins, etc) take so long to develop?
July 8, 2009 1:51 PM   Subscribe

In search of an aeronautical/science historian who can explain something to a history major with next to no engineering background. I understand that in 1852 Henri Giffard built an airship with a steam powered engine, but it wasn't until gas engines are more commonly used that zeppelins and other larger, more navigable craft were employed. Is the answer that gas is enough more powerful than steam, that smaller, lighter engines could be used? Was something wrong with his propeller design? Or was there a different path that could have been explored with the materials/technology on hand in the mid-nineteenth century that they didn't notice, that in hindsight is clear? Many thanks - no real reason, just terribly curious.
posted by korej to Science & Nature (20 answers total) 2 users marked this as a favorite

I think you actually hit the nail on the head in your question. Steam engines can have plenty of power, but they grow to be very large and typically very heavy. The power-to-weight ratio of an internal combustion engine is a lot better. It's fuel (some form of petroleum) also has a much higher energy density of typical steam engine fuel (coal).
posted by milqman at 1:58 PM on July 8, 2009

An internal combustion engine is more compact and lighter than a steam engine. A steam engine requires an external boiler (hell, you could call a steam engine an "external combustion engine", I suppose). Steam engines are more flexible in terms of fuel; you can burn fuel oil, or coal, or even wood to generate steam.
posted by mr_roboto at 1:59 PM on July 8, 2009

Steam systems take up (generally) more space than a similar hp output IC engine, as milqman says.

Additionally, looking at the Stanley Steamer may give you some hints. They took a notoriously long time to get going, though they were generally more efficient than comparable IC engines.
posted by chiefthe at 1:59 PM on July 8, 2009

I am also not a science historian but I know a little about the Stanley Steamer. One of the other things that was a big deal with steam engines is that they would sometimes explode. Maybe a small-scale problem when you were driving, but a big deal problem if you're flying a big baloon.
posted by jessamyn at 2:04 PM on July 8, 2009

Steam boilers by their nature have to be extremely heavy. They have to be strong enough to contain high pressures, and the water they carry is heavy in its own right. (One cubic meter of water weighs one metric tonne.)
posted by Chocolate Pickle at 2:08 PM on July 8, 2009

A steam engine is not necessarily heavier than a gas engine, but (elaborating on milqman) there are two factors at play, one of which is the major energy density of gas as opposed to coal (which add , and the other (and most important) is that a steam engine needs a constant supply of water to work unless you add a condenser to the rig.
In short: gas engine: gas tank + engine; steam engine: coal stock + water tank + engine + condenser; gas wins.
posted by _dario at 2:10 PM on July 8, 2009

You're pretty much spot on with your question, and Chocolate Pickle adds in the other major factor - steam engines require water as well as fuel, and that stuff is dense.
posted by Nice Guy Mike at 2:12 PM on July 8, 2009

Best answer: It isn't quite so much that "gas" is more powerful than "steam" than that internal combustion engines are more powerful per unit of weight than steam engines.

Think about the way the engines actually work. With steam engines, you use fuel, generally coal at that point in time, to boil water, and the expansion of steam is used to move pistons, giving you work. With internal combustion engines, you're exploding small amounts of fuel, either gasoline or diesel most of the time, and the explosions directly drive your pistons, giving you work. In both cases, you need to carry fuel and the actual engine. But steam engines also require you to carry around a lot of water, which is really heavy.

When your lift is provided entirely by buoyancy, weight is a huge concern. To top it off, gasoline has a much higher heat of combustion than coal does, by a factor of three, as it turns out. As a result, gasoline winds up being a much lighter fuel. Finally, steam engines, at least as they existed in the 19th century, really couldn't generate sufficient work to enable powered flight. Their output/weight ratio is just too low. Still largely is.

But the real reason Giffard probably used a steam engine instead of an internal combustion engine is that the first petroleum refineries were only constructed in the 1850s. A single refinery in Baku, Russia, produced 90% of the world's oil in the 1860s. So gasoline wasn't really being put to much in the way of commercial or industrial use. It was not until the late 19th and early 20th centuries that petroleum products began to replace coal as the dominant fuel source for transportation.
posted by valkyryn at 2:13 PM on July 8, 2009 [2 favorites]

It's power to weight ratio, as others have said above -- one of the problems with finding alternative energy sources is that gasoline has a fantastic energy density. If you look into the history of helicopters, you see a very similar progression; nobody really got anywhere until the internal combustion engine.
posted by Comrade_robot at 2:13 PM on July 8, 2009

In addition to what others have said, I'd like to emphasize the dual-stage nature of steam engines. First you heat water to get steam, which is inefficient, and then use the hot pressurized gas to do work with a piston, which is also inefficient. With petrol/diesel engines, you burn the liquid fuel in the piston in rapid small bursts and use the pressurized gas that results to do work - with only a single stage, it's much more efficient than the two stage steam process, plus the greater energy density of gas to start with. And no need to carry the water, as stated.

In answer to your other part of the question; no, even with current technology, a steam engine still wouldn't be a practical choice for flight, so we won't be seeing it come back for that purpose when we run out of dino-diesel. We still don't have a practical artificial replacement for kerosene for jet engines (which works at high altitude), though we can arguably replace most other uses with alternative technology, or other means of creating hydrocarbons.
posted by ArkhanJG at 2:33 PM on July 8, 2009

Leaving aside nuclear fuels, does not gasoline have the highest energy per unit fo any fuel?
posted by bz at 2:52 PM on July 8, 2009

Gasoline does not have the highest energy unit. Diesel is much higher energy per unit weight, and I think petroleoum(crude oil) has even higher-but good luck dealing with that stuff in a fuel delivery system. Of course crude oil would work pretty good for firing a boiler to use in a steam engine...and the circle is complete.
posted by bartonlong at 2:57 PM on July 8, 2009

It's possible to make closed-loop steam engines but mostly that hasn't been done. It isn't just that water is heavy, in classical steam engines, but that a lot of it is consumed, exhausted as waste steam from the cylinders after the stroke, or deliberately run up the stack in order to pull air into the firebox.

19th century steam locomotives consumed a lot of water, and it had to be replenished regularly, like pretty much at every station when they stopped. In some parts of the old West, that water had to be brought in by special freight trains when there was no reasonable local source.

That cubic meter of water I mentioned wouldn't have lasted all that long in a big steam engine, which routinely carried many tonnes of water when leaving a station.

To make the engine closed loop, so that the steam isn't exhausted, requires more plumbing and it requires some sort of cooling radiator, all of which has to be made of metal and which will weigh a hell of a lot. The main reason they used to exhaust the steam instead of trying to recycle it was because that was the main way they got rid of waste heat. (See the Second Law of Thermodynamics.)
posted by Chocolate Pickle at 2:59 PM on July 8, 2009

Strong, lightweight materials were few and far between back then. If they had the understanding of how to construct such materials, he could have made the thing air-powered; just compress the buoyancy gas into one balloon, and release it into the other (much larger) balloon, turning a prop while it passes through.

unless compressed gas is somehow less bouyant; something to research! whee!
posted by davejay at 3:26 PM on July 8, 2009

Yeah, ignore me; buoyancy is reduced by compression. Separate containers for the lifting gas and the propulsion air, then.
posted by davejay at 3:29 PM on July 8, 2009

Best answer: Energy density isn't the only factor when comparing fuel sources: Oxygen consumption is hugely important. For instance, gasoline contains about 3 or 4 times more energy than nitromethane (by volume and mass, respectively), yet because gasoline consumes more than 8 times the oxygen (by mass) during combustion that nitromethane does, it yields more power in a similar engine.

Back onto the airship topic, Wikipedia suggests that the development of the rigid airship was a big leap in technology. The page on airships lists many minor improvements in airship technology between Gifford and von Zeppelin. von Zeppelin wasn't the first to come up with the idea, but he was the first to have access to enough aluminum (rare and expensive in those days) to make it work.

The rigid design allowed the ship itself and the gas load to be much larger, more controlled, more durable, and easier to repair. Instead of the main balloon carrying the gas itself the main body on a rigid ship was not pressurized -- it was an aluminum frame covered with fabric for aerodynamics (similar to the wings and body of early airplanes). The gas was held in multiple cells directly to the frame. The rigid design also allowed for more sophisticated rudder control systems, as it can support the relatively high-tension control cables needed for their operation; larger and heavier payloads due to the increased strength; and more, larger engines.
posted by clorox at 4:29 PM on July 8, 2009

Another thing zeppelins had going for them was Blaugas, fuel that basically had the same density as air, which allowed the ships to carry fuel without worrying very much about its weight, or what happens when it is used up.

With a steam engine, not only do you have to carry lots of water weight, but as you use it up the ship keeps getting lighter, which means you would have to vent lift gas to remain at the same altitude.
posted by fings at 4:48 PM on July 8, 2009

Best answer: BTW, if you haven't read it, I can recommend 'Dr. Eckener's Dream Machine', (discussed here in the blue). It has a good amount of history about the development of the zeppelin.
posted by fings at 4:54 PM on July 8, 2009

Response by poster: this is remarkably helpful - thank you all!
posted by korej at 5:31 PM on July 8, 2009

Just in case you don't know, there were also steam-powered planes, for instance those created and flown by John Stringfellow, in the 1840s.
posted by AmbroseChapel at 9:05 PM on July 8, 2009

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