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My understanding is that regular steam engines could use instead compressed air (not sure what had to be done to allow this) and if so, would not such an arrangement, which did not require fuel and water to be turned to steam, would weigh a lot less I would think.

If so, would compressed air have been a way of achieving powered flight instead of/prior to the internal combustion engine which I believe was a key factor in the Wrights' success?

I believe 19th century attempts did use steam -- I wonder (as I asked in HSM but was told the question was not history-related) if compressed air was discussed or attempted and if there is any reason to believe it could have worked.

Note: I did am not asking about steam engines' ability to use compressed air -- they can. I am asking how much more efficient such a system is than using steam. I even wonder since compressing air was well understood by the late 19th whether a rocket-like usage of compressed air could be accomplished.

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  • $\begingroup$ how would you compress the air? $\endgroup$
    – jsotola
    Sep 16, 2023 at 19:24
  • $\begingroup$ @jsotola: air rifles which had a cartridge which was pressurized vis pump is a centuries' old invention. Lewis and Clark had such a rifle. Invented at least 100 years before. Their rifle was a repeater which could fire 30 shots without reloading when normal rifles were muzzle loaders and the rifle could bring down a deer. $\endgroup$
    – releseabe
    Sep 16, 2023 at 19:33
  • $\begingroup$ So how big does your compressed air cartridge need to be to be able to provide the equivalent power of 100 gallons of avgas? $\endgroup$
    – Solar Mike
    Sep 16, 2023 at 20:08
  • $\begingroup$ @releseabe an anecdote about an air rifle does not answer the question about compressing air to power an airplane ... would the compressor be on board? $\endgroup$
    – jsotola
    Sep 16, 2023 at 20:14
  • $\begingroup$ @jsotola: The technology to compress air certainly existed before the Wrights and was mundane technology by the time air could be liquified. $\endgroup$
    – releseabe
    Sep 16, 2023 at 20:33

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In theory, there's no reason it couldn't have worked at all. The engine part of a steam engine wouldn't really know or care that whether the high pressure gas you ran though it was steam or pressurized air. They just used steam, because it's pretty easy to store water, and boil it to get steam as a source of the pressurized gas to run the engine.

Nonetheless, let's try to keep things in perspective. For comparison, a steam locomotive typically used about 100-200 gallons of water per mile. Water expands by about 1600:1 when it's boiled. So for a steam locomotive, you need something like 1600x150 = 240,000 gallons of compressed steam per mile.

Depending on the pressure you used, you'd need about the same amount of compressed air. Let's say our aircraft needs 500 feet to take off, and we design it to run out of compressed air just as it takes off. Further, let's say it needs 1% of the power of a locomotive. That means we still need: 240,000 * 0.01 * 500/5280 = ~225 gallons of compressed air.

But that's not really powered flight, just powered take-off roll, followed by an unpowered glide and a landing.

I'm not at all sure we can extend that ever having even a hope of, say, 1 mile of powered flight. For 1 mile (plus takeoff roll), we need a pressure tank close to 3000 gallons, which (even with modern technology) weighs close to 4000 pounds. With a 4000 pound tank, our aircraft would probably need to weigh at least 4500 pounds. And to power that, we'd need a bigger engine that used more compressed air--and we're almost immediately caught in a vicious circle of bigger tank -> bigger aircraft -> bigger engine -> still bigger tank.

You can undoubtedly come up with a better estimate that this though. In particular, I've pretty much just pull the "1%" number out of the air. You can obviously come up with a better estimate by looking at the size of aircraft and speed of flight you want, and base your estimate on producing roughly the same power as some existing aircraft in that size/speed range. Likewise, you can find the minimum takeoff for that aircraft, then add the length of powered flight you want to support, and use that to get a better estimate of how much compressed air you'll need.

In the end, my guess is that yes, it's possible as long as you set your goals low enough--carrying virtually no payload, and a powered-flight distance that's probably better measured in feet/meters than in anything like kilometers/miles.

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  • $\begingroup$ Thanks for the details. Perhaps the Wrights thought, Sure, we could use compressed air but we are looking for a longer flight time. And gasoline engines were indeed already available and far from exotic by 1900. But if the goal was simply a flight of any length, perhaps the Wrights could have been beaten by years. I do know of prior claims and also Wright innovations that had nothing to do with engines. $\endgroup$
    – releseabe
    Sep 17, 2023 at 9:02
  • $\begingroup$ I am reminded of Flight of the Phoenix wherein the German engineer and the Captain discuss powered flight that occurred in the mid 19th (a rubber band-powered model). People were very optimistic about powered flight and expected to use steam engines to do it around 1850 -- one guy went from tethered model to trying to raise money for passenger service I think even in the 1840s. Admirable optimism. $\endgroup$
    – releseabe
    Sep 17, 2023 at 9:07
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Compressed air engines were developed by Whitehead for torpedoes in the late 1860s. In order to get high power outputs you have to warm the expander, he developed two approaches, one by heating the motor externally, or secondly (and this is still being used effectively) by injecting fuel into the air supply for the motor, in 1904.

The main weight related problem would be the pressure tank.

So, the tech for the motor itself was available in the right time frame, your big issue is the tank.

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  • $\begingroup$ Well, the goal is to generate enough power to fly -- distance is a separate issue. I am amazed that a steam engine could even use compressed air and have no info on power generated. Steam engines were pretty complex and dangerous and the engineers were probably the equivalents intellectually I would guess of modern s/w developers and perhaps in those days thought of as being bright guys like telegraph operators were. $\endgroup$
    – releseabe
    Sep 16, 2023 at 20:39
  • $\begingroup$ @releseabe steam boilers were dangerous before people know how to build pressure vessels, but steam engines are fairly straightforward and not dangerous at all, unless you decide to interact with moving parts. In that way they are no more dangerous than any industrial packing equipment. $\endgroup$
    – Tiger Guy
    Sep 17, 2023 at 7:32
  • $\begingroup$ @TigerGuy: I recall reading of a train, I think with a sophisticated 20th century steam engine and the engineers were dealing with IIRC a very steep grade and had to make decisions to increase power output which ultimately led to a horrifying explosion. My impression was that despite the simple concept of expanding steam, such engines were both complex and temperamental and the crew, even the stokers, had to understand their workings very well. Chrysler started his career in trains and that was enough education to found a decent-sized automobile business. $\endgroup$
    – releseabe
    Sep 17, 2023 at 8:51
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Model airplanes have been run off of compressed CO2 cartridges since the 1960s, using a basic steam engine cycle. They fly for a short while, then glide. Practical for fun, but not for full-scale, long-range use.

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An internal combustion car/truck engine is the equivalent of a piston steam engine, driven by expanding air with the expansion powered by diesel or gasoline (petrol) fuel. Jet engines are the equivalent of steam turbines with the jet powered by expanding air created by burning jet fuel.

The problem with powering vehicles is the density or the energy source. Fossil fuels have proven very effective at this for more than a century. Recently, electric batteries have proven effective as well, although their extreme weight makes them less effective for airplane use, where weight is at a premium.

Certainly we could put pencil to paper and determine the amount of compressed air we would need to power an airplane, but the plain fact is that the energy density of compressed air is pitiful compared to fossil fuels. You cannot carry enough of it to fly around for more than a few minutes.

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  • $\begingroup$ Well, even achieving a few minutes of powered flight would have been a big deal. My question is simply whether a steam engine powered by compressed air would have (by removing the weight of water and fuel and presumably saving much mass even when weight of air cannisters was added in) been able to power a plane not today but before the Wrights did. I am guessing there might be some limitation of compressed air which prevents generating enough power to take off at all, but I am asking, I do not know. Perhaps gasoline engines were the sole way to generate enough power IN THOSE DAYS for flight. $\endgroup$
    – releseabe
    Sep 17, 2023 at 8:57

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