That’s not the point in question.
It’s not a question of whether silk is the best material for making a balloon. It definitely is not. There are many materials which are better.
The question is whether silk is a possible material for making a balloon. Which it is, as evidenced by the fact that it’s been done.
It was the answer that was ludicrous.
I can sum up this concept in one word: Convergence.
This is such an obvious straw man that I couldn’t quite believe my eyes when I read your post.
No one here has ever argued that silk couldn’t be used to make a balloon. That was never “the question,” and you know it.
380m^2 is a bit over 600 feet of a 6-foot wide bolt of cloth. Before the days of mass production, that would have been a king’s ransom. Simply shipping it from China (impossible until the later 1500’s) would have been expensive. Even hand-made thinner linen cloth would be expensive. Ditton for paper and rope. By the time the Montgolfiers were playing with balloons, a pair of minor nobility with a factory family business could afford this sort of luxury disposable material from their petty cash drawer. Again, we forget the effect of the industrial revolution on production volume.
Also, silk can be used for a balloon if it’s sealed properly - especially a gas balloon. I assume they had a process for rubber-coating or something, that was not too heavy. Hot air balloons can be leaky, because the supply is always being replenished (has to be). For gas balloons, a bit more difficult.
BTW, what was the process for making hydrogen? That too probably required industrial-scale tech to produce in quantity.
It can be produced rather simply, by mixing hydrochloric acid and iron filings.
Which reduces the question to, how do you produce hydrochloric acid?
You can make it by mixing sulfuric acid and salt. Now let me guess what you next question is.
You need to find some pyrite, which is a naturally occurring mineral. Heat it up and collect the gas - sulfur dioxide - which comes off of it. You mix the sulfur dioxide gas with some chlorine gas. This produces sulfuryl chloride, which you can dilute with water to make sulfuric acid.
But here’s the punchline; you produce chlorine by running electricity through salt water. When you do that the water will emit chlorine - and hydrogen. So if you have the electricity you need to make the chemicals you can use to make hydrogen, you can skip all the chemistry and make hydrogen directly.
Really?
Really. History is outside my wheelhouse, but AFAIK the first practical application of hot air balloons was for military signaling about 2000 years ago. To the best of my knowledge, those balloons had paper envelopes.
Was a silk balloon theoretically possible at the time? Yeah, it was. But as far as I know, the first balloons were paper.
Silk could have worked if it could be sealed, sure. But paper seems to have been a better overall tradeoff between permeability and strength.
No one is saying a silk balloon couldn’t be done, but since it seems not to have been done prior to paper, there might be a compelling reason.
Again, a matter of scale. Something a yard or so in diameter and carrying a candle can be made out of paper - or silk coated with something. Make it carry 400 to 600 pounds (300kilos) and now we’re talking a whole different range of engineering.
Also, it’s a matter of experimentation. The Wright brothers were building on the backs of people who built kites, even Lillenthal’s gliders launched off hills, and people who built internal combustion engines (with the weight-to-power ration that worked for flight.) In fact, their major contribution was wing-warping to control flight, as once you added an engine weight-shifting was insufficient. Many previous attempts by others failed from inability to control and loss of stability. That wings could support a considerable weight for distances was already proven, and sails had proven the power of air.
For balloons, what’s between a signal balloon a foot or three across and something carrying a useful load? What other useful load is there besides dropping incendiaries on a besieged town - and how reliable (safe for the launchers) is a hot-air balloon full of flammables? Flaming arrows seem to be a better bet. The man-sized balloon had to wait for a bunch of experimenters with the time, money, and obsession to see the enterprise through. Nobody had found a reason to build, say. a 10-foot-diameter hot air balloon and say - “Look, it works”.
This is a bit muddled. The contribution of kite technology to what the Wrights did was scant. Lilienthal was a big inspiration, but his tables of lift proved misleading - his most useful contribution probably was (as you note) a demonstration that weight-shift was inadequate for proper control. And they wound up building their own engine, having found (to their surprise) that nothing suitable was available from others.
Their major contribution was 3-axis control. Wing warping controls one of the three axes (roll).
I think their major contribution was their systematic, scientific way they went about it. I recall that there were 7 basic ‘ideas’ that the Wright brothers came up with; I think most of those received patents.
One example was the ‘invention’ of the wind tunnel. This allowed them to actually test various shapes of wings, and confirm (or disprove) the aerodynamic properties of these. Iy was this kind of experimentation & “stepwise refinement” that seems to explain their success, I think.
This is true. Most of the experimenters in flight before them, and many since, took the approach of slapping something together, trying to fly it, and if they survived, trying some other slapped-together design. The Wrights, by the time of the Kitty Hawk flight, pretty much knew that their design would work, because they’d done all the experiments and calculations.
I follow your point, and it’s worth making. But some scaling factors work in the aeronaut’s favor: as balloon diameter increases, envelope weight goes up, but the enclosed volume—lifting power—increases even faster.[sup]1[/sup]
The material with the best net strength-to-weight ratio is what you want for your envelope. If a sealed silk envelope is structurally viable for a 1-meter balloon, it’s structurally viable for a 25-meter balloon. But supply chains don’t scale like this, of course, and while sourcing enough silk for a 1-m diameter balloon (~3.14 m[sup]2[/sup]), sourcing the 2000 m[sup]2[/sup] required for a 25-m diameter balloon would be much harder.
If you could pull that off, the larger envelope would weigh 625 times what the smaller one does, but its lifting power is over 15,000 times that of the smaller balloon (all of this is to a first approximation).
I fully agree that scaling balloons to carry people is hard for a number of reasons, but envelope size is an exception to that.
[sup]1[/sup] Many here know this, but it’s always good to show your work: a sphere’s surface area increases with the square of the diameter, while its volume increases with the cube of the diameter. And yes, a larger envelope size requires lots of other things to be bigger, and most of those don’t scale well at all.
Well, they didn’t invent this - though among early experimenters only they and Lilienthal were truly systematic. What they did invent (3-axis control) was the result of their steady, careful, scientific approach.
As the Wikipedia article on the wind tunnel points out, others, including Lilienthal, did experiment with the passage of air over the shapes they used – they just didn’t do it static in a wind tunnel:
John Stringfellow built and flew his (pilotless) steam-powered monoplane in 1848. It was based on Cayley’s designs and calculations, so it had the advantage of experimental design, although I have not read anywhere of Stringfellow himself testing out the design beforehand with a “whirling arm” apparatus or wind tunnel.
…how do you produce salt?
On the remote chance this isn’t a joke, salt is a naturally occurring mineral.