61–70 of 75 posts
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That's the main campus but part of the concept is for it to be distributed over most of the Northern part of the country, including, as the name suggests, the islands: https://www.uhi.ac.uk/en/#campuses
Just out of curiosity, do you have any relation to the Remarkable Tablet?
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Make a vacuum onion. 1d-compressium, 1d-tensilium, and 2d-tensilium are all allotropes of obtainium, being the materials with the highest uniaxial compressive strength to mass ratio, the highest uniaxial tensile strength to mass ratio, and the highest biaxial tensile/shear strength to mass ratio. Currently, those are probably diamond struts, buckytube fiber cables, and graphene sheets. Throw 2d-tensilium envelope aro…
Wouldn't all that inner material be too heavy to float after that?
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If helium gets really expensive, they could switch to hydrogen. Maybe even switch inflight, by replenishing lost helium with hydrogen. Maybe by hydrolysis. For a plane operating in remote areas at altitude, the explosion risk is not an issue.
That is an interesting idea, and I don’t know why this has been downvoted.
You’d still have to buy the helium (how else does it get off the ground?). Probably more if you intend to safely bring it back down.
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I'd argue that hydrogen is actually among the best, with helium of course being second. Helium wins out on the inertness, but has far lower lifting capacity, and of course has a supply issue. Hydrogen wins on lifting capacity, supply is not an issue at all - but it has a weird image problem, thanks to one singular accident - which was arguably not caused by the lifting gas! Prior to that accident, hydrogen had a fair…
The other problem with hydrogen is that it is hard to contain. Leakage and permeability of the envelope would probably end up being a bigger engineering concern than would flammability.
Most of the mentioned use cases involve high altitudes. Higher altitudes = higher winds. The air is smooth up there but it does move. For instance, the upper level winds above my head right now are pushing 130knots. This thing will have to do more than glide gently up and down if it wants to maintain station at 10km+, airliner altitude.
I was wondering about this too. Then again, I don't know the air density difference. 130 knots at half the density (not that I know if half density is a feasible figure) would impart something like half the force, I imagine. Then again, lower density affects the ability of craft that use density for lift to operate.
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> H2 is dangerously explosive. Does it matter for an unmanned vehicle? Such a thing could be inflated at a safe distance. In some cases, being able to self destruct is a safety benefit (to prevent crashes when control is lost) and a security benefit (to prevent analysis of captured aircraft). Particularly UAVs are popular in military / spying operations.
I'd argue that hydrogen is actually among the best, with helium of course being second. Helium wins out on the inertness, but has far lower lifting capacity, and of course has a supply issue. Hydrogen wins on lifting capacity, supply is not an issue at all - but it has a weird image problem, thanks to one singular accident - which was arguably not caused by the lifting gas! Prior to that accident, hydrogen had a fair…
* https://en.wikipedia.org/wiki/Lighter_than_air#Hydrogen_and_...
Agreed that the danger of hydrogen is less than perceived. In an accident it goes up which is normally where the people are not. When it burns it doesn't create much radiant heat. Outdoors in the daytime firefighters have to use something like a broom to find hydrogen fires. Otherwise you could just walk right by one ... which is an issue if you instead walk right into the fire.
With the soaring price of helium, I wonder what it costs to fill up that gas bag and how quickly it leaks out. And at what point filling it up costs more than the "almost expendable" aircraft. In the novel/film Contact the character S.R. Hadden lives in an airliner that rarely lands. With a larger Phoenix that lifestyle could become available to somewhat less wealthy billionaires. Maybe it could eventually become an…
There are no really great lifting gases. Steam is ok but must be kept hot. H2 is dangerously explosive. Vacuum is the best (a so-called "null ship") but no known material can maintain the hull pressure under vacuum.
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If helium gets really expensive, they could switch to hydrogen. Maybe even switch inflight, by replenishing lost helium with hydrogen. Maybe by hydrolysis. For a plane operating in remote areas at altitude, the explosion risk is not an issue.
You could switch in-flight, but you would actually increase the gas costs since you’d need 100% helium for the trip up as well as the trip down. Also, the risks would dramatically increase in exigent circumstances. What if the gas container fails, causing it to make an unexpected descent? Even for a planned descent, there has to be a way to switch back to helium. So now you have to have at least 2 times the helium ne…
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You could switch in-flight, but you would actually increase the gas costs since you’d need 100% helium for the trip up as well as the trip down. Also, the risks would dramatically increase in exigent circumstances. What if the gas container fails, causing it to make an unexpected descent? Even for a planned descent, there has to be a way to switch back to helium. So now you have to have at least 2 times the helium ne…
But for an expendible aircraft you don't need it to be buoyant on the way down. Just have a failsafe that dumps the hydrogen into the atmosphere below a certain altitude/air pressure.
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I'd argue that hydrogen is actually among the best, with helium of course being second. Helium wins out on the inertness, but has far lower lifting capacity, and of course has a supply issue. Hydrogen wins on lifting capacity, supply is not an issue at all - but it has a weird image problem, thanks to one singular accident - which was arguably not caused by the lifting gas! Prior to that accident, hydrogen had a fair…
The other problem with hydrogen is that it is hard to contain. Leakage and permeability of the envelope would probably end up being a bigger engineering concern than would flammability.
See Figure 2, Gas Permeability of Mylar vs. Temperature
Helium permeates Mylar significantly faster than hydrogen over the full temperature range tested. It looks like the helium permeation rate is nearly double that of hydrogen near room temperature. Surprising! I would have guessed that lighter gases permeate faster. Note on the same figure that oxygen permeates faster than nitrogen even though it's heavier.
There is more tabular data here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/196900...
It confirms the same trend. Helium permeates Mylar faster than hydrogen.