Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

SkyLifter is an eVTOL air crane

skylifter.eu

Post reply on HN
Print view View original

41–50 of 77 posts

Re: SkyLifter is an eVTOL air crane

#41

Post by lazyjones »

davidhyde wrote: post #21

I'm calling bullshit on this. Slick marketing driven website, low resolution photos of actual prototypes, hand-wavy FAQ and no other technical details. They claim speeds of 40 knots but does that mean that can stay stationary in 40 knot winds (the same as traveling at 40 knots) or that it can hitch a ride on high winds? The wind forces on the balloon look they would be far too high for those tiny fans to counteract e…

> 250 tonnes is A LOT to lift. Look how big a hot air balloon needs to be to lift a few passengers in a basket.

Does it scale? Can you strap 10 of those things together (perhaps using some sort of scaffolding) to lift 10x the weight?

Re: SkyLifter is an eVTOL air crane

#42

Post by masklinn »

ixfo wrote: post #30
CraigJPerry wrote: post #19

Earlier quoted context omitted.

>> that is 100mx100mx25m That’s huge! I wondered how big was the hindenberg, wiki claims 245m long and 41m wide, and 41m tall (excl. cabin). Only 200k litres of gas capacity. 232k tonnes lift.

So it is huge, but well within historic capabilities - and materials science has come a long way since then. I'm quietly hopeful for this.

> So it is huge, but well within historic capabilities - and materials science has come a long way since then. I'm quietly hopeful for this.

The problem is not building the thing (though it is one problem), it's that if you're using this as a crane you're moving an entire baseball field with a decimeter if not centimeter-scale precision.

Re: SkyLifter is an eVTOL air crane

#43

Post by lordnacho »

It doesn't look big enough. Basically it's Archimedes principle, same as for stuff that floats:

The force produced is the weight of the mass displaced. So a hole in the air would lift up an equivalent mass to what the air in that hole would have weighed. For a ship this is a heck of a lot, since water is a lot denser than air. You can have a huge cruise liner because the hole it makes in the water would weigh 1T/m3, which for the size of such a ship is enough to lift up a massive chunk of metal. But air is nowhere near as dense, so even a cruise ship water-hole sized balloon with magic gas that weighs nothing would only be able to lift ca 1/1000 of the ship.

One trick you can do with air is heat it up so that the atoms push the sides out more, making your balloon bigger for the same mass. I'm not sure how to quantify the difference though. I suppose you take the ideal gas law and say it's proportional to the absolute temp? Limited how hot you want to make the thing that's naturally at about 300K.

Can't tell how big they intend to make this but it just looks like isn't big enough. A big enough balloon would also give rise to other engineering issues, like what do you do with wind and how to you keep the helium inside?

Also if this kind of thing generally worked every moving company would have one. Stick a balloon your sofa, get the kids to take it to your new house.

Re: SkyLifter is an eVTOL air crane

#44

Post by masklinn »

lazyjones wrote: post #41
davidhyde wrote: post #21

I'm calling bullshit on this. Slick marketing driven website, low resolution photos of actual prototypes, hand-wavy FAQ and no other technical details. They claim speeds of 40 knots but does that mean that can stay stationary in 40 knot winds (the same as traveling at 40 knots) or that it can hitch a ride on high winds? The wind forces on the balloon look they would be far too high for those tiny fans to counteract e…

> 250 tonnes is A LOT to lift. Look how big a hot air balloon needs to be to lift a few passengers in a basket. Does it scale? Can you strap 10 of those things together (perhaps using some sort of scaffolding) to lift 10x the weight?

In the sense that lift is linear by volume yes, but the driving complexity I expect would increase superlinearly.

If you're strapping 10 things together, you're now dealing with a much less rigid structure, the straps/scaffolding are significant points of failure, and the attachment points don't scale the same way so you have to add an even more complex (and tangle-able) web of cabling for your payload.

Re: SkyLifter is an eVTOL air crane

#45

Post by Toutouxc »

lazyjones wrote: post #41
davidhyde wrote: post #21

I'm calling bullshit on this. Slick marketing driven website, low resolution photos of actual prototypes, hand-wavy FAQ and no other technical details. They claim speeds of 40 knots but does that mean that can stay stationary in 40 knot winds (the same as traveling at 40 knots) or that it can hitch a ride on high winds? The wind forces on the balloon look they would be far too high for those tiny fans to counteract e…

> 250 tonnes is A LOT to lift. Look how big a hot air balloon needs to be to lift a few passengers in a basket. Does it scale? Can you strap 10 of those things together (perhaps using some sort of scaffolding) to lift 10x the weight?

Yes, individual cells filled with lifting gas scale nicely (after all that's how rigid airships are made), but the main issue here is "big", not the actual arrangement or architecture. You need BIG to be able to lift HEAVY.

Re: SkyLifter is an eVTOL air crane

#46

Post by masklinn »

lifeisstillgood wrote: post #38
CraigJPerry wrote: post #19

Earlier quoted context omitted.

>> that is 100mx100mx25m That’s huge! I wondered how big was the hindenberg, wiki claims 245m long and 41m wide, and 41m tall (excl. cabin). Only 200k litres of gas capacity. 232k tonnes lift.

So that's 411k m3 with only half that as gas capacity ! Interesting. But back-of-the-envelope lighter than air is just hard . It's certainly possible to see this working in niche areas, but boy, it's a tough sell compared to "get a giant Sikorsky"

> So that's 411k m3 with only half that as gas capacity ! Interesting.

Not sure how you reached 411, 245 x 41 would be 323k for a straight cylinder, which the hindenburg was nowhere near[0]. And the envelope was larger than the useful gas volume owing to the internal scaffolding, and the internal volume being subdivided into 16 cells separated by structural rings[1].

And the 232t useful lift was pure lift, before taking in account the 215t of the airship itself (at basic empty weight). The useful lift (payload) was 40 crew, 50 passengers, their luggage, and 10t cargo.

[0] https://3iz4pu1r2cxqxc3i63gnhpmh-wpengine.netdna-ssl.com/wp-...

[1] https://3iz4pu1r2cxqxc3i63gnhpmh-wpengine.netdna-ssl.com/wp-...

Re: SkyLifter is an eVTOL air crane

#47

Post by Toutouxc »

aggrrrh wrote: post #34
davidhyde wrote: post #21

I'm calling bullshit on this. Slick marketing driven website, low resolution photos of actual prototypes, hand-wavy FAQ and no other technical details. They claim speeds of 40 knots but does that mean that can stay stationary in 40 knot winds (the same as traveling at 40 knots) or that it can hitch a ride on high winds? The wind forces on the balloon look they would be far too high for those tiny fans to counteract e…

I wonder if it would work in Venus atmosphere?

Operating a blimp on Venus would be a bit tougher than on Earth, partly because the density of Venus atmosphere is only 95 % of our air (less lift per lifting gas volume), and also because of the incredibly violent 100 m/s winds, 93 bar pressure and a temperature of 470 °C.

Re: SkyLifter is an eVTOL air crane

#48

Post by ZeroGravitas »

davidhyde wrote: post #21

I'm calling bullshit on this. Slick marketing driven website, low resolution photos of actual prototypes, hand-wavy FAQ and no other technical details. They claim speeds of 40 knots but does that mean that can stay stationary in 40 knot winds (the same as traveling at 40 knots) or that it can hitch a ride on high winds? The wind forces on the balloon look they would be far too high for those tiny fans to counteract e…

I thought the website was more engineery than slick, but more specifically, the up to 250 tonnes appears to mean, we can envision building one of a sufficient size to deal with that. They have mockups of a 2, 25 and 250 tonnes, and the scale of the big one does seem very large:

https://www.skylifter.eu/air-crane/

So is this reaction just getting caught up on combining images of the small model, with the load capacity of the (theoretical) biggest model? There's lots of things, like cranes, that have a fairly standard size and a few mega sized examples used for very specific tasks.

Re: SkyLifter is an eVTOL air crane

#49

Post by masklinn »

dogma1138 wrote: post #36
davidhyde wrote: post #21

I'm calling bullshit on this. Slick marketing driven website, low resolution photos of actual prototypes, hand-wavy FAQ and no other technical details. They claim speeds of 40 knots but does that mean that can stay stationary in 40 knot winds (the same as traveling at 40 knots) or that it can hitch a ride on high winds? The wind forces on the balloon look they would be far too high for those tiny fans to counteract e…

Indeed, the Hindenburg could lift over 200tons however it’s useful lift (lifting capacity minus its own weight and structural limitations) was only about 10 tons… Even if we ignore the lifting gas requirements just the structural requirements to be able to tie 250tons to the lifting body make this pretty much impossible. This makes solar roadways and the air condenser solar water bottles seem viable. For comparison t…

> Indeed, the Hindenburg could lift over 200tons however it’s useful lift (lifting capacity minus its own weight and structural limitations) was only about 10 tons…

TBF it was 10t cargo on top of crew (40), passengers (50), and luggage. So probably closer to 15~20 useful lift.

Re: SkyLifter is an eVTOL air crane

#50

Post by masklinn »

Toutouxc wrote: post #40
maxwell86 wrote: post #33

Earlier quoted context omitted.

Because it doesn’t work. You’d need a foot ball field of area, and a 3 story building, to life a small yacht like space. The wind forces on the surface would be extreme, and you’d need a lot of power to even stay somewhere stationary instead of flying away. All of this would add weight, increasing the volume of helium needed, increasing the wind exposed surface area, making the problem worse. You’d need a huge indust…

I'm not sure I understand your point, are you saying that airships don't work? Because the Hindenburg was able to take 100+ people across the Atlantic (86 years ago!), that's much more than the maybe 10-person "luxury RV" that the OP was suggesting. Today's Zeppelin NT semi-rigid airships are reasonably small and can carry 10+ passengers on shorter flights. Yes, airships are expensive, inconvenient and slow, they lea…

> Yes, airships are expensive, inconvenient and slow, they leak helium and they require huge hangars and mooring masts, but that's far cry from "can't work".

"Can't work" is a pretty good effective compression of "work on the barest of technicality while being more expensive, slower, less flexible, and less reliable than pretty much all alternatives".

Also the Hindenburg was absolutely not able to take 100+ people across the atlantic, half of that was crew which you don't usually consider "taken over" as they have to fly back. So Hindenburg took 3 days to carry 72 passengers across the atlantic, needing 40 crew to do so, at a ticket price of $7460 (one way, in modern USD).

By comparison, bloody Concorde transported up to 128, with a crew of 3, in 3.5 hours, at lower prices.

Post reply on HN