SkyLifter is an eVTOL air crane • Hacker News Board

Re: SkyLifter is an eVTOL air crane

#51

Post by kumarvvr » Sat, Jan 22, 2022, 1:43 PM UTC

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…

My thoughts could not have been captured better than this.

This whole thing, like that flying wind-turbine thing or the solar road thing, is just bordering on plausible but so far away from feasible that one has to doubt the whole effort.

Its hard to imagine, in todays world of information at our fingertips that anyone could fool or misguide someone else, but as the current state of the world is, not only is a con job possible, but its getting easier and more profitable. The trick seems to be to be to make an idea, as I said above, bordering on the plausible but far away from feasible.

Re: SkyLifter is an eVTOL air crane

#52

Post by lifeisstillgood » Sat, Jan 22, 2022, 1:58 PM UTC

masklinn wrote: post #46

lifeisstillgood wrote: post #38

Earlier quoted context omitted.

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 tak…

Thank you.

I got to 411k by 245x41x41 (figures in GP). Yes that's not a cylinder but I am just doing very rough maths.

I did not think about the useful lift - so while the Hindenburg is a 100 years old, a lift of 232k kg was competing with a empty weight of 215. incredible - and thanks for the links

It still seems back of the envelope that lighter than air lift is just not generally useful

Re: SkyLifter is an eVTOL air crane

#53

Post by masklinn » Sat, Jan 22, 2022, 2:53 PM UTC

joenathanone wrote: post #35

Toutouxc wrote: post #16

Earlier quoted context omitted.

So instead of having to move your 25 ton cargo around, you now have to move your 25 ton ballast to be swapped for the cargo at the drop off point so the SkyLifter doesn't yeet itself into stratosphere. The FAQ and literally everything else about this project is vague, disappointing and a little fishy.

Cranes also use counterweights.

Crane counterweights are a completely different matter. The crane doesn't have to drop the counterweight to take on load (the opposite really, unless it's a superheavy with active counterweighting the entire point is to be more stable once loaded).

So the issue with this thing is, any time you move an actual load from A to B, you need to have a weight waiting for you at point B. Or to offgas at which point you won't be able to make a second trip without regassing.

Re: SkyLifter is an eVTOL air crane

#54

Post by CraigJPerry » Sat, Jan 22, 2022, 2:56 PM UTC

ClumsyPilot wrote: post #39

ixfo wrote: post #30

Earlier quoted context omitted.

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.

I think the difficulty is not that its a huge airship, its the precision required to use it as a crane.

That's an area i'd be quietly hopeful in. Assuming propulsion motors are available which are both:

  a) powerful enough to defend against wind acting against such a huge object
  b) responsive enough to change their thrust vector (power & direction) such
     that the associated PID loop can operate within some reasonable set point
     boundary

Then there are already open source hardware and software solutions available for this - i'm not proposing someone slaps a pixhawk 4 on a huge airship and gets a few mates over to help tune the PIDs in Ardupilot - i mean that the know-how is there. Translating that into a product that would be suitable for controlling such an aircraft would be do-able. Certification costs and expensive hardware suitable to run it all on are a different matter.

I guess this is a long way to say i don't think it'd be easy or cheap, but i don't think they'd have to make a break through innovation to make it possible.

Re: SkyLifter is an eVTOL air crane

#55

Post by joenathanone » Sat, Jan 22, 2022, 2:59 PM UTC

masklinn wrote: post #53

joenathanone wrote: post #35

Earlier quoted context omitted.

Cranes also use counterweights.

Crane counterweights are a completely different matter. The crane doesn't have to drop the counterweight to take on load (the opposite really, unless it's a superheavy with active counterweighting the entire point is to be more stable once loaded). So the issue with this thing is, any time you move an actual load from A to B, you need to have a weight waiting for you at point B. Or to offgas at which point you won't…

If the weights remain on the ground you can use a pulley system to load and unload weight, just put slack in the cable and lighten the load… Could even be automated with the right sensors.

Re: SkyLifter is an eVTOL air crane

#56

Post by wcoenen » Sat, Jan 22, 2022, 3:24 PM UTC

nuccy wrote: post #28

wcoenen wrote: post #18

Earlier quoted context omitted.

I was wondering about the same thing. It doesn't seem to be explained on the company site. The only thing I could come up with is to have neutral buoyancy air blatters that can expand/contract. These would be inside the volume of buoyant gas but connected to the outside air. Then pump the buoyant gas into a pressure tank to reduce buoyancy, or release it from the tank to increase buoyancy.

Yes, but the size of the blatter would be enourmous for 250 claimed tonnes: 1 m^3 of air weights 1.21 kg, so if to reach neutral buoyancy you use helium (0.18 kg / m^3) or vacuum (0 kg / m^3, best case), then to counteract lifting/releasing of just one tonne (1000kg) you need to offset 833 m^3 with vacuum and 970 m^3 with helium. Having blatter inside and having such high expension requirements means that the vehicle…

That makes sense. It would indeed be simpler to make the buoyancy volume variable in that case.

I'm not sure though that fabrics exist which are both stretchable and can hold on well to small molecules like helium. (e.g. mylar can be stretched only 4% at most.) Maybe some type of "accordion" type connection between the bottom and top halves of the saucer-shaped balloon would work.

Re: SkyLifter is an eVTOL air crane

#57

Post by ClumsyPilot » Sat, Jan 22, 2022, 4:25 PM UTC

CraigJPerry wrote: post #54

ClumsyPilot wrote: post #39

Earlier quoted context omitted.

I think the difficulty is not that its a huge airship, its the precision required to use it as a crane.

That's an area i'd be quietly hopeful in. Assuming propulsion motors are available which are both: a) powerful enough to defend against wind acting against such a huge object b) responsive enough to change their thrust vector (power & direction) such that the associated PID loop can operate within some reasonable set point boundary Then there are already open source hardware and software solutions available for this…

I think this is fundamentally impossible, win loads are powerfull enough to ouright warp and destroy giant ground based cranes like they were tissue paper if the operator makes a mistake, like lifting oart of a stadium roof in high wind. there are scary videos all over youtube. Those things and made of hige steel girders.

This is going to be a light, fragile airframe with much bigger 'sail' in the form of the airship - its the size of a stadium.

Nothing short of a rocket engine will be able to keep it in place.

Re: SkyLifter is an eVTOL air crane

#58

Post by lstodd » Sat, Jan 22, 2022, 5:16 PM UTC

doikor wrote: post #3

H8crilA wrote: post #2

This will be a pain in the ass to manage in controlled airspace because it's so much slower than anything else. But I guess it would also use different flight levels, so maybe not a problem at all. I wonder how does the fuel usage compare to a plane, that's the real measure of green-ness.

Just fly it close to the ground and the only controlled airspace is near airports (and some big cities, military stuff, etc). Should not be that hard to stay out of those for the most part if you are transporting stuff like windmill parts to the middle of nowhere.

If you fly low how do you deice the thing while avoiding terrain? Most of the crashes were due to flying into the terrain in adverse weather conditions after all.

Re: SkyLifter is an eVTOL air crane

#59

Post by CraigJPerry » Sat, Jan 22, 2022, 6:15 PM UTC

ClumsyPilot wrote: post #57

CraigJPerry wrote: post #54

Earlier quoted context omitted.

That's an area i'd be quietly hopeful in. Assuming propulsion motors are available which are both: a) powerful enough to defend against wind acting against such a huge object b) responsive enough to change their thrust vector (power & direction) such that the associated PID loop can operate within some reasonable set point boundary Then there are already open source hardware and software solutions available for this…

I think this is fundamentally impossible, win loads are powerfull enough to ouright warp and destroy giant ground based cranes like they were tissue paper if the operator makes a mistake, like lifting oart of a stadium roof in high wind. there are scary videos all over youtube. Those things and made of hige steel girders. This is going to be a light, fragile airframe with much bigger 'sail' in the form of the airship…

The skin of a Boeing 747 is about 2mm thick. We’ve been hurling them at 600mph through storms for half a century at this point.

I don’t know for sure but i suspect the airframe of this concept is within reach of current tech.

Re: SkyLifter is an eVTOL air crane

#60

Post by maxwell86 » Sat, Jan 22, 2022, 6:45 PM UTC

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…

> 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.

You can also build a car with square wheels and cross north america in one.

> I'm not sure I understand your point, are you saying that airships don't work?

No, I'm saying that companies that try to sell airships don't work.

These companies are good at raising money, because the idea they sell is simple to explain, and many people don't do due diligence.

But in the same way that a car with square wheels is a worse solution to the problem, along pretty much any axis of comparison, than any of the alternatives available in the market, so are airships. With the difference that airships are also way more expensive than the solutions that are already in use.

This is why companies that build and try to sell them, default in 3-5 years after having raised the money.

---

The only types of airship that "works" are balloons able to cary 2-5 people. The weight is small, so the balloon surface is also small against the wind, the components required to drive them are simple and easy because the balloon is "small", and their use is purely occasional and recreational (or a tourist attraction where you can charge a bonus), so cost isn't a "huge" issue. People pay for the "fun", not to go from A to B.