Comment on High Altitude Solar Cruise
Dasus@lemmy.world 2 weeks agoOh yes, cargo planes which don’t have pools or greenhouses and which guzzle tons of fuel to power their huge engines?
Does the surface area of those planes determine how much energy they can get? Or is it the exceedingly high energy fuel which they pipe in to a tank inside the plane?
So you expect cargo planes to increase in size so much they’re not just lugging cargo, but also have greenhouses and swimming pools (and that’s ignoring the problems and pure stupidity of having a pool on a plane), but you expect solar to become so efficient it can actually deliver more energy from surface area of an aircraft than you can currently by pumping a metric ton of high-grade fuel in a minute?
The An-255 Mriya has six engines producing ~54,000kW each, meaning a total output ~324 000 kW.
The solar plane you mention, the Solar Impulse 2, has four engines producing 13.5 kW each for a total output of 54kW.
You can see the contrast, right?
I hope I would be wrong in this. But I’m not.
I think one would need something like a nuclear powered plane for shit like that. Which wouldn’t necessarily be a bad idea, honestly. I think we should look into that sort of tech because it would also work at the bottom of the ocean and it could power craft that could explore Venus.
Now don’t get me wrong I’m no nuclear shill, I think we should definitely power most things with renewables. And even planes, sure. But if you honestly want a plane which is large and stable enough to have a pool and a greenhouse, I don’t think we’re going to achieve that via solar. At least not directly. Perhaps planes like that could be powered via extremely high powered lasers from the ground and/or moon.
But like mathematically… roughly 1000 watts or 1 kW of energy comes from the Sun on a clear day for every m2 of ground. In space it’s like ~1300 at this distance. On a cloudy day way less than 1000. But well go with the 1kW/m2.
If we assume that this plane of yours needs to be able to capture the amount of power it uses and that it is not even that big, just has similar engines to the An-225, then you’d need a surface area of 324 000 m2.
The wing surface area of an A320 is ~100m2, so you’d “only” need 3240 of those to have enough area on the plane to have 100% efficient solar panels be able to produce the peak power of the An-255. Ofc you wouldn’t be flying with peak power all the time, and flying above clouds would mean good sun to panels.
The record for efficiency for solar panels in a laboratory setting is 47%. Those aren’t commercially available. Commercially available ones are currently around 22%.
Light clouds cover reduces solar panels to 75-80% output. Heavy clouds can reduce it to 10%.
And unless you’re planning to fly in one direction only and only during certain times, you’ll have to consider that you’re not always in the sun, nights exist.
So double everything assuming half of all time is night.
Then assume 22% efficiency.
Then keep in mind all clouds can’t be avoided so let’s say 90% output.
So it’s not 3240x the A320 surface area you need, but 6480 because nights, but then only ~22% efficiency for recharging so it’s ~30 000 times the surface area of an A320. Oh except cloud coverage. So ~33 333.33333 *(repeating of course) times the surface area of an A320.
And that’s why I find your suggestion improbable.
It’s hopeful and I’d like for you to be right. But I don’t think you are. Sorry.
If we could manage a bit of societal change so as the se rich motherfuckers weren’t stealing everything, I think we might actually speed the rate of technological growth by a metric fuckton.
But with this speed and looking at these facts? I just can’t believe in your dream, however nice it sounds.
keepthepace@slrpnk.net 2 weeks ago
Dammit, here I am, arguing over the feasibility of a fantasy, between a hamster in warhammer gear and a knitted armor. sigh
Dude chill, I merely mentioned the An-255 because you sounded like you were arguing that flying a pool and a greenhouse was somehow breaking a law of physics. It does not, you can fly both for the 250t (that’s payload only btw, that does not count fuel(+300t!), engine, structure) that this plane can lift.
I am not proposing to develop the same amount of thrust, speed, dry range that it exhibits, these are different beasts. Actually, in my fiction, these “sky palaces” only have the thrust needed for sustained flight, and can’t lift off unaided.
I am, but I am also an avid dreamer of new tech.
Sci-fi setting, honey. If 47% is achieved in the lab that’s the bare minimum of what is credible for future tech.
I am happy you made the calculation for something that can drag 300t of batteries at half the speed of sound and can produce the constant thrust the An-225 needs for take-off but that was never the proposition. I am proposing a slow vehicles, with a fairly big lift due to its large wings so probably able to fly at a much lower speed, generating far less drag, drag being the main lower bound for the thrust needs. Probably going at speeds where propellers are much more efficient than jet engines. All of this adds up to levels I don’t care to calculate because this is a fantasy.
However yes, that’s a proposition that still requires extremely large wingspans. And yes, putting a swimming pool in an airplane is kind of a ridiculous proposition, but it is kind of the point I want to make: nowadays that would be a very wasteful ridiculous thing to do. With this sort of tech? It does not harm anything or anyone. It does not burn fuel, it does not emit CO2.
All I know for sure is that eternal planes are a thing that is possible right now, and that better tech will allow us to make them bigger.
Dasus@lemmy.world 2 weeks ago
Like honestly I know I’m a salty person and am offending you, but that’s just how I am. I’m not trying to offend you, but my point is that while a nice dream, your dream is about as realistic as these drawings of what the 21st century would be like from the pov of 19th century
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Like okay sure we do have sort of “jetpacks” and we can do wingsuits with rocket boots but hovering like that with wings like that just isn’t plausible. The wings would have to be huge. Just like your imagined plane.
Do the same fantasy and use a blimp and I’m 100% in.
keepthepace@slrpnk.net 2 weeks ago
We do have helicopters. We have canadairs, we have hovering drones.
You are arguing about a technicality that has been worked around.
Dasus@lemmy.world 2 weeks ago
No, I’m not. You’re imagining something on a scale at which it can never work at.
It’s a physical impossibility to have a plane the size you’re proposing which would continously recharge itself via solar unless it’s 10-20 American football fields in size. No matter how peak your scifi tech the sun doesn’t output more energy.
Is that the size you’re proposing? How will it work aerodynamically? Would it even be counted as a plane? Well technically it would be exactly a plane, as in a plane, not airplane. A huge plane.
We also have flapping flying droids now, we have drones, etc etc erc but you still don’t see people with a set of flapping wings on their back. Why is that?
Because A) the wings would have to be fucking enormous or B they’d have to have an insane rpm.
Chill travel in the air can work. With blimps. Not solar planes.
www.youtube.com/watch?v=vDIojhOkV4w
Dasus@lemmy.world 2 weeks ago
“scifi setting, honey”
Oh fuck off.
As soon as I bring in hard math you start crying “lol I was just joking”, because you never actually thought about the viability of anything you were saying.
You disregard the space required for a greenhouse, and you disregard the physics of flying, proposing a pool.
In a blimp, sure. In a plane? Have you even thought about the amount of lift needed? No ofc you haven’t.
All of that is utterly utterly ridiculous.
It doesn’t really translate into kW and this is a huge oversimplification but as a wild guesstimate, I’d say the an255 needs some 40 000 to 120 000 kW for sustained flight in fair weather.
Even when you’re talking “scifi setting, honey” you’re not gonna change the laws of physics or how much energy the sun is producing, just the tech. So even if you have 100% efficient engines with 100% efficient solar panels, you’d still need at least 40 000 - 150 000 m2 as a surface area, at minimum for fair weather sustained flight. (That’s 7-26 handegg fields for our American friends)
No offense, but I don’t think you’re a professional aviator.
keepthepace@slrpnk.net 2 weeks ago
Let’s be clear, without joking I think you are wrong to dismiss these possibilities and that you have an almost pathological lack of imagination. Yes, science fiction is about techs that do not exist yet are plausible.
You can fit a pool and a greenhouse in 250t. 40 cubic meters of water is 40 tons, 40 cubic meters of soil is basically the same. You have room to spare for the tennis court.
I am not a pro aviator, but I am a pro engineer, on an unrelated field, but I can do my napkins calculations. I mentioned the An-225 to make a point on the physically possible payloads that are possible today, with proven tech. I am not proposing we need those neither do we need the exceptional specs of that exceptional plane.
We scale down speed, it scales down drag (and necessary thrust) quadratically. We assume better efficiency on solar panels, batteries and motors because that’s what we will have in the future. Needing thrust only for sustaining flight and not for take off is another x5 factor on your calculation.
Look at you! You managed to scale down your initial super confident 600 000 m² estimate by an order of magnitude! I am proud of you!
From what I am reading this is about the amount of power an airliner uses at max power on all the engines. You are looking at 1/10th to 1/20th of that for sustained flight, and quadratically less at lower speeds that those typical of those airliners.
Dasus@lemmy.world 2 weeks ago
You’re wrong to assert things without considering the utmost basics. Thats’ why you’re the exact same as those people who imagined those 21st century images in the 19th century.
Yes, it’s a fancy idea. But it’s completely ignoring reality.
There’s much better fantasies to be had of things we can actually build.
“I am a pro engineer”
No, you’re not, ROFL. You haven’t even done rounded up basic maths with basic physics fucking LOL
I didn’t even use a calculator for that shit and I have zero engineering experience or education.
Yeah a regular airbus. Which is why it’s 4-6 times higher for a AN255 in fair weather conditions. And what you’re proposing would need to be several times the size of the AN255.
But no, you’re not wrong. You can’t be mistaken. None of what you think can be unrealistic. It’s just me, the guy doing the math you refused to even consider, who’s utterly wrong and your fantasies of firemen with flapping wings are ofc completely realistic. Oh wait no that’s the 19th century guys, I get you confused you constantly because both of those are equally unrealistic.