19 ms·
For those curious about the physics of these aircraft, here's an analysis I did of the same concept. The goal is to determine the smallest aircraft configuratio
by gusgordon 5y ago
For those curious about the physics of these aircraft, here's an analysis I did of the same concept. The goal is to determine the smallest aircraft configuration that can indefinitely sustain flight: https://github.com/gusgordon/atmospheric_satellite#readme https://github.com/gusgordon/atmospheric_satellite#readme
- onychomys 5y agoIs there a reason you optimized the amount of starting energy in the battery? I know basically nothing about how solar power works, but surely you'd just fill the battery up to 100% with an extension cord on the ground before launching it?
- mkr-hn 5y agoBatteries are heavier when fully charged. Takeoff weight matters. It's not much heavier, but it might be enough to affect things at this scale. edit: remember the context. This is about an abstract optimization to find the minimum viable aircraft.
- luma 5y agoI can't tell if you're being serious. You are technically correct, but also incredibly wrong in suggesting that the increased weight would be substantial enough to impact anything measurable. Depending on the size and capacity of the cell, you might see a difference due to general relativity on the order of nanograms. see: https://physics.stackexchange.com/questions/34421/does-the-mass-of-a-battery-change-when-charged-discharged https://physics.stackexchange.com/questions/34421/does-the-m...
- p1mrx 5y agoA nanogram saved is a nanogram earned.
- rrss 5y agowhat kind of batteries are meaningfully heavier when charged? are you just talking about like E/c^2?
- jermaustin1 5y agoA water/gravity battery comes to mind. Definitely not the answer you are looking for, but an answer none the less.
- enchiridion 5y agoDepends on your definitions. Is the water pumped considered part of the battery before it’s elevated?
- jermaustin1 5y agoThe pumping of the water would be "charging" the barrel of water, I guess.
- einpoklum 5y agoI'm sure this will work great for powering an aircraft, too. You could just let it all hang from an anchor at the highest point in the battery :-P
- luma 5y agoGas tanks :D
- spijdar 5y agoI can't tell if this is satire or not, but taken in good faith, how? A fully charged battery would necessarily have more mass than a fully depleted battery, but the difference should be so tiny as to be immeasurable. Or am I wrong? We're essentially talking about the sum weight of a bunch of electrons, which are extremely light. There's no other exchange of matter going on when charging/discharging a battery, just the creation/destruction of chemical bonds, and associated movement of electrons.
- deleted 5y ago[deleted]
- btilly 5y agoA battery doesn't have a static charge. When it discharges, electrons move from one side to the other, then back through the batter, and you modify which atoms have which elections. But it continues to have no static charge. However it has less potential energy. And therefore you change mass by the mass associated with that potential energy.
- jcims 5y agoMaybe it helps surface how much charge is required to climb to altitude vs how much charge is required to sustain it? This may also help surface how much of a buffer you may have in takeoff time in order to survive night. E.g. if you require 100% charge then it's likely you have to take off at a fairly specific time of day.
- gusgordon 5y agoGood question. One requirement for the aircraft in this optimization is that they must have more energy in the battery than they did 24 hours prior. If the aircraft started at full energy, they wouldn't ever be able to satisfy this requirement, so that's why it's an independent variable. For example, an aircraft could "start" at 50% battery state of charge, then charge to 95% over the course of the day, then come back 24 hours later at 51%, and that would be valid. There are other ways around this, but this is what I came up with at the time. This is similar to why the starting altitude is allowed to float. The gravitational potential energy of the aircraft can be used as another "battery", but the aircraft is only a valid solution if it's not losing altitude over the course of 24 hours.
- pault 5y agoThe battery is too heavy if it's fully charged.
- dredmorbius 5y agoThere are actually electrochemical cells which do change mass as they charge and discharge, metal-air batteries. In these, oxygen from the air is the cathode used to reduce the metal anode. But mass gain goes the opposite direction: the batteries are actually heaviest when discharged. Various metals can be used. Iron is cheap, whilst aluminium-air cells actually offer some of the best performance in kWh/kg of available materials, exceeding that of LiON cells. https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemical_cell https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemi...
- algo_trader 5y agonice analysis Is it feasible to operate these at lower altitudes? e.g. can we have solar/air drones posted every 100 miles of interstate highway?!
- gusgordon 5y agoYes it's a lot easier at lower altitudes since you can get more lift, but you might run into some extra regulatory issues with that :)
- zucker42 5y ago> e.g. can we have solar/air drones posted every 100 miles of interstate highway?! What's the usefulness of this or was it just a random example?
- krisrm 5y agoAs someone who lives somewhere with photo radar, I assume photo radar. Nobody likes photo radar.