Wikipedia:Reference desk/Archives/Science/2019 July 26

= July 26 =

How will aeroplanes run without fuel in future?
I read many articles that after few years we will have no fossil fuel.

https://www.ecotricity.co.uk/our-green-energy/energy-independence/the-end-of-fossil-fuels

There can be electric cars, motorcycles, bus running on battery.

I don't think plane can run on battery.

Will Aviation fuel last forever?

https://en.wikipedia.org/wiki/Aviation_fuel — Preceding unsigned comment added by 2402:3a80:aba:b5ba:b02b:8bf9:d754:abec (talk)


 * Option A) Aviation biofuel, or otherwise synthetic aviation fuel. In principle jet fuel could be synthesized without ever involving fossil fuel ingredients, although this could get expensive. Option B) Really good batteries. There is such a thing as electric aircraft, but these do not get to commercial passenger liner sizes due to the poor energy density of electric storage systems. In theory the lithium-air battery could do the job, or hydrogen fuel cells as with hydrogen-powered aircraft. Someguy1221 (talk) 04:29, 26 July 2019 (UTC)


 * And note that conventional jet fuel might last longer than you would think, based on current petroleum usage rates. That's because, as it gets rarer, the price will go up, and this will make electric cars a more practical alternative to gasoline, and other materials and products more practical alternatives to petroleum-based materials, like plastic, and products, like petroleum jelly. Thus, the petroleum that would have been used in these ways will now be used in jets, but the cost to jet plane passengers will still go up, so there will be fewer passengers and flights, saving petroleum even more. Also, these high prices will make it worthwhile to exploit petroleum reserves that are too expensive to access at current prices. SinisterLefty (talk) 05:01, 26 July 2019 (UTC)


 * Indeed, I feel like virtually every declaration that "peak _____ is imminent, we're all doomed!" winds up being no big deal. Usually because the belief that the peak is approaching simply increases the incentive to find an alternative, which can even be cheaper than the original. See Category:Peak resource production, especially peak copper, where the technology to extract and purify copper has improved so much that the overall cost has actually gone down over time despite the "easy" sources having run out. Basically, large industries usually aren't stupid enough to actually use all of an essential resource without planning ahead. Someguy1221 (talk) 06:21, 26 July 2019 (UTC)
 * What about peak unfarmed farmable land? They aren't making any more of it and deforestation screws up the ecology. Sagittarian Milky Way (talk) 03:53, 27 July 2019 (UTC)


 * Yes, in the US currently we have a shortage of helium, which means we aren't using it for party balloons anymore, but we still have it available for more important things. SinisterLefty (talk) 06:31, 26 July 2019 (UTC)
 * Why didn't they start cutting it with hydrogen a long time ago? Sagittarian Milky Way (talk) 03:53, 27 July 2019 (UTC)
 * You actually can't add that much hydrogen to helium before the mixture becomes flammable, which was the whole point of stopping the use of hydrogen in the first place. Someguy1221 (talk) 04:09, 27 July 2019 (UTC)
 * Before things get dramatically catastrophically, they'll simply become gradually unpleasant. For example, in many parts of the world, airlines charge a "fuel surcharge."  What this means is that when you buy an airline ticket, you pay a ticket-price; and then later, at the time you fly, you pay an additional fee to account for how much more expensive the jet fuel has become since you booked your reservation.  Here's an example of those fees for ANA.  By making the passengers pay for the gas, some airlines move that variable expense out of their bottom line, and in to yours.  Some nations actually require this policy, as a matter of local law.  Here's IATA's Jet Fuel Price Monitor, from their economics department, which also has some links to some very practical economic theory research.
 * Over time, aviation fuel will become more expensive, and this may eventually manifest as symptom that's actually visible to the end-user: the price of air travel will increase.
 * As the costs gradually increase, other strategies will start to prevail: one of my favorite math problems is the "tanker" question - explained in this fantastic RAND report, Tankering Fuel on U.S. Air Force Transport Aircraft. Essentially, this is a question of the mathematical optimization at the intersection between economics and physics: when fuel is more expensive at Point B, compared to Point A, at what specific price-differential does it actually make more sense to buy extra fuel at Point A and carry it around with you until you get to Point B - given that carrying fuel is inefficient, and therefore causes the airplane to use extra fuel?  And this calculus becomes even more complicated when we add extra confounding variables, like taxes, incentives, and statistical or engineering questions about safety and risk.  If you're not an expert in mathematical optimization, consider undertaking a solid theoretical and practical study of this extremely-lucrative-career-path!  According to government statistics, the best operations folks earn almost as much as the CEOs who run the company and the engineers who actually build the airplanes!  Invest early in those K-12 math-skills, right?
 * Over the very long term, aviation fuel - in its present form - will become more difficult to source. This will change the types of airplanes that companies and governments build and operate.  The routes and services that commercial airlines will adopt may evolve, as well: presently, the big debate is whether an airline is more efficient - and therefore more profitable - when it uses the spoke-and-hub or the point-to-point service model.  See, this is a question about fuel: if you're flying from Austin to San Jose, it takes a very different amount of fuel if your airline sends you direct on a Boeing 737, or if it sends you via Dallas using an Embraer regional jet, and then connects you on an Airbus 319.  If you're in to the business of making money by betting on which of these options uses less total fuel, you probably want to do some comparison between, say, the monotypical fleet of Hypothetical Corporation A and the diverse fleet of Hypothetical Corporation B (... just to throw out a few examples).  The hard part is, airlines don't buy one single aircraft that is the maximally-efficient for one single passenger.  They have to use statistics to guess which options will be more efficient on the average, over the entire lifetime of the fleet.
 * Because, you see, while passengers buy seats, airlines buy airplanes, and this means that they're using their dollars to tell the people who build airplanes which types of airplanes they want. If you read aviation news, or if you are a passenger who values safe and efficient air travel, you might find this tight economic coupling of recent concern.
 * In the extraordinarily long time-horizon, as petroleum-based fossil fuels become more problematic, we're going to see a few more severe trends: first, it is probable that total air travel will reduce. Secondly, the air travel that does take place will become more expensive.  And as a third effect, a few "not-interesting" technologies will gradually become "more interesting."  For example, one major airline actively advertises that it uses some mixture of bio-fuels - beginning in 2016, it even used those alternative fuels on revenue flights (passenger-carrying operations, as opposed to flight-research testing).  This is kind of neat.
 * And if you're thinking about very far future, the hypothetical "electric airplane" makes an appearance from time to time - for example, Boeing has sponsored a small electric aircraft research project and there are a bunch of Silicon-Valley-style start-ups like the ever-evolving "Kittyhawk Aero" project. I think most aerospace engineers will tell you that physics is not in favor of these approaches: even though electric motors are pretty great, electric batteries simply aren't as "good" as jet-A or avgas, meaning that electric batteries are heavier, more expensive, and less powerful than an equal amount of jet-fuel.  But if there are some serious engineering breakthroughs - or if we stop playing around with batteries and decide, as a society, that we want to start putting nuclear reactors to power the electric motors - then we have a path to a sustainable aviation future.
 * So, in response to the original question, the answers really depend on your time horizon. In the next 24 months, not much is going to change; but in the next 60 to 96 months, you might notice that your commercial airline flights and fleets look a little bit different than they did in, say, 2005 or 1995 - if you're the kind of nerd who notices that stuff.  I mean, by golly does modern air-travel look different than it did in 1963 ... or 1949!  And if we look out to 2045 or 2055, and beyond, there could be some serious disruptions to the status-quo - but it's really really hard to predict that far away.  Besides, fuel is only one of the many factors that are going to affect the world's aviation economy over the thirty year time horizon.
 * Nimur (talk) 14:57, 26 July 2019 (UTC)


 * In the spirit of full disclosure, this entire posting is essentially a memorialization of a recent conversation I had while on a nineteen hour international flight - now there's a route that's unique to this particular century! - ...and the fellow sitting next to me was a professional aviation operations consultant and former executive at a major American air transport corporation... so, in the spirit of avoiding independent research, it is my hope that I have provided sufficient citations. The Pacific Ocean is quite extensive - and that provides a lot of time to ramble on about airplanes...! Nimur (talk) 15:44, 26 July 2019 (UTC)


 * Nuclear-powered aircraft ? Now that's an idea. So the next time one crashes we get to evacuate the entire city while the lucky clean-up crew scrapes the top layer of contaminated soil off the entire area. SinisterLefty (talk) 17:01, 26 July 2019 (UTC)


 * I do not raise the premise in jest: we have an article on the nuclear-powered aircraft. It has been actively researched, and although the concept has many advantages, it also has many very serious drawbacks.  At the present time, those "very serious drawbacks" are so very serious that no major government, corporation, or reputable researcher actually recommends that we switch to nuclear-power at this time - not even for research purposes.  On the other hand, the drawbacks are well-understood and well-characterized, and perhaps some time in the future, the situation might change.  I would propose that every time you see a respected research institution that proposes an electric airplane, those very-well-educated aerospace engineers know that they need something better than today's battery - but rather than expending their effort trying to solve that "known" problem, they are instead focusing on how we might build an aircraft if we knew that some time in the future, the source of the electricity was no longer a hard problem, banking on a "hypothetical" future solution.  Somebody is paying for this research, and whoever that is would be pretty well-situated to evaluate the fundamental limits imposed by physics.  Nimur (talk) 17:58, 26 July 2019 (UTC)


 * Let's see, to make it safe, we would need to move the nuclear reactor off the airplane to an underground bunker, and distribute it to the planes in flight. To do so, we would need them to be quite close to the ground, and we could provide that power via a maglev system. The wings, tail, and landing gear would be superfluous, so we would remove those, leaving just the fuselage. And now we have a bullet train ! (For routes over oceans, etc., we would stick with conventional airplanes.) SinisterLefty (talk) 18:37, 26 July 2019 (UTC)


 * In case people missed it, United is hardly the only airline who uses biofuel. The earlier linked article Aviation biofuel has a whole list. As with many wikipedia articles, it's a mix bag. Some of the stuff is old, e.g. it talks about targets for 2015 and stuff achievable by 2020. Still there are the two tables. Probably the biggest flaw with the table is that although it mentions the type of biofuel, it doesn't always mention the blend ratio although some are up to 50%. (From what I can tell, 100% biofuel has only been used in test flights, at least for large aircraft, see e.g. [//www.king5.com/article/tech/science/aerospace/historic-flight-commercial-jet-flies-on-100-percent-biofuel/281-550970736].) The article also mentions stuff like airports which can regularly provide biofuels. Nil Einne (talk) 17:51, 26 July 2019 (UTC)


 * I don't think plane can run on battery - see electric aircraft. Gandalf61 (talk) 16:20, 26 July 2019 (UTC)
 * Well, I attended the arrival of Solar Impulse 2 when it arrived to California in 2016... it was scheduled to land at sunset, but due to winds, it actually touched down long after the sun, in the wee hours of the morning. I can personally attest that I saw an electric airplane flying on battery for many hours.
 * It is not so much a question of whether any aircraft could fly on battery. We know that it is possible.
 * The issue is whether it would be economically feasible to use this type of unique vehicle to meet the needs of commercial transportation. It seems improbable that we can ever build an airline-transport style aircraft - one that meets the design-envelope for safety, speed, and mass - that runs entirely on battery.  This is because of the poor energy density of a battery, which probably will not change unless we learn something extraordinarily fundamentally new about the laws of physics and chemistry.
 * Nimur (talk) 17:55, 26 July 2019 (UTC)


 * I know that hydrogen-powered aircraft have been linked above, but see Hydrogen-powered aircraft proposes carbon-free future for aviation. Only four passengers, but that's three more than the Wright Brothers managed. Alansplodge (talk) 12:54, 27 July 2019 (UTC)
 * And of course there is the Solid Oxide Fuel Cell, like the one described in this NASA research report into commercial feasibility (for the APU); this contraption almost became a commercial option on select models of certain airliners. As of this decade, the power source was considered unsuitable for the APU, let alone for the primary powerplant; but it's still important that we research our options.  Nimur (talk) 14:26, 27 July 2019 (UTC)

Hmc coating
Is there a way you can tell whether glasses lenses have HMC coating applied? 82.132.222.31 (talk) 09:34, 26 July 2019 (UTC)
 * See if you can see a reflected bright light from the lens surface. With a coating, the reflection will be much dimmer and probably coloured, compared to a plain piece of glass. Graeme Bartlett (talk) 10:35, 26 July 2019 (UTC)
 * An illustration of HMC (Hard Multi-Coating) anti-glare lens treatment. DroneB (talk) 14:30, 26 July 2019 (UTC)

Modern car safety systems
Why is it that many modern car safety systems seem to be too sensitive? Technology such as front collision prevention etc are known to give many false positives. 90.192.122.54 (talk) 18:06, 26 July 2019 (UTC)


 * Because false positives are much less dangerous than false negatives, so they tweak it in that direction. There could also be overlap, where the same force that would be a serious accident to somebody not wearing a seat belt may not be at all serious to somebody with one on. SinisterLefty (talk) 18:23, 26 July 2019 (UTC)
 * Anecdotally, my 2017 (I think) U.S. Honda Accord's collision avoidance system never went off at all until I went into the settings and cranked it up to maximum sensitivity. (It has "stages", with the first stage being just a beep and visual warning on the dashboard display.) Even with that, it doesn't go off until you get fairly close to a slowing or stopped vehicle. When I observe how lots of people drive, going 80 mph on the freeway while 5 feet behind another vehicle, I imagine the car manufacturers hear lots of complaints about the collision alarm going off all the time for "no reason". --47.146.63.87 (talk) 00:03, 27 July 2019 (UTC)