91–97 of 97 posts
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> But x2 fuel consumption is a hard lower bound. Can't you gain a bit of that back by flying higher than a subsonic design could?
Lift and drag are proportional. You fly higher you need to go faster as to get the same lift, and you'll encounter the same drag.
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Methane is a more than viable alternative and there are a few others. Of course for both we'd need infrastructure to generate it from renewable energy (as opposed to extracting using or extracting hydrogen from natural gas). In terms of energy density, methane is good enough for space flight. E.g. the spaceX raptor engines burn methane. The long term plan for SpaceX is to use renewable energy to generate methane; whi…
> Methane is a more than viable alternative Is it? https://www.sightline.org/2019/02/12/methane-climate-change-... https://www.sciencedaily.com/releases/2019/12/191216140715.h... https://www.livescience.com/52715-natural-gas-not-as-clean-a... We're already coming to the conclusion that electric cars aren't that clean so when I hear about carbon neutral supersonic planes I kind of feel like I'm in a bad dream.
Also, electric cars are way cleaner than ICE vehicles over their life-time. I don't think there's any dispute about that.
In my opinion it is disingenuous to call any supersonic aircraft sustainable. Independently of any clever aerodynamic design to moderate the drag coefficient, aerodynamic drag always increases like the velocity squared. Doubling the speed will mean applying 4x the force for 1/2 the time, so all propulsive efficiencies being equal, you will expend twice the fuel to go the same distance - at an absolute minimum. In rea…
I flown many long haul flights. The first time I heard Musk propose using rockets for international travel I thought it was insane. I still do. But if they are accident free for the next 10 years; would I then? Probably - if they could manage to keep my trip under ~3Gs.
Yeah, I wonder, would a suborbital ballistic trajectory save fuel compared to chugging along in the atmosphere? If this were to become common, would need some thinking how to distinguish this from a ballistic missile attack, though.
In practice it'd be a nightmare to separate traffic. Additionally it'd increase the pilot workload significantly considering the cruise phase of flight is typically the "ahh, I'll order some coffee from back" time as the primary duties then are (a) monitoring aircraft state (i.e., scanning the gages) and, (b) changing the radio frequency each time the flight moves into a new sector and checking in with ATC.
[me: aircraft dispatcher for a US carrier in a previous life]
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The climate does not care how many people caused the co2 emissions.
The climate system itself doesn't, but the total carbon budget has to be allocated to and split between 7 billion people one way or another. What is a fair split? Of course, if you want to keep flying at 800 km/h around the globe AND get power for your home's computers and 4k TV, you will have to advocate for cutting electricity AND blocking air transport of some other people until their coal plants are powered with…
If you like capitalism and fear "socialism" (which I assume anyone needling people about "fairness" this way does) then that is what allocates resources given constraints of the real world. Accepting that one of the constraints is a limitation on burning fossil fuels for the entire globe does not require changes to society beyond normal responses to price signals. Nor decisions by some authority, other than the overall cap.
Figuring out who gives up what from a central command is both impossible and unnecessary, so it shouldn't be part of the discussion. What "socialists" even advocate Soviet style central planning anymore?
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Practical aerogel production makes a huge difference in insulation effectiveness. Lifting body designs provide plenty of interior room for tankage. Spherical/cylindrical tankage is needed only to contain high pressure, but we don't need to contain pressure. The greater energy density of hydrogen means much less fuel burnt at altitude, vs. diesel. Water vapor is a grrenhouse gas, but condensed into clouds they reflect…
> Spherical/cylindrical tankage is needed only to contain high pressure, but we don't need to contain pressure. You want the minimum surface area to volume, to minimize heat losses (and minimize the surface area that has to be insulated when weight matters such as in an aircraft). Spherical being the optimum, but obviously unpractical. If you look at tanks in current aircraft, typically in wings, they have huge surfa…
The NOx contribution argues for use of onboard LOX, which would then enable a much higher flight deck, increasing efficiency further on long-haul routes.
I wonder what mechanism transports water vapor out of the upper atmosphere.
Availability of aerogels radically alters the equations that have dictated tank shape for liquified gases.