Comment by MayeulC | Hacker News Reader

Comment by MayeulC | Hacker News Reader

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Thanks for the figures. I'd guess that most of that power is used to combat drag, which can be lowered by going slower. The rest is probably used to combat gravity, especially during ascent, which should be improved by lowering the amount of fuel.

A small battery, and/or a ground station at the airport could provide a bit of extra power during ascent, and the battery recharged during flight. I guess the extra power shouldn't amount to a lot more than 10kW...

Depending on the wavelength, it should be fairly easy to have the plane act as a Faraday cage to shield its passengers. I guess the geometry could be slightly tweaked as well to make a larger surface area, possibly using trailing metallic wires to improve the energy collection area at a minimal cost (I get that cylindrical wires are the worst aerodynamic shape, but it should be less of a problem behind the wing).

If the wavelength is low enough, a coarse mesh could collect power quite efficiently, but you'd have to worry a lot more about radio interference.

Drag and lift are related. Wings work by literally displacing lots of air towards the ground.

If you go slower, you need bigger wings (also no one really wants longer, slower flights in cramped airplane cabins).

Unless it's cargo. Cheaper than "normal air" / faster than sea shipping is a reasonable niche.

I don't know if it's a big enough niche. There are quite a lot of costs to air cargo aside from marginal fuel efficiency and somehow developing novel cargo-specific aircraft has to translate into both increased profits for Boeing/Airbus and decreased costs to shippers. Keeping in mind that these slower craft would be unsuitable for some of the most profitable uses of air freight today. I'm not sure it makes sense.

I guess that's part of the reason we still see propeller planes around (often with the military).

Answering to a cousin comment, buses and trains can't compete when you need to cross water :)

Well, there are boats. Passenger sailing as a means of travel is not especially popular these days.

If slower meant cheaper tickets I can guarantee that people would want to use it.

The lower cost, slower mode niche would have to compete with buses and trains, with the added penalty of TSA security theater. I'm not saying you're wrong, but I'm still not sure the financials work out.

https://en.wikipedia.org/wiki/Lift-to-drag_ratio#Examples_of... says the jumbojet, at cruising altitude, has 17 times as much lift as drag.

So it seems drag isn’t taking most of that power.

Also, “I guess the extra power (for ascent) shouldn't amount to a lot more than 10kW” seems unlikely to me. It’s too low compared to the 7MW used at cruise height.

Also, if my math is correct, 1kWh lifts one kilogram about 360,000 meters, or 36,000kg (less than the weight of an empty 737) by 10 meters. So, 10kW would lift the plane by only 100 meters in an hour.

I love posts like this that remind me that I'm on HN and that HN can solve world problems based on assumptions.

Take a scenario. Give it best-case figures. See if it works. If it doesn't, then it's impossible. If it misses the mark by just a bit, it's a remote possibility. If it works, try the worst case figures and the average case ones. Of course, you can also start with the worst case ones and show that it works.

I like to approach problems this way. Plus, one can have dreams, can't they?

Once you've shown it can theoretically work, it's time to consider the side effects: best/worst. With the above, someone now controls a multi-gigawat orbiting power source.

Upsides: well, it can power useful stuff just about anywhere on (two third of) earth when there's nothing else to do. That would be really useful to compensate renewables, or other grid fluctuations. One could even imagine making airplanes slower of faster depending on demand.

Downsides: well, somebody really does control that :)

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