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Comment by state_less | Hacker News Reader

Could we rethink short haul flights somewhat? What if instead of a 400 mph aircraft, we had a 200 mph aircraft with high aspect ratio wings? In other words try to make a more efficient aircraft to compensate for the lack of energy aboard.

I suppose people want to get there in a hurry, but a flight that goes from 30 min to 1hr or 1 hr to 2hr might not be too bad.

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Maybe, though you probably still want to fly above the weather, which puts a lower bound on your power requirements. To get above the weather, the energy needed is mgh plus whatever kinetic energy your aircraft still has (i.e. it's velocity); if you trade that for speed, you won't have a 200mph aircraft anymore.

Customers are definitely willing to trade time for cheaper flight (Boeing made this gamble and won in the last airframe generation), but there are certain practicalities that need to be met.

If you mean the airlines when you say customers, I would say you are correct. Planes are flying slower these days because it saves fuel and one can offer a lower fare. If you mean the people who fly, when you say customers, I would say that is incorrect. People have no idea that flights can have different lengths and the only way to search for fares is by destination, number of stops, and price. It would be great if airline ticket buyers had search parameters for leg room and flight time so that those very important parameters could be selected for. Otherwise evolution will continue to force slow flights and smaller seats.

I always look at flight time since I'm flying with kids.

You're right, this is an important clarification. Airlines like smaller airframes that are easy to fill, have fewer engines, and they're okay with breaking journeys up into multiple smaller hops. Passengers don't necessarily have a choice.

I agree getting up over the weather would be a good thing. And as long as we're dreaming, may as well dream big. Maybe we can do something like they did with jato bottles on the c-130 at takeoff.

Attach some batteries with wings to the aircraft that you release after you get up to altitude. These days you can put an autopilot on the batteries and fly them back to the airport for recharging. You'd save some weight once at altitude and could get a 'free' lift up to altitude. Sort of like how a sailplane can get a tow. Maybe you could take them up to 30-40k ft at a good speed and let them trade some height for speed along their path to the destination.

Clearly there is a cost for the added complexity, but it might be worth it given the cheap computation and improving autopilot software.

That sounds absolutely terrifying. Iirc, the first rule of building rockets is, always assume it will explode - not even starting on all the stress it would put on the frame.

Rather than JATO bottles, a better option may be to have an 'electric runway', that allows you to draw ground-power while accelerating down the runway, which might save a non-trivial amount of battery capacity, and may allow you to run your motors at a higher power output than the batteries would normally allow. As an added bonus, the runway could be shorter.

Slowing down does not make an aircraft more fuel efficient. Best efficiency, as in fuel per passenger-mile, occurs with large aircraft at the very high altitude where air resistance is least. And to fly up there you need to move quickly. An a380, almost supersonic at mach 0.85, is more fuel efficient than Cessna at down low at mach 0.2. Even at lower altitudes, there is little advantage in flying slower. You just end up spending more time/energy keeping yourself up rather than moving forwards. A high-lift wing, great for maximizing time aloft, becomes a big draggy airbrake when you want to actually go somewhere.

In the extreme, the most efficient place to fly is in the most cold and dry air. That occurs at the tropopause, which is generally between 35,000 and 50,000 feet (-60*C). You don't get to play around at that altitude without a large complex aircraft.

https://www.windows2universe.org/earth/Atmosphere/tropospher...

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