The age of electric flight is finally upon us • Hacker News Board

Re: The age of electric flight is finally upon us

#71

Post by gnode » Fri, Jun 21, 2019, 3:53 PM UTC

ginko wrote: post #2

I'm surprized hydrogen fueled flight isn't looked into more. Hydrogen can be produced using electrolysis and it's packs significantly more energy per weight even than kerosene. The main drawback is the low density which would require larger fuselages, but that should be offset by the significantly lower weight.

It would be much harder to engineer: you'd need a hefty tank; cryogenic fuel handling to increase density and lower tank weight.

Safety is critical on aircraft. Hydrogen is difficult to contain, and has very low viscosity due to its small molecules. It burns with an almost invisible yet very hot ultraviolet flame. It easily mixes with air to form an explosive mixture and has a very low minimum ignition energy (about a tenth of gasoline).

Combustion of hydrogen in a heat engine for propulsion would be very inefficient compared to a battery electric. Fuel cells are in between, at about 40-60% efficiency, but have a substantial weight cost.

Re: The age of electric flight is finally upon us

#72

Post by base698 » Fri, Jun 21, 2019, 3:54 PM UTC

whamlastxmas wrote: post #57

base698 wrote: post #40

Earlier quoted context omitted.

Engines don't stall, planes do. Plane stalls are about aerodynamics, and nothing to do with the engine. Current engine designs operate poorly at higher altitudes for a number of reasons: less air density meaning less oxygen to burn and less air to push against. Turbine engines can flame out, which maybe that's what you were referring: https://en.m.wikipedia.org/wiki/Flameout

Stalling is a term also used with engines, and it's pretty clear he's talking about engines not working at altitude so "stall" is probably the correct term

Only with layman and in the media when incorrectly describing an aerodynamic stall and conflating two.

Re: The age of electric flight is finally upon us

#73

Post by gnode » Fri, Jun 21, 2019, 3:56 PM UTC

falcolas wrote: post #26

This plane wouldn’t even be capable of getting me to the closest aircraft hub at its maximum range, let alone with a safety margin (I live an hour and a half, by jet, from Denver). Not to mention it will be slow and badly impacted by storms (since it has an operating ceiling of 10,000 ft).

There are flights shorter than 650mi.

Re: The age of electric flight is finally upon us

#74

Post by NeedMoreTea » Fri, Jun 21, 2019, 3:56 PM UTC

gingabriska wrote: post #70

I wonder if it can be possible to tap into the human body's energy store and use that to make flights over short distance.

Average human at rest puts out about 100w of heat. That's probably not enough to keep the cabin warm let alone power the aircraft.

Burning human fat stores seems a mite dystopian. ;)

Edit: Human at rest. I imagine Ryanair might be keen on pedals for everyone, but I can't see that being popular with the holidaymakers.

Re: The age of electric flight is finally upon us

#75

Post by dTal » Fri, Jun 21, 2019, 3:59 PM UTC

taf2 wrote: post #22

I wonder if with electric we can fly higher like much higher maybe 80k to 90k since we don’t have to worry about the engine stalling. Could this also make the flight times comparable or faster? For sure less turbulence. As someone who lives on a flight path I’m eager for the change in noise pollution too- though I’m worried the transition will take decades...

"Engines stalling" is not really the factor that limits altitude. The problem is that the thinner the air, the faster you have to go to stay up. Eventually the required speed enters the transsonic region, and you start needing way more power. There comes a point where your engines just don't have the oomph to push you fast enough to stay up. If you want to go higher, there are basically two ways - more oomph, and better wing loading (i.e. less weight or bigger wings.)

Electric aviation has many merits, but being a lightweight source of plentiful oomph is not currently among them.

Re: The age of electric flight is finally upon us

#76

Post by mannykannot » Fri, Jun 21, 2019, 4:00 PM UTC

maxxxxx wrote: post #43

marvin wrote: post #20

I fly gliders. Absolutely can't wait until my local club finally decides to get an electric single-seat self-launching glider, preferably with enough endurance to do some additional tens of kilometers after the launch, in order to avoid landing out if the weather dies out. It's a gamechanger with regards to both costs and convenience. No towplane, towplane pilot, no outlandings.

How about a battery that can glide by itself? You attach a big battery for the launch and once you are up you disconnect and it glides back to the airfield. That should be possible today technically. Not sure how safety would work.

What you are thinking of is not very different than an aerotow from an electric airplane.

Re: The age of electric flight is finally upon us

#77

Post by hfkajshfaks » Fri, Jun 21, 2019, 4:06 PM UTC

afiori wrote: post #4

wlesieutre wrote: post #3

Earlier quoted context omitted.

To store enough hydrogen to be useful you probably need it in liquid form like rockets use. Hydrogen is energy dense by mass, but not by how much space it takes up compared to liquid fuels. Otherwise you'll have a really giant bag of gaseous hydrogen which does help your bouyancy, but then you've made an airship instead of a plane and a spark accidentally turns it into the Hindenburg.

Is it so much less energy dense per liter to offset the gain in weight? In a plane energy per weight is rather important afterall

Its so bad that only the largest space rockets use liquid H2. All the others use kerosene or the like.

Either way, the Soviets tried gaseous fuels in the 80s - See Tu-155. They ran on liquid H2, CNG.

If I recall, the weight increase didn't make it practical. On the other hand it was a turbine powered plane. It might work out with fuel cells (although you'd need a big and heavy compressor to run it)

Re: The age of electric flight is finally upon us

#78

Post by maxxxxx » Fri, Jun 21, 2019, 4:07 PM UTC

mannykannot wrote: post #76

maxxxxx wrote: post #43

Earlier quoted context omitted.

How about a battery that can glide by itself? You attach a big battery for the launch and once you are up you disconnect and it glides back to the airfield. That should be possible today technically. Not sure how safety would work.

What you are thinking of is not very different than an aerotow from an electric airplane.

I was just thinking about something autonomous. Basically a battery with wings. That way you don't need a plane with pilot.

Re: The age of electric flight is finally upon us

#79

Post by marcosdumay » Fri, Jun 21, 2019, 4:08 PM UTC

mannykannot wrote: post #21

A battery fire is a scary prospect unless the fire can be effectively contained and the hot gases vented (I don't suppose extinguishing one is likely to be an option.) There has been at least one crash involving fire, though I have not been able to find out if it was a propulsion battery fire. [1] In Eviation's Alice, the failure or shutdown of one of the wingtip's motors would require the shutdown of the other, on a…

Why so few motors? Electric motors have low cost and low maintenance, so I would expect electrical planes to have many of them.

Overpowering the motor during the entire take-off would bring a high risk of having it fail too. But overpowering it to overcome the most common obstacles is perfectly viable in an emergency.

Anyway, about fires, they are a reasonably easy problem to deal with. Fires on liquid are much more dangerous than fires on solid, and batteries have a lower tendency of exploding and creating fumes than the gasoline that propels smaller planes. I imagine the largest problem of a fire would be on losing power. You can mitigate this by creating many independent battery banks, but this adds weight.

Re: The age of electric flight is finally upon us

#80

Post by hfkajshfaks » Fri, Jun 21, 2019, 4:09 PM UTC

ggreer wrote: post #60

gambiting wrote: post #39

Earlier quoted context omitted.

1kg of kerosone can be kept in a plastic tank that weighs nothing. 1kg of hydrogen has to be kept in a pressurized, pure-lead 70kg bottle, and even then hydrogen will diffuse through it in just few weeks. So to take 1kg of hydrogen with you you're taking a lot of weight in the tanks too.

Some rockets use hydrogen and their pressure vessels aren't so heavy as to keep them stuck on the ground. You only need to contain the hydrogen for hours, not weeks.

Few though, and only the largest ones and they have incredibly complicated and long (and dangerous - imagine having to deal with refueling a cyrogenic liquid after every leg) fueling.

Most rockets use hydrocarbons for this very reason.