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

Re: The age of electric flight is finally upon us

#81

Post by mannykannot » Fri, Jun 21, 2019, 4:11 PM UTC

Tade0 wrote: post #29

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…

Electric motors in their specs usually have an entry specifying a 30s or one minute window during which the motor can operate at around twice the power without damage. In this state the motor cannot maintain temperature, so going beyond that time window will shorten its lifespan or cause damage if continued. Hobbyst EVs often take advantage of this by having a small motor and overloading it when accelerating.

That's probably OK: having to replace a motor would be a small cost compared to that of an off-field forced landing that went badly.

Re: The age of electric flight is finally upon us

#82

Post by marvin » Fri, Jun 21, 2019, 4:13 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.

Oh, electric self launch planes are both viable and available already. It's just a question of manufacturers making them with slightly higher battery capacity, which seems perfectly feasible based on a napkin calculation. Current self-launch electric gliders can climb to cruise altitude and still have >20km of endurance as a contingency for recovery.

If that number was 100km with high reliability, it would almost qualify as a new type of aircraft. You could do cross-country flights that you'd never attempt in an unpowered glider, e.g. above big stretches of high, mountainous terrain. The Norwegian Hardanger plateau comes to mind as an example. Un-landable terrain, 1 km above sea level with a small window for unpowered navigation, national park and absolutely beautiful.

Re: The age of electric flight is finally upon us

#83

Post by hfkajshfaks » Fri, Jun 21, 2019, 4:13 PM UTC

pjc50 wrote: post #45

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.

Rather than mess around with hydrogen, with the proper mandates a lot of jets could switch over to renewable jet fuel. One of the main leaders here is, surprisingly, the US Navy: http://www.altenergy.org/new_energy/seawater-into-jet-fuel.h... directly from seawater and nuclear energy from a ship's reactor, or various other biofuel initiatives.

The Navy does a lot of this. They funded a program to make biofuels from algae.

But don't forget that the stated purpose of funded research is often a lie[0] and this is not necessarily viable outside the lab.

[0] You get other benefits from the research including subsidizing your national industry, training your workforce, doing research you're interested in with a more politically palpable purpose.

Re: The age of electric flight is finally upon us

#84

Post by sokoloff » Fri, Jun 21, 2019, 4:14 PM UTC

taf2 wrote: post #53

semi-extrinsic wrote: post #41

Earlier quoted context omitted.

You can't really go above the Armstrong limit (~60k feet) in a passenger airplane without adding huge complexity in handling the event of cabin pressure loss. https://en.wikipedia.org/wiki/Armstrong_limit

I see that does making exceeding 60k pretty scary. I was from London to Denmark and we had cabin pressure loss I think we were maybe at 30k and dropped pretty fast to 20 if I recall correctly. The sensation that I remember was slow motion and shock from the flight attendant as the masks did not deploy. Later after landing the captain told us during preflight they set the cabin pressure incorrectly such that as we wen…

Hard to puzzle the details there without knowing the aircraft type, but in the pressurized piston plane I fly, there is a main outflow valve used to regulate pressure that's under my (indirect) control and a safety outflow valve that's set just over the rigged max pressure differential (such that it partly dumps the cabin if that pressure is exceeded).

Given that your flight didn't get the "rubber jungle" of deployed masks, the cabin pressure probably never dropped precipitously low, but rather started to oscillate as the safety valve dumped and closed, but never dumped enough to deploy the masks and the crew declared and descended in order to sort things out.

A small number aircraft (non-airliners) are lost each year due to pressurization issues. It's a serious business, even in the high 20s and 30s (of 1000' MSL).

Single pilots are required to continuously wear O2 mask at/above FL350 (35000') and one pilot of a two pilot crew must continuously wear O2 over FL410. Between FL350 and FL410, two pilot crews may rely on quick-donning masks. This is believed to be a commonly violated regulation (in that air crews regularly do not wear the required mask when things are operating smoothly).

Re: The age of electric flight is finally upon us

#85

Post by sokoloff » Fri, Jun 21, 2019, 4:17 PM UTC

taf2 wrote: post #58

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

Yeah I’d imagine most of the reasons sited from this hat wiki article don’t apply to an electric plane. But yeah air density would definitely be an issue but I thought the nasa Helios flight showed 90k to be the upper limit? So figured pushing to bear that altitude could be achieved and possibly beneficial since it would avoid bad weather and reduce drag... I guess was imagining the bulk of the engine power would be…

In my estimation, the shortest practical path to less pollution (at least less net carbon emission) is to use electricity to synthesize jet-fuel. Take yesterday's carbon dioxide, turn it into tomorrow's jet fuel, making the fuel carbon-neutral.

Re: The age of electric flight is finally upon us

#86

Post by marcosdumay » Fri, Jun 21, 2019, 4:17 PM UTC

iambateman wrote: post #10

From the article: conventional fuel for a 100 mile flight costs $400, while electric energy would cost $12. This seems like such a tremendous difference that the market would be in an arms race to make it a reality. Especially considering electric motors have fewer moving parts and so require less maintenance. Oh and it would be so quiet.

> Oh and it would be so quiet.

It would make about as much noise as it makes now. Nearly all the noise of a commercial aircraft is caused by the air being pushed to propel it, not by the engine internals.

(You can reduce noise and increase efficiency by pushing more air at a smaller speed. You do that by having more engines or larger ones. I would expect electrical planes to have more engines, but that's a small secondary effect.)

Re: The age of electric flight is finally upon us

#87

Post by scrose » Fri, Jun 21, 2019, 4:18 PM UTC

aphextron wrote: post #68

Yizahi wrote: post #56

Earlier quoted context omitted.

The answer is - railway ;) . I doubt that small craft (any prop type) will ever be so quick overall - they are aircrafts and require all aircraft related checks and control, safety for passengers, safety from passengers etc. And about price I don't know, maybe it will be slightly cheaper than jets. So you'll have slightly cheaper businessjet prices, which are still astronomical.

Rail is an option in less developed countries, or places like Europe and Japan where the easements have existed for centuries. But building a new high-speed rail line in the US is basically a nonstarter at this point. Electrified aviation will be more than 10x cheaper vs turbine based. Practically the entire cost of aviation is in the engine, with its' associated fuel logistics, maintenance requirements, and pilot tr…

High-capacity / High-speed rail is a non-starter over low-capacity planes with a bunch of low-capacity airfields littering the country? Density is the future and a bunch of small electric planes will not come anywhere close to meeting the demands necessary.

Re: The age of electric flight is finally upon us

#88

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

gambiting wrote: post #39

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.

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.

> hydrogen will diffuse through it in just few weeks

This one is a non-problem. I don't think there is any civilian airport with enough fuel storage for two weeks.

(But the tank weight, well that is a problem.)

Re: The age of electric flight is finally upon us

#89

Post by dTal » Fri, Jun 21, 2019, 4:22 PM UTC

aphextron wrote: post #49

Yizahi wrote: post #37

Simple electric wheel on aircrafts for taxiing (as compared to the electric powered flight) took almost 10 years from first demo tests and it still hasn't entered production on commercial airlines. And that thing is completely possible with modern tech. I highly doubt we will see electric powered aircrafts (bigger than small* experimental crafts) in our lifetimes. Way too much limitations existing today. But it would…

>I highly doubt we will see electric powered aircrafts (bigger than small* experimental crafts) in our lifetimes. The whole point of electrifying flight is that it makes small aircraft economical for airlines. The future of inter-city transport will be light aircraft with less than 20 passengers flying out of of small regional airports. Driving to LAX and waiting in security to get on a huge jet and fly for 90 minute…

I dunno... cheap flights exist now. It's the security theater that ruins flying. Why would electric change that?

Re: The age of electric flight is finally upon us

#90

Post by sokoloff » Fri, Jun 21, 2019, 4:24 PM UTC

ac29 wrote: post #66

bdamm wrote: post #46

Earlier quoted context omitted.

Electric wheel propulsion on aircraft seems like an entirely unnecessary feature. Airplanes have no difficulty using their primary form of propulsion - moving air - to move on the ground, and it takes very little energy to do it compared to the energy required to move through the air while off the ground.

No, that's exactly backwards -- jet engines are far less efficient at low speed than at cruise speed. Various numbers I found say 100-300 kg of fuel used taxiing for single aisle planes like 737 [0][1] all the way up to two tons of fuel for large aircraft like 747 at large airports like JFK [0]. This can be extremely relevant for shorter flights: "[taxiing] aircraft fuel burn which is estimated to be as high as 27% o…

The taxi fuel is not primarily used for motivation of the airplane around the airfield, but just from idling the engines. (It's about minutes of ground operation more than miles of ground operation.)

Electric drive wheels don't eliminate that unless you don't start the engines until near the hold short line (in which case, you don't have air conditioning or electric power, meaning you end up running the APU [itself a small jet engine] to provide that power).