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

Re: The age of electric flight is finally upon us

#101

Post by VBprogrammer » Fri, Jun 21, 2019, 5:12 PM UTC

sokoloff wrote: post #84

taf2 wrote: post #53

Earlier quoted context omitted.

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…

> This is believed to be a commonly violated regulation

I believe that is an understatement. I've heard it described as the most commonly violated rule in aviation. There are a number of youtube pilots who commonly violate this rule seemingly without too much worry.

Re: The age of electric flight is finally upon us

#102

Post by Robotbeat » Fri, Jun 21, 2019, 5:14 PM UTC

semi-extrinsic wrote: post #41

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...

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

Pressurized cabins are going to be essential for electric flight to have any kind of reasonable speed (and range).

It shows that the most impressive electric aircraft specs are for the pressurized Eviation Alice (1000km, minus margin for contingency, and 250 knots cruise). If you stay low enough to not require pressurization, then you have to compromise the lift to drag in order to have a decent cruise speed or you have to tolerate a really low cruise speed.

Altitude is essential. Bite the bullet and build a pressurized cabin so we can get on with replacing fossil fuel aviation with full electric. https://www.eviation.co/alice/

Doesn't have to be above the Armstrong Limit, but it sure does help to be above 10,000 feet.

Eventually we'll have supersonic electric aircraft. To have sufficient efficiency, they'll need to be at or above the Armstrong Limit, like Concorde. (And perhaps higher, like the 96,000 feet record holder for horizontal powered flight, NASA's Helios... which just happens to be electrically powered. https://en.wikipedia.org/wiki/Helios_Prototype .)

EDIT: High altitude enables you to use an extremely efficient airframe with sailplane-like lift to drag but STILL achieve high cruise speeds. For instance, the Perlan II glider actually has no engine and is able to soar higher than any towplane, above 76,000 ft where it flies at about 250 knots (actual airspeed). Without any engine at all. https://www.youtube.com/watch?v=NnpE5xS1g80

And here's a solar electric aircraft aiming for similar goals: https://www.solarstratos.com/en/challenge/

Re: The age of electric flight is finally upon us

#103

Post by nradov » Fri, Jun 21, 2019, 5:14 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…

It will take a lot longer than 30 years to develop and certify such aircraft, then build out the infrastructure. Small general aviation airports just aren't set up to handle a bunch of passengers. A minor decrease in fuel costs won't have a transformational effect. And passenger security screening will still be required.

Re: The age of electric flight is finally upon us

#104

Post by tim333 » Fri, Jun 21, 2019, 5:16 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...

I'm doubtful about passenger aircraft but the Facebook solar plane was supposed to go to 90k feet https://en.wikipedia.org/wiki/Facebook_Aquila

Re: The age of electric flight is finally upon us

#105

Post by nradov » Fri, Jun 21, 2019, 5:18 PM UTC

sheldonth wrote: post #51

NickM wrote: post #17

Earlier quoted context omitted.

Yeah I have wondered about this option as well. Hydrogen fuel cell cars make very little practical sense for a lot of reasons, but most of those reasons don't seem to apply so much when you're dealing with air travel: - It'll be a long time before fuel cells are cost competitive with gas or electric cars, but for planes the cost of fuel and operation is much more significant than with a car, so the upfront cost for b…

I wonder what a YC application with such an idea might look like. Design the plane and the fuel containment/loading systems at 2 airports. Start America's first "carbon free" aviation route. Maybe move freight instead of people at first for an easier regulatory pipeline. It's absolutely crazy and would almost certainly fail but so are most of the revolutionary startup ideas that deal with earth heating in any meaning…

We can basically have "carbon free" aviation today if we want it by manufacturing synthetic liquid hydrocarbon fuels using renewable power. The US military has already run successful experiments. It works fine, it's just more expensive than burning fossil fuels.

Re: The age of electric flight is finally upon us

#106

Post by namirez » Fri, Jun 21, 2019, 5:21 PM UTC

As others have noted, electric flights require a major breakthrough in the battery technology. Here are energy density numbers for gasoline, jet fuel, and lithium-ion batteries:

Gas and jet fuel specific energy density ~= 45 MJ/kg;

Lithium-ion specific energy density Even worse, a jet engine is much better at generating power. A modern high-bypass turbofan engine can generate 10 kW/kg whereas an electric motor is around 1 kW/kg.

In short we need much better batteries and much lighter motors. This is not going to happen anytime soon. A more reasonable option is to create carbon-neutral fuels (biofuels, carbon sequestration, etc.).

Re: The age of electric flight is finally upon us

#107

Post by gameswithgo » Fri, Jun 21, 2019, 5:22 PM UTC

NeedMoreTea wrote: post #74

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.

A human can put out ~200W to the pedals (or 400 for an hour if you are among the best in the world). The amount of heat they put out when doing that is much more. The human body is about 30% efficient so if you are doing 200watts to the pedals you are putting out over 400w of heat. This can be a challenge for strong athletes on bike trainers in doors. you need a big fan, with somewhere for the air tog o.

Re: The age of electric flight is finally upon us

#108

Post by gameswithgo » Fri, Jun 21, 2019, 5:25 PM UTC

namirez wrote: post #106

As others have noted, electric flights require a major breakthrough in the battery technology. Here are energy density numbers for gasoline, jet fuel, and lithium-ion batteries: Gas and jet fuel specific energy density ~= 45 MJ/kg; Lithium-ion specific energy density Even worse, a jet engine is much better at generating power. A modern high-bypass turbofan engine can generate 10 kW/kg whereas an electric motor is aro…

Carbon sequestration and biofuels that are actually carbon neutral may be similarly implausible.

Re: The age of electric flight is finally upon us

#109

Post by stcredzero » Fri, Jun 21, 2019, 5:30 PM UTC

namirez wrote: post #106

As others have noted, electric flights require a major breakthrough in the battery technology. Here are energy density numbers for gasoline, jet fuel, and lithium-ion batteries: Gas and jet fuel specific energy density ~= 45 MJ/kg; Lithium-ion specific energy density Even worse, a jet engine is much better at generating power. A modern high-bypass turbofan engine can generate 10 kW/kg whereas an electric motor is aro…

Electric motors can enable something which jet fuel and gasoline cannot: beamed power. There could be a new class of vehicles which only have a small onboard power store for emergency purposes. The weight savings would be about 20%.

Re: The age of electric flight is finally upon us

#110

Post by rbanffy » Fri, Jun 21, 2019, 5:32 PM UTC

mannykannot wrote: post #92

marcosdumay wrote: post #79

Earlier quoted context omitted.

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…

A fire in an airplane is a lot more scary than a loss of power (proportionally more so in a small airplane, where an off-field landing is feasible, and increasingly they have ballistic parachutes), while there is currently a well-known problem of fires (that can't be extinguished) in high-power-density batteries. Gasoline is dangerous, but we have learned how to handle it safely.

You could mount batteries on pods that could be released if needed. Additional benefit would be that the pods could be replaced on the ground by fully charged ones for faster turnaround.