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

Re: The age of electric flight is finally upon us

#151

Post by rootusrootus » Fri, Jun 21, 2019, 6:45 PM UTC

nneonneo wrote: post #136

tristanb wrote: post #124

https://twitter.com/BenBrelje_says/status/106484220091004108... https://twitter.com/BenBrelje_says/status/106485722028904038... https://twitter.com/BenBrelje_says/status/106491195862390374... To recap, based on financial statements the company: used to be a "waste management" company that failed and was sold as a "public shell" to enable the formerly private company to go public and sell shares (the waste management…

Those tweets have been deleted, and where’s the evidence of these claims?

Try this link: https://twitter.com/BenBrelje_says/status/106484220091004108...

I believe tristanb cut & paste his own post from six months ago on this same topic, and it broke the links.

Re: The age of electric flight is finally upon us

#152

Post by mannykannot » Fri, Jun 21, 2019, 6:49 PM UTC

codeduck wrote: post #144

verelo wrote: post #119

Earlier quoted context omitted.

"Q. How much damage will be done to my plane if I land it with a parachute? A. In all likelihood the aircraft will suffer some significant damage. The terrain where you land will affect this greatly. Though the extent of damage has varied from plane to plane, most GA aircraft that have come down under a BRS deployment have eventually (or will soon) fly again." Call me a skeptic until they provide hard numbers and det…

If the plane is designed to take a BRS then there is a good chance that after some (admittedly costly) repairs it will take to the air again. A 172 or similar that has been retrofitted with a BRS? Yeah, not so much.

It seems that, at least until fairly recently, most Cirrus aircraft that used their parachute were written off, and that is still the most likely outcome.

https://aviation.stackexchange.com/a/1122

Re: The age of electric flight is finally upon us

#153

Post by cagenut » Fri, Jun 21, 2019, 6:51 PM UTC

maxxxxx wrote: post #78

mannykannot wrote: post #76

Earlier quoted context omitted.

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.

you might like rctestflight's youtube channel

here he gets a battery powered drone with solar to gain altitude and charge the batteries during clear skies: https://www.youtube.com/watch?v=xS2iCj-HSqY

here he shows off a new feature in arduinopilot, autonomous thermaling: https://www.youtube.com/watch?v=NwAX3cPvMqw

also, check out the "Sunseeker Duo" https://www.solar-flight.com/sunseeker-duo/ https://www.youtube.com/watch?v=2zvwqJpyahs

its only a matter of time before someone combines them

Re: The age of electric flight is finally upon us

#154

Post by Brain_Thief » Fri, Jun 21, 2019, 6:52 PM UTC

iosonofuturista wrote: post #48

davidrm wrote: post #14

Earlier quoted context omitted.

> Oh and it would be so quiet. would it? I was under the impression that proppelers were much louder! what is the biggest source of noise in an aircraft/type?

Ah, good ol' Thunderscreech[0]! > The XF-84H was almost certainly the loudest aircraft ever built, earning the nickname "Thunderscreech" as well as the "Mighty Ear Banger". On the ground "run ups", the prototypes could reportedly be heard 25 miles (40 km) away. Unlike standard propellers that turn at subsonic speeds, the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the sp…

This is fantastic - thanks for sharing!

Re: The age of electric flight is finally upon us

#155

Post by namirez » Fri, Jun 21, 2019, 6:53 PM UTC

namibj wrote: post #139

namirez wrote: post #125

Earlier quoted context omitted.

I stand corrected. I also found Emrax 268 which has a power to weight ratio of 10 kW/kg. But these are good only for small aircraft. It's much harder to maintain this power-to-weight ratio for larger motors. Emrax 268 is only 20kg, but a single engine of 777 weighs 8200kg. The ballpark for large motors at powerplants is currenly around 1 kW/kg [1]. But who knows; there might be a breakthrough in motors too. [1] https…

You can stack Emrax motors on a shaft. Also, the technology scales up in diameter. Not that you really want _that_ large props necessarily, if you can get away with smaller ones. This combination should be enough, I guess. Edit: I think I met the guy behind these. But I'm not sure, for lack of having asked for the name of the company. I certainly have seen a prototype that could have been the 348.

Generally you should prefer few large propellers over many small ones due to aerodynamic efficiency. Stacking up motors axially sounds like a very good idea though.

Re: The age of electric flight is finally upon us

#156

Post by rootusrootus » Fri, Jun 21, 2019, 6:54 PM UTC

newsoul2019 wrote: post #120

sandworm101 wrote: post #100

Earlier quoted context omitted.

>> off-field forced landing that went badly. Parachutes. They are now a very practical option for GA aircraft. More than a few cessnas have been saved. The concept of "off-field forced landing" should too be going away. https://brsaerospace.com/cessna-faqs/ " Q. How many aircraft saves are credited to a BRS Whole Aircraft Rescue Parachute System? A. As of August 2017, 376 ."

Wait, that's an astonishing number of would-be crashes.

A quick google search shows a page from the FAA saying that typically a couple hundred planes crash each year, and a few hundred people die. There's an order of magnitude more GA planes than commercial airliners.

Re: The age of electric flight is finally upon us

#157

Post by guntars » Fri, Jun 21, 2019, 6:55 PM UTC

gameswithgo wrote: post #108

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.

What’s the reasoning behind your statement? I think both are already being done, the economics are just not there yet. Digging up free energy from the ground is just too cheap.

Re: The age of electric flight is finally upon us

#158

Post by russdill » Fri, Jun 21, 2019, 6:55 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…

There are a lot of things that electric planes will not be able to do unless there are drastic changes in battery technology. They can still fill a niche for short flights with very little cargo/person capacity.

Re: The age of electric flight is finally upon us

#159

Post by drainge » Fri, Jun 21, 2019, 6:55 PM UTC

Patrick_Devine wrote: post #63

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.

It's a game changer for airlines such as Harbour Air in British Columbia and Mokulele Airlines in Hawaii. These are small regional airlines which operate from the water or from small airports with flight times usually less than an hour, and most of their operational expenditures are in fuel costs. Typically for these airlines you show up 15 minutes before the flight and there is no security screening, so it's very ha…

Unfortunately the battery weight is also currently prohibitive for small companies such as Harbour Air and Mokulele.

Several weeks before the Harbour Air / MagniX announcement I ran through an exercise to determine the range/payload of an electric Cessna 208 (Caravan) for a typical flight profile here in the bay area: the daily FedEx flight from Oakland International to some nearby city, such as Petaluma. This involves a 5min climb from take-off to 2000ft, some period of cruise flight (ultimately determined by range), and a 7min decent to land.

This calculation assumes that the C208 swaps the swaps its turbine (PT6A-114A) for the Magni500, saving 85lbs. It also accounts for the substantial increase in conversion efficiency between the MagniX and PT6 (roughly 0.94 from 0.32). Not accounted for are any differences in aircraft systems (de-ice, prop pitch, electric instruments, plumbing, etc).

The results are not surprising given what others have noted about the enormous difference between the specific energy densities of Jet A and LIB. At the specific energy density of today's production batteries, 250 w-hr/kg, the electric C208 could carry one 175lb pilot approximately 100mi in 39min. Due to FAA VFR regulations, this would in reality limit the flight to 9min (FAA requires daytime reserve of 30min), with the subsequent loss in range.

Let's consider the putative solid state battery at 500 w-hr/kg. Now a 60min flight time (really 30min plus 30min reserve) will allow 1080lb payload. Fantastic! That's a pilot plus 4-5 passengers. The catch, of course, is that the timeline for road worthy SS batteries is 5-10 years. How long for before an air worthy battery is available?

With this information parsing the press statements is a little easier. Will the Harbour Air / MagniX Beaver carry 6 passengers over a 30min flight? No. It may demonstrate electric flight of a utility category air frame with the pilot as the "soul" payload. After that both companies will likely be in the same position as the rest of us -- waiting on better battery technology.

Re: The age of electric flight is finally upon us

#160

Post by Robotbeat » Fri, Jun 21, 2019, 6:57 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…

This is constantly repeated, but it's not true. I work in the field of electric motors for electric aircraft, and the amount of nonsense constantly repeated on the Internet about how electric flight cannot be done without a breakthrough is breathtaking.

Electric motors can achieve FAR greater than 1kW/kg. Here's one used sometimes on electric aircraft capable of 10kW/kg, same as a jet engine: https://emrax.com/products/emrax-268/

The specific energy of lithium-ion is poor, but jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned. There's also some efficiency improvement possible, i.e. from airliner lift-to-drag of 16-20 (and like 8-10 for a Cessna) to a more glider-like L/D of 25-35 (the best gliders can do 70). Additionally, improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy (general aviation craft are only like 10-15% fuel, but 777s can be almost 50% fuel, and electric aircraft could be 60% battery).

So if you combine efficiency improvements and high battery mass, sure, electric planes still may have a tenth the range of jet liners. But jets like the 777 have a range of 10,000 to 15,000km. A tenth of that is still over 1000km! Quite doable for a very large portion of domestic flights. Since domestic flights often involve multiple hops anyway (due to hub and spoke model), you could fly basically anywhere up and down the eastern seaboard in just the typical two hops. And faster than high speed rail.

But of course, there are already better lithium batteries that are available in small quantities, like lithium-sulfur, metal electrode lithium batteries, solid-state batteries, or batteries that combine those various features. ~1.5MJ/kg cells are already demonstrated and you can buy them on an evaluation basis. ~2MJ/kg is feasible as well, enabling single-hop flights all over the eastern seaboard and enabling multi-hop transatlantic flights (as low as 1200km is the minimum range needed for transatlantic flights if you really wanted to do it).