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The age of electric flight is finally upon us

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Re: The age of electric flight is finally upon us

#231

Post by Misdicorl »

rootusrootus wrote: post #225
audunw wrote: post #206

Earlier quoted context omitted.

I think the biggest point that you and others that bring this up is missing, is not just how electric designs gives you higher efficiency and close the gap (as others have mentioned). The main thing you're missing is that modern jet planes have absolutely ridiculous range, and a huge number of flights use only a fraction of that range. Electric planes don't need to match modern jet planes to be viable. They just have…

Even medium range flying is tough to accomplish with near-term electric technology. A flight across the United States would involve 10 hours of flight time, assuming you did it in a single leg, which of course you cannot. Three stops, so probably 15+ hours total. People do seem willing to take one-stop jet rides across the U.S. now, but the gold standard is about 5.5 hours for a non-stop flight.

Why would a transcontinental flight be the relevant comparison here? The real disruptive/comparitive market is the DC NYC Boston corridor. I'm sure there are similarly busy and small corridors in the EU.

Re: The age of electric flight is finally upon us

#233

Post by Gibbon1 »

falcolas wrote: post #145
gnode wrote: post #73

Earlier quoted context omitted.

There are flights shorter than 650mi.

They'd have to be shorter than 400 miles to be safe. At which point, it's probably just as fast to drive (or faster, given it's a prop plane whose speeds are in the ~200mph range).

My GF's sister lives in central Nebraska. 300 miles from Denver, 120 miles from Omaha. An electric airplane with 600 miles range would be 'fine'. Driving would cost about $150 when you include fuel, maintence, and depreciation.

Also driving in winter blows.

Re: The age of electric flight is finally upon us

#234

Post by p1mrx »

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…

But they have a cool name; that has to count for something.

Re: The age of electric flight is finally upon us

#235

Post by petschge »

ph0rque wrote: post #218
stcredzero wrote: post #109

Earlier quoted context omitted.

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%.

As long as we're discussing beamed power, why not have just enough power to reach cruising altitude (presumably above any clouds), then use solar panels to continue flight? This would admittedly limit long-distance flights to just daylight, but still better than what is currently possible.

Let's run the numbers for say a Boeing 767. It has a wing area of 290 m^2 and the main fuselage of 5 meter width and 60 meter length, so lets assume another 200m^2 of surface area. 490m^2 of solar panel can generate 0.2 * 490m^2 * 500W / m^2 = 49 kW.

Compare that to the 800kW that the APU in the tail supplies to keep electric and hydraulics running if the main engines fail or the well above 200 MW that the main engines put out.

Re: The age of electric flight is finally upon us

#236

Post by aiisjustanif »

audunw wrote: post #206
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…

I think the biggest point that you and others that bring this up is missing, is not just how electric designs gives you higher efficiency and close the gap (as others have mentioned). The main thing you're missing is that modern jet planes have absolutely ridiculous range, and a huge number of flights use only a fraction of that range. Electric planes don't need to match modern jet planes to be viable. They just have…

> flights use only a fraction of that range. Electric planes don't need to match modern jet planes to be viable. They just have to compete on cost at a range that covers a significant amount of routes.

You do know plane routes have diversions and holding pattern minimum times set by the FAA?

Re: The age of electric flight is finally upon us

#237

Post by NickNameNick »

Robotbeat wrote: post #210
tristanb wrote: post #189

Earlier quoted context omitted.

FWIW my thoughts: 1. Rear prop strikes. 2. Wing tip prop strikes. 3. Wing tip inertia 4. Prop wash over a wing is a good thing If (big if) this thing ever flies, it won't be in this form

Prop wash over a wing is good if you're lift-starved at take-off (which you aren't with this design). But otherwise it actually increases drag. Pusher configuration is superior in that you can ingest boundary layer air which has been slowed down by the fuselage and get an increase in efficiency. That efficiency gain is partially why pushers are often used in long-duration drones.

I had the impression that pushers were typically less efficient than pullers.

A puller takes advantage of the volume behind the prop taken up by the body of the aircraft to offset the loss of air volume caused by accelerating the air (Bernoulli's theorem). A pusher can't do that.

Re: The age of electric flight is finally upon us

#238

Post by clouddrover »

trollied wrote: post #215
upofadown wrote: post #171

Earlier quoted context omitted.

Self launching on batteries means carrying around a fair bit of dead battery weight for the entire flight. Electric sustainers (can't take off but can stay up) are pretty interesting because gliders take hardly any power to fly level. Example: * http://front-electric-sustainer.com All this electric vehicle technology works really well for electric glider winches. You can get a whole lot of peak power off of a battery…

Are super capacitors lighter and a better choice for the self-launching use case? I have no idea, hence asking and wanting to know :-)

Maybe. Nawa's ultra-capacitors sound good:

https://newatlas.com/nawa-nanotube-ultracapacitor-production...

I hope they get adopted by Formula E. A bank of ultra-capacitors in front of the main battery should make the cars lighter with stronger regenerative braking.

Re: The age of electric flight is finally upon us

#239

Post by Retric »

Robotbeat wrote: post #187
tristanb wrote: post #183

Earlier quoted context omitted.

The design is "sound" ? It is ridiculous! Those engines are at each end of a wing. That is a 100% no no. They are feet from the ground, and would make one engine out operation impossible. Even someone with a cursory understanding of aerodynamic could see this is a ridiculous design.

Better tell NASA, then, which is building a design (X-57) with the same kind of wing-tip propellers: https://www.youtube.com/watch?v=No9Rq3VE0FI The key is that the Alice aircraft is capable of take-off with just the rear propeller. That's possible because electric motors (unlike jet engines) can operate at much higher power for short periods of time. It was addressed recently at the Paris airshow Q&A for Eviation. I…

Compare the number of propellers on NASA’s version. They have serious backup in the event any single engine fails.

Being able to take off with one engine that’s rapidly overheating, does not mean is safe to continue a flight with a single engine. Electric aircraft don’t get lighter in flight because they don’t burn fuel.

Re: The age of electric flight is finally upon us

#240

Post by Robotbeat »

NickNameNick wrote: post #237
Robotbeat wrote: post #210

Earlier quoted context omitted.

Prop wash over a wing is good if you're lift-starved at take-off (which you aren't with this design). But otherwise it actually increases drag. Pusher configuration is superior in that you can ingest boundary layer air which has been slowed down by the fuselage and get an increase in efficiency. That efficiency gain is partially why pushers are often used in long-duration drones.

I had the impression that pushers were typically less efficient than pullers. A puller takes advantage of the volume behind the prop taken up by the body of the aircraft to offset the loss of air volume caused by accelerating the air (Bernoulli's theorem). A pusher can't do that.

The opposite is true. The accelerated airflow over the body of the aircraft actually increases the drag whereas a pusher ingests the boundary layer from the fuselage and the suction also helps keep flow attached. The problem, however, is that turbine engines need a smooth airflow in order to operate efficiently, therefore they aren't suited for pushers as the wings (etc) produce an uneven airflow into the turbine core.
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