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71 votes
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Why do solar planes have many small propellers instead of fewer large ones?

Because they are very lightweight and fragile. Therefore, thrust and propulsion mass must be distributed over span - a single, large propeller and motor would put too much force into the structure ...
Peter Kämpf's user avatar
70 votes
Accepted

What energy density is required for the batteries in order to make an all-electric analogue of the Cessna 150 or similar plane?

Short Answer Batteries would need to be somewhere around 16.7MJ/kg to give the same range and performance as liquid fuels, this is about 18.5 times the capacity of the best lithium-ion batteries. ...
GdD's user avatar
  • 54k
46 votes
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Could there ever be a fully solar powered airliner capable of transatlantic flights?

Short answer: No Long answer: No. Look at the solar impulse project, this is some of the best solar-electric technology that's out there, and it's barely able to carry one person, very very slowly. ...
GdD's user avatar
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43 votes
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Could an electric engine provide the same performance as jet engines on current aircraft?

Not yet. To look at a medium-range aircraft, let's base the engine on the CFM56 or the IAE V2500. Those engines produce between 100 and 150 kN static thrust. In cruise, their thrust is considerably ...
Peter Kämpf's user avatar
28 votes
Accepted

What's the use of so much torque on propellers?

Even small 1 hp electrical motors can achieve that RPM Yes, but can it sustain that RPM when something tries to stop it, that is the question. 1 hp combustion engines can get to 2700 rpm as well, but ...
Koyovis's user avatar
  • 61.8k
20 votes

Are there any hybrid electric planes?

There are experimental electric planes. Some are promising enough that they might end up useful as trainers and private GA flown for the love of flying. Long-range electric will not work. The ...
Therac's user avatar
  • 27.6k
19 votes

What's the use of so much torque on propellers?

You're ignoring air resistance. A tiny electric motor can accelerate the prop to 2700 rpm in a vacuum. But at 1 bar, the prop moves against the air (effectively pumping air from one place to another), ...
Hobbes's user avatar
  • 10.2k
17 votes

Could there ever be a fully solar powered airliner capable of transatlantic flights?

To cover a current-design airliner in solar cells and hook them up to electric engines spinning the fans will not work. Ever. Read @GdD's excellent answer for the reasons. But today's car is also not ...
Peter Kämpf's user avatar
16 votes

What is an "all-electric APU"?

Usually an APU provides electricity and bleed-air, just like the aircraft engines do. An all-electric APU only provides electricity. This can be done in the Boeing 787 because of the bleedless ...
MadMarky's user avatar
  • 669
15 votes

How hard would it be to convert a glider into an powered electric aircraft?

"Hard" is a matter of opinion. But installing an electric motor on a glider is quite doable. You don't want to put motors on the outside, though. Would make more sense to do what most manufacturers do,...
Juan Jimenez's user avatar
14 votes

How many kilowatts to get an electric 747-8 airborne?

I can't quickly find the necessary numbers for 747-8, so I'm going to go with the numbers for Rolls-Royce RB.211-524G-T, one of options on 747-400, taken from here. The engine can produce static ...
Jan Hudec's user avatar
  • 56.3k
14 votes

Why do solar planes have many small propellers instead of fewer large ones?

Conventional commercial designs try to maximize kg-kms per dollar fuel cost or kg payload per dollar investment. Or minimize operating & maintenance cost. All these goals need an economy of ...
curious_cat's user avatar
  • 8,456
14 votes
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Is there a limit to the possible altitude for electric jets?

That electric propulsion needs no oxygen is of little help for flying high. The composition of the atmosphere does not change too much with altitude, so it is the low atmospheric density which limits ...
Peter Kämpf's user avatar
13 votes

Could an electric engine provide the same performance as jet engines on current aircraft?

Engines are great as they are. Electric engines can be fast, powerful and effective. I see two problems: First - the sheer amount of energy consumed by the commercial airplane. With a single engine ...
gusto2's user avatar
  • 273
13 votes

Why do solar planes have many small propellers instead of fewer large ones?

Don't forget the electrical advantages of multiple motors. No need to conduct all the current to a single place with long lengths of heavy wire, no need to control a large current. Also, many small ...
Bill IV's user avatar
  • 1,092
13 votes

What energy density is required for the batteries in order to make an all-electric analogue of the Cessna 150 or similar plane?

An all-electric craft similar to what you described has actually been created (IEEE Spectrum did a nice article about it). The batteries are described as 260 Watt-hours per kilogram with a power ...
bta's user avatar
  • 231
13 votes

How hard would it be to convert a glider into an powered electric aircraft?

It has been done! In 2008 an Edgley EA-9 Optimist glider was "converted" in very much this manner for a university project, by strapping eight pylons to the wings, each containing a battery pack and ...
Martin L's user avatar
  • 296
12 votes

Could an electric engine provide the same performance as jet engines on current aircraft?

There is one important disadvantage that batteries will always have compared with fuel combustion for aviation propulsion: the weight remains constant. Airliners (especially those used for long-haul ...
reirab's user avatar
  • 19.5k
11 votes

Could ducted propellers improve efficiency in small drones?

If the ducted propeller really increases efficiency, we would see more of these Rhein Flugzeugbau Fanliner (picture source) and fewer of these: Socata TB-9 (picture source) The ducting has benefits ...
Peter Kämpf's user avatar
10 votes
Accepted

If, one day, we have an electric airplane, will it be easier to control than a fuelled airplane?

There are a few electric aircraft now, and because batteries hold far less energy than fuel, they're low-performance and short-range compared to normal aircraft. If we imagine that at some point in ...
Robin Bennett's user avatar
10 votes

Could ducted propellers improve efficiency in small drones?

It is actually suprisingly easy to give a lower boundary and therefore an estimate of the power consumption in hover for any thruster. It is given by momentum theory which correlates the size of an ...
U_flow's user avatar
  • 3,840
9 votes

What energy density is required for the batteries in order to make an all-electric analogue of the Cessna 150 or similar plane?

You're missing the point. Electric vehicles don't even try to match energy density of petroleum. This isn't a matter of yank out a Lycoming and drop in a VFD and induction motor and battery bank. ...
Harper - Reinstate Monica's user avatar
9 votes

Are fully electric helicopters suitable for military operations?

Battery weight is a huge negative. Liquid hydrocarbon fuels have energy densities of about 45MJ/Kg, and the significant advantage that as you use them, their weight stops needing to be transported. A ...
John Dallman's user avatar
9 votes
Accepted

Why don’t ionocrafts (ionic propelled aircrafts) use ducted ionic thrusters instead of open air thrusters?

A problem of ionic thrusters is that they only generate a gram of thrust for every watt, which is really inneficient. The Wikipedia article says that about the early versions. I don't think it ...
Jan Hudec's user avatar
  • 56.3k
8 votes

What are some alternative benefits to electric propulsion?

For aircraft, none. Hybrid drive trains are used because: They offer, rather limited, efficiency improvement by being able to operate the engine closer to its optimal conditions. Because spark-...
Jan Hudec's user avatar
  • 56.3k
8 votes
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In what way(s) will making an airplane electric help to make it "quiet"?

You are right, propeller noise is dominant in case of GA aircraft, but not all propellers make the same noise. Much depends on blade loading and tip speed - making the propeller larger and letting it ...
Peter Kämpf's user avatar
8 votes

Could there ever be a fully solar powered airliner capable of transatlantic flights?

Yes. Note that your question does not specify how frequently the trips are to be made. Take your Boeing 737, put as many solar cells on it as you can, connect them to a plant that takes H2O and CO2 ...
Loren Pechtel's user avatar
8 votes

Are there any hybrid electric planes?

There are a number of small (ultralight, Light Sport categories) aircraft that run on pure battery power for anywhere from a few minutes to (as I recall) nearly an hour of powered flight -- a couple ...
Zeiss Ikon's user avatar
  • 17.1k
8 votes

Is it possible to reload Electric Aircraft in mid-air from a tanker aircraft?

This would certainly be possible, but the current status (pun intended) of the battery technology makes it pretty much pointless. The charging would simply take too long: for example, Eviation Alice ...
Jpe61's user avatar
  • 29.1k

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