71
votes
Accepted
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 ...
- 230k
69
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. ...
- 52.9k
46
votes
Accepted
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. ...
- 52.9k
43
votes
Accepted
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 ...
- 230k
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 ...
- 61.3k
24
votes
In helicopters, why not have electric motors controlling blade pitch?
How would you communicate with (and power) these motors?
The main rotor is spinning constantly - Wires won't work, they would wrap around the shaft and be shredded. A slip ring and brushes (as used ...
- 68.3k
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 ...
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), ...
- 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 ...
- 230k
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 ...
- 669
15
votes
In helicopters, why not have electric motors controlling blade pitch?
Because it would be too complicated (and failure prone) compared to the present system and would offer no great advantages.
First, for all the complexity in the helicopter upper controls, the ...
- 100k
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,...
- 12.6k
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 ...
- 56.2k
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 ...
- 8,436
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 ...
- 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 ...
- 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 ...
- 231
13
votes
Accepted
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 ...
- 230k
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 ...
- 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 ...
- 19.4k
12
votes
In helicopters, why not have electric motors controlling blade pitch?
I went on a little search on my university library database, and found a review paper. I'm not sure if you can access it without paying.
Active rotor control for helicopters: individual blade control ...
- 12.9k
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 ...
- 230k
10
votes
Does it make sense towing airplanes to the head of airstrip by external (eg electric) means?
This is an older question, and I have no answer, just experience:
When I flew from Frankfurt (FRA) to Geneve (GVA) in January 2015, we were towed by a tug nearly all the taxiway to the runway. We ...
- 7,227
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 ...
- 3,353
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 ...
- 3,272
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. ...
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 ...
- 56.2k
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-...
- 56.2k
8
votes
Accepted
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 ...
- 230k
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