What are currently the largest issues with purely electric commercial aircraft (large scale ones like the size of a Boeing 737)?
Are there any organizations right now that are trying to solve those issues?
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1$\begingroup$ It is not clear what you mean by "purely electric". Are you thinking of fly-by-wire? Issues, in what sense? Pilot training, or something else? "Large scale" is perhaps a relative concept, many operators would consider a B737 to be a rather small aircraft. Could you be more precise? $\endgroup$– ALAN WARDJul 17, 2015 at 18:32
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3$\begingroup$ All current electric aircraft are so inefficient (power to weight) that they have enormous wings and have to fly really slowly. The technology is nowhjere near advanced enough. $\endgroup$– SimonJul 17, 2015 at 19:07
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$\begingroup$ @Simon This is precisely why I could not comprehend the question at first read. Figure in the fact that aircraft need to get places fast to compete with other means of transport, and carry stuff from here to there, and as you say we are nowhere near the technology that would be needed. $\endgroup$– ALAN WARDJul 17, 2015 at 19:50
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$\begingroup$ How do you define "purely electric"? A fuel cell powered plane could use electric motors, yet still be powered by hydrogen or natural gas. Sounds like you're referring to a chemical battery powered plane. $\endgroup$– JohnnyJul 18, 2015 at 0:40
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$\begingroup$ @ALANWARD Sorry for not being clear, I meant in terms of fuel source being purely electric. And with regards to issues, I wanted to know what problems would arise in terms of the design and manufacturing of an aircraft about the size of a 737. Thank you for your help! $\endgroup$– pradkodaJul 18, 2015 at 22:49
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5 Answers
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The biggest problem with an all-electric-powered aircraft is the same as those plaguing all-electric cars; our current battery technology has nothing on the energy density of fossil fuels:
There's just no contest in being able to pack the energy needed to push a plane through the air into a volume and weight compatible with an airliner. Jet fuel is kerosene, which is pretty much right in between gasoline and diesel, while any battery technology we've developed can't even be accurately plotted on the scale of this graph.
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2$\begingroup$ To put things into perspective: the Airbus E-fan has power for one hour and cruising speed 86 kts. The EADS Cri-cri has 30 minutes at 60 kts. Even a small commercial A/C for local routes would need something like two hours at 300 kts to be competitive with existing models - and this, with a full commercial load on board, unlike the experimental models cited. $\endgroup$ Jul 17, 2015 at 19:47
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1$\begingroup$ Follow-up question- How efficient are current turbine engines? Does the efficiency of today's battery technology help decrease the gap between this energy density difference? Thank you very for both of your responses, I truly appreciate it. $\endgroup$– pradkodaJul 17, 2015 at 22:51
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3$\begingroup$ The latest, most efficient turbine engines are approaching the theoretical Carnot limit for operation of a heat engine using fossil fuels in ambient Earth temperatures, which is about 73%. The best one in production now is the Rolls-Royce Trent 890, which is used on the Airbus A380 and has a Brayton cycle efficiency of about 65%. That is about a 10% increase from the turbofans used on the 727 and MD-80. $\endgroup$– KeithSJul 17, 2015 at 23:06
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1$\begingroup$ Speaking of efficiency, modern electric motors can go up into the 85-95% range. However, batteries also loose some energy on charging and on restitution, typically more as they get older (number of charge/decharge cycles). This is an area that needs work. $\endgroup$ Jul 18, 2015 at 23:00
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2$\begingroup$ @ALANWARD - The motors are more efficient by 10-20%, but the energy density of the storage media for a pure electric vehicle is less by several orders of magnitude. There's a reason electric vehicle manufacturers are focusing on urban uses, like city buses and short-range commuter vehicles. When they make a purely electric tractor-trailer that can match the cargo capacity and daily range of a diesel semi, we might be able to look at powering commuter jets the same way. $\endgroup$– KeithSNov 10, 2015 at 19:41
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In addition to the energy density issue as mentioned there is a turn around time issue. The fact is that batteries just don't charge up that fast and any system that allows them to do so is often dangerous to be around. So if you are talking about an airliner (lets say we overcame the weight of the battery issues) it takes about 15-30 minutes to fuel up a 747, there is no way you are going to charge any kind of batter that we currently have today to the same energy potential capacity that fast.
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7$\begingroup$ That's not an insurmountable problem. The batteries could be physically replaced with fresh ones on the ground, and the empty ones charged before the next aircraft arrives, like some electric cars do. This could even be faster than conventional fuelling methods. $\endgroup$ Jul 17, 2015 at 21:38
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First, the term all-electric aircraft is already occupied for an aircraft in which all power sources except the engines are electric. No hydraulics, no pneumatics, but still hydrocarbon fuel to store the energy.
Steps towards the all-electric aircraft, taken from this source.
Countless programs try and tried to electrify aircraft systems, the first from as early as WW II. In most cases, the result is called "more electric" aircraft, because some systems like the landing gears in large aircraft still use hydraulics.
Full electric propulsion is discussed in the answers to this question. The gist of the answers is:
- Energy storage using batteries is out of the question, because the energy needs of aircraft are an order of magnitude greater than those of cars. Just because electric cars have become feasible with lithium batteries does not mean that electric aircraft are even remotely feasible.
- Electric propulsion using highly efficient electricity generators burning either hydrocarbons or hydrogen are an interesting object of study but need many more years of development until they become feasible for commercial use.
answered Nov 25, 2016 at 19:55
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$\begingroup$ "Just because electric cars have become feasible with lithium batteries does not mean that electric aircraft are even remotely feasible." Feasible for longer-range aircraft, no. Feasible for very short-haul aircraft, on the other hand... $\endgroup$– VikkiAug 31, 2019 at 0:25
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2$\begingroup$ @Sean: Planning to is not being in operation. You should know how much wishful thinking goes into the claimed performance of planned electrical aircraft. The realistic boundaries show in actually flying designs, like those from Pipistrel. $\endgroup$ Sep 1, 2019 at 7:37
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I would say your largest obstacles would be legal issues, and just using electricity itself.
first of all, the most efficient way to make an aircraft fly with purely electricity, would be propellers. Ion engines are not yet efficient enough to become a possible candidate for a propulsion source.
moving back to propellers, a fully-electric commercial airplane would likely incorporate propellers, which would be powered by high-torque electric motors and larger propellers, because that's more cost-effective. Slower, but cheaper.
the electric power source in itself is a major obstacle to overcome, because with today's technology, a cost-effective battery would weigh far too much for a handful of electric motors to lift into the air, even without passengers in the equation.
If we want to go into financial fantasy here, then yes. a fully electric commercial aircraft the size of a 747 is possible. think basic. stuff the plane with ultralight high-capacity batteries, give it large wings and 6 engines, with each engine being 4 tandem Formula E engines linked together, and slap some solar panels all over the place for ranged benefits, and voila! but oh, no! that'll cost you more than 4 AN-225's!
Don't lose hope though, there will come a day where technology will have advanced enough for an electric 747-sized commercial aircraft to be affordable.
but seriously though, there's nothing anyone can really do about how hard it will be to convince the FAA to make large electric commercial aircraft legal.
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I see commercially viable electric driven aircraft requiring major changes in several areas. Aircraft design is certainly one. It also requires changes in regulations and flight profiles. I'm convinced you could take a classic prop driven air frame, say a DC-3, and convert to electric. It was designed for relatively long flights but pulling out all of the fuel and power systems, replacing them with lithium batteries and electric driven composite props could yield shorter flights with less payload viably. Your flight profile would need to change. Climb high, glide down to extend your range. It's what the recent round the world solar powered flight did. What we need is a visionary like Musk, to depart from the linear thinking and designs that the major manufactures are stuck in. Technology is fast approaching a point where this could become a reality. We need someone to put multiple technologies together and challenge convention.
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4$\begingroup$ If you replaced all of the weight used by avgas in a DC-3 with Lithium batteries, you'd have about 1/26 the amount of energy available. Furthermore, the entire 4,932 pounds of that weight would remain with you for the entire flight, rather than burning off during flight as happens with avgas. We'll be generous and assume you can get 1/30th of the range out of it. That leaves you with around 50 miles range, though it's really probably less. You could probably safely make a couple of trips around the pattern before replacing/recharging the batteries. $\endgroup$– reirabNov 25, 2016 at 23:50
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$\begingroup$ You may add references and links to support your answer and for further readings. $\endgroup$– Manu HNov 26, 2016 at 10:33