Electric Airplanes have a basic physics problem, batteries currently don't hold enough energy to power the vehicle for a long enough flight to be commercially useful on a large scale. (the youtube channel Real Engineering does a great overview of the balancing of range of a plane relative to the size of the batteries) Commercial airplanes like the 737-900 has a range of 5900 kilometers ( a bit more than 3600 miles) current examples of passenger electric airplanes have a range of about 160 kilometers (100 miles). Flying 100 miles can be helpful, but not many people are going to want to take 25 legs to fly from Seattle to Boston. For electric aircraft to be able to actually begin to replace more conventional planes on a larger scale range will need to be drastically expanded. The range of electric airplanes are limited by how much energy can be stored in each gram of battery, this is referred to as the energy density. Battery energy density will often be listed in watt hours per kilogram, the idea being, under ideal circumstances if you have a battery technology that provides 100 watt hours/kilogram, you should be able to power ten 10 Watt LED bulbs for an hour using a 1 kilogram battery pack. Modern Lithium Ion batteries currently fall in around 150-190 Whr/kg impressive, but nowhere close to the 1000 Whrs/kg that you would need to make a commercially competative electric airplane under current paradigms.
The reason I mention current paradigms for electric airplanes is that the 1000 watt hour/kilogram calculation was done under the premise that you are designing an airplane that would have the same parts and components at both take off and landing. This is a valid assumption. for the last 100 years of the aerospace industry almost all planes have been designed under the impression that a plane will start its trip with everything it needs to complete a journey. For long haul electric aircraft to be considered a viable alternative, without allowing for revolutionary battery technologies, it may be necessary to look at our design parameters from a different perspective, what happens when you open your design considerations to include recharging in flight?
The United States' Department of Defense has been concerned with the range of its aircraft since they started to use them as part of our strategy for projecting American might around the world. This desire for extending the range of planes has lead to a littany of strategies and innovations including midflight refueling. In 2015 the US Navy released news that they had refueled an autonomous aircraft in mid flight. If an autonomous vehicle can refuel in midflight, would it be possible to do the reverse, have an autonomous aircraft dock with designated vehicle and resupply it. (At this time I can't find any materials that contradict this general premise so I'm gonna go with it)
Imagine a large electric plane that was designed from the ground up with the understanding that it was only required to carry enough energy for traveling 100-250+ miles while powered, this would provide a reasonable starting point for designers and engineers to work from. For longer journeys to be appealing to consumers it would be necessary to recharge the plane in mid-flight, one way would be to have small scall aircraft designed to meet planes along their flight path dock and top off onboard energy stores. These smaller aircraft would need to be able to be quickly charged and discharged so that they could rapidly cycle from their base of operations to charging a cruising plane to returning to their base to recharge and meet the next plane on their list.
There are several major challenges with respect to using support aircraft to keep bigger electric plane up in the air. The first is challenge is that of the efficiency of the recharging aircraft, if the drone supplying power cannot provide enough power quickly enough to appreciably extend the range of the electric plane the project would be a non-starter. Ex. If my parent electric plane has a range of 100 miles and a cruising speed of 300 mph and recharging provides enough power to extend my range by 10 miles and it takes more than 2 minutes to rechage the parent aircraft, the drone isn't helping that much*. Right after the concern of providing enough power quickly enough, the next big concern for our electric plane system is how much drag the recharging system is adding to the design of the plane. If the recharge system impedes flight range significantly the design will not be commercially viable. Infrastructure is another concern, each of the recharge drones will need a base of operations to get its power and be maintained. Realistically it would make the most sense to have the recharge drone stations near regions with existing grid infrastructure (or at least a low maintenance sustainable energy source) these requirements make water based platforms unlikely in any obvious narrative for a technology approach like this, as a result our electric aircraft would be limited to operating in regions with relatively short water crossings. Most importantly (and like super outside of the scope of an afternoon's writing and research) is the overall ecological impact of making the infrastructure necessary to make our rechargeable electric airplane viable, if the life cycle emissions of the plane, rechargeable drones, drone base stations, and increased grid supply exceeds that of carbon neutral fuels** then it is unlikely to be a good decision from just a green house gas emissions perspective.
(A possible vision of the future)
The year is 2045 and the eEU (expanded European Union) and the European parliment is celebrating beating their zero emissions goals by 5 years. Many attribute their success to the Airbus Electric Aircraft Network. Citizens and visitors are able to travel across the economic zone with mobility once thought impossible. Electric Heavy Lifters follow set routes connecting the continent's capital cities. Travelers wishing to quickly go from Budapest to Berlin simply request transit to the nearest Airbus Sky terminal, here they match with a Passenger Certified Recharge Drone, that will dock them with the Electric Heavy Lifter going towards their destination. Once they dock with their Electric Heavy Lifter they will have space to sit relax, or meet in a cafe for coffee. Ten minutes before they are set arrive at their target destination they are reminded by the EHL's systems that a smaller plane will be docking to take them to on of Berlin's many Sky Terminals. As new battery chemistries enter the market there are questions as to whether Airbus will continue to build out the Sky Terminal platform. Investors across the African Union and Brazil have answered with their wallets investing millions into bringing Sky Terminals into their countries, noting the advantage of standardized components and decade of safe operations.
I hope you enjoyed this post if you have any questions, feedback, would like more details please feel free to comment.
*to avoid making this more visually messy than it already is I'm moving the math down here, basically the electric plane is moving at 5 miles per minute so if the drone can only provide enough power to add 10 miles of cruising range it needs to dock, top off the batteries and get out of the way before the electric plane has exceeded that range boost, so it would need to be under 2 minutes (pretty darn fast) (please feel free to ask for clarification)
** so far I'm honestly pretty skeptical of claims of developments in "carbon neutral fuels" and how sustainable they would actually be. That being said if someone produces a peer reviewed article in nature (that I skim the synopsis of on slashdot) saying that they have developed a carbon neutral fuel that is legitimately sustainable I will be supportive of using that technology in airplanes while we develop better battery technology
random text I didn't use, but I might use if I do a different version of this post
Without a more indepth analysis it would be premature to provide exact specifications on things like flight behavior, size of vehicle
Your average passenger doesn't care about how their plane gets from point A to point B, so long as they can travel safely and affordibly, if this means that their airplane is recharged midflight.
There are several ways that an electric airplane can extend its range, wireless charging in flight, recharging in flight, and ejecting useless mass through out fligh. Ejecting useless mass through out flight is technically feasible, you design a plane with battery packs that can easily be released as their voltage falls below a certain value. Conceptually straight forward, but not too many people under a flight path would appreciate having massive battery backs rain down from the sky. The fact that these batteries are expensive would be another mark against tossing discharged batteries overboard through out flight. Wireless charging has more potential, as outlined in the web comic Saturday Morning Breakfast Cereal, you could build a network of towers (or airships) with lasers on them, as airplanes fly past the laser would aim at the airplane's recharge surface and top off the battery.
As of today there are no obvious innovations in battery technologies that seem likely to give an aircraft the necessary range at take off to take passenger distances in excess of 1000 miles.
The reason I mention current paradigms for electric airplanes is that the 1000 watt hour/kilogram calculation was done under the premise that you are designing an airplane that would have the same parts and components at both take off and landing. This is a valid assumption. for the last 100 years of the aerospace industry almost all planes have been designed under the impression that a plane will start its trip with everything it needs to complete a journey. For long haul electric aircraft to be considered a viable alternative, without allowing for revolutionary battery technologies, it may be necessary to look at our design parameters from a different perspective, what happens when you open your design considerations to include recharging in flight?
The United States' Department of Defense has been concerned with the range of its aircraft since they started to use them as part of our strategy for projecting American might around the world. This desire for extending the range of planes has lead to a littany of strategies and innovations including midflight refueling. In 2015 the US Navy released news that they had refueled an autonomous aircraft in mid flight. If an autonomous vehicle can refuel in midflight, would it be possible to do the reverse, have an autonomous aircraft dock with designated vehicle and resupply it. (At this time I can't find any materials that contradict this general premise so I'm gonna go with it)
Imagine a large electric plane that was designed from the ground up with the understanding that it was only required to carry enough energy for traveling 100-250+ miles while powered, this would provide a reasonable starting point for designers and engineers to work from. For longer journeys to be appealing to consumers it would be necessary to recharge the plane in mid-flight, one way would be to have small scall aircraft designed to meet planes along their flight path dock and top off onboard energy stores. These smaller aircraft would need to be able to be quickly charged and discharged so that they could rapidly cycle from their base of operations to charging a cruising plane to returning to their base to recharge and meet the next plane on their list.
There are several major challenges with respect to using support aircraft to keep bigger electric plane up in the air. The first is challenge is that of the efficiency of the recharging aircraft, if the drone supplying power cannot provide enough power quickly enough to appreciably extend the range of the electric plane the project would be a non-starter. Ex. If my parent electric plane has a range of 100 miles and a cruising speed of 300 mph and recharging provides enough power to extend my range by 10 miles and it takes more than 2 minutes to rechage the parent aircraft, the drone isn't helping that much*. Right after the concern of providing enough power quickly enough, the next big concern for our electric plane system is how much drag the recharging system is adding to the design of the plane. If the recharge system impedes flight range significantly the design will not be commercially viable. Infrastructure is another concern, each of the recharge drones will need a base of operations to get its power and be maintained. Realistically it would make the most sense to have the recharge drone stations near regions with existing grid infrastructure (or at least a low maintenance sustainable energy source) these requirements make water based platforms unlikely in any obvious narrative for a technology approach like this, as a result our electric aircraft would be limited to operating in regions with relatively short water crossings. Most importantly (and like super outside of the scope of an afternoon's writing and research) is the overall ecological impact of making the infrastructure necessary to make our rechargeable electric airplane viable, if the life cycle emissions of the plane, rechargeable drones, drone base stations, and increased grid supply exceeds that of carbon neutral fuels** then it is unlikely to be a good decision from just a green house gas emissions perspective.
(A possible vision of the future)
The year is 2045 and the eEU (expanded European Union) and the European parliment is celebrating beating their zero emissions goals by 5 years. Many attribute their success to the Airbus Electric Aircraft Network. Citizens and visitors are able to travel across the economic zone with mobility once thought impossible. Electric Heavy Lifters follow set routes connecting the continent's capital cities. Travelers wishing to quickly go from Budapest to Berlin simply request transit to the nearest Airbus Sky terminal, here they match with a Passenger Certified Recharge Drone, that will dock them with the Electric Heavy Lifter going towards their destination. Once they dock with their Electric Heavy Lifter they will have space to sit relax, or meet in a cafe for coffee. Ten minutes before they are set arrive at their target destination they are reminded by the EHL's systems that a smaller plane will be docking to take them to on of Berlin's many Sky Terminals. As new battery chemistries enter the market there are questions as to whether Airbus will continue to build out the Sky Terminal platform. Investors across the African Union and Brazil have answered with their wallets investing millions into bringing Sky Terminals into their countries, noting the advantage of standardized components and decade of safe operations.
I hope you enjoyed this post if you have any questions, feedback, would like more details please feel free to comment.
*to avoid making this more visually messy than it already is I'm moving the math down here, basically the electric plane is moving at 5 miles per minute so if the drone can only provide enough power to add 10 miles of cruising range it needs to dock, top off the batteries and get out of the way before the electric plane has exceeded that range boost, so it would need to be under 2 minutes (pretty darn fast) (please feel free to ask for clarification)
** so far I'm honestly pretty skeptical of claims of developments in "carbon neutral fuels" and how sustainable they would actually be. That being said if someone produces a peer reviewed article in nature (that I skim the synopsis of on slashdot) saying that they have developed a carbon neutral fuel that is legitimately sustainable I will be supportive of using that technology in airplanes while we develop better battery technology
random text I didn't use, but I might use if I do a different version of this post
Without a more indepth analysis it would be premature to provide exact specifications on things like flight behavior, size of vehicle
Your average passenger doesn't care about how their plane gets from point A to point B, so long as they can travel safely and affordibly, if this means that their airplane is recharged midflight.
There are several ways that an electric airplane can extend its range, wireless charging in flight, recharging in flight, and ejecting useless mass through out fligh. Ejecting useless mass through out flight is technically feasible, you design a plane with battery packs that can easily be released as their voltage falls below a certain value. Conceptually straight forward, but not too many people under a flight path would appreciate having massive battery backs rain down from the sky. The fact that these batteries are expensive would be another mark against tossing discharged batteries overboard through out flight. Wireless charging has more potential, as outlined in the web comic Saturday Morning Breakfast Cereal, you could build a network of towers (or airships) with lasers on them, as airplanes fly past the laser would aim at the airplane's recharge surface and top off the battery.
As of today there are no obvious innovations in battery technologies that seem likely to give an aircraft the necessary range at take off to take passenger distances in excess of 1000 miles.
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