[V.Narayan]

ELECTRIC POWERED AIRCRAFT

Commercial air travel results in 915 million tonnes of carbon emissions a year. This is about 2% of the 46,000 million tonnes of carbon put out into the atmosphere each year by all sources. Air travel accounts for 12% of all carbon emissions created by the transportation - road transportation weighs in at 74% with rail and sea accounting for the balance. Just as with automobiles so with aircraft, the clamour for reduction of the carbon footprints is alive and loud. A single passenger flying say London-New York emits as much carbon as a typical American surburban home does in a whole year on heating! The aviation industry is coming under pressure to cut emissions. More efficient engines and aircraft is one way. Better and faster trains is another way. And electric aircraft for regional traffic is a third way. For the foreseeable future all three will be needed.

Electric powered airplanes or flying dirigibles are not new. Like battery powered cars they have been around for a while. 1883 to be precise! Making an aircraft fly is all about lift ie the wings + the power of the engines on the plus side versus the weight of the aircraft + the drag of the fuselage on the minus side. Lift is so precious that designers go to extreme lengths to reduce weight. The introduction of composite materials has helped in this tremendously. Composites have made possible longer wings that generate greater lift but do so at lower weights than a metal wing. So the convergence in recent years of lighter longer bigger wings that give greater lift for a given power and air frames that are getting lighter has led to a convergence where modern Lithium-polymer batteries can just about give us a practical aircraft. The industry is not quite there yet but the future is in sight now. By 2030 at the latest I expect small all-electric commuter aircraft carrying say 19 passengers to be flying commercially. For larger commercial aircraft a hybrid electric-turbofan seems to be the more practical solution for the interim decade and a half at least.

As real commercially viable electric aircraft come to the fore the very look and arrangement of an aircraft will undergo changes to take advantage of blended wing and body designs that generate greater lift for a given weight and re-positioning of the engines and batteries. Due to fuel burn conventional aircraft get lighter as the flight progresses thus making it more efficient. An electric aircraft will have to carry all the battery weight through out the flight. Fuel burn + the aircraft getting lighter as it flies further + the resultant shifting of an aircraft's centre of gravity has a enormous impact of aircraft design today - that could change under electric aircraft in ways that at least I do not fully understand.

The crux of the matter is this - a lithium-ion battery has an energy density of 160 watt-hours/kg compared to 12,500 watt-hours/kg for aviation fuel. On the other hand electric motors being efficient at energy conversion give 145 wh/kg to the shaft or ~90%. Gas turbines give 6500 wh/kg at the shaft. But that still is a ratio of 1:45 in favour of aviation fuel. To bridge this gap for now we need lighter airframes, longer lighter high-lift wings, and blended designs for lower drags. These long wings (ie high aspect ratios) mean the aircraft cannot fly fast at sub-sonic speeds - it is better suited for short regional hops where speeds of 300 to 400 kmph will suffice.

Here are some of the more recent electric aircraft that are under development as experimental machines and precursors of the real thing.


Airbus E-Fan

Photo Source: Airbus
Photo Source: Airbus
Top speed 220 kmph; Cruise 160 kmph; endurance 60 minutes; Carries 1 pilot & 1 passenger/observer

The Airbus E-Fan is an experimental proof of concept aircraft that is flying to study and establish the aeronautics, weight, battery, electric motors' parameters and mathematics of electric flight. Other than the whole business of light and powerful motors there is the centre of gravity differences between a battery and a fuel tank that gradually empties out thus reducing weight as you fly further!

The E-fan is of all-composite construction and is propelled by two ducted, variable-pitch fans powered by two electric motors totaling 60 kW of power. Ducting increases thrust while reducing noise, and having the fans mounted centrally provides better control. The motors moving the fans are powered by a series of 250-volt Lithium polymer battery packs They have enough power for one hour and take one hour to recharge.

Unusually for an aircraft, the main wheel is powered by a 6 kW electric motor, which allows the plane to be taxied without the main motors, and is able to accelerate it to 60 km/h (37 mph; 32 kn) for takeoffs. Having the takeoff run performed by the undercarriage relieves some of the burden on the flight motors & main batteries. Accelerating an aircraft on a take-off through its wheels is more energy efficient than using the thrust of the main engines. You will notice it has a bicycle style landing gear arrangement with low weight tiny outriggers to keep balance while on the ground. This has been done to save weight on the main landing gear.


Harbour Air Seaplanes DHC-2 Beaver Electric Plane


Photo Source: Harbour Air Seaplanes
Top Speed, 260 kmph; Endurance, 1-hour; Payload, 6 passengers.

While almost all other projects are being led by manufacturers or scientifically minded enthusiasts Harbour Seaplanes of Vancouver, Canada converted one of their 40 commuter airplanes to an all electric configuration and test flew it for the first time in December 2019. They took an existing de Havilland Canada DHC-2 six passenger commuter and fitted it with a 750 shp electric motor from MagniX of Australia and added in a 60-minute charge Li-polymer battery. What will follow will be a 2-year testing and flight safety programme eventually leading to certification. Initially Harbour Air will deploy its electric fleet only on routes of up to 30 minutes flight duration. This is said to be the world's first test flight of a commercial aircraft.


Augusta Westland Project Zero

Of all the 200+ electric aircraft projects being pursued across the world one of my favourites is the Augusta Westland Project Zero concept tilt-rotor craft. It is half helicopter, half-aeroplane and fully rethinks the way fuselage, wings, engines and the ducted fans can be rearranged in newer ways making use of the new technology, materials, centre of gravity flexibility that is now up for offer.

Photo Source: Wikipedia
Photo Source: Augusta Westland

Here we see a blended wing design ie one where the wing and airframe blend into each other in a manner that reduces drag and increases lift the two most precious factors in flying. Further you see how the ducted rotors can swivel to provide thrust both vertically or horizontally or at an angle in between. Still further, uniquely, when parked at an airstrip the ducted rotors can be turned up and used as windmills to recharge the batteries. :-) . This is a proof of concept prototype and is now being converted to a hybrid configuration with a light weight diesel engine driven generator to help extend endurance when needed. This prototype is a glimpse of what the future will behold.


Eviation Alice

The aircraft we saw this far are those that have flown. But even more exciting ones are under final stages of development and we are likely to see them at our airports before 2025 is out.

Photo Source: Matti Blume

Eviation Alice is an Israeli-American design that was displayed at the Paris air Show in 2019. It is a 9 passenger aircraft designed for doing up to 500 nautical mile (~925 kms) hops at 240 knots (~440 kmph). It carries a 900 kwh charge in its Lithium Polymer batteries. Note it has three propellers each driven by a 260kw motor. Fitting two of the motors at the wing tips where the drag producing vortices flow actually reduces drag in a manner similar to winglets we see on airliners today. The body if you notice is flatish at the bottom ie it acts as a deliberate and significant lift inducing plane thus helping the overall lift.


Airbus E-Fan X

Photo Source: airbus.com

The largest aircraft by size being experimented with is the Airbus E-Fan X. A BAe -146 four-engined regional jet liner is being converted to have one of its turbofan engines replaced with a 2MW electric motor. A 3.4MW generator is fitted at the rear driven by a proven turboshaft engine and all this is mated to 2000kgs of batteries. The turbo-generator can recharge the batteries when needed., if needed. This aircraft again is a proving test bed for all these new ideas and pieces of equipment and to establish the operating protocols and safety norms. Airbus expects to have this flying by 2022 and will form the basis of a regional E-Liner they expect to put into service before 2030.

In terms of power out, weight and speed this testbed will be a multiple of anything electric currently flying.

These are only a few examples from leading companies of research and development that is now being poured into electric flight. Airbus seems to be the most far ahead in its development, but lets see how things emerge.

There have been several historical electric aircraft, most motor gliders or sail planes of some kind. Two landmark aircraft of the recent past deserve mention.


The Solar Impulse 2

Photo Source: Anthony Quintano

Solar Impulse 2 was a solar re-charged, electric airplane which in 2015-16 flew around the world in hops. On this circumnavigation it flew non-stop 7212 kms between Japan & Hawaii - the longest distance flown by a solar powered aircraft. Its wing span at a whopping 236 feet is just slightly less than that of the 500-tonne Airbus A380!! Longer wingspans give greater lift at lower speeds. So if you can get a wing made of a super light material, like composites, you can get to a point in the lift-drag-power matrix where only a little power is needed to render the lift workable.

Ultimately solar powered electric airliners will be the future. But that day may still be 50 years away. Maybe the youngest on this august forum will live to see it.


Militky MB-E1

Photo Source: Wikipedia

This little aircraft will in years ahead be remembered as the first full size piloted all-electric aircraft that could take-off on its own power. It first flew in 1973 and used to have an endurance of about 12 minutes. It was powered by a 10 kw motor!!! Its long glider like wing span enabled it to take off and stay aloft at low speeds.

Before pure electrics come in full force, if ever, on medium to large airliners it is likely that the most practical route will be the hybrid turbofan-electric motor engine. An aircraft needs X power at take off and climb and a lower power rating for cruise. This creates the situation of using all-electric for the cruise mode and clutch in the turboshaft/turbofan for the take-off and climb phases or when the batteries needed charging to increase the safety margin of endurance. How all this will be arranged I cannot say for now. That's the route Airbus is looking down for a 100-seater regional aircraft flying typical routes of 500 to 800 kms.

At the Singapore Airshow earlier this month Airbus flew a scaled down proof-of-concept demonstrator called Airbus Maveric ..... it indicates what aircraft in 2035 might look like...

Photo Source:airbus.com


The times they are a changing.....

[GTO]

Thread moved out from the Assembly Line. Thanks for sharing!

Will go to our homepage this morning .

[Keeleri_Achu]

Quite an interesting read sir. Thanks for sharing.

Development of electric aircrafts are bringing in a lot of changes in the industry. While propulsion is the obvious one, the changes we're seeing in terms of design are also staggering. Ever since the advent of jet age, IMO only very few aircrafts stood out in terms of design - 747, Concorde, A380. Even then they all had a lot of things in common. For the layman, it's too hard to distinguish between a Boeing and an Airbus. It makes me very happy to see that there is going to be at least some change happening in the coming decades. The AW Project Zero reminds me of a production spec Quinjet from the Avengers.

While it's obvious that electric airplanes will be used for short hops, I still expect to see them utilizing Solid State Batteries which might become available in the coming years.

Long range planes will still continue to use conventional engines, at least for the next 30-40 years. So it's safe to assume that the travel time for say a JFK-DEL flight won't change any time soon. For better or for worse. I'm just sad that with all the emphasis being given to electric planes, supersonic travel for the masses will still remain a distant dream. I know some players will market it for the CEOs of the world. But for the rest of us, it'll never be an option. Boeing thought that the 747 is going to be a temporary fix until supersonic planes took off. We all know how that turned out.

I'm adding a video about electric planes which I saw a while ago. It's an interesting watch.

https://www.youtube.com/watch?v=VNvzZfsC13o

[binoybnair]

Electric motors are far more efficient but weight of the current batteries will definitely make a large long-range battery-powered aircraft infeasible. There are two possible solutions: (a)come up with radically new battery chemistry to make them about 20-30 times more energy dense than what they are today OR (b) use Hydrogen as fuel.
IMHO Hydrogen +electric motors is an ideal combination for aircraft (Not so much for cars, as per the almighty Elon). Also, hydrogen storage in tanks is far less of a problem today, so there is almost zero likelihood of another Hindenburg.

[Jeroen]

Recent studies suggest that it is not just the carbon emission we need to worry about when it comes to conventional planes.

Airplanes contrails are changing the climate as well:

https://thebulletin.org/2019/07/airp...g-the-climate/

Jeroen

[ds.raikkonen]

Superb thread!

I think electric air taxis in Singapore will be the cornerstone for electric aviation as the need there is pushing companies/entrepreneurs as it has tremendous value for consumers (probably Mumbai too in some time). Till then it will always be a conflict of battery weight & specific energy density. Also, will we see any energy recovery systems in aircraft?

[Jeroen]

We were discussing something similar on this thread:

https://www.team-bhp.com/forum/comme...nts-one-3.html (An electric airplane? EasyJet wants one!)

I am somewhat skeptical on the air taxi idea for relative short hops; say less than 1000 km. Over time thing might change, but here is my thinking.

Currently a single engine 4-5 person plane will cost you in access of USD 1,000,00.-- Say for instance a nice Cirrus SR22. That will carry a pilot and 3-4 passengers in comfort, leather seats, Bose headsets, the works.

https://www.aeroprague.com/flights/cirrus-sr-22/

If I rent it Tthat will cost me Euro 340 per hour, + VAT + fuel. Fuel will be, give or take, Euro 90 per hour. Also, you are likely to have to pay landing fees. In Europe usually between Euro 15 - 45 per landing.

Now, I don’t know what the cost price of electric plane would be, but lets assume it is in a similar price bracket. The only difference in cost would be no fuel, but you would still need a pilot. And you need a pilot with a commercial rating. (I can fly this Cirrus, but not with paying passengers!). They don’t come cheap.

Some of these E-flying-taxi also promote their products as highly automated and very easy to fly. But from a pilot certification point of view that does not make any difference.

As you would be running a commercial aviation service you will need very different and more expensive insurance too.

The other thing is if I order an (electric) air taxi to take me from say Amsterdam to Paris for a meeting, that taxi gets stuck in Paris. Its not like taxi/Uber in a major city, that will just pick up new passenger within a few minutes. So very likely that air taxi will have to wait for me to finish my meeting in Paris and then fly me back to Amsterdam. Effectively it means I will need to pay for 6-10 hours of use of the plane and pilot with only maybe 3-4 hours actual flying.

An affordable taxi business model relies on heavy utilisation of the vehicle. Not possible in this model, unless it scales up to, well current road taxi volumes.

The other thing is, it sound pretty cool, being flown around in your own little air taxi. But I can tell you, quite a number of folks who came along with me, did not particularly like it all. These little plane, no matter how they are powered are very susceptible to turbulence. You get bounced all over the place. The only way to avoid that is to climb as high as you can get. There are a few problems with that too. Planes like the Cirrus can fly at altitudes up to 25.000 feet, but you need to put an oxygen mask on. You can not have pressurised cabins on these little planes, let alone on a small electrical plane. Too much additional weight.

Another factor is the very busy airspace here in the Netherlands. Such an air taxi needs to be fully equipped and certified for Instrument Flight. But effectively you will be operating at low altitudes under visual flight rules as it is the only way to avoid the congestion on the higher altitude corridors and routes in Europe.

Here in Europe on the 500 - 1000 km distance they will need to compete with trains. The most luxurious first class ticket, return, even for a couple of folks travelling together is likely to be considerable cheaper than an Electric air taxi.

I am sure there will be a use for it, but likely for pretty exclusive “taxi services” for those that can afford, or for whom time can be critical too.

There are very few air-taxi today. (I know a few, but that is either very exclusive, or very basic point A ->B and vice versa, e.g. shuttling people across a lake, taking skiers up a mountain). There is a reason for that. It is just very expensive and complicated to fly a small group of people, commercially, compared to current available modes of transportation.

I do not see air taxi’s taking off, electric or otherwise taking off anytime soon. Small Electric Regional airliners, could be a more sensible way forward I think. But then again, I do not run an airline business. I just know how to fly a few small planes

Jeroen

[AirbusCapt]

The simplest solution here may be the most workable as well. Considering current technologies, the best thing to do is mate a powerful APU to an electrical grid to enable ducted electric fan engines to run. An APU burns only about 2/300 kgs of jet fuel per hour compared to a turbofan burning 2000 kgs per hour. A savings of 1500/1800 kgs per hour per engine, on each flight is a substantial help to our environment.

[timuseravan]

Originally Posted by V.Narayan

ELECTRIC POWERED AIRCRAFT

The crux of the matter is this - a lithium-ion battery has an energy density of 160 watt-hours/kg compared to 12,500 watt-hours/kg for aviation fuel. On the other hand electric motors being efficient at energy conversion give 145 wh/kg to the shaft or ~90%. Gas turbines give 6500 wh/kg at the shaft. But that still is a ratio of 1:45 in favour of aviation fuel.

As you rightly point out, this is the cruz of the matter. For airplanes, weight is the number one consideration. There is a lot of research going on to improve the energy density of batteries but even in labs, the best achieved so far is about 700 watt-hours/kg. And this technology is nowhere near commercialization.

A second consideration is the total operating cost including the initial price. Again this is very expensive compared to gas options.

Sadly I do not see any large scale adoption of electric aircraft for the foreseeable future.

[Jeroen]

Originally Posted by AirbusCapt

The simplest solution here may be the most workable as well. Considering current technologies, the best thing to do is mate a powerful APU to an electrical grid to enable ducted electric fan engines to run. An APU burns only about 2/300 kgs of jet fuel per hour compared to a turbofan burning 2000 kgs per hour. A savings of 1500/1800 kgs per hour per engine, on each flight is a substantial help to our environment.

As already mentioned by AlphaKilo on the earlier mentioned thread: A hybrid plane:

https://e-sat.de/en/silent-air-taxi/

Jeroen

[arzala]

Very informative thread. However in-terms of practical acceptance of such planes, we first have to be happy (range, cost etc.) with on-road vehicles (cars, buses etc.) then only we can think about in-air vehicle because by law of physics you need more power to lift + push (airplanes etc.) than just push (cars, buses etc.)...

[Jeroen]

Originally Posted by arzala

Very informative thread. However in-terms of practical acceptance of such planes, we first have to be happy (range, cost etc.) with on-road vehicles (cars, buses etc.) then only we can think about in-air vehicle because by law of physics you need more power to lift + push (airplanes etc.) than just push (cars, buses etc.)...

For reference/comparison:

The world most sold single engine plane, Cessna 172 Skyhawk carries four and has an engine of only 150HP. That is exactly the same as our Ford Focus. Not much difference there.

With that 150HP the Cessna will cruise happily at 115 knots (210 km/h) for 435 NM (805km) using about 120 L of AV Gas. The diesel versions are a bit more economic. The Focus, if you could get it up to that speed, would likely be using more fuel!

The problem is as discussed weight, batteries will weigh so much more than fuel, so you will need a much more powerful engine to get similar performance. Or accept a much lower performance, usually range/duration

Jeroen

[AlphaKilo]

Contribution from my side:

https://www.dlr.de/content/en/articl...-aircraft.html

Following on from the first electrically powered small aircraft, the next big step for electric flight will be in the commuter class, with 19-seater aircraft. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) has teamed up with Bauhaus Luftfahrt to work on the CoCoRe (Cooperation for Commuter Research) project, which examines the possibilities and potential for hybrid-electric 19-seater aircraft. This has revealed that electric propulsion systems can be used to reduce carbon dioxide emissions from this class of aircraft on short, frequently flown routes over distances of up to 350 kilometres. In the future, this distance range will also include air taxi connections from airports in less well-connected, medium-sized cities.

[KL01toKA03]

Originally Posted by Jeroen

The problem is as discussed weight, batteries will weigh so much more than fuel, so you will need a much more powerful engine to get similar performance. Or accept a much lower performance, usually range/duration

I guess a smaller electric plane/drone for intercity commute would be the easiest to develop. If it can land on a rooftop helipad, it will make more sense than a normal helicopter because it could be refueled easily anywhere.

[V.Narayan]

World’s Largest Electric Commercial Aircraft Completes Its First Flight


The eCaravan is a modified Cessna Grand Caravan 208B nine-seater aircraft. On 31-5-2020 it completed a 30-minute concept demo flight of what has become the heaviest/largest (?) electric plane to fly. The flight took place at Washnigton State, USA. The aircraft cruised at ~100 knots {185 kmph}.

AeroTEC and magniX are the two companies that modified the aircraft.
It is powered by an all-electric motor, which makes 761PS of power and a whopping 2,814Nm of torque.

The Cessna Caravan 208 has a wingspan of 52 feet, length of ~37 feet and normal maximum take off weight of ~3600 kgs.

It has been modified by AeroTEC from a stock Cessna Grand Caravan 208B, a nine-seater, single turboprop utility aircraft. The all-electric powertrain is from magniX. Called the magni500, this liquid-cooled electric powerplant is capable of generating 761PS of continuous power and a staggering 2,814Nm of continuous torque. The electric motor is claimed to be capable of delivering full torque output even at low RPMs, unaffected by altitudes. The drive is direct to the propeller, so there is no need for any maintenance-prone reduction gearbox, which is usually the case with conventional turboprop engines. The motor has an efficiency rating of over 93 per cent and weighs 135 kg. This weight is similar to the PT-6A turboprop engine it replaced.

That’s because such a powerful motor commands the need for extremely high-capacity batteries. It needs a nominal voltage of 540V and the juice is said to have been supplied by a lithium-ion battery pack weighing about an insane two tonnes. The battery pack is so big that it basically occupied all the passenger space in the aircraft, leaving room only for the pilot. Nevertheless, it is still a considerable achievement for the short-distance air transportation industry as electric vehicles (including aircraft) are inherently a lot more affordable and easier to maintain compared to conventional ones.

The second photo clearly shows the size of the engine bay of the Cessna Caravan 208 showing the volume occupied by the turboprop and the much smaller space needed by the electric motor.