Leeham News and Analysis
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Leeham News and Analysis
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Eviation announces firm configuration for battery-powered 9-seater
By Bryan Corliss
July 1, 2021, © Leeham News: Seattle-area electric aircraft builder Eviation revealed Thursday that it has reached firm design configuration for its battery-powered, nine-seater Alice aircraft.
The announcement – which typically would signify that Eviation designers have locked-in design features, so that suppliers can use their drawings to begin work on their components – is more of a formality, however.
Eviation Executive Chairman Roei Ganzarski said suppliers already have delivered shipsets for the first production Alice, and mechanics at the company’s Arlington, WA, plant have begun final assembly.
“The plane is being built as we speak,” Ganzarski said. The company is on track for a first flight before year’s end, he added.
The suppliers include well-known European giant GKN, which is providing the wings, empennage and wiring systems for the plane. But it also includes industry newcomers like Multiplast, which is a French manufacturer best-known for fabricating composite yacht hulls.
Eviation’s sister company, magniX, delivered the first motors last month. Both companies are owned by Singapore-based Clermont Group, and Garzinski is both Chairman of Eviation and CEO of magniX.
Design changes
There have been significant design changes since the prototype Alice was unveiled at the 2019 Paris Air Show.
- The original plan to power the aircraft with three 350 kw motors has been scrapped in favor of using two 650 kw motors;
- The prototype had motors with pusher propellers mounted on the wingtips and tail; the production model has motors with tractor propellers mounted alongside the aft fuselage;
- The prototype had a V-shaped tail, which has been replaced with a T-tail for production;
- The prototype had tail-dragger landing gear, which has been replaced with a tricycle configuration.
Ganzarski said the changes were driven by customer feedback and were aimed at making the Alice “more applicable and attractive to the operators, so they can more-easily integrate the aircraft into the fleet.”
So far, Eviation has only one announced customer, regional airline Cape Air, based in New England, which has said it wants 92 Alices.
The Alice was designed with a range of up to 650 nautical miles (1,200 km) on a single charge, with a cruise speed up to 260 knots (480 km/hour), using current battery technology.
It’s not “potential, maybe, future batteries from a company that may go bankrupt,” Ganzarski said.
The battery technology is improving, however, he said, driven mostly by innovation in the electric car industry. Ganzarski said the performance of the batteries in Eviation’s flying testbed – a de Havilland Beaver floatplane operated by Canada’s Harbour Air – has improved more than 33% in 18 months of tests, through a combination of battery upgrades and learning how to better arrange them within the aircraft.
Eviation’s announcement is a sign that change is coming to an industry segment that’s produced a lot of press releases but few actual flying machines, Ganzarski asserted.
“It’s a huge step in that you look around at electric aviation and you see a lot of cool CGI graphics and quote-unquote ‘orders,” but you don’t actually see an airplane,” he said. “But this is real. It’s being built in our hangars in Arlington and we’re about to go fly it.”
650 NM with useful payload is quiet incredible!!! Can’t wait to see it fly. I don’t understand why the switch to tractor vs pusher props. Aren’t pushers more efficient? Is this for motor cooling?
Tractor propellers ‘see’ clean air, undisturbed flow. Pusher propellers face the pylon wake, plus the nacelle upstream disturbance. I don’t recall what Eviation argued, when they installed the wingtip engines with pusher propellers, in that previous awkward configuration. Going more ‘mainstream’ for engine location hints that tractor is better.
Generally the tractor or puller type of prop engine is more efficient, not the other way around. The result of tractor types being almost universal speaks for itself. The best known pusher is the Piaggio Avanti, but they were after other features.
https://airplaneacademy.com/pusher-vs-puller-propeller-aircraft-compared/
Very informative material on the comparison between puller and pusher propeller installations, thanks for bringing it up. Eviation seems to be on the right track with the latest Alice configuration. At least for the engines and propellers, which is no small feat.
A lot of wind tunnel testing showed that pusher propeller was more efficient than tractor at least on the specific case of the Convair B-36 hence its use on the B-36. A single tail pusher on a carefully designed fuselage can maintain laminarity in a properly designed fuselage eg Celera OTTO 500. I think it depends much on the quality of the design ahead of the pusher prop.
The original Alice’s wing tip pushers were designed to exploit wing tip vortices.
The New Alice is shown of course with rear podded pushers. That may also be to keep the props from impacting the tarmac on rotation, or further forward and out of the wings wake or it may be to ensure good airflow over the cooling intakes which would need to cool the batteries and engine in the high current takeoff phase.
The B36 used air cooled radial engines which had higher frontal drag than the other choice for large bombers the V12 liquid cooled engine with its lower frontal area. The long range mission required for this plane and the large radial engines at the leading edge weren’t as efficient as a smooth cowled rear pusher with a ducted leading edge air intake. It worked for that configuration with radials, not really applicable for small cross section turboprops that soon came along, example of long range passenger TP was the Bristol Britannia. Its predecessor the Bristol Brabazon, like the B36 another giant of the sky, used smaller radials coupled in pairs on leading edge but also used slim engine cowls and ducted cooling intakes showing a different take on the long range issue…..and with it went a possible era of bunk beds and dining tables, instead we got railway style seats and a meal on your lap.
My research has found a proposed B-36C version, never built, which was to have 4 turbo props on the leading edge as tractors , as of course the TP was a much slimmer profile. To boost the speed 4 turbo jets were integrated in the rear of the TP nacelles. More than likely the B-47 was preferred to this version
The YB-36C was to be turbo compounded with jet thrust recovery. The need for the jet nozzle meant a tractor arrangement. The engine was the Pratt and Whitney R-4360-51 VDT (Variable Discharge Turbine) prototype. The expanding gases of the 28 cylinder engine drove the CHM-2 turbocharger/jet engine to develop 4,300 horsepower+jet thrust. This turbo-compound monstrosity was the last gasp of the piston engine in aviation.
@Dukeofurl
There is actually a picture of the B36C in you link showing the R-4360-51 VDT in tractor.
https://www.secretprojects.co.uk/proxy.php?image=http%3A%2F%2Fi37.photobucket.com%2Falbums%2Fe68%2FGTwiner%2FF111%2FB36Cinfo.jpg&hash=ac449aebc7ed4088c558ad9ebe3abee8
“The B-36C was a modification to the B-36 design proposed in the mid 1940s. The R-4360 engines would be replaced with four Wright Aeronautical gas turbine engines for propeller drive and four General Electric TG-180 gas turbine engines for jet propulsion. The two engine types were paired and mounted in tandem nacelles. The jet nozzles were directed three degrees downward and three degrees outward to so that the hot gasses did not burn the horizontal tail.”
https://www.secretprojects.co.uk/threads/convair-b-36-derivatives-b-36c.12069/
What you suggest may have been another derivative from around 1945 ,before it first flew, but the change from pusher to tractor was possible for TP and made more sense than turbo compound.
They did fly a swept wing all jet YB-60 derivative.
And the B-36 was replaced by the B-52 , the B-47 was a smaller capacity plane (although they used the pylon and twin engines from that plane for jet add on)
Interesting specification on range and if you throttle back you get a lot more range for your buck.
Equally an interesting mix of who owns and where the parts come from.
As well as the best place to build it, Seattle USA!
Is any of it built in Seattle ? Eviation is an Israeli company , GKN and Multiplast are not US located either.
They seem to have an ‘office’at Arlington Municipal Airport WA after moving from Phoenix..maybe following the money.
All I know is its Washington Based (now) and who knows all the ins and out?
https://newatlas.com/aircraft/eviation-alice-magnix/
Stuff coming from all over like many mfg these days.
So with twin 650kW motors at the rear, its can be compared with the Piaggio Avanti which has the same ( turbine) power.
They dont seem to take on board the Avanti’s aerodynamic advantages of the engine spar through the cabin behind the cabin rather than the less than optimum under floor position. The 3 lifting surfaces isnt replicated either with the downward force T tail not being optimum either. I would have thought a mid wing location for the engines were better as well, as used by every other pax turboprop ( bar one)
With the Piaggio organisation having tanked I suppose that rules out them having a head start on the newbies with a simpler conversion of their turbo prop to electric 9 seater
Here we go again.
It shall be tough to fly a nine-seater for 2.5 hours at 265 knots (plus regulatory reserves), 100% on battery energy. And based on current battery technology.
Bjorn could verify the Alice numbers. This would be a similar exercise to the 19-seater that is currently being designed at the Bjorn’s Corner.
I think this is with the Aluminium Air Battery variant?
Aluminium–air batteries are primary cells, i.e., non-rechargeable. Once the aluminium anode is consumed by its reaction with atmospheric oxygen at a cathode immersed in a water-based electrolyte to form hydrated aluminium oxide, the battery will no longer produce electricity. However, it is possible to mechanically recharge the battery with new aluminium anodes made from recycling the hydrated aluminium oxide.
I believe the report is its with conventional battery.
Range listed seems far in excess of what is achievable currently.
I see the more specific details have been published here
https://electrek.co/2021/07/01/eviation-tesla-of-aircraft-production-version-unveiled-range/
Its clearly longer, wider wingspan and heavier than Avanti, but critical numbers are hard to compare , empty weight in a turbine plane excludes fuel, but EV would include the heavy batteries
https://en.wikipedia.org/wiki/Piaggio_P.180_Avanti#Specifications_(P180_Avanti_EVO)
If the Eviation Alice variant is the one using Aluminium Air Batteries it should gain weight as it flies and land heavier than it took off as the Aluminium Electrodes convert to Aluminium Oxide.
I doubt that conversions of existing aircraft into electrical will ever be half as good in performance as new designs optimised from the beginning but will serve well as test beds.
Having said that, I like the idea of a Cessna Skyvan conversion using the Underbelly Cargo Pack as a battery pack. Particularly appealing is the idea that it can be firewalled out of the structure of the aircraft and could be jettisoned when on fire. Batteries are starting to look like hypergolic propellant rockets.
Wrong approach, using a new carbon fibre fuselage and wing is not going to provide any useful benefits in this size of plane and the ultra short ranges they will be operating in. The weight of the batteries is still the hill to climb and existing plane conversions will take your market while a new design is going through truckloads of certification paperwork. The under floor battery location seems to work for existing planes ( as a pannier) and will be the same for a new design as easy access for repair and replacement will be critical. The best a new design might offer is a ‘built in pannier’ ?
The goal is to use batteries as structure which somewhat mitigates their weight.
The frames to hold the batteries has to be strong enough to carry the weight of the batteries, their power cables and the liquid cooling ( remember its going to recharge at a fast clip on the ground when stationary), thats a lot of extra weight that isnt stored energy battery itself You get into all sorts of design issues by having open frames rather than a semi monocoque with the skin as part of the structure. Thats just the wings, which probably can be ruled out as in this class they are unlikely to even have integral wing fuel tanks.
The fuselage storage needs some sort of distributed load panniers below the floor , again a reinforced heavier structure , if its to mimic a small TP with the baggage compartment on same level as passengers.
Compare with this.
https://www.tecnam.com/rolls-royce-and-tecnam-join-forces-with-wideroe-to-deliver-an-all-electric-passenger-aircraft-ready-for-service-in-2026/
It is based on existing airframe, with strong support from Rolls-Royce (RR bought Siemens aviation division) and a structured user like Wideroe (strongly motivated by Norway geography and policies).
Nevertheless the forecast entry into service is 2026.
Given the safety issues surrounding battery fires in electric aircraft while flying the belly pack to be used in the Tecnam is probably one of the safer options given it is an fixed undercarriage. It also potentially allows the pack to be easily changed out for a fully charged one. Waiting 1 hour for a full fast charge is likely to be unattractive. In addition fast charge reduces battery life and charge quality. This is why Volocopter has decided to go with exchangeable battery packs.
Still the belly pack isn’t totally ideal and one would perhaps want critical parts of the pack (such as a firewalls) made of stainless steal and venting directing flames towards the rear of the aircraft away from passenger doors. Pods under the outer wings also makes sense.
I was wondering if the batteries could be put in a place where they could be dropped in the (very unlikely) event they catch fire.
Ideally have two groups of batteries separated by a firewall so if you drop one group you would still have some power left.
Maybe having a “golden spike” that activates after the overheating battery is jettsoned to make sure it burns up instanly making only ashes hitting ground.
EASA/FAA joint approved self destruct demolition charges could be added as a safety device to the battery.
I hope these performance promises are not based on ground breaking new battery technology becoming available very soon. Again.
I suspect many electric flight and eVTOL projects are based around gaining certification and a small market and hoping for battery improvements to give the performance required for larger markets.
It makes more sense to make carbon neutral PtL (Power to Liquids) synthetic fuel or use the available SAF and power an aircraft 1/3rd the weight than an electric aircraft of the same payload range capability.
eVTOL is the only thing I take truly seriously in electric flight. Here is why: Aircraft are extremely expensive and inconvenient to operate because of the vast amount mount of land required for runways and airfields. It can easily take 2 hours to drive to a small airfield and board and deboarding can be almost as difficult. One is then left with the problem of a long taxi ride at ones destination. Helicopters are extremely expensive to operate, inspect. They require high levels of skill to fly and maintain due to their drive trains and their noise and the hazard of their rotor blades makes them further unusable.
eVTOL gets around the inconvenience of requiring long wide runways and vast airports in out of the way land. eVTOL will be easy to learn to fly due to the high level of automatic control. eVTOL will be safe (Lilium Jet has 9 battery packs and 36 electric ducted fans. Volocopter 18 rotors.) Losing a couple of battery packs or rotors/EDF has little impact on safety. If all fails deployment of a ballistics parachute is possible (almost impossible on a helicopters)
The battery packs will be expensive but maintenance will consist of swapping them out after 600 cycles (something that may become 5000 cycles before to long and many eVTOL like Volocopter will swap out battery packs each flight so as to optimize charging on the ground.
A 9 or 19 seater with 200NM range range doesn’t do much in many cases. The time taken to use a light aircraft must be in the order the 4 hours overhead. Time must be taken to pack ones bags carefully, drive to the airport, check in, fly and then drive from the airport with a taxi or hire car one can have travelled half way there by care.
eVTOL however can significantly reduce costs and time by reducing airport fees and making eVTOL ports much closer.
The only time I ever jumped out of an airplane, it had taken off from Arlington airport, a popular local skydiving center. Could that be among the reasons Eviation chose Arlington?
According to details published on FlightGlobal, the maximum take-off weight is now 6,668kg, of which 3,720kg (58 %) is the battery system. The maximum payload is 1,134kg.
Is it possible to reconcile these numbers with claimed speed and range?
https://www.flightglobal.com/airframers/eviation-changes-alice-design-performance-specifications-shift/144376.article
Claimed range and speed are 650 NM and 260 knots, respectively.
Disregarding take-off/climb and descent/approach, this is equivalent to 2.5 flight hours at cruise.
On top of that, energy equivalent to at least one more hour at cruise speed is needed, to account for regulatory energy reserves.
These numbers do not reconcile with a scant 3720 kgf, for an installed battery system.
The new version claims a more modest 440NM range with 22o knots cruise. The aerodynamics of alice are very sophisticated compared to other electric aircraft which are often adaptions of existing aircraft or use simple tube bodies of low aerodynamic sophistication. This is a range of over 800 km and much higher than the 400km Heart Aviation initially plan.
Using the google maps “measure distance” function one can see that while 400km is interesting a range of 600km produces some fantastic options for connecting Ireland with the British mainland and as well as Britain to Scandinavia and the Continent. In addition more interesting and deeper destinations between the Nordic countries across the Baltic to Mainland Europe become possible.
The fuel fraction of the A380, A330 series is over 45% so when one considers the use of carbon fiber composites on Alice and the fact that LiPo batteries are at least twice as dense as Jet Fuel it seems plausible to achieve a fraction of 58% if payload is compromised a little.
I imagine the aircraft, due to its CFRP construction has a smooth skin like a modern high performance sailplane, will maintain laminarity over say 85% of the wing and maybe 75% of the fuselage it might be possible to have glide ratios of 45:1. The fuselage looks like it will be a not only a lifting body but a substantial one.
If it can get to an altitude of 11000m/36000ft it could glide 500km if it achieved a ratio of 45:1.
Celera aviation’s OTTO 500L is in many ways of similar if not more radical aerodynamics.
There isnt going to be 15% empty weight saving by going composite airframe. Remember a large portion of empty weight is other ‘essentials’ like undercarriage, avionics, seating , cabin climate control, the engines etc. Really dont even know why you are comparing planes that can fly 12-18 hours as a benchmark. use the numbers for a 9-12 seater., like the Cessna 208 Caravan which gives fuel fraction in 28% class
Then of course in this weight class, the composite air-frame savings likely become less than 5% of overall weight as you cant make skins and frames even thinner. Already the range expectations are being managed down, expect more in that area.
Look at the troubles – insurmountable- that Beech/Hawker and Bombardier had making composite fuselages for their business jets, Learjet 85 and Hawker 4000. Honda has its Hondajet in production but they had the vast resources of their business to help them make it …over many many years.
Building a prototype is possible, seeing it flying with passengers is a pipe dream.
“benchmark. use the numbers for a 9-12 seater., like the Cessna 208 Caravan which gives fuel fraction in 28%”
Why should I benchmark against a 40 year old aluminium design that is aerodynamically very basic and inefficient? The aircraft is optimised for cheap payload flights around 200NM to locations inaccessible by sealed road or scheduled priority parcel/mail flights for FedEX. I may as well use the Ju 52/3m.
The four points I made need to be taken as a whole.
1 Fuel/MTOW ratio mass fractions of 45% are easily possible. Doesn’t matter if its an A380 or a Cessna 208 sized aircraft.
The Rutan Voyager took off on its 1986 around-the-world flight at 72 fuel/MTOW percent, the highest figure ever at the time. Steve Fossett’s Virgin Atlantic GlobalFlyer could attain a fuel fraction of nearly 85 percent, meaning that it carried more than five times its empty weight in fuel. So the Alice should be able to do 58%.
2 The higher specific gravity of batteries versus full fuel tanks helps.
3 The use of composites helps weight reduction. You say its only 5% (which I accept) but that still improves fuel mass fraction 5%.
4 In the case of the Eviation Alice the use of composites allows for compound 3D contours that allow lifting body, blended wing body, laminar fuselage and wing profile as well as smooth surface skin.
The same thinking is in evidence in the OTTO Aviation Celera 500L.
The Pipistral Alpha Electro trainer has the same configuration as a Cessna 208 Caravan (no wing brace though) and achieves around 60 minutes endurance at 85KIAS with 30 minutes VFR reserves. It’s 126kg battery pack means it has a mass fraction of 23%. It’s perfect as a trainer but not useful for commuter flights. It has a glide ratio of 15:1. If the glide ratio can be improved 15:1 to 35:1 (still less than a sail plane) and the battery fraction increased from 23% to 58% it would have the same range as Alice. This is all plausible.,
Theres a reason smaller plane designs like the Cessna Caravan and others are like the EverReady battery bunny – just keep going- there is no useful weight savings from modern design in aluminium. Composite design and construction in this weight class requires more than a startup funding and a small shed at a Municipal Airport outside Seattle. ( Notice the small business jets have really useful range where the weight saving matters).
They havent even used the experts like Scaled Composites to build their proof of concept demonstrator. A production line and series build will take even more resources, thats if they even make it through certification – will they try the Uber approach of ignoring existing rules and just going ahead anyway and using bluster to try and get their way approved by certifiers ( didnt work for Boeing either but thats a different story)
The last paragraph of the interesting comment shows everything that is critical with 100% batttery flight, when referring to the Alpha Electro:
(1) low cruise time = 1 hour
(2) low reserve time = 0.5 hour
(3) low cruise altitude = not mentioned, but should be couple of thousands of feet
(4) low payload = not mentioned, but equal to two (thin) humans
(5) low cruise airspeed = 85 KIAS
This is the application where 100% battery flight is practical: missions from A to A, with all the lows listed above.
When flying from A to B, and when real deal mission specs come in (9 pax, 650 NM, 260 KTAS, at a decent cruise altitude), 100% battery flight is not practical. Actually, it is not possible.
One observation on L/D ratio: for a given airplane size, and for a given cruise airspeed, there is very little that can be done to improve L/D significantly.
The Alice shall have a cruise L/D similar to the airplanes it matches in size and speed: the Pilatus PC-12 and Cessna Denali, with an estimated cruise L/D between 9 and 11:1.
Also, cruise altitude is crucial for efficient cruise airspeed. Batteries do not enjoy climbing and high flying.
I was referring to glide ratio not L/D but I think the two must be linearly related. The OTTO Aviation Celera 500L, which is based around laminar flow, claims a Glide Ratio of 22:1 (50% better than Pipersel Alpha) and I would expect Eviation Alice to be about the same. If they can use the fuselage to generate good lift at take-off rotation but modest amounts at cruise they can keep the wings small thereby reducing parasitic drag. Batteries probably don’t like climbing because of the high current levels but they also don’t need air (being anaerobic) so theoretically an electric aircraft can fly in the upper stratosphere free of parasitic drag only using power for induced drag.
This is probably behind Elon Musks supersonic transcontinental eVTOL proposal.
I envisage it as being somewhat like the Lilium Jet: very small wings and undercarriage can be used to save much weight and drag because its VTOL.
The idea is to get to the electric jet to the upper stratosphere and cruise at Mach 2 using the electric ducted fans where there is little parasitic drag.
At some point Musk says (at about 400wh/kg) electric aircraft become viable. I’m not sure at what battery energy density supersonic eVTOL becomes practical, I rekdon its about 500WHr/kg. It would be when there is enough energy to get to about 80,000 feet and then accelerate to Mach 2. The North American XB-70 Valkyrie had phenomenal L/D ratio as good as subsonic jets due to those downward folding wave rider wing tips.
Personally I’m arguing for the sake of arguing. eVTOL makes sense but for ordinary aircraft using PtL/SAF fuel makes more sense.
None of that makes any sense….
To you
1 One wants substantial lift from the fuselage of a combined lifting body with wings, such as the Eviation Alice, during take off. Once at cruise one wants the angle of attack of the lifting body fuselage at the zero lift angle of attack. This is because the low aspect ratio of the lifting body fuselage means it will generate large amounts of lift induced drag. Hence one wants a kind of Decalage between the fuselage with the wings at slightly higher zero lift angle than the fuselage so that the more efficient wings provide lift at cruise. In this way the wings of the Alice can be kept small thereby reducing parasitic drag while still obtaining satisfactory take of performance from the lifting body.
2 An electric aircrafts power plant, unlike a piston or gas turbine engine, is independent of the need for air to maintain power. Only the EDF or ‘electric ducted fan’ or propeller needs to be big enough to absorb this power in thinner air.
By flying as high as possible electric aircraft can almost completely eliminate parasitic drag (the major source of drag) and thus become highly efficient. For instance at about 60.000ft the air density is about 15% or less and therefore is parasitic drag only 15%. You can fly 2.5 times faster for the same drag.
Lift induced drag stays more or less the same irrespective of altitude and speed. This is why jets can compete with piston aircraft, their engines do not loose efficiency at high altitude and so simply fly higher to obtain thin air.
By using VTOL the wings of an eVTOL can be sized independent of the need to provide realistic take-off and landing speeds and need be only large enough to provide sufficient lift when at very high speed. The wings need only be large enough to provide lift at say Mach 0.8 at seal level or Mach 2 when in the upper stratosphere. The expensive and heavy undercarriage can also be eliminated.
The formulae for the potential kinetic energy of an object is:
KEpot = mgh (in joules). An object with a battery with an energy density of say 100WHr/kg (=360, 000 joules/kg) can be driven to an altitude calculated from:
mgh = 100 x 3600 which by making h the subject leads to:
h = 360000/g = 36000 meters.
Assuming an aircraft with 50% battery fraction of 200WHr/kg ie overall 100WHr/kg as above and a propeller/EDF of 75% efficiency and a Glide Ratio of 10:1 (90% efficient) the achievable altitude is
36,000m x 0.75 x 0.9 x 0.75 = 18,225.
The 0.75 term is to account for my assumption that the lift is being produced at 4 times the amount needed to sustain level flight so that the high climb rate ensures that only 0.25 of the energy is wasted in sustaining level flight.
If there were a energy density of at least twice this (batteries of 400WHr/kg) then there would be sufficient energy reamining at 18225m/60,000ft to propel the aircraft with very little drag at high speed at altitude. This would then be followed by a 10:1 glide from 24,300m i.e. 243km.
For instance if the wings were sufficient to support the aircraft at Mach 0.3 at sea level (about 200mph) they should also support the aircraft at Mach 0.9 at 75,000ft where air density is about 0.11 (since lift varies proportionately to the square of speed.
EDF Fans can operate supersonically. It doesn’t need a gas turbine at the core.
Supersonic L/D or Glide ratios are usually very poor 9qaround 5:1 or so but the North American XB70 Valkyrie had a supersonic L/D ratio of 15:1 which is about the same as a B737.
So the physics proves Musks supersonic transcontinental eVTOL electric aircraft is possible so long as battery energy densities are well in excess of 400WHr/kg.
500WHr/kg can be sourced in small quantities for lab use.
Since when is the Alice a lifting body ? The images showing a fuselage section in the hangar at Arlington are tube like to me, but nearer a ‘horseshoe’, the flattened base is likely to provide more space for the battery storage area.
https://www.eviation.co/company/#Who-We-Are
As for the ‘electric motor’ not needing air , its the propellors that provide thrust so they must be optimised for the thinner air at cruise , likely for this class of short hopper to be around 10,000 ft or less…its your fantasy that its getting to 60,000 ft…it would use up all the battery power in the climb to get less than halfway. The rest is still nonsense but instead of B-36 reference its now XB-70
@Dukeofurl, The Alice’s cross section is a sort of flattened Reuleaux triangle. A bit like an Me 262 Schwalbe. Lift is produced by downwash and a flat bottom will do that well. Forget the claim that the Bernoulli principle explains lift. . It’s also important to ensure the airflow doesn’t detach over the upper portions as well as this would produce vast amounts of drag, clearly the Alice isn’t going to cause that. The wing area of Alice looks tiny. It’s clearly relying on the fuselage for some of its lift.
Which geometrical shape produces lift more efficiently, id est, with a better L/D ratio: a fuselage or a wing?
Assuming that a wing produces lift more efficiently than a fuselage, why would someone ‘transfer’ production of a single pound-force of lift, from the wings to the fuselage?
@PAFranke, You would organise the Decalage angle of the lifting body fuselage with respect to the wings so that when at cruise the fuselage would be operating at its zero lift coefficient and the wings doing all of the lifting. The angle would probably be about 1.5 degrees. This would mean the lifting body fuselage would be producing no induced drag a cruise. It would be producing drag only at take-off. The parasitic drag is the bulk of drag and would be there anyway. In this way the wings can be made smaller (since they are not sized for take-off) and their parasitic drag reduced.
Induced drag mainly comes from the vortices of high pressure air caused by high pressure air from below the lifting surface migrating up to the low pressure zone above it. This mainly happens at the wing tips.
The Alice is a very advanced design in this regard.
Glide ratio is equal to L/D. And there is no way, repeat, no way, an airplane of the size and speed of the Alice can get to 22:1.
22:1 is the cruise L/D level of the superefficient Dreamliner B787.
Aircraft of PC-12 and Denali size and cruise speed come out at 9 to 11:1.
As for battery specific energy, it shall stay around 25o W/kg (installed specific energy, not basic cell level) for the foreseeable future, foreseeable meaning 20 years. At least.
Oxis came out swinging, with Lithium-Sulfur, promising wonders, around 400-500 W/kg. Next in line, please.
Keeping in mind that glide regardless of how good or less good are not part of a range calculation.
Glide is only relevant in an emergency as to where you can or cannot get to.
The OTTO Aviation Celera 500L, only a 6 passenger aircraft smaller than the Eviation Alice achieves 22:1 Glide Ratio . The Celera 500L has test flown so these are real world figures.
Sailplanes achieve glide ratios over 50:1 and there are a number of self launching electric sailplanes that operate at over 45:1 with typically 3-4 launches in a charge. The nature of self launching sail planes is that the engines are frequently started in flight to both boost range and increase safety. One can risk to fly to low level for a close view of the coast and start the engines to climb again if one fails to find an up draught.
The B787 used composites to reduce weight and increase skin smoothness but it is a conservative ‘tube’ approach that did not take any advantage of the ability of composites to be moulded into shapes that allow the aircraft to follow laws that achieve laminarity (maintaining a positive pressure gradient). The wing box area is tidier than other airliners but its still is not blended wing body or filleted.
The OTTO Celera is worth examining. They claim
Range: 4600 miles.
Cruise Speed 460 miles per hour.
Glide Ratio 22.
Fuel burn 18 to 25 mpg.
Its a diesel powered single prop 400kW at rear with a body of revolution fuselage shape…no connection to Alice in Wonderland
The original Alice concept – like the Cheshire cat it has shape distorting features – seem to have had much borrowed from Bill Lears ‘Lear Fan’ prototype, maybe the did more than ‘borrow’
https://en.wikipedia.org/wiki/LearAvia_Lear_Fan
The difference between then “Lear fan” and “Celera 500L” is that the shape of the Celera is optimised to provide laminar flow i.e. a positive pressure gradient over as much of the length as possible. The tail then reflexes out like the wing profile of a P-51 Mustang (to recover pressure) with the pusher propeller being used to provide suction so as to keep the airflow attached and laminar. Apparently it doesn’t scale up, Mr Reynolds apparently.
Agree. Glide ratio does not belong in this discussion. Cruise L/D is what matters.