Sean Wagner
Member
Very interesting. I checked their website, and they've switched to a hybrid-electric concept recently, enabling them to build an upsized 1:1 demonstrator. Knowledgeable people on the board too. I like that layout very much.
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Electric planes
- Thread starter doug
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Very interesting. I checked their website, and they've switched to a hybrid-electric concept recently, enabling them to build an upsized 1:1 demonstrator. Knowledgeable people on the board too. I like that layout very much.
voyager
Active Member
Battery-propelled aerial vehicles may actually rekindle one of mankind's oldest dreams: the Flying Car. With the rotors micro-second controlled (like with toy drones), you could even do without an aircraft's traditional control surfaces, that the XTI 600 is still featuring. Here is a modular Flying Car concept. The airfoil is also a battery container. Upon landing, the car disconnects, so passengers can straightaway continue their trip. No unboarding and walking towards a car on a wind-swept landing site.
I see that Lilium raised $90M in another round of funding Lilium raises $90M Series B for all-electric flying taxi
They are still claiming a range of 300 km at 300 km/h on the homepage today. Previously they claimed a top speed of 450 km/h and 500 km range.
London - Paris is also 340 km in a straight line, but nevermind...
The old website (thanks archive.org) showed 600 kg gross weight with a 200 kg payload.
They claim they are using a pack "comprised of several thousand Lithium-Ion cells similar to those in electric cars. It is designed to fully contain a thermal runaway of several cells while still delivering enough power to the propulsion system."
So if I assume a pack level energy density like the best Tesla offers (168 Wh/kg), a 21 kWh usable pack (80% of total capacity used) would weigh 150 kg. This leaves 250 kg for everything else (structure, seats, control system, motors and fans).
There are 36 fans so each would need to produce ~9 kW peak and ~2 kW constant. There are RC Helicopter motors out there that can do this in a little over 1 kg. I assume 2 kg for each motor/fan pod. That's another 72 kg.
The fuselage looks a lot like the old Aptera car, which had a Cd of 0.11 in prototype form. I can see from other sources that for a light aircraft, a Cd of 0.1 is considered good. I've not seen any dimensions for this thing but A=1.5 m^2 seems generous in their favour. It's a 2 seater side-by-side cabin so it it would be tricky to be any narrower.
So just on drag from forward motion alone, I calculate the range at 300 km/h (186 mph) is 82 km (59 miles) near the ground. At 3,000 metres altitude the range is 116 km (72 miles). In order to reach 300 km (186 miles) they would need to fly at ~11,000 metres (air pressures).
However just from calculating potential energy to lift 600 kg to those heights, assuming 80% efficiency of the ducted fans and 90% motor efficiency, they would need 6.8 kWh to reach 3,000 metres and 25 kWh to reach 11,000 metres.
If we flip the calculation around, to reach 300 km range at 3,000 metres it would need a 54 kWh usable pack, weighing 386 kg.
If we assume a climb rate of 1 km / minute (roughly the same as many helicopters) when using 320 kW, it would expend 16 kWh to reach 3,000 metres or 59 kWh to reach 11,000 metres. Furthermore, the pack would have to sustain 9 C for that period of time.
Thus if we add the battery mass needed to climb and the battery mass needed to cruise 300 km, at 500 kg the battery alone weighs more than the allowed net weight of the vehicle.
And all of the above assumes no margins.
If these guys are sitting on a battery that is 3x better than anyone else, would it not be easier to sell it to car companies rather than go to the trouble of building a whole new class of aircraft around it?
They are still claiming a range of 300 km at 300 km/h on the homepage today. Previously they claimed a top speed of 450 km/h and 500 km range.
London - Paris is also 340 km in a straight line, but nevermind...
The old website (thanks archive.org) showed 600 kg gross weight with a 200 kg payload.
They claim they are using a pack "comprised of several thousand Lithium-Ion cells similar to those in electric cars. It is designed to fully contain a thermal runaway of several cells while still delivering enough power to the propulsion system."
So if I assume a pack level energy density like the best Tesla offers (168 Wh/kg), a 21 kWh usable pack (80% of total capacity used) would weigh 150 kg. This leaves 250 kg for everything else (structure, seats, control system, motors and fans).
There are 36 fans so each would need to produce ~9 kW peak and ~2 kW constant. There are RC Helicopter motors out there that can do this in a little over 1 kg. I assume 2 kg for each motor/fan pod. That's another 72 kg.
The fuselage looks a lot like the old Aptera car, which had a Cd of 0.11 in prototype form. I can see from other sources that for a light aircraft, a Cd of 0.1 is considered good. I've not seen any dimensions for this thing but A=1.5 m^2 seems generous in their favour. It's a 2 seater side-by-side cabin so it it would be tricky to be any narrower.
So just on drag from forward motion alone, I calculate the range at 300 km/h (186 mph) is 82 km (59 miles) near the ground. At 3,000 metres altitude the range is 116 km (72 miles). In order to reach 300 km (186 miles) they would need to fly at ~11,000 metres (air pressures).
However just from calculating potential energy to lift 600 kg to those heights, assuming 80% efficiency of the ducted fans and 90% motor efficiency, they would need 6.8 kWh to reach 3,000 metres and 25 kWh to reach 11,000 metres.
If we flip the calculation around, to reach 300 km range at 3,000 metres it would need a 54 kWh usable pack, weighing 386 kg.
If we assume a climb rate of 1 km / minute (roughly the same as many helicopters) when using 320 kW, it would expend 16 kWh to reach 3,000 metres or 59 kWh to reach 11,000 metres. Furthermore, the pack would have to sustain 9 C for that period of time.
Thus if we add the battery mass needed to climb and the battery mass needed to cruise 300 km, at 500 kg the battery alone weighs more than the allowed net weight of the vehicle.
And all of the above assumes no margins.
If these guys are sitting on a battery that is 3x better than anyone else, would it not be easier to sell it to car companies rather than go to the trouble of building a whole new class of aircraft around it?
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voyager
Active Member
Lilium's far biggest problem is what's called disk loading. The 'swept fan area' directly linked to the weight the fan (thruster) is supposed to lift. In layman terms, there's a reason why a helicopter uses a big-diameter rotor with an adequate power source to provide the right amount of torque: efficiency. ALL aeronatics engineers agree on one thing with regard to Lilium: those 15 cm thrusters will never be able to lift the thing with passengers in it and enough batteries for adequate range. If the Lilium guys will succeed for some miraculous reason, the thing will be so noisy that it will not be allowed in the built environment.
Two ways of looking at the $90 million infuse. One: the Lilium guys have held a convincing pitch. Two: the people who are supposed to assess feasibility and viability before wallets were drawn, screwed up big time.
Two ways of looking at the $90 million infuse. One: the Lilium guys have held a convincing pitch. Two: the people who are supposed to assess feasibility and viability before wallets were drawn, screwed up big time.
During "frothy" times, a lot of VC money gets dumped on ideas that may not make a lot of sense. Bigger and bigger funds have too much money to invest, bidding up valuations. Pressure from LP's to put money to work, for the fund to "do something," and not miss out on the next big thing, etc. Unfortunately, this triggers boom/bust cycles (see 20 years ago).
voyager
Active Member
Here is a visualization of what Lilium claims. And I probably pictured the thrusters a bit too 'large'.
I wonder if they are using these Schubeler DS-215-DIA HST 195mm Carbon EDF Ducted Fan + Motor DSM10066-290 - Turbines RC - WEB EFFECT
Schübeler Jets - Home
http://www.schuebeler-jets.de/pdf/Datenblaetter/EN/215HST_Flyer-ENG.pdf
36 units x 9.8 kW = 353 kW so a bit over
36 units x 22 kg thrust = 792 kg so positive thrust / lift
Would make the disc loading 775 kg/m^2, which translates to efficiency of around 2 kg/kW so in line with other aircraft with tilt-rotors according to the chart earlier.
Certainly enough to build a model to show investors...
However 122.4 kg total mass of EDFs + 500 kg of batteries for the case above means we are into negative payload mass fraction before we even consider the rest of the aircraft. And this is a fully carbon fibre EDF.
Schübeler Jets - Home
http://www.schuebeler-jets.de/pdf/Datenblaetter/EN/215HST_Flyer-ENG.pdf
36 units x 9.8 kW = 353 kW so a bit over
36 units x 22 kg thrust = 792 kg so positive thrust / lift
Would make the disc loading 775 kg/m^2, which translates to efficiency of around 2 kg/kW so in line with other aircraft with tilt-rotors according to the chart earlier.
Certainly enough to build a model to show investors...
However 122.4 kg total mass of EDFs + 500 kg of batteries for the case above means we are into negative payload mass fraction before we even consider the rest of the aircraft. And this is a fully carbon fibre EDF.
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voyager
Active Member
That means that Disk Loading is fan swept area of 215 cm2 that is supposed to lift 16.6 kg each is 77.2 kg per sq m. is 378.32 lb per ft2. That should make for a very-very noisy Lilium Jet, despite what those guys are saying. There's no margin either. Which explains the shorter than 1 minute maiden flight with NO passengers onboard.
Schubeler DS-215-DIA HST 195mm Carbon EDF Ducted Fan + Motor DSM10066-290 - Turbines RC - WEB EFFECT
Schubeler DS-215-DIA HST 195mm Carbon EDF Ducted Fan + Motor DSM10066-290 - Turbines RC - WEB EFFECT
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voyager
Active Member
Good question (that more experts have wondered about).
It seems that those Technical University of Munich graduates started thinking about nicely integrating electric thrusters into a reasonably conventional airframe. So, those thrusters had to be small and multiple to provide adequate oomph.
Unless the Lilium guys will change the fundamental principle on which their VTOL craft was based, I don't see this ever taking off the ground, with a few hundred miles range AND enough batteries AND passengers on board. So, like I stated before, go figure why people are that stupid to invest 90 million.
The fundamental issue is that you have to compensate for the fact that small-diameter fans have limited thrust. So, you have to churn out more kW's... which is demanding in the battery dept.
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swaltner
Active Member
I saw the SureFly up at the "Innovation Center" at EAA AirVenture this summer. It looked to be pretty far along in the development cycle. As I remember, they were nearing first flight. To me,the mockup looked to be WAY too heavy, but my mind is calibrated to aluminum/steel aircraft structures, not carbon fiber. The landing gear would be incredibly heavy if they were built from steel, which it what is typically used in helicopters. I just not used to seeing that large of structures on light aircraft.
As I remember, a few of their automated decision points for in-flight failures include:
Engine failure: on-board batteries provide 5 minutes of flight time to safely land
Single rotor/motor failure: continue flight
Dual rotor/motor failure: pop the parachute
As I remember, a few of their automated decision points for in-flight failures include:
Engine failure: on-board batteries provide 5 minutes of flight time to safely land
Single rotor/motor failure: continue flight
Dual rotor/motor failure: pop the parachute
I keep seeing these ideas and I have significant skepticism about their practicality. Aircraft ownership is a niche. Automating and electrifying it won't do much to bring it out. Mass adoption would make the skies overhead noiser, since these electric passenger "drones" are flying relatively low and slow.
lolachampcar
Well-Known Member
JRP3
Hyperactive Member
lolachampcar
Well-Known Member
does that not dump another set of combustion products in the sky along with generating a lot of trash in the production of those fuels?
I ask as I really do not know and have never looked into it. Having PV on the back of my house and two MS in the garage, its easy for me to understand that, once the products were produced, I was no longer dumping crap in the air with my daily activities.
I ask as I really do not know and have never looked into it. Having PV on the back of my house and two MS in the garage, its easy for me to understand that, once the products were produced, I was no longer dumping crap in the air with my daily activities.
JRP3
Hyperactive Member
That's Elon Musk being sneaky. Renewable methane production is something that would be incredibly useful for renewable energy.
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