Lilium - Point to point small air transport reinvigorated?

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Grumpy Cynic
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I am however aware of who John Goodenough,
He does seem to be a person to monitor. When they talk about the improved energy density from the glass vs liquid are they talking density/mass or density/volume? Density/volume would be great for both cars and aircraft, but for us density/mass is more important.

People tend to confuse energy density and power density in batteries. .
No confusion. Those of us that lust for electric/hybrid aircraft already have more than enough power (Watts). We need the energy density(Joules)/mass to improve. Improved cycle life would be nice as well.
 

tspear

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People tend to confuse energy density and power density in batteries. The energy density has gone up very slowly with the LiPo technology, while the power density has risen dramatically.
I always thought power density was the amount of watts per cubic space. Energy density was joules per kilo.
For a plane, I am more concerned with energy density.
Is this correct?

Tim
 

BBerson

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Apparently it has not yet been proven that batteries have enough power density to lift a human vertically with small disc ducted fans.
Where are the electric ducted jet packs? You can't get any lighter than a back pack VTOL.

Caproni flew a 66 foot span motorglider with a small 45 lb thrust turbojet.
Where are the electric jet motorgliders?

VTOL should not be the first use if electric jets have any viability. The first use would be launching motorgliders and Jetman type stunts.
 

Highplains

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LiPo's have a fairly good energy density for a battery, but nothing close to liquid fuels. However newer cells can release the energy in a astonishingly quick fashion, giving a fairly high power density. In a hybrid aircraft designed as a parallel hybrid, I see no reason for a constant speed prop, since a hybrid motor could add enough extra power to an IC engine to turn a cruise prop at the rpm where the engine is rated at full power. Trainers need not apply, since flying touch and go circuits would not give enough time to recharge. But you could downsize the engine displacement, carry less fuel, use a fixed pitch prop and it would be about a wash in terms of gross weight for a equal passenger load.
 

revkev6

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Apparently it has not yet been proven that batteries have enough power density to lift a human vertically with small disc ducted fans.
Where are the electric ducted jet packs? You can't get any lighter than a back pack VTOL.

Caproni flew a 66 foot span motorglider with a small 45 lb thrust turbojet.
Where are the electric jet motorgliders?

VTOL should not be the first use if electric jets have any viability. The first use would be launching motorgliders and Jetman type stunts.
while they haven't done this with a ducted fan, they have done it with drone type craft ie this video

[video=youtube_share;At3xcj-pTjg]https://youtu.be/At3xcj-pTjg[/video]
 

cheesefactory

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There is plenty of power to do manned VTOL with batteries and electric motors. That's not the main concern. There's tons of people making bazillion-prop manned drones on Youtube like the Volocopter. Like I said, range and energy density is the primary problem, and this type of aircraft is entirely dependent on a battery revolution happening. These guys are just trying to get a head start on a gamble.
 

gtae07

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Yes and no... I've got a friend with one of those fancy Wren turboprops... Looking at their specs on their current model - 10.5L/H 7.5hp - in a 3lb package. You'd expect to get a good 6000w out of that even on a crudely built generator. If you're using it for recharge + some load boost at takeoff - that's not too bad...

Get fancy with the cpu time to flight plan - you can optimize that significantly. Yep it's still a big fuel burner - but when you're charging 6000w in a 5lb package... ;)
That's still terrible. Figure in charging inefficiency and you're looking at about 7ish hp on about 18lb/hr of fuel. BSFC = 2.57.

I'm going to spitball a number and assume that a Lilium-type winged vehicle with two seats will need, oh, 70hp to sustain level wingborne flight. I know some traditional two-seaters can fly on less, but we do have the extra weight of fans and batteries to carry around. Let's not even get into air conditioning loads yet (as any vehicle like this for mass use will have to have A/C).

Further, I'm going to mix between US and metric units based on what I'm used to working with for certain calculations, just to make everyone else's heads hurt :grin:

Let's further assume that takeoff transitioning to full wingborne flight requires 300hp for, I dunno, 3 minutes, and that it's all provided by the battery. I could be off somewhere but this is a rough order-of-magnitude estimate. And let's assume a 30 minute cruise flight. That's about 224 kW for three minutes, for a total of about 40 MJ.

Divide that out over a 30 minute charge time and assume 90% charge efficiency, and you wind up with a charge requirement of about 25kW.

So that's another 33hp our cruise engine needs to put out. That puts us right around 100hp for a nice round number, and a figure at which there are some off-the-shelf engines. If we use a BSFC of about .4, that gives us 40lb/hr of fuel.

If we assume a 150lb engine/generator setup, that's 20lb of fuel used, for a total of 170lb.

Even if we assume 60lb for the turbine and generator, and a BSFC of about .9, you're looking at 45lb of fuel for a total of 105lb. So 65lb lighter but more than twice the fuel burn.

Lighter weight would be nice but I think the purchase and operating expenses would rule in favor of the piston engine.
 

Victor Bravo

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BBerson mentioned something that makes a lot of sense to me. If the electric ducted fan and vertical axis propeller stuff was even close to being realistic for daily real-world VTOL, then we would already have hundreds of little BD-5-e's darting around, and backpacks, 1/2 scale WAR replica Me-262's and He-178's flying first. Remember the Solo-Trek flying backpack?

But all of the actually viable and usable electric airplanes available now use traditional propellers, and the airframes are more aerodynamically efficient shapes than any of the newfangled artist conception vaporware. It seems to me that the electric Cessna 172, or the electric Beech Bonanza, or at the very least the electric RV-6, will be in daily use before the electric Uber VTOL Taxi is a flying prototype. It will happen, that beautiful electric "racer" and aerobatic airplane exists now, and the electric CriCri exists.

What I haven't seen yet is a valid, compelling reason why Uber and all the futurists and Jetsons-mongers are not accepting the fact that larger diameter rotor blades, and a vehicle like Sockmonkey's coax e-copter is not being pursued with much more intensity than the others. The Volocopter takes up about the same amount of floor space with numerous motors with a large ring around them all. Why is it such a bitter pill to have X feet worth of real rotor blades instead of X feet of electric motors out on carbon tube tree branches? It solves the propulsive efficiency problem better than any of the other VTOL solutions. It solves the pink mist problem.

I'm no expert on rotorcraft whatsoever, but I believe that using co-ax and counter-rotating rotors has been done, is a known science, and can eliminate much of the mechanical complexity, swash plates, articulated rotor heads, etc. Coax helicopters can eliminate the tail rotor, but with electrics a tail rotor is really not that big of a deal.
 

revkev6

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BBerson mentioned something that makes a lot of sense to me. If the electric ducted fan and vertical axis propeller stuff was even close to being realistic for daily real-world VTOL, then we would already have hundreds of little BD-5-e's darting around, and backpacks, 1/2 scale WAR replica Me-262's and He-178's flying first. Remember the Solo-Trek flying backpack?

But all of the actually viable and usable electric airplanes available now use traditional propellers, and the airframes are more aerodynamically efficient shapes than any of the newfangled artist conception vaporware. It seems to me that the electric Cessna 172, or the electric Beech Bonanza, or at the very least the electric RV-6, will be in daily use before the electric Uber VTOL Taxi is a flying prototype. It will happen, that beautiful electric "racer" and aerobatic airplane exists now, and the electric CriCri exists.

What I haven't seen yet is a valid, compelling reason why Uber and all the futurists and Jetsons-mongers are not accepting the fact that larger diameter rotor blades, and a vehicle like Sockmonkey's coax e-copter is not being pursued with much more intensity than the others. The Volocopter takes up about the same amount of floor space with numerous motors with a large ring around them all. Why is it such a bitter pill to have X feet worth of real rotor blades instead of X feet of electric motors out on carbon tube tree branches? It solves the propulsive efficiency problem better than any of the other VTOL solutions. It solves the pink mist problem.

I'm no expert on rotorcraft whatsoever, but I believe that using co-ax and counter-rotating rotors has been done, is a known science, and can eliminate much of the mechanical complexity, swash plates, articulated rotor heads, etc. Coax helicopters can eliminate the tail rotor, but with electrics a tail rotor is really not that big of a deal.
there are two reasons imo that the electric ducted fan concept won't work efficiently scaled like this.
1. disk area. plain and simple they're just two small and tight to make enough thrust
2. part of that disk area is taken up by the motor itself compounding the problem. smaller diameter motors trying to spin faster tend to be less efficient as well.

the electric ducted fan has always been less efficient by a huge margin in RC craft. you put a lot of watts into a system for what you get. especially if what you want is thrust as opposed to speed. unlike a jet turbine where the thrust is relatively fixed regardless of speed the EDF is still just a shrouded propeller with a tail cone that increases the exit velocity by a certain %

Lilium is using the EDF to blow air over a wing or flap. I can see this being a great application for a vtol usage but still being inefficient for direct lift purposes. you can't get 300mph cruise with a small prop designed to lift and an edf that will have that much thrust will be something I would LOVE to see the specs on.


btw... aparrently the US military has a VERY similar drone concept under contract with a similar 3-400kt speed although this one is hybrid power. electric ducts powered by a central generator. currently flying a small electric proof of concept.
[video=youtube_share;F4jWzANJufc]https://youtu.be/F4jWzANJufc[/video]
 

karoliina.t.salminen

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Apparently it has not yet been proven that batteries have enough power density to lift a human vertically with small disc ducted fans.
Where are the electric ducted jet packs? You can't get any lighter than a back pack VTOL.

Caproni flew a 66 foot span motorglider with a small 45 lb thrust turbojet.
Where are the electric jet motorgliders?

VTOL should not be the first use if electric jets have any viability. The first use would be launching motorgliders and Jetman type stunts.
Casey Neistat's drone flight
was not ducted fan, and normal props, not fans, lifted the youtuber just fine, but nobody sane designs a vtol around small ducted fans with high disc loading.
Tesla battery pack is enough for 700 hp power output, in aircraft much less is required for vtol takeoff if disc loading is kept down. Lilium has unfavorable disc loading and lots of surface area from the ducts plus duct losses due to gap between prop and duct. I would not design electric vtol like that but electric vtol is feasible with today's batteries, especially because vtol does not need to hover unlike helicopter.
 

BBerson

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It looks to me like these are not blowing over the wing. But rather pushing all thrust air through the wing.
Rather absurd, considering the energy required to push air through a small nozzle compared with open props.

The Ryan Vertifan had doors that open in the wing for VTOL, made more sense, in my opinion.
 
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karoliina.t.salminen

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It looks to me like these are not blowing over the wing. But rather pushing all thrust air through the wing.
Rather absurd, considering the energy required to push air through a small nozzle compared with open props.

The Ryan Vertiplane had doors that open in the wing for VTOL, made more sense, in my opinion.
I have considered the doors. The wing geometry and spar locations make this approach very restrictive.
Unless the plane is a flying wing where there is more space for the props and doors.
 

cheapracer

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Well here's my current idea. I can't keep writing "current" without thinking it's a pun in this electric thread by the way!

Using what's available now pretty much eliminates all of the vehicles mentioned so far until a "magic battery" arrives, so an idea would be to take the Facetmobile, eg: a lifting body craft with very low wing loading, electrify that because it can take the increased weight while retaining low wing loading, and importantly you have plenty of room for battery positioning, and then stick a gyro rotor on top for ultra STOL (stopped and positioned during forward flight) ...

FacetGyro.jpg
 

tspear

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Well here's my current idea. I can't keep writing "current" without thinking it's a pun in this electric thread by the way!

Using what's available now pretty much eliminates all of the vehicles mentioned so far until a "magic battery" arrives, so an idea would be to take the Facetmobile, eg: a lifting body craft with very low wing loading, electrify that because it can take the increased weight while retaining low wing loading, and importantly you have plenty of room for battery positioning, and then stick a gyro rotor on top for ultra STOL (stopped and positioned during forward flight) ...

View attachment 61662

So when are you going to build the kit so I can order it? :D

Tim
 

revkev6

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Well here's my current idea. I can't keep writing "current" without thinking it's a pun in this electric thread by the way!

Using what's available now pretty much eliminates all of the vehicles mentioned so far until a "magic battery" arrives, so an idea would be to take the Facetmobile, eg: a lifting body craft with very low wing loading, electrify that because it can take the increased weight while retaining low wing loading, and importantly you have plenty of room for battery positioning, and then stick a gyro rotor on top for ultra STOL (stopped and positioned during forward flight) ...

View attachment 61662
wouldn't a large lifting body shroud the autogyro too much during steep decent... I'm thinking basically once you flare on landing you will lose the airflow over the rotor??
 
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