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 Post subject: Re: Lilium "Jet" flies
PostPosted: 23 Oct 2019, 22:44 
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Well, it’s a pretty big drone. Big enough for 5 people apparently.


Not if it is chock full of batteries. Then it has room for batteries. Which is still the total obstacle to electrically powered flight.

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The interesting part is that, according to their web site, they attracted $100 million in funding and have 300+ people working on the project. For that kind of dough, you can make anything fly.


Especially the dollars... the machine, well, not so much!


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 Post subject: Re: Lilium "Jet" flies
PostPosted: 23 Oct 2019, 23:18 
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All of these things are happening quite frequently right now with conventional airplanes. What's the difference?


I could argue all the ways that airplanes or helicopters are aerodynamically different than powered lift vehicles, but I think it comes down to the, "gee-whiz, these things are going to revolutionize urban transit" factor. No one mentions the dangers inherent with these types of vehicles and we're proceeding with all haste to have people flying in them commercially.

I could mention that there hasn't been a death in part 121 aviation in the United States since the unfortunate uncontained engine failure. There hasn't been a part 121 crash in the USA in ten years (Colgan). The safety record is phenomenally good. You are literally safer in a US commercial carrier than you are on your own couch.

I think the FAA needs to establish some guidelines for design. Make them at least as safe as helicopters. How are you going to protect the passengers from an electrical failure at a height of 50ft? A parachute isn't going to do it.

I know I'm coming off as a troll, but the most fascinating aspect of these electric urban vehicles is how the designers are going to make them safe. I've heard of parachutes, dual electrical systems, and redundant flight controls. I haven't seen a design I would fly in yet. Not even close.


I would say that these machines have a potential to be safer than comparable size helicopters or small planes (airliners are entirely different story). Helicopter, as we know, is a collection of hundreds of mechanical parts flying around together in loose formation. Lots of things can go wrong with that. These "drones", on the other hand, are dirt simple. A bunch of electric motors, a few batteries, and some electronics in between. Easy to make a system with completely independent triple or quadruple redundant systems. Lost a motor or two? No big deal, you've got 200 of them.

To be sure, I am very skeptical of this the whole urban mobility concept. These companies seriously underestimate legal, regulatory, economic and logistical challenges they have to overcome to make those systems viable. But the vehicles themselves look pretty good from the engineering standpoint and well-suited for the task they are designed to perform.

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 Post subject: Re: Lilium "Jet" flies
PostPosted: 23 Oct 2019, 23:21 
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Not if it is chock full of batteries. Then it has room for batteries. Which is still the total obstacle to electrically powered flight.

You don't need big batteries when your mission profile is a 15-minute hop.

Battery capacity is still insurmountable obstacle to making an electric plane similar to Bonanza or Cirrus. But for a vehicle with 25-mile range it's not a problem.


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 Post subject: Re: Lilium "Jet" flies
PostPosted: 24 Oct 2019, 00:26 
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I could mention that there hasn't been a death in part 121 aviation in the United States since the unfortunate uncontained engine failure. There hasn't been a part 121 crash in the USA in ten years (Colgan)

The recent fatal Dutch Harbor accident was part 121.

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 Post subject: Re: Lilium "Jet" flies
PostPosted: 24 Oct 2019, 00:33 
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You don't need big batteries when your mission profile is a 15-minute hop.

Battery capacity is still insurmountable obstacle to making an electric plane similar to Bonanza or Cirrus. But for a vehicle with 25-mile range it's not a problem.


Hmm.

Show your math?


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 Post subject: Re: Lilium "Jet" flies
PostPosted: 24 Oct 2019, 18:27 
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You don't need big batteries when your mission profile is a 15-minute hop.

Battery capacity is still insurmountable obstacle to making an electric plane similar to Bonanza or Cirrus. But for a vehicle with 25-mile range it's not a problem.


Hmm.

Show your math?


Let’s see... Tesla’s 85 kWh battery pack weighs 1,200 lbs. That energy can provide 170 kW, or 226 hp of power for 1/2 hr. Electric motors have around 90% efficiency, so we can get about 200 hp on the motor’s shaft for 1/2 hr. That’s plenty to take 3-4 people for a 15-min flight.

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 Post subject: Re: Lilium "Jet" flies
PostPosted: 24 Oct 2019, 19:51 
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But we’re forgetting reserves. If legal reserves are 30 minutes how does that work then.


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 Post subject: Re: Lilium "Jet" flies
PostPosted: 24 Oct 2019, 20:11 
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Username Protected wrote:


I could mention that there hasn't been a death in part 121 aviation in the United States since the unfortunate uncontained engine failure. There hasn't been a part 121 crash in the USA in ten years (Colgan)

The recent fatal Dutch Harbor accident was part 121.


Yes, sir, I stand corrected. My source must have been referring to the lower 48.

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 Post subject: Re: Lilium "Jet" flies
PostPosted: 24 Oct 2019, 21:51 
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But we’re forgetting reserves. If legal reserves are 30 minutes how does that work then.

Form the legal standpoint, rules will have to be changed. This whole concept totally doesn’t fit into existing regulatory framework. I bet FAA will have to develop a whole new set of rules to govern these operations.

From practical standpoint, you don’t need much reserve when you can always land vertically on dozens of readily available landing pads within a mile radius.


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 Post subject: Re: Lilium "Jet" flies
PostPosted: 25 Oct 2019, 05:40 
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Username Protected wrote:

Let’s see... Tesla’s 85 kWh battery pack weighs 1,200 lbs. That energy can provide 170 kW, or 226 hp of power for 1/2 hr. Electric motors have around 90% efficiency, so we can get about 200 hp on the motor’s shaft for 1/2 hr. That’s plenty to take 3-4 people for a 15-min flight.



Which is the equivalent of 2.6 gallons (15lbs) of avgas.


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 Post subject: Re: Lilium "Jet" flies
PostPosted: 25 Oct 2019, 08:25 
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It's really cool....but those small ducted fans are extremely inefficient at creating lift compared to a bigger prop. I mean, it's not even a case of like 20-30% difference, we're talking 200-300% difference. They look really cool tho, and I suspect thats the reason they're there.


Safety.

1) One of those having an issue and it's no big deal. Lose your one rotor and the vehicle is now descending, possibly very quickly. :bugeye:

2) It's much harder for someone to walk into one of those ducted fans.


But yes, inefficiencies and weight from batteries is not a great combination. If they get it to fit the market niche though it could be nice.

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 Post subject: Re: Lilium "Jet" flies
PostPosted: 25 Oct 2019, 11:20 
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Username Protected wrote:

Let’s see... Tesla’s 85 kWh battery pack weighs 1,200 lbs. That energy can provide 170 kW, or 226 hp of power for 1/2 hr. Electric motors have around 90% efficiency, so we can get about 200 hp on the motor’s shaft for 1/2 hr. That’s plenty to take 3-4 people for a 15-min flight.


Which is the equivalent of 2.6 gallons (15lbs) of avgas.

Well, 200 hp at the shaft for 1/2 hr will cost you more than 2.6 gl of gas, more like 7-8 gl. Everyone knows that energy density of the batteries is order of magnitude lower than the gas. But it’s besides the point. What matters is that currently existing batteries are adequate to support this particular application.

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 Post subject: Re: Lilium "Jet" flies
PostPosted: 25 Oct 2019, 12:17 
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Well, 200 hp at the shaft for 1/2 hr will cost you more than 2.6 gl of gas, more like 7-8 gl. Everyone knows that energy density of the batteries is order of magnitude lower than the gas. But it’s besides the point. What matters is that currently existing batteries are adequate to support this particular application.



I don't honestly see this working - at all, with any foreseeable battery technology. 1200lbs of battery for a 30 minute range doesn't make any sense. That's followed by an 8 hour charging cycle if you want to have any life out of the battery.

But lots of people want to throw their money into it, which is why it is being done, despite it flunking the basic physics reality check.


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 Post subject: Re: Lilium "Jet" flies
PostPosted: 25 Oct 2019, 14:58 
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Technically and regulatory issues aside, as a current helicopter operator, I think that the biggest hurdle to be overcome will be noise. It's an issue we face quite often considering most of our work is powerline construction/maintenance, ski lift construction, and firefighting, all operations that typically take place outside of heavily populated areas. NIMBY is a huge thing and these craft will have to be basically silent to not attract the ire of these types of people (who have a tendency to be a minority but a VERY vocal one). Most of the developers of these vehicles seem to have not even taken this obstacle into account (in my opinion).


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 Post subject: Re: Lilium "Jet" flies
PostPosted: 25 Oct 2019, 17:02 
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Small gas turbine generator and some Jet-A solves the battery problem.
If it only has to run at one speed and power level it can be more efficient than a general purpose turbine.


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