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Electric planes
- Thread starter doug
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Shouldn't a 3D environment make things easier? Trafiic from west to east can go on a different height than traffic from east to west and so on... defining virtual flying corridors is much easier than building autobahns.
Which parts do you think will make a VTOL jet expensive? The battery, the electric motors, the seats? I do not see expensive stuff on such a jet - maybe the skin, which I guess is a super-light material like carbon fiber. But even the cheap BMW i3 uses carbon fiber.
Or is the high price point simply economics of scale? But what if they plan to build a lot of these VTOL jets? Then it is just another vehicle like a Model 3.
I would love to take off in a VTOL jet from my backyard.
A car that dies just comes to a stop, and usually coasts gradually to a stop. An airplane that dies falls out of the sky. Therefore airplanes, and especially their engines, must be manufactured to much higher specs, and maintained much more rigorously. Beyond that, I guess "jet" says "expensive" to me. But since we're also talking about autonomous vehicles, they need very reliable computer and communications hardware and a very robust OS. Nobody is going to want to ride in an autonomous plane powered by Windows.
As for air space control, it's not as easy as different heights for different directions, because we're talking about city point-to-point transportation. Everywhere throughout the space, there will be planes ascending and descending. Even with today's commercial air traffic, you need air traffic control to keep planes from hitting each other. Start having everybody traveling by plane rather than car, and suddenly you have hundreds of thousands of times as many vehicles. You are likely to have a thousand planes within a mile of you. Your computer needs to track them all and communicate with every single one of them to coordinate avoidance. We do not have computers today capable of doing that. Maybe the most powerful supercomputers in the world would be able to coordinate the traffic over a very small city.
The only way this could work would be with a strictly limited number of air taxis, and that raises the cost of permits. Before Uber, a taxi medallion in NYC cost a million dollars.
The only thing stopping you from taking off from your backyard today is space and maybe regulations, and the cost of chartering a helicopter. For transportation within a city, a jet really has no advantages over a helicopter, and helicopters actually exist, and you can charter one just like hiring a taxi. Except that it's a lot more expensive. I think Lilium's promise of cheap air taxis is about as reliable as the promise, when I was young, that electricity from nuclear power would be free.
As for air space control, it's not as easy as different heights for different directions, because we're talking about city point-to-point transportation. Everywhere throughout the space, there will be planes ascending and descending. Even with today's commercial air traffic, you need air traffic control to keep planes from hitting each other. Start having everybody traveling by plane rather than car, and suddenly you have hundreds of thousands of times as many vehicles. You are likely to have a thousand planes within a mile of you. Your computer needs to track them all and communicate with every single one of them to coordinate avoidance. We do not have computers today capable of doing that. Maybe the most powerful supercomputers in the world would be able to coordinate the traffic over a very small city.
The only way this could work would be with a strictly limited number of air taxis, and that raises the cost of permits. Before Uber, a taxi medallion in NYC cost a million dollars.
The only thing stopping you from taking off from your backyard today is space and maybe regulations, and the cost of chartering a helicopter. For transportation within a city, a jet really has no advantages over a helicopter, and helicopters actually exist, and you can charter one just like hiring a taxi. Except that it's a lot more expensive. I think Lilium's promise of cheap air taxis is about as reliable as the promise, when I was young, that electricity from nuclear power would be free.
Yet another misconception.
Future VTOL crafts will be equipped with a BRS - Ballistic Recovery System.
When it failes to fly, it will slowly glide to the ground, maybe even offer some control where exactly to land i.e. gliding.
Etna
Member
None of the serious VTOL startups are considering a jet. Lilium calls theirs a jet but it is an unfortunate marketing gimmick.
The electric VTOLs taxis will not need much more than the technology level that exists today in a Model S.
And they will be inexpensive compared to a helicopter. You do not have to deal with crazy-expensive turbine engine maintenance and operating cost, and no pilot to pay. Huge difference. It is basically the same technology level (batteries, computing power, materials) as a model S.
As for autonomous air traffic control capabilities, it is going to be easier to solve than autonomous cars. No dogs crossing the road, no children running across the road hidden behind a parked car, no trees falling on the road, no drunk drivers... I mean there is a reason why autopilots have been ubiquitous in airplanes for decades. It is easier.
As much as autopilots are easier to incorporate into airplanes relative to cars, the same comparison applies to autonomous navigation. The example you provide is a chaotic environment but the reality is that you can simplify the problem by establishing corridors and traffic rules specifically for these vehicles.
Only two years ago if someone would have told me about autonomous cars I would have rolled my eyes. Now what, they are here today, with rapidly evolving capabilities. I really expect electric VTOLS to become a reality sooner than most are expecting, and this is an aeronautical engineer writing this. I have learned the hard way to be cautious about overly optimistic prospects of new markets and technologies (I am referring to the Very Light Jet craze of the 2000's).
I understand your scepticism in light of past overhyped technological advancements, but the more I look at this the more I am confident this will happen very quickly.
I think you're underestimating just how slippery planes can be. They don't have the car's requirement for square(ish) fronts, for example. NASA re the Beech Bonanza: "The zero-lift drag coefficient is a very low 0.0192". Also the frontal area is very small compared to most cars. No rolling resistance either. Our Bonanza quite easily gets 20 mpg "on the freeway", at about 180mph.I'm not sure how we got on "flying cars" - Lilium doesn't make that claim, and this isn't a road-going vehicle.
There are some eyebrow-raising claims on their site, like "energy efficiency will be better than or comparable to an electric car," "90% less energy than drone-style aircraft," and "in flight, the Jet's power consumption per km will be comparable to an electric car."
Really? At 300 km/hr? I guess the laws of physics don't apply in Lilium-land. At those speeds, your S would draw 9x the power than at 100km/hr.
Maybe they're comparing consumption per km to a 300km/hr electric car.
Compare this to the Model 3, aiming for 0.20!
Aviation today uses well-defined air corridors linking airports, usually away from the most dense population areas. Once you have aircraft taking off from and landing at every house in a city, the air space becomes entirely chaotic, requiring every airplane to communicate with every other nearby to coordinate collision avoidance. It's not enough to be aware of nearby craft; you need to agree with every one of them, collectively, regarding who turns which direction. And the ability of cars to stop at stop signs and stoplights is huge. It means that streets can cross each other throughout the city and coordination is trivial: You stop and wait for a green light, or every car stops and waits its turn at a 4-way stop sign. In the air you cannot do that. Teaching an autonomous car to avoid dogs and kids will be easy compared to coordinating collision avoidance in a very crowded air space.
Actually, I expect that it will be too expensive to reach that point. I am completely unconvinced that it will be comparable in cost to cars. Much more likely it will remain a luxury for the rich, for emergency vehicles, and for when you're late and willing to spend a bundle to get somewhere quick. Note that we are a long way from battery technology light enough and energy-dense enough to keep an aircraft in the air for more than an hour or so, and an air taxi must operate continuously. It will need to spend half its time out of service while charging. Note also, that a VTOL craft will use far more energy than a fixed-wing plane at cruising. For one, an air taxi will spend a lot of time climbing, and for another, an air taxi will need an airframe optimized for landing in small areas, compared to a fix-wing plane which has an airframe optimized for efficient cruising.
I do believe this is coming. But I think that the day when you can call your local taxi dispatcher and request an air taxi is not close enough that I'll see it in my lifetime (I'm 68) and will never be priced where a regular working person would use it on any but the most urgent of trips.
This would require re-writiing much of the aviation rules, and dispensing with the long-held "see and avoid" mantra. Remember that outside the Mode C veil, there's no requirement for a pilot to have any onboard communications or talk to anyone when flying (this fact often terrifies non-pilots!). If autonomous airplanes really become commonplace, and require real-time position/course communication with other aircraft, you'd have to ground a bunch of the GA fleet. Maybe they'll only be used inside the Mode C veil...
Just thinking out loud... I don't think that's necessarily true. You need a lot of thrust in a VTOL aircraft to offset weight with thrust only (no lift), but once you're airborne and moving forward with lift in play, you need normal amounts of thrust. Just shut off the extra fans. Or optimize motor efficiency for the cruise case.
I was thinking from the standpoint of cruise power and Wh/mi. I'm averaging 380Wh/mi with mostly highway at 72-75 mph. That's just over 27kW at cruise. Using an SR20 as an example of a modern, slippery airframe, I see numbers around 135kn cruise, 10gph at 70% power (200hp/150kW IO-360). So that's (150*0.7) = 105kW to go (135*1.15) = 155 mph (so around 15.5mpg "on the freeway"). In Wh/mi, the car gets (27kw/72mi) = 380Wh/mi and the SR20 gets (105kW/155mi)=677Wh/mi. Either way (instantaneous or Wh/mi), the plane has a ways to go to get numbers close to an electric car. Go from 155mph cruise to 186 claimed by Lilium, and the drag gets even worse.
The SR20 numbers are estimates I found on line. I have no real experience flying "modern, slippery airframes" other than one flight in a DA-20 early in my training. I'm mostly a Piper PA-28 guy.
But an in-city taxi service would involve relatively short trips. This means a lot more climbing proportional to trip length than flying between cities, which would probably still be done with conventional fixed-wing aircraft.
A conventional commercial jet, flying between cities, optimizes efficiency (as noted elsewhere) by a long glide back down at the end of the flight. But for a taxi service in a city, this would increase the chaos. In fact, everyone would want to stay as low as possible, to conserve energy, and this would concentrate the crowding. If you require certain elevations for certain directions, then again you require a straight vertical climb (while avoiding the aircraft at the intervening levels) and a straight vertical descent, again avoiding aircraft at the intervening levels.
The only thing that will make any of this practical, realistically, is far more computing power than we have now, or severe limits on the number of air taxis. Of course, I think the numbers will be limited due to the cost. We'll have police and ambulances using these crafts, and private people who are very wealthy or very desperate to get somewhere fast. If you are providing a service that a rich person is willing to pay a lot for, you'll be able to take an air taxi. There won't be much demand here in Spokane, because it just doesn't take all that long to drive anywhere here. Cities with bad traffic will have more demand.
Etna
Member
I does terrify me (especially when I have my family on board), fortunately starting January 1, 2020 this will no longer be true thanks to the ADS-B mandate.
All aircraft (including general aviation) will be required to be equipped with at least position broadcast (ADS-B out) capability to have access to most airspaces (class A B and C plus many airports): ADS-B – Frequently Asked Questions (FAQs)
Etna
Member
It is not as bad as your calculation suggests. The 70% power setting is at cruise altitude where you do not have the sea level 200hp available, at 10000ft I think it's only half that number. Unless you fly a turbocharged aircraft but then you should be zipping along at 180 kts.
I fly a DA40 and I often burn less fuel between two city pairs than I would with my car. This works very well between city pairs not connected by a straight line highway. In the air I fly direct 99% of the time.
Etna
Member
Come to think of it, going from point A to point B in one of those electric VTOL taxis - for example from downtown Manhattan to Newark airport, is going to take 4 minutes by air (9 nm at 130 knots) versus 30 minutes in a car or one hour+ with traffic. At 250$ per hour we are talking 17 dollars plus boarding fees so maybe 25$ . I am calling this "unfair competition" and I am not surprised heavyweights like Airbus are openly chasing this business opportunity.
I believe the 250$ per hour estimate by Airbus. I rented a helicopter last January and it cost about $1800 for a one hour flight but this was a fancy high performance Airbus EC130 with a one million dollar turbine engine and a professional pilot, both of which you are crucially getting rid off.
I believe the 250$ per hour estimate by Airbus. I rented a helicopter last January and it cost about $1800 for a one hour flight but this was a fancy high performance Airbus EC130 with a one million dollar turbine engine and a professional pilot, both of which you are crucially getting rid off.
But those airspaces already require radio communications. From a quick glance, it looks like ADS-B out is not required in uncontrolled airspace (class G). But I'll admit I haven't flown in a while so I'm not up on the regs.
Good point, I forgot about altitude's impact to HP (and prop thrust, etc). That's what happens with quick and dirty, back of the envelope calculations.
I'm not sure why that has to be a constraint. Its not a difficult exercise to imagine corridors that allow safe traffic flow in a manner more structured than everyone-flies-PTP. First/Last mile activity can happen at slower speed and lower altitude, like residential streets manage automobiles today. Distances can be covered with increasing speeds and altitudes. Flight paths could follow a longer, but more orderly route. Think less contemporary odd/even FLs and more Coruscant.
lolachampcar
Well-Known Member
From a practical standpoint, flying transport is where we will end up. Its not if, its just a matter of when.
As for the video, I did that years ago..... I built a quad copter and took off from my back yard and flew around using a LION battery and multiple motors. All we saw in the video was a very large RC model with some neat flight management hardware (which is available on the current generation of quads with MEMs based flight managers). No person on board and a trip around the pattern. I'm not so interested in it doing its flying demo as I am in initial and sustained power consumption verses energy density and its ability to lift. I suspect the battery it is capable of lifting today would make it one more time around the pattern or a landing, not both and that is without people ballast.
Neat RC model. Just add pure capacitance gel and you're there.
As for the video, I did that years ago..... I built a quad copter and took off from my back yard and flew around using a LION battery and multiple motors. All we saw in the video was a very large RC model with some neat flight management hardware (which is available on the current generation of quads with MEMs based flight managers). No person on board and a trip around the pattern. I'm not so interested in it doing its flying demo as I am in initial and sustained power consumption verses energy density and its ability to lift. I suspect the battery it is capable of lifting today would make it one more time around the pattern or a landing, not both and that is without people ballast.
Neat RC model. Just add pure capacitance gel and you're there.
Looks like I was a bit too conservative in my 5 year estimate, and our buddy @daniel was ever further off on his 50 year estimate.
Uber plans flying taxi service in 2020:
Uber unveils plans for electric flying taxis by 2020, ChargePoint will provide charging for first stations
JRP3
Hyperactive Member
What Uber is planning may have nothing to do with what actually happens. I think Uber is dreaming.
The article reads: "Uber will attempt at unveiling the first public demonstration as part of the 2020 World Expo." Clickbaity title aside, it seems plausible that they could attempt a demo in 2.5+ years. The technical barriers--the ones in the way of attempting a very planned demo--shouldn't be difficult to scale. Build e-plane. Press "go". Result!
The barriers blocking commercial implementation will be a bit more greasy. The main one is regulatory, which really boils down to the theoretical convenience and frequency of an air taxi service. Can you fly a lot of units from a lot of places all the time? Or can you only fly a few units from very specified locations and under strict air-use control? The secondary one is financial, which really boils down to the timeline on which an air taxi service can grow. If the hardware [and regulatory approval] costs a lot, there will be a small number of units and a high end user price, and that means a very slow rollout and ramp up.
For a not-so-apples-to-apples comparison, All You Can Fly Membership | Home | Surf Air can provide a little insight into what a not-so-competitor of an uber air taxi is doing. Its basically an all you can fly [in CA] service for $2000/month.
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