Hacker News Reader

Comment by alistproducer2 | Hacker News Reader

I have to say I'm impressed. This is a game changer for several reasons. The first is that full autonomy is much easier in aviation than with ground transport. Second is successful implementation of flying cars would change things (for the middle class and rich) in a major way: potentially for everyone if the economics of sharing these works out where regular folks could afford to hail these and the system could scale.

Something like this that connects the exurbs to the city would be a game changer. I would imagine inner city luxury housing would take a big hit. Anyways, super cool to see that thing take off.

View on HN

I'm calling bullshit. See my calculations in the other thread. ~1600lbs of batteries to hit their specs with current tech and that's VERY generous. Likely closer to 2k. Lipo capacity going up at 5% a year so 2025 isn't happening unless new battery tech is announced and commercialized in the next 8 years.

Also, steering appears to be entirely based on differential thrust. Power loss = uncontrolled descent. Good luck getting that certified...

I'm not a pilot, but the fan pods are flaps, so I think there's some steering there.

Also, it has a full aircraft parachute as a last resort.

Air frame parachutes are great at high altitude but under ~500ft (where you're going to have the highest load on your electrical system during landing/takeoff) they do absolutely nothing.

As far as the flaps, they are not sufficient for controlled flight. Increasing the angle of one of them increases both lift and drag on that wing so you have at best a dutch roll/adverse yaw and at worst a flat spin.

https://www.faa.gov/regulations_policies/handbooks_manuals/a...

Helicopters, as opposed to this vehicle, have the ability to be controlled even when power is lost. This is a much safer failure mode for personal aircraft then depending on a chute: useless at altitudes high enough to be fatal but low enough to result in a failed chute deployment.

Similarly, winged aircraft can glide, where this one cannot, given enough forward velocity.

This thing will drop like a rock in an incidence of power failure at low altitude and the operator will have no way to control where it hits the ground (for either their safety or the safety of those on the ground).

That's why this is so frustrating. It seems like everyone is just missing the point. Flying cars are not a mechanical design problem. We have the tools, engines, designs, etc. all nailed down at this point. Any aerospace engineering grad could design a flying car tomorrow if the energy source existed in such a density that would make it feasible. It is fundamentally an energy problem, not a mechanical one. Maneuvering around that fact, and spending time on problems that aren't solving the core issue of battery technology is a massive waste of resources.

Yes, and it always has been. From the Moller Sky car to the Lilium here, making the craft is the easy bit (well, apart from the thrust vectoring but with modern computers that's solvable). Getting it to run for more than 2 minutes with a realistic load is the hard part. Those small ducted fans are horribly inefficient by the way, a regular shaped plane with a pusher prop and the wingspan of a glider would have a much better chance achieving the range (but no VTOL).

Too good to be true usually isn't true.

Thank you, my thoughts exactly. We need to be focusing on high density energy storage. An electricity source with a similar or greater specific energy to gasoline would transform transportation to the point of being unrecognizable within a couple years. It would be as much of a singularity as AI, high temp super conductors or low cost graphene. Just putting electric motors in current generation airframes would cut costs ten-fold.

> Just putting electric motors in current generation airframes would cut costs ten-fold.

Absolutely. I didn't mean to disparage the idea of an electric drivetrain for aircraft in general. Check out Pipistrel (https://www.youtube.com/watch?v=WiADDbeFanU) they're doing some incredible things right now. They have a LiPo powered twin seat LSA trainer in production that gets an hour of flight time at 80 knots and 600lb useful load with hotswap batteries. This is the future of trainers IMO.

Please use SI units: 150 km/h speed, 300kg useful load.

Thank you for the Pipistrel link!

Aviation units/specifications are unfortunately almost always specified in knots and pounds.

A liquid-hydrocarbon fueled turbogenerator would appear to meet your criteria. You can use synthetic or biofuels if you're worried about the environmental impact. Of course the aircraft will be more efficient if you omit the generator and mechanically couple the turbine to the props.

I talk about this elsewhere in this section. Pipistrel tried this on the Panthera and the system complexity is enormous. The whole advantage of electric propulsion is it's simplicity. Might as well just use the turbine for lift.

Yes that was exactly my point. Barring major advances in battery technology, if you want to build a powered lift VTOL aircraft safe enough for civilian passengers with useful range and payload then you probably need to use a turbine engine. Batteries just aren't good enough yet.

Why energy density storage and not wireless power transmission and/or reception?

Sure, it's possible, but it's a much longer way off at the moment. There are all sorts of technical problems that need to be solved in that space for it to be viable. You need to be able to transmit in excess of 100kW through clouds without any dispersal and not set the target on fire. We at least have the groundwork laid for potentially very high capacity batteries (LiAir, LiS, etc).

I thought a fixed wing or even heli/drone type aircraft for one, two pax could fly with, say, 50 kW?

50kw is still an incredible amount of power to transmit wirelessly without cooking the target and anything that may pass between the power transmitter and the target. Go put an egg in your microwave and watch what 1kw does to it.

It would also almost certainly require line of sight and a directional antenna that can track the aircraft. Batteries could be used in the aircraft to at least land safely if there were a loss in power.

But currently we have trouble transmitting 5 watts across the 7mm gap between a wireless charger and a phone. 50kw over a distance of 1-300km is a very long way away.

Thanks. (Note that I think the wireless transmission idea is entirely fanciful and can safely be discarded for the foreseeable future. Just got hung up on the 100 kW figure...)

It may need 100kw during certain phases of flight --take off and landing for a VTOL craft, or just take-off for a standard aircraft. Cruise power is generally far less than take off/hover power.

If the craft were entirely wirelessly powered, then of course the system would have to be able to transfer 100kw. But the link(if even 50kw were ever feasible) could be designed for a lower power level, and the aircraft could draw from an onboard battery bank for extra power during these phases of flight.

Kind of like how hybrid drive vehicles undersize the internal combustion engine and then draw power from the ICE and the electric system during heavy acceleration.

But we still need to find a reasonable way to wirelessly transmit large amounts of power safely and efficiently.

100kW is the likely cruise power for that aircraft at 300kmph. It's likely many times that for VTOL

Very possibly. I'm by no means an aerospace engineer.

A quick google turned up this[1] which has a top speed of 296km/h with a 120hp(89kw) engine, and it's likely a good bit lighter than the Lilium with a full battery load.

[1] http://www.aircraftspruce.com/catalog/kitspages/nexaer.php

edit: added [1]

Any aerospace engineering grad could design a flying car tomorrow if the energy source existed in such a density that would make it feasible.

Beamed power?

Impossible for safety reasons in populated areas. And even ignoring safety issues, the conversion efficiency on beamed power is so low as to make it uneconomical.

I thought the conversion efficiency for microwaves was 80%.

Maybe in a kitchen microwave oven. You're not accounting for transmission path losses and receiver conversion efficiency.

Actually, I think that's a figure including transmission and receiver conversion efficiency, but it doesn't include path losses. That's still quite impressive, though.

http://spectrum.ieee.org/energywise/green-tech/solar/japan-d...

That's for short range transmission to a fixed receiver. So not really relevant for powering aircraft.

Such microwave systems have been proposed for solar power satellites. They have useful ranges up to 100's of miles.

Maybe, but unlikely. Lasers need line of sight and would generally be a bad idea at the power levels required (basically a weapon), and microwave power transmission requires large receiving apertures. Current "wireless charging" technologies are pretty much universally near field.

How would this work through clouds? The water vapor would in theory block or scatter everything from UV to microwave radiation. Also, I don't want to be near a 1W laser/maser, and if our energy budget is 100kW, you'd need at least a 100,000W laser pointed at your tiny air taxi.

That's called target practice.

These guys do it all the time:

https://www.youtube.com/watch?v=JtxwT6PQIw8

I'm surprised they didn't include an internal combustion engine in it to charge the battery. That's the solution for the terrafugia tf-x. https://www.terrafugia.com/tf-x/

Lipo capacity going up at 5% a year so 2025 isn't happening unless new battery tech is announced and commercialized in the next 8 years.

What about a small fuel/turbogenerator drop pod for just the takeoff/climb?

Pipistrel was trying to do this (along with a few other companies). At that point, the mechanical complexity is prohibitive along with the insane operating costs. You still need enough batteries to get back on the ground if something fails but you have the added weight of a combustion engine and it's fuel as well.

The whole appeal of electric motors is that they are basically solid state. You don't need to change oil or perform a ton of regular maintenance. Just replace bearings every few years if ever and you're good to go. Gas/jet engines need to be overhauled regularly which contributes a large portion of the operating costs. For instance, a Cessna 172R/SP uses a 180 hp I/O-360 engine that needs to be overhauled (completely disassembled) every 4000 hours at a cost of around $20,000. That's $5 an hour just for the engine replacement assuming no excessive wear or metal flakes in the oil are found.

you have the added weight of a combustion engine and it's fuel as well

Note I said drop pod.

The whole appeal of electric motors is that they are basically solid state.

I think beamed power has a lot of potential for electric jets. It's sort of magic. You get to ditch the heavy fuel tanks/batteries, and you still get the benefits of low maintenance costs for electric motors.

Even still, you would need to have the thrust to lift it in addition to your regular operating equipment and some way for it to be recovered (more weight, complexity, operating and upfront cost)

I'll pass on sitting in the tiny plane with a 100kw laser pointed at it.

> I'll pass on sitting in the tiny plane with a 100kw laser pointed at it.

Now that's one place where a tinfoil hat might come in really handy.

> It's sort of magic.

It's not sort of magic, it would be actual magic.

Perhaps Magnet bearing mounted flywheel as your kinetic energy storage would be better and lighter than battery power?

Range is helped A LOT by good lift to drag. In fact, range is proportional to lift to drag. A quadcopter cannot get very good range, but add wings, and you all of a sudden can go places.

300km is probably optimistic for this prototype. Wings are pretty short. But with extremely good lift to drag ratio (as seen in gliders, the best of which can get over 70 lift to drag), you could definitely get even 1000km range even with existing battery tech.

Range = (ratio of battery mass used for horizontal flight to total mass) * (lift to drag ratio) * (efficiency of propulsion system) * (specific energy of batteries)/(acceleration due to gravity)

So, if cruise-batteries are 0.5 of the total mass, lift to drag is 50, propulsion system is 0.75 efficient (75%), battery specific energy is 1MJ/kg (or 10^6 m^2/s^2 in alternate units, about 300Wh/kg, as good as very best lab-scale lithium ion batteries... lithium-sulfur is better), and gravity is 10m/s^2 (rounded), you have a range of:

0.5 * 50 * .75 * 1(MJ/kg)/(10m/s^2) = 0.5 * 50 * .75 * 10^6(m^2/s^2)/(10m/s^2) = 1875km.

Of course, 50% useful cruise battery weight is probably optimistic (although not too different from long distance airliners whose take-off mass can be roughly half fuel) and a lot of weight will be needed for the vertical take off and landing motors plus the payload, but it does show you what's possible even with existing battery tech.

I tend to think the prototype they showed probably won't get 300km range. Probably need longer wings for that. But their eventual goal is achievable. By the way, for long range, they're not likely using LiPo but lithium ion, perhaps those ubiquitous 18650 cells that Panasonic makes (of Tesla fame). And greater range is possible, especially as lithium-sulfur batteries start becoming more widely available (to speak nothing of lithium air).

As far as losing power to an engine, well, there are lots of engines. Also, electric motors and batteries are very simple and can be built to have extremely high reliability. The batteries and propulsion system can be built to be totally distributed, in which case there's really no feasible scenario where power is lost (unless control is lost, in which case you'd be screwed in a conventional airplane or helicopter, too). Additionally, a ballistic parachute can be and is used.

I don't think this flight is a breakthrough. A decent team could do the same thing they just did, and lots of people (including at NASA Langley) have been working on the same goal. Teaming a bunch of electric motors capable of tilting is a thing that several groups are pursuing, lots of people have done at smaller scale already, and it's only a matter of time before it's done at a large scale as well.

How do you cancel out the total system mass? I'm not completely following your derivation. Keep in mind with your math that you have to account for the VTOL component of flight too. Also, the ducted fans they're using are not efficient at all in your stated flight regime.

There are other considerations at work here as well. Having a 70l/d ratio means huge wings on something that will be this heavy. Gliders have big wings for their size and they have a very very low gross weight (ASK 21 2 seater at 900kg and a 17m wingspan). On top of just being absolutely massive, having all that wing area can cause problems in other than optimal weather situations. An ultra low wing loading will mean that the craft responds like a kite to any air movement so it would be very uncomfortable for the passengers who just want to get where they're going.

I agree that the chances of power loss are remote, especially compared to the current tech in use, but especially with new designs, you need a way of handling it. The issue isn't so much any individual motor but the batteries and support systems. They'll need a cooling system most likely and any failure will turn the whole thing into a Note 7. Also, sorry about using LiPo as a generic term. LiS batteries will definitely help the situation somewhat.

And intra-pack screening of batteries to avoid cascading failures.

It's all in that first 0.5 ratio. Basically, that ratio says that if I have a 10 ton aircraft, 5 tons is for the payload, airframe, engines, miscellaneous structure, and takeoff/landing batteries while 5 tons is for the cruise batteries. That 0.5 ratio is probably very optimistic for a real-world vehicle, but not crazily so. Burt Rutan's Voyager and the Virgin Globalflyer got much more ambitious figures, like 0.75 and 0.83, respectively (in this case referring to fuel mass instead of battery mass).

You refer to L/D ratio and lack of wing loading as if it's the same thing but it isn't. High performance gliders are generally ballasted (sometimes about half the weight is ballast) in order to increase the wing loading and increase flight speed. Our aircraft would have a 300km/h cruise speed, and so will similarly have a fairly high wing loading, even if it does need long, high aspect-ratio wings. This is helped by the fact that the sort of high performance lithium-ion batteries that you'd be likely to use (i.e. like Tesla uses) would be a good twice as dense as fuel. This increases your effective wing loading for the same outer mold line, allowing higher speed efficient cruise at the same altitude.

As far as battery and support system being a central failure point:

One interesting thing with electric propulsion is it's fairly easy to split the batteries and subsystems up /as well/ as the motors. So each motor pod could have its own small battery nearby for (possibly emergency) take-off and landing (this could also help reduce cabling mass, especially for the high currents you're likely to need for the vertical takeoff and landing portions). The cruise batteries could remain centralized, since you'll need a lot more of them and mass efficiency will be critical (and you could rely on your very good glide ratio).

I am squarely middle class... how in the hell would I be able to afford this, pilot training, maintenance and more if I can't afford to buy a 1960's Cessna 172? Nevermind the maintenance, training and more?

Flying cars for the masses are a delusional pipe dream.

If it's fully autonomous, which as has been noted is easier for aviation, you don't buy it, you rent it for a few minutes.

Imagine ordering a Lyft and this show up. This is amazing.

I laughed at the thought that you might one day use a ride sharing app and forget to specify that you wanted a car.

They're aiming to make it a taxi service. You wouldn't have to own one or deal with maintenance, you'd just pay the $X for your trip. And if it's fully autonomous (which it appears to be), then you -- as a passenger -- wouldn't have to be licensed any more than if you were flying commercial. I have no idea what sort of regulatory hurdles would exist or how easily they'd be overcome. But the fact that they've already built the plane would indicate that they've already taken that into consideration.

> And if it's fully autonomous (which it appears to be),

It's clearly not, since they describe situations in which onboard systems would provide notifications to "the pilot" directing them to land the plane.

alistproducer2 is operating under the premise that full autonomy, or a self-driving VTOL is easier than self-driving cars, or at least that flying cars for the masses would hinge on top-tier automagical flying to deal with the training issue.

A fleet of these forming an aerial taxi service would be the next step

The vision is an air taxi service serving the public, not personal aircraft owned or piloted by members of the general public.

> The first is that full autonomy is much easier in aviation than with ground transport.

> potentially for everyone if the economics of sharing these works out where regular folks could afford to hail these and the system could scale.

The idea is:

- You don't need pilot training

- The cost of the aircraft is shared among many people. You're not meant to buy one for yourself, you're meant to hail it like a taxi or Uber.

Plus, the only price I could find for a 1960s Cessna 172 is $12k. If you can't afford that, you can't buy a decent car either.

> Plus, the only price I could find for a 1960s Cessna 172 is $12k.

Seems unusually low, compared to the offer prices listed here: http://www.aircraftdealer.com/aircraft_for_sale/Cessna_172/9...

I was looking at this, though I admittedly know little about purchasing used aircraft: https://www.trade-a-plane.com/search?category_level1=Single+...

Ditto, I just though it might be useful to look at a larger sample size (taking "a 1960's Cessna 172" as more of a general example than an exact requirement).

Even if it's a real price, that's hardly the only cost to owning an airplane, if you actually fly it.

Similarly, the purchase price of a car isn't the only cost of owning it. Someone else later in the thread broke down small plane ownership costs (about $8000, without flying, about $10k if you actually want to fly some).

I was just replying to the price comparison with a car. Going up the thread, part of the premise was that they couldn't afford to buy a Cessna "Nevermind the maintenance, training and more".

Anyhow, the point's already been made (several times) that the purchase price isn't the only consideration.

~30k-40k for a mid 60's 172 that will actually fly, after some maintenance.

Plenty of decent cars available for $12K.

And don't forget about fuel. My horse, for example, costs me only $50/mo to keep well fed and gives me transportation year round. These sound like a huge drain on the wallet just to keep them running.

You ride it to work?

Horses were and are pretty expensive.

I think that underestimates the TCO of horses - shoes, medical care, grooming etc!

$300/month is a more realistic figure.

You dont afford it. You hail it like an uber. And its autonomous, so you dont need a pilots license. And because its picking up and dropping off dozens and dozens of 'rides' a day, the cost is shared by the user base. A short flight 2 hours away could be $100. Hell of a lot better than spending your time stuck in traffic. Also begins the process of easing congestion on highways.

The other thing is that they could still be flown a few feet above ground but without an actual road. It would eliminate the need to maintain a road system and if the thing fails at least it will not be the high altitude crash landing that kills you( although traveling at 300km/hour and loosing power will still be really bad even if you are just a few feet above ground). I think it would make it an easier sell to the public.

[Edit] Obviously I know nothing about aviation. So based on the comments below I stand corrected.

That's totally unrealistic. Low altitude flight is extremely dangerous due to the risk of hitting trees, towers, power lines, hills, etc. Military helicopter pilots are well trained and have good equipment but they still have frequent crashes during low-level training missions. If anything goes wrong you impact the ground and die with no chance to recover. The general public won't tolerate that level of risk, and the FAA would certainly never permit it.

> And because its picking up and dropping off dozens and dozens of 'rides' a day, the cost is shared by the user base.

I imagine charging time would be an issue; there would have to be well-stocked supplies of batteries near each dropoff point, and some way to quickly swap them out.

$39K for 1967 Cessna 172 seems affordable

http://www.aircraftdealer.com/aircraft-for-sale-detail/Cessn...

Annuals are at least $1000 a year, with insurance, taxes, and other costs you'd probably spend $8K a year to have it sit not flying. Add in flying costs and engine reserve you'd spend $10K or more a year.

Source: Am a pilot.

Taxes for what exactly?

Insurance is about ~600 a year from what I gather.

So not sure how you go from 1k to 8k

When you have large assets, the gov makes sure to charge property tax.

Local tax of a few hundred up to $1k, $300 loan a month, insurance is more like $1200 depending on experience. Hangar and tie down fees...

Cant find anything on taxes on personal aircraft (past purchase of course).

Loan?

Hangers are indeed expensive depending on the area, but tie down fees are like $60 a month

Many states/counties have a property tax on airplanes. But compared to other costs (insurance, maintenance, fuel) it's a drop in the bucket.

It would be cheaper (and far more effective) to just run a rail line to the exurbs in question. Why don't we do that first if connecting them is that valuable/important.

Because fundamentally thats still less convenient for the customer. In a perfect world, you want to be picked up from your front door and dropped off at the front door of your destination. And if you can avoid highways and traffic, even better. This provides the infamous 'last mile' solution to transportation, instead of forcing everyone onto mainline routes and artery networks.

I don't see something like this scaling in the way that a rail network can. Shuttling a few people at a time won't be enough for morning/evening rush hour, you'd need loads of these to match the carrying capacity of a train, and then you've reinvented the problem of traffic (although presumably much less dense; e.g. I imagine you'd join a queue and have to wait until the airspace isn't congested before your journey is permitted).

That's also an optimistic outlook. One contributor to traffic is people using a whole car just for themselves; since we've not figured that out after several decades of having cars, I doubt making them fly will solve the problem.

I can imagine niches for this, and wish them luck, but I don't think it'll make a dent in mass commuter transport.

This doesn't even remotely provide a last mile solution because even if they get the aircraft working the landing pads will be more than a mile apart. Just because it's a VTOL aircraft didn't mean you can land it on a city street. A large, securely fenced area free of nearby obstacles will be needed. Where are you going to put those in a dense city? And don't try to tell me that they're going to land on building roofs; most roofs are unsuitable because they're too small or not flat or full of ventilation equipment and antennas.

Parking lots we don't need after autonomous cars.

And even the ones that are large, flat, and uncluttered won't take the weight of an aircraft.

There's a NASA study ("Concept of Operations", CONOPs) on VTOL taxis in Silicon Valley:

"Silicon Valley Early Adopter CONOPs and Market Study"

https://nari.arc.nasa.gov/sites/default/files/attachments/An...

Running a rail line point to point is cheap? More like impossible.

For a speculative look at how a global network of flying cars might play out 'Too Like The Lightening'[1] was a pretty enjoyable read for me last year.

One of the consequences was that global borders essentially become worthless, and people instead join hives that best represent their ideals.

[1] http://www.npr.org/2016/05/10/476483675/science-fiction-and-...

It's also impressive that it can each 300KM already. In 10 years, it could be about 1,500 or 1,000 miles. But 300 is a great start.

I'd be surprised if their current prototype had a range of 300km. I think that's what they hope to achieve.

You're joking, right?

It would be impressive if it could reach 300km already, but the actual evidence we have is of it flying a small circle above the middle of a runway, implying a range of the order of 300m

and physics of course, that would suggest a 300km range to be exceptionally unlikely. But what use is physics in the face of such reckless marketing hype?

> It's also impressive that it can each 300KM already.

That's a target, not what they've demonstrated.

Reply on news.ycombinator.com