Flying cars and jet-powered batwing

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stoppedcaring
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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Fri Nov 14, 2014 3:47 pm UTC

wumpus wrote:I'd probably look at Elon Musk's decision that electric cars are going to be expensive for awhile, so try to compete with Porsche buyers instead of Prius buyers. If I was trying to not only build flying cars, but simultaneously build a startup that makes flying cars I would ponder why cars that cost more than airplanes seem to outsell airplanes. I suspect that it is mostly because you can show off such a car by just driving it (the other is time&money: choose at most one). People only see you and your aircraft at airports (who likely already have a plane...). Sell the most dramatic entrance and you will have a backlog of orders well until you are officially "started up".

Yet another reason to have something you can take to a public function (necessitating VTOL) rather than being restricted to airstrips, something small enough to fit into one or two parking spaces, small enough to navigate on a roadway. And something that doesn't look just like a crumpled-up plane. Two-seat capacity is nice too.

This guy has the right idea:
"For me, it has to be vertical take-off and landing," said Daniel Lubrich, the managing director of Krossblade Aerospace Systems. "I think this idea of an aircraft you can drive on the street but you still have to find an airport for is nice, but it doesn't really solve the problem."

SkyCruiser is a concept 5-seat hybrid VTOL transformer airplane with road-drive ability. VTOL, vertical take off and landing, enables a traveler to travel directly from point A to point B, instead of going from point A to an airport in a car say, then fly from the airport to another airport, and then drive with a car from the other airport to point B. Rather than spending 3 to 4 hours going from LA to San Francisco, for example, SkyCruiser takes you directly to your destination, point to point, in just a little over 1 hour.
This concept uses folding wings and four fold-out vertical-lift rotors, but it's really long, too long to effectively navigate in an urban environment.

wumpus wrote:Note that medivac can likely get away with STOL (assuming the hospital can build whatever they need and that the medivac and takeoff and land on a road). The thing to remember is that a helicopter fights the air every inch of the way while an airplane tends to ride the air. For less dense areas, gaining speed from using wings (let alone the relative safety of planes vs. helicopters) would make them more cost effective (after startup costs. The startup costs are likely the killers, thus my notes above on building high-cost flying cars).

Eh, Medivac can't always get away with STOL. In fact, I would say STOL is the exception rather than the rule. Real estate is limited, especially in urban environments. And you may not always be able to clear enough road space for STOL; powerlines and buildings really complicate STOL but VTOL less so.

It seems like a basic rule: achieving energy-efficient (i.e., sustainable) lift of any kind requires a large area of air against which to push (whether rotor or wing), which clashes nastily with anything that can fit in a parking space.

ucim wrote:
stoppedcaring wrote:Certainly, something like this would start out as a police/emergency responder sort of thing...
Sounds good, but it's because that's a "money is no object" kind of application. And even so, money is an object. Is it better to have one flying car, or six ordinary police/emergency helicopters?

It's more "time is of the essence" than "money is no object".

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Re: Flying cars and jet-powered batwing

Postby ucim » Fri Nov 14, 2014 4:13 pm UTC

stoppedcaring wrote:[police/emergency responder is] more "time is of the essence" than "money is no object".
Well, then would you rather have six helicopters, ensuring that one of them is already near the problem, or one flying car that's on the other side of town (and maybe in the middle of another mission)

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Fri Nov 14, 2014 6:11 pm UTC

ucim wrote:
stoppedcaring wrote:[police/emergency responder is] more "time is of the essence" than "money is no object".
Well, then would you rather have six helicopters, ensuring that one of them is already near the problem, or one flying car that's on the other side of town (and maybe in the middle of another mission)

Jose

Eh, a police helicopter runs $500k-$3m; a Martin Jetpack costs $150k.

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Re: Flying cars and jet-powered batwing

Postby ucim » Fri Nov 14, 2014 7:19 pm UTC

stoppedcaring wrote:Eh, a police helicopter runs $500k-$3m; a Martin Jetpack costs $150k.
Yeah, and a Martin Jetpack can't carry anything besides a pilot and a leatherman.

Jose
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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Fri Nov 14, 2014 7:42 pm UTC

ucim wrote:
stoppedcaring wrote:Eh, a police helicopter runs $500k-$3m; a Martin Jetpack costs $150k.
Yeah, and a Martin Jetpack can't carry anything besides a pilot and a leatherman.

But it can land in spaces a helicopter can't even approach, and it takes much less time to power up and take off. A LOT cheaper to operate, too. Lots of times, first response is not about getting particular equipment to a scene, but about getting any responder to the scene, even if that responder only has what he or she can carry. Active shooter, heart attack/stroke, etc.

wumpus wrote:I think the only "real" flying cars on or near the market are autogyros that effectively only do this (I think they are more or less off road vehicles that fly to ignore otherwise impassible terrain).


On the autogyro front, the Pal-V One seems promising, especially with how neatly it all folds up. It's just too bad it doesn't have an optional VTOL mode, perhaps using tipjets? The thing about this is that you don't need sustained hover capability, just "burst-hover" for the transition to and from forward flight.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Fri Nov 14, 2014 10:50 pm UTC

I have a quick aerodynamics/physics question. The whole concept of vertical lift is based on conservation of momentum; lifting force is proportional to the momentum imparted to a given mass of air. It takes more power to impart a high amount of momentum to a small mass of air; it takes less power to impart a low amount of momentum to a large mass of air. If you want an untethered craft that can stay aloft for any significant amount of time, you need to be able to do work on as large a mass of air as possible.

This usually comes down to rotor area. A helicopter does this with a very large disc, but exposed blades are noisy, hazardous, and don't really fit well into the profile of a parkable/drivable vehicle. Ducted fans are safer and quieter, but they add weight cost and are even harder to collapse/retract.

But do we actually need rotors at all? Is it possible to impart momentum to a large mass of air without using blades?

The Dyson Bladeless Fan still has a bladed air compressor inside, but claims that inducement and entrainment multiples the amount of air it pushed through by a factor of fifteen. If that same principle could be applied to a vertical lift fan, it would effectively cut power consumption by a factor of four for a given fan intake area.

Obviously, this isn't going to be as efficient as simply using blades would be, but for purposes of safety and space considerations, it might be promising. The bladeless fan design doesn't have to be circular; it works just fine as a flat panel that could be extended away from the vehicle prior to takeoff.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Sat Nov 15, 2014 6:03 pm UTC

ucim wrote:
stoppedcaring wrote:[police/emergency responder is] more "time is of the essence" than "money is no object".
Well, then would you rather have six helicopters, ensuring that one of them is already near the problem, or one flying car that's on the other side of town (and maybe in the middle of another mission)

Jose


The first number I saw during a google of medivac speeds was 150mph cruise speed, so a 300mph plane could presumably replace 4 150mph helicopters assuming they spend more than half their time on the ground. Presumably with sufficient horse trading between counties, some rural areas would be better served by a faster VTOL plane that could cover a larger area.

A more interesting question is: at what point does an ambulance routinely carry drones to load a single patient in to fly to the hospital? An even better [hopefully] technology would be to use a drone to deliver some sort of cryochamber (probably closer to 0C than ~40K, but the idea is to extend the "golden hour" to be plenty long enough to deliver the patient to the hospital (possibly by a leisurely ambulance ride followed by full checks and tests then perform any operation required at a standard speed). The biggest issue (assuming freezing helps at all) would be if random onlookers could be trusted to move an injured patient onto the stretcher (actually it would be hard enough to get them to do anything at all, but we will assume that people are present and working). Maybe some of these drones would be safe enough for an EMT to ride in the (off) cryochamber?

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Re: Flying cars and jet-powered batwing

Postby wumpus » Sat Nov 15, 2014 6:08 pm UTC

stoppedcaring wrote:This guy has the right idea:
[i]"For me, it has to be vertical take-off and landing," said Daniel Lubrich, the managing director of Krossblade Aerospace Systems. "I think this idea of an aircraft you can drive on the street but you still have to find an airport for is nice, but it doesn't really solve the problem."


My initial thought when I saw that was "6 servos that either work or you die". After looking at it some more, it might not quite be that bad (as in, 10 times worse than the Osprey by design), but still I'd have to worry about flying with rotors partially out/failed. The drone probably works well (and at least will be safe enough for drone use), and might at least keep them in business long enough to come up with something workable.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Sat Nov 15, 2014 6:55 pm UTC

wumpus wrote:
stoppedcaring wrote:This guy has the right idea:
[i]"For me, it has to be vertical take-off and landing," said Daniel Lubrich, the managing director of Krossblade Aerospace Systems. "I think this idea of an aircraft you can drive on the street but you still have to find an airport for is nice, but it doesn't really solve the problem."


My initial thought when I saw that was "6 servos that either work or you die". After looking at it some more, it might not quite be that bad (as in, 10 times worse than the Osprey by design), but still I'd have to worry about flying with rotors partially out/failed. The drone probably works well (and at least will be safe enough for drone use), and might at least keep them in business long enough to come up with something workable.

Yeah, I'm not a fan of the design either. But in terms of what they're trying to accomplish, I think they have the right idea.

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Re: Flying cars and jet-powered batwing

Postby Copper Bezel » Sun Nov 16, 2014 7:19 am UTC

Isn't flying inherently much more energy-expensive than traveling by land? Like, literally the same energy cost at cruising speed except that one has to add the "keep the vehicle off the ground" term? I'm not really sure what the goal of a consumer flying car would be. Or rather, what the goal of a consumer VTOL craft would be, and additionally, what the goal of having that craft able to be transported by road is. A computer-controlled network could pack more of them into a given space for commuting than cars - maybe, since there are three dimensions but also much wider buffer zones needed - which could mean a larger throughput, but for daily hops, a land vehicle is always going to be much, much more sensible. For visiting Grandma in another state / EU member nation / whatever, well, you just use high speed rail or a mass transit plane, right?

Flying cars seem like the exact opposite of infrastructure development and urbanization, like they're really designed to encourage suburban sprawl and carbon emissions. I don't think we actually want people to have them, even if they're possible and safe.
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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Sun Nov 16, 2014 5:21 pm UTC

Copper Bezel wrote:Flying cars seem like the exact opposite of infrastructure development and urbanization, like they're really designed to encourage suburban sprawl and carbon emissions. I don't think we actually want people to have them, even if they're possible and safe.

Blasphemy! Blasphemy!

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Mon Nov 17, 2014 2:18 pm UTC

Copper Bezel wrote:Flying cars seem like the exact opposite of infrastructure development and urbanization, like they're really designed to encourage suburban sprawl and carbon emissions. I don't think we actually want people to have them, even if they're possible and safe.


Why do we need to urbanize humanity?

Even if we do so, transit is still necessary. Faster transit is generally good...if you can take a more straight line approach than roads allow, it could even save fuel, potentially, and certainly could save time. I do not see desirability as a problem, even though the concept has a great many practical concerns.

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Re: Flying cars and jet-powered batwing

Postby stoppedcaring » Mon Nov 17, 2014 3:38 pm UTC

You know, I think we could relax my original #3 requirement -- fuel-efficient cruise mode -- as long as VTOL and "drive mode" were functional. Just having something that could VTOL or drive is big.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Tue Nov 18, 2014 1:11 am UTC

Copper Bezel wrote:Isn't flying inherently much more energy-expensive than traveling by land? Like, literally the same energy cost at cruising speed except that one has to add the "keep the vehicle off the ground" term?


My understanding is that you use roughly the same amount of fuel per-person in a commercial jet as in a car. One thing to remember is that at 30,000' you only have 1/3-1/4 the air resistance you would have at sea level (and half that at Concorde heights). The other is that you get an aerodynamic shape around all the people at once, rather than each car (consider the differences if the cars drove while drafting peloton-style. Or even a bus).

Yes, a flying car will use more fuel than a car (unless by traveling as the crow flies reduces the length enough). I've assumed that with sufficient mass-production, pretty much all the personal flying vehicles (of whatever form) would be pressurized to at least get some efficiency advantages for flying, but for personal vehicles that won't be much.

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Re: Flying cars and jet-powered batwing

Postby Copper Bezel » Tue Nov 18, 2014 6:04 am UTC

Right, we're not really talking about typical cruising altitudes in this thread, so I don't really think either of those advantages apply. And you're right to mention buses, and might as well jump to high-speed rail, too, for the efficiency comparison with cars and commercial airliners; putting more people in a larger vehicle massively increases efficiency, and commercial airliners have the full benefit of that. A flying car isn't going to be any more efficient than a Cessna as a commuter vehicle.

Tyndmyr wrote:
Copper Bezel wrote:Flying cars seem like the exact opposite of infrastructure development and urbanization, like they're really designed to encourage suburban sprawl and carbon emissions. I don't think we actually want people to have them, even if they're possible and safe.


Why do we need to urbanize humanity?

It's an efficiency thing and a population thing. The carbon footprint of a city dweller is much smaller than that of a suburbanite or rural resident (and they even reproduce less!) It's one of the things that's actually helping us get toward a place where we could actually have energy production and manufacturing and so on for a global population that's gradually moving toward first-world standards of living.

Even if we do so, transit is still necessary. Faster transit is generally good...if you can take a more straight line approach than roads allow, it could even save fuel, potentially, and certainly could save time.

Well, as a transit system, today's approach to cars kinda sucks - or at least, it's more inefficient than it seems like it ought to be. A straight line approach vs. following a grid isn't really ever going to save you more than (sqrt 2 -1) of your travel cost, but commuter cars spend a lot of time in "in-town driving," the regime dominated by rolling resistance rather than air resistance, in which efficiency drops drastically and lower speeds cost more fuel than higher ones per mile and so on, and you basically eliminate all of that with a plane. So that's something at least, but I can't really understand how it could cancel out the cost of staying in the air.

Speed of transit for passengers (not so much for cargo) has a variable significance. If a vehicle is comfortable and controlled by someone other than the passenger, whether that's a computer or a bus driver, it's arguably less a loss of "time" than a commuter experiences driving for the same interval. One can, after all, read a book.

A realistic and desirable future for transportation is, to me, one dominated by mass transit. Personal airplanes for commuters seem as impractical to me as using monster trucks to get to work instead of building roads. Airplanes are useful for applications where the speed benefits can be truly significant, where the mass of cargo or passengers in a flight can be sufficient to offset the inefficiency of the basic system, or where the destination is simply inaccessible by road. If it's practical enough to take an airplane between two points in a city that it's worth putting down the regulation and infrastructure and training that make that possible, it's almost certainly going to be more practical still to link them by some kind of rail system instead.
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Tue Nov 18, 2014 4:30 pm UTC

Copper Bezel wrote:
Even if we do so, transit is still necessary. Faster transit is generally good...if you can take a more straight line approach than roads allow, it could even save fuel, potentially, and certainly could save time.

Well, as a transit system, today's approach to cars kinda sucks - or at least, it's more inefficient than it seems like it ought to be. A straight line approach vs. following a grid isn't really ever going to save you more than (sqrt 2 -1) of your travel cost, but commuter cars spend a lot of time in "in-town driving," the regime dominated by rolling resistance rather than air resistance, in which efficiency drops drastically and lower speeds cost more fuel than higher ones per mile and so on, and you basically eliminate all of that with a plane. So that's something at least, but I can't really understand how it could cancel out the cost of staying in the air.


In addition to that, there's idle time due to stop lights, stop signs, braking, and...even assuming grid efficiency is dubious. A *lot* of areas require a less efficient means to reach your destination, simply due to layout of roads.

Speed of transit for passengers (not so much for cargo) has a variable significance. If a vehicle is comfortable and controlled by someone other than the passenger, whether that's a computer or a bus driver, it's arguably less a loss of "time" than a commuter experiences driving for the same interval. One can, after all, read a book.


One could listen to a book on tape in a car now. Time spent is still time spent. Mass transit is efficient in some circumstances(nobody is arguing for the end to the commercial airplane, for instance), but not in all circumstances. Full or mostly full loading numbers look good, but if the number of passengers needing to go to a given destination is small at a given time, using a large vehicle becomes remarkably costly.

A realistic and desirable future for transportation is, to me, one dominated by mass transit. Personal airplanes for commuters seem as impractical to me as using monster trucks to get to work instead of building roads. Airplanes are useful for applications where the speed benefits can be truly significant, where the mass of cargo or passengers in a flight can be sufficient to offset the inefficiency of the basic system, or where the destination is simply inaccessible by road. If it's practical enough to take an airplane between two points in a city that it's worth putting down the regulation and infrastructure and training that make that possible, it's almost certainly going to be more practical still to link them by some kind of rail system instead.


Many mass transit systems operate at a loss. They are simply ineffective. This is particularly true for rail systems. Generation of all the resources to subsidize such a system is not carbon neutral, yet nobody ever seems to include those numbers. I dare say that if you did, their purported efficiency would decrease sharply.

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Re: Flying cars and jet-powered batwing

Postby elasto » Wed Nov 19, 2014 10:47 am UTC

Tyndmyr wrote:Many mass transit systems operate at a loss. They are simply ineffective.


All 'operating at a loss' means is there has been a political decision as to how much of the upfront and ongoing costs the commuters fund and how much the taxpayers fund (choosing the latter over the former in the case of an 'operating loss', or vice-versa in the case of an 'operating profit').

I'd be surprised if many mass transit systems actually work out more expensive per commuter-mile than personal transportation - given that each person has to invest thousands of dollars in their own often sharply depreciating vehicle with gas, repairs etc on top. Otherwise, when a city in China, India or wherever modernizes, why do they invest taxpayer funds in brand new bus, tram and train services if simply handing out a free car to everyone would be more efficient?

Obviously there may be portions of a mass transit system that have become uneconomic - eg. a train station was built in a place 50 years ago that has become a ghost-town that trains none-the-less still pass through, so modernization is a never-ending task, but, a few white elephant vanity projects aside, I'd imagine most mass transit systems as a whole are not 'simply ineffective' compared to the alternatives.

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Re: Flying cars and jet-powered batwing

Postby Copper Bezel » Wed Nov 19, 2014 11:37 am UTC

And highways and their maintenance do not occur for free due to friendly highway elves.

Listening to a book on tape is dividing your attention; it still takes some level of concentration to drive. All of the time you have is spent in some form or another. If I could be sitting at home as I am now typing this discussion post, or doing it on a train, then I got the train ride for "free."
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

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On cars vs. planes.

Postby wumpus » Mon Nov 24, 2014 4:05 pm UTC

One thing to remember about mileage on a car vs. a plane is just how bad car engines are at delivering mileage.

Typically, we think of cars as being efficient at lower speeds and such, but in reality that is simply the fact of air resistance. The engine itself runs most efficiently delivering about half of peak power at the point of peak torque (roughly 1/4 of the listed hp). Keep an engine producing that power for awhile (you will need a CVT or a lot of gears) and you will find yourself going at "car impounding imminent" speeds (also air resistance will kill your mileage). This is a large part of the reason the Toyota Prius gets such great mileage. With about 90hp due to the gas engine, it typically putters around peak production (also the reason a lot of tiny econo cars of the 80s got better mileage than today's high-mileage cars: vastly less power to pull less weight).

It is also the reason you can't [or shouldn't] just take an engine out of a car and shove it in your kit plane. The car engine expects to produce something like 30hp nearly all the time and producing >200 hp (otherwise you would likely be using a "real" aircraft engine) will get dangerous fast. It isn't quite clear that a highly aerodynamic "flying car" running with an engine near peak efficiency won't do slightly better than a car. Or we could be using nuclear power to produce "enough" power to not worry about it.

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Mon Nov 24, 2014 5:50 pm UTC

elasto wrote:
Tyndmyr wrote:Many mass transit systems operate at a loss. They are simply ineffective.


All 'operating at a loss' means is there has been a political decision as to how much of the upfront and ongoing costs the commuters fund and how much the taxpayers fund (choosing the latter over the former in the case of an 'operating loss', or vice-versa in the case of an 'operating profit').

I'd be surprised if many mass transit systems actually work out more expensive per commuter-mile than personal transportation - given that each person has to invest thousands of dollars in their own often sharply depreciating vehicle with gas, repairs etc on top. Otherwise, when a city in China, India or wherever modernizes, why do they invest taxpayer funds in brand new bus, tram and train services if simply handing out a free car to everyone would be more efficient?


Many reasons. China, for instance, is making a fair amount of money building such systems elsewhere.

Another is that cities may be wildly lacking in parking, due to having been around for a while, land prices being high, etc. The fact that it is being done in some areas does not mean that it is obviously most cost/effective in general.

I note that my nearest metro(DC metro area) is much more fond of obfuscating numbers than showing true costs, and estimated future costs have historically been significantly underestimated. This is complicated by the number of funding sources, etc. Additionally, even if it is more efficient in strict passenger/miles, that may not make it actually more efficient, as the number of stops serviced by a metro system and the number of routes available are vastly fewer than those available by road. Therefore, it is extremely likely that more miles will be traveled in reaching a given destination via train. This is particularly true for those with a central hub model, where it is routine to take one train to the hub, then another train to your destination, resulting in a very long overall trip to cover a fairly short distance.

I suggest perusal of some of the various justifications for the DC metro, taking into consideration that those hired to provide metro justifications are only paid if the government is happy with the conclusions, and it will be blindingly obvious that they are attempting to justify the metro via any means necessary, not actually producing an unbiased comparison.

In particular, they rely on "high property value" quite heavily, as well as avoiding congestion. As a result of spending on metro works instead of roads, the area has some of the worst congestion in the nation. This comparison makes the metro appear to be "saving" more and more time, as the problem gets worse and worse.

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Re: Flying cars and jet-powered batwing

Postby elasto » Tue Nov 25, 2014 11:47 am UTC

Tyndmyr wrote:Many reasons. China, for instance, is making a fair amount of money building such systems elsewhere.

That wouldn't explain why they'd choose the inefficient option for themselves though.

Another is that cities may be wildly lacking in parking, due to having been around for a while, land prices being high, etc. The fact that it is being done in some areas does not mean that it is obviously most cost/effective in general.

I'd suggest this is the case for most cities, and a big part of why mass transit systems work out more efficient per commuter-mile. It's irrelevant if theoretically individual cars would be more efficient if when everyone has one there's permanent gridlock.

I note that my nearest metro(DC metro area) is much more fond of obfuscating numbers than showing true costs, and estimated future costs have historically been significantly underestimated. This is complicated by the number of funding sources, etc. Additionally, even if it is more efficient in strict passenger/miles, that may not make it actually more efficient, as the number of stops serviced by a metro system and the number of routes available are vastly fewer than those available by road. Therefore, it is extremely likely that more miles will be traveled in reaching a given destination via train. This is particularly true for those with a central hub model, where it is routine to take one train to the hub, then another train to your destination, resulting in a very long overall trip to cover a fairly short distance.

I suggest perusal of some of the various justifications for the DC metro, taking into consideration that those hired to provide metro justifications are only paid if the government is happy with the conclusions, and it will be blindingly obvious that they are attempting to justify the metro via any means necessary, not actually producing an unbiased comparison.

In particular, they rely on "high property value" quite heavily, as well as avoiding congestion. As a result of spending on metro works instead of roads, the area has some of the worst congestion in the nation. This comparison makes the metro appear to be "saving" more and more time, as the problem gets worse and worse.

You've focused on rail here but I'd think they'd be one of the least efficient options - only really useful in taking pressure off an overloaded road system, or for specialist situations like transporting goods from docks to regional hubs. As such even if they technically can't be justified in and of themselves, if they make the road system more efficient they might still make economic sense. Or they might be less efficient economically but provide a time benefit (eg. a bullet train)

But you've ignored what I think is probably the most efficient mass transit system: A well planned and funded bus system. Where I live in China I can travel from one side of the city to the other (about 20 miles) for 10-20 US cents; the buses are frequent and go virtually everywhere; Payment is by contactless prepayment cards; and many bus shelters have LED displays showing the times of all incoming buses.

Yes all that costs money for local government and obviously technically 'operates at a loss' (meaning, as I say, that it's principally taxpayer funded rather than commuter funded), but I would dispute any claim that transportation would be more efficiently handled overall were this bus system to be replaced by cars (or anything else really).

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Re: Flying cars and jet-powered batwing

Postby Tyndmyr » Tue Nov 25, 2014 9:17 pm UTC

elasto wrote:You've focused on rail here but I'd think they'd be one of the least efficient options - only really useful in taking pressure off an overloaded road system, or for specialist situations like transporting goods from docks to regional hubs. As such even if they technically can't be justified in and of themselves, if they make the road system more efficient they might still make economic sense. Or they might be less efficient economically but provide a time benefit (eg. a bullet train)

But you've ignored what I think is probably the most efficient mass transit system: A well planned and funded bus system. Where I live in China I can travel from one side of the city to the other (about 20 miles) for 10-20 US cents; the buses are frequent and go virtually everywhere; Payment is by contactless prepayment cards; and many bus shelters have LED displays showing the times of all incoming buses.

Yes all that costs money for local government and obviously technically 'operates at a loss' (meaning, as I say, that it's principally taxpayer funded rather than commuter funded), but I would dispute any claim that transportation would be more efficiently handled overall were this bus system to be replaced by cars (or anything else really).


That trains are less efficient is probably correct. Certainly bus routes can be changed more easily than train routes can at a minimum...but this is due to the extant road system. If one only built roads where bus routes ran, that flexibility would be mostly lost. In addition, current bus routes run where traffic warrants it. A full bus going from point A to point B is more efficient than individual cars. The same is not true of an empty bus, or a minimal number of passengers. Using a bus for everything instead of just the most efficient cases would dramatically reduce the efficiency of busses.

So, replacing cars altogether remains an unviable option.

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Re: Flying cars and jet-powered batwing

Postby wumpus » Wed Nov 26, 2014 2:15 pm UTC

Tyndmyr wrote:I note that my nearest metro(DC metro area) is much more fond of obfuscating numbers than showing true costs, and estimated future costs have historically been significantly underestimated.


The DC metro was designed to be ridiculously expensive*. The claim was to not take any money away from all the other up and coming subways around the US. In practice, I doubt that any functional subways were actually added at the time (BART may be from that time, not sure) and presumably the effects were just to make the pork even sweeter.

* no really. Buying parts for 10 times the market price was a feature. Note that having been in the defense field, you can go broke selling things to Uncle Sam at less than 10x markup (due to changes, requirements, testing, more unfunded changes, etc.).

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Re: Flying cars and jet-powered batwing

Postby sevenperforce » Thu Sep 03, 2015 2:02 pm UTC

Reviving this thread to point out the similarity between the jet-powered batwing craft and the District 13 hovercraft depicted in Mockingjay Part 1:

Image

A lot larger, but extremely similar, with an overall flying wing design, twin engines feeding off a central air intake, ducted fans in the wings, a nose-down cabin, and high-mounted horizontal/vertical stabilizers.

The only difference is that the fans seem to be mounted a little aft of the center of gravity (though the weight of the engines may pull the CG farther back than it appears). But that's easily correctable during takeoff by vectoring a bit of turbofan engine thrust upward.

Obviously it's fiction, but I'm not sure whether a much larger version would be better or worse than the single-seat version.

And there's always the larger Capitol hovercraft but they're clearly using some sort of wacky ion thrust entrainment disc for hovering lift:

Image
But it would be neat to see what people could come up with for making this work IRL...because damn that's beautiful.

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Re: Flying cars and jet-powered batwing

Postby Neil_Boekend » Sun Sep 06, 2015 8:30 pm UTC

The District 13 craft also has "Ion thrusters" as lift engines.
Mikeski wrote:A "What If" update is never late. Nor is it early. It is posted precisely when it should be.

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Re: Flying cars and jet-powered batwing

Postby sevenperforce » Tue Sep 08, 2015 12:52 pm UTC

Apparently they found a way around the extremely poor T/W ratios of ion thrusters?

More likely they engineered a way to suck a lot of air through that giant open space using something vaguely representable as an "ion thruster".

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Re: Flying cars and jet-powered batwing

Postby Neil_Boekend » Tue Sep 08, 2015 6:07 pm UTC

it's in atmo so it could be ionocraft based.
Mikeski wrote:A "What If" update is never late. Nor is it early. It is posted precisely when it should be.

patzer's signature wrote:
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Re: Flying cars and jet-powered batwing

Postby Copper Bezel » Tue Sep 08, 2015 6:31 pm UTC

I'm going to ask an incredibly stupid question that reveals that I simply don't know how stuff works.

Is ionized air really blue?
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

she / her / her

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Re: Flying cars and jet-powered batwing

Postby sevenperforce » Tue Sep 08, 2015 6:54 pm UTC

Neil_Boekend wrote:it's in atmo so it could be ionocraft based.

Would room-temperature superconductors permit virtually-lossless ionocraft?

Copper Bezel wrote:I'm going to ask an incredibly stupid question that reveals that I simply don't know how stuff works.

Is ionized air really blue?

Ionized oxygen glows blue; ionized nitrogen glows purple.

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Re: Flying cars and jet-powered batwing

Postby Neil_Boekend » Sat Sep 12, 2015 10:36 am UTC

sevenperforce wrote:
Neil_Boekend wrote:it's in atmo so it could be ionocraft based.

Would room-temperature superconductors permit virtually-lossless ionocraft?

Main problem is usually the limited voltage difference due to arcing, exacerbated if you want to be able to fly in rain. This limits the max thrust. I don't think that superconductors would really help, since there isn't all that much current in the wires They are still dangerous because the current is usually still big enough to kill you.
Mikeski wrote:A "What If" update is never late. Nor is it early. It is posted precisely when it should be.

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flicky1991 wrote:I'm being quoted too much!

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Re: Flying cars and jet-powered batwing

Postby sevenperforce » Sat Sep 12, 2015 7:35 pm UTC

I wonder whether a toroidal electromagnet between the two wires, surrounding the opening, could be used to curve the path of the electrons into a vortex passing near the center of the opening. This would not only prevent arcing, but would also cause the electrons to act on a massively larger volume of air and thus multiply thrust exponentially.


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