"It's strange to imagine now, but prior to the 1920s, city streets looked dramatically different than they do today. They were considered to be a public space: a place for pedestrians, pushcart vendors, horse-drawn vehicles, streetcars, and children at play."
I think this point is very important. After the automobiles took over, the street slowly ceased to be the #1 public space where people hangout, shop, play or shoot the bull. Fast forward to today's US, spending an extended time on the street is associated with being poor, homeless or conducting criminal activity. Streets' sole purpose is for travel and commute.
Countries with less developed economy still enjoys a vibrant street life much like the pre 1920 US (i.e. Mexico, Brazil, Turkey, China, Thailand etc). As they get richer and purchase more automobile though, the same street transformation is happening again. One can notice a big difference if one visited China in 2000 vs today. They are in some dire need for parking lots.
Of course, there are definitely developed wealthy countries in Europe that also enjoy vibrant street life. However car ownership there is not as widespread as in the US due to a number of economic constraints (space cost, gas price, taxes).
> However car ownership there is not as widespread as in the US due to a number of economic constraints (space cost, gas price, taxes).
As someone living in one of those cities (not owning a car), I can say that the reason is certainly not the cost. It's just that 99% of the time taking the bike or using public transport is way more comfortable. For the remaining transports to the country side (where the public transport is insufficient), car sharing fills my needs just fine.
> Countries with less developed economy still enjoys a vibrant street life much like the pre 1920 US
You're connecting the dots wrong. Most European cities lead urban planning so that mixed zones are vibrant and busy, sometimes banning or punishing cars from city centers. It's intentional policy that (in Europe) is a result of policy, so is lowering car ownership in Denmark or the Netherlands.
Bigger wealth doesn't indicate that everyone will follow the US and create unwalkable suburb monstrocities.
This. In some European countries (e.g. UK, Scandinavian countries) there is no such thing as jaywalking. Pedestrians always have the right of way, except on motorways.
I guess I might not be interpreting you correctly, but pedestrians have no right of way. AFAIK, if someone is crossing the street you must stop your vehicle (which seems obvious because if not, you'd run them over). This doesn't mean that you can just cross the street wherever and whenever you may please, neither does it mean that you can actually walk in the street. Still focusing on Europe, it's not that uncommon to see drivers disrespect the law and not stop at a crosswalk when there's someone trying to cross it.
> This doesn't mean that you can just cross the street wherever and whenever you may please, neither does it mean that you can actually walk in the street.
Yes, that's exactly what I meant. I couldn't find it when this discussion was going on, but last time I looked at the Swedish law it said something like this about pedestrians: Pedestrians may travel wherever and whenever, except on motorways. If there is a dedicated pedestrian walkway nearby, it is recommended to use it. If there is a pedestrian crossing signal, and it is red, it is strongly recommended not to cross.
I.e. pedestrians have right of way always, outside motorways, and may walk on the street as they please.
pedestrians have right of way always, outside motorways, and may walk on the street as they please.
With the caveat that it is illegal to so in a reckless manner that that causes danger to others. Also you can be held financially responsible for any injuries or damage this recklessness causes.
When I lived in Lausanne, the local police were definitely giving tickets to pedestrians for crossing against the light. So its not all European countries (though the Swiss are more law and order than most).
The interesting thing about this is that it's very nearly a First Amendment infringement on the right to assemble. In order to assemble on a street–a fairly obvious place to do so, for a protest, since it has good exposure and visibility–you have to ask the police to explicitly redirect traffic on your behalf. That's not a small hurdle.
It is absolute if you aren't a weasel or have a political axe to grind (the supreme court):
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
Old city centers often still have some vibrant street life, and in some places, particularly the shopping districts, cars are banned completely or at least strongly discouraged. Much of Amsterdam is far too narrow for two-way traffic, so often it's one-way anyway, and so bumpy and twisty that it's just not very practical for cars. These are places where you can still see people walking in the streets.
Some years ago, Netherland changed the default blame in car-pedestrian collisions back to the car. Even if you have right of way, if you hit a pedestrian, you're still at fault.
> However car ownership there is not as widespread as in the US due to a number of economic constraints (space cost, gas price, taxes).
Compared to the US, the primary difference is space. It's just hard to find a place to park a car in Amsterdam, and you can get everywhere in the city by bike or public transport (and why would you ever want to leave the city?). Outside the city, car ownership is much more common, and poverty becomes the primary reason not to own a car.
By the way, I once heard that 75% of New Yorkers also don't have a car. Again primarily because space is simply scarce in a city.
One of the funniest things was to see a bicycle pile-up in Amsterdam when a tourist walked into the bike lanes. OK, well, it wasn't funny at the moment. This jay walking thing is dangerous, cars or not.
I am all for personal responsibility. However, here in the US the driver would get sued to hell and back if a person were to jaywalk and get hit. Going back to the Netherlands, it was interesting to take tours of windmills and find no safety barriers between the tourists and the internal mechanism. Here in the US we'd probably add a full plexiglass barrier to prevent accidents. So I have to wonder how much of this is due to differences in the laws around the world.
Oh god, jaywalking tourists on bike paths! It's totally fine to cross the bike path, but you really should watch before you cross. Pedestrians can behave very erratically, and it can be incredibly hard for a cyclist to predict what you're going to do (though I've gotten pretty good at it over the years). Fortunately such collissions are rarely serious.
Reminds me walking through the streets of Saigon. You just slowly start crossing and the motorbikes 10-20 deep on main streets magically separate around you. Traffic doesn't move more than 40km/h anywhere in the city.
> However car ownership there is not as widespread as in the US due to a number of economic constraints (space cost, gas price, taxes).
It's not just economic constraint here in the Netherlands. A lot of people can reach anything they need using their bike and public transport (you can take your bike on the train).
If you don't need a car, why bother getting and maintaining one?
and once we get flying car (more specifically - an octocopter scaled up to carry 2-4 peoples, not that big of a problem if you take time to look into it), we'll be able to get back to the situation, and even better - the streets can be more like park style space and of irregular shape (with some bike paths for short distance travels using bike or something like golf-cart). The massive asphalted/concreted surfaces will become a thing of the past. The only main roads/highways will be left for self-driving cargo-trucks.
more specifically - an octocopter scaled up to carry 2-4 peoples, not that big of a problem if you take time to look into it
An octocopter will have even worse range than a normal helicopter, so you cant get very far, and everyone having flying cars based on pushing air will not be able to use them from the street due to the problem of blowing pedestrians over. Flying cars as envisioned in sci-fi require reactionless drives, at least if you want to be able to take off from the street without endangering everyone.
Imagine a dozen 20 pound wild turkeys flying together. They are quite a bit more efficient than a single 240 pound craft/passenger because air displacement grows by the surface area of an object (by the square) while weight grows by the cube. That's why birds get off the ground easily while a human powered airplane needs a hundred foot wingspan.
Mathematically, the efficiency of a helicopter rotor is roughly proportional to its length. Double the diameter and fuel usage falls by roughly half for the same lift. However the lift for an array of rotors grows by the square of length, even though efficiency stays constant. So if you start with a quadcopter running on batteries that’s 10 times as efficient as a full-scale helicopter running on gas, an array of them with the same lift will still be 10 times as efficient. It will also have a smaller cross sectional area at the cost of greater complexity.
So the future of high efficiency lift is almost certainly in using arrays of rotors. The reason that hasn't happened yet is that most aircraft are designed for high speed travel, not hovering. I still want my reactionless drive though!
"So if you start with a quadcopter running on batteries that’s 10 times as efficient as a full-scale helicopter running on gas"
This I have never heard of. In a ratio of energy efficiency against carrying capacity I was under the impression that a normal helicopter massively outperformed a small quadcopter.
My impression with doing lifts with lots of small drones was that you get around this by constantly cycling the swarm.
Also, this still doesn't get around the problem of downwash. Either you shift a massive cross section of air for your force and get very little downwash, but then you end up with something much bigger than a car, or you focus it and get lots. You cannot get around the fact that to suspend a mass you have to move something equivalent downward.
edit - I get what you are saying with the turkeys. However, in a vehicle carrying four people, you have replaced the turkey bodies with a giant blob that has much less lifting potential, especially at low speed, than lots of turkey bodies. You have to dump a lot of useful surface area. Also I note that turkeys do not hover much.
> a normal helicopter massively outperformed a small quadcopter.
not really. The power loading (power divided by surface of the propeller's circle) is the key factor what matters for efficiency (until of course Reynolds number - air viscosity factor - starts to change - happens when we come to Kolibri scale)
In general, helicopter with 3m long blades (6m diameter) on one 500kw turbine or something like 16 of 30kw motors with 1.5m diameter propeller (with the same number of blades as helicopter) each is pretty much equivalent. That is pretty theoretical starting point. After that we can optimize these systems in different ways. 16-copter allows to use somewhat bigger, yet less-bladed, like 2-3 bladed propellers which are more efficient than multi-blades of helicopter (and you can't really have 2 bladed rotor on helicopter). You can use ducts on 1.5m propellers - not a case for helicopter. So all this allows to increase efficiency.
Ya there are definitely many ways of looking at this. I found the link about rotor power halving for each doubling of diameter (where it says: "So in this process the power is halved to (2m)(v/2)2/2 = mv2/(2x2) = P/2."):
Downwash definitely figures into this, as well as using fewer blades.
But, the key point is that we intuitively know that smaller craft require exponentially less power than larger craft. We could build a large craft with a very wide rotor to approach the efficiency of small craft, but I think it will turn out to be easier to use multiple small craft and scale how much weight we lift linearly.
"the key point is that we intuitively know that smaller craft require exponentially less power than larger craft."
This is where your intuition has let you down. Think about a normal helicopter's lifting capability and range as you go between models and full size aircraft. Or why you see bees walking.
>An octocopter will have even worse range than a normal helicopter, so you cant get very far
not really. Octocopters are much easy for a scheme with tilting of a couple of rotors and thus having efficient plane style horizontal flight than tilting the whole machine like helicopter. As result - higher speed, longer range.
> and everyone having flying cars based on pushing air will not be able to use them from the street due to the problem of blowing pedestrians over.
You statement is true for helicopters. The octocopters are much efficient with pushing of the air. Google e-volo. https://www.youtube.com/watch?v=CzP0Zqxam7E
(or the old work - Piasecki VZ-8 Airgeep - much less of airwash effect)
lotsofmangos is right! I have designed and built RC helicopters, tricopters, and quadcopters, from scratch. More blades is usually a lot less efficiency. There is something to be said for tricopters. From the point of view of pure efficiency, one large blade is always more efficient than 3 or more smaller once. Don't trust me, take a look at any static thrust calculator[1]. However, I found that with large and voluminous loads sometimes a tricopter can be more efficient because it allows you to mount the props away from the center load, so that the thrust of the prop isn't lost by pushing against the frame of the craft. This works in RC vehicles, but probably wouldn't be much of a benefit in full scale vehicles.
As for the prop wash of an octocopter, try standing right next to one that's taking off caring just 5 kilos of payload (batteries and DSLR). I have, and trust me, it gets really, really, windy. And that's with a 5 kilo payload, with a copter capable of generating maximum of 12 kilos of trust. No scale that up to 1000 kilos.
with correct design for the frame and ducts, the same airmass down flow would generate 20-30% more of static trust than the same airmass flow in case of helicopter. And that airflow will not have that blade end vortex which causes helicopter crashes and is just straight efficiency loss until that.
I did spend my time with trust calculators and some other systems :)
Yes, but 8 props will be considerably less efficient then one prop in generating that thrust in the first place. For instance:
One 300x8 inch prop will generate roughly 1 ton of thrust while spinning at 330RPM and consuming 12kW of energy. So, let's say we go with your prediction, and assign a 30% air flow efficiency to the one prop system. So in reality, according to you, it is generating 700 kilos of thrust. 700/4 is 87.5 kilos. So now we need to figure out how big of a prop we need to generate 1/8 of the thrust of the 300 inch prop, or roughly 88kg. I am going to use 60 inch props, because that will allow us to space 8 props in a circle roughly the same size as the original 300 inch prop.
Ok, so a 88x8 prop, spinning at 2350 RPM will generate roughly 88 kg of thrust wile consuming 6.7 kW of energy! That's 6.7 kW x 8 props, or a total of 54 kW, or almost 4.5 times less energy efficient than the one prop system, and that's taking into account your proposed 30% efficiency gain from multi-bladed systems and ducts.
I build these things all the time, there is a reason why the industry still uses helicopters with a single prop. It IS more efficient.
You're making a mistake. There is no 1 ton helicopters with 12 kW power on shaft. Even with 24 or 36 kW. I'm on iPhone so can't say exactly what thrust 12kw would produce on 6m prop. Around 300kg I'd estimate.
And another thing. 8 60in props aren't equivalent to 1 300 in wrt power loading. You need 16 of 60in to get equivalent of 1 240in prop.
Anyway, you've just calculated an octocopter with 700kg+ thrust on 60kw power. Is it bad? My neighbor's 400kg single-seater has 100kw gas turbine and it isn't 4x excessive power.
>You're making a mistake. There is no 1 ton helicopters with 12 kW power on shaft. Even with 24 or 36 kW. I'm on iPhone so can't say exactly what thrust 12kw would produce on 6m prop. Around 300kg I'd estimate.
Based on what, please provide at least some reference to an equation or calculator.
>And another thing. 8 60in props aren't equivalent to 1 300 in wrt power loading. You need 16 of 60in to get equivalent of 1 240in prop.
>Anyway, you've just calculated an octocopter with 700kg+ thrust on 60kw power. Is it bad? My neighbor's 400kg single-seater has 100kw gas turbine and it isn't 4x excessive power.
Can you give me an example than using some kind of calculations from a reliable source, not the "my neighbor" anecdotes. For instance, what makes you think that equivalent for a 240in prop would be 16 x 60 inch props? I understand that 16 60 inch props would have roughly the same area, but you do realize that 16 props arranges in such a way as not to create interference with each other would take up significantly more area? This is the main problem of a multirotor, you wither have to use smaller, less efficient props, or you have to make it much larger to accommodate the props.
In any case, when you are at your computer, if you feel like it, please do calculate, with references, a single prop machine lifting 1 ton vs an octo lifting the same 1 ton. I understand that a machine that lifts 1 ton would need to provide more than a ton of thrust, of course, but let's make it simple. Just a simple calculation. One prop producing 1 ton of thrust vs 8 props which can be arranged in such a way at to take up no more then 150% as much area as the original 1 prop, producing the same 1 ton of thrust.
If you really can show me that 8 props can be as efficient as 1 prop, please, by all means, prove me, and every one else who designs flying machines, wrong. But please do so with calculations I can verify.
Trust me on this. Blade efficiency is not only a swept area game, but also the middle of the blade is extra useless due to horrible vortex effects. One big blade massively outperforms eight little ones. And you cannot get away from the fact that you are hovering around a minimum of a ton. Either you have a really big cross sectional area of downwash from massive blades, or everyone falls over.
> One big blade massively outperforms eight little ones.
taking just blades into account - yes, though not that "massively". But the moment we consider the whole system - attach the blades onto a shaft, connect that shaft to reductor, to gas turbine, etc... ie. if that system is helicopter than bigger blade is still better, but if we change the whole system, ie. octocopter built using electric motors - the equation starts to change and we have good efficiency with octocopter and, which is more important, - much better control (eight electric motors with some of them allowed to be tilted gives precise control compare to very sluggish system of one big rotor driven by one big gas turbine), which addresses your point about " hovering around a minimum of a ton" - impossible task to do safely for helicopter in urban environment and pretty easy to do with ducted octocopter (you can't really have ducted helicopter precisely because of the size of the blades)
As far as i see, the lack of good control (not efficiency, range, payload, etc..) and direct danger from unshrouded blades is that doesn't allow to fly helicopters in any (even close to)urban environment, and especially for regular people.
I don't know what country you're in but in the US something like 80% of the population lives in urban areas where playing in the street is essentially impossible.
I live in the US. If you had been there and not just read some statistic you would have a better idea what you are talking about. The majority of the US live on quiet suburban streets. It is quite humorous how confused people get about America.
As of 2011, about 250 million Americans live in or around urban areas. That means more than three-quarters of the U.S. population shares just about three percent of the U.S. land area.[48]
And many suburbs are deliberately designed with tree-like roads, maximizing cul-de-sacs, and minimizing the probability of rat-running and other through-traffic.
Of course, without shortcuts and bike lanes, the same road pattern destroys walkability, because such road networks involve a trip to and from the trunk to get anywhere.
Then you have the gated communities of southern Florida, which are much worse.
Actually, China has gates, fences around everything, there is no such thing as an "open" campus or open apartment complex (unless it is very very urban). It is annoying to the say the least (especially when the gate you want to use is locked).
I think this point is very important. After the automobiles took over, the street slowly ceased to be the #1 public space where people hangout, shop, play or shoot the bull. Fast forward to today's US, spending an extended time on the street is associated with being poor, homeless or conducting criminal activity. Streets' sole purpose is for travel and commute.
Countries with less developed economy still enjoys a vibrant street life much like the pre 1920 US (i.e. Mexico, Brazil, Turkey, China, Thailand etc). As they get richer and purchase more automobile though, the same street transformation is happening again. One can notice a big difference if one visited China in 2000 vs today. They are in some dire need for parking lots.
Of course, there are definitely developed wealthy countries in Europe that also enjoy vibrant street life. However car ownership there is not as widespread as in the US due to a number of economic constraints (space cost, gas price, taxes).