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Thread: Flying cars

  1. #1
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    Flying cars

    If this drone taxi is to be believed, link below, and the several different flying cars now being reported, maybe we are on the dawn of the flying car era long predicted in sf. The multi ducted fan type seem most likely to have the necessary redundancy And self stabilising controls. And they can hover, which seems to me to be essential for a new popular vehicle. I also like the idea of a lift platform that can pick up different modules, so some choice of fuel load for example, I guess we now have the technolgy to avoid mid air collisions too.

    http://www.cnn.com/2017/03/17/tech/e...r-drone-dubai/
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    For some stuff, I can see this working, but I'm still skeptical.

    They need to use energy just to stay in the air, and related to that, when they lose energy, they fall.


    There are cars now that turn off their engines when stopped (e.g. at traffic lights) so they're not using energy just to sit still. May not be such an issue with air-cars that perhaps can always be moving towards their destination, but still, the idea they have to continuously use energy just to be there seems wrong.

    If the engine cuts out in my car (seldom these days, but it happens to people), I'm already on the ground. On the motorway I suppose that could mean being rear-ended, but falling out of the sky doesn't seem much better.

    I'm wondering when the first lawsuit from an Amazon delivery drone dropping on the head of a pedestrian will occur.
    Last edited by pzkpfw; 2017-Apr-30 at 10:43 PM.
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    They may be touted as "cars" but they will still be regulated like aircraft.

    And if they do get treated like cars, it means the same yahoos who make the highways deadly will be allowed to fly over your home.
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    Quote Originally Posted by Noclevername View Post
    And if they do get treated like cars, it means the same yahoos who make the highways deadly will be allowed to fly over your home.
    They're self-piloting drones that take people along for the ride.

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    If it has a glide path of 90 vertical in an " Engine out " situation, I certainly won't fly it. When a toy falls out of the sky, it only does so much damage. Then there is something like this.
    Is there a fine line between clever and fool-hardy ?
    If you are going to fly people, you have to ask yourself..... " What kind of a ' Glide Ratio ' does this thing have ? " .
    There are three kinds of aircraft : Fixed Wing , Helicopters , and ...well .... a brick .

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    Thread moved from OTB to S&T
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    Quote Originally Posted by danscope View Post
    If it has a glide path of 90 vertical in an " Engine out " situation, I certainly won't fly it. When a toy falls out of the sky, it only does so much damage. Then there is something like this.
    Is there a fine line between clever and fool-hardy ?
    If you are going to fly people, you have to ask yourself..... " What kind of a ' Glide Ratio ' does this thing have ? " .
    There are three kinds of aircraft : Fixed Wing , Helicopters , and ...well .... a brick .
    It could have a parachute that is triggered automatically by an engine failure. Not perfect, but better than nothing.
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    Quote Originally Posted by Noclevername View Post
    And if they do get treated like cars, it means the same yahoos who make the highways deadly will be allowed to fly over your home.
    I'm figuring it was unintentional. But the choice of the word "yahoos" seems weird in this context. I first thought you were criticizing Yahoo's self-driving cars!
    As above, so below

  9. #9
    Quote Originally Posted by Noclevername View Post
    They may be touted as "cars" but they will still be regulated like aircraft.

    And if they do get treated like cars, it means the same yahoos who make the highways deadly will be allowed to fly over your home.
    Begs the question if a "car" is flying such that it needs regulation, then is it a car?

    A hover-car (carriage) I can understand.

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    If everyone gets flying cars, what will people complain about not having?

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    Quote Originally Posted by KaiYeves View Post
    If everyone gets flying cars, what will people complain about not having?
    Practical jet packs, practical hover boards, teleportation...

    Believe me, what I want will always increase no matter what I am given (when it comes to technological gadgets)

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    Quote Originally Posted by Jens View Post
    I'm figuring it was unintentional. But the choice of the word "yahoos" seems weird in this context. I first thought you were criticizing Yahoo's self-driving cars!
    https://en.wikipedia.org/wiki/Yahoo_...r%27s_Travels)
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    Quote Originally Posted by danscope View Post
    If it has a glide path of 90 vertical in an " Engine out " situation, I certainly won't fly it....
    I believe the Ehang 184 has eight independent motors driving eight props, and at least a double redundant flight control system. Just like a twin-turbine helicopter or the twine-engine V-22 Osprey, it can keep flying after an engine failure. It could probably keep flying after multiple engine failures, depending on where they happened.

    By contrast a single-engine piston-powered Robinson R22 hovering 400 ft over your subdivision cannot auto-rotate if its only engine fails -- it's coming down: http://www.copters.com/pilot/hvcurve.html

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    Quote Originally Posted by KaiYeves View Post
    If everyone gets flying cars, what will people complain about not having?
    Affordable flying car insurance.
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    Quote Originally Posted by Swift View Post
    Affordable flying car insurance.
    I think that hits the button! Toys for the super rich, but airplanes were like that. A taxi spreads the cost out. If you work on policy for urban transport, people want to to move point to point not really hub to hub, which existing public transport does. I could imagine (insured) hover taxis working well, point to point. It's IT meets helicopter.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    I don't think the number of engines / motors would have much to do with auto-rotation ability. Auto rotation is using whatever energy is stored in your rotor(s) at the moment you lose power to get to the ground in a (hopefully) controlled manner. When power is lost the rotor is disengaged from the engine ASAP so that it is free to continue rotating without the energy sapping drag the drive-train would impose. If there is enough energy left in it you can safely get to the ground.

    I am not sure how well, or if, the Ehang 184 would be able to auto-rotate. Can the rotors be disengaged from the motors? If not the motor is going to sap the energy in the rotor more quickly. Also the individual rotors are much smaller than, for example, a conventional helicopter and will not be able to store as much energy. At first glance I'd guess auto-rotation would not be a useful contingency for the Ehang 184 or similar drone configuration aircraft and that redundancy would be the only effective way to deal with loss of power emergencies.

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    Oh boy - less road rage, more air rage.

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    Quote Originally Posted by Darrell View Post
    I don't think the number of engines / motors would have much to do with auto-rotation ability....I am not sure how well, or if, the Ehang 184 would be able to auto-rotate....
    The point is the Ehang 184 has redundancy options missing from traditional helicopters today. I frequently see law enforcement and municipal Robinson R22s flying in my area, sometimes hovering at fairly low altitude. They have a single piston engine. They (or similar helicopters) *cannot* auto-rotate below about 400 ft from a hover. That is why that region of the height/velocity graph is called the "dead man's curve". If your engine fails, you're dead.

    The Ehang 184 can probably cannot auto-rotate, but it can tolerate at least one engine failure and possibly more depending on which one fails. The final production configuration isn't known, but it could easily have a ballistic chute as yet another safety method. You can't use ballistic chutes on traditional helicopters. This video shows a ballistic chute test on a Martin Jetpack: https://www.youtube.com/watch?v=Ale1U1fgw1I

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    I notice my gps is very patient even when I totally ignore her instructions. I hope the AI making my flying taxi navigate to my restaurant is similarly free of air rage. It's the AI that makes flying taxis possible, not just the new electric motors and batteries. The energy question is a fair point but solar electricity is coming along nicely. And I begin to believe drone parcel drop might actually happen too!
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by profloater View Post
    I notice my gps is very patient even when I totally ignore her instructions. I hope the AI making my flying taxi navigate to my restaurant is similarly free of air rage. It's the AI that makes flying taxis possible, not just the new electric motors and batteries. The energy question is a fair point but solar electricity is coming along nicely. And I begin to believe drone parcel drop might actually happen too!
    maybe for a few, but I think self-drive delivery trucks will be for the majority. When they arrive, they ring you, or text you and you go to the road and pick up the delivery. You would have a code to open the latch.
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    Quote Originally Posted by Frog march View Post
    maybe for a few, but I think self-drive delivery trucks will be for the majority. When they arrive, they ring you, or text you and you go to the road and pick up the delivery. You would have a code to open the latch.
    I guess that's true for our road based society. With a little more development, delivery can time share too, to avoid congestion, with say, a fridge that has a roadside door and is auto stocked with food and a box that receives parcels. With ever better video, the only reason to travel would be ...what? The fun of it?
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by Darrell View Post
    I don't think the number of engines / motors would have much to do with auto-rotation ability. Auto rotation is using whatever energy is stored in your rotor(s) at the moment you lose power to get to the ground in a (hopefully) controlled manner. When power is lost the rotor is disengaged from the engine ASAP so that it is free to continue rotating without the energy sapping drag the drive-train would impose. If there is enough energy left in it you can safely get to the ground.

    I am not sure how well, or if, the Ehang 184 would be able to auto-rotate. Can the rotors be disengaged from the motors? If not the motor is going to sap the energy in the rotor more quickly
    You might be right but my understanding is different. I thought it was the energy of the object falling that causes the rotor to spin, slowing the fall just like those spinning seeds. Which is why you need a certain altitude to be able to do it. It seems that based on your explanation it would only work if you were close to the ground.
    As above, so below

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    Quote Originally Posted by Jens View Post
    You might be right but my understanding is different. I thought it was the energy of the object falling that causes the rotor to spin, slowing the fall just like those spinning seeds. Which is why you need a certain altitude to be able to do it. It seems that based on your explanation it would only work if you were close to the ground.
    You are right, I was completely wrong about that. Autorotation is when the rotor is turned by aerodynamic forces, airflow through the rotors like an autogyro, rather than being turned by the engines. It is analogous to gliding in fixed wing aircraft.

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    Quote Originally Posted by Darrell View Post
    ...I was completely wrong about that... Autorotation is when the rotor is turned by aerodynamic forces, airflow through the rotors like an autogyro...
    You were partially correct about rotor inertia. That is one mechanism behind autorotation, and a high-inertia rotor system is more tolerant of autorotation and in limited cases can do a few things on rotor inertia alone. E.g, the Bell UH-1 "Huey" has such high rotor inertia that it can bring the rotor to operating rpm, cut power, lift off into ground effect and do a 360 "pedal turn", then set down gently -- all from stored rotor energy. The Robinson R22 and Hughes 300 series have low inertia systems and are more finicky to autorotate.

    In fact a helicopter or drone with very low rotor inertia cannot autorotate at all. No matter how well airflow maintains rotor speed during the descent, there must be enough rotor inertia to arrest the final descent rate and land. A drone has such low rotor inertia this by itself makes it impossible. Bell did a study showing how even higher rotor inertia could enable a helicopter to autorotate from even very low altitude/airspeed combinations, thus eliminating the "dead man's curve": www.dtic.mil/dtic/tr/fulltext/u2/a071648.pdf

    Ability to autorotate is also affected by "disk loading", or ratio of the craft's weight to the total swept area of the rotor disk(s). Each rotor in the Ehang 184 has a disk area of two square meters, or eight square meters total (86.5 square feet). The vehicle gross weight is 340 kg (749 lbs), thus the disk loading is 42.5 kg per square meter, or 8.7 lbs per square foot. By contrast a Robinson R22 has a disk loading of 2.6 lbs per square foot. That said, the Ehang's disk loading is not impossibly high so as to preclude autorotation on that basis alone.

    However autorotation also requires the rotor have variable collective pitch control to adjust rotor speed and descent rate. Multirotor drones don't have this -- their rotors are fixed pitch.

    So in general autorotation by a multirotor drone is not possible, whether a DJI Phantom or an Ehang 184. This is mainly because of low rotor inertia and inability to control rotor rpm and descent rate with collective pitch. However the Ehang has other compensating safety factors such as (apparently) eight-motor reliability and probable ability to fly with one or more failed motors. It could also have a ballistic parachute (like many ultralights do), which is not possible on normal helicopters. By contrast Robinson R22 hovering at about 400 feet cannot safely autorotate and is totally dependent on a single piston engine. That is why medivac helicopters often are twin turbine -- each engine is far more reliable than a piston engine, and they can fly on a single engine for brief periods.

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    While inservice I saw a Sea King have a severe malfunction of some sort at take off and the helo was spinning under its rotors.

    Just prior to it ending up in the ocean, of course. (No fatalities, but it wasn't from a lack of trying.)

    What I thought odd was the helo, though spinning under its rotor, was still maintaining its position over the flightdeck relative to its take off point until they actually steered the ship out from under it. We were doing about thirty knots.
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    Quote Originally Posted by BigDon View Post
    While inservice I saw a Sea King have a severe malfunction of some sort at take off and the helo was spinning under its rotors....
    Here is a CH-53 flying with half its rotor blades removed:

    https://photos.smugmug.com/photos/i-.../i-kCQq77R.jpg

    CH-53 doing an aerobatic roll: https://www.youtube.com/watch?v=MQ7pVjQ5Y5g

    So even though traditional helicopters are complex and finicky, they are refined by decades of development. It will be interesting to see if multirotor manned aircraft like the Ehang 184 can be developed to compete with these. OTOH remotely operated drones need not compete directly in all cases, sometimes they can provide similar functionality in a smaller package. I wonder how many local law enforcement helicopters could be replaced by drones?

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    I would expect a parachute to cover a lot of emergency scenarios. The high energy low range nature does imply taxi or commuting type of journeys. I wonder about ducted versus open props. I gather the sensitivity to side gusts is worse with ducts but otherwise for slow flight they seem superior and safer for bystanders.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    It would seem that the multi engine/rotor scheme has problems of severe instability with engine-out situations.... ie imbalanced lift from an odd lift profile. IE two engines out on the same time = an uncontrolled spin out , corkscrew . And in that situation a deployed
    ballistic parachute system will just wrap the main support chord around it's body , further compounding the safe landing scheme.
    This platform relies on balanced lift at all times. Any degradation in this balanced thrust should generate an instant moment response.
    Simply put, if you lose two engines forward, your going down, tumbling.

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    Quote Originally Posted by danscope View Post
    It would seem that the multi engine/rotor scheme has problems of severe instability with engine-out situations.... ie imbalanced lift from an odd lift profile...
    This is true only in the case of a four motor, four rotor drone. A six and higher rotor drone can usually survive a single motor/prop failure. At first glance the Ehang *looks* like a scaled-up drone with four motors/rotors on four arms. However I believe it has eight motors and eight props -- two on each arm. Given proper programming it could probably survive one (or even more) motor/prop failures, provided two don't fail on the same arm.

    The Moller Skycar is similar: it looks like a single engine failure would send it out of control, but it actually has two engines per fan and can keep flying if one fails: https://en.wikipedia.org/wiki/Moller_M400_Skycar

    If one motor/prop fails, the Ehang would simply increase/decrease thrust on the surviving units to balance this and immediately descend and land. This is similar to how six and eight rotor drones work today. If an engine or prop fails, the flight control system automatically detects this and balances the thrust. It's also similar to modern twin-turbine helicopters. Given an engine failure they can go to over 100% power on the surviving engine for brief periods to enable a safe emergency landing.
    Last edited by joema; 2017-May-04 at 11:09 AM.

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    Also, a research team (I think from Germany) has developed a software algorithm that allows a quad drone to keep flying even with the failure or one or two motors. Basically it compensates for the rotation caused by the imbalance, and keeps the drone flying by taking into account the torque difference. But I think that if there are people inside, having the redundancy is a good option.
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