Personal Aerial Vehicle (PAV) to take your commute into the third dimension

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Kingfisher, Aug 4, 2016.

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  1. Mar 26, 2019 #41

    Kingfisher

    Kingfisher

    Kingfisher

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    You are looking at this the wrong way. If your baseline is VTOL requirement, the motors have to be sized to enable vertical climb and additional power for control movements. Then you have to look at next how to make it more efficient and more socially acceptable than a helicopter. No point at comparing it to fixed wing aircraft that cannot take off vertically. There will be a flight distance point beyond which tilting rotors and wings will be beneficial. Vahana is exceptional in sharing their experiences. This is the way of the future, not shrouding everything in secrecy. They've done these studies. For the comment that tilting the rotors "will not do", check out their flight test:
    https://vahana.aero/flight-test-update-50-flights-53af963e1750
     
  2. Mar 26, 2019 #42

    Dusan

    Dusan

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    I'm not so sure I'm looking at it the wrong way. Wings benefits are not based on distance but on speed. At any non zero speed and proper AoA they provide much more lift than drag. Fighting gravity all the time with direct thrust is a bad thing to do, regardless of distance. The characteristics that make the fixed wing so good at transporting stuff and helicopters so good at hovering, distills down to high L/D and respectively low disk loading. For a winged, transitioning VTOL, having just tilting rotors, these characteristics are mutually exclusive. You cannot have high L/D with big rotors nor low disk loading with small rotors, as demonstrated by the most successful VTOL out there, the V-22 where L/D and disk loading is at best, a compromise.

    Your statement "motors have to be sized to enable vertical climb" is wrong as the lift is created by rotors, not motors, and bigger rotors need less induced power, but obviously they create more drag at cruise speed. This approach of brute force and assuming everything will follow will not work as demonstrated by so many VTOL failures in the past. Aerodynamics needs to be figured first, and here I mean to find a configuration to have low cruise L/D and capability to transition to hover low disk loading. "If you want to know the future, look at the past" NASA tried this before with Tazenflugel and Samara (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100031107.pdf), and even extending variable diameter rotors (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19970005490.pdf).
    Vahana (and most of the others "personal VTOL") seems to be a primarily aesthetic design (https://vahana.aero/vahana-design-process-part-i-putting-pen-to-paper-cdc0fa88a6ac) and apparently the aerodynamics is so bad that somehow their figure of merit decreases with the rotor diameters (interference perhaps? see here: https://vahana.aero/vahana-design-process-part-ii-preparing-for-lift-off-a75b7ef6d583)
    The Vahana videos looks good, but not because of their aerodynamics, but of flight software control, some based on the previous multi-copter enthusiasts out there.

    Electric propulsion offers a big benefit for VTOL, and contrary to what people are thinking, it is not its high efficiency per se, but high efficiency regardless of power setting. This is in contrast with piston and especially turbine ICE, and is valued as the cruise setting for "flying on a wing" requires so less power than hover. One big disadvantage is the low battery specific energy (compared to fuel) and this enhances my point of needing to make the aerodynamic design as efficient as possible, especially in hover, but without compromising drag at cruise speeds.

    From the little aerodynamics I know, smaller rotors have less FoM than big rotors at the same disk loading, (just considering Reynolds numbers perspective), so I still think that single rotor helicopters will always be more efficient than multi-rotors. A historical single rotor personal VTOL that worked great in hover was the Hiller VZ-1 Pawnee. Making an electric single rotor that can transition to cruise, I believe will be an awesome personal VTOL aircraft (see the concept here: http://aliptera.com/#ADR-1)

    Flying on a wing, at slow speed, means that the wing lift provided is not enough, a significant portion of lift needs to be generated by direct thrust. This is where matters become complicated, to control and maintain the wing at max AoA. just before stall (to get most lift of it, so less direct inefficient rotor lift) and to get the rotor thrust magnitude and direction exactly right, to balance the drag and remaining lift, is where I'm at.

    I think that public acceptance will follow a good, efficient design and not one that just looks "futuristic" and good.
     
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  3. Mar 26, 2019 #43

    Toobuilder

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    Several years into this thread and I have yet to see even basic performance requirements. Without defining range, speed, payload and ground environment at an absolute minimum this is just another dreamers thread.

    Define the "commute problem" this thread is intending to solve
     
  4. Mar 26, 2019 #44

    Dusan

    Dusan

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    You are perfectly right here, Toobuilder, and we're trying to do exactly that, plus 100 things more: https://nari.arc.nasa.gov/wghome
     
  5. Mar 26, 2019 #45

    choppergirl

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    [​IMG]
    Computer Controlled Balance via Collective instead of Rotor Speed

    I have a question about an alternative configuration of propellers on these things... that I want to design plans for a quadcopter like gasoline powered aerial multi-use multi-role sled*, but I've never seen done before.

    Could instead of changing the speed of each electric motor to change the amount of lift propeller each produces...

    All four propellers be driven at a constant governed speed regardless of load, and...

    the balancing computer, instead of changing the propeller speed, changes the collective / pitch of each propeller blade via a swash plate moved by a servo.

    This works on a helicopter via the collective handle in the cockpit when you want to raise or lower the helicopter by changing the angle of attack of the main rotor blade. Same idea as airplanes with adjustable prop pitches... basically, that's all you need to change, the prop pitch, to change the amount of thrust the propeller is producing.

    Why would I want to do this?


    Gasoline Powered


    Because I want to scale up to super size and build a gasoline engine powered payload carrying quad with hard point attachments (for, for example, agricultural spraying via main computer control), with an engine centrally located, and all the propellers driven off of belts/drive shafts/chains from the central engine out to drive the propellers.

    Gasoline power has several benefits, namely, longer run time, higher energy density per fuel pound. Also I'll be centrally locating all the weight of the engines into one engine, which might increase roll/pitch/yaw response. I would further increase the number of propellers for finer grained balancing control.


    Ejection Seat

    I have another innovative idea, regarding passenger carrying pilotable quads.

    Since these things fall like a brick with loss of power or failure, an ejection seat with parachute seems like it would be perhaps the best way to save the passenger in the event of system failure or vehicle attitude crisis.

    The ejection seat could be configured to deploy by pilot control, and/or also automatically... for example, upon the craft tilting in excess of some angle beyond which is non-recoverable (say, 45 degrees)... or by detection of sudden acceleration downward (a plummet) when pilot controls do not agree with that course of action.


    Initial Applications

    An Aerial Sled would be a boon to agriculture.... all the crop duster pilots are retiring and nobody is going to be around to spray the crops, and yet the planet population continues to grow. We have to grow more food with the same amount of arable land. (side note - a chemical reaction that fed the world: Haber Bosch Process).

    These things could be like little worker bees the size of small passenger cars, spraying the fields... and would sound like it too... and you'd see them out in the fields when you went driving in the countryside.

    When they run out of spray and gasoline, they just fly back to the supply truck and dip their little "honey sucking straws" into the feed spouts and load up on both gasoline and spray, and then back out into the field to do more spraying...

    You have one main computer that maps the field and outlines a grid pattern for them all to follow for total coverage and to avoid collisions.

    When the work is done, they land on flatbed trucks or trailers for the ride home or to the next field.

    Theoretically, they might be used to harvest some crops, but I don't think that would be economically feasible. But they could do other things, like work on cell / power grid antennas or be aerial cranes or transport vehicles on a job site.

    [​IMG]
    *I'm coining the term "aerial sled": I got it from sledge in this historic video .
     
    Last edited: Mar 26, 2019
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  6. Mar 26, 2019 #46

    Dusan

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    Hi choppergirl,

    The gas powered variable pitch multicopter was done multiple times before, one example EWZ-Z110 (see here: https://en.wikipedia.org/wiki/Ewatt_UAV)
    or this one: https://newatlas.com/soapdrones-variable-pitch-multirotor-endurance/48202/

    An ejection seat is a good (saves the pilot) and bad idea(the aircraft falls on somebody's head). The best, I think is to have a parachute system that saves both without pilot ejection, something similar to Cirrus Airframe Parachute System. What I don't know how it will work is when the batteries are on fire. I guess the answer is to use chemistry less prone to ignite...
     
  7. Mar 26, 2019 #47

    choppergirl

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    [​IMG]
    Cool. Maybe I will build a test bed frame around an engine out of aluminum tubing. Time to learn how to weld aluminum.

    I wonder if an 8hp vertical shaft engine would be enough to get it off the ground, and then get it beyond ground effect; the price on this one is right - free or rather my labor to wrench remove... maybe soup it up with some mods. Eight Horses at a walk should be able to pull this engine's weight up into the air, or?

    [​IMG]

    I'm thinking I supply power to the rotors via a hollow drive shaft through the arms... that is tubing inside of tubing. That way, perhaps the drive shaft provides some additional structural strength to the arms, and can't be interfered with.

    What I need is to find a very big RC airplane variable pitch prop and engineer to design a servo controlled prop pitch mechanism... (might be sold with the propeller already, boom! If such things exist on the large RC airplane scale level).

    Test Bed 1.0 wouldn't have to lift a person or payload, just itself... the weight of the engine and vehicle, so I can tweak the low level balancing and flight programs for a whole different system of control, mount some FPV cameras, and get started writing a high level computer program behind it.
     
    Last edited: Mar 26, 2019
  8. Mar 26, 2019 #48

    Toobuilder

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    From your link:

    "Objective: The objective of the Working Groups is to establish a formal means of continually refining current versions of the Transformative Vertical Flight Roadmap to create an increasingly compelling argument for pursuing this capability."

    Translation: "if we create a formal process, we might get enough people to discover the problem that our cool air machine fixes."

    Sounds like the classic "solution in search of a problem".

    Setting aside the "...100 things more.."
    This thread discusses the "commute"... What is the current problem and what is the desired state?
     
  9. Mar 26, 2019 #49

    choppergirl

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  10. Mar 26, 2019 #50

    henryk

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    -the greatest problem with propeller thrusters
    is bad energy efficiancy=for 500 kG thrust we need moore 100 kW power=big noise,many weighty batterys...

    -the only real ,today solution we see in dr Sorokodum works (inventions,discovery) is drag ANIHILATION weavy system and OSCILLATING
    thrusters with one order moore thrust force,simple and silent.

    see= vortexosc.com

    (imagine 100 heli or multicopters flying upon yours head !)
     
  11. Mar 26, 2019 #51

    pictsidhe

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    As size increases, changing rotor pitch instead of speed becomes the only realistic way of getting sufficient dynamic response. The power required to rapidly vary the speed of a large rotor just gets insane. I suspect that this is why many of the "coming soon" pavs are only demoed in dead still air and/or look wobbly...
     
  12. Mar 27, 2019 #52

    Dusan

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    Well "the problem" now, is millions of people commuting every day to work, to buy groceries and generally driving places. With population increase, this number is growing every day. The current roads barely can support the traffic now, and it is estimated soon we'll exhaust the space even to build new roads. The second problem is traffic jams, a commute that usually takes 30 minutes easily transforms into a nightmare taking a couple of hours. Sure, automatic driver-less cars will alleviate this problem somewhat, create new problems (e.g. time sharing, you cannot drive your car whenever you want), but we'll still need to build and maintain new roads. This is a big infrastructure cost, not mentioning the extra space usually needs to be taken from agriculture(we don't have enough of that anyway, globally) or from expensive real estate, that increases the expense of roads.

    If a VTOL aircraft can be developed to be used as we use current cars (fly to work, buy groceries, vacation etc), or to be used as air taxis (some organisations are very interested in this) then the users don't only save time (usually tenfold), but also can expand drastically the commuting distance, and this can change the current urban landscape (e.g. create real estate markets that are inaccessible now). A lot of US cities landscape are infrastructure restrictive, the landscape features, as lakes, mountains, rivers and overall configuration makes very hard to build new roads, subways, and streetcars, and will benefit enormously for aerial methods of transportation that does not need too much infrastructure.

    This gets me to "100 things more": What is safe enough? Current aviation safety statistics is 30 fatalities per billion operating hours (4 times better than cars), can this new thing match or surpass that? What will need to change in regulations to make possible a VTOL personal aircraft to fly from your driveway and land at your local supermarket? Will you and the supermarket need to install vertipads? How weather will affect this? What about pilot license? Will automation be enough to require a lighter licence that will be available and affordable to everyone? What about autonomous flight for air taxis that companies are so interested in? What about the automated ATC and how to integrate it into the current ATC, What about automated package delivery? Safer VTOL aircraft are very interesting also for police, ambulance, firefighting, military and other public services. What are each of these public services requirements? And the list goes on and on...

    This was tried before, a lot of US cities had public helicopter intra-city services in 70's that was discontinued because of safety and other perceived public disadvantages (as noise). In Brazil it seems to be thriving. We're learning from past mistakes and trying to make this better.
     
    Last edited: Mar 27, 2019
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  13. Mar 27, 2019 #53

    Kingfisher

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    Hi Dusan,
    sorry I'm a bit blunt sometimes. The problem of having excess power and therefore excess weight for cruise flight indeed exists for a VTOL aircraft. If ideally one could use the whole wing for propulsion as well as lift generation, like a bird, that is probably the most efficient. It looks like that is what the Tazenflugel and Samara were trying to do. Wasn't the Samara developed further into the Joby Lotus? Whatever happened to that design? I thought that was very elegant. However I was trying to look at a solution that is based on more conventional technology. I don't think the tandem wing layout is new and futuristic, and I didn't know about Vahana when I thought it out. It's basically like a Quickie or Dragonfly. I was thinking of combining two concepts that are proven to work, which is a quadcopter and a fixed wing. It's less futuristic than the various tail sitter designs in your interesting links. The tail is the most fragile structure of and airplane, and landing on it is just not very practical, especially in wind.
    For control I think it is more beneficial to place the rotors in a symmetric pattern around the CG as opposed to having a small tail rotor and main lifting rotors near the longitudinal CG position. This way, all rotors are positively loaded, and one is able to hover easily regardless of the wind direction. Of course this is assuming fixed pitch propellers. with variable pitch this would be less of a problem. Assuming that the rotors are mounted to the wings, this then led me to the tandem wing design. I also wanted the wing to have minimum effect on the controls during hovering, hence the free-wing idea.

    I do now think that if you have a tilting wing like the Vahana, and the distributed propulsion concept that basically immerses all of the wing in the slip stream, the wing is anything but dead weight and will start to contribute to the lift as soon as any forward speed is achieved. One does not "fight gravity all the time with only direct thrust", that's why the wings are there. Based on the disc loading diagram on the Vahana page, they are also close to a heavy helicopter, that does not look so bad. Regarding single rotor efficiency, I have been wondering about the trade-off. It appears that on a helicopter, the blades are not twisted like a propeller, so the pitch is not constant over the span. That should mean that the portion of the blade closer to the hub produces less thrust than it theoretically could. The V22 seems to be an exception there, since it has "proper propellers". I assume all this has to do with the need for autorotation capabilities. All the multi rotors have "proper propellers" in that sense.
    Regarding the motor sizing, one has to obviously make some assumptions about the propeller size and the weight and then figure out how much power is needed to overcome the weight for VTOL. I figured I needed at least 500 W per motor to lift 3-5kg with 4 motors. The size of the propeller will depend on the power it needs to absorb. If I use a 5 cell battery, I calculated I'll have to use 12 inch props at a higher rpm, with a 4 cell pack I could use 14 inch props at lower rpm and higher motor current, hence higher capacity batteries, but less of them. Not sure what is best yet.
    Agree that a well functioning design is needed to convince everyone. I think Vahana and Opener Blackfly are on the way there.
     
    Last edited: Mar 27, 2019
  14. Mar 27, 2019 #54

    Kingfisher

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    See Dusan's reply regarding the commute problem, I have absolutely nothing to add to that.

    Yes I agree, I wish I had the guts to leave my day job and devote my full attention to this matter. It puzzles me that most people don't yet see the potential of merging the information technology with aerial transportation, finally. At least I have had some success on a small scale, which is better than many people. Anyway, the point of the thread was to point out that the type of vehicle I proposed should be technically feasible and I find validation and great satisfaction in the fact that now several independent enterprises have proven that it is. If you want specs, check them out, they have reached that point. Watch their videos, if that doesn't convince you, I don't know what will. It would be the same as saying the earth is flat despite all the evidence otherwise.
     
  15. Mar 27, 2019 #55

    Kingfisher

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    Brilliant, I haven't seen this video before. Regarding your idea, you will want to scale up the stingray:

    There is a version that is powered by a combustion engine. The rotors are belt driven and have variable pitch. Manoeuvrebility is insane.
     
  16. Mar 27, 2019 #56

    Kingfisher

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    First it's: "Never seen one leave ground effect", next "only demoed in still air", after that probably "Well, I haven't seen one go supersonic yet". What about some acknowledgement of what these people have achieved?
    Regarding the variable pitch: Vahana has it, I think Opener does not. The "flying sled" in choppergirl's video looks pretty steady and responsive to me with fixed pitch. Agree though, variable pitch is probably needed to cater for hover as well as cruising, depending on the speed range one wants to cover.
     
  17. Mar 27, 2019 #57

    Toobuilder

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    "traffic sucks" is not even close to defining the problem. And describing some form of Jetsons utopia does not help design the first product.

    Start with one commute. Define the problem in discrete, measurable terms. Then define the performance requirements of the vehicle that is "the solution" to this one commute. Finally, project the discrete, measurable reasons WHY this is an improvement. If you actually get through that very basic process then you can start thinking about discussing "disc loading" and other minutiae.

    I suspect though, that it's just more fun to jump straight to flying cars as the obvious and forgone conclusion so you can all make cool sketches and daydream.
     
    Last edited: Mar 27, 2019
  18. Mar 27, 2019 #58

    henryk

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  19. Mar 28, 2019 #59

    Kingfisher

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    Yes, way more fun!
    But agreed, the mission requirements should be defined, as in here:
    https://www.uber.com/elevate.pdf
     

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