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Lift Engine

  1. Jul 10, 2018 #1

    bob012345

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    I'd trying to design a vertical lift engine to lift about 30 pounds in the air about one foot off the ground with minimum power. The device has to hover. The engine should itself weight 5 pounds or less and have a footprint no larger than one square foot. By minimum power, I mean something like 1-3 KW. I'm not asking for specific ideas (I've got about a dozen) but just if folks think it's going to be possible or not and why. Thanks.
     
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  3. Jul 10, 2018 #2

    berkeman

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    What does that mean? You mean like a drone? 1 foot off the ground will not give you much ground effect assist, so if you make 1 foot with a drone, you can make a lot more too.

    If you mean like a drone or other aircraft, look up what it takes for a drone to lift 30 pounds. I'm sure they exist, and their engine size and power are probably about what you will need.

    If you can include a 1-foot long air skirt, then you can make it more like a tall hovercraft, and the power requirements will go down some. You will still have stability and control issues, but hopefully it won't take much extra power to maintain position and stability.
     
    Last edited: Jul 10, 2018
  4. Jul 10, 2018 #3

    berkeman

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    I did a quick google search for Drone Payload Versus Engine Size, and got good hits. Here is one with a drone listed that can lift 20kg:

    https://www.dronethusiast.com/heavy-lift-drones/
     
  5. Jul 10, 2018 #4

    bob012345

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    Thanks. I trying to avoid simply making a drone type quadcopter lifting device. They take a huge amount of power because they are using brute force lifting. I've investigated hovercraft technology but prefer a skirtless design. I'm hoping to minimize power by using various effects. I've seen jet engine designs but they are super complex and expensive.

    I'm looking at skirts though.
     
  6. Jul 10, 2018 #5

    berkeman

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    Looks like this 8-rotor drone (8 x 300W = 2.4kW) has about a 20 pound payload capability: https://freeflysystems.com/alta-8/specs

    Without a skirt, I'm not sure you will get much more efficiency than a multi-rotor drone. The 1 foot max height would seem to lend itself to the skirt feature to reduce the power needed...
     
  7. Jul 10, 2018 #6

    bob012345

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    Thanks. I'm thinking of a lift engine that has a small footprint of around one square foot.
    Thanks for the link! Yes, I think it's either going to be hovercraft technology based or another effect besides pure brute force lift with a battery powered prop. The small footprint and low power is so the engine concept can be chained to lift more weight. I'm also looking at other aerodynamic effects such as blown wings, Coanda and Magnus effects.
     
  8. Jul 10, 2018 #7

    cjl

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    Why do you prefer a skirtless design? A hovercraft-style vehicle with a skirt will take by far the least power (assuming you aren't able to physically hook to something and lift that way). Beyond that, a multi-rotor style is probably your best bet. For minimum power, you want the largest possible rotor surface area - small, high speed things like ducted fans (or jet engines) are horribly inefficient for producing static thrust.
     
  9. Jul 10, 2018 #8

    bob012345

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    Frankly, because it's cooler to be visibly floating even though with a skirt you really are floating. But I can also design the skirt to fit in with my concepts of 'cool' too. I'm also exploring new concepts for more efficient 'momentum curtains' formed with air.
     
  10. Jul 10, 2018 #9

    russ_watters

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    Please note that the smaller footprint you are looking for will make this device substantially less efficient than a drone with, for example, 8 one sq ft propellers.

    Also, you can't do it with a single rotor and be stable.

    I don't think the sum of your constraints is possible.
     
  11. Jul 10, 2018 #10

    bob012345

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    This is why I'm trying to get away from brute force propeller driven lift devices. Also, I plan on using multiple lift engines together if it works for stability and higher loads.
     
  12. Jul 10, 2018 #11

    russ_watters

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    What, then, do you mean by "lift engine"? If it isn't a motor driven propeller I don't know what you mean.
     
  13. Jul 10, 2018 #12

    CWatters

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    Hovercraft are only efficient when the gap around the skirt is small compared to say the area/footprint. A 1sqf hovercraft with a 4 sqf gap can't really be called a hovercraft.
     
  14. Jul 10, 2018 #13

    CWatters

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    Think about the effective "wing" loading.... If you have a 1sqf "wing" or swept area and a 35lb minimum weight you have a 35lb/sqf effective wing loading. I think only something like a gas turbine might get there.
     
  15. Jul 10, 2018 #14

    berkeman

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    I'm picturing a 1 foot tall skirt. Is that what you are picturing? I know it's a bit weird, but it will help to confine the downstream air...
     
  16. Jul 11, 2018 #15

    CWatters

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    I assumed the lower edge of the craft had to be 1ft off the ground. Perhaps to clear obstacles?

    If that's wrong how small can the gap be?
     
  17. Jul 11, 2018 #16

    bob012345

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    It could be a motor driven propeller but it could be something else also. For example, it could be some sort of compact small footprint hovercraft device or an aerodynamic device such as a 'blown wing' where the airflow is self generated as opposed to using forward motion. It could be magnetic lift if it weren't for having to have a special conductive surface to react against. It's just a means of providing a certain lift in a specified footprint and power usage. It may end up having to be either a hovercraft device or a propeller device if I can't get anything more clever to work.
     
  18. Jul 11, 2018 #17

    bob012345

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    Yes, it might have to be such a power source.
     
  19. Jul 11, 2018 #18

    bob012345

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    It wouldn't strictly be a hovercraft but rather a hovercraft-type lift engine applied to a different kind of device if that's the way I have to go. I do know it's not going to be just slapping a few common elements together and presto, it works! It's going to take a lot of engineering. It may end up being something combining several concepts together.
     
  20. Jul 11, 2018 #19

    cjl

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    Nah, you could definitely do that with an electric motor and propeller, but the power requirements will be very high. Ballparking the math here...

    Mass flow rate will be the product of air density, area, and velocity through the prop. Thrust force is the product of mass flow and velocity. Therefore, F = ρav2. Rearranging this and solving for the discharge velocity to achieve 35lbf through 1 square foot, you get 37 m/s (or about 83 mph). This is high, but definitely doable with a propeller. The power in this jet will be one half the product of the mass flow rate and the exhaust velocity (this is just the rate of kinetic energy addition to the jet), which for this example gives 2.88 kW. Propellers are not perfectly efficient though (80% or so is probably achievable with one optimized for this case), so you'd actually need about 3.5-4kW of shaft power to achieve this level of thrust. It's not impossible, but it will be loud, and it will have an 83mph jet of air coming out the bottom at all times (which may or may not be a problem, depending on the intended application).

    To show how much this is impacted by the disc area, a 1 square meter rotor area gives 11.3m/s (25mph) discharge, with a jet power of 878 watts and a required motor power of a bit over a kilowatt.
     
  21. Jul 11, 2018 #20

    bob012345

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    Thanks. Is this a hovercraft with a skirt or a direct lift propeller you are calculating?
     
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