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New drone design idea, pull air for lift

  1. Jul 11, 2014 #1
    I have read a discussion about a centrifugal fan on a wheel system

    The fan pulled air to itself and push the air outward from center. Most flying machines that I aware of push air down, as Newton describes. Since air is move downward, but toward machine could a new drone work this way? Would it create small lift or not work .... To much energy needed maybe

    I attach the picture from other thread that show movement, but for this it would be in air. Thanks to all, you are big help!
     

    Attached Files:

  2. jcsd
  3. Jul 11, 2014 #2
    Judging by the diagram, the red arrows indicate airflow. This machine will not fly ! First it would need wings,2nd it appears to have airflow going up and down, canceling any lift. Not an efficient design for ground movement either as while the air is sucked in, even though the air is directed to exit up and down, some air will still be hitting in the center pushing against its forward momentum.
     
  4. Jul 11, 2014 #3
    I use the picture to show only concept. Imagine it where the opening where the air comes in is pointed up, where the air moves radial outward and horizontal to ground. I was wonder if it could VTOL. I see that some air may indeed push against the machine.

    The air moved radially would leave a vacum and air would move to the center. This is why I think it work.
     
  5. Jul 11, 2014 #4
    why try to redesign ? Just use a jet engine design, it pulls in air and sends it straight through and out the back :)
    If you do try to stick to your design, you might want to consider 2 fans that counter rotate to prevent rotational torque.
     
  6. Jul 13, 2014 #5
    I'm just an aircraft mechanic and pilot, but I've made a few observations over the years. For decades I was told that the low pressure on the upper surface of an airfoil creates the lift. This sole explanation never sat well with me, and I pondered it for many years. I remember as a kid making gobs of balsa wood gliders with a friend of mine. He showed me a glider that a friend of his father made (everyone I knew were pilots, aircraft owners, builders, etc.) that had a unique airfoil shape: forward of the main spar was normal, but aft of the spar, the upper trailing edge made a gentle "S" shape where it met with the lower trailing edge, and then both surfaces extended aft, parallel and attached to each other approximately another 20% chord aft. When I asked my friend why he gave it to him, he had said it didn't fly very well at all.
    Fast forward to more recent years- A&P school, pilot training, and the airfoil shape stuck in the back of my head, and the Bernoulli principal thing just wasn't adding up. I kept thinking everyone talks of the airflow over a wing, but I reasoned that there is no airflow around the wing. The air is just sitting there, randomly moving about, then this wing of a certain shape quickly zooms by, and then the air is once again just sitting there. The air didn't flow over the wing, the wing moved through the air. The difference is subtle. What happened to the air after the wing passed by is important.
    I finally found an article about a decade ago that addressed the very thing I was thinking: There's more to lift than low pressure. The article proceeded to explain that the low pressure on top of the wing only accounted for a percentage of the lift. The majority of the lift occurs when the mass of air over the upper surface of the wing is imparted a downward force by the tapering of the trailing edge as the wing passes through the relatively motionless air. This air has mass, and is accelerated downward: Ha! F=ma! I can live with that!
    That explains why a high aspect ratio wing generates more lift for equal wing area then one of low aspect ratio.
    The final selling point for me was when I considered a turbofan engine, specifically that of the Hawker Harrier jump jet. The bypass fan in the front of the engine generates most of the thrust for any turbofan engine (upwards of 80%). The fan blades themselves are nothing more than little high speed wings whirling around the shaft hub. The Harrier jet's forward lift nozzles on the fuselage pivot downward to direct this bypass air coming off the fan downwards and provide lift. (The rear nozzles include the engine exhaust.) If the lift off the fan blades was generated by the low pressure on top of the blades, wouldn't the jet then rotate its inlets up? but it doesn't.
    So all this made sense to me, and explained why my childhood friends' glider wouldn't fly. The airflow off the back of the wing was redirected at the trailing edge to travel parallel with the direction of movement. No air moved downward, and no lift carried the wing upward.
    So I think any vehicle attempting to generate lift by low pressure only will be almost impractical to make work.
     
  7. Jul 13, 2014 #6

    russ_watters

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    Staff: Mentor

    That's just a centrifugal fan. All you need to do is shroud the top so the air can't go up and leave the bottom open and you'll have lift:

    CentrifugalFan.png
     
  8. Jul 13, 2014 #7
    russ_watters
    Not really, some movement yes, but no stability, as I mentioned previously rotational torque is a problem.Then once you start adding stuff like a power source, stabilizers etc. your weight is too great.

    riscoe Nice write up. You are correct in the movement of the air, it is the movement of the wing through the air and not vice-versa which is why you need an engine to propel. A glider has no engine but will fly for a while(actually fall slowly). The wing does create a low pressure above the wing which does give lift as the air under the wing is thicker than above it otherwise you would just slice through the air evenly not being able to gain altitude.When trying to visualise these concepts, it is easier to do with thinking of a craft under water ,same principle applies (FLUID DYNAMICS).
     
  9. Jul 17, 2014 #8
    More movement

    If a Coanda skirt is attached at the air exit, as shown, the exiting air can be used efficiently to create movement.
     

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