Coandă Effect Makes A Better Hovercraft Than A Quadcopter

Leaving no stone unturned in his quest for alternative and improbable ways to generate lift, [Tom Stanton] has come up with some interesting aircraft over the years. But this time he isn’t exactly flying, with this unusual Coandă effect hovercraft.

If you’re not familiar with the Coandă effect, neither were we until [Tom] tried to harness it for a quadcopter. The idea is that air moving at high speed across a curved surface will tend to follow it, meaning that lift can be generated. [Tom]’s original Coandă-copter was a bit of a bust – yes, there was lift, but it wasn’t much and wasn’t easy to control. He did notice that there was a strong ground effect, though, and that led him to design the hovercraft. Traditional hovercraft use fans to pressurize a plenum under the craft, lifting it on a low-friction cushion of air. The Coandă hovercraft uses the airflow over the curved hull to generate lift, which it does surprisingly well. The hovercraft proved to be pretty peppy once [Tom] got the hang of controlling it, although it seemed prone to lifting off as it maneuvered over bumps in his backyard. We wonder if a control algorithm could be devised to reduce the throttle if an accelerometer detects lift-off; that might make keeping the craft on the ground a bit easier.

As always, we appreciate [Tom]’s builds as well as his high-quality presentation. But if oddball quadcopters or hovercraft aren’t quite your thing, you can always put the Coandă effect to use levitating screwdrivers and the like.

22 thoughts on “Coandă Effect Makes A Better Hovercraft Than A Quadcopter

  1. After watching this, I wondered if it wouldn’t have been more effective with the props not having interaction with the body, like a, you know, quad-copter. This is just not how hovercraft are done, they do use the coanda effect but it is all within the skirts. Few are simply a pressurized cavity.

    1. The fact that it’s less efficient at actually producing any lift than either a helicopter or a hovercraft.

      You could make holes in the top of the craft and put a duct around the fans, and observe that the whole thing would lift much easier.

    1. I’d wager it’s a combination of COM, COT, COL, and the fact that it’s too light and too skinny to make those sharp turns.

      He might have better luck with 3 motors for lift in a triangle, since that would define a plane, and probably help a bit with the fact it looks quite rear heavy.

        1. He would also do well to counter-rotate the propulsion propellers at the stern… it’s slightly auto-rotating at high throttle because of blade inertia and the slight thrust off the tips of the blades creating a low-pressure area to port. Maybe if he ducted the propulsion fans a bit that would help.

          and I was wondering if it wouldn’t be possible to mount the fans under the deck, with “nozzles” lining the deck for the air to be pushed out from underneath to the sides at 90º to the fuselage… tho that would create a suction from underneath, so you’d have to do it with a 2-compartment body.

  2. Canards and a rudder and tail plane controlled by an IMU would certainly help keep it on plane, at the cost of complexity. Lateral inertial control is another matter altogether. A larger horizontal rotating mass perhaps?
    Nevertheless, he’s proved the concept, which is the whole point.

  3. I taught people a lot of lifting physics with McD’s and my Dodge van. It had one of those tables in back the mount broke so I had a hole the size of a McDonald’s ball pit ball. I put the ball there to keep heat and exhaust gas out with AC on, when you opened a window it would float right above that hole no matter what you did driving. Also would take their straws and if you cut them about 1/3 and flicked them they would fly pretty far. I had other stuff for people to try to make fly with the pressure, but nothing worked as good as the ball.

  4. Vertical lift props rotating in the same direction may be causing the yaw which seems to be to starboard. Suggest having lift props rotate in opposite directions to correct.

  5. So fun! Seeing the video, it amuses me to think what would happen if you tried opening holes at the rear, like exhausts, for the air that gets in the bottom to exit from the back and maybe create a little thrust?

  6. You did ok.. you should have placed the batterys in a balenced place instead of the back.. this is the reason it kept lifting to hard in the front… or even ofset them a tad forward to balence out the weight of the rear drive motors then it just may fly like you would think it should.. if stays unstable with the balenced batterys then move them to the bottom inside the curve… but you did get pretty close… only needed alittle more testing..

    1. Inside the skirts to counterbalance against the lift… having it at the right distance below the vertical thrusters should keep it more stable just by adding ballast. Putting them on each side should keep the whole mass more stable by expanding the existing load across a larger surface plane.

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