Propeller Shroud Project

Shroud-Proto-290511.jpgSince several months, my interest in shrouded propeller is increasing, and I started to prototype a shroud.
What are the advantage of a shrouded propeller?
We can list 3 main points:
1 - Increased thrust, compared to the same unshrouded prop. (Possible gain 30% to 100%)
2 - Propeller protection. This adds security and allows to "touch" a wall, by example.
3 - Reduced noise. The propeller tip overpressure/underpressure vortex is encaged.

The prototype is for a 10'' prop, and several pitch will be tested.
The tests consists in comparing the generated thrust, for a given amps (and RPM), between shrouded prop and same unshrouded prop.

If there is an interest, I plan to design a CAD/CAM plastic mold, to produce such shroud in quantity.
The shroud will be in 2 or 4 parts, easy to mount, with a plate connexcting motor and shroud arms.

Here is the ready to assemble shroud.
Diameter is 32 cenitmeters, height is 11 centimeters, weighting 79 grams.

The next step is the shroud/frame/motor assembly.
Two motors will be used in different setup, with a choice a various propellers.
2 blades propellers are not well suited to maximize the effect, so some custom rotor (multi blades) will be conceived.

When the assembly is okay, bench testing will compare thrust (and other aspects) with and without shroud, using different propellers, and custom rotors later.



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  • How did the results of the shroud test turnout in terms of efficiency and increased thrust ?

  • My DJI S900 Hexacopter has 14 7/8 inch  diameter props. I would love to have 6 of them shrouding my flying lawnmower. Increased efficiency would allow greater flight times also.

    I believe there is a real market out there for these high end UAV users...greater payload, longer flight time, SAFETY.

  • Hey Coptaire, how's your shrouded prop project going?

  • Hello Cory,

    Indeed, assessing the real performance of the rig is why am designing this, to get a real life configuration, and see the advantage(s) in this range of dimensioning (Reynolds number).

    Project is going well, taking advantage of 3D printing to reach a detailed design.

    It is a long-term work, patience is required, but next milestone will be exposed here.

    thanks for your encouraging post!

  • Coptaire.  You go man!  I'm an airflow guy myself, and a believer.  So many variables. Forgive me if I'm not technically accurate on all of this as I'm going from memory and my own theories. I'm guessing +/-  6% on my statements here. First, the main reason of ducting is to keep the airflow constrained. Spray some water on a spinning prop and see where it goes.  Much of the flow is outside of straight line.  Of course water is not air, but it is easier to see regardless of it's miss matched properties.  Add in a 360 degree airfoil and now you have straighter line directional flow and most importantly, more lift. Better directional flow assuming you have proper stators and some extra vanes/strakes on the inside perimeter beyond just the outer foil.  About 60 to 140 percent more lift depending on your airfoil and inner cone matching.  Weigh this against approx 10 to 25 percent gain in added weight (Not to the craft but to each Rotor Main 'Engine/Motor, Battery/Fuel, Prop combination), and wallah!  More lift; and in a Vtol craft, more control.  There should be a fight between the extra weight and inertia and the ability of the craft to rapidly balance itself, but the extra force of inertia required for balance is actually of mute point because the added weight actually helps compliment balance as the added weight at each rotor vertice is what helps keep the craft from becoming rapidly unbalanced in the first place. Add in the increased thrust and you have a win, win, win situation.  I agree with some of the things MarcS mentions. "Depending on the position you put it, you can get control problems." Don't be disheartened by the crash at 3 min. because the ducted prop/fan was placed above the vertical center of gravity of pull/or push, it was fighting the planes natural lift. The forward thrust was basically mounted on top of the planes wing not as a pusher or puller but as a real 'downer' lol. Creating down thrust instead of forward thrust, basically pushing the plane out of control.  Keep going!  :)  Cory 

  • I needed 3D printing capability to develop this project.

    So, I conceived and print another kind of propeller shroud, and I 3D printed it. It is a kit made in ABS, consisting of 9 parts, to be glued around the hub, and screwed for the outer parts.

    This shroud can be used as a blade protection, and could interact slightly with the airflow. Curious about the aerodynamics effect of it, the propeller blade tip can be very close to the inner wall.

    This was my first 3D printed project, and now I ordered a 3d printer to go on developing my initial shroud project.

    With this capability, all parts (stator/duct, rotor, hub/vanes) can be conceived and printed in an easier way than manual prototyping and hand molding.


  • In order to perform with the shroud, using several propellers, several kind of rotors (size of hub, multiblade, ...) and single prop or contrarotative, am currently building a polyvalent framing dedicated to test.
    Now, am pretty close to clip some propellers to assess the mount and the centering method.

    The good news of today is that the roundness of my prototype shroud is permitting an average of 1mm gap between propeller tip and shroud wall.
  • See how the shroud shape is qimilar to the HILLER VZ-1. Have some performance expectations!



  • Here is the rough alu frame in order to assemble the shroud and the motor.
    My first goal is: Not destroying my shroud caused by a lethal blade!
    So, the aerodynamic of the arm and the holding plate is not optimized (at all!).
    My intend is to confirm that the system can be stressed (high RPM) without problem, for a given prop tip to wall gap.
    The motor shown here is a 2217 Turnigy, and another motor plate will hold a really bigger AXI brushless (2820/14).
    I have in mind the specific tri/quad frame in which I will incorporate 3 or 4 shroud motors like this. The build could be a molded version or a reinforced foam version of it.


    Shroud-Proto-020611.jpgPS: At this step, I don't want yet to integrate the holding arms into the shroud wall. Later the aerodynamic arms will be integrated upper in the structure. That's why there are below, at the shroud base.

  • Indeed.

    My intent is to provide real life test and values, first, using different propeller/motors scenarii.

    Then, if there is an interest, I plan to either produce units by molding (I have a specialist close to me), or by making a molded plastic design. In this case the product is in several parts (3 x 120° or 4 x 90°) with anchorage.

    When you talk about "standard props", it could true pitch tri blade, not thin electric.

    The kit would have everything needed, specifying standard blade, or providing blades.



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