Propeller Shroud Project

Since 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.

Thanks for these inputs!

Turboplan: Interesting approach, really, but it is aerodynamically different from "classical shroud design".

About lip geometry, I really shape my shroud with a good wall profile, and the lip curve should be quite accurate, will show you the curved wall profile.For static aerial AP, I expect an enhancement, not targeting VTOL app for now.

Russell, after my composite prototype, my idea is to custom wirecut foam in a circular way. I used nitrocellulosic in this design, making it non porous and rigid. The wall is a sandwich with balsa, nitrocellulosic and adhesive alu. The outcome at 79g is not bad at all.

Now, am designing an alu framing, and a good method to center the rotor, to try a good (small) gap. This is a POC where the look is not really important, my concern is on rigidity and a good testbed to try different prop/rotor setup. My first attemp is based on cutting 16x10 prop reduced to 10' blade to retain a good pitch and width.

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Comments

Ivan June 1, 2011 at 2:09pm

Perfect idea to design the mold and mass-produce the shroud. Many people will be interested to experiment with this, but they have no mean to easily make the shrouds themselves, and would like to buy one especially for standard 10" props.
C.P. Ryan May 31, 2011 at 12:01pm

VERY INTERESTING. I USED THIS TECHNIQUE WITH MY POWERED PARA-FOIL. ALL PARA-PLANES HAVE A SHROUD AROUND THE PROPELLER TO KEEP THE SUSPENSION LINES FROM BEING WRAPPED AROUND THE PROPELLER. I NEVER GAVE MUCH CONSIDERATION TO THE BENEFITS OF THE REDUCED NOISE AND INCREASED THRUST BENEFITS SINCE THIS WAS SOP. I AM INTERESTED IN THE EFFECTS/BENEFITS FOR A CONVENTIONAL PUSHER CONFIGURATION. KEEP GOING.

BEST REGARDS

C.P. RYAN
Coptaire May 31, 2011 at 2:48am

Thanks for these inputs!

Turboplan: Interesting approach, really, but it is aerodynamically different from "classical shroud design".

About lip geometry, I really shape my shroud with a good wall profile, and the lip curve should be quite accurate, will show you the curved wall profile.For static aerial AP, I expect an enhancement, not targeting VTOL app for now.

Russell, after my composite prototype, my idea is to custom wirecut foam in a circular way. I used nitrocellulosic in this design, making it non porous and rigid. The wall is a sandwich with balsa, nitrocellulosic and adhesive alu. The outcome at 79g is not bad at all.

Now, am designing an alu framing, and a good method to center the rotor, to try a good (small) gap. This is a POC where the look is not really important, my concern is on rigidity and a good testbed to try different prop/rotor setup. My first attemp is based on cutting 16x10 prop reduced to 10' blade to retain a good pitch and width.
Russell B. Sutton May 31, 2011 at 1:50am

I build my quads out of 1-1/2 thick blue foam board. Its cheap, strong, lightweight, and sands easy in to shape. I use my rotozip as a router to cut pockets and channels. I use a homemade hot wire to cut airfoiled wings out of it as well. If needed you can cover the foam with brown paper and water base acrylic. maybe some paint.
DuctAR May 31, 2011 at 1:23am

Thrust gain will depend on duct lip geometry, I think that those papers go into the geometry a little bit. It also depends whether you are wanting good static thrust or high speed thrust (for VTOL/hover applications, static is more desirable). If you design the duct well you should get a 30-50% static thrust gain for a similar sized non ducted prop (higher level, specific design should yield better results).

Let me know how it goes, I don't get much time outside of work for hobbies but would be interested in knowing how your project goes.
MarcS May 31, 2011 at 1:22am

Hi, now a fiend told me again: It´s called "Turboplan"

The pages are in german but I think you can see how it´s suuposed to work. And the actually fly, but when I remeber right they are too stable because of high rotating mases.

http://www.cr-modelltechnik.de/turbopla.htm

http://www.ostertag.name/tweety/Modellbau/index.shtml

Turboplan
Coptaire May 31, 2011 at 1:06am

Than you for raising these issues and the 2 very interesting papers.

Weight, wind, VTOL issue are points I have in mind. But the first step of the project is to build a valid shroud/rotor assembly and evaluating the performance, thrust gain being one of the goal.

My application is rather a multirotor where I am looking for a very stable hovering, this is the easiest case, compared to applications like VTOL.

The current focus is on the rotor, customizing props, perhaps making multiblades rotor, and having a good overall rigidity, to reduce the gap (prop tip / wall).

Will post project pictures of this next step!
DuctAR May 31, 2011 at 12:00am

Here are a couple: Should give some background.

http://scholar.lib.vt.edu/theses/available/etd-05262005-170916/unre...

http://researchbank.rmit.edu.au/eserv/rmit:6872/Zhao.pdf
DuctAR May 30, 2011 at 11:59pm

At the wind speeds expected from a VTOL application the form drag is likely to be an order of magnitude (I just like that saying, not actually being technically accurate - you can substitute a lot if you want) less than the expected ram drag.

There are a couple of great papers out there on ducted fans, a couple which were done by a masters student on the T-Hawk MAV (made by Honeywell). I will have a quick search but my beer and quad are beckoning to me so may get distracted....
Russell B. Sutton May 30, 2011 at 11:13pm

Another question that comes to mind is " what about wind resistants and how much more power it will consume trying to fight wind and the drag caused by the increased surface area.

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