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Old May 26, 2011, 12:34 PM
spokeshave is offline
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Ducted fans for a quad?


Has anyone explored using ducted fans for a quad (or other multi)? It would seem to me that the greater efficiency would be ideal even with the added weight. Not only that - it would save on broken props...
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Old May 26, 2011, 12:51 PM
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I don't think it's greater efficiency, infact it won't be even close
Forget about yaw unless you tilt motors and when you do that, you lose more power
And you would end up with a very loud setup

Don't get me wrong, it would be a very cool setup but that's it

Moe
Old May 26, 2011, 01:28 PM
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I was under the impression that ducted fans were more efficient than propellers alone. As for yaw, I believe motion in yaw is accomplished by varying the speeds of the pairs of like-directioned propellers to change the overal angular momentum. I din't see why this couldn't be done with ducted fans as well.
Old May 26, 2011, 01:48 PM
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My understanding of this is that EDF units (as fitted to scale jet models, etc.) operate at very high rpm and that their purpose is to produce high thrust in a compact package. As such, their small diameter and additional weight would make them a bit redundant for a quad. (Remember that thrust is always proportional to swept area, i.e. diameter).

"Shrouded" fans, on the other hand, might be more relevant to quads: larger diameter, using a shroud (generally a much shorter tube than a "duct"). The efficiency gain (i.e. the additional thrust/watt) is likely to be very small, but if you needed to enclose the propellers anyway (e.g. for flying indoors) then you might as well attempt to recoup some of the thrust lost to the additional weight.

But note: I've heard of some "casual" shroud setups causing problems - something to do with interference with tangential airflow. So a shroud needs to be very carefully designed.
Old May 26, 2011, 02:08 PM
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Tri-Quad-Hexa-Octo-copters!!
Hi,
It has been done. Here is one link from 2007 on a quad EDF build from the Mega Index: https://www.rcgroups.com/forums/show...light=edf+vtol
Cheers,
Jim
Vote for my Bro Joe here: Quadrocopter and Tricopter Mega Link Index
Old May 26, 2011, 02:35 PM
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If you are asking about efficiency, amp for amp props are more efficient
EDFs have no torque, so no yaw control
They are normally used for the scale look and the sound they make

But if you are looking for the wow factor, EDFs are super cool you can even build a UFO style quad
Old May 26, 2011, 03:12 PM
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I'd like to see a micro quad out of 30mm fans. Something in a 8-10in frame. Then wrap it with some thin depron and make a small UFO
Old May 30, 2011, 11:17 AM
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Would be cool to see a thrust vectoring system like on a mig 28. Don't think they make a flight control system for that. Go for it!
Old May 30, 2011, 12:18 PM
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Quote:
Originally Posted by spokeshave View Post
Has anyone explored using ducted fans for a quad (or other multi)? It would seem to me that the greater efficiency would be ideal even with the added weight. Not only that - it would save on broken props...
I am currently evaluating shrouded prop, building my own shroud like this.
I plan to build a quad with 4 shrouds, after testing.

There is a thread for this project:

Propeller Shroud Project

Old Jun 04, 2011, 11:56 AM
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Very nice man.... What's the wieght of this ring?
Old Jun 05, 2011, 05:06 AM
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79 grams. It is just the prototype to conduct thrust test. Later, we could have molded version.
You could read more details from:
https://www.rcgroups.com/forums/show....php?t=1447212
Old Aug 25, 2016, 02:21 AM
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EDF is low efficiency


As I know that ducted fans is more efficient, I've made some research about EDF and surprised that they're about 2 times lower efficient than usual multicopter motor+prop:
The purpose of EDF is to imitate jet engines, so they are small > small prop:
1) smaller prop > much loswer eff.
2) to rotate small prop need more kv, which lowers eff.
You can compare by yourself:
1. Some EDF: 7.5kg weight/1kg thrust = 7.5 ratio.
2. Some coax (flat is 20-30% more efficent than a coax, I show this because there's a thrust stated):
1320g thrust/79g motors+props = 16.7 ratio.
You can compare this ratios, remember that coax is low efficient than flat.
So building EDF copter is not an option for higher efficiency, what we need is make a shroud for usual motor+prop.
Btw if you look for EDF because they're small and gives good thrust for their size – compare EDF copter with same sized Y6 or X8 (which can be even Y12 or X16 with 2 coax like this one under another).
Old Aug 25, 2016, 06:58 AM
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They're more efficient, but only if they remain in one orientation. If you want to tilt them (like moving your quad forward) then it messes things up.

How ducting a propeller increases efficiency and thrust (18 min 18 sec)


Edit: Sorry, I see the poster before me posted the same video.
Last edited by OrangeJuice; Aug 25, 2016 at 07:04 AM.
Old Aug 25, 2016, 08:11 AM
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It is true that ducting a propeller can increase efficiency. But for that to be relevant on a multicopter, you would have to duct the same size propeller as you would normally use. And at those sizes, the added weight of the ducts will most likely eat up any gain. The ducting also needs air moving at high speed to come into effect and increase propeller efficiency, making multi hover a worst case scenario.

Normally EDF is all about spinning tiny propellers at insane RPM's to get continued trust at higher speeds. As such EDF noise levels are trough the roof, they are terrible at static trust (hover), response times are very slow and they have the worst efficient of any propeller system. The only place they make any sense to use is for jet models, where speed is king (and you don't want a visible propeller for realism).
Last edited by jab; Aug 25, 2016 at 08:17 AM.
Old Sep 01, 2016, 02:08 AM
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Quote:
Originally Posted by OrangeJuice View Post
If you want to tilt them (like moving your quad forward) then it messes things up.
Not if they're not high, copter with low ducts is anyway more efficient.
Anyway testing needed to see the eff. difference of ducts.
Quote:
Originally Posted by jab View Post
duct the same size propeller added weight of the ducts will most likely eat up any gain.
But if you'd check a link I gave..
Quote:
Originally Posted by jab View Post
The ducting also needs air moving at high speed to come into effect and increase propeller efficiency
?
At any speeds of prop's airflow ducting willl raise eff. There's a video above about how it works.
Quote:
Originally Posted by jab View Post
Normally EDF is all about spinning tiny propellers at insane RPM's
I wrote above why it's lower efficient, but you can duct any prop.


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