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Old Jul 03, 2012, 10:02 AM
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I think as the diameter increase and the RPM's decrease, the noise levels goes down, at least the ones that I have witness.
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Old Jul 03, 2012, 10:12 AM
James not bond
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the noise comes from vib... thus good damping will help reducing the sound
also.. good balancing and fixture will also help

the proj up there is a small duct fan... what we are going after is more like a prop prot/duct on AR drone (the dont have much noise.. also maintain a good efficiency)
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Old Jul 03, 2012, 10:14 AM
Tri-Quad-Hexa-Octo-copters!!
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R,
A shroud is good protection too, but like we found with the old XUFO it becomes a wind sail causing oscillations and stability issues in any wind.

As far as safety and blade shrouding, this Gent had a clever idea combining a sphere flyer with a multicopter: http://www.rcgroups.com/forums/showthread.php?t=1683769

Remote Control Sphere American Made (10 min 35 sec)


Cheers,
Jim
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Old Jul 03, 2012, 10:27 AM
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I have seen lots of videos of the Japanese Sphere, very interesting design/concept using just one prop/motor with ducting. You should know me by now, once I set my sights on something, I will make it work.

I have liked the Duct idea for a long time and will see it to the end.
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Old Jul 03, 2012, 10:30 AM
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Quote:
Originally Posted by jy0933 View Post

@rim
tip loss: at the tip... the air acts a circle alone the tip.. that amount of air instantly comes back to the top of the blade.. unable to contribute to thrust force... when a duct is applied (close margin... again) the air is forced to go downward to contribute the thrust


Thank you for this information, I had a gut feeling the spacing makes a huge impact but never realize just how much. See I have lots to learn.
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Old Jul 03, 2012, 10:49 AM
James not bond
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it is suggested to have as smaller margin as possible... for what I have seen on some ducts... about .5~1cm clearance might work best...


scale it down then you might have a good estimation of the clearance
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Old Jul 03, 2012, 11:04 AM
Tri-Quad-Hexa-Octo-copters!!
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R,
No doubt you will succeed
Note that Hallstudio had a different sphere concept with an enclosed tricopter.
Cheers,
Jim
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Quote:
Originally Posted by rimshotcopter View Post
I have seen lots of videos of the Japanese Sphere, very interesting design/concept using just one prop/motor with ducting. You should know me by now, once I set my sights on something, I will make it work.

I have liked the Duct idea for a long time and will see it to the end.
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Old Jul 03, 2012, 11:40 AM
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Quote:
Originally Posted by jy0933 View Post
it is suggested to have as smaller margin as possible... for what I have seen on some ducts... about .5~1cm clearance might work best...


scale it down then you might have a good estimation of the clearance
So that I can get a better understanding, we are attempting to reduce the Tip Vortex by decreasing the clearance between the wall of the duct and the blade tip?
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Old Jul 03, 2012, 11:53 AM
James not bond
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correct.. look at this draft.

the red line is the duct.. blue line is the modded air flow.. you can see the circular flow will be forced to go down contribute as thrust force

and yes.. the closer the tip is to the duct wall.. the better improvement

noted.. the duct should probably be longer downward cuz the you want the flow goes down a bit further
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Old Jul 03, 2012, 11:58 AM
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Very Interesting. Believe it or not, I have a nearly completed test stand that we can put this to some trials. I just happened to have some 8" plastic buckets and some 8" props setting collecting dust.

The hard part is creating a funnel entree for the duct.
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Old Jul 03, 2012, 12:01 PM
James not bond
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cool

i'm waiting for my new x250 kit.. and will start work on that as soon as i get it...

btw .. you need to make sure they are close identical.. cuz buckets are usually having a D decrease over length... not identical could result in unbalance of thrust
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Old Jul 03, 2012, 02:17 PM
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Hi guys - Thought I'd jump in (hopefully not over my head )

A practical distinction should be made between 'ducted' and 'shrouded' fans. Ducted fans, as in duct, have a significant length of it downstream and in some cases upstream of the blades. Its purpose is to create a large pressure difference across the blades.
A shrouded fan does not. Its main purpose is to aid in creating a large velocity difference across the blades by reducing blade tip losses. The upstream end is configured as a nozzle to efficiently draw air in from the sides, as well as from the front. The downstream end is as short as possible to reduce friction losses.

Of course there's a continuum between these extremes, but high pressure applications use high blade count, low pitch, high RPM blades where high volume uses low blade count, high pitch, low(er) RPM blades.

For multis, the discussion should be, "are free blades more efficient than shrouded blades" and "is the net weight penalty, if any, worth the safety increase" And by safety I also mean for the craft flying near trees or other hard objects.

shrouded-ducted fan discussion + many textbook references
http://www.eng-tips.com/viewthread.cfm?qid=58711

Commerial RC ducted fan calculator
http://www.s4a.ch/eflight/fancalc_e.htm

@rsc - have you considered vacuum forming?

Jim
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Old Jul 03, 2012, 02:22 PM
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Awe!! Jim, Thank you for this Information!
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Old Jul 03, 2012, 02:27 PM
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P.S. @Jim, No I have not but I have read some interesting stuff about it.
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Old Jul 03, 2012, 02:38 PM
James not bond
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@jim awesome jump in... right hit the target..
the original thought is for safety.... but now... since it's definitely doable... I might also consider increase the efficiency for operation..

@R if we are looking for something net shape..with high strength.. RTF might work for high end use..( expensive AP set)
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