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Old Mar 24, 2015, 02:29 PM
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Series Ducted fans

I'm new to ducted fans but assume placing ducted fans in series has been discussed and tried. Does any manufacturer make such an item? Save me a hassel of a DIY version. Does it work would be the next question.
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Old Mar 24, 2015, 02:50 PM
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[QUOTE=Aaron 1;31150435]I'm new to ducted fans but assume placing ducted fans in series has been discussed and triedyes it has
Does any manufacturer make such an item? NO
Save me a hassel of a DIY version. Does it work would be the next question.[/QUOTE Save your time and money., and no they don't



Set the search date to start at the beginning- and look it up. Not one ever worked.
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Old Mar 24, 2015, 02:52 PM
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I suppose you could have a larger fan followed by a smaller fan running at a higher speed to increase the exit velocity but extra weight , two motors , two fans etc etc I don't think the gains would out weigh inefficiencies . I'm sure it must have been tried but give it a go and let us have some results . What size fans are you thinking of ?
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Old Mar 24, 2015, 02:56 PM
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In the automotive world some "twin turbo " cars have two turbos in series but that isn't to make more pressure ( it doesn't ) but to reduce turbo lag .
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Old Mar 24, 2015, 03:06 PM
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Quote:
Originally Posted by FANtastic View Post
I suppose you could have a larger fan followed by a smaller fan running at a higher speed to increase the exit velocity but extra weight , two motors , two fans etc etc I don't think the gains would out weigh inefficiencies . I'm sure it must have been tried but give it a go and let us have some results . What size fans are you thinking of ?
Yup unless you can get two rotors closely spaced with stators, running off the same motor with a gearbox and shaft.
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Old Mar 24, 2015, 03:11 PM
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Gearbox = complex and inefficient in terms of power consumption.
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Old Mar 24, 2015, 08:10 PM
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[QUOTE=CoolerByTheLake;31150617]
Quote:
Originally Posted by Aaron 1 View Post
I'm new to ducted fans but assume placing ducted fans in series has been discussed and triedyes it has
Does any manufacturer make such an item? NO
Save me a hassel of a DIY version. Does it work would be the next question.[/QUOTE Save your time and money., and no they don't



Set the search date to start at the beginning- and look it up. Not one ever worked.
================================================== ===

I did a search" EDF's in series" but found little. It seemed to think I was looking for series batteries. Can you give me a link? I also googled" Series axial fans" and got information that industry uses them when higher CFM and pressure are needed.

One post said they tried two GWS units in series but it only produced 1 oz more in thrust. NG because of weight.

Lots of ways to go wrong on this subject. This is a totally different app but when I set up my wood working hobby shop I ended up with two 5 HP radial fans in series to get the CFM I needed. That was 25 years ago and has worked better then anything you can buy. Yet every one says it won't work on the woodworking sites and the suppliers are not interested.

I'm not sure yet how EDF works but maybe there are some engineering papers on it. I see no reason why a thrust increase of about 80% more could not be obtained. Would not cost much $ to mess around with it. Time is nothing for the retired,

Thinking it though the obvious popped up. Weight is critical in aircraft, the inefficiency of running two units in series would mean you would be better off just running one larger one. At least that's the way I see it right now. My wood shop blowers don't care about efficiency or weight as long as the CFM goal is met.
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Old Mar 24, 2015, 10:48 PM
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I see no reason why a thrust increase of about 80% more could not be obtained.
First of all - why would you think that? It's simply a fan. There is no pressure increase - you are simply accelerating the air. Sticking another one in the accelerated air is not going to boost your output.

Quote:
the inefficiency of running two units in series would mean you would be better off just running one larger one
Bingo.

People need to stop confusing turbines and fans.
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Old Mar 24, 2015, 10:49 PM
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There was a commercial unit years ago - but it did nothing. Search RCG and RCU for the "force air" fan
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Old Mar 25, 2015, 12:13 AM
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Time is nothing for the retired,
I too am retired. But not by choice-. I had to . There was another guy with grandiose ideas of running fans in series , not more than 6 weeks back-- go thru the treads- Some links may be there for others, follies.

If that's where you want to go, just buy a Turbine.
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Old Mar 25, 2015, 01:34 PM
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Quote:
Originally Posted by Aaron 1 View Post
I'm new to ducted fans but assume placing ducted fans in series has been discussed and tried. Does any manufacturer make such an item? Save me a hassel of a DIY version. Does it work would be the next question.
Since you would rather ask than search, it works great!

I'm surprised no one has thought of this before. Thanks for the idea and report back your progress, and don't forget the pictures and videos!

Daren

p.s.
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Old Mar 25, 2015, 06:18 PM
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So an increase of 80% thrust for doubling the weight and power consumed.......
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Old Mar 25, 2015, 08:15 PM
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Ralf Dvorak Start your search there. I'm currently building the RBC/Offshore P-80. The plans are originally by Hanno Dittmar. He used Ralf's tandem fan and two counter rotating SP-480 brushed motors. The fan was designed to run in restrictive scale area ducting @ 66mm. WeMo then came out with the 66mm 505, cut down Minifan. Which was lighter and over all more efficient. A rough sketch of the fans outlines are on the P-80's plans. There are references to this fan in this forum. Goes back about 14yrs.

Fuzz
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Old Mar 26, 2015, 12:17 AM
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Quote:
Originally Posted by Aaron 1 View Post
I'm new to ducted fans but assume placing ducted fans in series has been discussed and tried. Does any manufacturer make such an item? Save me a hassel of a DIY version. Does it work would be the next question.
Discussed literally hundreds of times worldwide. No it won't work. Accept that as it stands or spend some time searching for the large amount of available literature on ducted fans. You have to THINK about your search. For example. any mention of 'electric' will simply confuse the issue. Then you will be able to figure out why it won't work.

"I'm not sure yet how EDF works"
So why haven't you done the above BEFORE getting into 'advanced' stuff like in line fan units?

"that industry uses them when higher CFM and pressure are needed"
'Industry' doesn't have clue about what we are doing. From where we stand they are only 'gentle wafting' air about. A mere zephyr . And there is NO pressure increase in our ducted fans as the literature will tell you (though it is possible there might be a microscopic one as a side effect but it is of no importance).

You have one thing right. Power/weight. I compared a typical EDF motor I have to the motor on the pillar drill in my workshop. The EDF motor is TEN times more powerful than the drill motor and ONE TENTH of the weight. (It also cost five times the price of the entire 'DIY warehouse quality' drill.)

Here's a starting point on some literature. Follow its links.

http://www.southamptonmac.org.uk/edf_discussion_36.html
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Old Mar 26, 2015, 09:40 AM
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Originally Posted by Aaron 1 View Post
I'm new to ducted fans but assume placing ducted fans in series has been discussed and tried. Does any manufacturer make such an item? Save me a hassel of a DIY version. Does it work would be the next question.
In my opinion, DIY is the only way that YOU will get an answer that YOU will be satisfied with. Don't let anybody discourage you and tell you it can't be done. Find out for yourself and learn more than you ever expected.

my $0.02
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