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Old Jan 11, 2012, 05:39 PM
Not Funny......
Mike Warren's Avatar
United States, CO, Redstone
Joined Dec 2010
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Quote:
Originally Posted by bobbit4447 View Post
.......
Please don't confuse readers with dribble.
.......B
Oh, I don't think long time EDF guys would EVER accuse Klaus/Winmodels of spouting "dribble"
Careful who you cross swords (keyboards) with.
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Old Jan 11, 2012, 05:55 PM
Fly it like you stole it !
bobbit4447's Avatar
Australia, QLD, Coolum Beach
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My apologies to Klaus if interpreted that way.
B
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Old Jan 11, 2012, 09:51 PM
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Quote:
Originally Posted by bobbit4447 View Post
The statement I made is correct. I attach a reference from AMCA (The authority that Certified American Fan Manufacturers use) in order to calculate HP/watts for fans of varying diameters. Please don't confuse readers with dribble.
B
Hi bobbit
Please read my post again. I did say that you were quite correct!!
But even in the pdf you coppied are five (5) equations not just the one quoted initially. But you must consider all of them to get the right picture.
Particularly with EDFs your concern is mainly thrust, and for that you need a bit more than than just the fan laws!

To give you a bit more to read have a look at
http://www.rcgroups.com/forums/showthread.php?t=536911

Have fun with fans

KRS

btw. what do you actually mean by "confuse readers with dribble" ?
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Old Jan 12, 2012, 12:52 PM
EDF rules... :)
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Joined Nov 1999
13,592 Posts
Since the difference in area is only ~38% for 80mm fan cut down from a 90mm fan the difference between them is only ~38% of the amp load, If the 80mm is pulling 100 amps the 90mm will be pulling ~138 amps. This is all things equal except fan swept area.

Eric B.
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Old Jan 12, 2012, 02:07 PM
Fly it like you stole it !
bobbit4447's Avatar
Australia, QLD, Coolum Beach
Joined Oct 2011
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Eric
My reference was made to geometrically similar fans.
The discussion on cut down fans is on another thread.

Bob
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Old Jan 12, 2012, 02:08 PM
You win again gravity!
SMorrisRC's Avatar
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But that's only applicable if the load on the fan is constant across its radius, which it isn't (twist and speed are different). It's probably a decent enough ballpark assumption though if you err on the side of caution.
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Old Jan 12, 2012, 02:10 PM
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England/uk
Joined Oct 2007
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cs 90 mm

Hello,
Well some good news my CS fan will be staying in my L39.I had a re think on how to loose some weight,by changing the rear mounted elevator servo, moving the fan forwards enabling me to shed some nose weight and use a smaller rx batt.
I also had a play around with the motor timing and changed my lipos to some new 45c ones getting me an extra 200 watts.I had two flights today and its a lot better with ample performance and the great sound,
cheers Euan..
ps lads stop all the high brow testing/arguing and actually stick it in an airframe you will love it
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Old Jan 12, 2012, 02:59 PM
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United States, TX, Grand Prairie
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Originally Posted by egall232 View Post
...he high brow testing/arguing and actually stick it in an airframe you will love it
lol...everytime I bring out the airframes I want to "stick" it into I ended up flying them...

Damn this hobby is addictive..
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Old Jan 12, 2012, 04:02 PM
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Quote:
Originally Posted by SMorrisRC View Post
But that's only applicable if the load on the fan is constant across its radius, which it isn't (twist and speed are different).
It looks as if the same misconceptions reappear every five years or so, because there is no continuity of knowledge.
Certainly the load on the fan accross it's radius should be constant. It must be the aim of the designer to achieve this as well as possible in his search for efficiency. But then I think that you don't want to design an EDF.
On the other end, how do you want to judge the quality if you don't know the desgn principles?

BTW, I don't agree with the majority here, that the CS90 is a "clone" of Stu's fan, because the characteristics of Stu's "original" have been used long before, i.e a large number of individual blades fitted to a hub and the use of "scimitar" shape blades with a “hook” at the tip.

KRS
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Old Jan 12, 2012, 04:29 PM
Bypass Ratio = Infinity
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United States, NC, Jacksonville
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Quote:
Originally Posted by Rudi3000 View Post
It looks as if the same misconceptions reappear every five years or so, because there is no continuity of knowledge.
That is because reading is different than understanding.
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Old Jan 12, 2012, 04:37 PM
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Originally Posted by scatsob View Post
That is because reading is different than understanding.
Do you say that the newer members of RCG are stupider than in the past?

KRS
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Old Jan 12, 2012, 04:57 PM
Bypass Ratio = Infinity
scatsob's Avatar
United States, NC, Jacksonville
Joined Apr 2006
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Quote:
Originally Posted by Rudi3000 View Post
Do you say that the newer members of RCG are stupider than in the past?

KRS
Not at all, just a comment from observations during my education and in my professional life that happens to apply here as well. A generality if you will, reading about a concept is a lot different than understanding the fundamentals behind them. I guess I was not really speaking to timelines of misconceptions.
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Old Jan 12, 2012, 06:20 PM
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United Kingdom, England, North York
Joined Oct 2010
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heres a 12 Blades 90mm EDF sounds good and looks good to me for just $40 lol you have to see the landing thow its brill

heres the link to buy one

http://www.xtremepowersystems.net/pr...?prod=CS90-8mm


L-39.wmv (2 min 59 sec)
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Old Jan 13, 2012, 01:23 AM
You win again gravity!
SMorrisRC's Avatar
UK
Joined Jan 2010
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Actually, I do understand.
The most efficient fan, much like any aerofoil, will have an elliptic loading, to give the best lift to drag ratio (in this case equivalent to thrust vs shaft power required). This is always the case as the tips cannot carry any load by definition, so you can never achieve a constant load across the fan.
The closer to it you try to get, the more thrust you'll get, but it won't be as efficient by definition as you'll have changed your oswalds efficiency factor (or whatever the equivalent term is in fan design).
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Old Jan 13, 2012, 07:17 AM
Bypass Ratio = Infinity
scatsob's Avatar
United States, NC, Jacksonville
Joined Apr 2006
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X-Flight now sells just the 8mm adaptor for about $10.

http://www.x-flight.com.hk/index.php...=&lang=en&ev=#
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