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Old Oct 12, 2012, 01:10 PM
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Maxthrottle's Avatar
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Originally Posted by mopetista View Post
....PS: thanx Maxthrottle for the link, after reading lots of Klaus' (Winmodels) postings I have to say that it all sounds sensible and subtle, and there is no talk about THE correct exhaust diameter for ANY 70mm fan, and there is also not talk about doing away with efflux speed measurements altogether (as some claim, because you should just calculate it from the thrust and exhaust diameter...) - it's mainly in German forums where resistance to the CS70 is still strong, e.g., people refuse to open the rear ends of some models to make the CS70 work - and then it's the fan which is terribly inefficient, or it is claimed that a 70mm fan must be crap if it doesn't perform well (static) with a 55mm nozzle..You can also read that nacelle installations like in the Dynam Me-262 or ariliners are the most efficient setups (short, straight (!) ducting) - clearly seen by the superb performance of the big Dynam bird...
? What are you reading? The fact that you are looking for a set dia for 70mm tells me you missed something... actually most of what was said.
Klaus explains where and how that may vary. Even this main post where he start breaking it down into english http://www.rcgroups.com/forums/showp...&postcount=111 he starts explaining why. And earlier he gives the link to the white papers that details the mathematical reasons for all of those. See also http://www.rcgroups.com/forums/showp...&postcount=130
The explanations are far longer for you to have already come back saying that its not there.
Post 147 "Thrust equals { mass flow times velocity difference } but the energy necessary to accelerate the air flow to this velocity difference is { mass flow times velocity difference squared }. Therefore it is sensible to use the maximum air flow possible with the least velocity difference. For the static case this leads to large diameter fans and exit areas, because the velocity difference here is the absolute air exit velocity. But in flight the velocity difference is measured against the flying speed, i.e. the fan air flow velocity difference is { air exit velocity minus flying velocity }. In many cases the air flow through the fan itself is not fast enough to have a sufficiently high velocity difference to produce any meaningful thrust at higher flying speeds. So the exit area is reduced to increase the velocity differential. The amount of reduction possible depends on the fan characteristic, which is what it is all about here."
Review of understanding
Diagram of Static flow and Dynamic flow regarding velocity momentum of air and pressure induced by the fan and duct
Volume/Mass Flow
As Klaus commented this is typical with many to have an aversion to the math and the details.

Most models do not give the attention to the inlet which can change the other factors greatly. But you've already discounted several videos, not just the ones posted here, of many following the practice of less than 100% FSA exhaust to great avail. If that can't convince you I'm not sure what will. Horse meet water, water horse. You can take it from there or not. Your disbelief won't make it any less true... I guess its just magic then.
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Old Oct 12, 2012, 01:10 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
13,455 Posts
There is no correct exhaust area for different fans of the same size fan area, there are many variables that change performance, the only commonality is exhaust area.

Odysis is mostly correct from my glance thru his posts and we have discussed a lot of this in the past.

The duct changes the physics for props as it defines exactly how much volume moves thru for every rpm the rotor turns.

If anyone wants wants links to all of Klaus Schornhorst postings I have it at home and will post them tonight.

Eric B.

Links:
KRS EDF FAQ
http://www.rcgroups.com/forums/showt...ight=winmodels

KRS Edf 3
http://www.rcgroups.com/forums/showa...mentid=1192118

KRS Edf 1
http://www.rcgroups.com/forums/showa...mentid=1192117

KRS Edf 1-1
http://www.rcgroups.com/forums/showa...mentid=1192112

KRS Edf pt2 construction
http://www.rcgroups.com/forums/showa...hmentid=885564

KRS EDF ROTOR MEASUREMENT FOR VELOCITY
http://www.rcgroups.com/forums/showa...hmentid=724184

KRS references
http://www.rcgroups.com/forums/thumb...attach&u=24787
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Old Oct 12, 2012, 04:54 PM
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Canada, BC, Surrey
Joined Jul 2011
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Im too lazy to go back and reread all of this thread on my iphone...

I just want to know what esc everyone's using to get the most out of this fan?

Tyia
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Old Oct 12, 2012, 05:06 PM
Extreme CNC Alloy EDF
Extreme_RC's Avatar
Australia
Joined Mar 2006
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Quote:
Originally Posted by PAPE View Post
FWIW I found on my F16 the best performance was with a 58mm outlet. here is my F16 with Extreme 4s alloy 10 blade. Jump to the 30sec mark to se the plane.
Yours flies perfect, and 58mm is 85% FSA for my fan housing (not including stators) but mine proves that even with chucking a stock wemotec glass exhaust on the back it still performs, doesnt bog right down and lose all airspeed as some claim. I had the wemo exhaust nozzle in the F16 since it was built so I simply stuck it on the back of the new fan. This was also before talk of exhaust diameter started.

The vampire as I said was not planned, I made it a little too short so when cutting it back flush I didnt get to the 57-58mm I was looking for, its a pita to remove it and redo so I left it and tried it, we have two identical vampires at the field, the other has stock airframe exhaust, and mine is very noticeably faster even taking into account the huge drag compared to an F16 airframe. I also logged my vampire with Hyperion RDU unit and the amp draw was 64A peak then dropped slowly over 2 mins, compare with 59.5A on the bench open backed, its not a huge jump at all.
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Old Oct 12, 2012, 05:15 PM
You are a "go" for reentry
Maxthrottle's Avatar
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Quote:
Originally Posted by WhalleyB0Y View Post
Im too lazy to go back and reread all of this thread on my iphone...

I just want to know what esc everyone's using to get the most out of this fan?

Tyia
Power Systems may be a thread for you. You haven't specified battery, motor or end result you're shooting for.

Or

The Consolidated CS70/10 tests
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Old Oct 12, 2012, 05:25 PM
3DHOG
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USA, CA, Aromas
Joined Sep 2010
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we run our cs70/10 on 6s with BL32 2150kv motor and it pulls around 75amps. we use castle ice lite and ice100 esc's
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Old Oct 12, 2012, 06:59 PM
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Canada, BC, Surrey
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Quote:
Originally Posted by jcdfrd View Post
we run our cs70/10 on 6s with BL32 2150kv motor and it pulls around 75amps. we use castle ice lite and ice100 esc's
Thanks, I was at the hobby shop when I posted. I ended up buying a Castle Ice 100 for use on 5s with the 2950kv motor and CS 10 blade fan. I really hope it is going to be big enough.
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Old Oct 12, 2012, 07:04 PM
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Quote:
Originally Posted by Maxthrottle View Post
Power Systems may be a thread for you. You haven't specified battery, motor or end result you're shooting for.

Or

The Consolidated CS70/10 tests
ah yes, the consolidated results! Thanks kindly!
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Old Oct 12, 2012, 08:45 PM
It should fly at least once
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Australia, NSW, Grenfell
Joined Mar 2006
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My God what a read.......while I do agree that it is on topic, I think it would be nice if all those who would like to talk Physics or change the world of Physics started a new thread and had a link from here to it.
This discussion only serves to complicate things for the larger community who are trying to use this fan, after all were trying to enjoy flying our models not redesigning the propulsion system. Most of us just want good power for a reasonable cost and how and where to get it.
Sorry if this does sit well with you all but I'm here to help get my fan working at its best and the results that some have posted have done just that without the science lesson.
I will be back in a few minutes as I have got to put on my flame proof suit and helmet
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Old Oct 12, 2012, 09:09 PM
Life begins at transition
Australia, WA, Perth
Joined May 2007
3,521 Posts
nope, sounds fair!
this was way off, and wearing out an oft tread path.

I'm surprised. Just ran it up, and it's surprisingly not too far out of balance. Not what I'd call smooth, but even with the plastic spinner it's better than most cheap fans.
I guess it's the luck of the draw... time to get some proper numbers, and perhaps balance properly.
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Old Oct 12, 2012, 09:19 PM
Don't Move I've Dropped My Nut
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United States, AL, Huntsville
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A big +1, Clive45!
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Old Oct 12, 2012, 11:11 PM
You are a "go" for reentry
Maxthrottle's Avatar
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Quote:
Originally Posted by clive45 View Post
...a link from here to it.
...redesigning the propulsion system. Most of us just want good power for a reasonable cost and how and where to get it....put on my flame proof suit and helmet
Are you suited up yet Kidding. We just posted the links to the Duct and Fan discussions; so way ahead of you.

But you realize, its all your fault Again kidding. Quick and easy answers are great right up until, quick and easy isn't agreed on or doesn't work. Then all the theories come out and how is one to tell which one is right.

Klaus, who is an engineer specializing on the topic set out to dispel these misunderstandings years ago as EDFs became popular and came up with common understanding. He did still say though its usually more complicated than most realize.

And if no one read it or understood it you wouldn't have any accurate answers. So its good for these conversations to come up every once and a while because everyone is just looking to help and give the right answer.

No need to argue it though. The answers, physics and math has been discussed and is already there for all to read. A lot of good talent on RCG!
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Old Oct 13, 2012, 01:18 AM
chuck
santa barbara, CA
Joined May 2009
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just a thick skin will do! there are so many ideas and opinions flying around here, you are sure to find some u like

so..... given that u are a believer , where are we buying rotors and or whole units as of now?

anybody know anything about these guys http://www.hobby-paradise.com/en/pro...ct_detail.html ???

chuck.
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Old Oct 13, 2012, 05:08 AM
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Originally Posted by chas650r View Post
just a thick skin will do! there are so many ideas and opinions flying around here, you are sure to find some u like

so..... given that u are a believer , where are we buying rotors and or whole units as of now?

anybody know anything about these guys http://www.hobby-paradise.com/en/pro...ct_detail.html ???

chuck.
I have bought from them and rc-castle. I am almost certain they are the same co as rc-castle(same name charged on paypal).

Very good support. Had a motor arrive with a bent shaft and after sending them a video, they sent me a new one.
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Old Oct 13, 2012, 09:38 AM
chuck
santa barbara, CA
Joined May 2009
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Originally Posted by anlucas View Post
I have bought from them and rc-castle. I am almost certain they are the same co as rc-castle(same name charged on paypal).

Very good support. Had a motor arrive with a bent shaft and after sending them a video, they sent me a new one.
thanks , good info and for the fan , the price is right. all my dealings w/ rc castle have been favorable also.

chuck.
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