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Old Aug 24, 2014, 09:30 PM
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Help!
Electric ducted fans

Hi Guys
What is there any difference between 4 , 6 , 7 bladed ducted fans.
If so do you use different size motors.
Cheers
Len
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Old Aug 24, 2014, 11:20 PM
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Quote:
What is there any difference between 4 , 6 , 7 bladed ducted fans.
The difference is that the four-blade fans have four blades, the six-bladed fans have six blades, and the seven-bladed fans have seven blades.

Quote:
If so do you use different size motors.
Sometimes.
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Old Aug 25, 2014, 03:14 AM
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Sorry for your "welcome" to RCGroups. But if you ask again in one of the EDF forums http://www.rcgroups.com/aircraft-electric-jets-375/ you should find some sensible and even helpful answers.

Steve
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Old Aug 25, 2014, 05:11 AM
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It's similar to two, three and four blade props. As a general rule more blades allows more power to be transmitted through a certain diameter of fan (or prop) at a certain RPM, albeit with less efficiency.

So yes, all other things being equal, because you are transmitting more powerthrough the fan then the motor will pull more power from the battery. But there are other variables such as blade pitch and blade area to contend with too, so direct comparisons can be tricky.
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Old Aug 25, 2014, 08:07 PM
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Len, I'm no expert with EDFs myself, but from what I've read, the more blades you have, all else being equal, the more static thrust you will have, at the expense of top speed. The fewer blades you have, the less static thrust you will have, but your top speed would be faster.
This is assuming the same motor in both, same number of lipo cells, etc.

There are some advantages and disadvantages to both.
If you have a jet that doesn't have enough intake area and is challenged in that way, then having a greater number of blades helps. Also, there is a sound advantage. The greater the number of blades, the more jetlike the whistling sound from the EDF.

If you have a jet that has plenty of breathing ability and no problems there, and high speed is your goal and you have enough runway to build up take off speed, then fewer blades is probably what you want.

But yes, ignore the first reply you got. That was about as helpful as a mosquito bite on your butt cheek. (rolling eyes...)
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Old Aug 25, 2014, 08:38 PM
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butane did answer the question though. the question has such a vague motive that trying to guess what that is will be subjective and speculative at best.
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Old Aug 25, 2014, 11:50 PM
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The reason I am asking is because I bought a STARFIRE ME2008 the recommended engine is a 4 inch Ducted fan, motor B36-36/1900k, but this motor is not made.
I can get either a 4 blade or 7 blade fan .
One place suggesting a 4 blade fan with a 36-50 2100k motor with 85A ESC
and the other is suggesting a 7 blade fan with 36-45 1200k with 60A ESC
I am not sure which to use
Cheers
Len
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Old Aug 26, 2014, 12:05 AM
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which places suggested these setups? would be helpful getting links to these sites.

also, would be helpful if you provide a link to the plane to be certain we know which one you refer to. i'm guessing you mean this one: http://www.rcgroups.com/forums/showthread.php?t=983270
if so, search/ask about the motor there. dedicated threads like that have the most information and proven setups tested by other users.

amp draw increases with number of blades and kv (rpm/volt) of motor. keep that in mind when you decide.
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Old Aug 26, 2014, 08:35 AM
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Personally, I prefer to start out with the maximum number of blades I can get on an EDF.
But that's me.
I like the improved jet-like sound when you get more blades, and the improved static thrust.
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Old Aug 30, 2014, 10:55 PM
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I found this video to better demonstrate what I was talking about.

5 Blade Vs Change Sun 10 Blade SOUND UPGRADE (1 min 54 sec)
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Old Sep 05, 2014, 09:04 PM
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Quote:
Originally Posted by C₄H₁₀ View Post
The difference is that the four-blade fans have four blades, the six-bladed fans have six blades, and the seven-bladed fans have seven blades.



Sometimes.
Another one with huge post count numbers ...... and as usual (one goes with the other) nonsense answers or posts. I see these people on all sorts of forums and they are all the same. Post a few words of nothingness only to get their post count up. Like that actually means something. Pathetic and irritating.
OK - rants over. Sorry. Those clowns bug me.
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Old Sep 05, 2014, 09:07 PM
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Quote:
Originally Posted by builderdude View Post
I found this video to better demonstrate what I was talking about.

http://www.youtube.com/watch?v=qvWGDk1htjw
Great post - very informative and helpful.
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Old Sep 05, 2014, 09:25 PM
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Originally Posted by Redbone311 View Post
Another one with huge post count numbers ...... and as usual (one goes with the other) nonsense answers or posts. I see these people on all sorts of forums and they are all the same. Post a few words of nothingness only to get their post count up. Like that actually means something. Pathetic and irritating.
OK - rants over. Sorry. Those clowns bug me.
i will wager butane has helped a lot more folks than you have. and if you took the time to read carefully the one with "nonsense" in his answers is not him. he answered the question - move on.
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Old Sep 06, 2014, 09:11 AM
buyer of the farm
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Quote:
Originally Posted by Redbone311 View Post
Another one with huge post count numbers ...... and as usual (one goes with the other) nonsense answers or posts. I see these people on all sorts of forums and they are all the same. Post a few words of nothingness only to get their post count up. Like that actually means something. Pathetic and irritating.
OK - rants over. Sorry. Those clowns bug me.
Okay I'm going to have to jump on here. There is nobody on RC Groups who has cut through the picky details and come up with what matters more than C4H10 has. He helps people just about every time he posts, and this is no exception. The OP said "What is there any difference between 4 , 6 , 7 bladed ducted fans. If so do you use different size motors."

Well, one could say the same thing about propellers as well. And we know that if you pick 10 propellers of different manufacturers of the same pitch and diameter we will have ten different sets of characteristics. We'll have different amp draw, different amounts of static thrust. In fact we can say nearly nothing at all about what a 10x5 prop will do! My APC 11x4.7 SF propeller draws more amps than many 12x6 props do. The numbers would suggest otherwise and they lie. Actually they don't lie, they just aren't enough information to say anything at all about the performance of the props.

Well, ducted fans are the same way. Unless you are including exact manufacturer and model associated with the info, there isn't enough information to say anything more than what C4H10, I prefer to call him isobutane, a higher class term, has said, "The difference is that the four-blade fans have four blades, the six-bladed fans have six blades, and the seven-bladed fans have seven blades."

In fact, that is nearly the only truthful answer that can be given. Instead of derision, his observation should be followed by questions, to which you can be sure, he most certainly has helpful answers. Shame on people who make his answer to be what it is not, and who call him what he is not.

Welcome to RCG Len! Remember how difficult it is to determine emotions and intent by the written word. Even if someone IS a bit crusty (I am. I admit it) they're most often very helpful people. C4 is a prime example of that. He's a valuable resource and you can take his advice to the bank. Why don't you ask him your questions. His answer to your first post merely indicates that he needs more information to help.
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Old Sep 06, 2014, 07:16 PM
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Thanks, guys.

Redbone, if you click on the little magnifying glass under my name, you'll actually be presented with a list of the last 600 posts I've made. It can be an awfully useful feature.
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