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Old Sep 22, 2015, 02:38 PM
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Spinner on an edf

What's the purpose of the spinner on an edf where the rotor is already held by an alternative fitting ?

I've done some searching on the subject, even researching the purpose of spinners on real turbofans, but I can't find any detail for edfs as far as efficiency/purpose is concerned.

There's people who say that you mustn't run without a spinner, but give no reason and there's a few people saying they run without and can see or feel no difference or problems.
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Old Sep 22, 2015, 03:11 PM
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Aerodynamics?

Air is moving through the duct at like 100mph, there will be wind resistance that will kill your edf's efficiency.
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Old Sep 22, 2015, 03:46 PM
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I would say reduce not kill...many people fly with out them
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Old Sep 22, 2015, 03:47 PM
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Oliver at WeMoTec says there is no difference. But...I like them for dynamic balancing. Rotors may be balanced, but not all motors. Clocking the spinner gives that final smoothness. It can make quite a difference in the sound and volume of the fan vs not having one. And the more power(watts) that are being consumed, the more noticable.

Fuzz
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Old Sep 22, 2015, 04:41 PM
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Interesting replies so far.

I must admit to struggling to see how much difference a spinner would make, since the air is still flowing down the duct and hitting the face of the fan disc.

I can see that maybe some air that otherwise would hit the flat face of the hub area and perhaps slow down and become turbulent would be directed more smoothly into the fan but I wonder just how much difference it makes and it seems from at least one reply, in practice it makes no difference so long as the rotor is properly balanced.

I can also now see the balancing issue from a positive aspect. I was only considering the balancing as a negative, since I was just seeing it as another component to not only balance but add another fastener and a little more weight.

It's probably quite obvious that I'm quite new to edfs and I've spent quite a bit of time researching and getting my current fan balanced. Certainly I've found that trying to balance a 90mm cs12 with a loose fitting, off centre adapter is a nightmare .
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Old Sep 22, 2015, 05:07 PM
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You find lot of opinions here! Some good some not so.. But nothing better then testing for yourself! For me I try to keep the spinner. Even if most could never notice the difference in flight. But I also try to get every little bit i can..The only time not having a spinner is good is if you cant get it ballanced or it has flaws and can fail .But that is just my 2 cents
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Old Sep 22, 2015, 07:34 PM
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I also try to make the spinner work but in some cases the plastic versions can crack if tightened just once too tight. If you see any stress (crack) in a plastic spinner, you are better off without it.

As for a loose fitting adapter, the only solution is to make it solid! If that means glue it on, so be it. Once it stops moving then you can balance it.
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Old Sep 22, 2015, 07:48 PM
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According to Oliver, the airflow does not hit the face of the hub, with no spinner. Pressure builds in front of the hub and flows around it. Almost the same thing happens at the rear of the motor, except in low pressure. I have noticed no measurable difference in performance. If there is, you would have to have a laboratory in flow dynamics to measure it.

As an example, recent aluminum spinners that are included with WeMoTec fans, have faulty spinners. They are out of round. They will not "clock". So I have had to use the old Pro aluminum spinners, or the even older plastic version. But the new EVO rotors work just fine, sans spinner.

On the use of the plastic spinners. It is true they will crack and virtually explode, if the retaining screw is over tightened or allowed to. I have used them with no problems up to 800W. But, with an ESC that allows soft start-up. Instant start will tighten the screw to the point of causing the spinner to fail.

Also, A very small dab (use a pin to apply)of red thread sealer on the threads, clock the spinner, and let sit over night. This will not allow the spinner screw to self tighten, and still be removable. Besides, soft start sounds much more realistic. Real jets do not have a rev-up like a small block chevy...

Fuzz
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Old Sep 23, 2015, 02:28 AM
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Quote:
Originally Posted by St. Martin View Post
According to Oliver, the airflow does not hit the face of the hub, with no spinner. Pressure builds in front of the hub and flows around it. Almost the same thing happens at the rear of the motor, except in low pressure. I have noticed no measurable difference in performance. If there is, you would have to have a laboratory in flow dynamics to measure it.

As an example, recent aluminum spinners that are included with WeMoTec fans, have faulty spinners. They are out of round. They will not "clock". So I have had to use the old Pro aluminum spinners, or the even older plastic version. But the new EVO rotors work just fine, sans spinner.

On the use of the plastic spinners. It is true they will crack and virtually explode, if the retaining screw is over tightened or allowed to. I have used them with no problems up to 800W. But, with an ESC that allows soft start-up. Instant start will tighten the screw to the point of causing the spinner to fail.

Also, A very small dab (use a pin to apply)of red thread sealer on the threads, clock the spinner, and let sit over night. This will not allow the spinner screw to self tighten, and still be removable. Besides, soft start sounds much more realistic. Real jets do not have a rev-up like a small block chevy...

Fuzz
That's good info. Thanks.
I've just balanced up my spinner and it's no wonder it put the balance out so much when I initially fitted it because it's certainly taken quite a lump of epoxy inside.
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Old Sep 23, 2015, 03:56 AM
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In small, higher rpm EDF units like 70mm it actually create more trouble than good IMO, unless you can balance it to an absolute perfection which is well out for an average modeller.
On other hand, there is such a tornado of air inside the air intakes that using spinner or no spinner it will make a very little or no difference in performance.
I just did some test runs of the 70mm fan today I'm going to fit in my new build and no matter how much I played with the spinner the fan was running much smoother with out it, tho aesthetically it looks better with it.
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Old Sep 23, 2015, 10:08 AM
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Been down that road before

This has been investigated by myself and others and have found a loss of from 3 to 5% on a typical edf with no spinner. It is a little more loss than I would be willing to give up. The inlet lip is a much bigger deal.
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Old Sep 23, 2015, 01:36 PM
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Quote:
Originally Posted by jofro View Post
In small, higher rpm EDF units like 70mm it actually create more trouble than good IMO, unless you can balance it to an absolute perfection which is well out for an average modeller.
On other hand, there is such a tornado of air inside the air intakes that using spinner or no spinner it will make a very little or no difference in performance.
I just did some test runs of the 70mm fan today I'm going to fit in my new build and no matter how much I played with the spinner the fan was running much smoother with out it, tho aesthetically it looks better with it.
I have never had to use any kind of ballast inside a spinner, other than a 1/8-3/16"sq piece of masking tape. Some times motors, esp slotted designs, are just not well balanced. Kontronics and Hackers are a dream to set-up.

If I cannot dynamically balance a motor/rotor by just clocking, I add a square of tape and try it. If it still is no good...I move the tape 45deg.(this is inside the spinner BTW) If better I move the tape an 1/8th turn in the same direction, till it is good. Sometimes I have to enlarge the square of tape. But rarely.

If your rotor is already balanced, and you balance the spinner, too.. you will not be accomplishing the goal. The goal is to dynamically balance the rotor/motor/adapter/spinner in unison, not individually. But starting off with the greatest mass at the further out circumference, already balanced, is a good start(rotor).

On another note: I have balance fans outside the airframe(as I usually do) and installed it in the airframe to sound and feel horrible. It was the ducting. The bad ducting in a certain design afforded poor flow to one side of the fan. Causing an aerodynamic inbalance. I scratched my head on that one for quite a while. It turned out to be the ducting had too high an angle mid way through the duct. New ducting cured the problem.

This is a big reason why some designs have a pleasant sound than others, if the fan is set-up correctly.

Fuzz

BTW, if that is a WeMo EVO, the spinner is at fault. They are bad. I hope Oliver corrects this problem. The problem is also with the 80/90mm Evo
s
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