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Mar 27, 2018, 01:30 PM
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Lynxman's Avatar
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I use six stators. I tried a few different stator shapes and haven't found a different that I can attribute to them, but I haven't done any controlled runs with just stator changes. The current stators are angled to absorb the motor torque better. When I had the stators radial/straight out the motor tube would twist from the torque.

One thing I noticed is that having the stators close to the fan made a lot more whining noise. When I moved them away from the fan it got a lot quieter. I think that's why my F-5 still has a lot of whine even though it has twelve blades.
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Mar 27, 2018, 01:50 PM
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jumo004's Avatar
I know that there is a force vector coming off the fans trailing edge and performance to be gained
but I have no idea on how to make it work for me.

So as always it's trail and error ....

If only I had a PhD. in Aerodynamics !
Last edited by jumo004; Mar 27, 2018 at 02:17 PM. Reason: spelling
Mar 27, 2018, 02:12 PM
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Dirty Dee's Avatar
Very promising!

I have recently been interesting in attempting to make a large diameter/lower RPM EDF to mimic an airliner high bypass fan. Your developments gives me hope for the idea I want to try out.

What material, nozzle size, and layer height are you using for these?
Mar 28, 2018, 03:55 AM
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Lynxman's Avatar
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The undercambered fan performs worst so far by a clear margin. 840 g @ 250 W and 1370 g @ 500 W.

My fans are made with Primavalue PLA. 0,4 mm nozzle and 0,2 mm layer height. Four perimeters and 1,4 mm top and bottom, with 0% infill.
Mar 28, 2018, 09:55 AM
Registered User
Quote:
Originally Posted by Lynxman
I use six stators. I tried a few different stator shapes and haven't found a different that I can attribute to them, but I haven't done any controlled runs with just stator changes. The current stators are angled to absorb the motor torque better. When I had the stators radial/straight out the motor tube would twist from the torque.

One thing I noticed is that having the stators close to the fan made a lot more whining noise. When I moved them away from the fan it got a lot quieter. I think that's why my F-5 still has a lot of whine even though it has twelve blades.
An odd/even mix will reduce the noise level too. Odd number of rotor blades and an even number of stators. One of the highest performing 120mm fans on the market uses nine rotor blades and ten stators...
Mar 28, 2018, 11:32 AM
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Lynxman's Avatar
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I figured that would be the case. I wondered if I should try staggering the blades a little as well so the distance between the blades isn't the same for each blade that passes.

I flew my first 3D printed plane today. A glider. Very gusty and overcast, so it was a bit rough. The 3D printed propeller worked great:
Melusine - A 3D printable electric glider and FPV platform. (7 min 9 sec)


Wondering which plane I'm going to design for the fan now. Maybe a He-162, L-39, SAAB Tunnan or possibly just a sports jet of my own design.
Mar 28, 2018, 11:39 AM
Micro-Turbine Superhero
henke's Avatar
Quote:
Originally Posted by jumo004
If only I had a PhD. in Aerodynamics !
It's not that hard to get the basics.

I've been involved in fan development and snapped the following,

*Blade velocity changes with radius. So the tip travels faster, hence less pitch for the same work load. Center of the blade close to the hub is almost vertical as the travels speed is much lower then at the tip.

*Stators is also a part of the fan! you make a rotating vortex of air leaving the fan. The stators stops the rotation giving more thrust as they do it.

*Intake lip can do as much as 50% more, you want atleast the fans thickness in a stright infront of the blades and a nice bell mouth in. If that bellmouth is in front of the fan or the aircrafts inlet does not matter.

*Blade count has nothing to do with it! Its the combines chord of the blades. Example, you can have three larger blades or 11 smaller as long as the combined chord is the same. If a fan uses more power with more blades it's because you added combined chord, not because you added blades.

Wemotec as example, same diameter fan, different number of blades, same combined chord.

Thinking of it, it's all very obvious.

More smaller blades


Fewer larger blades
Mar 28, 2018, 11:41 AM
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henke's Avatar
One last ting, point that 3D printed decaputator west when throttling up
Mar 28, 2018, 11:45 AM
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Lynxman's Avatar
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Fortunately I can't power up the glider until I have thrown it, or my hand gets caught in the prop.

Seriously though. PLA is more than strong enough as long as it's printed in the right orientation and has a little extra meat where it matters. It's 50% stronger than ABS, as an example.
Mar 28, 2018, 01:49 PM
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jumo004's Avatar
Quote:
Originally Posted by henke
It's not that hard to get the basics.

I've been involved in fan development and snapped the following,

*Blade velocity changes with radius. So the tip travels faster, hence less pitch for the same work load. Center of the blade close to the hub is almost vertical as the travels speed is much lower then at the tip.

*Stators is also a part of the fan! you make a rotating vortex of air leaving the fan. The stators stops the rotation giving more thrust as they do it.

*Intake lip can do as much as 50% more, you want atleast the fans thickness in a stright infront of the blades and a nice bell mouth in. If that bellmouth is in front of the fan or the aircrafts inlet does not matter.

*Blade count has nothing to do with it! Its the combines chord of the blades. Example, you can have three larger blades or 11 smaller as long as the combined chord is the same. If a fan uses more power with more blades it's because you added combined chord, not because you added blades.

Wemotec as example, same diameter fan, different number of blades, same combined chord.

Thinking of it, it's all very obvious.


Thanks henke ! Good stuff, I'll give it a try !
Mar 28, 2018, 02:01 PM
Registered User
Be advised that printed ducted fan rotors are NOT strong enough for use in 120mm sizes even for low power applications(3000 watts). You are deluding yourself if you think they are. Cheap Chinese rotors of pure injection-molded thermoplastic are only a little stronger. Carbon fiber-weave molded rotors are strongest but have a very low bend modulus (brittle) and upon reaching ultimate load, they come apart explosively and do not tolerate even small, hard FOD.

After 30+ years of development, Fiberglass Reinforced Thermoplastic individual blades arranged around a two-piece, capturing hub is the safest system yet designed for high-power applications.

Keep in mind that high-blade-count fans have a lower efflux velocity and higher static thrust (higher climb rate). My racing jets use a seven blade rotor with a very high efflux velocity but climb more slowly on departure. At 200 mph they sound like a hair dryer on steroids....
Mar 28, 2018, 02:33 PM
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Lynxman's Avatar
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If possible I will test to destruction and actually find out . Please don't dismiss it out of prejudice agains 3D printed parts. It's possible to make strong parts, just not as thin as carbon parts. I'm here to actually find out what it can do, with safety precautions when I test at high power. Please don't assume I'm an idiot who is putting my eyeball next to the fan at 1+ kw. I hate it when a thread like this is derailed by safety trolling. If I make a jet out of it it will be within the limitations of the technology. For what it's worth I've been making propelers out of wood for over ten years, and have printed almost non stop since 2015, pushing the process further and further in mechanical engineering.

I understand that efflux may suffer if I only tune for thrust. I mentioned it early in the thread that I don't know what the efflux is. The efflux depends on the efficiency too, which is unknown. As long as I haven't measured the efflux for all we know it might be way better than expected, not worse as is assumed here. I only know what the pitch speed will be. With propellers the efflux is usually somewhere around 80% of the pitch speed. I believe it will be close to that with ducted fans as well.

Low blade count is out of the question. I hate screamers.
Mar 28, 2018, 02:50 PM
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Lynxman's Avatar
Thread OP
I found this. Here's how much a very basic fan design can take, in a weaker material than I use. 12 kW. Look at the ammeter as it accelerates:
Flying Like Iron Man Update: EDF EXPLOSION!!! (2 min 8 sec)
Mar 28, 2018, 03:41 PM
Registered User
Whoa there, no prejudice against printed parts, just saw a full-size automobile that was printed up. The technology is slowly making its way into full-size aviation as well. Your demonstrated familiarity with the technology denotes someone who's far and away from the level of idiocy. Launching your glider first and then throttling up is an indication that you are a cautious sort.

Been at this fan thing for a long time now. Some things work better than others for a given goal. Printed rotors have been thoroughly explored with currently available printable materials. Printed airframes tend to be heavier than other building techniques in terms of structural integrity - costlier too.

Experimentation is to be lauded, wherever it occurs.
Mar 28, 2018, 11:00 PM
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erh7771's Avatar
Quote:
Originally Posted by Lynxman
I found this. Here's how much a very basic fan design can take, in a weaker material than I use. 12 kW. Look at the ammeter as it accelerates:
https://youtu.be/4mYzpIjFKco
wow, looked like 200 amps !!

I didn't get the voltage though

Looks like ABS can take a beating


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