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Mar 26, 2018, 01:49 PM
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Quote:
Originally Posted by Lynxman
Here's a screenshot from 3D Studio Max 2018. The colored spirals are the pitch guide lines I use for the different positions along the blade. I am trying different blade shapes and pitch distributions.


Hi Lynxman, I really enjoy your posts.
By pitch distributions do you mean varying the pitch along the length of the blade or
are you using a constant pitch ?

Thanks
Last edited by jumo004; Mar 26, 2018 at 02:31 PM.
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Mar 26, 2018, 04:01 PM
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Varying pitch along the length of the blade. Most of the lift is generated at the tip of the blade.
Mar 26, 2018, 05:01 PM
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Quote:
Originally Posted by Fanflyer
Varying pitch along the length of the blade. Most of the lift is generated at the tip of the blade.
Is the difference in pitch measured in percentage from the root to the tip ?

ie. 300mm pitch at the root and 360mm pitch at the tip would equal a 20% difference ?

Thanks
Mar 27, 2018, 04:01 AM
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Yes, constant pitch along the blade will give a twisted blade with the same length per rotation at all points along the blade. Some of the "secrets" in EDF design may be a variation in blade pitch, or it may just be a gimmick.

The 300 mm pitch blade printed just about perfectly. It has about 300 mm along the whole blade. I tested it just now and it gives the best thrust to watt ratio so far, as expected. 3250 g thrust at 1500 W, even with this tiny motor which probably is inefficient at that power level. At 16200 rpm it should give a full throttle pitch speed of 292 km/h, which should be plenty to fly around. I'll try to print an even shallower fan later. With the new and more powerful 880 kv motor I should be getting a pitch speed of around 350-380 km/t, which is crazy.
Last edited by Lynxman; Mar 27, 2018 at 05:30 AM.
Mar 27, 2018, 10:32 AM
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Quote:
Originally Posted by Lynxman
Yes, constant pitch along the blade will give a twisted blade with the same length per rotation at all points along the blade. Some of the "secrets" in EDF design may be a variation in blade pitch, or it may just be a gimmick.

The 300 mm pitch blade printed just about perfectly. It has about 300 mm along the whole blade. I tested it just now and it gives the best thrust to watt ratio so far, as expected. 3250 g thrust at 1500 W, even with this tiny motor which probably is inefficient at that power level. At 16200 rpm it should give a full throttle pitch speed of 292 km/h, which should be plenty to fly around. I'll try to print an even shallower fan later. With the new and more powerful 880 kv motor I should be getting a pitch speed of around 350-380 km/t, which is crazy.


Hi Lynxman, a couple a years ago I started a thread on trying to 3D print 30mm (and 20mm) EDFs. I say trying because I didn't know where to start.
So I started first with an airfoil and then with pitch. I chose a Clark Y for an airfoil but was at a lose for pitch and didn't even know how
to set it up in cad. In my searching's I found a diagram showing a graphical method of drawing a constant pitch propeller so I tried it in
my cad program and have had good results from it.

I was wondering do you use a similar method to design your fan blades at a certain pitch ?

Thanks.
Mar 27, 2018, 10:44 AM
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I use a different method. I make a few spirals that go a full turn and are the same length as the pitch I want, with a diameter that corresponds to a certain point along the blade. Then I make a loft and create the shapes for the loft so that they intersect with the spirals. Right now I'm trying an even finer pitch of 260 mm and it's actually printing well.

As for the profile shape I didn't use a known profile. I just draw one that looks about right. At this tiny scale I doubt that the microscopic differences between known profiles will make a significant difference, especially since the trailing edge has to be flattened so that it can be printed from a bed. What I think matters is the thickness and overall form. I believe a thinner profile will be more efficient as long as it's stiff enough to not bend under load. I make the root profile slightly undercambered and the tip profile semi-symmetrical, which seems to work pretty well so far. I think I will try a fully undercambered profile later.
Mar 27, 2018, 11:02 AM
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Wow ! That's different. I have to study that one for awhile ...

Have you tried the 'sculptured' leading edge before and have you noticed a difference in performance ?
I only ask because I thought that at my 'nano' size I think that blade size (surface area) is 'King' ....... but
I'm going to give it a try anyways just to see.
Mar 27, 2018, 11:06 AM
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By sculptured do you mean wavy? I have tried different variations of wavyness to the leading edge, and I get about the same thrust to watt. I made one fan with an extreme leading edge wave that looks like a copy of the 737 MAX engine fan, and it was the worst performer so far. Attached a picture of it from my slicer.
Mar 27, 2018, 11:26 AM
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Yes wavy ... sorry.

I think it looks like it's the product of a lot of R&D and obviously works in real life but like you say
at our sizes something gets lost and the performance doesn't seem to scale down.

Thanks
Mar 27, 2018, 11:56 AM
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Yeah it's probably very good on the big fan.

I just tested the 260 mm pitch fan and it's not as good as the 300 mm fan. I've tested 260, 300, 360, 400 and 420. 300 mm pitch gives the best thrust to watt so far. 930 g @ 250 W and 3250 g @ 1500 W. Weird pitch numbers, I know, but it just happened. :P I don't think I will find a better fan unless I stumble on something out of the ordinary. I'll try undercambered blades next.
Mar 27, 2018, 12:15 PM
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Interesting pitch numbers.

With my nano 20mm fans I find 70mm pitch ( 420mm pitch scaled up to 120mm dia.) is about as high as I can go.
But then again I'm using only 5 blades compared to your 13.

Very Cool
Last edited by jumo004; Mar 27, 2018 at 12:22 PM. Reason: changed 11 to 13
Mar 27, 2018, 12:18 PM
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Undercambered fan.
Mar 27, 2018, 12:25 PM
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Very nice !

The test results should be interesting !
Mar 27, 2018, 01:12 PM
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My EDF printing shenanigans started when I made a new 70 mm fan for my Starmax F-5 a little while ago to replace the five blade screamer. It made me want to try a bigger high power fan.
Mar 27, 2018, 01:27 PM
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Just curious , how many stator blades are you using with your 120mm 13 blade fans ?

I've tested 3 and 4 blade stators and haven't found much of a difference between them.

I realize given the huge difference in size of our 2 fans that's there's probably no sense in comparing
but it interesting to talk with somebody with the same interests.

Thanks


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