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Nov 22, 2001, 10:35 AM
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JonJohnston's Avatar

Electric Ducted Fan Design

I would like to design my own fan 3.50" fan units for a 1/8th scale
Horten IX V3 <just received the plans last weekend>. Anyone have any information that would help me in starting this project on the right foot? I am a Meachanical Engineer so I know my way around formulas. I do happen to have copies of Robert Kress' Ducted fan design programs from 10-12 years ago. I do not have a copy of his EDF version. Thanks for the help!
Jon Johnston
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Nov 22, 2001, 11:08 AM
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Ed Waldrep's Avatar
Not to stiffle innovation, but do you know about the WeMotec line of electric ducted fans (EDFs)? They have several sizes, with rotors of diameters of 50mm, 69mm, 75mm, 89mm, 105mm, and 124mm. You can get some info on these fans at www.electricjetfactory.com. The 3.5" diameter you are looking for would be matched by the WeMotec Midi fan which has a rotor diameter or 89mm which is very close to 3.5 inches. People seem to really like this fan, it's got a fairly high quality construction.

Maybe you are looking to design a fan around a particular motor and RPM range and these wont fit the bill, but you'll probably find with research that these fans offer a wide range of capabilities. There are other 90 mm class fans out there, the Jepe and the Schubler from Europe for instance. All these are what I would call second generation fans. Earlier fans in WeMotec's range were based on the old Kress rotors with lots of pitch and thus needing very high torque motors. These newer designs have slightly less pitch which is more suitable for the high revving motors available. This is based on what I've read in electric magazines over the past several years. If I'm incorrect on some of this others will correct it.

Good luck, and keep us updated on your model's progress. You can post pictures directly into your posts, and pictures can be worth a lot in inspiration.
Nov 22, 2001, 08:51 PM
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JonJohnston's Avatar

Electric Ducted Fan Design

I have checked out the WeMoTec and Shubeler website. Those are options but I would really like to try my hand at my own design. Using some ofthe formulas in Andy Lennon's book I have come up with a weight of about 9 - 9.5 pounds. 1000 square inches of wing area with an 82.25 inch wingspan. I am planning on making this my winter project. I know as an engineer I should not reinvent the wheel, but...

I helped a friend in Floridia by the name of Lou Davila, about 11 years ago design a mini ducted fan, he did most of the design work, I did some test flying. The test plane was a semi-scale Heinkel He162. It flew well. It was powered by a Cox TD 020. It was a screamer. I still have a set of plans for the fan and the plane. Not on CAD, but if anyone is interested I will draw them up and post them as a dxf file.
Nov 22, 2001, 09:23 PM
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dave morris's Avatar
Hey I know lou, great guy, we fly at the same field RCACF. I saw the fan you are refering to, helped me with my own design of a small glow DF using a norvel .061 engine. Good luck on you design.

Nov 22, 2001, 09:42 PM
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JonJohnston's Avatar

Lou Davila

Dave, if you would email me at acmetooldesign@aol.com and I will give you my phone number to give to Lou. We were jut in the Orlando area on vacation about 3 weeks ago. I could not find lou in the phone book.
Nov 22, 2001, 10:41 PM
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Chad Sullivan's Avatar
Jon you should look in E.F.I issues running from July 1998 to Nov.1998. I have the Augest and September issues, and there are some very good articles written by Manfred Malten. If you dig formulas this is the good stuff. He also really gets into the construction. This stuff is not in layman terms. From what I've managed to figue it is possible to design an EDF unit to a motor and get better results then buying EDF units and trying to find the best combo of motor and cells. You can design to a specific altitude, motor efficencies, and cells counts. But to do so you got to be able to read the language. Chad
Nov 23, 2001, 04:40 PM
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Electric Ducted Fan Design


There are some constructiion atricles in the e-Zone archives you might find interesting. Also, you might read the many threads on the R/C Group Discussions, Electric Flight, Jets . . . .

Nov 25, 2001, 01:04 AM
Registered User
Hey Jon-

I second Ed Waldrep's advice : from one Engineer to another, this wheel already turns good, no reinventing necessary . So OK, you design a better mousetrap now you have to build it. Have injection molding equipment handy? CNC machining center available? All that work for what, 4 parts? (I'm just guessing at how many fans a Horten IX V3 uses).

Just the airframe alone sounds like a sufficiently ambitious project. I recommend working a couple of Saturdays to rationalize paying for the commercial fans and get on down the road!

My $ .02,

Steve Manganelli AKA Prof. Maneuver
Nov 25, 2001, 07:25 AM
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JonJohnston's Avatar

EDF Design

Well as a matter of fact I have a close friend here in Indiana that owns a machine shop. 5-axis CNC Lathe and mill. One of te best tool and die makers I ave ever had the pleasure of knowing. The response has been so great here and on two other forums that I think I will continue to press everyone for the help and information to design my own fans and in the meantime I will also ask everyone to suggest an 89mm to 95mm ducted fan that will put out about 15N with the use of 16 cells or less. I would much rather use less cells but this is a starting point. I will need two of them. Like I stated earlier the plane will weigh in at about 9-9.5 pounds.
Nov 26, 2001, 11:47 AM
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Ed Waldrep's Avatar
Well I just looked at the charts at the WeMotec site. The best fan for your application would seem to be the 90 mm midi fan. It's got more static thrust than the bit smaller 85mm HW620, which is has lower static thrust but higher exit velocity. I guess it depends on what you're aiming for and how big your intakes can be (cheater holes are to be avoided if possible).

On 16 cells an HP 220/30 A3P4S puts out 18.1 Newtons of thrust. Other motors can put out that thrust depending on which wind you chose. Most of the motors in the chart are more common in Europe and I'm not that familiar with the nomenclature. I tend to be able to speak Aveox and now my new favorite Kontronic. An Aveox 1409/2Y on 16 cells in the Midi fan may be a bit less. I'm sure there's some info on the board somewhere on what level of thrust that setup would put out, the search function may be able to find it.

A problem you can run into is trying to get lots of thrust out of lower cell counts. You can pull 50 amps out of RC2400s but flight time is short and heating becomes an issue. It's usually better to use a slightly higher wind motor and more cells of a smaller capacity (but at the size of plane you are planning 2400s should be fine depending onthe motor choice). Now that the CP1700s that are the same energy density as 2400s but lighter and smaller, the smaller cell/higher count makes more sense. I resisted this at first because I didn't have any of the old 1250SCRs. They were 2/3rds the weight and only half the capacity of the 2400s. But now that same size cell has 1700mah of capacity, and the new CP1300 size cell weighs a bit over an ounce. I love these new cells.

If you know a CNC master, by all means design a new fan. The more choices we have the better.
Nov 26, 2001, 07:00 PM
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JonJohnston's Avatar

EDF Design

I checked the page out. I am sure that someone <:-)> can do those numbers with less cells and the right motor. But that is a different discussion altogether. To get this part of the hobby into the hands of the other people we need to develope fans that produce a high thrust to cell count ratio. I know I am asking alot but I know it can be done, if we pull our heads together. I have the software, half a brain, and the motivation to do it. In the meantime however, I will use the Midi fan. Anyone have any installation drawings?
Nov 27, 2001, 04:29 AM
Ain't Dutch? Ain't Mutch!
Kimble_Schmitz's Avatar
If you realy want to use a low cell count wich is a good idea i think, becous the cp-1700 don't have the same density as the cp-2400 it's close tho, you might want to vieuw this baby;


Now you have a wel made fan and you only have to figure out the angle of the blades. Wich is what you have to do when u use a low cell count motor.

Nov 27, 2001, 07:43 AM
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JonJohnston's Avatar

EDF Design

I took a gander at the page. The fan looks interesting. Do you know of anywhere I can find some more information about this particular unit? I did a search and came up with only a few links that had little or no information on them.
Nov 28, 2001, 06:34 AM
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Doc Watson's Avatar

If you are stuck for thrust/watts in numbers then I have produced a series of graphs for all Wemotec fans at www.awatson1.fsnet.co.uk look under the 'fan data' section.

I have 3 HW620's and Plettenberg HP220/30 A4 S P3 brushless motors. Cell count is 24 x 2400 but I'm thinking of using 24 x CP1700 to save some weight (or use more cells for the same weight).

Keep us informed on your progress...

Nov 28, 2001, 11:11 PM
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gkamysz's Avatar
"To get this part of the hobby into the hands of the other people we need to develope fans that produce a high thrust to cell count ratio"

It has nothing to do with the number of cells. The whole problem is the weight of the battery pack needed to provide the amount of energy required for the power we want for the amount of time we want. NiMH is improving and may offer more runtime with good power in the years to come but lowering the cell count has nothing to do with anything. Ideally you would run a lower current higher voltage system to reduce losses in the wiring and ESC. These losses will be there regardless and will be lower when the system current is lower.

For a given runtime and power you can have any number of cells. The cell capacity required would be lower for higher cell count systems.

Making 15N of thrust with a 85-95mm fan will require 460-560 shaft watts. There is nothing you can do to lower this. Assume 85% eff for the motor and you need about 590W. 590W / (16 cells*1.1V) = 33.5A. 33.5A with RC2400 will give over 4 minutes of wide open runtime. This isn't all that unreasonable. But adding cells will only make it fly longer. 32 cells will weigh 66+ ounces or 40% of AUW. This would be very good if it can be attained.

This is the link for the Aeronaut fan info.

I would stay with Schubeler or Wemotec for best efficiency.


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