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Electric Ducted Fan Jets Discuss electric ducted fan jets here including setup tips, power systems, flying techniques, etc.

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Old 12-24-2010, 12:36 AM   #1
quorneng
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Default A low power ducted fan

Compared to a light weight park flyer most ducted fans fly fast & use a lot of power to do it so I asked myself a question. Is it possible to build a lightweight park flyer with a fan?
The emphasis would be a shrouded fan rather than ducting to emulate a turbo jet. So a bit of experimenting.
First the fan. 7 blade 76mm diam fixed directly to the bell of a 2812 1600kV out runner.
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With a simple shroud on a test stand.
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On a 3s LiPo it produces 6oz (170g) thrust drawing 13A which should fly a 40" span 12oz plane ok.
This was the sort of thing I had in mind.
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Keeping weight to a minimum a test fan shroud made of a paper/depron/paper sandwich. It weighs 0.14oz (4g)
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Of course this may not work at all!


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Old 12-24-2010, 10:30 AM   #2
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Is that a CPU cooling fan that you've modified? I'm really not sure for how long that will cope with the strain of high speed use... Still, only one way to find out!

Your design strikes me as awefully similar to the real full size plane, the Edgely Optica. I reakon you could make a pretty nice scale model of the full size with a little work.

EDIT: And seeing as performance will almost certainly be below what a prop could provide, scale appearence is really the only practical application of this. That, and the fun of seeing whether it will work or not!


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Old 12-24-2010, 06:10 PM   #3
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Default Edgley Optica

What is your bill of material (BoM) AUW?

Believe a set of Edgley Optica plans~multiple views are available for a basis of design...which I believe to be a ducted prop, not
a ducted fan blade. Using a ducted prop will simplify construction as it affords less cost and more internal room than helix blades.
There is a diameter to duct length ratio providing greater thrust...copying the multple view spec should accomplish what's desired.


ENGINE1 x Avco Lycoming IO-360 flat-four piston engine driving a ducted fan, 149kW WEIGHTS Take-off weight1236 kg2725 lb Empty weight850 kg1874 lb DIMENSIONS Wingspan11.99 m39 ft 4 in Length8.15 m27 ft 9 in Height2.31 m8 ft 7 in Wing area15.84 m2170.50 sq ft

Plans available from MODEL AVIATION June 2000 issue plan#890 Construction pictures


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Old 12-24-2010, 08:11 PM   #4
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Default

It is indeed a PC case fan. They are remarkably well balanced and it certainly runs happily up to about 12000 rpm.
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
My design is very loosely based on the Optica simply because it is a good practical layout for a fan. When does a prop become fan? The Optica had a 5 blades.
My Ductfan park flyer will be 36" span and weigh no more than 12oz. It is intended to explore the feasibility of the power system and layout.
I have got this far.
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The ailerons will be cut out and the servos, radio and motor added before the top skin goes on.


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Old 12-24-2010, 09:24 PM   #5
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Default When Does A Prop Become A Fan?

When does a prop become fan? The Optica had 5 blades. My Ductfan park flyer will be 36" span
and weigh no more than 12oz. It is intended to explore the feasibility of the power system and
layout. I have got this far. Attachment 140939 The ailerons will be cut out and the servos,
radio and motor added before the top skin goes on.[/QUOTE]

The depth of the root from leading to trailing edge and helix are what I'd consider the point where
a prop and fan blade are differentiated.

I am curious how you plan to construct this and have it weigh no more than 12 ounces when lipo
is going to rapidly accumulate mass without so much as an airframe and onboard systems.

No intention to boo-hoo...simply pointing our sustained flight is what we all look in these things,
not a simple loft across an indoor basket ball court.

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Old 12-24-2010, 11:23 PM   #6
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I think 'fan' and 'prop' are really just semantics.
  • By definition a fan is a device to move air
  • By definition a propeller is a device which reacts with air (or water) to create forward thrust.
In reality they are both the same thing because you cant create thrust without moving air and vice-versa.

Anyway... your homebrew fan looks like it's very inefficient in terms of how much thrust you are getting for the power consumed. A commercial ducted fan would get about twice the thrust for the same power and a normal prop would be at least three times more thrust.

I think your fan is losing out at least in part because you don't have any stators. Stators are the vanes that you see on all commercial ducted fans, usually mounted just behind the fan itself. They are shaped and angled to convert the swirling air coming off the fan into additional forward thrust. They also serve the purpose of holding the fan and motor central in the shroud.

Generally even the best ducted fans are less efficient in terms of static thrust than ordinary props; this is mainly because for a given input power they are usually smaller in diameter than props. Prop/fan efficiency is closely related to diameter, bigger diameter is more efficient. Small diameter ducted fans will always tend to be less efficient than props given the same input power.

Steve
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Old 12-25-2010, 01:43 AM   #7
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I don't see why it wouldn't work. So then what is the point of ducted fans in the first place if they are so inefficient? Do they just produce more thrust for high speeds than a prop would or what? If it's such a big deal why don't they just use little propellors in place of fans? Seems to me that there has got to be a better way here... perhaps I could make some money on a new electric jet system.

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Old 12-25-2010, 02:04 AM   #8
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Because, a ducted jet looks more scale and has the appeal of more closely replicating a true turbine (no external blades). In fact, most modern jet engines are more similar to ducted fans than turbojet engines are... At least, the high-bypass turbofans used in airliners are. They essentially use a small turbine engine to drive a large ducted fan... most of the air entering a modern airliner engine does not burn with fuel or go through the combustion chamber at all...

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Old 12-25-2010, 09:30 AM   #9
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Originally Posted by skyman View Post
I don't see why it wouldn't work. So then what is the point of ducted fans in the first place if they are so inefficient? Do they just produce more thrust for high speeds than a prop would or what? If it's such a big deal why don't they just use little propellors in place of fans? Seems to me that there has got to be a better way here... perhaps I could make some money on a new electric jet system.
I never implied that it "wouldn't work".. just that it will be inefficient.
As insomniac say: The main reason people use ducted fans is because they want the plane to look like a jet and that means not have an external prop, so the fan/prop has to fit inside the fuselage. In order to fit inside the fuselage fan or prop diameter must be small. A ducted fan is the best way of getting a lot of power into a small diameter, it might not be efficient but if you are stuck with a small diameter then it's the best you can do other then by having a 'proper' turbojet.
Ducted fans do start to work better and their efficiency increases at higher speed, but they will never match a prop for efficiency unless their diameter is similar to the prop.

So 'yes' there is a better way to do it if you want efficiency; just use a large diameter prop.. but that spoils the look of your jet model. For model airplanes efficiency is not the only consideration, In fact for scale/fun models it's hardly any consideration at all.

The ducted prop on the real Optica is a bit different.. It is not 'hidden' inside the fuselage and it's probably close to the diameter of a normal prop, so it's efficiency might be quite good. They probably went with a ducted system to prevent the prop striking the ground and because the duct can form part of the plane's structure.

Steve
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Old 12-25-2010, 10:44 AM   #10
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Flite-Metal
In answer to your question I am fairly confident it will come out at no more than 12oz.
Using a 1500mAh 3s LiPo this 40" weighs just 10oz all up.
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Yes the fan, duct and motor weighs 3/4oz more but at 13A it too only needs a 1500mAh and the rest of the structure should be about the same so 12oz is quite possible.
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Old 12-25-2010, 06:04 PM   #11
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Somehow this thread seems to be more and more investigative DIY. Sustained flight being the difference more or less. Trying to
use a PC cooling fan aka Boxer Fan blade unit will be a greater disappointment than purchasing a cheap edf.

The shallow pitch of the PC fan...yields less than exciting results. Its either high pitch for greater volume per minute or diameter
to increase FSA and proportional 25% of a blade responsible for most of the bite.

The greatest effeciency so far has been witnessed with helix blades, helix stator mounts and stator sets...by Stu Maxwell. The
magic will occur when someone invests in high pitched smaller diameter helix blade sets driven by the newer motors. This will
permit us to utilize many more existing fiber glass fuselages originally created for recip ducted fans.

Nothing wrong with DIY and the like... Things are well beyond that point today for not any real $ differential to traditional r/c
modeling.

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Old 12-25-2010, 08:07 PM   #12
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I know you didn't NJ, I was just stating what I thought about the project. I was thinking last night about the possibility of a gas/electric jet hybrid system. You have a battery, and a tank of water on the plane. The battery sends an electric shock to the water making hydrogen. The the hydrogen is then ignited and shot out the ducts by heat, the byproduct of the reaction. I know it sounds far fetched, but there could be some potential here.

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Old 12-25-2010, 08:41 PM   #13
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Originally Posted by skyman View Post
I know you didn't NJ, I was just stating what I thought about the project. I was thinking last night about the possibility of a gas/electric jet hybrid system. You have a battery, and a tank of water on the plane. The battery sends an electric shock to the water making hydrogen. The the hydrogen is then ignited and shot out the ducts by heat, the byproduct of the reaction. I know it sounds far fetched, but there could be some potential here.
You have been drawn in by the water power car 'HHO' nonsense.. it's a total scam.

The first law of thermodynamics says you can't get out more energy than you put in. The energy that you get when you burn the hydrogen will be no more (in practice actually much less) than the electrical power you supply to the water from the battery to make the hydrogen. Add to that the fact that any form of combustion engine that burn hydrogen will be much less efficient than an electric motor (about 25% vs 80+%) and you should see that you would be MUCH better just using the battery to drive an electric motor.

On top of that for a airplane application you have all the added weight of the water and the hydrogen engine.

Basically it's a non starter, just like the water power car scam. I'm afraid there is no potential in the idea whatsoever.

sorry....

Steve

Edit.. We have gone rather badly off topic so probably best to take this discussion elsewhere if you want to continue it.
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Old 12-26-2010, 12:59 AM   #14
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Flightmetal
I think you will find that my "home made" fan unit is not so far off the thrust to watt ratio of commercial units. It just does it a much lower power.

What I wanted to explore was the area between a commercial fan unit and a prop in a lightweight park flyer.

We shall see.
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Old 12-26-2010, 01:52 AM   #15
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I can't help agreeing that a commercial ducted fan unit will give better results... However, I really want to see if you can get this off the ground with a modified cooling fan. Go for it! It's obvious this model isn't going to be the most efficiently or well designed plane out there, but at least it's interesting.

Skyman, that wouldn't be practical for a few reasons... Firstly, as Jetplaneflyer already pointed out, you are only going to lose energy by having the electrolysis rig on the plane. Electrolysis is horribly inefficient, and water is not an energy source so you're just sacrificing energy in the conversion from electrical to chemical energy. Secondly, the size of the electrolysis rig in order to feed a model sized engine of any sort is going to be absurd... These things really don't produce an awful lot of hydrogen unless they're huge.

And JetPlaneFlyer, I'm not sure he was suggesting that the water would act as a power source (unlike the hundreds of HHO scammers). I think what he was getting at was to use the battery as the only source of energy, but use the electrolysis rig as a way of making the system more 'jet' like, by using ignited fuel to propel the model foward.

At any rate, if you want to experiment with hydrogen powered models, you'd be much better off producing the hydrogen on the ground and simply filling a tank on the plane.

And now I'll try and stay on topic.

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Old 12-26-2010, 09:23 AM   #16
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Originally Posted by quorneng View Post
Flightmetal
I think you will find that my "home made" fan unit is not so far off the thrust to watt ratio of commercial units. It just does it a much lower power.
I think you might find that's not actually the case.. no fault of what you have done in the build, but without stators and suiotable blade design you are always going to be struggling to get any where near a unit thats designed for the job.

If we take a cheap and cheerful GWS 64mm an unit as an example..

GWS EDF-64 fitted with a GWS GWBLM005A brushless motor. This fan draws 10.8A on 3 cells (11.1V), which is 2.2A less than your unit is pulling an a similar battery. The GWS fan gives 301g of thrust
http://www.gwsus.com/english/product...stem/edf64.htm

This shouldn't stop it being a interesting and fun project but a modified PC cooling fan isn't ever going to work as well as a specially designed EDF unit.

Steve
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Old 12-26-2010, 12:22 PM   #17
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Steve
If I read the tables correctly the EDF-64 itself weighs some 67g then the motor adds another 57. My motor, fan and duct only weighs 57g.
Its aerodynamics may not be as good but its thrust to weight ratio is about the same.
The aerodynamics of a slow park flyer are pretty poor anyway so weight tends to be the dominant factor hence my lightweight construction.
Some more progress.
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The booms fixed and the ailerons cut out and top skins added.


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Old 12-26-2010, 12:53 PM   #18
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Still, the lack of stators HAS to reduce efficiency while not decreasing weight an awful lot. The build looks nice, but what are you using for tail booms? It looks almost like brass tubing, but surely that's not the case.

A crashed airplane is like a jigsaw puzzle...
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Old 12-26-2010, 04:46 PM   #19
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They are thin wall glass fibre being the 3rd section of a 6 section 1.8m fishing pole bought in a 1 shop!
Maybe not quite as light as carbon but nicely tapered and ever so cheap.
I have used the slightly bigger diam first and second sections in other planes already so technically they cost 33p!

With such low air velocity the effects of drag are significant. At some point the benefit of stators is lost against the drag they produce.
Obviously an area for later experiment.

The build is a rather more conventional at the moment.
Fitting the radio
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and aileron servos.
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Next bit is harder - mounting the motor.


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Old 12-26-2010, 05:30 PM   #20
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Originally Posted by quorneng View Post
Steve
If I read the tables correctly the EDF-64 itself weighs some 67g then the motor adds another 57. My motor, fan and duct only weighs 57g.
No, they are a lot lighter than that. The motor is about 57g but the fan unit is only around 25g. I don't have a 64mm GWS unit but I do have a 50mm. For the 50mm unit the case and rotor, without motor weighs 12g, with 12mm brushless inrunner motor ready to run it's 30g. The 50mm fan with the brushless conversion will give 200g thrust, but does run hot.

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Old 12-27-2010, 01:17 AM   #21
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Default nothing wrong with trial and error

Most of my planes are experimental, as that is where my interest lies. When I was a kid I built a ducted fan Mig 15 using a cox 049 glo motor with an integral tank. The impeller ( well, that was what it was supposed to look like) was made from a design out of a much loved aeromodelling book that I sadly no longer have. A piece of sheet metal cut out round and then cut towards the hub, which had a shaft diameter hole drilled in it. A number of cuts with a hacksaw to make the seperate blades, and these strips were then twisted to the same angle and bolted to the motor. The starter spring was modded slightly to engage the blades. Twisting the blades with pliers varied the pitch. Still awkward to start, but it flew successfully as a free flight plane, slowly and predictably. That little motor could not compare to the output of a modern brushless in terms rpm, and the "fan' vibrated horribly, but the very light weight ( stick and tissue) construction was the key to its success. Fast forward to 3 years back and I experimented with about 5 hairdryer and pc fans. One worked, the others just did not have the grunt, or had too much vibration, or spun off the shaft mount. Tried internal and external ducting and nacelles, homemade variable thrust nozzles, and all types of motor/esc/battery combo's. The pc fan from an ex games computer was successful, but primarily because it was married to an ultra light weight glider that was very efficient but just as fragile. Broke something on 3 successive flights, and was at the total mercy of the wind. Had an enormous amount of fun interspersed with many failures and dead end designs. So go ahead with this plane of yours, and the best of luck
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Old 12-28-2010, 02:08 PM   #22
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Originally Posted by quorneng View Post
Flite-Metal
In answer to your question I am fairly confident it will come out at no more than 12oz.
Using a 1500mAh 3s LiPo this 40" weighs just 10oz all up.
Attachment 140957
Yes the fan, duct and motor weighs 3/4oz more but at 13A it too only needs a 1500mAh and the rest of the structure should be about the same so 12oz is quite possible.
Depron is wonderful stuff.
Guorneng I admire your desire for a DIY EDF but... a commercial EDF like
my GWS 55 mm clone EDF running on 3.2KV walkera motor consumed 12-13 amps can easily haul a 350grams model almost vertically up. I am not sure if your DIY EDF can achieve the same level of a efficiencies. Moreover, the clone EDF cost less than USD5.00. so am not sure if you are taking the right route ?

All the best.
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Old 12-28-2010, 02:28 PM   #23
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I am a little surprised at the amount of negativity here.

The guy is having fun with a project.

Even if it doesn't work, he's likely to enjoy the process.

Self proclaimed dictator of the Flite Test fan club.
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Old 12-28-2010, 02:56 PM   #24
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Originally Posted by FlyingMonkey View Post
I am a little surprised at the amount of negativity here.
Not meant to be negative, just relaying factual information according to the facts as I understand them based on my own knowledge and experience and that of others.

Totally agree that as long as it's fun then go for it.... Fun is what the hobby is about at the end of the day.

Steve
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Old 12-28-2010, 06:12 PM   #25
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I would not claim anything for my set up other than it is cheap!
All the bits are about the cheapest you can buy. The whole thing, motor, radio, ESC, battery, servos, glue and Depron (but not the TX) has cost not much over 20 ($30) and of course quite a lot of time but that is half the fun.
If it flies reasonably I shall be satisfied.
The first test of the fan and shroud mounted in the airframe.
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
The elevator servo mounted in the port fin.
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Not particularly elegant but admirably simple.
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The nose will be completed (along with the final battery position) once the tail assembly is complete.


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