DualDesertEagle Show full post »
DualDesertEagle
Thanks for this whole lot of replies, I do have to say it intrigues me to try such a thing but what would it be good for if even to me the problems mentioned in alot of the answers make sense? I guess I'm gonna get back to an idea I had quite a while ago, which was swapping the simple 2-channel control board of an X-twin Turbo Express (throttle and differential thrust for turning only) for a fully grown receiver with 2 onboard servos and making the rear elevons controllable. My guess was that that would turn the cheap-ass kids' toy into a 3D-capable fun flyer. Unfortunately I somehow managed to kill the IC that controlled one of the servos and ended up putting the receiver with the remaining servo aswell as the 2 EDFs into my tiny hovercraft.
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Kiko12
It will work !! That is my new build, two EDP inline (not EDF) . I will make thrust measures soon.
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Kiko12
Remember when we talk about it ?
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Kiko12
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If you want to answer that question, why don't you take 2 EDF's, make a tube, install with tape and try. My guess is that the second set of fan blades would probably destroy itself due to stress and vibration.


Remember when we talk about it ?
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Wildthing
So who's to say the 2 have to be exactly the same, massive testing but different kv ratings plus different pitches for the props. Or same motors but say the front one has a 3 pitch and the back one has a 4.5 pitch, or visa versa?
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whatmovesyou
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Remember when we talk about it ?


Kiko, now you are peaking my interest. I explored setting one motor/prop so the radius of first prop/motor was in line with the second setup. Then moved it axially to see what happened.
I like to design and fly unique planes.
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Skydiver
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Skydiver,

Actually you can buy outrunners with counter rotating props. I just haven't seen them placed in an EDF housing/shroud.

How well these units work is anybodies guess but if you have $50 to throw away it would look cool on the shelf and might even make a good conversation piece

Initially,what I understood was two edf's , one in front of the other, and if they are counter rotating then the rear unit would be trying to change the direction of the airflow from the one in front. And the rear edf would be under a tremendous load trying to utilize the airflow from the front unit and changing airflow direction at the same time. I dunno, maybe the only way to prove this is to put these two counter rotating edfs in a common tube as suggested and crank them up and monitor volts and amps of both, one at a time then simultaneously. Then interchange the edfs and repeat, use a regulated adjustable power supply and two separate ammeters. I think the only way to keep from being totally baffled by all of the answers you'll get, is just to experiment on your own and post the results. Think out of the box..
The moral: On this forum there are no simple answers to simple questions.
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Nightswatch
Personally i think when dealing with electronics is its never the same draws are different etc having 2 of the same motors in line .
I am thinking more like ok have a 105 mm EDF infront of a 90 mm forcing air into it would it then become better efficient ?? or in time kill its life expectancy or burn it up by creating way to much heat .
Contrary to popular belief , by increasing the buffer zone in a ESC does not mean you cannot burn it up
Electricity no matter how you shake it is HEAT and yes Heat is Horse power to a point
If you think you got your flying under control, Your not going fast enough
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Flybyknight22
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Initially,what I understood was two edf's , one in front of the other, and if they are counter rotating then the rear unit would be trying to change the direction of the airflow from the one in front. And the rear edf would be under a tremendous load trying to utilize the airflow from the front unit and changing airflow direction at the same time. I dunno, maybe the only way to prove this is to put these two counter rotating edfs in a common tube as suggested and crank them up and monitor volts and amps of both, one at a time then simultaneously. I think the only way to keep from being totally baffled by all of the answers you'll get, is just to experiment on your own and post the results. Think out of the box..

Yup, I agree, build it, crank it up and see what happens.

Not all that happy with some of my EDFs using 4-blade impellers. What I usually do is immediately discard the 4-blade impeller and replace it with one that has more blades like to an 8, 10, or 12-blade impeller so I have several 4-blade impellers laying around collecting dust.

Tandem 4-blade might be an interesting test even though it won't counter rotate.

First test with standard single impeller for comparison and actually I already have that data from an Eflite EDF using a 4-blade impeller.

Now all I need to do is try the two identical 4-blade EDF impellers glued together with epoxy with 1st and 2nd impeller blades offset approximately 45 degrees from each other.

Doubling up two separate impellers on the same shaft should increase thrust but also current draw and should give different thrust/current readings from the standard 8,10 and 12-blade impellers whose data I already have from previous testing.

Probably need to Change the shaft length in the motor so the tandem impellers fit, then slap it all back in the EDF housing and give it a go.

Turnigy Thrust Stand will measure max thrust, current, watts etc.

The only thing the Thrust Stand won't do is put out the electrical fire from the excessive current draw.
And on the 8th day God said: "Go NAVY",.. and it was good! Pray like everything depends on God. Prepare like everything depends on you.
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Skydiver
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Personally i think when dealing with electronics is its never the same draws are different etc having 2 of the same motors in line .
I am thinking more like ok have a 105 mm EDF infront of a 90 mm forcing air into it would it then become better efficient ?? or in time kill its life expectancy or burn it up by creating way to much heat .
Contrary to popular belief , by increasing the buffer zone in a ESC does not mean you cannot burn it up
Electricity no matter how you shake it is HEAT and yes Heat is Horse power to a point

Yeah, like 746 watts is equal to 1 horsepower!
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Skydiver
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Yup, I agree, build it, crank it up and see what happens.

Not all that happy with some of my EDFs using 4-blade impellers. What I usually do is immediately discard the 4-blade impeller and replace it with one that has more blades like to an 8, 10, or 12-blade impeller so I have several 4-blade impellers laying around collecting dust.

Tandem 4-blade might be an interesting test even though it won't counter rotate.

First test with standard single impeller for comparison and actually I already have that data from an Eflite EDF using a 4-blade impeller.

Now all I need to do is try the two identical 4-blade EDF impellers glued together with epoxy with 1st and 2nd impeller blades offset approximately 45 degrees from each other.

Doubling up two separate impellers on the same shaft should increase thrust but also current draw and should give different thrust/current readings from the standard 8,10 and 12-blade impellers whose data I already have from previous testing.

Probably need to Change the shaft length in the motor so the tandem impellers fit, then slap it all back in the EDF housing and give it a go.

Turnigy Thrust Stand will measure max thrust, current, watts etc.

The only thing the Thrust Stand won't do is put out the electrical fire from the excessive current draw.

But still, the original post involved two edfs that rotated in opposite directions. A fair test of efficiency would be to put them in a common tube, with separate power supplies and meters, both voltage and amps. Then run each one individually and take readings. Finally, run them together at exactly the same voltage, and since they are of opposite rotations, you would be able to determine how they interact with each other. Why is everyone making a simple question so complicated to solve?? Finally switch edf positions and repeat the test!
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Flybyknight22
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But still, the original post involved two edfs that rotated in opposite directions. A fair test of efficiency would be to put them in a common tube, with separate power supplies and meters, both voltage and amps. Then run each one individually and take readings. Finally, run them together at exactly the same voltage, and since they are of opposite rotations, you would be able to determine how they interact with each other. Why is everyone making a simple question so complicated to solve?? Finally switch edf positions and repeat the test!

Here is a link to a contra rotating EDF that was posted on RC Groups some time ago but supposedly no longer available and didn't catch on because of cost?

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"Looks like the 55mm size one if still available. A little pricey but worth it since it seams to be the only one in existence.

Fan name- Φ55×H33 Outrunner Brushless Motor DuctedFan W/ Motor 2409H-7T
http://www.rchotdeals.com/Products/r...fans_home.html
And on the 8th day God said: "Go NAVY",.. and it was good! Pray like everything depends on God. Prepare like everything depends on you.
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Skydiver
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Here is a link to a contra rotating EDF that was posted on RC Groups some time ago but supposedly no longer available and didn't catch on because of cost?

Quote:

"Looks like the 55mm size one if still available. A little pricey but worth it since it seams to be the only one in existence.

Fan name- Φ55×H33 Outrunner Brushless Motor DuctedFan W/ Motor 2409H-7T
http://www.rchotdeals.com/Products/r...fans_home.html

It really sounded as if the original querant had the motors from an old Radio Shack twin edf airplane. I seem to remember seeing something of that sort in the store before they closed here in my area.
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Flybyknight22
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Thanks for this whole lot of replies, I do have to say it intrigues me to try such a thing but what would it be good for if even to me the problems mentioned in alot of the answers make sense? I guess I'm gonna get back to an idea I had quite a while ago, which was swapping the simple 2-channel control board of an X-twin Turbo Express (throttle and differential thrust for turning only) for a fully grown receiver with 2 onboard servos and making the rear elevons controllable. My guess was that that would turn the cheap-ass kids' toy into a 3D-capable fun flyer. Unfortunately I somehow managed to kill the IC that controlled one of the servos and ended up putting the receiver with the remaining servo aswell as the 2 EDFs into my tiny hovercraft.

Perhaps this is beyond the scope of the average RC Scratch builder but because of the success achieved in other real world application this is being seriously considered and experimented with.
IMG_3312.JPG 

https://www.researchgate.net/publication/281293346_Experimental_study_on_EDF_with_multistage_axial_compressor_for_electric_propulsion_of_UAV%27s
And on the 8th day God said: "Go NAVY",.. and it was good! Pray like everything depends on God. Prepare like everything depends on you.
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doccjohnny
99% of science is trial and error.. i came by this forum searching for this answer..obviously its not an everyday experiment.. then again small scale edf ares pretty new.. i looking for something bigger myself..
im guessing it will work.. a turbojet engine is just a series of overlapping turbo fans.
will it work well?? that depends on your combinations.. large in front or large in rear .. same size .. same direction or contrarotating.. your using twice the power so your doubling the air speed thru the fans.. so in theory you should get twice the thrust or more.. in reality you have losses..
science is the art of getting to theoretical values in reality..
build it and they will come.. i like the idea of sticking them in a tube and measuring the rear wind speeds.. seems simple enough to set up 100 different combinations at different lengths and different fans... it works for edp props so it should EVENTUALLY work for fans.. it may take a day or a decade to find out.. doc johnny
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