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Namwons · 10-03-2013, 12:15 AM

Hi, I joined this forum just because of all the hype of Phantoms ESC has generated. This has gotten my creative juices flowing too and see if I could possibly do a DIY. I would like to share what I have gained from reading studies and other forums. Thomas Knight electrofied a roots and Phantom electrofied a centrifugal but I am going to focus only on Axial Compressors, like in jet engines.

WARNING: Wall of Text.

First, I wanted to know, Why doesnt electric superchargers, the scam bilge blowers or ducted fan, not work? Then I wanted to know, How does a jet engine compressor section work and whats the difference? Heres what I found out.

Contrary to popular belief, dynamic compressors, ie centrifugal and axial, DONT try to stuff big air into smaller volume like a positive displacement type like roots or screws. They generate high VELOCITY (air flow), then CONVERT that air flow into PRESSURE by slowing it down with the venturi effect (DIVERGENT duct). Fast flow = low pressure, low flow = high pressure, just like an airplane's wing. Each blade in an axial flow compressor are actually wings that create high and low pressure differences (pressure ratio) depending on blade pitch and number of stages, usually about 1.2 PR per stage in a typical jet engine.

OK...so Why doesnt an EDF not create boost? Because it is only designed to create air flow, or velocity. There is nothing after the fan that converts that flow into pressure. The most any of these ducted fans can accomplish is to negate the vacuum created in the intake when your engine is in need of air, mostly at higher rpms. This DOES do something and its not entirely useless as it would be exactly like Phantom's drag reduction system, increasing throttle response, but not performance, and wasted electricity with no control. I would actually be interested in a cold air intake vs electric "supercharger/fan" test. I would actually put my bet that the electric fan would beat out the cold air intake, but thats just a guesstamate.

http://www.tppowerusa.com/edf-ducted.../tp-cnc-90-edf
(this is a new EDF thats all CNC which I found to be the best candidate to convert to a compressor due to being all metal with the tightest tolerances, .5mm rotor to housing, and powerful motors)

So next up, How does a jet engine (compressor stage) work and how does it convert that flow to pressure? The main difference is in the STATOR. Every STAGE of a jet has a ROTOR (fan) to acellerate the incoming air, and a STATOR, to slow that air down to create pressure. There are stators in EDF's, but they are more like air flow straighing vanes. An EDF would have to try and pressurize all volume of air from the fan to the valves to create pressure. In a jet, there are COUNTER ROTATING blades/wings in the stator instead of straight vanes, properly pitched to be balanced with the incoming velocity of the fan. Since the stators slow the air down to create pressure, to prevent stall, the air is pasted through smaller and smaller CONVERGENT DUCT. So, pressure in a jet compressor is created by the blades of the rotor and stator, and NOT stuffing more air in a smaller hole. Each stage in a typical jet compressor is good for about 1.2 PR, so for small boost applications, you would need a highly efficient single stage, or two stages.

[ame="http://en.wikipedia.org/wiki/Axial_compressor"]Axial compressor - Wikipedia, the free encyclopedia[/ame]

Now that we know how an actually axial flow compressor works, and why the regular EDF doesnt, how would we convert it into a compressor? A counter rotating stator ring/motor holder needs to be created to slow the velocity and create boost. So, the simplest way I could think of would be to CAD/Print a counter rotating stator ring to to slip over the motor inplace or behind the normal straight flow stator. Closest to the rotor (fan) would probably be most efficient. This would be considered a 1Motor/1Stage setup (or Vane Axial Fan for industrial fans). This would create more pressure than a standard EDF, but might not be enough for automotive use, as one stage doesnt produce a lot of pressure difference (PR), we would probably need two stages. Guess what...digging around, the RC aircraft scene has already modeled a 1Motor/2Stage "cold jet" compressor designed to run at 50k rpm Warhead 3545-1850kv motor. The motor could easily be swapped to a more powerful unit by designing a different mounting disk into the back of the compressor.

http://grabcad.com/library/two-stage...ric-ducted-fan (not sure if this is a ready to prototype design as its missing some screw threads but looks 95% complete. guy who designed this also use to work for General Electric turbos so im guessing he knows a thing or two about blade design)
[ame="http://www.youtube.com/watch?v=-2WPx6uCIGY"]http://www.youtube.com/watch?v=-2WPx6uCIGY[/ame] (front on, you can see that there are no air gaps which is ideal for holding back pressure, but you can still see that air can pass at an angle even if the blades are stationary)

Of course if we need more power, and/or more speed, I thought why not use two motors? Have one motor spinning the rotor as normal, and the other spinning the otherwise stationary stators (already counter rotating blades) in the opposite direction. So in a design like this, you would have two motors spinning two seperate rotors (no stators as the stator has now become a rotor) in opposite directions, in a push/pull manner (first rotor pushes air into second, counter rotating rotor). This I would consider a 2Motor/1Stage setup. What are benefits of this setup? Relative speed between the two rotors compared to the rotor/stator is twice as fast. In dynamic compressors, just like centrifugals, the faster you spin it, the more efficient it becomes and the more pressure difference you can create (given the same power). Another benefit is velocity drop is now negated due to the stator, which would normally slow the air, has now been turned into a rotor to increase velocity again. Now, since the second rotor now increases velocity back up, we could also now put a stator ring behind the second rotor to create a second compressor stage in a R/R/S config. First stage would be the high efficiency/high flow rotor to rotor stage, and second would be second rotor to stator like a normal stage. I call this a 2Motor/2Stage setup. This 2Motor/2Stage setup is getting pretty complicated compare to a regular 1Motor/1Stage, but we can get more complex. Instead of stationary stator rings, we can replace those with variable pitch guide vanes in the intake and exaust to direct and control flow into and out of the compressor. So the ultimate setup I have come up with is a 2Motor/2Stage w/vVanes to control BOTH flow and pressure. If this kind of compressor could be designed (I dont think its impossible) you could essentially get rid of the throttle body all together.

For a 2Motor setup I would start with something like this:

http://rc-castle.com/shop/product_in...oducts_id=3339
flip one set of blades to be a pusher, and set it up inline nose to nose with blades closest to each other for max efficiency. You would end up with something like this 2Motor/1Stage:

then ultimately this 2Motor/2Stages with Variable Guide Vanes:

All rings (Variable Vanes=green; Intake rotor=blue; Compression rotor=orange; Compression stator= yellow) modular for ease of install and custom ring configurations from 1Motor/1Stage up to 2Motor/2Stages.

Well thats what I have gathered from reading various studies on counter rotating ducted fans and axial flow compressors. Dont throw out the ducted fan idea just because no one has made it work yet. Motor power and battery capacity (and super capacitors) have matured enough in the past few years that it is now possible to electrify a compressor (lower pressures and duty cycles) as Phantom has proven.

...I read both the this thread and the Phantom thread fully...it was tedious but informative.

10-03-2013, 12:15 AM	#381
Namwons Junior Member Join Date: Sep 2013 Drives: 91' Honda Civic; 91' 240sx; Location: WI Posts: 7 Thanks: 0 Thanked 5 Times in 5 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	EDF's Why they dont work, and how they could work. (Electric Ducted Fans) Hi, I joined this forum just because of all the hype of Phantoms ESC has generated. This has gotten my creative juices flowing too and see if I could possibly do a DIY. I would like to share what I have gained from reading studies and other forums. Thomas Knight electrofied a roots and Phantom electrofied a centrifugal but I am going to focus only on Axial Compressors, like in jet engines. WARNING: Wall of Text. First, I wanted to know, Why doesnt electric superchargers, the scam bilge blowers or ducted fan, not work? Then I wanted to know, How does a jet engine compressor section work and whats the difference? Heres what I found out. Contrary to popular belief, dynamic compressors, ie centrifugal and axial, DONT try to stuff big air into smaller volume like a positive displacement type like roots or screws. They generate high VELOCITY (air flow), then CONVERT that air flow into PRESSURE by slowing it down with the venturi effect (DIVERGENT duct). Fast flow = low pressure, low flow = high pressure, just like an airplane's wing. Each blade in an axial flow compressor are actually wings that create high and low pressure differences (pressure ratio) depending on blade pitch and number of stages, usually about 1.2 PR per stage in a typical jet engine. OK...so Why doesnt an EDF not create boost? Because it is only designed to create air flow, or velocity. There is nothing after the fan that converts that flow into pressure. The most any of these ducted fans can accomplish is to negate the vacuum created in the intake when your engine is in need of air, mostly at higher rpms. This DOES do something and its not entirely useless as it would be exactly like Phantom's drag reduction system, increasing throttle response, but not performance, and wasted electricity with no control. I would actually be interested in a cold air intake vs electric "supercharger/fan" test. I would actually put my bet that the electric fan would beat out the cold air intake, but thats just a guesstamate. http://www.tppowerusa.com/edf-ducted.../tp-cnc-90-edf (this is a new EDF thats all CNC which I found to be the best candidate to convert to a compressor due to being all metal with the tightest tolerances, .5mm rotor to housing, and powerful motors) So next up, How does a jet engine (compressor stage) work and how does it convert that flow to pressure? The main difference is in the STATOR. Every STAGE of a jet has a ROTOR (fan) to acellerate the incoming air, and a STATOR, to slow that air down to create pressure. There are stators in EDF's, but they are more like air flow straighing vanes. An EDF would have to try and pressurize all volume of air from the fan to the valves to create pressure. In a jet, there are COUNTER ROTATING blades/wings in the stator instead of straight vanes, properly pitched to be balanced with the incoming velocity of the fan. Since the stators slow the air down to create pressure, to prevent stall, the air is pasted through smaller and smaller CONVERGENT DUCT. So, pressure in a jet compressor is created by the blades of the rotor and stator, and NOT stuffing more air in a smaller hole. Each stage in a typical jet compressor is good for about 1.2 PR, so for small boost applications, you would need a highly efficient single stage, or two stages. [ame="http://en.wikipedia.org/wiki/Axial_compressor"]Axial compressor - Wikipedia, the free encyclopedia[/ame] Now that we know how an actually axial flow compressor works, and why the regular EDF doesnt, how would we convert it into a compressor? A counter rotating stator ring/motor holder needs to be created to slow the velocity and create boost. So, the simplest way I could think of would be to CAD/Print a counter rotating stator ring to to slip over the motor inplace or behind the normal straight flow stator. Closest to the rotor (fan) would probably be most efficient. This would be considered a 1Motor/1Stage setup (or Vane Axial Fan for industrial fans). This would create more pressure than a standard EDF, but might not be enough for automotive use, as one stage doesnt produce a lot of pressure difference (PR), we would probably need two stages. Guess what...digging around, the RC aircraft scene has already modeled a 1Motor/2Stage "cold jet" compressor designed to run at 50k rpm Warhead 3545-1850kv motor. The motor could easily be swapped to a more powerful unit by designing a different mounting disk into the back of the compressor. http://grabcad.com/library/two-stage...ric-ducted-fan (not sure if this is a ready to prototype design as its missing some screw threads but looks 95% complete. guy who designed this also use to work for General Electric turbos so im guessing he knows a thing or two about blade design) [ame="http://www.youtube.com/watch?v=-2WPx6uCIGY"]http://www.youtube.com/watch?v=-2WPx6uCIGY[/ame] (front on, you can see that there are no air gaps which is ideal for holding back pressure, but you can still see that air can pass at an angle even if the blades are stationary) Of course if we need more power, and/or more speed, I thought why not use two motors? Have one motor spinning the rotor as normal, and the other spinning the otherwise stationary stators (already counter rotating blades) in the opposite direction. So in a design like this, you would have two motors spinning two seperate rotors (no stators as the stator has now become a rotor) in opposite directions, in a push/pull manner (first rotor pushes air into second, counter rotating rotor). This I would consider a 2Motor/1Stage setup. What are benefits of this setup? Relative speed between the two rotors compared to the rotor/stator is twice as fast. In dynamic compressors, just like centrifugals, the faster you spin it, the more efficient it becomes and the more pressure difference you can create (given the same power). Another benefit is velocity drop is now negated due to the stator, which would normally slow the air, has now been turned into a rotor to increase velocity again. Now, since the second rotor now increases velocity back up, we could also now put a stator ring behind the second rotor to create a second compressor stage in a R/R/S config. First stage would be the high efficiency/high flow rotor to rotor stage, and second would be second rotor to stator like a normal stage. I call this a 2Motor/2Stage setup. This 2Motor/2Stage setup is getting pretty complicated compare to a regular 1Motor/1Stage, but we can get more complex. Instead of stationary stator rings, we can replace those with variable pitch guide vanes in the intake and exaust to direct and control flow into and out of the compressor. So the ultimate setup I have come up with is a 2Motor/2Stage w/vVanes to control BOTH flow and pressure. If this kind of compressor could be designed (I dont think its impossible) you could essentially get rid of the throttle body all together. For a 2Motor setup I would start with something like this: http://rc-castle.com/shop/product_in...oducts_id=3339 flip one set of blades to be a pusher, and set it up inline nose to nose with blades closest to each other for max efficiency. You would end up with something like this 2Motor/1Stage: then ultimately this 2Motor/2Stages with Variable Guide Vanes: All rings (Variable Vanes=green; Intake rotor=blue; Compression rotor=orange; Compression stator= yellow) modular for ease of install and custom ring configurations from 1Motor/1Stage up to 2Motor/2Stages. Well thats what I have gathered from reading various studies on counter rotating ducted fans and axial flow compressors. Dont throw out the ducted fan idea just because no one has made it work yet. Motor power and battery capacity (and super capacitors) have matured enough in the past few years that it is now possible to electrify a compressor (lower pressures and duty cycles) as Phantom has proven. ...I read both the this thread and the Phantom thread fully...it was tedious but informative. Last edited by Namwons; 10-03-2013 at 02:17 AM.