chris398mx
Master member
I sent you the stls
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F18 with twin EDF/BDF Options
- Thread starter Splinter189
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Guy S.
Well-known member
How is the power comparison between similar size BDF or EDF. I’m having a hard time wrapping my head around this. If I can squeeze a 3” (76.2mm) BDF in a plane that is designed for a 70mm can I get acceptable power? I just ask because I can run a 3” 3052 with a 1408, but my 50mm edf is way bigger. Thanks,
perhapsleiana
Elite member
Gremlin 1106 on a 2" 4-blade prop, running on 4S. Mount it on aluminum fins. It spins up to 70k rpm and screams, generating about half a pound of thrust. But note that the motor gets hot, so it has to be mounted on steel screws to keep the printed spider mount from deforming. Someone with more experience could probably get more thrust out of it by redesigning the housing- I used a skinny seltzer can. Just note that you have to have a really fast ESC- BLHeli32 is pretty much required. I also designed an 1106 spider mount that gets folded from aluminum sheet, but that's designed for the seltzer can. Hopefully it provides some inspiration though. Here's a link to my Fusion 360 design for the 1106 EDF-ish-thing. https://a360.co/33ZVGYb I currently don't have access to the desktop program though, since it's not compatible with my Windows Insider build.
Be careful with this- at these RPMs, failures are almost always highly destructive. Do not let gravel or sand get in your intakes, I learned with an early iteration that the pebbles will go right through the can.
The basic concept behind the BDF physics-wise is to reduce the power output and increase the efficiency at the speeds we fly. If you're going 250 mph, then a real EDF would be more efficient. But we aren't. So the thrust pressure (ounces per sq. in. of prop disc area) is lower, increasing the effective efficiency, and the blade count is also lower, increasing the efficiency. Bigger prop with fewer blades generally means higher efficiency but lower airflow speed.
perhapsleiana
Elite member
Onshape isn't so bad at sheet metal. Much more intuitive than Fusion 360. Not perfect, but still.
Here's a technical drawing for an aluminum 3" spider mount- no fancy sheet metal tools needed, just a printer, some adhesive, a drill, a center punch/awl, a scroll saw (or tin snips and a file works too!), and two pairs of pliers. This should allow the motor to get hotter than a printed BDF would, and improve motor cooling drastically. So much that I recommend thermal paste between the motor and the mount. Keeps temps nice and comfy. For opposite rotation, make your bends the opposite direction.
The shroud can be 3D printed, or even better, made of soda can metal. Makes me wonder if there are 3" soda cans, maybe the big Monster Energy cans with the screw tops? Not sure. But it should be easy to find out once the pandemic backs down some.
Here's a technical drawing for an aluminum 3" spider mount- no fancy sheet metal tools needed, just a printer, some adhesive, a drill, a center punch/awl, a scroll saw (or tin snips and a file works too!), and two pairs of pliers. This should allow the motor to get hotter than a printed BDF would, and improve motor cooling drastically. So much that I recommend thermal paste between the motor and the mount. Keeps temps nice and comfy. For opposite rotation, make your bends the opposite direction.
The shroud can be 3D printed, or even better, made of soda can metal. Makes me wonder if there are 3" soda cans, maybe the big Monster Energy cans with the screw tops? Not sure. But it should be easy to find out once the pandemic backs down some.
perhapsleiana
Elite member
Unfortunately it's not that simple.
perhapsleiana
Elite member
As for a metal spider BDF (no I'm not gonna call that a CDF, Ben deserves it), here's something I drew up: https://cad.onshape.com/documents/2735a66ca6aa33bdd1720241/w/c9ea206465f1f53a3ed92655/e/1de7a7f971999fe63440beb4
Edit: I drew up a 4" version, a full analogue to the flagship BDF: https://cad.onshape.com/documents/a...d8a1c4bf45d4d4e4ad/e/034b5cff6a3a1faf1c1d8c20
Edit: I drew up a 4" version, a full analogue to the flagship BDF: https://cad.onshape.com/documents/a...d8a1c4bf45d4d4e4ad/e/034b5cff6a3a1faf1c1d8c20
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perhapsleiana
Elite member
Yeah EDFs have a much higher thrust pressure, that's why they're so inefficient at low speeds.
Leaded50,
Would you be able to weigh your Ducted Fan and compare it to the 2 EDF's for us?
Thanks,
Lane
perhapsleiana
Elite member
It’s my ducted fan, and it weighs under 2 ounces.
perhapsleiana
Elite member
yeah, my little can fan wasn't too well designed. It was more an exercise in high RPMs.
leaded50
Legendary member
yeahh, i also see most of high effency 1106 motors at approx 6000 Kv, by a 2" propeller gives approx 181g thrust ast 7.8V, (64W)
3" propeller , 3s approx 244g thrust, ( 145w) - as whats given on specs on a motor found. Then, at 4s if similar, it should given a better thrust, even without the BDF part.
3" propeller , 3s approx 244g thrust, ( 145w) - as whats given on specs on a motor found. Then, at 4s if similar, it should given a better thrust, even without the BDF part.
leaded50
Legendary member
Prop have a better thrust at launch/low speed than EDF, and mainly lower wattuse.
As BDF , im unsure if can be a better alternative in smaller sizes, since seems lacks thrust vs a EDF unit (vs weight) in all info ive seen. In bigger size more "normal" propel size, yes, then perhaps, also since EDf in such sizes aint to be found? to compare with. 4,3 inch i think is the biggest EDF seen. By a 110mm EDF its not unusual se thrusts given to 7-9000g, at unitweight at 500-700g. a 4.33 inch propeller would never give that thrust, as a BDF? well, i dont know..
Anyway its a new way of thinking, and gonna develope the hobby anyway. In the 30´s though, "flying barrel plane" who uses same techique, didnt show such great innovations, to be a "norm" by airplanes. ..it seems be more a "step back" to the developing of a EDF..
https://www.microfarads.com/times-articles/77-throwback-vintage-stipa-caproni-flying-plane
As BDF , im unsure if can be a better alternative in smaller sizes, since seems lacks thrust vs a EDF unit (vs weight) in all info ive seen. In bigger size more "normal" propel size, yes, then perhaps, also since EDf in such sizes aint to be found? to compare with. 4,3 inch i think is the biggest EDF seen. By a 110mm EDF its not unusual se thrusts given to 7-9000g, at unitweight at 500-700g. a 4.33 inch propeller would never give that thrust, as a BDF? well, i dont know..
Anyway its a new way of thinking, and gonna develope the hobby anyway. In the 30´s though, "flying barrel plane" who uses same techique, didnt show such great innovations, to be a "norm" by airplanes. ..it seems be more a "step back" to the developing of a EDF..
https://www.microfarads.com/times-articles/77-throwback-vintage-stipa-caproni-flying-plane
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perhapsleiana
Elite member
Well, BDFs are typically much lighter than the same size EDF. They have a higher thrust to weight ratio than an EDF in most cases. Mine was heavy because it was poorly designed.
perhapsleiana
Elite member
You try to run over 170W through an 1106, it will burn up. they're just tiny. If you want to run them on 4S, you need to use a smaller prop.
perhapsleiana
Elite member
Unit weight of a 4 inch BDF had better not be over 70g, if it is, well, that's not the best design.
I don't remember the weight of the BDF+motor off hand, but it's not simply a power/weight benefit that I was going for. I actually believe a good EDF will probably beat the BDF in thrust/weight regardless of diameter, simply because they are putting out so much more power.
The big "benefit" the BDF was really going for was cost and accessibility. You can get a large diameter "ducted fan" for WAAY less cost than a similarly-sized EDF. Now, you can't go put that 4" BDF in a 'regular' 100mm EDF airframe, but again they weren't designed for that either. They were designed to work in lightweight foamboard planes. When you scale up an airframe, and design it around a lightweight concept and lightweight powerplant, the whole aircraft actually comes out much lighter and is able to fly on very little thrust (relative to other planes of similar size). This lighter-weight & lighter-thrust & bigger-size combination makes for jets that can still be flown relatively fast, but can also slow down a LOT slower than other big jets, and therefore can be flown in smaller spaces, and consequently also don't hurt themselves so bad in crashes.
They're really aimed at a different style of build, they were never meant to be a "swap in" replacement or even 1-to-1 comparison with EDFs.
Look at the monster B-52 I built that was powered by eight 4" BDFs: If that was powered on eight 100mm EDFs it would have required the following:
8 x 100mm EDFs
8 x 150-200A ESCs
Higher gauge (thicker) wire extensions (there was over 120ft of motor wire in the wings)
4 to 8 x High-C rated batteries
All those listed things would dramatically increase the weight of just the powerplant total, which would necessarily require an increase in the strength of the supporting airframe, which increases the weight of that airframe. All that rolls up to a much heavier and faster airplane overall, not to mention drastically more expensive cost.
Designing around the BDF allows you to run that weight-death-spiral the other direction, reducing both weight and cost a LOT.
The big "benefit" the BDF was really going for was cost and accessibility. You can get a large diameter "ducted fan" for WAAY less cost than a similarly-sized EDF. Now, you can't go put that 4" BDF in a 'regular' 100mm EDF airframe, but again they weren't designed for that either. They were designed to work in lightweight foamboard planes. When you scale up an airframe, and design it around a lightweight concept and lightweight powerplant, the whole aircraft actually comes out much lighter and is able to fly on very little thrust (relative to other planes of similar size). This lighter-weight & lighter-thrust & bigger-size combination makes for jets that can still be flown relatively fast, but can also slow down a LOT slower than other big jets, and therefore can be flown in smaller spaces, and consequently also don't hurt themselves so bad in crashes.
They're really aimed at a different style of build, they were never meant to be a "swap in" replacement or even 1-to-1 comparison with EDFs.
Look at the monster B-52 I built that was powered by eight 4" BDFs: If that was powered on eight 100mm EDFs it would have required the following:
8 x 100mm EDFs
8 x 150-200A ESCs
Higher gauge (thicker) wire extensions (there was over 120ft of motor wire in the wings)
4 to 8 x High-C rated batteries
All those listed things would dramatically increase the weight of just the powerplant total, which would necessarily require an increase in the strength of the supporting airframe, which increases the weight of that airframe. All that rolls up to a much heavier and faster airplane overall, not to mention drastically more expensive cost.
Designing around the BDF allows you to run that weight-death-spiral the other direction, reducing both weight and cost a LOT.
I feel like this question has been answered in this thread already, but what's the largest diameter prop that can fit in the F-18? Is the 4in bdf the max, or can it be pushed to 5 in or even 6? And can the F-16 in this thread fit a larger prop (because there aren't two engines)?
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