EDF systems

[kookie_guy]

So I'm tinkering around, and I have a couple nice 64mm EDF systems with a 45A ESC each. They push an impressive amount of air, so I figured, hey, let's build some crazy air boat thingamabob.

The problem is my spektrum will not run it. The throttle is backwards. So when I squeeze the trigger, it stops. When in neutral is yells, when is full reverse is screams. Reversing the throttle did not help. Is this one of those cases where I need a stick radio, since they are airplane ESC's?

[Alexgar]

Buy a pistix or I use a rubberband to hold it in rev and rev th channel

[kookie_guy]

Buy a pistix or I use a rubberband to hold it in rev and rev th channel

from what I hear, pistix are hard to come by these days. I will try the throttle reverse like you mentioned.

[Alexgar]

17 in stock here
http://www.offshoreelectrics.com/pro...pistix&cat=136

[kookie_guy]

17 in stock here
http://www.offshoreelectrics.com/pro...pistix&cat=136

lol, sweet. Didn't even think to check. Google searches turned up a bunch of 'discontinued' threads.

[Alexgar]

Alot of us use these on our mini builds where tiny escs are needed

[bwells]

Kookie guy, What are you planning on doing with the EDF? I'm currently building a copy of Chop's air boat build with a 90mm fan

[sailr]

Just like any other brushless motor, if it's running the wrong way, reverse any two wires.

[kookie_guy]

Kookie guy, What are you planning on doing with the EDF? I'm currently building a copy of Chop's air boat build with a 90mm fan

Not quite sure yet. But I'll be using both of em on it, with concentrator nozzles, both mounted on a steerable system for great thrust vectoring.

[bwells]

Does concentrator nozzles increase the work the EDF's have to do and will it gain anything? It seems like it would put more of a load on the motor than what you would gain in output force of the fan. Just questions, not statements. Still thinking about the steerable fan verses vanes.

[kookie_guy]

Does concentrator nozzles increase the work the EDF's have to do and will it gain anything? It seems like it would put more of a load on the motor than what you would gain in output force of the fan. Just questions, not statements. Still thinking about the steerable fan verses vanes.

It seems like common practice among the airplane guys to put exhaust cones on the fans. I'm not talking about pinching it down to 1", just reducing the diameter a bit to help focus the air stream.

Ya, I am also not sure if it's better to go with vanes or have the whole edf move.

[NativePaul]

Nozzle diameter is like gearing on a car, the smaller the exhaust diameter the higher the efflux velocity and the lower the static thrust, its faster but with slower acceleration. so if you have something with very low drag like a sleek plane you want a small nozzle and if you have something with very high frag, you wont want any restriction on the nozzle at all.

Its one of those rare instances where you do get something for nothing though, as if you take the nozzle smoothly down in diameter to match the fan swept area you will gain efficiency and get an increase in efflux velocity whist maintaining static thrust.

Moving the EDF vs vanes is a personal choice, moving it has less drag but will be heavier, more complex, and may be weaker. Vanes are simple and sturdy but have drag even when going in a straight line, still the drag is likely to be minor compared to the drag of the hull on the water.

[kookie_guy]

Nozzle diameter is like gearing on a car, the smaller the exhaust diameter the higher the efflux velocity and the lower the static thrust, its faster but with slower acceleration. so if you have something with very low drag like a sleek plane you want a small nozzle and if you have something with very high frag, you wont want any restriction on the nozzle at all.

Its one of those rare instances where you do get something for nothing though, as if you take the nozzle smoothly down in diameter to match the fan swept area you will gain efficiency and get an increase in efflux velocity whist maintaining static thrust.

Moving the EDF vs vanes is a personal choice, moving it has less drag but will be heavier, more complex, and may be weaker. Vanes are simple and sturdy but have drag even when going in a straight line, still the drag is likely to be minor compared to the drag of the hull on the water.

thanks for the info. Sounds like you dabble in planes? I love seeing the guys with the big jets. Takes balls to take that much time and money into the air, lol. I tried it with a basic plane. Took off, got 10 feet in the air, then crashed. lol. That's the extent of my flying experience.

[NativePaul]

I've built a few in my time all were electric and several of them were EDFs so I've done a fair bit of research and testing on ductwork, I never flew anything bigger than 20cells (Nicad) or 4s LiPo so the cash investment was much less but on the other hand it was still all the money I had and it hurts watching something you've spent hundreds of hours designing and building go in hard and laughing it off (its either that or cry), luckily they all lasted more than 10 seconds, but most died eventually. I stopped buying and building planes in '05 and got back into FE boats and by '07 I was racing boats again (which while just as expensive (again all my money) is more fun, and I chose to stop using my old boat and make the next one rather than have it forced on me by the predecessor's untimely death which is less depressing) and stopped flying, with my Futaba FASST radio that has been rock solid for years I'm tempted to start flying again as I attribute over half my crashes to radio issues, but I really don't want to lose my last few, especially to pilot error (which always hurts the worst).

One thing that I didn't twig about EDFs at first is the importance of a nice smooth large radius on the inlet lip, as well as making it easier to suck in air to chuck it out the back faster, there is a low pressure area at the inlet that sucks it along and helps with static thrust, also don't make the mistake of just using a trumpet shaped inlet lip, roll it right round into a full nacelle, a significant amount of air will come forward around a smooth inlet lip from behind the inlet at low speeds.