Chis

I have edf experience in RC, in fact just flew a new one yesterday, an F-86 and I have 2 others on hand to be built including a 3D edf. The issue I see with them for our application is that they provide fairly little power for the most part. They require velocity to get power. The faster they go the better they perform. I also fly glow ducted fan. To take off grass generally requires a .91 powered fan and a big one to do it with authority. We are not seeing anything that big being flown electric. A 5 inch fan is usually a high speed fan and requires a .91 or larger glow motor and will not take off grass very well but with a few planes. There are glow systems that will turn those fans, Bob Violett's electric fan will do it. You are looking at a 10 to 12S power system to drive than fan and when it gets in the air its a 120 to 150 mph system in RC. The smaller stuff might work in a foamie off a paved circle but it would have to be a good circle. Any grass and forget it and you will need a long takeoff run... possibly a lap or two to get enough velocity to get the fan working well enough to get off. For a scale model you might be able to pull it off on pavement but for any aerobatics I would be surprised. Battery consumption is pretty high. In RC where you can do throttle management a pack that will fly a 3D RC plane for 8 or 9 minutes will come down after 4.5 to 5 minutes and be quite warm... compared to what I get normally in 3D RC I would call it hot and would call it hot in any CL stunt application. Since we drain a battery a lot harder in CL aerobatics than in 3D RC my guess is you would probably be seeing a max 3 minutes in cl edf on the same packs.

These systems just are not efficient at all at the speeds we normally fly at. Granted a 4S driven foamie jet is only going to be a 60 to 70 mph bird you really stumble them into the air and then keep the speeds up . They have nothing you would associate with torque or tons of thrust.

A launch is not something with these that happens with authority because there is no high speed air going into the fan yet. You would have to plan on whipping to get off a hand launch would be my guess.

Your milage may differ and as I said I am relating based on what I have experienced in RC edf. If someone has some real world cl edf experience please step in and don't feel bad about saying I'm wrong. I can take it...... but I'll go to my closet and have a good cry. 

bob branch

Thank you both for the info, like I said I wasn't sure it would really work for the application, but I'm always interested in doing something outlandish and weird... even if it wouldn't be the most solid stunter the experience of putting it together and making it work may provide some experience for other applications for something else down the road... I may decide to try something I may not it really all hinges on time and cash flow. Either way it would most certainly would probably be a smaller plane most likely not intended for anything other than making it work.

Thank you both for the info, like I said I wasn't sure it would really work for the application, but I'm always interested in doing something outlandish and weird... even if it wouldn't be the most solid stunter the experience of putting it together and making it work may provide some experience for other applications for something else down the road... I may decide to try something I may not it really all hinges on time and cash flow. Either way it would most certainly would probably be a smaller plane most likely not intended for anything other than making it work.

I think a ducted fan scale jet would be exceedingly cool, even if all you did with it was speed runs.

While a true ducted fan may not be applicable( and I dont think it would for all the reasons stated) perhaps a SHROUDED prop would be more to our needs. between a ducted fan, and an open propellor. I know there was a pylon racer designed in the 70's (?) that used a pusher configuration with a shroud around the prop..

I dunno -- given the success that folks are having with big diameter, low-pitch props, I suspect that anything that restricts the diameter is going to degrade the 'constant speed' quality that we all seem to want.

A prop with bent-down tips (i.e., winglets), may make sense, but I think you'd need several degrees in aerodynamics, and maybe a grant from NASA, to get one that did more than just look cool.

There are two problems:

1/ As Tim already wrote, the prop better reacts to load (better thrust at lower speed) compared to EDF. So the EDF will be probably worse, but you can still use some active controll. The question comes, how large and heavy EDF can create the same static thrust like the prop, I affarid you will come to heavier power train.

2/ The wing, flaps and elevator of the model with ususla prop is in high speed air also when models slows down, but model with EDF will change properties regarding actual speed, I affarid it will be far worse and difficult to control (I mean for PA).

See, now John is speaking my language... Thrust vectoring and nacelles, it's great! I could create a small set of paddles that move with the elevators inside the nacelle so that it can remain firmly attached but with the added thrust vectoring benefit... again, I'm fully aware that the chances of this being a PA bird are so low that spinners could get stuck in them, but if one had a fully paved flying site and some time to kill and creativity to waste it would be a heck of a lot of fun!