Me again. Sorry for being so dense... I've got a tiny problem. Friend
wants a nice big foamie jet, but she prefers EDF instead of my usual
pusher prop setup.
Now, the default layout has air ducts in there anyway, but they're only used to cool the electronics. They're basically like "Y", with the upper part of the "Y" being the intakes near the nose, and the stem of the "Y" being the main fuselage and out at the tail end.
I'm a bit clueless with EDF but did some testing - after reading a lot of information on the web. What I know so far is this:
- Ducted fans seem generally less efficient than an old fashioned prop. - Making the ducts as smooth as possible yields about 5% more output. I've only tried that by smoothing the inside of the test tube with normal tape, properly coating it should be better.
- The intake size need only be about the same diameter as the fan itself I've only tested this with static setup (i.e. not in the air). * Q: Does it make any sense to have bigger intakes in flight? Kinda "scooping up" air while zipping around the skies?
- The exit duct should be about 3/4 to 2/3 of the fan diameter. Decreasing it further increases current draw without providing significant additional thrust. * Q: What happens if I'd use two EDFs through the same exit pipe? i.e. one in each of the upper branches of the "Y"? Could I gain additional thrust that way, providing I mess with the exit to optimize efficiency (current draw vs. thrust) or will turbulence or whatever else make that kind of setup not feasible? * Q: On the other hand, would it be beneficial to increase compression by putting two fans in series, with the first EDF running slower than the second (closer to the exit) EDF? * Q: Are there any other ways to get higher output per watt?
My basic problem is simple: It will be a rather large model and EDF seems a bad choice for large models. Weight is fairly low, the whole plane without electronics weighs less than 2 pounds, with electronics and battery it's just slightly over that. Except that I'm used to having a little over 2 pounds of thrust in there, and I just don't see a way to get even near that with EDF. I'd like to use mostly standard EDF components, pretty much to keep it easy for her to get spare parts if she needs them.
Thanks for your help! Jenni
Now, the default layout has air ducts in there anyway, but they're only used to cool the electronics. They're basically like "Y", with the upper part of the "Y" being the intakes near the nose, and the stem of the "Y" being the main fuselage and out at the tail end.
I'm a bit clueless with EDF but did some testing - after reading a lot of information on the web. What I know so far is this:
- Ducted fans seem generally less efficient than an old fashioned prop. - Making the ducts as smooth as possible yields about 5% more output. I've only tried that by smoothing the inside of the test tube with normal tape, properly coating it should be better.
- The intake size need only be about the same diameter as the fan itself I've only tested this with static setup (i.e. not in the air). * Q: Does it make any sense to have bigger intakes in flight? Kinda "scooping up" air while zipping around the skies?
- The exit duct should be about 3/4 to 2/3 of the fan diameter. Decreasing it further increases current draw without providing significant additional thrust. * Q: What happens if I'd use two EDFs through the same exit pipe? i.e. one in each of the upper branches of the "Y"? Could I gain additional thrust that way, providing I mess with the exit to optimize efficiency (current draw vs. thrust) or will turbulence or whatever else make that kind of setup not feasible? * Q: On the other hand, would it be beneficial to increase compression by putting two fans in series, with the first EDF running slower than the second (closer to the exit) EDF? * Q: Are there any other ways to get higher output per watt?
My basic problem is simple: It will be a rather large model and EDF seems a bad choice for large models. Weight is fairly low, the whole plane without electronics weighs less than 2 pounds, with electronics and battery it's just slightly over that. Except that I'm used to having a little over 2 pounds of thrust in there, and I just don't see a way to get even near that with EDF. I'd like to use mostly standard EDF components, pretty much to keep it easy for her to get spare parts if she needs them.
Thanks for your help! Jenni