Lets say you have a profile model ... for arguments sake an F16 ....
The model is basically formed from a vertical profile fuselage and a horizontal outline wing / tail etc. In essence a X frame.... (sorry cannot do an X upright !)
Lets assume we cut that frame near the middle or just back from there - similar to a slot prop and install an EDF unit with wing outline in line with rotor hub centre.
We end up with a model that has an EDF unit sandwiched between two X's ...
How much loss of performance would there be ?
Why I ask - is I have a profile F16 sitting at home that I hate !! Still to this day I do not understand why I wasted the Depron on it. But it has dropped in my mind as to whether to convert to EDF unit.
It's quite big as well ... 1.2m long, but too light and flexible.
Hi Nigel Just cut out the top profile fuselage foam on top of the wing, to fit the EDF, making the edf rear part flush with the trailing edge of the wing, no need to go into the middle of the planes X section, and lay it on top of the wing, add a strip of Basswood 1/16" x 1/4" x 10" to 15" on the bottom of the profile fuselage to make the fuselage stronger, I know you wont get as much elevator control at slower speeds this way, but it will work fine, just keep the speed up,
I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
I thought about sitting it on the wing as you suggest ... but was hoping to lose a bit of it's bulk lower set in.
I added extra strips along the wing to fuselage joint - if you look closely = you notice a paint line. It stiffened it but still I wasn't too happy to think of fitting a high power pusher on it. So it's sat there for more than a year.
Will check out your suggestion once I get of this hulk of steel !!
There must be some edf experts out there who would know. I'd think not using the 80 to 90 % fsa rule for the exhaust would be a loss of top speed, and having some blockage to the exhaust would be a loss to overall thrust. How much? I've seen plans like this in magazines and online though, so it must work if you have a good enough fan unit.
Edit: A random idea just popped into my soggy brain. Maybe having some of that 'x' structure going into the aft portion of the fan, and shaped gradually as possible to a point, if that makes sense, would act as the reduction in exhaust area towards the fsa rule?
You lose top speed by not putting an exit cone on the EDF, but you get a bit more static thrust. Similarly not having a good inlet ring reduces the fan efficiency. Drag from the X of material in the eflux is just that... drag.
But there are EDF designs with the fan buried in the middle of the plane, having essentially a bare EDF, fuselage section partly blocking inlet and part of the fuselage splitting the efflux and they do fine.
(note the horiz in my avatar pic splits the eflux and the fuselage partly blocks the inlet... 120mph)
Sure you could do a lot of work and make it more efficient... and add weight... and probably not really gain anything except a higher minimum speed to maintain level flight (stall speed).