| This is to make it feel more like a .40 aircraft, just hate the idea | of flying something with elevators used as aelerons and motor power | used to provide pitch.
Huh?
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Looking at the picture, it's a standard three channel plane with throttle, rudder and elevator control. Rudder turns, elevator (and throttle, of course) controls pitch.
The elevator isn't used as ailerons, and motor power always controls pitch, but it's not the only way of doing so in most `serious' planes.
Adding ailerons to this plane sounds OK to me, though I suspect it flies fine without them. rudder/elevator/throttle planes can be fun to fly and the lack of ailerons really isn't that serious unless you're looking to do aerobatics -- and even then they can do quite a few maneuvers if the throws are high enough and the CoG is far enough back.
| Even though Ive never successfully flown it.
You might want to try it with the stock wing. You might find it to be OK. With that much dihedral, it won't fly that differently with rudder turning vs. aileron turning.
| So where do I put the C of G on this airplane? Similar to the original | mark on the main wing?
The CoG is pretty much always in the same place, for any plane of this general shape -- 25% to 33% back from the front of the wing. Since it has a landing gear, set the CoG at 25% and try to rise off the ground. Move it back a little at a time until it's right.
| Is there any other 'theory' I need to understand | to make sure this thing flies apart from balance of C of G?
CoG is extremely important, but the 25%-33% rule of thumb works for most planes. Only if the plane has swept wings, or is a flying wing or canard or is a bipe does it really get more complicated.
CoG more forward = stable, but inefficient. Less aerobatic. CoG more backwards = unstable, but efficient (to a point.) More aerobatic, though if you get too far back it will be so aerobatic that you won't be able to fly it.
As for other theories, you may have added so much weight that it can't fly well anymore. Or maybe not -- I don't know exactly what you've done.
| As a side question, the RX on this thing uses a 'single conversion' | xtal which shows a great deal of interference in my area (random | jitters outdoors, main cause of last crash). Where do I have to go to | get rid of these jitters? Or do I have to use a double conversion rx?
Random (minor) jitters shouldn't cause a crash on a slow park flier like this. But full scale deflections certainly can, and if you're having intereference problems, a dual conversion receiver (or a good single conversion one, like by Berg) is probably a good idea.
It may not make the problem go away, however -- it depends on what the source of the interference is. And we can't really debug that for you here ...
You mentioned the crystal. Single conversion crystals go with single conversion receivers, and dual conversion crystals go with dual conversion receivers. You can't just put a dual conversion crystal into a single conversion receiver to reduce interference -- instead, it just won't work. Or more accurately, it'll be listening to a totally different channel than you expect.