Could someone explain the basics of CG placement? I've head about calculating the MAC based of wing cord and sweep but still don't "get" the effect that different % would have on flight performance. For example, I have heard (perhaps falsely) that moving the CG back makes the plane more aerobatic/less stable. I have a heavily modified BUSA Eindecker on which I've moved the wing forward into the scale location. Can I still used the balance point indicated on the plans?

BTW, the root cord and tip cord are both 11" (therefore sweep is 0) and the half span is 28.5". I've plugged these into the Palo R/C calculator but have just been using random MAC numbers.

The center of gravity must be ahead of the location on the airplane where all the aerodynamic forces operate, the neutral point (NP). This location depends on a whole herd of things, but much experience has shown that having the c.g. about 10% ahead of this point ensures a flyable airplane.
With most conventional configurations, the c.g. then is nominally located between 25% and 35%. The 25% location normally results in a very stable airplane, as the restoring moment due to its location ahead of the NP. The closer the c.g. is to the NP the more manuverable the airplane.
I don't know of any easily accessible method of computing the NP, so the "rule" is the 25-35% thing, for a normal configuration.
The NP is generally found (after some tedious work) to be around 40%.. Can be less, can be more, but that's a nominal location.
25% to 30% is probably safe for your Eindecker.

Picture in your head, your aircraft as a balance beam, & your main wing 1/4 cord as the fulcrum,
"just as an example"
Break your aircraft up into "fuselage stations" example for this explanation 0= nose 100=tail
@ fuselage station 40 is your 1/4 cord location/fulcrum
forward of the fulcrum is a 100 lb moment
@ the aft moment is 100 lb

Your main wing will want to nose over/pitch do to its basic design (unless it is reflexed or twisted or sym)

The tail will be designed in such a way to counter the pitching moment of the main wing (by design of airfoil, location & size)

As you move the fulcrum point or the balance of weight, the response to your inputs will change how the aircraft reacts (to far aft the plane may stall & never recover)

Weight forward of the folcrum lends itself to an aircraft that will recover from a stall (nose over)

You may be able to fly with a cg that is to far aft but there will come a point when you exceed the the limitations of the control surface to bring the attitude back/stall of control surfaces
Flying to far forward of the fulcrum has its own issues but not as bad as aft

You can find your neutral point by using some math. It takes the tail volume coefficient and compares that to your wing chord. I'd have to look up the forumulas.

But an old cheap and dirty way to figure it out is to cut out a top view of your airplane from card stock. Then balance it so it sit's level for and aft when balanced. That point is roughly your neutral point. From there your center of gravity should be about 10% of the wing chord ahead.

In your case your MAC is pretty much 11 inches. It'll be a trifle less thanks to the wing tip shape but you can pretty much ignore that. MAC is mostly just a fancy way to say "average chord size and location".

For your Eindecker the wing shift will have only a small effect on changing the CG location. If you put the new CG as far behind the wing's leading edge as it was on the original model it'll be fine. On the other hand if you meant to leave the CG at the same spot back from the model's nose then it won't work. The CG MUST always be located as a distance back from the wing's leading edge. (basic I know but in case you didn't know)

Thanks to all for the lessons in introductory aerodynamics! The long and the short of it seems to be that I can just go ahead and use the same point on the wing as on the BUSA plans. Now the challenge is to pack that much weight the 4-6 inches fore of the CG point! I've got a .52FS, a dummy engine, false firewall, aluminum cowl and cheeks, gas tank, and at least two servos so maybe I won't have to add too much lead.

I have 14 (fourteen) ounces of lead in the nose of my BUSA .91 powered Eindecker. And I built the tail end light!

Paul, thanks in large part to your earlier advice on modifying my BUSA Eindecker 40 is has almost ceased to be a BUSA Eindecker! The only part of the kit I ended up using was the wing and I split that in two to be able to have a full cockpit. I also changed the way the servos were mounted (I prefer them hidden). But I'm sure I'll still need nose weight.

What is that motor? Looks like it could run!

Paul, yep that's the dummy! The prop conveniently hides the cylinder of the 52 FS. This is a heavily modified William's Bros 2" scale LeRhone kit made to look more like the Oberursal in the Eindecker. Here it is before the "magic" coat of paint. The rods are made of music wire wrapped with FliteMetal. The bottom photo shows the kits as it would normally turn out.