Trimming a RC Airplane & Determining CG from Mean Area Chord in Airplane Designing

In the background, Scott and I have been working on a Mig-35 version of the RCP Mig-29v4.  We have referred to this plane in many ways including using NAMC.  I have had more time to think than fly and build lately.  As they say, "a little bit of knowledge is a dangerous thing."

In the test flight of my last prototype build, I set the CG using the "arc" method that is basically a powered glide test.  I personally like the arc over the glide method for several reasons.  I prefer to be climbing at altitude when I am doing surface control adjustments; it gives me more room for recovery.  More importantly, the arc method is more dynamic visually.  Another method I found in Googling away my time was to fly inverted and the attitude of the plane and amount of elevator required indicate the CG.  Next time out, I will do all three maneuvers.  Here is a great summary of trimming a RC plane (arc method was found in a different post):

Trimming a RC Plane

How do you determine the CG on a wing?  Off to Google and my textbooks and the best method is to determine the mean area chord (MAC).  MAC is the line that divides the wing into equal areas.  Depending on the wing type, the CG is 25-33% of the MAC from the leading edge for straight and delta wings respectively.  Using my program, I calculated the MAC in two different ways.  First I used the "true" wing lateral to the side plates (blue in picture) and second I used the "full" wing to the centerline of the plane (green).  The picture has a lot of overlays:  the original Mig-29v4 wing, Mig-35 prototype wing, and the MAC drawings.  The black and red CG are what I determined after test flights with Mig-35.  The Mig-29 v4 CG is marked in simple text.  The red CG was where I determined the plane to be very slightly nose heavy and just ahead of the calculated MAC CG for a full wing. Clearly, the "true" wing in blue is not the way to calculate the MAC.

From a design standpoint, now that I know the wing CG,  what is the relationship between the  fuselage and the wing?  It's simple, balanced with varying polar moments (see my prior posts about polar moment of inertia). The CG of a fuselage including the tail but without the wing would intersect the CG of the wing. In RC we have battery and ESC as the movable components to adjust the CG and polar moment.  On my present build that is foam only stage of construction without KFs or components, the CG is presently 2 inches aft.

My next question to ponder is how do the KFs affect the wings center of lift (COL)?  Will they change the COL and hence the calculated CG?  For straight wings from wind tunnel testing, we know the ideal KF is 40%.  There is no similar data on the best KF ratio for swept or delta wings.  In some prior flight testing on the Mig-29v3, I found that 40% was better than the stock KF that was varied from root to tip.  With this present build I am going to trim the plane with and without 40% KFs to see if the wing COL changes the measured CG.

The epoxy has set, back to building the latest prototype.

Stephan