General Rule for Calculating Center of Gravity of any Aircraft Configuration

Question

I'm looking for method(s) to determine the CG of any fixed wing aircraft for it to be reasonably stable. I only know for conventional aircraft, placing the CG between 1/4th and 1/3rd of MAC behind MAC leading edge usually works but when it comes to unconventional configurations like canards or tandem wings or even more lifting surfaces I don't know what to do.

I drew some examples to ask what kind of approach should I use for each of these aircraft configs to find their desirable CG position.

Also how can I decide if a surface is better suitable as a positive or negative lift producing surface? For example for a canard we know that both wings produces +lift but if we shift the CG on the forward wing as if it was a conventional airplane the main wing becomes a down force generating surface (assuming it can fly) doing that is obviously wrong but when it comes to model B or E it gets blurry for me.

Answer 1

A and C have some merit. Throw the rest away. Center of Gravity needs to be placed first where the plane is directionally stable and directly under the net lift vector of the entire aircraft. Next determine what pitch characteristics you want. To be staticly stable, the aircraft must pitch down below its trim speed and pitch up above it. The only difference with a canard is that it provides upforce from the front rather than downforce from the back.

In this sense canarded or tailed aircraft are actually bi-planes. The wing in front must stall first to be safe.