RE: Are My Calculations Right???
The SWAG approach works as well as any for this application
Here is the math
Take one pencil
draw four straight lines which make a scale representation of the the wing planform (a bird's eye view) and roughly draw in the tip shapes .
using scissors-cut out the the little drawing
THIS is the shape which is doing the lift work- so cut carefully and watch your fingers!.
Fold each tip to the center
Unfold and note the location of each fold
make a dot on each fold - 1/4 back from the leading edge.
connect the dots.
make a second set of dots 1/3 back from the leading edge
connect these dots
the space in between is a workable location for a flyable CG location
You could use math and calculate all the various parameters of the model
But
this approach will give you the same results and you will also learn how to use a pair of scissors
This works for 3D , one ounce flat foam aerobats AND 100 pound scale Piper Cubs and all the others in between.
The best location - in that range -will vary somewhat