RC plane CoG finder

Finding the Center of Gravity (CoG) of your plane is something that all RC pilots have to do before maiden flight (and after !).
There are many ways to do this.
"modern" solutions require 2 scales and simple maths that can be done with an arduino or an excel sheet.

This solution is based on a single hobby scale and scrap arrows found broken in a club (Thanks Michel)

My design allows to find CoG of almost any RC planes and gliders. Origninal design was found here : https://www.rcgroups.com/forums/showthread.php?2909285-3D-printed-DLG-CG-locator-stationary. It was published in 2007 great idea !

I have changed a few things :

• capability of weighing bottom or top wings planes
• fuselage width can be adjusted
• wing cord can be adjusted

[edit] V2 model allows to use 7mm arrows and replaces the saw blade by arrows ! Files are suffixed _v2
4x hex nuts M4 are inserted into the vertical arms during printing (color change into the .3mf files). They can be used to block the arrows in place when device is tuned. But this is not mandatory as friction of the carbon rod into the PET parts is enough to prevent motion.

How does it work ?

knowing the "lever" length (L = 200mm on my system) between wing Leading Edge and scale and knowing the strength "W" applied on the scale you can determine the CoG position (from the Leading Edge).
You must measure (on the same scale) the total weight "M" of the plane.
Then you simply apply this formula :

CoG x M = L x W

Or CoG = L x W / M

So just put the middle part (trailing edge side) on the scale, push the "tare" button. Then measure W and compute CoG

It's that simple and very accurate (single sensor, same sensitivity for measuring M and W), accurate lever lenght measurement, accurate positioning on the Leading Edge of the wing...
As in the original design the plane sits on its wings and not on "knife" edges as often, so no damage on the wings !

I have compared this solution to a more traditional "balance CoG finder" and the result is of course exactly the same .
I have also tested with "big" 2.5m glider and small Lidl one. Width and length scalabilities are definitively a good trick.
I have performed a stress test with 6kg load without problem. V2 version is very rigid and 7mm arrows do not flex.

Another advantage of this design is that it can be folded into a very small size parcel!

Finally It only uses 2 arrows (700mm ones cut at 600mm to remove feathers and tips).
One is cut into 2x300mm horizontal spars
the other is cut into 4x 150mm spars (for width)