RC plane CoG finder (laser cut)

This is a remix of my 3d printed RC plane Center of Gravity finder.

It's exactly the same device but laser cut into 5mm plywood sheet.
Dimension of the sheet is 250 x 280 mm

To build it, simply glue the parts 3 by 3 to get the 1.5cm width of the final "plywood". Use white wood glue
Let it dry at least 3h before drilling the holes

• Use the 5mm little square slot to drill with a 5mm drill bit. This will remove the little tab in the middle of the part
• DON'T forget to firmly clamp the plywood when drilling to avoid delaminating it...
• Then widen the hole with a 6mm drill bit
• Then use a 7mm drill bit to finish the hole. The arrow should "stick" a little but should be able to slide into the hole

Do the same for the 4 legs. Then assemble the balancer and use it.

The formula are burnt on the legs !

Here is the same wording as in the previous design

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

How does it work ?

knowing the "lever" length (L on the picture) between wing Leading Edge and scale and knowing the Measure "Me" read on the scale you can determine the CoG position (from the Leading Edge).
You must measure (on the same scale) the total weight "Mtot" of the plane.
Then you simply apply this formula :

CG x Mtot = L x Me

Or CG = L x Me / Mtot

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

It's that simple and very accurate (single sensor, same sensitivity for measuring Me and Mtot), 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)

The horizontal arrows should be parallel to the table when the balancer sits on the scale. My design is for hobby scales 16mm height. You might tweak the middle part which sits on the scale for another height... (or wedge the front legs!)