Simple CG Marker

Eliminate measuring errors when marking the center-of-gravity.

I have always measured the CG on my planes with a rule. I could never get it just right with the curved wing surface. Soooo…I made a simple tool:

Materials

• 1 — Dowel (1/2" for pencil or 5/8" for both pencil and Sharpie) appoximately 8" to 12" long. Some of my scale planes need the longer dowel.
• 1 — 1.5" x 3" x 1/4" (approximate) block of wood

The first one I made was for a pencil, so I used a 1/2" dowel and drilled a 9/32" diameter hole in the block:

I then decided I wanted one that would do both a pencil and a Sharpie. I used a 5/8" dowel and drilled one end 9/32" for pencil and the other 13/32" for felt tipped marker. I drilled a 5/8" hole in the block. I also cut a notch to the hole to prevent end splitting. Not much to it. About 15 minutes including sanding and finishing:

The dark marker for light surfaces and the light one for dark colored surfaces. Here’s how to use it in practice:

Left: Simply measure from the face of the block to the tip of your pencil or marker. | Center: Block goes to front of wing at root and the marker marks the spot. Right: Here’s how much I was off with hand measuring — the dot is by hand and the line is with gauge (click images for closer look).

As always, have at it and let me know if you have a need to do something but not the tool to do it. Thank you for reading!

©2022 Tom Broeski

All images are by the author. Check out all of Tom’s Tips here in RC Soaring Digest. Read the next article in this issue, return to the previous article in this issue or go to the table of contents. A PDF version of this article, or the entire issue, is available upon request.