Estimating the balance point.

[Dan Tandberg]

When making a new glider from scratch or from scavenged pieces of other crashed models, the question of locating the CG is often discussed.  Buzz Averill taught me the rule of thumb that "35% of the mean aerodynamic chord (MAC) is almost always safe. and ~37% is where it will eventually fly best."  I always read on the internet to review how to estimate the  MAC.  Here you see my balancing rig and the sharpie marks on some tape at 35% MAC. The mirror makes alignment much easier.

I design my fuselages so that I can build the wing saddle late in the sequence. That way I can temporarily install all the radio gear, motor, batter, spinner, prop, servos, pushrods, etc. and then use a balancing rig to locate wing saddle for optimal CG.

Here you see all the gear taped in place.  The battery, spinner, props, and a bit of lead to represent the canopy still need to be added. My new Hacker A20-20 evo has not come yet in the mail, so an equivalent  55g bundle of lead scraps has been taped in the nose.

I start with the battery placed in the middle of its range of positions. Now the wing can be perfectly placed on the fuse and its position marked.  This sequence of steps almost always results in not having to add lead to your model to get the optimal CG.

[daniel roberts]

Dan....what a great article. Thanks for sharing. I've often thought about putting a mirror under the wing to better see the balance marks. My current setup doesn't allow that so I'll have to change it. 

Dan R

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From: soa...@googlegroups.com <soa...@googlegroups.com> on behalf of Dan Tandberg <tandb...@gmail.com>
Sent: Saturday, April 4, 2026 9:46 AM
To: soarabq <soa...@googlegroups.com>
Subject: [ASA] Estimating the balance point.

 

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[Carris Mike]

Dan always has good stuff.

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