Model Aircraft CG Calculator

Uses the three-point weighing method to find your model’s true CG. Tap “Instructions” below for the full step-by-step process, or jump straight to the calculator if you already have your measurements.

Instructions

1. Prep the airplane. Fully assemble it and make it flight ready. If gas powered, do this without fuel. If electric, the battery should be installed.
2. Level it to its flying attitude. Place the airplane with the nose or spinner against a wall, and level the airplane to its flying attitude — this may mean removing the canopy or another hatch to get a flat surface to level from (just reinstall it before weighing). On tail-wheel airplanes, the tail will have to be raised to level the model.
3. Mark the wheel centers. Place a piece of masking tape near each wheel, parallel to the flight path, and mark the center of each wheel on the tape.
4. Measure the arms. Measure the distance from the wall (where the nose or spinner touches) to each mark on the tape. These are your “Arm” measurements below — essentially the distance from the tip of the spinner/nose to the center of each wheel with the model level. Typically both main wheels will measure the same distance from the wall; if not, reposition and re-measure.
5. Weigh each wheel. Place a scale under each wheel individually. If you only have one scale, keep the airplane level (both left/right and fore/aft) while you take each reading. Enter each wheel’s weight in the “Weight” boxes below.
6. Read your CG. The calculator computes the CG from the tip of the nose or spinner toward the tail. If the model is still positioned with the nose against the wall, this is also the distance from the wall to the CG.
7. Adjust as needed. Move weight (battery position, ballast, etc.) and re-measure/recalculate until the CG lands where you need it.

How it works: Moment = Arm x Weight for each support point. Total Moment / Total Weight = the CG’s distance from your datum line.