RC Aircraft Center of Gravity Calculator
Calculate the correct center of gravity position for RC planes based on wing chord, sweep, and aircraft type.
Why CG matters in RC aircraft:
The center of gravity (CG) is the single most critical setup parameter for any RC airplane. A CG too far forward makes the plane nose-heavy — it needs excessive up-elevator to fly level, stalls at higher speeds, and lands hard. A CG too far aft makes the plane tail-heavy — it becomes twitchy, oversensitive, and dangerously close to unrecoverable pitch-up stalls.
CG position formula:
CG is expressed as a percentage of the Mean Aerodynamic Chord (MAC), measured from the leading edge:
CG position (mm) = MAC leading edge position + (MAC length × CG percentage / 100)
Safe CG ranges by aircraft type:
| Aircraft Type | CG Range (% MAC) | Recommended Start | Notes |
|---|---|---|---|
| Trainer | 25–30% | 28% | Nose-heavy is forgiving |
| Sport aerobatic | 25–33% | 28% | Adjust for 3D vs precision |
| Pattern plane | 28–32% | 30% | Precision requires neutral |
| Warbird | 20–28% | 25% | Often need nose weight |
| Flying wing | 15–25% | 18% | Very sensitive to CG |
| Delta wing | 15–22% | 18% | Swept wings shift CG aft |
| Glider/sailplane | 28–35% | 30% | Adjust for thermal vs slope |
| 3D aerobatic | 30–40% | 33% | Aft CG for extreme maneuvers |
Finding the Mean Aerodynamic Chord (MAC):
For a rectangular wing, MAC = wing chord (root to tip same width).
For a tapered wing:
MAC = Root chord × 2/3 × (1 + Taper ratio + Taper ratio²) / (1 + Taper ratio)
Where Taper ratio = Tip chord / Root chord
Example calculation:
Sport aerobatic plane with:
- Root chord: 300 mm
- Tip chord: 200 mm (taper ratio = 0.667)
- MAC = 300 × 2/3 × (1 + 0.667 + 0.444) / (1 + 0.667)
- MAC = 200 × 2.111 / 1.667 = 253 mm
- CG at 28% MAC = 253 × 0.28 = 70.8 mm from MAC leading edge
How to check CG:
Support the plane on your fingertips at the calculated CG point (one finger under each wing). The plane should balance level or with the nose slightly down. If the tail drops, the CG is too far aft — add nose weight.
Adjusting CG:
Move the battery forward or backward first — it is the heaviest single component and has the most effect. If the battery is already at the firewall and the plane is still tail-heavy, add lead weight to the nose. Every 10 grams at 100 mm from CG shifts the balance point approximately 1 mm (depending on total aircraft weight).
The golden rule:
A nose-heavy plane flies poorly. A tail-heavy plane flies once. Always start at the forward end of the CG range and move aft gradually until handling feels neutral.