AeroBalance

Mean Aerodynamic Chord & CG Calculator

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Precision Airframe Balancing & MAC Solver

Designed for RC scratch-builders, aeromodellers, and UAV drone designers. Determine the exact Center of Gravity (CG) balance point and Mean Aerodynamic Chord (MAC) without uploading classified CAD or custom airfoil designs to external servers.

1. Select Wing Geometry Preset

Choose a baseline planform to auto-fill inputs

2. Configuration & Units

3. Wing Planform Geometry

Wing width at the fuselage centerline / root
Wing width at the extreme wingtip
Total tip-to-tip wingspan ($b$)
in
Distance Tip LE extends back from Root LE
Distance from nose tip to Root LE (set 0 to measure CG from Root LE)

4. Stability & Static Margin Tuning

10.0%
0% (Neutral) 10% (Trainer) 25% (Ultra-Stable)
ℹ️

Static Margin: The distance between aircraft Neutral Point (NP) and Center of Gravity (CG), expressed as a percentage of MAC. Higher values increase pitch stability; lower values increase agility.

Scaled Vector Blueprint

Hover blueprint to inspect coordinates
Wing Outline
MAC Chord Line
Recommended CG Target (🎯)
Neutral Point (⚓)
Recommended CG Position
3.45 in
Measured from Root Leading Edge
CG from Nose Datum
3.45 in
Measured from Fuselage Nose Tip
Mean Aerodynamic Chord (MAC)
10.13 in
Effective aerodynamic chord length
MAC Y-Span Location ($Y_{MAC}$)
10.40 in
Spanwise distance from centerline
MAC LE Setback ($X_{MAC}$)
1.52 in
Leading edge offset at MAC span
Wing Neutral Point ($NP_X$)
4.05 in
Aerodynamic center (25% MAC)
Total Wing Area
480.0 sq in
3.33 sq ft
Aspect Ratio ($AR$) & Taper ($\lambda$)
4.80 AR
Taper Ratio $\lambda$: 0.67

Understanding Mean Aerodynamic Chord & Center of Gravity

What is Mean Aerodynamic Chord (MAC)?

In aerodynamics, a swept or tapered wing produces lift differently along its span compared to a uniform rectangular wing. The Mean Aerodynamic Chord (MAC) is the chord length of an equivalent rectangular wing that has the exact same aerodynamic force, pitching moment, and center-of-pressure characteristics as your actual planform.

Finding the MAC is essential because all stability and control calculations — including Center of Gravity (CG) placement and static margin — are referenced to the MAC rather than the physical root chord.

Aerodynamic Formulas & Equations

AeroBalance computes MAC, spanwise position ($Y_{MAC}$), and setback distance ($X_{MAC}$) using exact planform integration formulas:

Taper Ratio ($\lambda$):

\lambda = \frac{C_t}{C_r}

Mean Aerodynamic Chord (MAC):

MAC = \frac{2}{3} \cdot C_r \cdot \left( \frac{1 + \lambda + \lambda^2}{1 + \lambda} \right)

MAC Y-Span Location ($Y_{MAC}$):

Y_{MAC} = \frac{b}{6} \cdot \left( \frac{1 + 2\lambda}{1 + \lambda} \right)

MAC Leading Edge Setback ($X_{MAC}$):

X_{MAC} = X_{sweep} \cdot \left( \frac{1 + 2\lambda}{3(1 + \lambda)} \right)

Recommended CG Location ($CG_X$ from Root LE):

CG_X = X_{MAC} + MAC \cdot \left( 0.25 - \frac{\text{Static Margin \%}}{100} \right)

What is Static Margin & Why Does It Matter?

The Static Margin measures pitch stability. It is defined as the distance between the aircraft's Neutral Point ($NP$) and the Center of Gravity ($CG$), expressed as a percentage of the MAC:

  • Optimal (8% – 12%): Standard recommendation for maiden flights, trainers, and scale models. Provides positive pitch stability — if a gust pitches the nose up, the plane naturally returns to level flight.
  • Acrobatic / Pitch Sensitive (3% – 7%): Used by 3D aerobatic RC pilots. Requires less elevator input for rapid maneuvers, but demands constant pilot attention.
  • Neutral / Tail-Heavy (0% or Negative): 🚨 DANGER ZONE. A negative static margin means the CG is behind the Neutral Point. The aircraft becomes divergent — any slight pitch pitch-up will rapidly amplify, causing an unrecoverable stall and flip.

Practical Field Guide: Maiden Flight CG Balancing

  1. Mark the Calculated CG: Use masking tape on the underside of both wing halves at the calculated $CG_X$ distance from the root leading edge.
  2. Use Fingertip or Balancer Rig: Place your fingertips (or a dedicated balance stand) directly under the CG tape marks.
  3. Check Pitch Angle: The fuselage should rest level or slightly nose-down (1°–2°). A slightly nose-heavy model flies safely; a tail-heavy model crashes.
  4. Shift Equipment: Move the LiPo battery or receiver pack forward/aft before adding dead lead weight.