Center of gravity before maiden — safely with cgCalc

The first flight is the wrong place to “find” the CG. Tail-heavy models can go unstable abruptly; nose-heavy ones get sluggish and landing-critical. cgCalc helps compute and verify CG, neutral point (NP) and aerodynamic center (AC) on the ground — described for up to multiple wing panels.

Why before maiden

Longitudinal static stability depends on the distance between CG and neutral point. Plan CG figures are starting points — pack position, servos and build variance move reality. Measure and calculate to cut risk.

Tone: calm and clear. No heroics.

What to prepare

• Plan or geometry: span, chord, sweep, multiple panels if needed
• Weights and locations of major masses (or an assembled CG measurement to cross-check)
• Target CG as % of local chord or mm aft of a datum

cgCalc is a membership tool (see signup pricing); note demo limits. Private vs commercial: Hobby vs commercial.

Rules of thumb (not a substitute)

1. Maiden slightly nose-heavy within the recommended range — never tail-heavy “for agility”.
2. Use a sliding pack tray when the design allows.
3. Recheck CG after major changes.
4. Validate the drive in propCalc — Airplane drive.
5. First flight: altitude, calm air, control-direction double-check.

Worked example: 1.6 m trainer, rectangular wing

Assumptions:

• Span 1600 mm, chord 280 mm, little sweep
• Plan CG: 28–33 % chord from LE
• Nose motor 280 g, 4S 3300 mAh pack (~320 g) on rails, wing servos

Enter panels and mass stations in cgCalc. Compare computed CG to the plan window. If CG sits at 35 %+ with no move room → add forward ballast or move the pack before maiden.

Steps in cgCalc

1. Open cgCalc.
2. Enter wing panels per geometry.
3. Enter masses and moment arms (or cross-check with measured CG).
4. Read CG, NP/AC and margin.
5. Iterate pack position into the plan window — prefer the forward half for maiden.
6. Document (photo of pack position, mm mark).

No invented prefill URLs.

More practice: measure and document

Beyond the calc:

• Mark the datum and photograph it.
• Record pack position in millimetres (e.g. “pack LE 12 mm aft of former 3”).
• For multi-wing or added masses, enter every relevant weight — cgCalc supports multiple panels.
• After maiden, trim carefully; large CG moves belong back on the bench with a new calc.

Safety culture: postpone a day rather than force a tail-heavy first flight. Have a clubmate spot-check inputs — a span typo moves NP and CG meaningfully.

FAQ

Plan CG only?
OK if you built exactly to plan. If weights differ: recalculate/reweigh.

Finger-balance under the wing?
Rough; inaccurate with sweep/multi-panel wings. cgCalc is for finer geometry.

Does software replace maiden caution?
No. It removes known CG mistakes. Fly conservatively anyway.

Avoid typical maiden mistakes

Tail-heavy from a late camera install, packing the battery “visually centred”, or mixing plan vs workshop datums: everyday traps. cgCalc forces geometry and masses into the open. When the calc and a balance/scale check roughly agree, you are ready; if not, fix inputs or measurement on the ground — not in the air.