What is center of gravity in aviation?

Center of gravity (CG) is the point at which the aircraft would balance if suspended. It's expressed as a distance from the datum (a reference point). The CG must fall within limits specified in the POH for the aircraft to be controllable and stable in flight.

What happens if CG is too far forward?

A forward CG makes the aircraft nose-heavy, requiring more up elevator to maintain level flight. This increases stall speed, requires higher approach speeds, increases fuel consumption, and may prevent achieving full flare on landing. Elevator authority may be insufficient in extreme cases.

What happens if CG is too far aft?

An aft CG is more dangerous than forward. The aircraft becomes increasingly unstable - small pitch inputs cause large attitude changes. Stall recovery becomes difficult or impossible. In extreme cases, the aircraft may become uncontrollable. Aft CG violations have caused fatal accidents.

How do you calculate moment?

Moment equals weight multiplied by arm (distance from datum). Total all individual moments (passengers, baggage, fuel) and divide by total weight to find CG position. The formula is: CG = Total Moment ÷ Total Weight.

The datum is an imaginary vertical reference plane from which all horizontal distances (arms) are measured. It's defined by the manufacturer and can be the firewall, nose, or any fixed point. All arm measurements in the POH are referenced to this datum.

Does CG change during flight?

Yes, CG shifts as fuel is burned. In most light aircraft, fuel tanks are near the CG, so the shift is minimal. But some aircraft have significant CG changes with fuel burn. Always verify CG is within limits at takeoff AND at landing (minimum fuel) weights.

Weight & Balance Basics - CG and Aircraft Safety

Core Concepts

Datum

Reference point from which all distances are measured (often the firewall or nose)

Arm

Horizontal distance from datum to item's CG (in inches)

Moment

Weight × Arm = Rotational force (lb-inches)

Total Moment ÷ Total Weight = Balance point location

CG = ΣMoments ÷ ΣWeights

CG Position Effects

Forward CG

• Higher stall speed
• Increased fuel consumption
• More stable (resistant to pitch changes)
• May not achieve full flare
• Longer takeoff roll

Inconvenient but survivable

Aft CG

• Lower stall speed
• Reduced stability
• Difficult stall recovery
• Possible loss of control
• Extreme: unrecoverable

DANGEROUS - has caused fatal accidents

The CG Envelope

The POH defines CG limits that vary with weight. Your calculated CG must fall within this envelope at all phases of flight:

Takeoff

Max weight, full fuel

Landing

After fuel burn

CG Shift During Flight

As fuel burns, weight decreases and CG may shift. Always check that CG remains in limits at landing weight too.

Common Loading Mistakes

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Using "standard" passenger weights

Actual weights can vary significantly. Use real weights when possible.

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Ignoring baggage location

Baggage placed in aft compartments dramatically affects CG.

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Not recalculating after loading changes

Adding a passenger or moving baggage requires recalculation.

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Assuming "it flew last time"

Different loading = different CG. Always calculate.

Best Practice

Calculate weight & balance for every flight with passengers or significant cargo. It takes 2 minutes and could save your life.

Weight & Balance Basics