Weight — Forces

Gravitational force pulling the aircraft toward Earth's center. Weight acts through the center of gravity and is opposed by lift.

What it is

Weight is simply mass multiplied by gravitational acceleration (W = mg). For an aircraft, it includes the airframe, engines, fuel, crew, and payload — everything aboard. Weight acts as a single downward vector through the center of gravity (CG).

Unlike the other three forces, weight is always present and always pointing the same direction. The only way to reduce it is to reduce mass — burn fuel, jettison payload, or land.

Center of gravity

Where the CG sits relative to the wing's aerodynamic center profoundly affects aircraft stability and handling. A forward CG is inherently stable — the aircraft tends to pitch nose-down when disturbed, and the tail must work against this tendency, requiring more back pressure. An aft CG reduces stability and can make the aircraft uncontrollable if it moves too far back.

Quick reference

Direction	Straight down toward Earth's center
Opposing force	Lift
Acts through	Center of gravity (CG)
Changes during flight	Yes — weight decreases as fuel burns
Measured in	Pounds (lbf) or Newtons (N)

Weight decreases in flight: As fuel burns, the aircraft becomes lighter. On a long flight this allows the pilot to reduce power and climb to a higher, more efficient altitude — or maintain the same altitude at lower power. CG also shifts as fuel burns, which must be managed within limits.

Related terms

Lift — the force that opposes weight
Drag and Thrust — the other pair of forces
Level Flight — the state where lift equals weight

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