Definition
A weight installed on a moving part to balance it about its pivot or axis of rotation, reducing the force required to move it and helping prevent unwanted movement, vibration, or flutter. Counterweights are used on flight control surfaces, propeller blades, crankshafts, and rotor blades.
Plain English
A small weight added to a moving part so that the part is balanced around its pivot point. Once balanced, it takes less effort to move and is less likely to flap, shake, or shift on its own.
Context Anchor
Seen in maintenance and aircraft systems discussions involving flight controls, engines, propellers, and other moving parts.
Derivation
From 'counter' (against, opposite) and 'weight'. Literally a weight placed opposite something else to balance it out. The name describes exactly what it does: pushes back against an unbalanced load.
Why Pilots Care
On flight controls, an out-of-balance surface can develop flutter — a rapid, destructive oscillation that can tear the surface off the airplane. Counterweights are part of why control surfaces stay safe at high speeds, and damage to them must be reported and properly repaired.
Analogy
Like the small lead weights a tire shop clips to a wheel rim. The wheel still spins, but with the weights added it spins smoothly instead of shaking.
Intuition Check
Do not think of a counterweight as baggage or general ballast added to the aircraft. It is a specific weight installed on a part to balance that part or control how it moves.
Example Sentence 1
During the preflight, he checked the aileron counterweights for security and any sign of damage.
Example Sentence 2
During overhaul the technician checked that each counterweight moved freely on its pin.